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COMPRESSORDedicated To Gas Compression Products & Applications
Mexico’s case study: PuMPtechGrowinG ThirsT Torsional analysis issue
APRIL 2013
Compressor Efficiency Drops With Black Powder Build-Up
Managing Screw Compressors In The Field
compressormaintenance
www.compressortech2.com
CT_AprilCover.indd 1 3/20/13 1:38 PM
HOERBIGER Engine Solutions
Click on company logo to see ad page
This issue Driven By
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C O M P R E S S O R S n T U R B I N E S n G L O B A L S E R V I C E
EBARA CORPORATION
www.elliott-turbo.com
n Customers: Global oil and gas producers.
n Challenge: Changing compression requirements as fields mature and production peaks.
n Result: Flexible, reliable compressor designs for extended, cost-efficient operations.
They turned to Elliottfor reliable compression solutions.
From Aberdeen to Rio de Janeiro, Calgary to Jakarta, Elliott compressors, turbines, and expanders deliver the reliable, efficient performance that producers and processors require. And every piece of Elliott equipment is backed by our unmatched global service network. Customers throughout the world turn to Elliott for critical turbomachinery and service because our resources are global and our execution is local. Who will you turn to?
The world turns to Elliott.
Elliott.indd 1 3/15/13 10:26 AM
Ariel reciprocating compressors from 100 to 10,000 BHP are utilized in the upstream, midstream, and downstream sectors. Our compressors are designed and built for long service life and ease of maintenance. Ariel is there every step of the way, offering you the best customer service in the industry. For all your compression needs, choose Ariel.
Learn more about unit F40,000 at www.arielcorp.com/unit40k
IF NOT, TALK TO US ABOUT YOUR COMPRESSION NEEDS. WE’LL SHOW YOU THE ARIEL DIFFERENCE.
ARIEL CORPORATIONWorld Standard Compressors
35 Blackjack Road Mount Vernon, OH 43050 www.arielcorp.com
40,000COMPRESSORS SHIPPED TO OVER 100 COUNTRIES SINCE 1966...
CHANCES ARE, ONE OF THEM IS YOURS.
Ariel’s 40,000th compressor being assembled in November 2012.
Ariel.indd 1 12/20/12 9:00 AMAriel_ComprTab_CTSS2013.indd 1 1/29/13 9:54 AM
TechTransfer_CT2.indd 1 2/22/12 9:11 AM
Joe Kane
Compressortech2 Founder
our attention is focused mostly on the economy, government spending, taxes, our national debt and a heap of other issues that seem to be numbing our senses.
a carbon tax, that onerous item that is expected to sneak into the govern-ment’s revenue quest again, is one that seems to rest below the public radar. It was attempted during the Clinton ad-ministration, but met with such opposi-tion that it was dropped.
The two reasons expressed for a car-bon tax were to gain more revenue for the federal pocketbook and to address climate change. The public was advised that it wouldn’t hurt the large energy pro-ducers and it would avoid the necessity of raising taxes on american citizens. The former might be true because big ener-gy producers would pass the additional costs on to consumers. so the american public would inevitably foot the bill.
This whole issue was discussed more succinctly late last year by William o’Keefe, Ceo of the George C. mar-shall Institute, in a column for The Wall Street Journal. He stated that energy is so paramount to our national well-being that any tinkering with its natural product- to-market flow could be disastrous.
He said an energy tax would place our manufacturing sector at a compet-itive disadvantage globally, causing a further shifting of production and jobs outside the U.s. But, worse, it would have its greatest impact on the low-income bracket of our population.
moreover, o’Keefe asserted, “The climate-change justification for a car-bon tax is bogus. Greenhouse gas emissions are rising in China and other
emerging economies, not in the United states. Carbon-dioxide emissions in the U.s. have been declining, and by 2035 will return to 2005 levels, the energy In-formation administration projects.
“advances in climate science, mean-while, raise even more doubt about the assertion human activities are the pri-mary cause of warming. Former nasa scientist roy spencer, for example, has shown that temperatures since 1976 have risen and stabilized in parallel with the pacific Decadal oscillation, a natural climate pattern affecting all sorts of natural phenomena. an increas-ing number of experts now admit that natural variability is poorly understood and poorly reflected in the models that are the foundation of so much climate-change dread.”
sleep is beautiful when it comes at the right time but embarrassing other-wise. some people sleep through classes. They sleep at meetings. They sleep during concerts. They mean well, but they miss out on the important mo-ments of life.
others sleep through life in other ways. They are unaware of political issues, unconcerned for the needs of others, devoid of manners, aloof from people seeking their attention. some people sleep through relationships and through events that impinge upon deep-seated beliefs. In short, they live in the darkness of ignorance.
our so-called main line media con-tributes too much to this snooze factor by not addressing both sides of the climate change debate.
may the Lord hold you in the hollow of His hand. CT2
An Issue We Should Lose Sleep Over
Page4a member of The Diesel & Gas Turbine publications Group
President & CEO .................... michael J. osengaExecutive Vice President ...michael J. Brezonick
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COMPRESSORDedicated To Gas Compression Products & Applications
CT172.indd 1 3/20/13 9:40 am
More power on less fuel with lower emissions. Recognized leader in the energy production industry.GE’s Gas Engines business has a track record of more than 170 years of reciprocating engine technology experience. This legacy of innovation goes into each new engine developed to meet the demands of future generations. Waukesha gas engines are a driving force to leverage natural gas reserves and deliver powerful gas compression solutions for global applications.
For more information on GE’s Gas Engines business, visit us at www.ge-waukesha.com.
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Featured Articles 16 Compressor Efficiency Drops With Black Powder Build-Up
24 Caring For A Compressor
42 Mexico’s Growing Thirst
46 Mecos Acquisition Opens Opportunities For MAN
72 Lubes Evolve With Higher Turbine Performance
74 Turbine-Driven Compression For China
88 IEA Urges More Competition In Asia Pacific Gas Market
90 Case Study: Torsional Analysis
PUMPtech 52 Warning: Contents Are Hot
58 Wärtsilä Pumps It Up
62 Unusual PD Pump Pulsation Solutions
TECHcorner 32 A Review Of Reciprocating Compressor Crosshead Pin Nonreversals
76 Vector Analysis Of Crankshaft Web Deflections
Departments 4 Page 4 — An Issue We Should Lose Sleep Over
8 Global Perspective — Russia Looks Toward Asia Pacific Energy Market
10 Meetings & Events
12 About The Business — Compression Industry Reports Strong 2012 Business Despite Low Gas Prices
14 Monitoring Government — Meltdown Looms For Europe’s Carbon Trading Program
40 Literature
73 Prime Movers
86 Featured Products
95 Snapshot — Oklahoma School Tops Out Building
96 Scheduled Downtime
97 Marketplace
98 Advertisers’ Index
100 Cornerstones Of Compression — Waukesha VHP Series Gas Engines
Compressortech2 (ISSN 1085-2468) Volume 18, No. 3 — Published 10 issues/year (January-February, March, April, May, June, July, August-September, October, November, December) by Diesel & Gas Turbine Publications, 20855 Watertown Road, Waukesha, WI 53186-1873, U.S.A. Subscription rates are $85.00 per year/$10.00 per copy worldwide. Periodicals postage paid at Waukesha, WI 53186 and at additional mailing offices. Copyright 2013 DIESEL & GAS TURBINE PUBLICATIONS.
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COMPRESSORDedicated To Gas Compression Products & Applications
April 2013
Cover Designed By Amanda Ryan
MEMBER OF BPA WORLDWIDE®PRINTED IN THE U.S.A.
CT_Apr13_TOC.indd 1 3/21/13 9:21 AM
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APRIL 2013 8 ComPRessoRtech2
For many years, Europe has been the primary ex-port market for Gazprom, the Russian natural gas monopoly.
If on one side, the European marketplace is seen as a slow-growing area with high competition from North Sea, African and Middle East gas source. On the other side, the growing economies of the Asia Pacific region ensure a fast-growing demand for energy. That’s especially true for lique-fied natural gas (LNG), since Japan and South Korea are the world’s largest LNG importers.
Strong energy demand has brought very lucrative prices, and several international oil companies are investing in LNG plants to monetize the gas reserves of Indonesia, Australia, the Middle East and the East African coast. The low price of gas in the United States has even prompted proposals to export LNG to Asia Pacific.
Russia is looking at this market area with great interest. It has significant hydrocarbon resources in East Siberia and on the Russian Continental Shelf (RCS). The easiest, and the most economical, option would have been a gas pipe-line from East Siberia to South Korea through North Korea. Although technically feasible, the political situation in the area could jeopardize the substantial investment required.
Instead, on Feb. 21, Gazprom decided to invest in the Vladi-vostok LNG export project. The three-train export terminal will be built at Perevoznaya Bay on the Lomonosov Peninsula and will have annual export capacity of about 15 mtpa (20.7 x109 m3/year). The first train is scheduled to start up in 2018.
Last October, Russia had finally decided to invest in the development of the Chayanda gas and condensate field. It will build a 2000 mi. (3200 km) pipeline from Yakutia to Vladivostok to provide feedstock gas for the Vladivostok LNG project.
The Vladivostok terminal also will draw on gas from Sakhalin Island area gas fields and from the Irkutsk produc-tion center (also in East Siberia), which will be linked to the Yakutia-Vladivostok (“Power of Siberia”) trunkline.
Gazprom did not disclose a construction cost of the Vladi-vostok venture. However, it is likely to be greater than the US$12.7 billion originally estimated, given the increased
scale of the project. The final cost, including the develop-ment of Chayanda and pipeline construction, likely will be more than US$50 billion over five years or longer.
The gas export monopoly that Gazprom holds is in-creasingly threatened by pressure from Russian Presi-dent Vladimir Putin, whose political allies include Rosneft chairman Igor Sechin. In fact, Rosneft has made over-tures to ExxonMobil, as well as Chinese and Japanese companies, for possible LNG collaboration in its conces-sions, although a liberalization of Russia’s gas export framework has yet to occur.
Gazprom is wise to speed its entry into Asia through the Vladivostok LNG project while Russian politicians consider ex-tending its export monopoly. However, rising competition in the Asia Pacific LNG market could give consuming nations more bargaining power. Gazprom could find it difficult to secure long-term contracts at prices that would give it a comfortable profit margin for the expensive Vladivostok LNG investment.
Rosneft has also offered opportunities for cooperation on the RCS to Chinese companies and is expected to make similar offers to Japanese firms. Those deals will probably follow the pattern of agreements it had inked with ExxonMo-bil, Eni and Statoil: entry into the prospective Russian shelf, which could hold 733 billion barrels of oil equivalent (BOE) of resources, in exchange for the capital and expertise to develop the fields.
These promise to be beneficial partnerships for the oil giant Rosneft. Thanks to legislation in 2008 that effectively granted it and Gazprom exclusive rights to the RCS, the two firms have been sitting on licenses that could be rich with hydrocarbon potential.
However, due to the high costs of exploration and produc-tion, as well as the specialized knowhow needed to operate offshore — a relatively new area of operations for both com-panies — they have been slow to develop the RCS.
In recent months, both firms have been under increas-ing pressure from political figures such as Prime Minister Dmitry Medvedev and Natural Resources and Environment Minister Sergei Donskoy to speed development of the RCS or risk a forfeit of their licenses. CT2
Russia Looks Toward Asia Pacific Energy Market > BY ROBERTO CHELLINI
ASSOCIATE PUBLISHER
Global Perspective
Gazprom, Rosneft under political pressure to exploit gas, oil resources
CT162.indd 1 3/20/13 9:42 AM
They may display a proud old name on the outside, but the driving force within the world’s best-engineered, most efficient, pipeline gas compressors is Rolls-Royce. The heritage name, Cooper-Bessemer, still carried by older machines, echoes the engineering excellence that has
earned Rolls-Royce an unparalleled reputation for quality. Today, in a business where productivity and dependability mean so much, the unsurpassed engineering experience of the past makes Rolls-Royce the compressor name of the future.
A proud past leads to a new future
Trusted to deliver excellence
It’s all in the name...
Cooper-Bessemer is a registered trade name of Cameron Corporation, used under license by Rolls-Royce plc
www.rolls-royce.com
RollsRoyce_BessAd.indd 1 1/31/12 4:39 PM
APRILApril 7-10*Gas Processors Association Annual Convention — San AntonioTel: +1 (918) 493-3872Web: www.gpaglobal.org
April 10-11*Turkish International Oil & Gas Conference 2013 — Ankara, TurkeyTel: +44 207 596 5147Web: www.turoge.com
April 15*Gas Compressor Association Expo & Conference — Galveston, TexasTel: +1 (972) 518-0019Web: www.gascompressor.org
April 15-17North Africa Technical Conference & Exhibition — CairoTel: +971 4 390 3540Web: www.spe.org/events/natc
April 16-17*Gas Compressor Institute —Liberal, KansasTel: +1 (620) 417-1171Web: www.gascompressor.info
April 29-May 3*Gulf South Rotating Machinery Symposium — Baton Rouge, LouisianaTel: +1 (225) 578-4853Web: www.gsrms.org
MAYMay 1-4Baghdad International Oil & Gas Conference and Exhibition — BaghdadTel: +90 212 356 00 56Web: www.baghdadoilgas.com
May 6-9*Offshore Technology Conference — HoustonTel: +1 (972) 952-9494Web: www.otcnet.org
May 14-16*Eastern Gas Compression Roundtable — Moon Township, PennsylvaniaTel: +1 (412) 372-4301Web: www.egcr.org
May 14-16 *Sensor+Test — Nuremberg, GermanyTel: +49 5033 9639-0Web: www.sensor-test.de
May 14-16Uzbekistan International Oil & Gas Exhibition — Tashkent, UzbekistanTel: +44 207 596 5233Web: www.oguzbekistan.com/2013
JUNEJune 3-7 *ASME Turbo Expo — San AntonioTel: +1 (404) 847-0072Web: www.asmeconferences.org/TE2013
June 4-6 *Power-Gen Europe — Vienna
Meetings & EventsFor a complete listing of upcoming events, please visit our website at www.compressortech2.com
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CECO.indd 1 1/22/13 1:57 PMMeetings_Events.indd 1 3/20/13 9:45 AM
Tel: +44 1992 656 617Web: www.powergeneurope.com
June 4-6Sensors Expo & Conference — Rosemont, IllinoisTel: +1 (617) 219-8375Web: www.sensorsmag.com/sensors-expo
June 4-7Caspian Oil & Gas 2013 — Baku, AzerbaijanTel: +44 207 596 5000Web: www.caspianoil-gas.com
June 5-6Energy Exposition — Gillette, WyomingTel: +1 (307) 234-1868Web: www.energyexposition.com
June 11-13Calgary Oil & Gas Expo — Calgary, CanadaTel: +1 (403) 209-3555Web: www.gasandoilexpo.com
SEptEmbErSept. 17-19*Gas Compressor Conference — Norman, OklahomaTel: +1 (405) 325-3891Web: www.engr.outreach.ou.edu/gascompressor
Sept. 18-20*Wyoming Natural Gas Fair — Jackson, WyomingTel: +1 (307) 234-7147Web: www.wyogasfair.org
Sept. 25-26ChemInnovations Conference & Expo — Galveston, TexasTel: +1 (713) 343-1884Web: www.cpievent.com
Sept. 30-Oct. 3*International pump Users Symposium — HoustonTel: +1 (979) 845-2924Web: http://turbolab.tamu.edu
Sept. 30-Oct. 3*turbomachinery Symposium — HoustonTel: +1 (979) 845-7417Web: http://turbolab.tamu.edu
Oct. 1Pittsburgh Chemical Day — PittsburghTel: +1 (855) 807-9814Web: www.pittchemday.com
Oct. 2-4*power-Gen Asia — BangkokTel: +1 (918) 835-3161Web: www.powergenasia.com
Oct. 6-9Gas machinery Conference — Albuquerque, New MexicoTel: +1 (972) 620-4026Web: www.gmrc.org
Oct. 7-10Argentina Oil & Gas Expo — Buenos Aires, ArgentinaTel: +54 11 4322 57Web: www.aog.com.ar
*Indicates shows and conferences in which Compressortech2 is participating
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APRIL 2013 12 ComPRessoRtech2
Compression fabrication and contract services compa-nies reported strong results for 2012 even though natu-ral gas prices were subdued.
Enerflex recorded sales 22% higher than in 2011 due to strong activity in the southern United States, South America, and other international segments. Cameron Process & Com-pression reported revenues were 21% higher, led by strong process equipment sales. Dresser-Rand’s new-unit sales in-creased 20%.
USA Compression Partners, which closed its IPO in Janu-ary 2013, had record 20% higher revenues. Exterran Holdings’s revenues were 17% higher for the quarter and 7% for the year, with growth in all business sectors, but especially in fabrication. Compressco Partners increased its revenues 23% due to strong international growth, primarily in Mexico. UE Compression, which opened a facility in Denver to handle larger packages, reported re-cord packaging sales in 2012. And SEC Energy enjoyed its highest volume since 2008.
Nevertheless, tepid economies and low gas prices limited results for a number of companies. Caterpillar’s Power Systems group re-ported sales 6% lower in the fourth quarter of 2012, with soften-ing in all geographic regions except Asia Pacific. Cat noted that dealers are not building inventory like they did at the end of 2011. Rolls-Royce Energy revenues decreased 11% due to the delay of several large international projects. Small regional packagers, such as Abby Services in the U.S., and Compass and Sage in Canada, reported slower activity. That sent them searching for more interna-tional business and new markets, such as vapor recovery.
Exterran reduced its contract compression fleet (the industry’s largest) by another 3% to 4,461,000 hp (3326 MW), but grew oper-ating horsepower by 3% to 3,907,000 hp (2913 MW) as utilization improved to 84%, nearer the industry average. International growth rates were strongest.
USA Compression’s fleet grew 27% during the year to 919,211 hp (685 MW), although utilization fell from 95.7% to 92.8%. Compressco reported 3149 compressor units in ser-vice, up 8%, with growth focused on Latin American, European
and Asia Pacific markets, as well as unconventional applica-tions supporting associated gas from liquids production, vapor recovery and casing gas systems.
