46 www.paintsquare.com JPCL March 2010 ince mid-2008, ocean- going freight compa- nies have felt the pinch of the world- wide recession with a dramatic decline in orders for transport. The decline has affect- ed almost every type of vessel, including oil tankers, cargo vessels, cruise ships, and even luxury yachts. It is estimated that over 1,000 ships are in either hot or cold storage all over the world, and about half of these are con- tainer vessels while 200 are bulkers. Additionally, many cargo ships are leav- ing port at 50% to 70% capacity, which negatively affects the profitability of their trips. Recently, low demand in crude oil left many oil tankers at sea with no apparent destination. The ship- ping industry is in a crisis. Given the recession and the enormous operating costs of ships, laying up under- utilized vessels and running fewer ves- sels with higher loadings to maximize profit per sailing often makes more eco- nomic sense. Therefore, it was no sur- prise to see an increasing number of ships being laid up in 2009. With the increase, cost-effective, corrosion-preven- tion strategies for long-term cold lay-ups are essential. This article will discuss the use of tem- porary desiccant dehumidification and climate control equipment as a strategy to prevent corrosion and other damage to ballast tanks, electronic systems, engine rooms, and other parts of a ship during cold lay-up, thereby reducing mainte- nance painting and other costs and pro- tecting one’s investment in a ship. The article will look at the science of psychro- metrics and discuss how its use can help predict the optimal conditions to effec- tively control moisture in a ship indefi- nitely. The article will also discuss the corrosion cell and how it can be manipu- lated with climate control technologies. Finally, the article will compare different types of climate control methods used for mothball applications and make recom- mendations for what technologies are best for certain seasons. Why Lay-Up? The laying up of a vessel makes sense when consumer demand is low. Low demand will reduce the profit for the Protecting Ships with DH during Long-Term Lay-Ups By Russ Brown, Munters Corporation, Indianapolis, IN Editor’s Note: This article is based on a paper presented at PACE 2010, the joint conference of SSPC: The Society for Protective Coatings and the Painting and Decorating Contractors of America, held February 7–10, 2010, in Phoenix, AZ. S Hereʼs an approach to reducing painting and other maintenance costs on ships in lay-up.
Transcript
46 www.paintsquare.comJ P C L M a r c h 2 0 1 0
ince mid-2008, ocean-going freight compa-nies have felt thepinch of the world-wide recession with adramatic decline inorders for transport.The decline has affect-ed almost every typeof vessel, including oiltankers, cargo vessels,
cruise ships, and even luxury yachts. Itis estimated that over 1,000 ships are ineither hot or cold storage all over the
world, and about half of these are con-tainer vessels while 200 are bulkers.Additionally, many cargo ships are leav-ing port at 50% to 70% capacity, whichnegatively affects the profitability oftheir trips. Recently, low demand incrude oil left many oil tankers at seawith no apparent destination. The ship-ping industry is in a crisis.
Given the recession and the enormousoperating costs of ships, laying up under-utilized vessels and running fewer ves-sels with higher loadings to maximizeprofit per sailing often makes more eco-nomic sense. Therefore, it was no sur-prise to see an increasing number ofships being laid up in 2009. With theincrease, cost-effective, corrosion-preven-tion strategies for long-term cold lay-upsare essential.
This article will discuss the use of tem-porary desiccant dehumidification andclimate control equipment as a strategy
to prevent corrosion and other damage toballast tanks, electronic systems, enginerooms, and other parts of a ship duringcold lay-up, thereby reducing mainte-nance painting and other costs and pro-tecting one’s investment in a ship. Thearticle will look at the science of psychro-metrics and discuss how its use can helppredict the optimal conditions to effec-tively control moisture in a ship indefi-nitely. The article will also discuss thecorrosion cell and how it can be manipu-lated with climate control technologies.Finally, the article will compare differenttypes of climate control methods used formothball applications and make recom-mendations for what technologies arebest for certain seasons.
Why Lay-Up?The laying up of a vessel makes sensewhen consumer demand is low. Lowdemand will reduce the profit for the
Protecting Shipswith DH during
Long-Term Lay-UpsBy Russ Brown,Munters Corporation,Indianapolis, IN
Editor’s Note: This article is based on a
paper presented at PACE 2010, the joint
conference of SSPC: The Society for
Protective Coatings and the Painting and
Decorating Contractors of America, held
February 7–10, 2010, in Phoenix, AZ.
