N COMMITTEEROVEMENTSRODUCTION AIDSIG FOR SHIPBUILDERSANDARDS THE NATIONALION INTEGRATION SHIPBUILDINGOR SHIPBUILDING RESEARCHON AND COATINGS PROGRAMAL EFFECTSTRANSFERINGPS Feasibility Study:
Tank Blasting UsingRecoverable Steel Grit
July 1993NSRP 0387
U.S. DEPARTMENT OF THE NAVYDAVID TAYLOR RESEARCH CENTER
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National Steel and Shipbuilding CompanySan Diego, California
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National Shipbuilding Research ProgramSNAME Panel SP-3
Surface Preparation and Coatings
Feasibility Study:Tank Blasting Using
Recoverable Steel Grit
July, 1993
prepared and submitted by
National steel and Shipbuilding Co.San Diego, California
PROJECT 3-89-2
TABLE OF CONTENTSPage
FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
PROJECT OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
BLASTING WITH STEEL GRIT VS. OTHER ABRASIVES . . . . . . . . . . . . . . . . . 53.1 Tank Blasting Techniques (Current Methods) . . . . . . . . . . . . . . . . . . . . . 53.2 Advantages and Disadvantages of Recycled Steel Grit . . . . . . . . . . . . . . 5
CURRENT INDUSTRY PRACTICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.1 Shipyard Survey of Current Methods of Abrasive Blast
Cleaning and Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.2 Steel Grit Usage in Related Industries . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
OVERVIEW OF CURRENT REGULATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 105.1 Environmental Regulations for Abrasive Blasting . . . . . . . . . . . . . . . . . 105.2 Health and Safety Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125.3 Hazardous Waste Handling and Disposal . . . . . . . . . . . . . . . . . . . . . . . 13
GRIT BLAST AND RECOVERY TESTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176.1 Test Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196.2 Screen Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.3 Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236.4 Vacuum Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
ECONOMIC ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287.1. Abrasive Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297.2 Recovery andClean-UpCosts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297.3 Waste Disposal Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327.4 Equipment and Operating Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327.5 Labor Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
RECOMMENDED PROCEDURES FOR TANK BLASTING WITHRECOVERABLE STEELABRASIVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358.1 Current Commercial Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358.2 Current U.S. Navy Specification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358.3 Recommended Procedures for Blast Cleaning and Recovery . . . . . . . . . 35
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . . . . . . . 40
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43APPENDIX A SAMPLE SHIPYARD SURVEY FORM . . . . . . . . . . . . . . . 44APPENDIX B EQUIPMENT MANUFACTURERS DATA . . . . . . . . . . . . 46APPENDIX C PROPOSEDSSPC SPECIFICATION FOR
STEEL ABRASIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . ...49APPENDIX D SAMPLE FORMAT FOR PROCESS
CONTROL PROCEDURE (PCP) FOR TANKBLASTING WITH STEEL ABRAHVEABOARD NAVAL VESSELS . . . . . . . . . . . . . . . . . . . . ...60
i
TABLES AND FIGURES
Page
TABLES
TABLE 6-ATABLE 6-BTABLE 6-CTABLE 6-D
TABLE 6-ETABLE 7-ATABLE 7-BTABLE 7-CTABLE 7-D
TEST PARAMETERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19SCREEN ANALYSIS RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22MINERAL GRIT VS. STEEL GRIT TEST RESULTS . . . . . . . . . . . . . . . . 23ELEVATED NOZZLE PRESSURE AND BLENDED ABRASIVETEST RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25VACUUM RECOVERY TEST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27COST SUMMARY FROM TEST RESULTS . . . . . . . . . . . . . . . . . . . . . . 28PROJECTED TANK BLASTING COSTS . . . . . . . . . . . . . . . . . . . . . . . . 29COST COMPARISON STEEL GRIT VS. SLAG ABRASIVE . . . . . . . . . . 30EQUIPMENT, OPERATING AND MAINTENANCE COSTS . . . . . . . . 33
FIGURES
Figure 6.1 Interior of Connex Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Figure 6.2 Typical Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Figure 6.3 Blast Cleaning with Mineral Abrasive . . . . . . . . . . . . . . . . . . . . . . . . . . 21Figure 6.4 Blast Cleaning with Steel Grit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Figure 8.1 System Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Figure 8.2 Vacuum Unit and Collection Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Figure 8.3 Abrasive Recovery and Cleaning Stations . . . . . . . . . . . . . . . . . . . . . . . 39
i i
FOREWORD
This research project was produced for the National Shipbuilding Research
Program (NSIW) as a cooperative cost-shared effort between the U.S. Navy
and National Steel and Shipbuilding Co. (NASSCO) of San Diego, California.
The Surface Preparation and Coatings Panel (SP-3) of SNAME’S Ship
Production Committee sponsored the project under the technical direction of
Lyn Haumschilt of NASSCO, NSRP Program Manager.
The research was conducted and this final project report was prepared by
NASSCO. NASSCO participants included Jerry Keener as Project Manager
and Alan Coffer as Project Engineer. H. William Hitzrot of Chesapeake
Specialty Products in Baltimore, Maryland supervised the project testing and
co-authored the report. Les Hansen, an independent engineering consultant
in San Diego, co-authored and edited the final report.