Year-end backlogs and order rates were mixed. Dresser-Rand reported record new-unit orders, a gain of 9%, driven by stronger worldwide energy infrastructure markets, especially oil produc-tion and gas transmission. D-R’s year-end unit backlog was 14% higher than 2011, and new unit orders are forecast to increase another 10 to 20% in 2013.
Exterran’s compression fabrication backlog was up 11% from the third quarter and 3% from year-end 2011. Manage-ment reported the highest profitability in more than three years, and expects further progress in 2013, mostly in the second half of the year.
Caterpillar and Ariel projected 2013 volumes would match 2012 levels. SEC Energy reported a six-month backlog with a full shop and a large expansion of its Houston plant and offices near completion. Cameron’s process and compression equip-ment orders and backlog declined 2% and 4%, respectively. Rolls-Royce Energy, dependent almost entirely on internation-al markets, reported orders down 9% due to delays of several large projects.
Enerflex’s backlog decreased 31%, with orders slowing in all areas due to lower gas prices, but especially in Canada and the northern U.S. The decrease was also affected by a large Omani gas processing plant that had been included in 2011 bookings. The company expects continued softness during the first half of 2013, but is optimistic about opportunities in the southern U.S., South America and other international markets. Enerflex doubled its Houston fabrication facility in 2012 to serve demand in those markets.
Low gas prices sent many small, regional fabricators and con-tract compression fleets searching for business in new markets. For example, Bidell, Compass, Sage and Abby all reported their 2012 fabrication backlogs were down from 2011. Dearing Com-pression, positioned uniquely in the Marcellus and Utica Shale plays, was an exception.
Niche companies, such as Cobey and ANGI Energy Systems, are benefiting from strong growth in natural gas vehicle refueling infrastructure. Vapor recovery compression is also growing as op-erators try to reduce fugitive emissions. CT2
Compression Industry Reports Strong 2012 Business Despite Low Gas Prices > BY NORM SHADE
About The Business
More-or-less flat outlook sends small, regional players search-ing for new markets
BY NORM SHADE
Norm Shade is president of ACI Services Inc. of Cambridge, Ohio. A 43-year veteran of the gas compression industry, he has written numerous papers and is active in the major industry associations.
CT168.indd 1 3/21/13 2:39 PM
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Monitoring governMent
Approval for a ‘backloading’ fix won’t come easily
BY PAtrick crow
Meltdown Looms For Europe’s Carbon Trading Program >
APRIL 2013 14 ComPRessoRtech2
Europe’s greenhouse gas emissions trading scheme is near collapse, presenting the European Union with some tough choices.
the Emissions trading System (EtS) was the first, and is by far the largest, international framework for trading green-house gas emissions allowances.
the fate of the EtS will be closely monitored in the United States. President Barack obama is pressing con-gress for global warming legislation and most plans to reduce greenhouse emissions include cap-and-trade pro-grams like the EtS.
compressor manufacturers also should be watching with interest. they would like to see market growth for compres-sors used in co2 injection/sequestration projects.
the EU launched the EtS in 2005. it affects nearly half of all co2 emissions in the 27 EU member nations, plus croatia, iceland, Liechtenstein and Norway.
working from a 2005 baseline, the program’s goal is to cut emissions from targeted industrial sectors 21% by 2020. EU nations have allocated free carbon permits to 11,000 industrial firms and power plants.
An allowance permits a facility to emit 1 tonne of co2 or its carbon equivalent. companies can sell any permits that they don’t need. the limit on the total number of allowances available theoretically ensures that they have a value.
the paper-trading system is a good idea — on paper. the market mechanism should allow polluters to either invest in emissions controls or purchase allowances from companies who don’t need them, whichever makes economic sense.
But cap-and-trade systems work best when demand for allowances is brisk. that’s not been the case recently in Europe, where industrial activity still is recovering from the economic slowdown. in particular, demand for electric power has dropped and generating plants are the major sources of co2 emissions.
Since 2009, the supply of EtS allowances has consis-tently surpassed demand — building to a surplus of about 2 billion tonnes — and thus the price of traded carbon credits has trended downwards.
Earlier this year, the price of credits slipped to a low of €2.80 (US$3.75) for each tonne allowance of co2. that was down from €9 in 2012 and €30 in 2008.
in late February, the imminent collapse of the EtS forced the EU’s committee on Environment, Public Health and Food Safety to draft a bailout plan. to tighten the market, it proposed “backloading” future allowances: deferring the issuance of 900 million tonnes of carbon permits that were due to be auctioned from 2013 to 2015. that would be about a fourth of the planned offering.
“the environment committee has sent a clear signal in favor of a strong and healthy emissions trading system,” committee chairman Matthias Groote said. “A stronger carbon price will help catalyze Europe’s transition towards a low-carbon economy.”
that bailout plan now must be approved by the European commission, which represents all of the governments of EU member states, and the European Parliament. their ap-provals may not come easily or may not come at all.
Some members of Parliament oppose “backloading” be-cause the temporary fix threatens to swamp the market when the deferred permits are ultimately issued in 2019 and 2020.
in the European commission, nations that benefit from the current low carbon prices will argue against changing the trading program. in the forefront will be Poland, a major consumer of coal, which is the fuel that generates the most carbon emissions.
the European Association for coal and Lignite has com-plained to the EU that “backloading” not only is contrary to the founding principles of the EtS, but also would make the program “a scheme subject to political manipulation.”
Environmental groups are divided. Some say the EtS needs permanent structural reforms to be viable. others argue that the EtS should be scrapped and replaced with tougher mandates to reduce pollution. they do agree that the abundance of cheap permits has removed any incentive for polluting firms to cut their emissions.
the EU might consider some alternatives to “backload-ing” but all of them are at least as controversial. it could reduce the 2020 target, permanently remove a large block of allowances, increase the annual emissions cuts, bring more industries into the program, or set a floor price for the allowances.
only one thing is clear. if the EU does nothing, EtS car-bon prices will dip toward zero. Ct2
ct167.indd 1 3/21/13 2:42 PM
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The formation of black powder — a chemical reaction of hy-drogen sulfide (H2S), water and
iron — is a problem for compressors that can escalate if preventative and removal actions are not taken.
Black powder is a common chal-lenge that spans all phases of the
natural gas industry from the wellhead to the burner tip. Its removal is nec-essary to improve or maintain opera-tional efficiency and safety.
This paper assimilates information from several sources and provides ex-periences from operator’s perspective on the difficulties that foreign materi-als in the gas stream pose for produc-tion, gathering, processing and pipe-line transportation.
Typical contaminants in the gas stream are water, glycol, amine, methanol, compressor lubricating oils, salts, chlorides, liquid hydrocar-bons, sand, dirt, production stimula-tors and black powder.
Of those, black powder is the most troublesome. Black powder contami-nation manifests itself through re-duced pipeline efficiency, clogged instrumentation, fouled measurement equipment and valves that cannot op-erate due to an accumulation of debris. It can clog compressor valves, com-pressor cylinders, compressor pistons, and filter/separators.
Additionally, black powder can af-fect pipeline integrity programs that rely on magnetic flux leakage inspec-tion and geometry tools due to debris-induced, liftoff of sensors. Sometimes the contamination is dry and powdery. At other times it is wet or has a tar-like appearance. Black powder is not just a corrosion issue; it is produced in the gas stream from chemical reactions or from microbial activity.
Black power can be an expensive problem. One pipeline has stated that it spends US$5.2 million a year in direct costs associated with black powder re-moval. A single compressor station that has had a filter/separator compromised due to filter collapse can have remedia-tion costs of more than US$400,000.
Other expenses would include fil-ter element replacement, solid waste volume disposal of filter elements, increased horsepower to pump the same throughput, compressor valve replacements and substitution or re-pair of fouled instrumentation.
ChemistryAs stated earlier, black powder is
formed through the chemical reaction of H2S, water and iron in a pipe. The major components of these reactions are iron sulfide (Fe + S) and iron oxide (Fe + O). The resulting compounds
Compressor Efficiency Drops With Black Powder Build-Up > Preventative, restorative measures
can minimize iron sulfide, iron oxide contamination
By Fred MUeller
Fred Mueller is president of Mueller Envi-ronmental Designs Inc., Houston. Mueller worked for several years in engineering, operations, service and sales, incorporat-ing his company in 1991. He holds a patent for a helical coil separator used to remove black powder from pipelines. E-mail him at [email protected].
APRIL 2013 16 ComPRessoRtech2
n This compressor suction valve was fouled by black powder.
continued on page 18
CT165.indd 1 3/21/13 2:50 PM
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are black in appearance, therefore the term black powder.
H2S + Fe g FeS + H2
Iron sulfide
2H + Fe g Fe2+ + H2
Iron oxide
Iron sulfide and iron oxide particles, whether wet or dry, are extremely small. Laboratory analysis of both wet and dry samples indicates a range 0.2 < particle diameter < 4 µ, with more than 81.6% of the particle sample being less than 1 µ with the greatest concentration of that particle range being 0.2 < particle diameter < 0.4 µ. Subsequently, dry black powder has a smoke-like appearance.
Wet black powder may exhibit as clumps, but when it is subjected to high velocity or impinges upon hard sur-faces, it may shear into smaller submi-cron particles. When black powder is in suspension as a liquid, it presents the same characteristics as when dry. Typi-cal density for iron sulfide and iron oxide are 151 lb./cu.ft. (1.9 kg/m3) and 355 lb./cu.ft. (4.6 kg/m3), respectively.
The common chemical forms of iron sulfide include pyrrhotite, troilite, mackinawite, pyrite and marcasite,
mous surface area-to-volume ratio. Subsequently, when exposed to air, it is oxidized back to iron oxide and ei-ther free sulfur or SO2 gas is formed.
This reaction between iron sulfide and oxygen is accompanied by the gen-eration of considerable amount of heat. In fact, so much heat is released that in-dividual particles of iron sulfide become incandescent. This rapid exothermic oxidation with incandescence is known as pyrophoric oxidation and it can ignite flammable hydrocarbon-air mixtures.
Iron sulfide in the chemical forms of mackinawite, smythite and greigite are typical indicators of microbial activ-ity in the gas pipeline. Additionally, the confirmation of sulfate-reducing bacte-ria (SRB) and acid-producing bacteria (APB) in the pipeline is a positive indi-cation that microbial corrosion exists.
The SRB microbes Clostridium and Desulfovibrio desulfuricans consume sulfates and produce H2S. While APB microbes do not produce H2S, they supply nutrients and provide hospi-table environments for SRB to grow.
Reducing black powderRegardless of the origin of H2S in the
APRIL 2013 18 ComPRessoRtech2
n This orifice plate also shows black powder fouling.
n There are many forms of black powder.
ferric sulfide, smythite and greigite. Of these forms of iron sulfide, pyrrhotite exhibits pyrophoric tendencies.
Pyrophoric iron sulfide oxidizes exothermally when exposed to air. It is formed in the gas stream where H2S exceeds the concentration of oxygen. As stated, due to the submicron par-ticle size of iron sulfide, it has an enor-
continued on page 20
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gas stream, a concentration of 1 ppm and a throughput of 500 MMscfd (14 x 106 m3/d) potentially could produce as much as 3600 lb. (1630 kg) of black powder in a month.
Operators who can minimize the introduction of water and reduce the H2S content in their gas stream will see a resulting reduction in black pow-der formation.
Microbiologically influenced cor-rosion cannot exist without water, so water should be removed wherever it is known to accumulate.
The best barrier to black powder production is tariff enforcement. Un-fortunately, even when some con-stituents in the gas stream (such as CO2, H2S, oxygen, water, and sulfur compounds) meet the existing tariff requirements of a few percent to a few parts per million, they still can allow significant corrosion.
The greatest impediment to black powder formation is a conservative tariff that limits H2S to 1 ppm, total sulfur content of five grains per 100 scf, 5 lb. of water per MMscf, 1.4% by volume of CO2 and 10 ppm of oxygen.
Removal methodsUnder current technology, black pow-
der can be removed from gas pipelines through chemical or physical means.
In the chemical process, water or an oil-soluble chemical agent is inject-
APRIL 2013 20 ComPRessoRtech2
ed into the gas stream. The chemical agent should be compatible with the solids to be removed and is based on pipeline operating parameters. The important operating parameters include the type of compressor, dew point, and waste disposal plans.
In addition to operating parameters, the nature of the deposit is critical. Hy-drocarbon deposits comprised of waxes and paraffin are easier to remove with an oil-soluble chemical while salts are easier to clean with an aqueous clean-ing solution. It is important to remember that when using a water-soluble chemi-cal agent, the pipeline must be thor-oughly dried after debris is removed.
Another important aspect of injecting a chemical agent into the gas stream is solvent compatibility. Solvents include water and methanol for water-soluble cleaners or diesel and hydrocarbon condensate for oil-soluble cleaners.
An effective cleaning agent must form either a stable dispersion or a complete solution. A solution is clear or translu-cent in appearance with no distinct phases. A stable dispersion for pipeline injection applications must remain in a homogenous single phase for a mini-mum of 72 hours to be effective. Should the cleaning solvent separate from the cleaning agent, its performance will be significantly reduced.
Physical removal of black powder is accomplished through pigging and
filtration/separation. In the pigging pro-cess, a tool is inserted and pushed through the pipeline using compression.
There are two methods of pigging: dry and chemical. The cleaning action of the pig is a function of brushes or cups that scrape the pipe wall. The scraping action loosens black powder on the metal and pushes loose debris ahead of it.
Four aspects of chemical pigging are important for optimal cleaning results: solids penetration, solids sus-pension, mixture viscosity and mix-ture separability.
Solids penetration is the ability of the chemicals to break the surface contact of debris and loosen it from the pipe sidewall. After the debris is loosened, it must be carried down the pipe in suspension in large quantities.
The carrying capacity of the chemi-cal agent and solvent is much greater than the original density. Therefore, the mixture viscosity is extremely im-portant; it must not increase greatly in viscosity or surface tension.
The final aspect, mixture separa-bility, is the tendency of the debris to separate into distinct phases in order to facilitate disposal. Should an emul-sion be present, the entire quantity of material will require disposal.
Optimally, three phases will pres-ent — oil, aqueous, and solids. This will enable the capture of the cleaning agent for a subsequent chemical pig-ging project and the removal of solid debris for reduced volume of hazard-ous waste material.
Physical removal of black powder also involves a filtration/separation function that typically is installed up-stream of a compressor station or gas processing facility.
Multiple filters in parallel are placed in the gas stream to capture and retain solid particles. They must be suitable for submicron particle retention and they must be able to coalesce and pass liq-uids for capture by the mist extraction section of the filter/separator.
Most filter element designs are un-able to perform both processes. A primary problem with a filter element that is designed to remove submicron
n This pig run removed a pile of moist black powder.
continued on page 22
CT165.indd 3 3/20/13 10:08 AM
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particles is that it can become plugged rapidly and require frequent changing.
If operating conditions do not allow bypassing or shutdowns, the filter element pressure differential may become so great that the elements collapse, compromising the filter/separator completely.
Several manufacturers of helical coil, swirl tube, and cyclone separat-ing elements are working on technolo-gies to address these issues.
SamplingTesting of black powder in pipelines
and compressors is essential to de-termine the chemical pigging and/or cleaning process that will be required.
Analysis of the chemical constituents and particulate sizes of pipeline debris is needed for the selection of new filtra-tion/separation equipment.
When samples are taken for test-ing, they must be sealed immediately. As soon as the debris sample is ex-posed to atmosphere, it begins oxidiz-ing and potentially forming magnetite (Fe3O4). If that occurs, when the pipe-
APRIL 2013 22 ComPRessoRtech2
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ACI.indd 1 1/24/11 3:38:12 PM
line debris is sampled and analyzed, it is often presumed that sulfides do not exist and only pipeline corrosion byproducts are present.
Type of analysis performed on the debris should include full particle iden-tification, bulk density, and particle size and distribution. Minimum capabilities of the laboratory should include:
• Polarized light microscopy,• Epi-reflected light microscopy,• Scanning electron microscopy,• Energy-dispersive X-ray spectrometry,• X-ray diffraction,• Attenuated total reflection-Fourier
infrared spectroscopy,• IMIX image processing software,• and ASTM D 854-98 standard test
methods for specific gravity of soils.
ConclusionPipeline and compressor operators
should take a two-pronged approach to battling black powder.
They should minimize the content of water and H2S in the pipeline, pref-erably through effective tariffs that
restrict the foreign constituents of the gas of the gas stream.
When necessary, operators should use chemical processes and pigging methods to remove black powder build-up from gas pipelines.
ReferencesBaldwin, R.M.: “Black powder in the
gas industry — sources, characteristics and treatment,” Gas Machinery Re-search Council (1997). See: www.gmrc.org/technology-reports.html
Brownlee, J.K.; Dougherty, J.A.; Salma, T.; and Hausler, R.H.: “Solv-ing iron sulfide problems in an off-shore gas gathering system,” Nace International (2000).
Campbell, S.: “The ins and outs of pipeline cleaners: testing and evalu-ation for chemical cleaners,” Nace International (2000).
BJ Services: “Improved black pow-der removal.” See: www.bjservice.com
Sahdev, M.: “Pryophoric iron fires,” Cheresources Online Chemical En-gineering Information (1991). See: www.cheresources.com. CT2
CT165.indd 4 3/20/13 1:46 PM
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APRIL 2013 24 ComPRessoRtech2
A screw compressor can be a very fickle piece of equipment, or it can be your best piece of equipment and make your operations very profitable. It all de-
pends on the proper fit for the application and the mainte-nance program.
Screw compressors were not designed for the natural gas industry. They have been adapted for the natural gas industry from the industrial air and refrigeration industries, where the compressor works in a clean, closed system. The natural gas industry is totally opposite, utilizing an open-ended system that will feed the compressor package what-ever comes from the well. Operators must be ready for all the different gases, liquids and trash that the well will throw at the compressor.