SHereʼs an approach to reducing paintingand other maintenance costs on ships in lay-up.
and heart of the ship, such as the naviga-tion electronics and engine components,are not as easily replaced (Fig. 1).
Mold can also create costly remedia-tion efforts due to these long-term lay-ups. Typically, where there is moistureand an organic food source such as dirtin unprotected areas, there is mold.Mold can damage materials on the shipand create health risks for the crewwhen the ship returns to service.Additionally, excess moisture can leadto the rotting of materials on board.Again, the replacement of these itemswill be costly and may lengthen theamount of time required to re-commis-sion the ship. When the ship is ready toreturn to normal trade, dry preserva-tion is recommended, and all preserva-tion actions should be carefully docu-mented.
The Corrosion Cell SimplifiedSo moisture presents a major challengefor protecting a vessel at sea. How doesmoisture affect the corrosion processand what can be done to predict itsonset?
Corrosion is an electrochemical reac-tion. The typical corrosion cell consistsof an electrolyte as well as a cathodeand an anode (which steel contains andhelps conduct electricity for the reac-tion). Corrosion occurs only when allthree parts are present. Moisture is the
that emergency equipment and otheressential systems, such as navigationlighting, winches, and mooring equip-ment, are operable. Re-commissioningafter an extensive lay-up period (over 5years) might require more than 30 days.
The cold lay-up process is an arduoustask, with an extensive checklist of pro-cedures. The procedures are intended toensure that the preservation of the vesselis done in the most cost-efficient waypossible. The lay-up site is usually well-sheltered from heavy winds, strong cur-rents, and swells. It should not be in trop-ical cyclone areas, and the seabed charac-teristics should be able to provide ade-quate anchoring. In most cases, the vesselwill be kept in “blacked out” mode withminimal crew on board and power beingsupplied to essential equipment from aportable generator placed on deck. All ofthis careful planning is done in anticipa-tion for the day when the ship is calledback to duty so that it can be brought upand running in the shortest possible timewithout the need for major repair causedby corrosion, mold, or material rot.
Challenges during Cold Lay-UpThere are many challenges to protectinga ship during a long-term lay-up, includ-ing vandalism, natural disasters, and gen-eral deterioration. However, the biggestthreat to the well being of a vessel in coldstorage might come from the abundanceof moisture at sea. Continuous high levelsof moisture (relative humidity) can pro-vide the catalyst to corrosion on thesevessels, which are made up primarily ofsteel. During re-commissioning, corrosioncan create havoc by causing motor anddrive trains to seize up, which results incostly and potentially long-term repairs.Additionally, excess corrosion canseverely damage the onboard computersand navigational equipment inside thecontrol rooms. Whereas body panels canbe replaced relatively easily, the brains
owner and will eventually create a finan-cial burden. Often, laying up the vesselprovides a solid business case by reduc-ing excessive deterioration (and subse-quent repair) of the ship’s mechanicaland electrical systems. Additionally, onlya small crew is required to maintain alaid-up ship, thus reducing overall coststo the owner. Other benefits includereduced costs for fuel, oil, maintenance,equipment replacement, and insurance.
Typically two types of lay-up proce-dures are used: hot and cold. This articlewill define both processes but will con-centrate primarily on the cold lay-upprocess, in which, compared to hot lay-up, ships are more affected by thedestructive nature of long-term moistureinfiltration.
Hot Lay-UpsIn hot lay-ups, the machinery is kept inoperation for the sake of fast re-commis-sioning. However, measures are stilltaken into consideration to lower theoverall operational costs, includingreducing crew size or eliminating somemechanical operations such as heatingand ventilation systems. The length oftime that the vessel is laid up will deter-mine the required restart protocol. Forexample, a ship that has been laid up for1 month would require a 24-hour restartprocedure.