The project team acknowledges Al Hamilton, NASSCO Paint Department
Manager, and other members of the Paint Department for their support and
cooperation during the project. Appreciation is also extended to the following
agencies, shipyards and their representatives for the valuable assistance they
provided:
Byron Hammer of Puget Sound Naval Shipyard;
Jim Fuller of NAVSEA 07011;
Gene Bossie of SUPSHIP San Diego; and
Long Beach Naval Shipyard
1
1. INTRODUCTION
Abrasive blasting of tanks and otherenclosed spaces on-board ships comprisesa large part of the work effort and budgetallocated to surface preparation andcoating for both new construction andrepair contracts. Traditionally, disposableabrasives such as copper and coal slaghave been used for tank blasting,primarily due to familiarity, effectiveness,low initial cost, and relative ease of cleanup. However, in recent years shipyardshave begun to reevaluate their use ofhighly friable mineral and slag abrasivesin light of economic concerns and recentchanges in environmental regulationsimpacting blast cleaning and disposal ofabrasives. Section 5 of this reportprovides an overview of the regulationsaffecting abrasive blasting.
Mineral abrasives are commonly usedonce and then the resulting waste must betransported from the job site for disposal.Due to a high breakdown rate, theseabrasives cannot be effectively reused orrecycled. This results in large volumes ofabrasive waste that must be transportedand disposed of in an economical andenvironmentally compatible manner.Spent abrasive may be considered ahazardous waste, depending on the typeof paint removed and the chemicalcomposition of the abrasive itself.
If the abrasive waste does prove to betoxic or hazardous, disposal optionsbecome limited and disposal costs caneasily exceed the original cost of theabrasive. Waste minimization is mandatedunder the federal Resource Conservationand Recovery Act (RCRA). As landfillsacross the country reach capacity andenvironmental regulations strengthen, theoption of landfill disposal for abrasivewaste may soon become prohibitivelyexpensive or be eliminated completely.
Another significant factor related to theuse of friable abrasives is the amount ofdust generated during the blastingoperation. Copper and coal slags andother mineral abrasives are known togenerate excessive dust due to the rapidbreakdown of the grit particles. This“nuisance” dust creates several problems,such as
● Reduced visibility: The dust cloudformed during blasting limits theoperator’s ability to clearly see theworking surface, resulting in inefficiencyand lost time.
● Environmental and respiratoryhazard: Although blast operators arerequired to wear air-supplied breathingapparatus, excessive dust can exceed thepermissible exposure limit (PEL) of theprotective equipment. Also, airborne dustcan be inhaled by nearby workers orpassers-by. Uncontained dust alsocontributes to air pollution.
● I n c r e a s e d operational costs:Excessive dust necessitates larger andmore costly dust collection equipment. Inaddition, dust clings to the newly blastedsteel surface, adding to clean-up costs. Ifnot removed, this dust layer can contibuteto premature paint failure.
Slag and mineral abrasives are coveredunder the Navy’s new mil-spec forabrasives, MIL-A-22262A. This speci-fication requires extensive and costlysampling and testing for Type 1, inorganicabrasive. The mil-spec is primarilyintended to limit allowable levels ofhazardous substances found in abrasives,such as heavy metals and free silica.
The use of recoverable steel grit for tankblasting would appear to reduce oreliminate many of the problems associated
with slag and mineral abrasives. Due tothe durability and toughness of steel, steelgrit can be reused many hundreds of timesbefore individual particles become toosmall to be effective. As a result,significantly smaller volumes of abrasivewaste are generated for disposal. Thedurability of steel grit also results in verylow dust generation, since the particles donot readily break down into fines.
The recovery of steel abrasive through avacuum recovery system greatly decreasesenvironmental hazards by trapping paintchips and dust, which are segregated fromthe reusable abrasive. The higher densityof steel grit in comparison to otherabrasives produces increased cuttingability, while improving worker visibilitythrough decreased dust generation. Theincreased cutting and low dust equate toincreased productivity. Finally, the use ofsteel grit would not trigger the costlysampling and testing requirements of MIL-A-22262A, since steel abrasive is notcovered under this specification.
3
2. PROJECT OVERVIEW
The primary objective of this project is toinvestigate and analyze the economic feas-ibility of using steel grit as a replacementfor non-metallic abrasives for tankblasting. Recoverable steel grit can poten-tially overcome the environmental prob-lems associated with the use of slag ormineral type abrasives. Blasting with steelgrit also appears to be more cost effective.
This study will examine the types ofequipment available for blasting with andrecovering steel grit, as well as themethodology and procedures necessary toeffectively utilize the equipment. Infor-mation will include the latest state-of-the-art with regard to steel grit blasting. Acost and benefit analysis will be performedto compare steel to slag abrasive in termsof abrasive consumption, productivity ,effectiveness, clean up and disposal.
The original intent of the NASSCO projectteam was to conduct an actual productioncomparison test of steel and slag abrasivesusing a Navy vessel being overhauled atNASSCO. However, at the start of thisproject, steel grit was not fully approvedfor use aboard Naval vessels. Therefore, adecision was made to perform limited-scope comparison testing of steel andcopper slag abrasives using a prototypestorage container to simulate a tankenvironment. (See Section 6 for testdescription.)