To ensure that you have a successful screw compressor you must first make sure the compressor package is de-signed properly. The screw compressor package must be designed to control three items for a successful and profit-able piece of equipment — separation of the liquids from the gases, the filtration system and the temperature of the gas. There are as many separation system designs as there are compressor packagers and manufacturers. Some work better than others.
The F
irsT
sTa
ge o
F sep
araT
ion
Gas Expands And Slows In Velocity
Shown here are two compressor packages that include separators. There are four stages for successful separation.
By LEE LEVISAy
Lee Levisay is the sales manager for The PROS Company in Lubbock, Texas. He is a graduate of Texas A&M University.
CaringFor a Compressor
Screw CompressorPreventative Maintenance
Illus
trat
ion
by K
athy
Bux
kem
per o
f PRO
S C
o.
continued on page 26
CT174.indd 1 3/20/13 10:16 AM
APRIL 2013 26 ComPRessoRtech2
The separation of the liquids from the gasesThere are two separation systems on a typical natural
gas screw compressor package — the gas suction separa-tor from the well and the oil discharge system to separate the gas and oil after the compression process. We will dis-cuss both because they both have to be working properly to insure success.
The majority of the liquids from the well should be sep-arated prior to the gas stream coming to the compressor package. Sometimes this is not the case for wellhead com-pression systems. The gas suction separator should be de-signed with the four stages of separation working properly; this will ensure the minimum amount of liquid carryover to the compressor. It does not matter if the system has a hori-zontal or vertical separator system as long as it is designed correctly for the application.
The first stage of separation is to have the gas enter and immediately hit an inlet deflector, which forces the gas to expand, change direction and slow down in velocity. This will drop out a lot of the heavier fluids. The second stage is to have the gas change direction and continue to slow in velocity. The third stage is to have a mist pad so the finer droplets of liquid can collect and drop out. The fourth stage is to have the gas stream run through a filtration system.
The filtration systemThe filtration system removes any particulate matter from
the gas stream so as to not damage the screw compressor. The suction filtration filters should have a minimum µ rating of no larger than 10 to 20 µ, the smaller the better. If you have iron oxide or coal dust in your system then it is recom-mended no larger than 1 to 3 µ. If your filters keep getting plugged up, that means they are working properly.
Filters are designed very differently and have maximum differential pressure allowances. Be sure to check with your filter supplier and never allow the differential pressure to ex-ceed the maximum design for that filter. If it does exceed the maximum, the filter could collapse and send particulate mat-ter into your compressor to damage the rotors and bearings. That is not good and normally will lead to excessive down-time and a screw compressor rebuild or replacement. Filters should be checked regularly for proper operation.
Once the gas passes through the separator and is head-ed to the screw compressor it should be free of liquids and particulate matter. This is not always the case with an open ended natural gas application.
The temperature of the gasThis is where the gas analysis is required. The operating
temperature must be 10 to 20° above the highest dew point in the gas stream. This will ensure that the gas variables will stay in a vapor state and not liquefy. By keeping the gas stream variables in vapor form, they will move out of the system with the discharge gas. If any of the gas variables liquefy and stay in the oil, they will dilute the oil and create lubrication problems.
The T
hird
STa
ge o
f Sep
araT
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Gas Passes Through Mist Pad
The S
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Gas Slows And Changes Direction
Illus
trat
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by K
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Illus
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continued on page 28
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APRIL 2013 28 ComPRessoRtech2
Prior to the gas stream entering the screw compressor, it is mixed with the oil. The oil serves multiple functions in the screw compressor compression process. It is the lubricant, sealant and coolant. It will lubricate the bearings and other moving parts. In the screw compressor, there are very tight toler-ances and the oil will act as the sealant between moving parts to create a seal for compression. As with any compres-sion process, heat is created and the oil will help disperse the heat and remove it from the compression process to pre-vent excess heating. If the compressor has too much gap in the clearances be-tween the rotors and housing from ex-cessive wear or damage, the oil cannot seal and there will be a loss in efficiency.
After the compression process, the oil and gas must be separated so the gas can be sent down line and the oil can be reused. The oil must be kept clean and free of foreign material, whether it is liquid or particle, therefore the importance of the discharge sepa-ration system being designed properly and well maintained. The discharge system works similar to the suction gas separation system with a more refined fourth stage of separation. On the dis-charge separation system the filtration is designed specifically for separating the oil and gas. This is called a coalesc-ing filtration system. The coalescing fil-ter is designed for the separation of the oil from the gas and will allow the oil to return to the system. Coalescing filters should not be rated for greater than 1 to 5 microns and should be checked reg-ularly. In the opinion of the author, the smaller the better. This will prevent ac-cumulation of particulate matter in the oil and damaging bearings over time.
The oil is the “life fluid” of the screw compressor package. Selection of the right type of oil for your application is very important. Please consult a trusted oil supplier to get the right kind of oil for your application. If the screw compressor package is designed for petroleum-based oil and a decision is made to change to synthetic-based oil, you could experience many prob-lems, because the discharge sys-tem was not designed for the lighter synthetic oils. Be aware that a major
change in the type of oil will also come with a major change in the discharge oil separation system.
Regularly scheduled oil analysis is the key to maintaining consistent oil throughout the life cycle of the oil. Oil analysis is the method for determining the useful life cycle of the oil and com-pressor. By analyzing the components in the oil you will be able to determine problems before they become cata-strophic events. Oil analysis will point you in the direction where issues need to be addressed, whether they are ex-cessive liquids in the oil (separation and temperature) or too much particu-late matter (filtration). If there is a high metallic flag on the analysis, this may tell you that the compressor is getting near the end of its life cycle, parts are wearing out and that a rebuild or ex-change needs to be scheduled.
The F
ourT
h ST
age o
F Sep
araT
ion
Coalescing And Filtration
No well-balanced, preventative maintenance program can be com-plete without the incorporation of the vibration analysis. Vibration analysis can show the operator the existence of an issue well before it becomes a major problem.
In summary, a well-designed and implemented preventative mainte-nance program will incorporate oil analysis, vibration analysis and con-trol of the separation, filtration and temperature of the screw compres-sor system. These factors will allow the operator to schedule downtime for maintenance and equipment ex-changes, eliminating the midnight call alerting the operator to a catastrophic event. When all this is done properly, the screw compressor will become a very dependable and profitable asset for natural gas production. CT2
Illus
trat
ion
by K
athy
Bux
kem
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f PRO
S C
o.
CT174.indd 3 3/21/13 2:53 PM
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crankshaft can be converted to linear motion of the piston. While the pin may appear to fit snugly, it must have some clearance around it so that lubrication oil can prevent metal to metal rubbing, and hence excess friction and the result-ing undesirable extreme temperatures to 300°, 500°, 700°F (149°, 260°, 371°C) and beyond. Repair costs can be minor (downtime to replace bushings and/or crosshead shoes) to daunting (extended downtime, new rods, new crossheads, new cylinder liners, and new crankshafts). Damage-related costs due to crosshead failures could exceed US$1 mil-lion per unit. Therefore, safety and good business practices would suggest that reciprocating compressor controls in-clude the ability to keep a unit out of potential areas where pin nonreversals may occur.
Pin reversal calculations and concepts can quickly be-come complex, but the basic thing to keep in mind is that the clearance between the pin and the connecting rod (Fig-ures 1, 1A) changes sides as the piston moves out from the frame, stops, and then moves back towards the frame. If the side with the clearance does not change (Figure 2), then little to no lubrication fluid can be introduced between the two metal parts. And when metal rubs against metal, the resulting friction forces will lead to increased temperatures extremely fast.
continued on page 34
Dwayne A. Hickman serves as director of Software Development with ACI Services Inc. He taught university math and com-puter science courses for 13 years, and has been in the reciprocating compressor industry for the last 15 years.
A Review Of Reciprocating Compressor Crosshead Pin Nonreversals >
Many operators of reciprocating compressors are very familiar with safety issues related to unit per-formance, such as high pressures and high tem-
peratures, as these are fairly straightforward to conceptual-ize and even measure in real time. Other issues, such as low-volumetric efficiencies and static gas force rod loads, can be readily explained and operators are often provided a clear method, like a maximum differential pressure or a maximum compression ratio, to help them identify safe from potentially unsafe conditions.
Other issues, like calculating rod loads based on internal gas pressures and inertia forces, or determining when a unit is operating in pin nonreversal conditions, can be nonintui-tive and complex. These issues become especially cumber-some to manage when dealing with higher-speed units due to their potential for operating over a very wide speed range. For example, if a high-speed unit is rated at 1200 rpm, its driver may be able to vary speed to the compressor across a range of 900 to 1200 rpm. Within that range, 900 to 1075 rpm may be safe, from 1075 to 1100 rpm may be unsafe as determined by the OEM, and from 1100 to 1200 rpm may be safe again. Thus, even if your OEM or packager had checked high (1200 rpm), medium (1050 rpm), and low (900 rpm) speeds, they would have not identified the subset of unsafe speeds. The only way to get from 900 to 1200 rpm is to traverse through the 1075 to 1100 rpm range.
The fundamental mechanical issue related to pin nonreversal is ultimately just a lubrication issue. That is, proper lubrication of the pin that connects the connecting rod to the crosshead as-sembly so that the rotating motion of the
TECHcorner
April 2013 32 Compressortech2
Operators should be alert to risky operating conditions
By DWAynE A. HICkMAn
n Figure 1. The clearance gap between pin and connecting rod switches sides when the piston changes direction.
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OEMs typically specify at least two constraints when set-ting safety limits based on pin reversals. First, each throw must have a sufficient number of degrees of pin reversal. The second constraint is that opposite forces (compression vs. tension) must be sufficient to ensure that when operat-ing in the face of real-world phenomenon like pulsations, dynamic pressure drops and valve wear, the predicted amount of pin reversal should be realized.
• API618 section 6.6.4 states that the minimum degrees of pin reversal range from 15° to 45°, depending on bushing designs. Most OEMs require at least 30°, and some require at least 60°.
• API618 section 6.6.4 also states that during one crank-shaft revolution, at least 3% magnitude is required of opposing forces, and as high as 20% magnitude de-pending of bushing design. Most OEMs require at least 15%, and some require as high as 25%.
When calculating the degrees of pin reversal, the internal dynamic gas pressures are applied to the outside piston faces exposed within the head end and crank end portions of the cylinder. These results are then applied when deter-mining the effective gas forces acting on the pin via the pis-ton rod (e.g. blue curve shown in Figure 3). Additionally, the weights of the piston and rod assembly plus the crosshead assembly contribute inertia forces acting on the same pin (e.g. magenta curve shown in Figure 3). Those two forces are combined to give the net forces acting on the pin (e.g. black curve shown in Figure 3).
When forces act in the direction that stretches the rod, they are called tension forces, while forces acting to com-press the rod are called compression forces. To have any degrees of pin reversal during a complete revolution, the forces on the pin must reverse at least once between com-pression and tension. This always happens when only the inertia forces are considered (magenta curve in Figure 4). However, since the cylinder is usually sealed and com-pressing gas, the internal gas forces can make a good situ-ation better, or a good situation bad.
n Figure 3. This chart displays 170° of pin reversal, with max tension about 56% of max compression. All forces are within their limits (green lines). This throw’s pin loading forces indicate safe operation here.
n Figure 4. This chart shows about 40° of reversal, but only about 3% opposite forces. Most OEMs would identify this as a condition where unit operations are not permitted.
For the engineers and programmers, inertia forces are readily calculated by the following equation:
Here, U represents the degree of crank angle and WRE-CIP is the sum of the combined weight of the piston and rod assembly and the crosshead assembly for the throw being considered. (Note: No portion of the connection rod weight is included in these calculations — those additional weights get used in other calculations such as torsional forces. Equation also omits unbalanced rotating weights. Units used are inches and pounds.)
Additionally, Internal Gas Forces are based on the equation:
The sum (∑) is across all cylinders on the throw being considered (e.g. in cases were tandem cylinders are used). The head end (HE) and crank end (CE) pressures are in
continued on page 36
n Figure 2. The clearance gap does not switch sides when piston changes direction.
n Figure 1A. This cutaway shows the crosshead pin referenced in Figures 1 and 2.
CT137.indd 2 3/21/13 2:57 PM
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April 2013 36 Compressortech2
gage pressure units, not in absolute pressure units. Crank-case and tailrod catcher (when present) assumed to be at atmospheric pressure.
Actual prediction of specific head end and crank end in-ternal pressures (PressHE(u) and PressCE (u)) during the compression cycle depend on current line pressures, gas temperatures, unit geometry, valves, pressure drops, gas being compressed, unit operating speed, and a few other items. OEMs develop their own unique approach for mod-eling these internal pressures, albeit most are very simi-lar. Figure 5 and 6 show some typical internal pressures (known as pressure-volume and pressure-time diagrams). The compression (suction to discharge) and expansion (discharge to suction) sections follow the thermodynamic rules for the gas being compressed, are exponential, and tend to be very consistent across the OEMs. The discharge and suction valve open events tend to vary a bit more be-tween OEMs (based on valve designs, passageways, valve porting, liner restrictions, piston masking).
n Figure 5. PV diagram: blue = head end pressures, magenta = crank end pressures.
n Figure 6. PT diagram: blue = head end pressures, magenta = crank end pressures.
Since the results from both equations are required to de-termine the effective forces at the crosshead pin, whenever any condition of the unit changes (suction pressure, dis-charge pressure, suction gas temperature, speed or load step) these forces must be recalculated. API Standard 618, Fifth Edition (2007) section 6.6.3, requires checking these in at most 5° increments. If we had a six-throw unit, we would
need to calculate 12 PV diagrams (two ends per cylinder, one cylinder per throw) and then six throws of inertia data. Also, all load steps should be calculated so that the PLC knows which ones are safe and which ones are unsafe. Convolute this with the thermodynamic modeling needed for the gas pressure calculations and you can potentially slow down even a fast desktop PC. And as for PLCs, the slowdown would be completely unacceptable. Most PLCs do not consider pin nonreversal issues as they control the unit. And this omission is not good.
Fortunately, pin nonreversal issues are not that common, especially when the packager or OEM size the compressor frame and cylinders to best meet your operating require-ments. In general, pin nonreversals tend to happen when a crank end is deactivated or significantly unloaded via added clearance volume, or when tandem cylinders are used and one of the tandem cylinders is double acting, or when small-bore, high-pressure cylinders are used.
Unfortunately, because high-speed units typically allow for more significant speed turndown, high-speed units are poten-tially more susceptible to pin nonreversals. Also, due to industry changes in lubrication fluids to meet environmental needs, some slow-speed units that survived running units near or at pin nonreversal areas in the past may now have problems. Fi-nally, the number of degrees of pin reversals can change quick-ly with pressures changes and speed changes (Figure 7).
n Figure 7. Degrees of pin reversal can fall quickly — shown above falling from 180° down to about 40° when suction pressure varies only about 50 psig (3.4 bar) in some areas.
Thus, severe compressor-based dangers can lurk quietly and then suddenly wreck a unit with little warning. Coding these unsafe areas into a PLC can be a challenge since prediction of unsafe areas is nontrivial (Figure 8). Fortunate-ly, there are some reasonable options available for dealing with potential pin nonreversal concerns: real-time online measuring systems, and preventative performance control.
One option is to install real-time internal pressure sensors. Once calibrated, correctly installed and programmed to each throw’s appropriate reciprocating weights, these devices
continued on page 38
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happen. By preventing the unit from even operating in or near areas of concern, the probability of a pin nonreversal incident is minimized, with risks also significantly reduced.
n Figure 8. Unlike gas rod loads, discharge temperatures, and low volumetric efficiencies, the predictability of where unsafe areas ex-ist due to pin nonreversals is not a trivial task.
Reference: A Discussion of the Various Loads Used to Rate Reciprocating Compressors, K.E. Atkins, Martin Hinchliff, Bruce McCain. CT2
can alarm and/or trigger a shutdown whenever internal cyl-inder conditions approach desired limits of safety. In fact, even if something else, such as a broken valve, creates pin nonreversal issues, these real-time systems can often react fast enough to prevent serious unit harm. For compressors running near areas of pin nonreversals, or for units where a review has indicated that damaged valves can quickly put a unit in pin nonreversals, these real-time systems are ideal.
Another option is to actually prevent unit operations of a healthy unit near or at conditions leading to pin nonreversals by having the unit controller change load steps, adjust speed or adjust pressures to avoid letting the unit damage itself. OEM performance software determines safe and unsafe areas based on hardware configuration (load step), speed, pressures, temperatures, and gas thermodynamics. A con-trol panel does not have the luxury of being able to run such sophisticated calculations — if it was programmed to model complex thermodynamics, then by the time it calculated the results the unit might already be severely damaged. Howev-er, those supplying the units or the performance can prere-view millions of potential operating points across the defined operating map and develop reasonable constraint equations to prevent operations at undesired conditions.
For packagers, operators, and owners concerned with the damages that pin nonreversals can cause, there are reason-able options available to mitigate those concerns. Remember, quantitative risk is defined as the probability that an accident will happen multiplied by the expected loss if the accident does
CT137.indd 4 3/20/13 3:21 PM
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AC Drives
Toshiba Mitsubishi-Electric Industrial Systems Corp. has literature on its TM-drive MVG, a medium-volt-age, variable-frequency AC drive for industrial power ratings up to 10 MW. The drive works with existing or new induction or synchro-nous motors.
www.tmeic.com
Vertical Pumps
Afton Pumps has printed literature on its model MPV pumps, which are medium-pressure vertical pumps that combine a diffusor bowl assembly and a steel outer case. The literature includes technical data and construction details of the pump model.
www.afton-pumps.com
Progressive Cavity Pumps
Netzsch has released a capability brochure, which highlights the company’s products, technology and application areas. The com-pany manufactures a range of pumps, such as progress-ing cavity pumps, immers-ible pumps, and rotary lobe pumps, as well as joints and other accessories.
www.netzsch.com
Mag-Drive Pumps
Warrender Ltd. has pub-lished a brochure on its mag-drive pump range. That pump range includes compact horizontal, process horizontal, vertical sump, horizontal molded thermo-plastic, vertical sump ma-chined thermoplastic, and multistage cast. The compa-ny also offers replacement spare kits and components.