Cold Lay-UpsIn cold lay-ups, the machinery is takenout of service, and the vessel is kept elec-trically dead, except for its emergencypower. This condition usually implies athree-week re-commissioning time ormore depending on the preservation andmaintenance during lay-up. Minimummanning covering fire, leakage, moorings,and security watches should be kept.The lay-up site is usually in a remotearea and access is limited. Power is keptto a minimum but is sufficient to ensure
tainty, the ambient condi-tions that will provide thegreatest chance of corrosionoccurring on the vessel. Thepsychrometric chart haseight indices to measure themoisture levels within theair. Dew point temperature,relative humidity, dry bulbtemperature, and wet bulbtemperature are the mostcommonly used indiceswhen calculating moisturelevels in a space. By know-ing any two of the eight vari-
ables on the psychrometric chart (Fig. 3),you can calculate any of the other val-ues. For example, by knowing the rela-tive humidity and the dry bulb tempera-ture, you can easily find the dew pointtemperature or vapor pressure.
The use of psychrometrics allows shipowners to make critical decisions aboutthe best time to install the temporary cli-mate control equipment and to deter-
electrolyte that provides the conduitfor the reaction to occur. If any of thethree parts of the cell can be con-trolled, corrosion growth will be limit-ed but will never stop unless a struc-ture or component is in a vacuum. Therate of corrosion depends on theamount of moisture present. Forexample, relative humidity—the per-centage of moisture that air can holdat a specific tempera-ture—will lead to lesscorrosion at levels below50% than at 70%.Relative humidity above50% creates conditionsthat accelerate corrosionexponentially, leading toflash rusting. As such,the key to corrosion con-trol is to control the mois-ture level or relativehumidity (Fig. 2).
Moisture Analysis:The Science ofPsychrometrics
To understand how mois-ture might affect the steel,it is important to under-stand psychrometrics, thescience of moisture in air.Psychrometrics is relied onheavily when engineeringa moisture-control method.Psychrometrics can predict, with cer-
mine the type and quantity of equipmentneeded to safely protect their ships.Correct sizing is vital to ensure that aship owner gets the exact conditionsdemanded from the specifications so thatcosts are not incurred for unnecessaryequipment and fuel. Psychrometrics isthe tool that ensures that the moisture ismanaged and thus will keep the corro-sion cell in check as much as possible.
The ConceptThe general concept behind the use oftemporary dehumidification or climatecontrol equipment to lay up a ship is tocreate an environment that reduces therelative humidity in the space below50%. The conditioning process shouldcreate a differential between the dewpoint temperature in the space and thetemperature of the actual surface. If thesurface temperature reaches the interiordew point temperature, moisture vaporfrom the air will condense on the sur-face. The steel surface will then be at risk
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Fig. 3: The psychrometric chart (IP version) can map out moisture changes from the airFrom www.linric.com
Fig. 2: Corrosion rates vs. relative humidity
for corrosion. In the control rooms,excess moisture can corrode electroniccomponents, resulting in short-outswhen restarted.
As noted above, mold can also growin these confined areas, creating remedi-ation concerns. Often, typical air condi-tioners providing cool air cannot createeffective conditions to ensure that con-densation will not form.
Dehumidification equipment is funda-mental to bringing air in the enclosedareas of the ship, such as ballast tanks,storage tanks, and control rooms, to arelative humidity not exceeding 50%.
DehumidifiersDehumidification is the process bywhich moisture is removed from the air.There are primarily two methods ofdehumidification:• Refrigerant—Removing moisture bypassing wet air over a refrigerated coil• Desiccant—Using substances thatattract moisture (desiccants) to removethe moisture by vapor pressure differen-tial
Refrigerant DehumidificationRefrigerant dehumidification is an effec-tive way to remove moisture from theair in small, confined spaces (Fig. 4).With refrigerant dehumidification, moistair is passed directly over refrigerationcoils and cooled below the dew point;the moisture condenses from the air. Theair comes off the coil saturated andmust be reheated to lower the relativehumidity. It is then pushed into thespace. This type of unit typically canprovide a relative humidity range of15% to 20%. Additionally, most refriger-ation units are too small to conditionlarge areas and are limited in their abili-ty to significantly change dew point in aspace. They can be used effectively incontrol rooms and living quarters, espe-cially to reduce the threat of mold.