The project approach was divided into fiveprimary tasks as summarized below:
● Survey abrasive reclamation equip-ment manufacturers and suppliers anddevelop an equipment comparison list.
● Survey shipyards around the countryto determine blasting methods as well asabrasive handling and disposal costs.
● Perform cleaning rate and vacuumrecovery tests to compare steel and slagabrasives.
. Develop an economic analysis tocompare abrasive consumption, productionrates, equipment costs, disposal costs andany other costs that may impact the bottomline of an abrasive blasting project.
● S u m m a r i z e f i n d i n g s a n drecommendations in a final report.
This report begins with a discussion of thecurrent methods of tank blasting and thepros and cons of using recyclable steel gritin place of slag or mineral abrasives. Thenext section provides a summary of theresults of surveying shipyards as well asrelated industries employing recoverablesteel grit. (A sample shipyard survey formis included in Appendix A.) An overviewof the current environmental regulationsand safety issues relative to abrasiveblasting is also provided, with particularattention paid to the all-important issue ofwaste disposal.
Section 6 describes and summarizes theresults of the comparison testing that wasperformed at NASSCO using steel grit andcopper slag. These test results form a basisfor the economic analysis included in thenext section. The economic analysis coversthe entire spectrum of abrasive blast-related costs. The report concludes with asummary of recommended procedures fortank blasting with recoverable steel grit,based on input from consultants, surveydata and project research. A list ofmanufacturers of steel grit recyclingequipment is included in Appendix B.Appendix C provides a draft of theproposed SSPC specification for steelabrasives. Appendix D shows a sampleprocess control procedure for tank blastingwith steel grit.
4
3. BLASTING WITH STEEL GRIT VS. OTHER ABRASIVES
3.1 Tank Blasting Techniques(Current Methods)
Ship tanks such as ballast, fuel, cargo andvoids historically have been blast cleanedusing various mineral type abrasives.Since many of these tanks arecontaminated with oil, salt or other cargocontaminants, using an abrasive blastcleaning material that is used once anddiscarded meant that there was no concernabout contamination resulting from use ofrecycled abrasive. However, it has beenwell established in the literature that blastcleaning will not remove contaminantssuch as oil, grease and salts from the steelsubstrate. It is necessary, therefore, tothoroughly clean tanks prior to blastcleaning using water blasting and cleaningagents to remove oils, grease and saltsfrom the surface. This has become moreimportant with the advent of sophisticatedcoating systems and with the use of waterbased coatings.
The removal of surface contaminants priorto blast cleaning overcomes abrasivecontamination, which is one of the majorobstacles to the use of recyclable abrasivesin tank blasting. With clean tanks, therecycled abrasive will not pick up oils,grease, or salts. Thus the potential forcontamination through recycling isremoved.
The present method of using single usecoal and copper slag mineral abrasives hassome major worker safety, environmentaland productivity drawbacks, which arebriefly outlined below.
● Breakdown - Mineral abrasives andmineral slags in particular tend todisintegrate on impact, generating largevolumes of airborne dust. The dustcreates a health hazard for blasters andothers in the work area, causes poor
5
visibility and reduces the blaster’sproductivity.
. Material Handling - More abrasive isrequired, both in volume and in poundsper square foot, to clean with mineralabrasives compared to steel abrasives.This translates into greater handling costsand more complex logistics to continuallybring in new material and take away usedmaterial.
• Cleaning Efficiency - A recentinnovation to abrasive blast cleaning hasbeen the use of higher nozzle pressures, inthe range of 120 - 150 psi, resulting inproductivity increases of 125- 150% whenusing steel abrasives. Using mineralabrasives at these elevated nozzlepressures does not dramatically increaseproductivity because most of the addedenergy is expended in particle breakdownand increased abrasive consumption.
. Environment - Disposal of the largevolumes of potentially hazardous mineralabrasives typically generated by mostshipyards is becoming increasingly moredifficult and costly, and creates anenvironmental problem. Generating largevolumes of waste is also contrary to theFederal mandate of waste minimization,particularly when there is a viable wastereduction option steel abrasive.
3.2 Advantages and Disadvantages ofRecycled Steel Grit
The previous section discussed the currenttrends using non-recyclable mineralabrasives in tank blasting. This sectionwill outline the major advantages ofrecycling steel abrasives and will alsoaddress some of the often cited reasons that steel abrasives should not be used.
Steel abrasives have two major advantagesover alternative abrasives: durability anddensity. The importance of durability anddensity in terms of abrasive recyclability isdiscussed below.
To be truly recyclable, an abrasive must bedurable, that is, an abrasive mix must
MINERAL GRIT
Wt% Coarser than #40 Sieve
Before Blast After Blast
98% 50%
The data above shows that after a singleimpact mineral abrasive loses almost 50%of its original size compared to steelabrasive, which lost only 1%. Steelabrasives are extremely durable and canbe reused hundreds of times withoutlosing size or cleaning ability. Mineralabrasives, on the other hand, if recycledwould, after one or two recycles, be toofine and dusty to bean effective abrasive.