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literAture
APRIL 2013 40 ComPRessoRtech2
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April_Literature.indd 1 3/20/13 4:19 PM
Centrifugal Pumps
CPC Pumps International has released a brochure on its capabilities. The company offers pump designs and pump products to serve the hydrocarbon industry. The brochure provides informa-tion on the company’s pump models, which include the Model HR/HOR, VP-B, VP-C, VP-M, HDR, H2R and HM.
www.cpcpumps.com
Suction Pumps
SPP Pumps has published literature on its pump range. The company offers end suction pumps, horizontal split-case pumps, verti-cal inline pumps, split-case pumps, and single and multi-stage pumps. SPP Pumps has locations worldwide.
www.spppumpsusa.com
Rotary Lobe Pumps
Boerger has a brochure on its rotary lobe pumps. The company has six rotary lobe pump series with 19 sizes, as well as a wide se-lection of rotors, including dual-lobe and tri-lobe vari-ations. A glossary of pump terms and a pump output chart is included.
www.boerger.com
Vacuum Pump Systems
Dekker Vacuum Technolo-gies provides oil-sealed liq-uid ring vacuum pump sys-tems. A brochure reveals the company’s capabilities, as well as its pumps and systems. Dekker also offers spare parts and accesso-ries, and repair and mainte-nance services.
www.dekkervacuum.com
LiteRatuRe
APRIL 2013 41 ComPRessoRtech2
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April_Literature.indd 2 3/21/13 2:34 PM
The Energy Information Adminis-tration (EIA) released its Short Term Energy Outlook in March.
The report highlights a rise in natu-ral gas consumption in Mexico which is great news for its closest neighbor, which currently sits atop a glut of gas.
According to EIA’s report, U.S. nat-ural gas exports to Mexico grew by 24% to 1.69 Bcfd (47.8 x 106 m3/d) in 2012, the highest level since the data collection began in 1973. With imports now accounting for over 30% of its to-tal supply, Mexico’s natural gas use is also at its highest level ever.
Natural gas consumption is ris-ing faster in Mexico than natural gas production, and as a result, Mexico is relying more on natural gas im-ports from the United States. Be-tween 2007 and 2011, natural gas consumption in Mexico rose 4% per year on average, while average an-nual natural gas production climbed only 1.2%. Growing demand in the industrial sector drove the increases in natural gas consumption in Mexi-co to a record-high level in 2011, ac-cording to Petróleos Mexicanos (PE-MEX) — the state-run oil and natural gas producer in Mexico.
The EIA report shows that pipeline shipments from Texas to Mexico be-tween 2009 and 2012 rose 34% on average per year to 1.3 Bcfd (36.8 x 106 m3/d), which was about 75% of the U.S. natural gas exports to Mexico in 2012. Most of the U.S. exports to Mex-ico departed the country from Hidalgo County in southwest Texas, where the supplies were likely coming from the Eagle Ford play.
Several U.S. pipeline export proj-ects that could support additional nat-ural gas exports to Mexico have been announced. According to company re-leases, these projects are expected to be completed by the end of 2014 and, if they are all built, could add up to 3.5
Bcfd (99.1 8 x 106 m3/d) of additional export capacity to Mexico, doubling the existing capacity.
One such project was announced in February. Houston-based NET Midstream announced plans build a 124 mile (200 km) pipeline to trans-port natural gas from the Eagle Ford Shale region to the Mexican border. The deal is anchored by a long-term agreement to transport 2.1 Bcfd (59.4 x 106 m3/d) with MGI Supply, a subsidiary of Mexico’s state-owned gas company. NET Midstream’s sub-sidiary, NET Mexico Pipeline LP, will build the 42 in. (106 cm) pipeline from a hub in Agua Dulce in Nueces Coun-ty to a point near Rio Grande City in Starr County.
Although Mexico has vast natural gas reserves, it hasn’t been able to develop them quickly enough to meet the country’s consumption, which has been climbing at four times the pace of overall economic growth at times in the past decade.
This additional capacity would serve an expected increase in natu-ral gas demand from Mexico’s elec-tric power sector. Mexico plans to add about 28 GW of new electric generating capacity between 2012 and 2027, mostly in northern Mex-ico, according to Comisión Federal de Electricidad (CFE) — Mexico’s state-run electricity provider. CFE estimates that this could raise natu-ral gas needs for power generation
Mexico’s Growing Thirst > Rise in Mexican gas consumption bodes well for U.S.
By BRENT HAIGHT
APRIL 2013 42 ComPRessoRtech2
Sour
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EIA
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EIA
CT173.indd 1 3/21/13 3:02 PM
by 5.1 Bcfd (144 x 106 m3/d). This level of growth would likely require increased natural gas imports from the United States.
Looking at the difference between demand and local production high-lights the need for increased imports. BP’s Statistical Review of World En-ergy (June 2012) reported Mexico’s demand for natural gas in 2011 av-eraged 6.7 Bcfd (189 x 106 m3/d). In 2012 demand increased to 7.8 Bcfd (220 x 106 m3/d) according to PEMEX — largely driven by higher gas fired power generation burn to meet the country’s growing industrial sector’s electricity needs.
By contrast, domestic natural gas production has fallen in Mexico since 2009 and it fell again by nearly 5% in 2012. This declining produc-tion has come in spite of huge natu-
APRIL 2013 43 ComPRessoRtech2
ral gas reserves. The EIA estimates that Mexico has 680 Tcf of natural gas including the world’s fourth larg-est reserves of shale gas.
EIA reports list Mexico as the world’s seventh biggest oil producer. State-owned PEMEX has a monopoly of all Mexico’s exploration and production and has prioritized oil over gas produc-tion. Add to that the fact that PEMEX also consumes up to 40% of natural gas production for oil recovery in its aging heavy oil fields — effectively re-moving it from the market and reducing available supplies — and we see why Mexico’s natural gas imports are rising.
Before 2006, almost all of Mexico’s natural gas imports came from the United States. More recently, Mexico has diversified its supply sources by importing liquefied natural gas from Nigeria, Qatar, Indonesia, Peru, and
Sour
ce:
EIA
Sour
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EIA
Sour
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EIA
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Yemen, although the vast majority of its natural gas imports continue to come from the United States.
The bulk of Mexico’s LNG imports — over 90% in 2011 — arrive at the Altamira plant in Tamaulipas state, on Mexico’s northeastern coast. The plant, which has a capacity of 500 MMcfd (14 x 106 m3/d), received its first LNG cargo in August 2006. CFE, the state-owned electricity monopoly, has signed a 15-year contract to pur-chase the entire volume of natural gas received at the terminal.
Mexico has two operational LNG re-gasification terminals besides Altamira. The Costa Azul terminal near Ensena-da, on Baja California, began receiving LNG in 2008. It is operated by Sempra Energy. The current send-out capacity of the plant is about 1 Bcfd (28 x 106 m3/d). Most of the natural gas imported at Costa Azul supplies domestic cus-tomers in northwest Mexico.
A new LNG import terminal at the port of Manzanillo, also on the Pacific coast, reportedly began initial operations in 2012. However, Mexican government data do not cite significant LNG flows into Manzanillo as of September 2012. According to industry reports, LNG sup-plies for the Manzanillo plant will come from Peru under a long-term contract. The plant was built by a consortium of Mitsui, Korea Gas Corp., and Samsung, with an initial capacity of 500 MMcfd (14 x 106 m3/d). CT2
CT173.indd 2 3/20/13 10:19 AM
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Little has changed for the Swiss magnetic bearing company Mecos since MAN Diesel &
Turbo acquired it last May — except for increased coordination with its new owner.
COMPRESSORtech2 recently in-terviewed Uwe Lauber, CEO of MAN Diesel & Turbo Schweiz, of Zurich, and Florian Lösch, CEO of Mecos, in Winterthur, Switzerland.
Lauber said MAN’s strategic acqui-sition of Mecos reflected its philoso-phy of having in-house all of the key components needed to further devel-op its centrifugal compressors used in the oil and gas industry.
He said future orders would be
more and more oriented to the use of high-speed, electric-motor-driven compressors for ecologic reasons (noise and atmospheric emissions) and the use of active magnetic bear-ings (AMB). The latter not only en-able machinery to reduce emissions because they do not require a lube oil system, but also extend the mean time between overhauls (MTBO).
Lauber said the market offers motors designed for maximum efficiency that can be used in sealed compressors handling mid and downstream clean gas. But in upstream applications, when the compressor is handling untreated wellhead gas (dirty and/or sour), reli-ability is more important than efficiency.
That is why, in 2005, MAN began developing high-speed, variable fre-quency electric motors and introduced them in the market in 2010.
“The Mecos acquisition has been a further step in the same direction,” Lau-ber said. “We started a very close coop-eration in 2005 and since 2011 we have on our test bed in Zurich a 24,000 hp (18 MW) motor compressor (Mopico) run-ning on Mecos AMB.” The radial bear-ings feature a 10.5 in. (270 mm) internal diameter and a 5850 lb. (26 kN) capac-ity while the axial thrust bearing has an 18,000 lb. (80 kN) capacity.
Alfons Traxler founded Mecos in 1988 with the specific intention of develop-ing AMB, Lösch said. The company achieved the first application of AMB on a 671 hp (500 kW) turboexpander in 1993.
Volume production of AMB for laser power systems began in 1997. Sys-tems for the high-vacuum pump indus-try were introduced in 2010. Mecos now has three AMB lines: small ones for powers up to 135 hp (100 kW), medium ones up to 1340 hp (1 MW) and the large ones to 26,800 hp (20 MW).
Although MAN acquired 100% of Mecos, Lösch said the company would continue to operate independently in its traditional market segments. It will keep the name and logo that its cus-tomers recognize.
Lauber said if other compressor man-ufacturers wanted to develop projects with Mecos, MAN would not considered it a problem. “As previously stated we have our own electric motor line, but we continue to buy electric motors from the marketplace, and just to mention one name, from Siemens,” Lauber said.
Lauber said it is important for MAN to have the magnetic bearing technol-ogy in-house so that its teams of com-pressor and motor specialists can work
Mecos Acquisition Opens Opportunities For MAN > Swiss magnetic-bearing specialist will continue
independent operationsBY ROBERTO CHELLINI
APRIL 2013 46 ComPRessoRtech2
n This compressor end cover shows a Mecos radial active magnetic bearing.
continued on page 48
CT163.indd 1 3/20/13 11:07 AM
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APRIL 2013 48 ComPRessoRtech2
in close cooperation with the Mecos team of magnetic bearings specialists. “Winterthur is only 18 mi. (30 km) from our main facility in Zurich, so we have face-to-face collaboration,” he said.
Lauber said MAN’s philosophy be-hind acquisitions is to maintain the management and the team of spe-cialists of the company unchanged in order to maximize the results of the deal. “Personnel are the core of a company,” he said.
The final assembly of the bear-ings is performed in-house, as are the final tests. All electronic compo-nents are tested for at least six hours to discover possible early failures. Functional tests are followed by en-durance tests that include power and temperature cycling.
For the large AMB systems, Mecos has developed a nine-channel control cabinet that allows simultaneous con-trol of both the compressor (also in a tandem configuration) and its electric motor drive. The system, as well as being more economic than one with separate controls for the compres-sor and the motor drive, guarantees faster tuning and simplifies the motor- compressor operation.
When the bearings must operate in a wet or sour gas environment, sensor isolation with special resins is essential to prevent failures. Mecos has engi-neered sealed sensors that can be re-motely set through an electronic system without touching the sensor itself.
Mecos engineers commission of individual AMB systems although in some cases (for bulk supplies) the customer may commission units under guidance from Mecos. MAN teams now will take responsibility for complete compressor, motor and AMB systems. CT2
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n Large Mecos active magnetic bearings have been checked on this compressor test stand at MAN’s Zurich plant.
Lauber said for the time being, MAN’s major interest in Mecos is the development of compressors for the oil and gas industry, but in perspec-tive, magnetic bearings also can be of interest to other MAN businesses such as diesel engines or gears.
Mecos personnel focus on engi-neering and electronics. Coil windings are outsourced to long-term partners operating in the area that have been selected for their quality standards.
CT163.indd 2 3/21/13 3:06 PM
Pressure-sensitive valves and integrated flow nozzles allow the FFP�piston to travel on a thin cushion ofprocess gas
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APRIL 2013 52 ComPRessoRtech2
In the light of limited gas and oil re-serves, coal is experiencing a renais-sance as a raw material. In countries
such as India, China, and Indonesia, as well as in Malaysia and Australia, coal gasification in particular has been receiving lots of attention of late as a process that yields synthesis gas (syn-gas) for use in fuelling diverse facilities. The primary advantage is that even
(domestic) coal of inferior quality can be converted to syngas, hence reducing dependence on imported oil.
The same trend is taking hold in In-dia, too, where Jindal Steel & Power is building a coal gasification plant to obtain synthesis gas for producing pig iron. Measuring upwards of 7.72 sq.mi. (20 km2), the site has room for an air separation plant, coal-pressure gasifiers, a power plant and the steel mill itself plus all the requisite infra-structure. The core components of the process are the coal gasifiers, in
which coal is converted to synthesis gas by means of partial oxidation with steam and oxygen. The process takes place at high pressure and tempera-ture. Seven fixed-bed pressure gasifi-ers and the requisite downstream gas conditioning and desulfurization pro-cesses are currently being installed. A total capacity of 7.9 MMcfh (225,000 Nm³/h) of synthesis gas is being tar-geted for the downstream direct re-duced iron (DRI) process that yields the pig iron.
Warning: Contents Are Hot > Coal gasification plant uses hybrid
pumps to handle gas liquorBy SABINe MühleNkAMP
PumP
tech
Sabine Mühlenkamp is a chemical engi-neer working as a journalist in Karlsruhe, Germany.
n A performance test is being conducted on a KWP pump destined for use in the new coal gasification plant in the east Indian state of Odisha.
Credit: KSB Aktiengesellschaft
continued on page 54
CT166.indd 1 3/22/13 10:39 AM
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APRIL 2013 54 ComPRessoRtech2
n Designed for use in a gasification plant, this cutaway shows the interior of a special nonclogging impeller pump type RPKx 150-400.
Handle with careThe process demands peak perfor-
mance from the plant and equipment, the dimensions of which are accord-ingly huge. Each pressure gasifier, for example, is nearly 13.1 ft. (4 m) in diam-eter. Temperatures of 1832°F (1000°C) inside the reactor and as high as 932°F (500°C) on the outside surface are just the face of the challenge.
“The real problem for components like the pumping systems is the com-bination of abrasive, aggressive and corrosive constituents in the gas li-quor,” said Thomas Wallner, a Pegnitz, Bavaria, Germany-based KSB project engineer who has been on the project since the start. The fluids can contain particles of coal measuring up to 0.23 to 0.31 in. (6 to 8 mm) across and ac-count for as much as 10% by weight.
“This combination imposes particu-larly stringent demands on the choice of materials and the design of the sys-
tem,” Wallner said. Specially designed pumps were needed for handling the gas liquor, because they have to last at least 15 years, despite the harsh service conditions.
Reliability requiredThanks to years of experience with
similar projects in South Africa, KSB is familiar with the application param-eters, the company said. The process is heavily dependent on the employed grade of coal, and coal can vary wide-ly in composition, depending on its origin. This factor must be kept in mind when designing the process and the components to ensure that each and every solution is specifically appropri-ate to the task.
In the present case, the pumps are a hybrid type comprising the best traits of the RPK volute casing pumps and KWP nonclogging impeller pumps. Each has a Norichrom wear plate and double me-chanical seals. Describing the specific properties of KSB’s favored material for the application, Wallner said, “This KSB cast material is unbeatable in terms of resistance to wear and corrosion.”
INFO BOX 1Process with perspectives
Altogether, 149 plants with a to-
tal of 430 gasifiers are in service
around the world, producing near-
ly 80.5 million hp (60,000 MW)
worth of synthesis gas, with other
plants coming online all the time.
While the synthesis gas produced
in Angul, Odisha, India is used for
making pig iron, pressurised coal
gasification is also used in fuel
production in coal-to-liquid plants,
and for power generation in in-
tegrated gasification combined-
cycle (IGCC) power stations. The
latter technology is generating
lots of interest because it produc-
es electricity in a more ecological-
ly viable manner than in conven-
tional pulverized coal-fired plants.
In addition, the environmentally
relevant CO2 can be captured at
low cost. Finally, pressurized coal
gasification plays a major role in
the production of biofuels.continued on page 56
CT166.indd 2 3/21/13 3:27 PM
APRIL 2013 56 ComPRessoRtech2
Cre
dit:
KSB
Akt
ieng
esel
lsch
aft
n A simplified cutaway shows the interior of coal- pressure gasifier.
INFO BOX 2Details of the pressurised coal gasification process
Lumpy coal and other solid fuels can be gasified
in counter-current fixed-bed pressure gasifiers. The
vertical cylindrical reactor has an external water
jacket. The coal is fed into the gasifier from above,
while oxygen and steam are blown in from below.
A rotating grate ensures uniform distribution of the
coal. The coal is dried and the gases desorbed in the
upper part of the gasifier.
The reaction takes place at the next lower level,
where high temperatures and pressures act on the
coal in a reducing atmosphere to produce synthesis
gas consisting of CO, H2 and small amounts of CO2
and methane. Gas purification and desulfurization
equipment is needed.
The main advantages of this method are its reliabil-
ity, relatively low initial cost and long-term operational
reliability. Moreover, coal of inferior quality can be gas-
ified. The only drawback is that the raw gas contains
tar and the throughput is limited by the maximum di-
mensions of the gasifiers. The only way to increase
the capacity is to install additional gasifiers. New ap-
proaches, however, are already being developed.The entire process runs constantly in a potentially explosive atmosphere. The KSB pumps need to be reliable to keep the pressure gasifiers from fail-ing, which is why specially developed auxiliary shaft seal systems offering increased redundancy are provided.