Desiccant DehumidificationDesiccant dehumidification is the work-
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on the deck outside, with temporaryducting used to move the air into the pro-tected areas. Often, refrigerant units areplaced directly in the smaller spaces tobe controlled, and the condensate is dis-posed of through a hose to a nearbydrain. The desiccant units are extremelylarge and often cannot be placed in thespace that is being controlled.
Closed Loop Dehumidification SystemClosed loop system dehumidification isused where the enclosed air volume is re-circulated through the dehumidifier (Figs.7 and 8). Often the moisture load outsideis so great that re-circulation is the onlyviable way to create a cost-effectivedehumidification system. A closed sys-
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horse for moisture removal from the airin large spaces (Fig. 5). Desiccantsattract moisture from the air by creat-ing an area of low vapor pressure at thesurface of the desiccant. The pressureexerted by the water in the air is higher,
so the water molecules move from theair to the desiccant, and the air is dehu-midified. In one type of dehumidifier, asthe process air passes through what iscalled the desiccant wheel, moisture isabsorbed and trapped. As the wetwheel rotates, it is dried out by heatedreactivation air (Fig. 6). Once the wheelis dried, it is ready to absorb more mois-ture. Desiccants in this application arebased on silica gel, which is ideal forhighly saturated air streams. The desic-cants have very good moisture removalcapacity over a broad range of humiditylevels. Because desiccant dehumidifiersare available in large capacities, they arethe most appropriate for use in lay-ups.Depending on the time of year of thelay-up, different measures should betaken to control the temperatures in thevessel. For example, an air conditioningpackage can be combined with the desic-cant to optimize the controlled climate ifthere is a need to work in the space inwarmer climates.
Power is always an issue on a shipthat has been laid-up. Often, the dehu-midification equipment has to share thesame generators that provide power toall the other onboard utilities (such asfire suppression systems). The unitsselected will have to be energy efficientto reduce the overall running costs of
the vessel during the lay-up period. Also,the equipment selected must be extreme-ly reliable to minimize unplanned down-time.
Designed Dehumidification SystemsDehumidifiers can be placed inside thecontrolled space, or they can be placed
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tem works most efficiently when allopenings in the space are sealed to mini-mize air infiltration from the outside.Air from inside the space is returned tothe dehumidifier to be dried again. Thereprocessed air is then redistributed tothe space through an air distributionmanifold. Due to this continual dryingprocess, the air is extremely dry (<1%RH). The manifold should be placed inthe center of an internal room, such asthe engine room, or a hold for bestresults. The distribution hoses need to bespread out evenly to cover all the sensi-tive parts of the vessel without usinglengthy hoses.
Navigation and Radio RoomAccommodationsThe navigation and radio rooms are usu-ally above deck, where they are directlyexposed to the elements. The exposureenvironment creates varying tempera-tures and relative humidity levelsthroughout the day. Since these locationsall contain electronic equipment, wood-work, and textiles, it is important to con-trol the humidity by placing humidistatswhere they can accurately read the rela-tive humidity levels. Using humidistats,the dehumidification can be turned onwhen humidity rises above 50% and canbe turned off once a safe humidity levelis achieved. Controlling the humiditywill protect woodwork and textiles fromcracking and splitting. These locationsare normally linked by the air condition-ing system, which, when turned off andproperly sealed, can be used to distrib-
Fig. 8: Closed loop dehumidification systemwith even distribution set up
ute dehumidified air throughout theaccommodation, navigation, and radiorooms.
Emphasis is placed at the lowest sectionof the engine room where moisture maygather; the heated dry air will dry thelow area and then rise to other parts ofthe engine room.
Humidistats are placed in the dehu-midified space to keep the relativehumidity levels from exceeding the setvalue. Reactivation air is obtained fromthe air vent leading to the outside of theship, and the wet air is vented outthrough a similar vent.
Case StudyA 3500 TEU (twenty-foot equivalentunits) container ship was laid-up in thesea of Batam because of decreaseddemand for her services. The ownermade the decision to complete a cold lay-up application for an unspecified period.(Due to privacy policies, the name of thevessel cannot be disclosed.)