The second major attribute of steelabrasive, density, is the key torecyclability. Steel has a specific gravity of7.4 compared to mineral abrasives whichare typically 2.5 to 3.5. Therefore, steellends itself to simple air classification as ameans to remove lighter paint chips, finesand dust from used abrasive. The mostcommon method of air classification is the“air wash” which passes a controlled flowof air through a measured flow ofabrasive. The air flow is set such that itwill sweep out the paint chips, fines anddust leaving a cleaned steel abrasiveproduct for reuse. Mineral abrasives, onthe other hand, have close to the samedensity as the paint chips, fines and dustcontaminating the abrasive. Air washingmineral abrasive is not practical since itwill remove almost all the abrasive alongwith the contaminants.
6
be able to withstand numerous impactswithout dramatically altering it’s sizedistribution. Abrasive durability can bestbe illustrated by comparing a steelabrasive and a mineral abrasive before andafter a single use. The data shown belowis taken from the project test results, Table6-B in Section 6.
STEEL GRIT
Wt% Coarser than #50 Sieve
Before Blast After Blast
100% 99%
Maintaining abrasive cleanliness is the keyto successful abrasive recycling. Periodicsampling and checking of the recycledabrasive for contaminants such as salt, oilor heavy metals should be incorporatedinto the production schedule. The SteelStructures Painting Council has a draftspecification for recycled steel abrasives.This proposed specification outlines thespecific physical and chemical tests thatshould be run to assure abrasivecleanliness. A copy of the draftspecification is included in Appendix C.
Steel abrasives are the ideal recyclableabrasive product based on durability anddensity. However, there are someprecautions to be considered when usingsteel abrasives. Of primary importance iskeeping steel abrasive dry. Steel will rustif allowed to sit in water and with timethis rusting can cause the abrasiveparticles to form lumps which can plugthe system. A small amount of moistureis no problem if the abrasive is keptmoving and the moisture can then beremoved by air dryers in the blastingprocess.
To summarize, steel abrasives, because oftheir durability, can be recycled hundredsof times before the particles become too
fine for reuse. With recycling, many of thelogistical problems encountered withmineral abrasives, such as daily receivingand disposing of truckloads of abrasiveare eliminated. Higher nozzle pressurescan be used with steel abrasive thusincreasing productivity by 125 - 150%while reducing disposal costs by 99%.Steel abrasives offer increasedproductivity, long life and excellentrecyclability compared to mineralabrasives. To realize these advantages,abrasive cleanliness must be maintainedalong with moisture controls on allcompressed air sources.
7
4. CURRENT INDUSTRY PRACTICE
4.1 Shipyard Survey of CurrentMethods of Abrasive BlastCleaning and Recovery
A number of shipyards along the EastCoast, Gulf Coast and West Coast weresurveyed to determine the proceduresbeing used for tank blasting and some ofthe problems with current methods. Theresults of this survey are divided into twoareas: new construction and repair. Eachof these areas is discussed below.Appendix A shows the format used for theshipyard survey.
New Construction. In new constructionmost tanks are blast cleaned and paintedas subassemblies prior to shipboarderection. With this methodology mostyards are blast cleaning subassemblies inlarge abrasive blast rooms using steelabrasives. This scenario is typical of BathIron Works, Newport News Shipyard,Norfolk Naval Shipyard, Ingalls Shipyardand Avondale Shipyard to name a few.NASSCO Shipyard, due to San Diego’sfavorable climate, is able to perform open-air blasting with steel grit.
All of these yards have found steelabrasive to be the most economicalapproach to blast cleaning, based onproductivity, reduced dusting, wastedisposal and ease of recycling. Theseyards have demonstrated that steelabrasive blast cleaning, recovery, andrecycling is a viable and economicalapproach for shipyards. Although steel isthe abrasive of choice for new constructionblasting, mineral abrasives are sometimesused for limited field blasting whenreclamation and recycling equipment isnot available.
Shipyard Repair. Mineral abrasives,particularly copper, coal and nickel slags,are the abrasives of choice for on-board
8
tank blasting. A few yards, such as PugetSound Naval Shipyard and NASSCO, havebegun limited tank blasting with steel grit.Some of the problems associated with theuse of steel grit in tanks were discussed inSection 3.
The major deterrents to switching to steelgrit have been resistance to change; lackof approved specifications and procedures,particularly for work on Navy ships;maintaining a dry tank environmentduring blasting; and assuring thecleanliness of the recycled abrasive. Thecleanliness problem has been studied andsolved by equipment suppliers to the leadpaint removal industry. When removinglead paint from steel abrasive, theresultant recycled steel abrasive must meetthe cleanliness standards of new abrasive.This topic is covered further in thefollowing section on related industrypractice. Appendix B lists availableequipment that will meet the cleanlinessrequirements for effective steel abrasiverecycling.