The KWPK nonclogging scrubber pumps installed further downstream have to contend with enormous loads. Consequently, they are made of cast steel and particularly wear-resistant modified duplex Noridur DAS instead of grey cast iron. This type of pump is nor-mally built to pressure class PN10, but the KSB engineers extended the range by modifying their design and materi-als. The process’ high solids content is not only hard on the materials, but also means that the pumps’ hydraulic sys-tems and geometry, particularly of the impellers, had to be carefully fine-tuned to the job. Moreover, all pumps had to have as much free passage as possible and impart as little shear as possible to the pumped fluid.
“The gas liquor contains sulfur and ammonia as well as dissolved oils that
would tend to become so homoge-neously distributed at elevated rota-tional speeds that they could no lon-ger be separated out,” Wallner said.
KSB pumps also serve in the down-stream subprocesses. Altogether, 40 KSB pumps are employed in the core process, and another 60 units in such peripheral processes as coal handling, air separation and coolant circulation in the DRI process. The pumps’ nominal diameters range from DN 65 to DN 350.
Sole sourceIn addition to supplying the pumps
and the auxiliary systems, the Peg-nitz-based specialists were also re-sponsible for sizing and selecting the motors and frequency inverters. For example, ambient temperatures of around 122°F (50°C) made it neces-sary to install the inverters in air-con-ditioned cabinets away from the plant, which put 1476 ft. (450 m) between
the pumps’ motors and the inverters and provided EMC effects, Wallner said. The job of connecting the alu-minium cables also posed a challenge because they have much larger cross-sections than the customary European copper cables.
Plenty of potentialCoal gasification has plenty of po-
tential, and opens up new perspectives independent of fossil gas and oil as the prevalent energy sources. To be cost-effective, the relevant facilities must operate uninterruptedly for years on end. That, in turn, calls for robust, reli-able systems consisting not only of the pumps themselves, but also of things like frequency inverters and mechani-cal seals. The first few pumps demon-strated their reliability on KSB’s own test rigs in Pegnitz, and were delivered in April 2011, with the entire plant com-missioned that same year. CT2
CT166.indd 3 3/21/13 3:45 PM
Wärtsilä Hamworthy Ltd. will supply a series of pumps to be installed on a new floating
storage unit (FSU) being built by Sam-sung Heavy Industries in South Korea for Statoil. When completed, the FSU will be located on the Heidrun oil and gas field in the Norwegian Sea.
The Heidrun field has been produc-ing oil and gas since October 1995 from a floating tension leg platform with a concrete hull. Heidrun was dis-covered in 1985 by Conoco, which
served as operator for the exploration and development phase. A total of 76 wells are planned on the main field, in-cluding 51 producers, 24 water injec-tors and one gas injector.
Gas from Heidrun is piped to Tjeld-bergodden in mid-Norway and pro-vides the feedstock for Statoil’s meth-anol plant there. The field is also tied to the Åsgard Transport system. Heid-run gas is piped through this trunkline to Kårstø north of Stavanger and on to Dornum in Germany — a total dis-
tance of roughly 870 mi. (1400 km).Delivery of the Wärtsilä equipment
is scheduled for February 2014.The order includes 38 deep-well
cargo pumps produced by Wärtsilä, at Wärtsilä Svanehøj in Denmark, three fire water pump skids and two ballast pumps. The latter items are produced by Wärtsilä, at Wärtsilä Pumps in Singapore.
“The 2012 acquisition of Hamwor-thy added years of experience and
Company providing 43 pumps for Norwegian Sea-bound FSU
By BreNT HAIGHT
APRIL 2013 58 ComPRessoRtech2
n Wärtsilä’s Svanehøj range of electrically driven deep-well pumps can be delivered according to API 610 standards.
PumP
techWärtsilä PumpsIt Up >
continued on page 60
CT171.indd 1 3/25/13 9:33 AM
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April 2013 60 Compressortech2
extensive know-how on pump tech-nology to our in-house competences,” said Timo Koponen, vice president Wärtsilä, Flow & Gas Solutions. “This contract is further testimony to the reputation of our pumping solutions, and strengthens our position as a ma-jor player in the offshore oil and gas industry. The reliability, ease of instal-lation, and cost effectiveness of these solutions were all contributing factors in the award of this contract.”
This is not the first pump-related contract between Wärtsilä and Sam-sung. Wärtsilä and Samsung Heavy Industries signed a cooperation agreement in 2010 to develop gas-fueled ships. The collaboration has been beneficial to myriad Wärtsilä business units, including Hamworthy.
Wärtsilä Hamworthy offers a wide range of deep-well pumps for process and cargo handling for offshore appli-cations. The company has delivered
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pumps to Samsung Heavy Industries’ yard for other floating production, stor-age, and offloading (FPSO) vessels for the offshore sector.
For FPSOs/FSOs requiring a distrib-uted pump system, Wärtsilä offers the Svanehøj range of electrically driven deep-well pumps. Wärtsilä Svanehøj deep-well process and cargo pumps are designed for continuous operation with pumping mediums such as crude oil and produced water and oil. The type OPC pumps (offshore process and cargo) can be delivered accord-ing to API 610, and are designed with a capacity from 706 to 63,566 cfh (20 to 1800 m3/h).
According to Wärtsilä, its shaft lubri-cation system enables less onboard maintenance to the electric system. The pump housing is easily dismantled, and cards on the converters are easily interchanged. During the operational phase, the electrical equipment offers environmental sustainability, since CO2 emissions are minimal due to the higher efficiency and lower power utilization, and there is no risk of hydraulic oil spills, according to Wärtsilä.
Wärtsilä Svanehøj deep-well and booster pumps have been developed specifically for LPG/ethylene, small LNG and combined LEG/chemical carriers:
• Fully pressurized tankers, with the cargo at ambient temperatures and a tank pressure of up to 261 psi (18 bar).
• Fully refrigerated atmospheric tankers, with the cargo cooled down to the saturation tempera-ture, typically -54°F (-48°C).
• Semi-refrigerated tankers, with the cargo maintained in liquefied form by a combined cooling/pressure process at temperatures down to -155°F (-104°C).
• LNG tankers, with the cargo cooled down to -261°F (-163°C).
Deep-well pumps are designed to meet the requirements for low tem-perature-resistant materials, using a gas-tight shaft sealing system with a pressurized quenching fluid, and an extremely low NPSH to pump gases at a condition very close to their boil-ing point, according to Wärtsilä. CT2
CT171.indd 2 3/21/13 3:46 PM
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APRIL 2013 62 ComPRessoRtech2
Editor’s comment: This article first appeared in the No-vember 2012 issue. It is being reprinted because of errors that occurred in the graphics during production, which now have been corrected. We apologize for any confusion these errors may have caused.
Acoustic pulsations are not as frequent or common a source of vibrations or dynamics problems in plung-er pumps or other liquid pumping systems as they
are for gas piping systems.However, when resonant pulsations do develop in a liquid
pumping system they tend to be higher in amplitude and can cause more severe problems (e.g. cavitation) than in gas piping systems (Heveron, 1978). Therefore it is very important to have effective pulsation suppression solutions.
One common pulsation suppression device is a gas-liquid dampener (Figure 1). A gas-liquid dampener consists of a liq-uid volume and a gas-filled bladder precharged to a fixed per-centage of line pressure. The precharged gas creates a rela-tively large effective liquid volume to absorb pulsations. The gas volume acts as a spring compressing and expanding with line pressure changes and acts as a flow-smoothing device.
This type of pulsation device is best for use in applica-tions that have little space for the dampener because it is a small device that has an equivalent volume many times the size of an all-liquid volume. A detailed discussion of various types of dampeners and how they work is given by Wachel and Price (1988).
A more unusual pulsation suppression device is a low-pass acoustic filter. The low pass filter consists of one large volume split into two or more volumes connected with an internal choke tube (Figure 2) or two volumes connected with an external choke tube (Figure 3). The low pass filter attenuates frequen-cies above the filter response frequency (Hicks and Grant, 1979). The concept is analogous to a low-pass electrical filter or mechanical system where the volumes are springs and the choke tube is a mass (Blodgett, 1998).
For single-acting positive displacement pumps, the response frequency of the acoustic filter needs to be placed below the first pump running order (pump speed/60 times the number of plungers) to filter out all acoustic piping frequencies that may coincide with a pump running order. For low speed pumps or pumps with a large speed range, sizing the acoustic filter vol-umes to ensure that the response frequency is below the first pump running order often results in very large volumes that are unrealistic to install at the pump flange. For that reason, this type of pulsation control device is most feasible for higher speed pumps and/or multiplunger pumps (where the first pump running order is at generally 5 Hz or higher and therefore small-er chamber volumes are needed) and/or onshore applications that have the space necessary for large volumes.
Acoustic filters need to be carefully sized and designed,
Unusual PD Pump Pulsation Solutions > Pulsations in piping systems can cause
serious problems that sometimes require creative solutions
By EuGEnE BrOErmAn III And SArAH SImOnS
PumP
tech
Eugene (Buddy) Broerman III is a senior research engineer in the fluid machinery systems section at Southwest Research In-stitute (SwRI) in San Antonio, Texas. He has performed many acoustic analyses of machinery piping systems for compres-sors and pumps. He also has been a principal contributor in the research and development of advanced pulsation con-trol system prototypes and other pulsation related research. Sarah Simons is a scientist in the SwRI fluid machinery sys-tems section. She also has performed many acoustic and thermal analyses of complex existing and new machinery pip-ing systems, and currently is involved in pulsation research. This article is based on a paper the authors presented at the recent Gas Machinery Conference in Austin, Texas. For more information, contact the authors at [email protected] or [email protected].
n Figure 1. This sketch shows a typical gas-liquid dampener.
continued on page 64
CT140.indd 1 3/20/13 11:52 Am
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because they have internal choke tube responses that will have the effect of “passing” relatively discrete, unattenuated frequencies into the attached piping system. Therefore, it is important to model the filter and attached piping system with a computer simulation tool to ensure that the pass band fre-quencies do not cause problems in the piping system (McK-ee and Broerman, 2009). Because of the design complex-ity and space requirements, acoustic filters are rarely used; however, they are an ideal solution in many cases since they are maintenance free and extremely effective.
Unusual application of a gas-liquid dampenerTwo positive-displacement duplex methanol pumps oper-
ating in parallel in the same discharge piping system were experiencing small-piping connection failures and high vi-brations even with a gas-liquid dampener installed. The du-plex pumps are described in Table 1.
A field study (Figure 4) measured approximately 225 psi (15.5 bar) pk-pk pulsation amplitudes, which could equate to 4086 N of shaking force, in the main 2 in. (50.8 mm) line for the pumps operating at a fixed speed of 170 rpm.
The operating company wanted to install two additional triplex pumps operating in parallel with the existing duplex pumps. Before installation of the new pumps, the company requested a pulsation analysis of the existing duplex pumps to eliminate the current pulsation problem and a preventative pulsation analysis of future triplex pumps to ensure effective attenuation of any excessive or undesirable pulsations.
The unusual problem this station had was a large dis-
APRIL 2013 64 ComPRessoRtech2
charge operating pressure range that varied from 696.2 to 4550 psig (48 to 314 barg). The suction pressure was fixed at 36.3 psig (2.5 barg). The installed gas-liquid dampener for each existing pump had a gas volume of two liters and was precharged to 80% of 4003 psig (276 barg).
The operating company also wanted to install two new positive-displacement triplex pumps operating in parallel in the same piping system with the existing duplex pumps. Before installing the new pumps, the operating company requested a solution for better pulsation control.
n Figures 2 (left) and 3 (right). These are examples of single volume and two volume all liquid acoustic filters.
n Figure 4. Field study data is given for duplex methanol pumps. Note: High 1x = possible valve leakage; unclear if dampener was correctly precharged when data was taken.
continued on page 66
Duplex Pump Details Operating Conditions
2 Parallel Pumps(Plunger)
50.7 psig (3.50 barg)Suction Pressure
2 Plungers Per Pump80°F (26.7°C)Suction Temperature
1.65 in. Bore (4.19 cm)700 to 4550 psig (48 to 314 barg)Discharge Pressure
4.72 in. Stroke (12.0 cm)140°F (60°C)Discharge Temperature
170 rpm 11 gpm (3 m3/hr)
n Table 1.
CT140.indd 2 3/20/13 11:52 AM
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Since this was an offshore installation, there was not enough space for an all-liquid filter for pulsation control. Pressure pulsations can often be significantly reduced by the use of an orifice plate; however, orifice plates alone were not effective enough. Using a gas-liquid dampener was determined to be the best solution for pulsation control.
When choosing a dampener size, the large pressure range of this system had to be taken into account. To deter-mine the optimal size, an understanding of how and when a dampener is effective is needed. When the precharge pres-sure of a dampener is greater than line pressure (which was the case for most of the pressure range with the installed dampeners), the dampener is ineffective. Gas-liquid damp-eners typically close off when the line pressure drops below the dampener precharge to keep from failing the bladder inside the dampener.
When the precharge pressure is less than line pressure the liquid pressure compresses the bladder in the dampener. This decreases the gas volume, and therefore the effective volume, directly in proportion to the increase in line pressure per the ideal gas law. Thus, if the gas-liquid dampener is pre-charged to the lowest pressure in a large range, the highest pressure could compress the bladder too much, such that the bladder ruptures and/or the equivalent volume of gas in the bladder is too small to be effective.
Given the wide pressure range for this application, 696.2 to 4550 psig (48 to 314 barg), it was determined two gas-liquid dampeners were needed. One 1.3 gal. (3.5 L) damp-ener precharged to 80% of the lowest operating pressure would be open when operating over the lower half of the pressure range 696.2 to 2103 psig (48 to 145 barg). At 2103 psig (145 barg), the 0.9 gal. (3.5 L) dampener was less effective, so a 1.3 gal. (5 L) dampener precharged to 80% of 2103 psig (145 barg) would provide pulsation con-trol for the upper half of the operating pressure range 2103 to 4550 psig (145 to 314 barg). Figure 5 shows the pulsation reduction data predictions for the new triplex pumps operat-ing at 140 rpm.
APRIL 2013 66 ComPRessoRtech2
Unusual pulsation control deviceEight positive-displacement triplex pumps operating in
parallel at 303 rpm as described in Table 2 were experi-encing high suction and discharge piping vibrations and failures of discharge vessel drain connections and gussets.
The discharge side of these pumps had a single three-chamber vessel acoustic filter installed that was inade-quately designed. A field study of one of the eight pumps captured a measurement of 27 mils p-p at 15 Hz (first pump running order) at the discharge valve flange and 19 mils p-p at 15 Hz at the discharge recycle valve.
The vibration severity chart in Figure 6 shows a graph with acceptable and danger or correction levels of vibration at each frequency; the vibration measurements observed during the field study are plotted on the chart. Each of those two measurements was in the correction range of the chart.
The discharge vessel outlet piping pulsations were mea-sured to be 58 psig (4 barg) p-p at 15 Hz. This raised safety and reliability concerns and SwRI was contacted to help improve the system vibrations such that the piping failures
n Figure 5. Tables show pulsation reduction data.
continued on page 68
Triplex Pump Details Operating Conditions
8 Parallel Pumps(Plunger)
160 psig (11 barg)Suction Pressure
3 Plungers Per Pump80°F (26.7°C)Suction Temperature
2.25 in. Bore (5.7 cm)3000 psig (207 barg)Discharge Pressure
5 in. Stroke (12.7 cm)140°F (60°C)Discharge Temperature
303 rpm 75 gpm (17 m3/hr)
n Table 2.
CT140.indd 3 3/20/13 11:53 AM
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APRIL 2013 68 ComPRessoRtech2
will no longer occur. By designing a better pulsation control device, the cause of the vibrations was significantly reduced.
When SwRI analyzed the existing acoustic filter (Figure 7) to determine why it was ineffectively attenuating pulsa-tions in the system, it was noted that the resonant frequency of the existing acoustic filter was not placed below the first pump running order. This was seen in the high amplitude response of the first running order in the field data. Also, the existing pulsation bottle had multiple pass band frequencies associated with its multiple choke tubes. It is best practice to minimize the number of frequencies that the filter will “pass” (not attenuate) into the attached piping system.
SwRI designed a larger diameter single-volume, two-chamber acoustic filter as shown in Figure 8 with lower
n Figure 6. This chart shows vibration severity.
n Figure 7. The original, ineffective acoustic filter design is shown.
pressure drop than the existing filter. The original pulsation filter reduced the pressure by 100.1 psi (6.9 bar), which was approximately 17.4 psi (1.2 bar) above the pressure drop associated with the recommended vessel.
The client initially installed the new acoustic filter on only one pump to verify its effectiveness at attenuating pulsations in the piping system. After installation of this new design, the client was so pleased with the system that they installed the new filter on all eight pump discharge piping systems.
ConclusionPulsations in piping systems can cause serious problems
that sometimes require creative or unusual solutions. Add-ing two or more gas-liquid dampeners when operating over a large pressure range or using an acoustic filter when a maintenance free solution is needed can solve unusual pulsation problems that are not sufficiently attenuated with typical solutions.
It is very important when sizing dampeners to understand the acoustics and filtering properties of each specific type of dampener to ensure pulsations are adequately damped and to avoid making costly mistakes.
continued on page 70
CT140.indd 4 3/20/13 11:53 AM
It would be much easier if every molecule reacted exactly the same way when it reaches the surface of the catalyst. Since they don’t, the engineer sizing a catalyst has to evaluate what is in the exhaust and what performance is required in order to meet the permit limits. The process is especially challenging when evaluating high-level hydrocarbon conversions for oxidation catalysts on lean-burn engines.
Defining the Target Often a lean burn engine’s emission of concern is CO alone, so the sizing process is straightforward. However, there are instances where the control of the hydrocarbon emissions becomes the primary issue because of where the engine is located. After learning what engine is involved and what to expect for a catalyst inlet temperature, the engineer next needs to know whether your permit is written for Non-Methane Hydrocarbons (NMHC) or Non-Methane, Non-Ethane Hydrocarbons (NMNEHC), and what is the emissions limit. Your permit may use the term VOC or Volatile Organic Compound, which the EPA defines as NMNEHC. Because the EPA doesn’t consider formaldehyde a VOC, for simplification purposes this article will omit formaldehyde. However, be aware that the new RICE MACT rules and individual states may have additional restrictions that govern its emission. The engine’s spec sheet or technical information will reveal its total expected raw hydrocarbon emissions. A fuel analysis for the site should also be provided to reveal what hydrocarbons,
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such as ethane, propane, butane, hexane, etc., are present. The chemistry of what happens in the cylinder when the spark plug fires is rather complex. Because it is rare for a complete site specific chemical breakdown of the hydrocarbons in the exhaust to be available, a simplifying assumption is made that the hydrocarbons survive to be emitted in the same proportion as they exist in the fuel gas. From this information, the required conversion efficiency for each species will be made so that the catalyst will hit the permitted emissions.