ChallengesThe key challenge for the completion ofthe project included power supply forthe units and the distribution of the airinto the affected areas. The power wasto be supplied by an onboard generator;however, there was concern that therewould not be enough capacity to powerthe dehumidifiers and the necessaryequipment to maintain the lay-up. The
solution included a dehumidifier thatprovided an energy-efficient design toreduce the overall capacity needed. Theequipment provided a 30% decrease inoverall use, helping to reduce the overallpower required and the long-term fuelcosts for the generator. The logisticsproblem was solved by creating a uniquelabyrinth of ducting, manifolds, andplenums to effectively distribute the airin all the protected areas (Figs. 9 and 10).
SolutionThe solution involved entry of the dryair system into two specific areas:A) One desiccant dehumidifier that pro-vided 2500 cfm (4000 m3h) of dehumid-ified air and had a gas burner reactiva-tor, making it less energy intensive, wasdedicated to the engine room and accom-modations deck• Unit was placed on deck next topower generator.• Dry air was channeled to the engineroom and accommodation decks viaflexible tubing connected to a butterflyjoint with air damper.• Flexible tubing was connected to anair-distribution manifold which distrib-utes the air to various parts of theengine room via lay-flat temporary duct-ing.• Air was channeled to various parts ofthe accommodation deck utilizing the airconditioning vents.• Doors to rooms were sealed to pre-vent any air leakages.B) One desiccant dehumidifier that pro-vided 600 cfm (1000 m3h) of air and
also had a gas burner reactivator wasdedicated to the forward mechanicalroom• Dehumidifier was placed in the for-ward bow thruster room.• 20 m of flexible ducting was used tochannel air into the bow thruster areavia air vent.
Costs for System• Installation, shipping, and fabrication:$8,300K (US)• Monthly rental rate (DH equipmentonly): $6,900K• Estimated fuel for generators (permonth): $3,400K
ConclusionsThe shipping industry is laying up moreships then ever because the worldwideeconomic recession has reduced theoverall demand for shipping goods andservices. Ship owners are finding thatlaying up ships is a viable and profitableoption for protecting their ships whennot in use. Cold lay-up applications cancreate costly re-commissioning issuesdue to corrosion and mold created byexcess moisture on board the vessel. Theuse of psychrometrics is the only trueway to ensure that you are controllingthe corrosion cell by eliminating mois-ture during a cold lay-up. The use of tem-porary dehumidification systems caneffectively control moisture onboard,thus reducing these costly problemseven for the longest lay-ups. Energy effi-cient units and engineered distributionsystems provide an economical alterna-tive to other lay-up alternatives.Desiccant dehumidifiers are the mosteffective and efficient equipment for con-trolling moisture in large areas such ascontainer ships.
Sources ConsultedDNV Interim Guideline on Lay-up of
Ships; A systematic and costeffective approach to laying upships, DNV Maritime AdvisoryServices, January 2009.
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Fig. 9: Part ofsystem forcold lay-up ofship in Sea ofBatam
Fig. 10: Part ofsolution wasthe shaft forair to enter
Munters Dehumidifying of vesselsduring lay-up guide, MuntersCorporation, www.munters.us.
Recommendations for Laid Up Ships,Germanischer Lloyd Aktiengesell-schaft, www.gl-group.com, 2009.
“Tankers head into lay up as ratesplunge,” Seatrade Asia Online,www.seatradeasia-online.com, 2009.
“Ships ride out global economicstorm by dropping anchor inMalalag Bay,” Mindanews,www.mindanews.com, June 2, 2009.
“Ocean Going Vessels to be laid up,”Turkish Maritime Magazine,www.turkishmaritime.com.tr, 2009.
Russ Brown is currently the GlobalBusiness Development Manager forMunters Moisture Control Services and isbased out of Indianapolis, Indiana. Brownhas worked in the paint and coatings
industry for thepast 25 yearsin severalcapacities andfor the MuntersCorporation forthe past 13years. Withinhis currentposition, hehas been
active in the expansion of the core prod-ucts and services for Munters MoistureControl Services on a global basis.Brown has a BS in Liberal Arts andSciences from the University of Illinois.He is currently serving as President Electon the Board of Governors of SSPC: TheSociety for Protective Coatings (SSPC)and is also active in the ConstructionSpecification Institute (CSI), AmericanWater Works Association (AWWA), andthe American Institute of Architects (AIA).
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