4.2 Steel Grit Usage in RelatedIndustries
Steel abrasives are replacing non-metallicabrasives for maintenance of steel bridges,oil storage tanks and water tanks to namea few. The forces driving this change arethe same as those driving the shipbuildingindustry, namely
• Waste Minimization● Worker Safety● Improved Costs● Reduced Air Pollution• Improved Surface Profile and
Cleanliness
This trend toward steel abrasives for usein surface preparation for maintenance
applications demonstrates the effectivenessof steel abrasives in providing the industryneeds cited above.
The removal of lead paint has created amajor problem in maintenance of steelstructures. During blast cleaning the leadpaint contaminates the abrasive, producinga hazardous waste that can only be sent toa hazardous waste landfill. This hasincreased abrasive disposal costs 100 timesfrom $5.00 to $500.00 per ton and higher.These costs are driving those involved inmaintaining steel structures to look atmore cost effective methods of blastcleaning.
Steel abrasives have become the abrasiveof choice primarily because of theirrecyclability. Steel abrasives, when usedwith good containment and recoverymethods, can be recycled hundreds oftimes.
The equipment used has three basicfunctions: abrasive blasting, recovery andclassification (cleaning spent abrasive).These functions can be combined in asingle unit or as separate integrated units.When adapting these units to shipyardapplications it is important to consider anindividual yard’s needs and existingequipment. In many cases portions of ayard’s existing equipment can be used aspart of the abrasive blast, recovery andclassification system.
In addition to recyclability, steel abrasivesoffer some other major advantages overnon-metallic abrasives. Steel is two tothree times denser than non-metallicabrasives. This high density means thateach steel abrasive particle can do two tothree times the work of a comparable non-metallic particle, making steel abrasiveparticles far more effective andsignificantly increasing cleaning rates.
Because steel abrasives do not breakdownon impact there is virtually no dust
9
generated, so the blaster has improvedvisibility and is therefore more productive.Since steel abrasives are recycled 100 ormore times, the waste generated is onlypaint and other contaminants removedfrom the surface. Disposal is reducedfrom tons per day when using non-metallic to pounds per day with steel.
Surface profile plays a major role in paintconsumption. The more profile, the morepaint required to provide adequate coatingthickness over the peaks. The bridgemaintenance industry has found that steelabrasive cleans faster, gives a lower profileand reduces overall paint consumption.
The advantages demonstrated when usingsteel abrasives in related structural steelapplications suggests that similaradvantages and savings can be realizedwhen used in shipyards. To realize theseadvantages, steel abrasive recycling mustaccomplish the following
• Maximize containment to minimizeloss of abrasive
• M a i n t a i n a m o i s t u r e f r e eenvironment to prevent abrasive frombecoming wet
● Provide abrasive recovery andclassification equipment that will generatea clean recycled product to be recycled tothe blaster
• Use adequate ventilation to assure asafe environment for the blaster
This SP-3 project is verifying much ofwhat has already been learned in relatedindustrial maintenance blast and paintprojects. The results of this project areexpected to provide the shipbuildingindustry with a proven system for moreeffective tank blasting.
5. OVERVIEW OF CURRENT REGULATIONS
The envi ronmenta l regula toryrequirements pertaining to an abrasiveblasting operation are determined byseveral factors, including job location (stateor locality), job size, type of coatingremoved and composition of abrasiveused. Abrasive blasting may be subject tofederal and state regulations governing airpollution, water pollution, and thetransportation, handling and disposal ofhazardous waste. Waste disposal isdiscussed in Section 5.3. The scope of thissection is to provide the reader with asummary overview of the regulatory, aswell as health and safety issuessurrounding abrasive blasting of tanksaboard ship. Since this discussion is notintended to cover these issues in greatdetail, each shipyard should ensure thatthe appropriate personnel become familiarwith their local laws and regulationsrelative to tank blasting.
5.1 Environmental Regulations forAbrasive Blasting
The federal Clean Air Act (CAA),originally enacted in 1955, has been thebasis for regulating emissions of airpollutants to protect human health and theenvironment. The Act has been amendedand strengthened several times over theyears, most recently with the 1990 CleanAir Act Amendments. Administration andenforcement of the CAA ultimately fallson the Environmental Protection Agency(EPA), however individual states mustsubmit their implementation plans to theEPA for approval. Although the CAAdoes not specifically regulate abrasiveblasting operations, the 1990 Amendmentsinclude a provision to control emissionsinto the atmosphere of fine particulatematter (particle size smaller than 10microns - “PM 10”). PM 10 is essentiallydust, which contributes to the persistent
10
problem of ambient air pollution in somelarge sties and industrial areas. The PM10 regulations apply only to areas thatcurrently have a moderate or seriousairborne dust problem.
The control of airborne dust as mandatedby the CAA would appear to have apotential impact on abrasive blastingoperations, particularly for open-airblasting. However, the degree to whichblasting contributes to PM 10 pollution hasyet to be determined through testing andmeasurement. The initial results of arecent NSRP project to measure PM 10emissions during blasting (Ref. 10) indicatethat mineral abrasives can generatesignificant levels of PM 10 dust.