A Data Driven Process Figure 1 is a graph showing the conversion efficiency of various hydrocarbons as a function of the Gas Hourly Space Velocity (GHSV). This is the type of data that the engineer will use to size the catalyst. The most conservative approach sizes the catalyst by using the GHSV for the compound expected to be in the exhaust that is the hardest to convert. Provided the fuel constituents do not change over time, this conservative approach
does compensate for changes in their relative concentration so that the catalyst will always meet the permit. A more sophisticated approach calculates a GHSV based on the blended contribution of each constituent species to the required conversion efficiency. Such a process will yield a higher GHSV and thus a smaller catalyst compared to the method
above, but it is typically used for sites where the fuel composition is very stable. As an example, let’s stipulate that the raw NMNEHC emissions for an engine are 0.45 g/bhp-hr and the permitted emissions are 0.12 g/bhp-hr, requiring a conversion efficiency of 73.3%. In Figure 1, you see that the GHSV for propane is 71,000, butane is 83,000 and pentane is 97,000. So, depending upon what is in the fuel, the size of the catalyst can vary considerably. Proper design for a lean-burn engine requires more effort, but giving your catalyst company all of the appropriate information better enables them to select the correct catalyst to keep you out of trouble on your hydrocarbon emissions.
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ReferencesHeveron, G.C., 1978, “Pulsation Dampeners and Stabiliz-
ers Help Protect Pump Systems in Nuclear Plants,” Power 122 (10), pp. 28-32.
Wachel, J.C. and Price, S.M., 1988, “Understanding How Pulsation Accumulators Work,” Pipeline Engineering Sym-posium, PD-Vol. 14.
Hicks, E.J. and Grant, T.R., 1979, “Acoustic Filter Con-
n Figure 8. This is the newly designed acoustic filter.
trols Recip Pump Pulsations,” Oil and Gas Journal, Volume 77, Issue 3, pp. 67-73.
Blodgett, L.E., 1998, “Reciprocating Pump Dynamic Concepts for Improved Pump Operations,” 15th International Pump Users Symposium Proceedings.
McKee, R. and Broerman, E., 2009, “Acoustics in Pump-ing Systems,” Proceedings of the Twenty-Fifth International Pump Users Symposium, pp. 69-74. CT2
Voith.indd 1 10/22/12 3:27 PMCT140.indd 5 3/20/13 11:54 AM
It is widely known that the prevention of a gas turbine failure is crucial to operators and original equipment
manufacturers. One of the key factors to a turbine’s reliability is also one of the least visible parts of the power gen-eration process: lubricating oil.
Theoretically, turbine oils should last for years, although exactly how long is subject to a variety of factors, especially as the fluid must have good thermal and oxidation resistance.
“Modern lubricants need to keep pace with advances in turbine tech-nology,” said Peter Smith, Shell’s tech-nical manager for industrial special-ties, Shell Lubricants, which focuses on turbine, electrical and process oils.
“Gas turbine firing temperatures are increasing to up to 1450°C (2642°F) and, although the oil is not directly ex-posed to this temperature, this means that the whole gas turbine system is under much more stress than ever be-fore,” Smith said.
“Therefore, lubricating oils have to be more resistant to such things as
deposit formation due to oxidation and thermal degradation. Firing tempera-tures in gas turbines over the years have gone up by hundreds of degrees. The temperatures have increased so much because operators want to pro-duce even greater megawatts of pow-er. For example, a Siemens gas turbine can produce up to 375 MW [503,000 hp]; the lubricants have to be able to withstand the demands placed upon them in such conditions.
“As OEMs and operators try to achieve higher and higher efficien-cies from their gas turbines, we can provide a lubricant able to help them achieve that, especially as some oper-ators want more than 50,000 operat-ing hours from their lubricants before a service. Of course, OEMs want their gas turbines to last longer and provide maximized reliable service between extended maintenance intervals.”
Shell said it is currently redeveloping its top-tier Turbo GT using its propri-etary additives and Group 3 base oil. It is being designed for use in industrial
light- and heavy-duty gas turbines and turbo compressors. According to Shell, Turbo GT has up to 50% better oxida-tion stability compared with the indus-try standard for gas turbines.
Shell uses gas to liquid (GTL) tech-nology, utilizing the Fischer-Tropsch process that converts gas and feed-stocks to liquids. Shell’s Pearl GTL plant in Qatar makes synthetic oil products from natural gas, including cleaner-burning diesel and oils for advanced lubricants.
“Another trend we are noticing dur-ing discussions with turbine manufac-turers concerns the growing demand for smaller lubricant reservoirs for gas turbines,” Smith said.
“Not only do OEMs want to optimize the power and efficiency of their ma-chines, but they want to control the cost of manufacturing their gas tur-bines. They prefer smaller lubricant reservoirs as smaller amounts of lu-bricants can now be considered using the latest generation of top-tier oils. If the reservoirs are smaller, then the turbines can be downsized and the cost of components reduced.
“Good surface properties of the oil, such as rapid air release, are essen-tial. If these are poor, that can lead to foaming of the oil. Under changing load, entrained air can be released, causing bubbles and foaming. In highly loaded regions, this can cause the air and oil vapor bubbles to literally implode and burn, thus potentially causing cavitation damage to the turbine’s bearings.”
Shell has 60 years of experience in developing oils for gas turbines and supplies fuel and lubes to more than 1500 power plants in more than 80 countries — some 100 people work in its power sector product area. The company has technology centers in the U.S., U.K., Germany, India, China, and a joint venture in Japan. CT2
Lubes Evolve With Higher Turbine Performance > Oils redeveloped to accommodate hotter firing,
smaller reservoirsBY IAN CAMERON
APRIL 2013 72 ComPRessoRtech2
n Shell has 60 years of experience in de-veloping oils for gas turbines and is cur-rently redeveloping its top-tier Turbo GT for use in industrial light- and heavy-duty gas turbines and turbo compressors.
CT159.indd 1 3/25/13 9:57 AM
APRIL 2013 73 ComPRessoRtech2
HydrotexHydrotex, a manufacturer and distribu-
tor of lubricant and fuel improvement prod-ucts, has hired Eric Cline as research and development director and John Alecu as research and development manager.
Cline had been CEO and chief scien-tist of ZT Solar, a startup company that developed antireflective coatings for solar cell and optical applications. He also held positions at Merck and the Southwest Re-search Institute.
Alecu’s areas of expertise include kinetics, thermodynamics, quantum mechanics, combustion chemistry, at-mospheric chemistry, physical-organ-ic chemistry, computational chemistry, and free radical chemistry.
Cook CompressionCook Compression has begun sup-
plying the Chinese and other Asian markets from a new 11,000 sq.ft. (1020 m2) manufacturing and service facility at Suzhou, China.
Cook China makes valve assemblies, rings and packing, with internal metallic and nonmetallic parts supplied from Cook operations in Europe and the United States. It also performs valve and packing case repairs. It will begin full production of all ring and packing products this year.
Willa Qu has been named general manager of Cook China Operations. She previously was China sales director for Dresser Wayne Fuel Equipment China.
Also, Cook Compression Russian Op-erations has been established in Moscow, five years after Cook first began opera-tions in the Russian Federation. Sergey Kalabekov has been named area sales manager and Irina Benediktova assis-tant sales manager.
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April_PrimeMovers.indd 1 3/20/13 4:24 PM
Rolls-Royce has announced a US$75 million contract to supply PetroChina with equip-
ment and related services to move gas through Line III of the West-East Pipeline Project (WEPP), the world’s longest pipeline.
It will supply PetroChina with six RB211 gas turbine-driven RFBB36 compressor units for WEPP Line III. When completed in 2015, the 4350 mi. (7000 km) WEPP Line III will link China’s western Xinjiang autono-mous region to Fuijan province in the Southeast, transporting up to 1.1 Tcfy (30 x 109 m3/yr).
Rolls-Royce has provided equip-ment and services to WEPP since 2004. Including the latest contract, it has sold 37 RB211 units to WEPP.
“WEPP natural gas will boost China’s economic growth and ensure greater security of electricity supply to China’s fast-developing cities,” said Andrew Heath, Rolls-Royce president, energy.
“In terms of servicing the installed base, in addition to our in-country field service representative based at the site to provide ongoing service for the pipeline, we work with PetroChina to train their operators before they begin to manage the equipment at the sites along the pipelines.
“In addition, we are providing licens-ing support to a maintenance repair and overhaul facility that PetroChina is building in Langfang, Hebei province, not far from Beijing, expected to be operational in mid-2013. All of these factors strengthen our role on the proj-
ect and our relationship with and sup-port to PetroChina.”
Efficiency is a key factor in the proj-ect, Heath said.
“The high efficiency of the Rolls-Royce RB211 units and our compres-sors means more gas will reach the consumer, ultimately increasing gas volumes and potential profit for the operator,” he said. “As gas prices con-tinue to increase, efficiency really be-comes the most crucial factor driving the value equation.
“The high simple-cycle efficiency of the engine also makes it ideal as a driver of pipeline compressors. Its low weight and the ability to quickly remove the gas generator for transport and maintenance is another key feature for this application, which, like the WEPP
Turbine-Driven Compression For China > Rolls-Royce secures additional orders for turbine-driven
compressor packages in ChinaBy IAn CAmERon
n This Rolls-Royce RFBB36 gas compressor was installed at the Zhongwei compressor station on the WEPP Line I gas pipeline in China.
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installations, are often in remote loca-tions far from maintenance facilities.”
Commenting on the specific proj-ect tasks faced by the engineering teams, Heath said: “Along with the station design teams we faced several challenges, including the desert sand storm environment experienced at many of the stations in or close to the Gobi desert and in the winter months’ extremely cold temperatures.”
Heath said the RB211 gas turbines would have to operate in temperatures from -40° to 104°F (-40° to 40°C).
“Transportation is another challeng-ing issue, as on some parts of the pipeline route the low loaders carrying the turbines and compressors could travel at less than 30 mph (50 kph) and sometimes down to walking pace. On the western section of the line there was no land access so roads had to be built just to deliver the equipment.”
Rolls-Royce will make and pack-age the equipment for WEPP at its facilities in Montreal, Quebec, Canada and Mount Vernon, Ohio. In-cluding WEPP, Rolls-Royce has sold 56 RB211 units for installation on Chinese and Central Asian natural gas pipeline networks. That includes five RB211 compressor sets to the Shaanxi-Beijing Third Gas Pipeline running from northwestern China’s Shaanxi province to Beijing. The 550 mi. (896 km) pipeline can move 550 Bcfy (15 x 109 m3/yr) to Beijing and other areas in the Bohai Rim region.
Rolls-Royce also received a US$40 million contract to supply equipment and services for an Uzbekistan com-pressor station on the Turkmenistan-China natural gas pipeline. It will sup-ply Asia Trans Gas, a joint venture between Uzbekistan’s Uzbekneftegaz and China’s National Petroleum Corp., with three RB211 gas turbine driven pipeline compressor units for a station on the 330 mi. (530 km) Uzbekistan section of the pipeline.
The 1140 mi. (1830 km) project will transport 880 Bcfy (25 x 109 m3/yr) of gas from Turkmenistan and across Uzbekistan and Kazakhstan to China. Rolls-Royce also will manufacture and package that equipment at Montreal and Mount Vernon. CT2
MoversPRIME
Ansaldo Sistemi IndustrialiThe Japan-based Nidec Group has ac-
quired Ansaldo Sistemi Industriali (ASI) of Italy, a global supplier of electric motors and generators for compressors, pumps, turbines, and other applications.
Formed in 1973, Nidec has expand-ed from its original product base of mo-tors for information and communication
technologies to motors for home appli-ances, automobiles, office equipment and industrial machinery.
The ASI acquisition will enable Nidec to supply a wider range of products, such as high power range industrial mo-tors, medium- and low-voltage drives and industrial automation systems.
continued on page 93
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Mark Noall is pipeline engineer with KMI Pipeline. His respon-sibilities include technical support for reciprocating and tur-bine engine driven compression in West Texas and southeast New Mexico. He has 30 years of experience in the energy industry and has a Bachelor of Science degree in mechani-cal engineering from Brigham Young University. David Maas is a mechanical supervisor for Kinder Morgan Inc. He gradu-ated from Colorado State University with a Bachelor of Sci-ence degree in electrical engineering and a master’s degree in mechanical engineering. His graduate work was done at the university’s engines and energy conversion laboratory. This article is based on a paper the authors presented at the Gas Machinery Conference in Austin, Texas, last October. Contact the authors at [email protected] or [email protected].
Vector Analysis Of Crankshaft Web Deflections >
Crankshaft web deflection measurements have his-torically been used to evaluate crankshaft align-ment and as criteria to take action to prevent crank-
shaft failure [1].Research has correlated web deflection measurements
to peak stress levels in the crankshaft fillets. Web deflec-tions can now be converted into calculated stress values on a throw-by-throw basis. These calculations account for variations in pin and stroke dimensions and provide more reliable criteria to evaluate the risk of failure.
Web deflection readings from one throw to the next can also point to a bending reversal in the crankshaft. For example a bending reversal occurs when the web deflection of one throw shows the web opening at the bottom while the adjacent throw shows the web opening at the top. Bending reversals in crank-shafts may be part of the crankshaft failure mechanism.
Crankshaft reversals cannot be detected with the web deflection to stress calculations, as they do not take into account the influence of the adjacent throws. One effective way to identifying the locations of these reversals is to con-struct a maximum web deflection vector graph and com-pare the throw-to-throw vertical and horizontal components for changes in direction.
In 1998 and again in 2010, the crankshaft in a Clark TLA-
10 integral engine failed. In an effort to better understand why we had two crankshaft failures on the same engine, op-erating history, mechanical maintenance records and web deflections were reviewed from 1993 to 2010. The historical data when combined with optical, laser and wire-line frame measurements made after the 2010 failure provided valu-able insights into the root causes of these failures.
One of the pertinent findings was that both failures did not occur in a high-stress area of the crankshaft, as calcu-lated from web deflection readings. One of the failure loca-tions closely coincided with a web deflection “reversal.” The other failed where the crankshaft was bridging a bearing.
n Figure 1. Web location is shown on the crankshaft.
Measuring web deflectionsWeb deflections are a measure of the change in distance
between the crankshaft webs. The change in distance oc-curs as the crankshaft moves through 360° of rotation. The maximum web deflection across a throw is the difference between the maximum and minimum distances between the webs. (See Figure 1.)
When the engine frame and bore lie in a straight line the crankshaft will also be straight. The distance between the webs will not change and the web deflection readings will be zero. If the engine frame is misaligned the crankshaft will
TECHcorner Deflections can be converted into calculated stress values on a throw-by-throw basis
By MARk NOALL AND DAvID MAAS
April 2013 76 Compressortech2
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n Figure 2. Web deflection is shown in three conditions.
not lie in a straight line. For example, if the frame sags in the middle so will the crankshaft. A sagging crankshaft results in the webs opening at the bottom and closing at the top. (See Figure 2.)
Web deflections are measured with a micrometer placed across the crankpin throw. The pointed ends of the microm-eter are placed in punch marks on the webs. (See Figure 3.) The punch marks are typically located at the diameter of the main bearing journals. Prior to taking measurement the gauge is spun to seat the points in the punch marks.
The crankshaft is manually rotated and deflection read-ings, measured in “mils” (0.001 in. or 0.0254 mm), are typi-cally taken every 45°. Connecting rods attached to the crank-pin prevent data collection over the full 360° rotation. Often, deflections can be measure only for 180° of the rotation.
n Figure 3. These punch marks are for positioning the micrometer to read web deflection.
Web deflections and crankshaft stress
When a bend or bow exists in the crankshaft, most of the bending occurs in the webs. The webs have the smallest cross section of the crankshaft and are there-fore subject to the highest cyclic bending stresses. The
continued on page 78
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Gas Machinery Conference paper, “An Improved Criteria for Assessing Crankshaft Misalignment,” developed this relationship [2].
The stress is concentrated in the webs at the fillets be-tween the main and crankpin journal. Elevated bending stress in the webs combined with hundreds of millions to billions of crankshaft revolutions or bending cycles can eventually lead to a high-cycle fatigue failure. High-cycle fatigue failures are almost exclusively across crankshaft webs. (See Figure 4.)
n Figure 4. This is the usual location of fatigue failure across crankshaft web.
Maximum web deflectionFigure 5 shows a typical set of web deflections as ini-
tially recorded. Connecting rods attached to the crankpin prevented data collection over the full 360° rotation. Deflec-tion readings were measured every 45° from 135° to 315°. Measurements were taken in mils.
The maximum web deflection across a throw is the dif-ference between the maximum and minimum measured
deflections over the full 360° rotation. But what if the mini-mum or maximum deflection reading occurs at an angle that can’t be accessed by the deflection gauge? How can the maximum deflection value be determined if it cannot be measured? The answer to this problem comes in the form of a mathematical curve fit that calculates the maximum de-flection and the angle at which it occurs.
The sinusoidal curve fitAs with many rotational systems, web deflection measure-
ments exhibit a sinusoidal behavior. (See Figure 6.) Measure-ments taken at regular crank angles will fall on a sine wave. The maximum deflection will be the difference between the minimum and maximum values of the sine wave.
n Figure 6. These readings were taken while the crankshaft is be-ing rotated to generate a sine wave.
The sine wave for web deflections can be written as fol-lows using a sine function that operates on degrees of an-gle rather than radians.