Further research is needed since differentabrasive types, used under differentconditions, would be expected to generatevarying amounts of dust. In particular,slag and mineral abrasives generatesignificantly more dust than metallicabrasives. Type and age of the coatingbeing removed, or condition of theuncoated surface, will also influence thelevel of dust generation. In the case ofremoval of coatings containing toxicelements such as lead, zinc or other heavymetals, dust control and containmentbecome a more critical concern. Stringentlimits on airborne emissions of these typeof toxics are imposed by the CMAmendments.
The PM 10 regulation will probably notbecome a major issue for tank blasting.Most tanks are, in effect, enclosed spacesthat tend to confine the airborne dustcreated during blasting. Air exhaust anddust collection equipment is typically usedfor tank blasting. The use of thisequipment improves operator visibilityand prevents the escape of most dustthrough tank openings into the
atmosphere. Therefore, the release of PM10 appears to be a potential factor in tankblasting only if adequate exhaust and dustcollection equipment is not used.
While federal environmental legislationdoes not specifically regulate abrasiveblasting operations, some states orlocalities may. For example, California’sAir Resources Board first enactedCalifornia Abrasive Blasting Regulations(CABR) in 1974 under the auspices of theHealth and Safety Code. Theseregulations have since been amendedseveral times, most recently in 1990. Theprimary motivation for the Californialegislation is control of the respirable dustproduced during dry abrasive blasting. Inessence, the latest amendments to CABRlimit the permissible amount of visibleemissions from outdoor blastingoperations to a maximum of 40% opacity(Ringlemann 2), which equtes to a 40%reduction in visibility. The Regulationsalso specify the blasting methods andabrasive types (low dusting) that must beused for blasting “outside of a permanentbuilding: including ship tanks. Steel (oriron) grit is the only abrasive approved forunrestricted outside blasting. Other statesmay currently have, or may beconsidering, blasting laws similar toCalifornia’s.
The Clean Water Act (CWA) of 1977 andthe CWA Amendments of 1987, whichregulate water quality, may also impactabrasive blasting operations and wastedisposal. The CWA regulates quantities ofparticular hazardous substances orpollutants that may be discharged intosurface waters or municipal sewers. Oneof the primary goals of the CWA is toachieve “zero discharge” of certainpollutants. Therefore, even the smallestdischarges of designated pollutants couldbe subject to regulatory action.
As with the Clean Air Act, the CWAwould most likely impact open air blasting
11
operations more than tank blasting. Toensure compliance with the CWA, spentabrasive and paint residue must beprevented from entering surface waters,storm drains or sewer systems. Both theabrasive and paint wastes may containsignificant quantities of regulatedpollutants. For example, pulverizedcopper or coal slag, as well as metallicpaint dust, may contain high levels ofleachable heavy metals such as copper,zinc or nickel. In open air blasting,complete containment of abrasive wastesduring operations can be difficult.Precautions need to be taken to keep anyfugitive wastes from finding their way intoa water source, particularly near bays andestuaries, where toxic sediments arebecoming an increasing problem. Tankblasting provides an enclosed space tocontain waste debris. Dust collectionsystems are commonly used to trapairborne fines. Chances are much lowerthat any of the waste products from tankblasting would end up in a nearby watersource.
There is, however, one potential methodfor abrasive or paint waste to enterwaterways as a result of either open air ortank blasting. Following the blastoperation, blast waste must be collectedand transported to a central storage areain the shipyard to await final dispositionaccording to the yard’s current policy forabrasive waste disposal. Care must betaken during this collection, transportationand temporary storage process to ensurethat waste products are not accidentallyreleased into or near any water source.Prevention methods include protectingstorage areas from the weather, providingsecondary containment such as berms, anddeveloping and enforcing comprehensiveshipyard “Best Management Practices(BMPs)” relative to waste management.Waste disposal is discussed further inSections 3.3 and 5.3.
One additional national environmental lawhas potential to significantly influenceabrasive blasting operations. The ResourceConservation and Recovery Act (RCRA),originally adopted in 1976 and revised in1984, governs all aspects of hazardouswaste handling and disposal. Theconsequences of this law relative toabrasive waste are discussed in Section 5.3.
5.2 Health and Safety Issues
In addition to the state and federalenvironmental laws and regulationsmentioned in the previous section, theState and Federal Occupational Safety andHealth Administration (OSHA) regulatesabrasive blasting and related activities.Many of the OSHA regulationscomplement the environmentalregulations. In general, the federal andstate OSHA regulations pertain toadministrative responsibilities includingstandards-setting, recordkeeping, activitiesof advisory committees, access toemployee medical records, duties ofemployers, enforcement actions,accreditation of testing laboratories, on-siteconsultations, and examination andcopying of documents.
One of the main health issues associatedwith abrasive blasting is the respirabledust commonly generated during blastingoperations (PM 10, as described in Section5.1). Dust can be produced either by thebreakdown of the abrasive or the removalof the old coating. Both types of dusthave potential to contain toxic elements,such as copper or nickel from slag, lead orchromium from old coatings and zincfrom newer coatings. Although silica-based abrasives have generalIy beenphased out of shipbuilding work, OSHAhas established strict limits on workerexposure to silica dust. Silica dust hasbeen associated with the debilitating lungdisorder known as silicosis.
An air-purifying respirator with full facepiece and hood is the most effectiveprotection from respirable dust availableto a blast operator. While this type ofprotection may be optional for open airblasting, it is normally required inconfined areas such as tanks. OSHA hasestablished standards, known asPermissible Exposure Limits (PEL), forworker exposure to many of the toxicsubstances that may result from abrasiveblasting. For example, the eight-houraveraged PEL for lead dust is 50micrograms per cubic meter.
The OSHA standards permit theconcentration of toxic substances in thevicinity of the worker to be reducedthrough engineering or work practicecontrols. Engineering controls include thedesign and installation of an adequate airexhaust and ventilation system in tanks.Where engineering and work practicecontrols are not feasible or sufficent toreduce worker exposure below the PEL,respirators are required to supplementthese controls. A respirator must alwaysbe made available to an employee thatrequests one. Only approved respiratorsmay be used, of a type based on the levelof toxic concentration. The employer mustalso provide a worker training program toinclude the proper selection, use andmaintenance of respirators.
In addition to the lung protectionprovided by the OSHA PEL limits, skinprotection is also required to preventabsorption of toxics. All exposed operatorskin surfaces should be covered whenconcentrations are above the PEL.However, skin protection from toxics isusually not an issue, since blast operatorsmust cover themselves completely andseal all openings to prevent discomfort orinjury from rebounding abrasive,particularly in confined spaces such assmall tanks.
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In situations where hazardous by-productsof blasting are known or suspected to bepresent, worker exposure monitoring isrequired under OSHA. A preliminarysample of the dust and fines beingproduced by an abrasive cleaning job canfirst be analyzed to determine whetherhazardous substances are present insignificant amounts. If this preliminarytesting indicates a potential problem, theoperator’s breathing zone (outside ofprotective equipment) should bemonitored with a portable collectionapparatus. Testing and monitoring shouldbe conducted by a state certifiedlaboratory or a certified industrialhygienist.
Other existing or proposed O S H Astandards may impact abrasive blastingoperations. Shipyard management andpersonnel involved in these operationsshould be fully aware of all pertinentstandards and requirements. Furtherinformation on health and safety issuescan be obtained from the state or localOSHA enforcement unit.
5.3 Hazardous Waste Handling andDisposal
Disposal of both hazardous and solid(nonhazardous) waste may be governedby one or more federal laws. The mostcomprehensive of these laws is theResource Conservation and Recovery Act(RCRA), originally adopted in 1976.Sweeping amendments to RCRA, knownas the Hazardous and Solid WasteAmendments (HSWA), were passed byCongress in 1984. RCRA covers the fullspectrum of generation, treatment, storage,handling and disposal of waste. RCRA, ineffect, mandates “cradle-to-grave” (i.e.,generation to ult imate disposal)responsibility for hazardous wastegenerators. The ComprehensiveEnvironmental Response, Compensation,and Liability Act (CERCLA) of 1980, ALSO
1
known as Superfund, and the 1986Superfund Amendments and Re-authorization Act (SARA) may alsopotentially impact abrasive waste disposal.CERCLA and SARA primarily address theclean up of existing hazardous wastedisposal sites and releases or spills ofhazardous substances. All federalenvironmental regulat ions areadministered by the EnvironmentalProtection Agency (EPA).
As previously mentioned, the wasteproduced during abrasive blasting may beconsidered hazardous in some cases. Thesource of the hazardous ingredients couldbe either the paint removed or theabrasive itself. A sample of the wasteproducts must be tested by a state certifiedtesting laboratory to determine the degreeto which the waste is hazardous, if at all.(Testing procedures are described later inthis section.) If the waste sample provesto be nonhazardous, several options existfor disposal of the waste.
The most common method for solid wastedisposal is in a “Subtitle D“ landfill,named for the RCRA section coveringnonhazardous solid waste. However, highvolume solid waste disposal in municipallandfills is becoming more difficult andcostly as landfills reach capacity. Withincreasing environmental awareness andrecognition of the potential for land andwater contamination from landfillleachates, many localities are reluctant toapprove the opening of new landfills.Therefore, the trend is to establish newlandfills further away from urban areas,resulting in higher disposal fees andtransportation costs. (See Section 7.3 for adiscussion of waste disposal costs.)
The use of recyclable steel abrasive offerssignificant opportunity to reduce spiralingwaste disposal costs. The volume of wasteproducts resulting from the operation of asteel grit recovery and reclamation systemis significantly lower than with the use of
3
non-recyclable abrasives. Test results fromthis project show a 99% reduction in wasteusing steel abrasive. This reduced wastevolume equates to sharply lower disposalfees.
Other options exist as alternatives tolandfilling o f h a z a r d o u s andnonhazardous abrasive waste, and theseshould be explored whenever practical.Alternative uses for spent mineral abrasiveinclude,
● Inclusion of grit waste as anaggregate in concrete or asphalt pavementmaterials, used to pave highways, roadsand airport runways
• As an aggregate additive in themanufacture of various types of bricks forresidential and commercial construction
• As an additive to replace fines in theproduction of Portland cement
A 1990 study performed by PittsburgMineral and Environmental Technology,Inc. for the Pennsylvania Department ofTransportation (Ref. 11) explored severalbeneficial reuse options for mineralabrasive waste contaminated with lead.The options included use in Portlandcement concrete, asphalt concrete mixes,cement kiln feeds, polishing abrasives,lead smelter feeds and structural clayproducts. This study concluded that, fromboth an environmental and economicperspective, the most viable option for thereuse of spent abrasive in Pennsylvania isin clay brick manufacturing. The additionof spent abrasive containing lead actuallyincreased brick strength while reducingmanufacturing costs.