Where A is the zero-to-peak amplitude of the sine wave and 2A is the peak-to-peak value or maximum web deflec-tion. w (phi) is the phase angle and C is an offset value from arbitrarily setting the deflection micrometer to zero at the first measurement angle.
Fitting the web deflection data to a sine wave is a matter of calculating the amplitude A, the phase angle, w, and the offset, C, to minimize the error between the data set and the equation. This can be accomplished iteratively or by solving a set of linear equations.
Three data points are needed to solve for values of A, w and C. A sinusoid can be perfectly drawn through any three data points. It is recommended that four or more readings be measured on each web. This allows for a correlation co-efficient to be calculated which expresses how well the data exhibits a sinusoidal behavior. The correlation coefficient R2 is a measure of the error between the data points and the sine curve. An R2 value of 1.000 indicates a perfect cor-relation, whereas values less than 0.900 could indicate er-rors in data collection or other problems such as damaged bearings or excessive crankshaft run out.n Figure 5. This is a set of initially recorded web deflections.
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The maximum web deflection, 2A , is used to calculate the peak fillet stress of the throw. When 2A and w are viewed as a vector with magnitude and direction, and in conjunction with similar data from each throw of the crankshaft, additional infor-mation can be inferred about the crankshaft alignment.
VectorsThe phase angle w, tells us where in the 360° of crank-
shaft rotation, the sine function, starts. Reviewing Table 1 of basic sine function results, it’s clear the maximum value of a sine wave is one and occurs at an angle of 90°.
Sin (0°) = 0.000Sin (45°) = 0.707Sin (90°) = 1.000 Maximum Value
Sin (135°) = 0.707Sin (180°) = 0.000Sin (225°) = 0.707Sin (270°) = 1.000 Maximum Value
Sin (315°) = 0.707Sin (360°) = 0.000
n Table 1. This table shows basic sine function results.
The phase angle simply shifts where, in the 360° of rota-tion, the maximum value occurs. So +90° is the angle of maximum web deflection or greatest distance between the webs. Conversely -90° is the angle where the webs are closest together.
The example below shows a maximum web deflection occurring at 253°. The w value of the vector is 163°.
So, w +90° indicates the direction of the maximum de-flection vector and the amplitude 2A indicates the magni-tude of the vector. This technique enables constructing web deflection vectors for each of the throws of the crankshaft. The vectors now can be compared from one throw to the next. The horizontal and vertical components of these vec-tors can provide additional insights into crankshaft align-ment. First, consider three simple examples. The real world is combination of these examples.
n Figure 7. These are typical web deflection readings of the max deflection vector.
continued on page 80
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n Figure 8. This is the sagging crankshaft.
• All throws have the same deflection.• All throws open at the bottom and close at the top.• All throws have maximum deflection vectors pointing
down.• The vertical components are equal to the maximum de-
flection values.• The horizontal components are zero.• Note the crankshaft is depicted with all of the throws
at same angle. Real crankshafts do not look like this but since web deflection angles are recorded with respect to a specific throw it is a valid simplification to visualize what is otherwise a complicated piece of geometry.
n Figure 9. This is the bowed crankshaft.
• All throws have the same deflection.• All throws open at the top and close at the bottom.• All throws have maximum deflection vectors pointing up.• The vertical components are equal to the maximum de-
flection values.• The horizontal components are zero.• All throws have the same deflection.• All throws open to the right and close to the left.• All throws have maximum deflection vectors pointing to
the right.• The vertical components are zero.• The horizontal components are equal to the maximum
deflection values.
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Real world exampleTable 2 shows “as found” web deflection readings mea-
sured during an annual mechanical inspection of a Clark TLA 10 engine. The deflections were measured at 45° intervals and recorded in mils. At first glance throws two and three have deflections of 2, throw six has a deflection of -2.75 and throw nine has a deflection of -2. This table contains the web deflections, sinusoidal curve fits, cor-relation coefficients, calculated crankshaft stress, max deflections and angles.
The sinusoidal curve fit of the deflection data shows
n These tables show web deflections.
n Figure 10. This is the side bowed crankshaft.
continued on page 82
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little change to the max deflection on throws two, three and nine. However throw six changed from a max de-flection of 2.75 to 4.5 mils. The correlation coefficients show a good sine wave agreement for throws one, two, three and 10. The data for throws four through nine have correlation coefficients less than 0.9, indicating question-able data or potential problems. The calculated stress on throw six is 10,216 psi (705 bar). All other throws range from 1438 to 5113 psi (99 to 353 bar).
This example demonstrates the benefits of the sinusoidal curve fit, correlation coefficient and the stress calculations. Furthermore, it shows a crankshaft at risk of failure caused by high stress levels on throw six.
n Figure 11. The chart shows crankshaft deflection vectors.
Crankshaft web deflection vectorsNow look at the maximum deflection vectors for each
throw and their associated vertical and horizontal com-ponents. The stress vector on throw six is primarily in the horizontal direction. This indicates that something might be pulling or pushing on the side of the engine frame. It is important to note that the highest max web deflection on the crankshaft, at throw six, yielded the largest stress and longest vector.
Predicting crankshaft alignmentThe vertical and horizontal crankshaft profiles can
be approximated by using crankshaft geometry and the vertical and horizontal components of the max deflec-tion vectors.
The horizontal and vertical crankshaft profiles, shown in Figure 12, provide valuable insights to the shape of the crankshaft and what might be influencing the crankshaft alignment. The horizontal profile shows an abrupt bend at throw six and a crankshaft side displacement of 26 mils. The vertical profile shows the crankshaft is 10 mils low at bearings two to five and bearings nine to 11 are 5 mils high.
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n Figure 13. This is an example of the “S” shaped crankshaft.
• All webs deflections have the same amplitude.• The left half of the crankshaft is bowed up.• The right half of the crankshaft is sagging.• The horizontal components are zero.
continued on page 84
n Figure 12. Horizontal profile (top) and vertical profile (bottom) are shown.
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• There is a reversal in the direction of the vectors be-tween webs five and six.
• The “reversal” occurs at a point of inflection.
Case history (Roswell #3 1993 – 1998)• 1958 — engine installed.• 1994 — engine regrouted on epoxy chocks.• 1998 — crankshaft failed.• 1998 — installed used crankshaft and re-grouted on
epoxy chocks.• 2004 — engine regrouted on shimmable chocks.• 2010 — second crankshaft failed.
n Figure 14. This graph shows the stress occurring in each web.
The fracture location of the 1998 crankshaft failure did not occur in the throw with the highest stress. The crankshaft failed at throw nine. See Figures 14 and 15. For the five years preceding the failure the average calculated stress at throw nine was 2700 psi (186 bar).
n Figure 15. Arrow points at the web failure of throw nine.
The horizontal crankshaft profile shows a side bow of 26 mils with an abrupt change in direction at throw six.
n Figure 16. The horizontal profile (top) and vertical profile (bottom) are given.
The horizontal graph has no indication of any problem at throw nine. The vertical crankshaft profile shows a slight “S” shaped curve at the fracture location. Based on these two graphs and the calculated stress there was no reason to suspect that throw nine was subject to any undue stress levels that might initiate a cyclic fatigue crack.
The only irregularity we could find was that the frac-ture location coincided with an obvious crankshaft re-versal between throws nine and 10. Resolving the max web deflection vectors clearly shows a reversal in the vertical direction. (See Figure 17.) It is strongly be-lieved this “reversal” played a key role in the crack ini-tiation, the fatigue crack propagation and the eventual failure of the crankshaft.
ConclusionWeb deflections, sinusoidal curve fits, correlation co-
efficients, calculated crankshaft stress, max deflections
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coincide with the calculated peak stress. The crankshaft failed in an area where there was a “reversal” between adjacent throws nine and 10. “Reversals” in the crank-shaft web deflections could be contributing factors to crankshaft failures. Web deflection vector analysis can be an additional set of metrics to evaluate crankshaft align-ment and risk of crankshaft failure.
Additional work• Apply this analysis to other engines that have experi-
enced crankshaft failures and see if similar conclusions can be drawn.
• Mathematically compare adjacent max web deflection vectors to develop a quantitative measure.
• Determine if there a correlation between “reversals” and main bearing bridging.
References 1. Advances in Crankshaft Reliability Methods. Harrell,
John P. Jr.; Wattis, Gregory N. and S.; Rennick, Timo-thy. 1999. Houston: Gas Machinery Research Council, 1999.
2. An Improved Criteria for Assessing Crankshaft Mis-alignment. Harrell, John P. Jr.; and Wattis, Gregory, 2000. Colorado Springs, Colorado: Gas Machinery Council, 2000. CT2
and angles are valuable diagnostic tools to evaluate the crankshaft alignment. The information they provide is throw specific and independent of the other throws on the crankshaft. Plotting the maximum deflection vectors and their vertical and horizontal components provides a way to identify “reversals” in the crankshaft profile.
The 1998 Roswell unit No. 3 crankshaft failure did not
n Figure 17. This chart shows crankshaft deflection vectors. Note the two vectors indicating location of crankshaft reversal.
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Vibration Monitoring System
IMI-Sensors, a division of PCB Piezotronics Inc., has introduced the Echo wireless vibration-monitoring system, designed to monitor the over-all health of critical machinery and provide immediate notification when warning or critical levels are reached. The system can be applied to several industrial applications in the power, steel and chemical industries.
The system uses the Echo wire-less vibration sensor and the Echo-Plus wireless junction box to trans-mit vibration data to a single, central receiver. The system allows for the integration of wirelessly transmitted data into existing legacy vibration systems and plant-monitoring con-trollers, all made possible through the Modbus interface.
Battery life of the sensor typically exceeds five years when transmit-ting data three times a day, and a 24 Vdc source can power the EchoPlus box without battery life limitations, the company said.
www.imi-sensors.com
Thermal Mass FlowmetersCook Compression has released
the Sentrix thermal mass flowmeter, which is designed for measuring vent gas flow and helping compressor op-erators satisfy Environmental Protec-tion Agency reporting requirements for greenhouse gases. The flowmeters are available in inline, insertion and portable configurations to suit various gas-monitoring needs and line sizes, the company said.
Sentrix flowmeters use thermal mass flow technology, which provides accuracy at ±1% reading, ± 0.5% full scale at calibrated conditions. With 0.01 to 559 cfm flow range and a low-flow sensitivity of 100:1 turndown, Sen-trix flowmeters also give operators the ability to proactively spot gas leakage trends, improve repair planning and use condition-based maintenance for rod packing, Cook Compression said.
All units feature automatic pressure and temperature compensation and are provided with preset gas calibra-tions. Inline meters are calibrated for a specific gas composition and portable meters offer multiple calibrations that can be selected in the field using high-resolution, touch panel displays.
www.cookcompression.com
Level MeterKrohne Inc., a global technology
specialist in the development, manu-facture and distribution of measuring instruments for the process indus-tries, has released the OptiFlex 2200 C/F level meter for liquids and solids. The device features software-based dynamic parasite rejection technology that eliminates false reflections caused by environmental disturbances and product build-up. It is the newest addi-tion to the company’s time domain re-flectometry guided radar level meters.
OptiFlex 2200, designed for tank and silo applications in the chemical industry, as well as in the oil and gas, energy and wastewater sectors, is available with several probes to mea-sure liquids up to 130 ft. (40 m) and solids up to 66 ft. (20 m), and can han-dle process temperatures up to 572°F (300°C) and pressures up to 580 psi (40 bar). The device also provides a remote convertor that can be installed up to 328 ft. (100 m) from the probe.
www.krohne.com
Level VF SystemAlignment Supplies Inc. has added
the ALiSENSOR level VF system as an option package for advanced us-ers. The system differentiates itself from the core ALiSENSOR Level system by replacing the 3.9 in. (100 mm) fixture base with the VF fixture
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package, which features a cross-functional L-shape fixture base that is designed for several different measurement applications, the com-pany said. The L-shape fixture base can be reconfigured in seconds to accommodate measurements for straightness, level, squareness, flat-ness, plumb, shaft straightness or level, horizontal spindle direction and vertical spindle direction.
The VF fixture package will be offered as an accessory available to customers who already own the ALiSENSOR level with the 3.9 in. (100 mm) fixture base, and will also be available to new cus-tomers. The ALiSENSOR level core sys-tem, which includes the 3.9 in. (100 mm) fixture base, will continue to be offered as well.
www.alignmentsupplies.com
Diagnostic Display
FW Murphy has introduced the PowerView model PV25, a diagnostic display designed for Tier 4/Euro Stage 3B/4 and below engines. The PV25, which displays engine parameters and diagnostic trouble codes, is part of the company’s existing PowerView display portfolio.
The display allows operators to
view engine performance by reveal-ing 20 J1939 parameters broad-cast from the ECU. Operators can use the up and down pushbuttons to scroll through the parameters, and be alerted by the device’s LED lights, which indicate warning and shutdown conditions. It also can in-strument mechanical engines with
an additional MeCAN module, as well as replace the existing hour-meter function.
Other features include displaying DEF and soot levels, as well active DM1 and store DM2 faults using the suspect parameter number, failure mode indicator and occurrence count.
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The International Energy Agen-cy (IEA) has reported that the Asian market needs a natural
gas trading hub that reflects supply/demand fundamentals.
The region’s gas market is charac-terized by long-term contracts, most of them designed to establish the economic bases for expensive lique-fied natural gas (LNG) production and transportation projects that serve Ja-pan, Korea and other nations.
“Asia is expected to become the world’s second-largest gas market by 2015,” the report said. “And yet this market is dominated by long-term contracts in which the price of gas is linked, or indexed, to that of oil.
“In recent years, this has helped keep Asian gas prices much higher than those in other parts of the world, leading to serious questions about the sustainability of the system and its ef-fects on Asian competitiveness.”
The IEA study outlined how the Asia Pacific region’s natural gas market could evolve from one in which prices are linked to crude oil to one featuring
a more competitive and dynamic net-work of trading hubs that better reflect local gas demand and supply.
IEA said long-term contracts can play a beneficial role in providing in-vestment security, but their current pricing does not accurately reflect gas market fundamentals or the competi-tiveness of gas relative to other fuels. Moreover, without a competitive spot market for natural gas, there is little incentive and little scope to change current commercial practices.
“This leaves both consumers and producers with insufficient room to ex-plore different options, and limits the degree to which natural gas can serve as a flexible source of energy for both growing and mature economies,” it said.
The study found:• Current market structures discour-
age gas consumption and impact Asian competitiveness vis-à-vis more flexible markets in the U.S. and even Europe;
• Experience by the Organization for Economic Cooperation and Development suggests that the
single biggest obstacle for an ef-fective gas market is a lack of in-frastructure access;
• The role of governments must change: Instead of focusing on price regulation along the value chain, governments must main-tain and supervise competitive market conditions;
• Credible state commitment to re-gional gas market competition can instill confidence, encourage new market participants, and promote the use of transparent hubs to bal-ance producer portfolios;
• Gas transport and commercial ac-tivities should be separated and prices deregulated at the whole-sale level;
• Singapore holds the best initial prospects for gas hub development, with Japan, Korea, and China as likely competitors in the future.
“The prospects are there, but even the prime candidates will need to do more,” lEA Executive Director Ma-ria van der Hoeven said. “China’s fast-growing domestic gas network is still underdeveloped, and the en-tire production chain remains heavily regulated. Singapore’s small domestic market means that to grow as a hub it must rely on re-exports, which are hindered by regulation.
“Last but not least, Japan has a great potential to act as a hub, but it will have to take some important steps. Domestically, that means im-proving infrastructure access and further developing its domestic power market. But externally, it also means engaging with exporters to affect the terms of gas contracting so as to im-prove efficiency while maintaining energy security. The LNG producer-consumer dialogue initiated recently by Japan can be effective to facilitat-ing that engagement.” CT2
IEA Urges More Competition In Asia Pacific Gas Market > Report says long-term contracts
distort price signals
APRIL 2013 88 ComPRessoRtech2
n Asia Pacific gas demand will continue to outstrip production. Source: International Energy Agency.
CT160.indd 1 3/20/13 11:27 AM
Most turbo and reciprocating machines operate over a wide range of speeds. Some
of these speeds can coincide with lat-eral or torsional resonant frequencies (aka critical speeds) of their shafts.
Operating at these critical speeds can be damaging to the machine or its seals and bearings, and must be avoided. Thus, it is important to be able to accurately predict critical speeds of a machine prior to instal-lation in the field. This is especially true for reciprocating machines that are subject to high-amplitude, low-frequency excitations from the cylin-ders of either the engine driver or the driven compressor. Excessive tor-
Case Study: Torsional Analysis > Investigation of torsional influence on vibrations of motor-
driven reciprocating gas compressorBy NaThaN W. POErNEr,
ChrIS D. KulhaNEK aND
Dr. KlauS BruN, Ph.D.
Nathan Poerner is a research engineer in the Fluids and Machinery Engineering De-partment at Southwest Research Institute. He received his B.S and M.S. degrees in mechanical engineering from Texas Tech University. Dr. Klaus Brun is the director of the Machinery Program at Southwest Research Institute. He is the chairman of the ASME-IGTI board of directors and the past chairman of the ASME Oil & Gas Applications Committee. Chris D. Kulhanek is a research engineer in the Fluids and Machinery En-gineering Department at Southwest Research Institute. He received his B.S. and M.S. degrees in mechanical engineering from Texas A&M University.
APRIL 2013 90 ComPRessoRtech2
n Table 1. The chart displays predicted torsional natural frequencies (critical speeds).
n Figure 1. This graphic shows torsional spectrum peaks during shutdown.
CT170.indd 1 3/20/13 4:36 PM
sional vibrations have led to coupling breakages and sometimes can inter-act with lateral vibrations resulting in catastrophic shaft failures.
These critical speeds can be al-tered by adjusting the rotating mass (inertia) or torsional stiffness of com-ponents in the system. Some com-mon modifications include adding flywheels or other masses to the sys-tem and the use of flexible couplings (usually with some kind of elastomer-ic material) that changes the stiffness between the driver and equipment shafts. Critical speeds and torsional response of the system are typically predicted using a computer model via a finite element method (FEM) that divides the rotating elements into dis-crete sections with assigned masses and stiffnesses. With any computer model, there is some uncertainty of the predictions due to both the analy-sis method and the input boundary conditions; it is imperative to validate computational predictions using field testing. The following presents a tor-sional analysis case study where field data and analysis predictions were compared to validate the fidelity of the predictions.
The subject study began when the lateral vibrations of an electric motor that was part of a reciprocating gas compressor package with an elasto-meric coupling reached levels that tripped a local vibration alarm. To in-vestigate the theory that these vibra-tions were being generated due to torsional vibrations, measurements of the torsional and lateral vibrations of the system were recorded during numerous startups and shutdowns of the unit, and also while the unit was run over its effective operating-speed range.
Torsional vibration data recorded during the start-up and shutdown of a unit is critical for determining the tor-sional critical speeds, as one or more orders of running speed are likely to pass through the modes. As an example, data from one of the shut-downs of the current study is shown in Figure 1. In this data, there are two peaks that are prevalent: the first ap-pears at 11.25 Hz, and the second
appears at 101 Hz. These peaks show up similarly on both the motor and compressor torsional measure-ments, although the peak at 101 Hz is much more prevalent on the compressor side, which was due to the particular shape of the resonant mode. Two peaks were also present in the startup data, with the first peak at 14 Hz and the second again at 101 Hz. The shift in frequency of the first mode between start-up and shut-
down is typical due to differences in loading and temperatures, also veri-fied by the torsional model. The ac-tual torsional mode can be expected to exist within this range (11 to14 Hz).
These measured critical speeds were significantly different from values previ-ously analytically predicted (18 and 75 Hz) by a third party. This large difference was initially thought to indicate possible damage to the coupling’s elastomeric
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APRIL 2013 91 ComPRessoRtech2
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CT170.indd 2 3/20/13 4:37 PM
APRIL 2013 92 ComPRessoRtech2
n Figure 2. The chart shows motor DE horizontal vibrations during speed ramp.
n Figure 3. The chart displays motor torsional spectral response during speed sweep.
material. To investigate this difference and determine if a drastic change in the elastomer was at fault, Southwest Research Institute (SwRI) created its own torsional analytical model using SwRI’s proprietary torsional software and the manufacturer’s machine data. From this model, SwRI was also able to investigate the effect variable elastomer stiffness and orientation of the coupling would have on critical speeds.
Results in Table 1 show that the fre-quencies of the first and second criti-cal speed with the nominal stiffness and the coupling oriented with heavy side on the compressor match excep-tionally well with the measured values;
that is 13.8 Hz, which is within the range of measured values, and 97.2 Hz, which differs by less than 5%. Ad-ditionally, the mode shapes for each of these critical speeds also match the relative observed torsional levels.
With the same stiffness but op-posite orientation (heavy side on the motor end) the first two critical speeds were predicted to nominally be 18.7 Hz and 82.7 Hz, which matches the previously predicted values. Check-ing with the facility did confirm that the heavy side of the coupling was, in fact, on the compressor. Therefore, it was concluded that the coupling elasto-meric material had not degraded, and
the coupling was operating in the best possible configuration.
It was still left to determine whether it is a torsional effect that is driving the lateral vibrations of the motor. The measured lateral vibrations indicated a strong 3x response that decreased in amplitude with speed; the most severe of these vibrations was observed at the motor drive end in the horizontal direc-tion (Figure 2). An operating deflection shape of the motor at this frequency re-vealed that the motor was vibrating in a yawing motion; a lateral motion that is not likely to be excited by a torsional vibration of the motor shaft.
This frequency also falls in between
CT170.indd 3 3/20/13 4:37 PM
the first two torsional critical speeds and does not coincide with either critical speed over the entire operating range. Still, the measured torsional vibrations of the motor shaft for the same time (Figure 3) do show a peak at the 3x fre-quency; but given the layout of the unit (six-throw unit in offsetting pairs), a 3x response was expected. However, the amplitude of the torsional vibration at 3x does not vary relative to speed like the lateral vibrations did, so it was unlikely that any coupling between the lateral and torsional vibrations of the motor was occurring at this frequency.
Some additional torsional peaks did show changes over the speed ramp. Specifically, the 9x and 10x or-ders show drastic peaks as they pass through 101 Hz. But as found earlier, this was the frequency of the second critical speed, and since there are no related peaks found in the lateral vibrations, it was concluded that this response was not coupling with lateral vibrations on the motor, either.
The results from this torsional field testing and analytical comparison showed excellent coincidence between SwRI predictions and field measure-ments when proper boundary condi-tions are applied. Specifically, the first critical speed of the unit was measured in the range of 11 to 14 Hz, and the second critical speed was near 101 Hz. A torsional model of the system con-firmed these by predicting the first criti-cal speed at 13.8 Hz and the second at 97.2 Hz and indicated that the coupling was operating as intended. The lateral yawing vibration that was occurring on the motor at 3x running speed actu-ally falls in between the first two critical speeds and causes no interference.
Furthermore, the expected 3x tor-sional vibration that did exist due to the machinery did not indicate any cou-pling with the lateral vibrations. Hav-ing determined that there was no sig-nificant coupling between the torsional and lateral vibrations, it was ultimately determined that the vibrations on the motor were developing as a result of forces being transmitted by lateral vi-brations, and involve coincidences with lateral mechanical natural frequencies in the system. CT2
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CENTAMAX – HTC“High Thermal Capacity” design - patent pending
for higher Power LossSizes thru 45 kNm nominaltorqueTorsionally very soft –linear characteristic
Since 1970
Centa.qxp 6/1/10 12:02 PM Page 1
APRIL 2013 93 ComPRessoRtech2
J-W EnergyJ-W Energy Co. President G. Gene
Gradick has been given the additional duties of chief executive officer with the responsibility of managing day-to-day operations.
Gradick joined J-W Energy in 1998 as chief operating officer and was promot-ed to president in January 2005. During
his tenure, the company has grown from US$70 million to more than US$800 mil-lion in gross revenue and from US$147 million to US$1.5 billion in assets.
Prior to joining the company, Gradick was president of Delhi Gas Pipeline Corp. He is a mechanical engineering graduate of Texas A&M University.
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CT170.indd 4 3/20/13 4:37 PM
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APRIL 2013 95 ComPRessoRtech2
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Advertiser’s Index
Aavolyn Corporation ...........................................63 www.aavolyn.com
ACI Services, Inc. .................................................22 www.aciservicesinc.com
Altronic, LLC ...................................................40-41 www.altronic-llc.com
ARIEL ......................................................................1 www.arielcorp.com
Argentina Oil & Gas Expo 2013 ..........................89 www.aog.com.ar
ARMCO Compressor Products Corp. ................25 www.armcocompressor.com
Arrow Engine Company ......................................71 www.ArrowEngine.com
AXH air-coolers ....................................................73 www.axh.com
BG Service Co. Inc, The ......................................27 www.bgservice.com
BETA Machinery Analysis ...................................53 www.BetaMachinery.com
BORSIG ZM Compression GmbH .......................43 www.borsig.de/zm
Burckhardt Compression AG .............................33 www.burckhardtcompression.com
Cameron ..........................................................50-51 www.c-a-m.com
Catalytic Combustion Corporation ....................69 www.catalyticcombustion.com
CECO, Compressor Engineering Corp. .............10 www.tryceco.com
CENTA Corporation .............................................93 www.centa.info
Compressor Products International ...................13 www.c-p-i.com
Continuous Control Solutions ............................21 www.ccsia.com
Cook Compression ..............................................49 www.cookcompression.com
DCL International Inc. ............................................7 www.dcl-inc.com
* Dresser-Rand .................................................35, 37 www.dresser-rand.com
Eastern Gas Compression Roundtable .............97 www.egcr.org
ECOM America .....................................................87 www.ecomusa.com
E Instruments International ................................79 www.E-Inst.com
Elliott Group .....................................Second Cover www.elliott-turbo.com
Ellwood Crankshaft Group ..................................80 www.ellwoodcrankshaftgroup.com
Exterran ...........................................................44-45 www.exterran.com
FLP, Fluid Line Products .....................................85 www.fluidline.com
Gas Drive Global LP ............................................61 www.gasdriveglobal.com
GE’s Waukesha gas engines ................................5 www.ge-waukesha.com
GE Oil & Gas .........................................Third Cover www.geoilandgas.com
GUARDIAN Engine + Compressor Control .......57 www.guardiancontrol.com
Hahn Manufacturing Company ...........................80 www.Hahnmfg.com
Harsco Industrial Air-X-Changers ......................23 www.harscoaxc.com
ITW Chockfast Grout ...........................................83 www.chockfastgrout.com
KB Delta Compressor Valve Parts Mfg. .........................................................30-31 www.kbdelta.com
Kiene Diesel Accessories, Inc. ...........................83 www.kienediesel.com
Korea Rotating Machinery Symposium .............79 www.krmea.or.kr
Kobelco/Kobe Steel Ltd. ......................................29 www.kobelcocompressors.com
LIONOIL ..........................................................73, 86 www.lionoil.be
Lufkin Industries, Inc. ..........................................82 www.lufkin.com
MIRATECH ............................................................11 www.miratechcorp.com
MOTORTECH GmbH .............................................15 www.motortechamericas.com
Murphy, FW .........................17, 19 & Fourth Cover www.fwmurphy.com
Neuman & Esser Group .......................................39 www.neuman-esser.com
Nidec ASI S.p.A. ...................................................67 www.nidec-asi.com
Petro Canada – Suncor .......................................59 sentron.ca
Reynolds French ..................................................77 www.r-f.com
* Rolls-Royce ............................................................9 www.rolls-royce.com
Rottler Manufacturing ..........................................47 www.rottlermfg.com
Samsung Techwin Co., Ltd. ................................65 www.samsungcorp.com
Southwest Research Institute .............................55 pulsations.swri.org
Summit Industrial Products ................................75 www.klsummit.com
SYNTHOSOL .........................................................91 www.mastersprocess.com
Tech Transfer, Inc. ..............................................2-3 www.techtran-hou.com
Testo, Inc. .............................................................48 www.testo350.com
Turbomachinery/Pump Symposia ......................94 turbolab.tamu.edu
Universal LLC .......................................................38 www.UniversalAET.com
* Voith Turbo Inc. ....................................................70 www.voithturbo.com
Waukesha Bearings .............................................60 www.waukeshabearings.com/CT
*Further information on this company’s products can be found in the 2012 Edition of the Global Sourcing Guide (at GSGnet.net) and 2013 Compression Technology Sourcing Supplement (at CTSSnet.net).
Advertiser’s Index
Web: www.compressortech2.com • Phone: 262-754-4121 • Fax: 262-754-4175E-mail: [email protected] • Address: 20855 Watertown Road, Suite 220, Waukesha, WI 53186
74 Natural Gas Production77 Gas Gathering Company70 Natural Gas Process Plant
Operations72 Gas Transmission Pipeline
Compressor Operations75 Natural Gas Storage Company73 Chemical or Petrochemical
Process Company76 Refinery Operations91 Consulting Engineers or Contractor54 Distributing, Servicing and
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cu.in. (57.5 L) was introduced.The direct ancestor of the fu-ture VHP engine series was the model VLRO. Introduced in 1954, it was the first V12 (12-cylinder vee) version of the 8.5 x 8.5 series. With a displacement of 5788 cu.in. (94.8 L), it doubled the power output of the popular 6LRO.
According to the Waukesha Engine Historical Society, Waukesha went to a new model designation scheme in 1963. The 6LRO was renamed the F2894, the 6LRZ be-came F3520, and the VLRO became L5788G.
That same year, the model L7040 was introduced as a 9.375 in. (238 mm) bore x 8.5 in. (216 mm) stroke V12 engine with a displacement of 7041 cu.in. (115.4 L). The 1964 Diesel and Gas Engine Catalog listed the 7040G gas engine with a rating of 1186 hp (884 kW) at 1200 rpm for continuous duty and 1005 hp (749 kW) for “extended con-tinuous duty” with the footnote “for extended engine life.”
In 1967, Waukesha extensively redesigned the 12-cylinder engine series. Among the improvements were open cham-ber diesel technology, four valve heads, angle-split serrated rods, new manifolds and a stronger lower end.
The F2894 and F3520 six-cylinder engines were also completely redesigned in the same manner, and togeth-er with the L5788, were designated as the VHP family of engines. Traditionally, the letters VHP stood for Very High Power, but historical accounts vary as to the source of the name. All the engine models in the VHP family were renamed, with the L5788 becoming L5790 and the L7040 becoming L7042.
Also in 1967, the GSI turbocharged and intercooled ver-sions of the VHP were developed with increased power rat-ings and performance. A 1969 advertisement showed the L4042GSIU rated at 1300 hp (969 kW) at 1200 rpm. It also alluded to a 16-cylinder VHP, rated up to 2250 hp (1678 kW) to be available in 1970. Actually developed in 1969, the
P9390 V16 engine is the largest of the VHP engine series with a 9388 cu.in. (153.8 L) displacement.
With demand for lower emissions, a series of VHP “lean-burn” gas engines was first introduced in the mid-1980s. The VHP lean burn models were designated as 2895GL, 3521GL, 5108GL, 5790GL, 7042GL and 9390GL. In 1998, the Series Four six- and 12-cylinder 9.375 in. (238 mm) bore, models 3524GSI and 7044GSI, respectively, went into production with new improved cylinder heads.
In the 1980s, the largest VHP engines — the 16-cylinder P9390GSI and P9390GL — had a continuous rating as high as 2063 hp (1538 kW) at 1200 rpm. Similarly, the L7042GSI and L7042GL were rated as high as 1547 hp (1154 kW) at 1200 rpm.
Waukesha continued to manufacture both diesel and gaseous-fueled versions of the VHPs for a number of years, but eventually discontinued building diesels to focus on their major niche in the gaseous engine market.
Today, under GE Power & Water, the Waukesha gas en-gine series ranges from 160 to 4835 hp (119 to 3606 kW) for driving gas compressors in applications from the wellhead through processing, storage and distribution pipelines.
Central to this lineup is the versatile, gaseous-fueled six-, 12- and 16-cylinder VHP Series with both rich-burn and lean-combustion systems. Total production volumes are not available, although GE indicated that from 1985 through mid-2012, some 10,849 VHP engines were produced, with 7120 for gas compression applications.
The VHP V12s remain popular, a half-century after their introduction. The L7042GSI has evolved to a current rat-ing of 1480 hp (1104 kW) at 1200 rpm with an 8:1 com-pression ratio that provides a wider range of fuel tolerance. Introduced in 2001, the upgraded rich-burn Series Four L7044GSI is rated at 1680 hp (1253 kW) at 1200 rpm. CT2
n Current VHP Engine Series Specifications – 1200 rpm rated speed.
Cornerstones Of Compression story continued from page 100
Model No. Of Bore Stroke Displacement Compression Combustion Max Rated Power
Cyls. in./mm in./mm cu.in./L Ratio hp/kW
F3514GSI 6 9.375/238 8.5/216 3520/58 8:1 Rich Burn 740/552
F3521G 6 9.375/238 8.5/216 3520/58 10:1 Rich Burn 515/384
F3521GL 6 9.375/238 8.5/216 3520/58 10.5:1 Lean Burn 738/550
F3524GSI 6 9.375/238 8.5/216 3520/58 8.0:1 Rich Burn 840/626
L5774LT 12 8.5/216 8.5/216 5788/95 10.2:1 Lean Burn 1450/1081
L5790G 12 8.5/216 8.5/216 5788/95 10:1 Rich Burn 845/630
L5794GSI 12 8.5/216 8.5/216 5788/95 8.25:1 Rich Burn 1380/1029
L5794LT 12 8.5/216 8.5/216 5788/95 10.2:1 Lean Burn 1450/1081
L7042G 12 9.375/238 8.5/216 7040/115 10:1 Rich Burn 1025/764
L7042GL 12 9.375/238 8.5/216 7040/115 10.5:1 Lean Burn 1480/1105
L7042GSI 12 9.375/238 8.5/216 7040/115 8.0:1 Rich Burn 1480/1105
L7044GSI 12 9.375/238 8.5/216 7040/115 8.0:1 Rich Burn 1680/1253
P9390GSI 16 9.375/238 8.5/216 9388/154 8:1 Rich Burn 1980/1476
P9390GL 16 9.375/238 8.5/216 9388/154 10.5:1 Lean Burn 1980/1476
CT158.indd 2 3/25/13 8:44 AM
C ornerstones Of Compression
APRIL 2013 100 ComPRessoRtech2
The Waukesha VHP series natural gas engine was intro-duced in 1963. Since then it has been applied in some of the harshest and most demanding gas compres-
sion, power generation and mechanical drive applications.In particular, the model 7042 V12 has been widely used
for driving gas compressors. In 1969, the Diesel and Gas Turbine Catalog featured an installation of two dozen 7042s rated at 1000 hp (746 kW) at 1000 rpm driving Worthing-ton CUB compressors in reinjection service at the Kaybob South gas field in Alberta.
But the VHP’s roots go back as far as the early 1920s, when Waukesha Motor Co. introduced multicylinder internal combustion engines to the oil fields of East Texas. As the
oil operators needed more power, Waukesha introduced an engine with 8.5 in. (216 mm) bore and 8.5 in. (216 mm) stroke in 1930. That six-cylinder model 6LRO, with a dis-placement of 2894 cu.in. (47.4 L), became the standard of the oil fields.
Enjoying a niche in the oil patch, by 1935 Waukesha evolved this frame size into the model 6LRH engine, a low-compression, fuel-injected, spark-ignited, multifuel engine that could burn just about any kind of fuel. In 1949, the model 6RLD, the first diesel version of the 8.5 x 8.5 engine, went into production. That same year, a 9.375 in. (238 mm) bore version, the model 6LRZ with a displacement of 3520
Waukesha VHP Series Gas Engines >
By NORM SHADE
After a half-century, workhorse V12s are still popular
n This 1380 hp (1029 kW), 1200 rpm Waukesha L5794GSI gas engine, one of the cur-rent VHP models, drives an Ariel JGE-4 compressor in a gas compression application.
continued on page 99
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