Since waste products from a recoverablesteel abrasive system consist solely offines, the use for this waste in some of theapplications mentioned above may belimited. Additional alternate uses forabrasive waste may exist or be under
1
development in a particular region of thecountry. Abrasive manufacturers andsuppliers, as well as environmental andwaste management companies, are goodsources of inquiry for further information.
If sample testing indicates that the wastefrom an abrasive blasting job is hazardous,disposal becomes a more complicated andcostly issue. The handling, transportationand final disposal of hazardous waste arestrictly controlled under RCRA. RCRAdefines a hazardous waste as any wastethat either has been identified or listed byEPA as hazardous, or that exhibits thecharacteristic of toxicity in excess ofestablished concentration limits. Someabrasive wastes, especially thosecontaining heavy metals, fall under thisdefinition.
The “generator” of the hazardous waste isultimately responsible for compliance withRCRA regulations. Controversy oftenexists over the question of who is thewaste generator, the shipyard or shipowner. Generally, since the ship owner isspecifying the removal of the coating, theowner is considered the generator if thecoating is hazardous. However, undercertain contractual agreements, theshipyard may take the responsibility ofgenerator, particularly where the abrasivemay contain hazardous elements.
Generators of less than 100 kg (220 lb) permonth of non-acute hazardous waste arenot required to comply with the detailedRCRA regulations, but must assure thattheir waste is properly disposed of orrecycled. A typical tank blasting job usingunrecycled mineral or slag abrasives couldeasily generate tons of waste. However,the amount of waste generated from thesame job using steel grit could conceivablybe less than the 100 kg limit.
Prior to HSWA in 1984, hazardousabrasive waste was commonly disposed ofin a hazardous waste, or “Subtitle C:
4
landfill. However, HSWA introduced landdisposal restrictions that require hazardouswaste to be treated prior to disposal torender it nonhazardous. Since no viabletreatment method exists for abrasive wastecontaminated with heavy metals, a“stabilization” process is used. Withstabilization, the hazardous waste isbound into a cement block to preventtoxics from leaching at the disposal site.After stabilization, the waste may bedisposed of in a Class C, hazardouslandfill. Also, the regulations prohibitdilution of the waste, or residual aftertreatment of the waste, in order tocircumvent the land disposal prohibition.For example, additional abrasive or soilcannot be added to the paint debris in anattempt to create a “non-hazardous”material.
Most shipyards choose to contract with acertified Treatment, Storage and DisposalFacility (TSDF), or a TSDF broker, toremove and arrange for the disposal oftheir hazardous wastes. Since thegenerator is ultimately responsible for thewaste from “cradle-to-grave,” the shipyardmust ensure that they are dealing with areputable hazardous waste hauler orfacility. The facility must have allrequired state and local permits andshould not have a history of violations.RCRA requires all TSDFs to have a federalpermit to operate their facilities. While theshipyard, as waste generator, is notrequired to have a federal permit,individual states may require permits forhandling or processing waste materialsunder certain conditions.
The EPA currently endorses one methodfor testing waste to determine if it ishazardous. This test is the ToxicityCharacteristic Leaching Procedure (TCLP),which was designed to simulate long-termleaching that might exist in a sanitarylandfill. The TCLP procedure iscommonly used to test abrasive waste todetermine if stabilization is required prior
15
to land disposal. States may also havetesting methods for the analysis ofhazardous waste. For example,California’s two test methods, TotalThreshold Limit Concentration (TTLC) andSoluble Threshold Limit Concentration(STLC), are more stringent than the federalprocedure. EPA procedures also specifythe size and quantity of samples that mustbe taken for testing, as well as samplingtechniques. Testing should be conductedonly by a qualified industrial hygienist ora state approved laboratory.
Due to increased environmentalrestrictions on hazardous waste disposal,waste management companies arecontinually exploring new options forwaste reduction, reuse or recycling. Mostof the options for non-hazardous abrasivewaste, mentioned earlier in this section,are also available for hazardous abrasivewaste. These include use as an additive inpaving materials, brick manufacturing andas a cement additive. However, in somecases the toxic components may exceedRCRA limits, thus restricting the use of thewaste. This is particularly true for use inasphalt or concrete paving materials,where toxics could be released as thepaved surfaces wear down.
Some states are considering regulatorychanges to permit the use of hazardousabrasive wastes in construction andbuilding materials. For example, at thetime of this writing, the CaliforniaDepartment of Health Services was in theprocess of finalizing the development of aCalifornia regulation covering the use ofhazardous waste in asphalt concrete andconcrete. This regulation would permitabrasive waste contaminated withmoderate levels of heavy metals, such aslead, copper or tin, to be used in themanufacture of asphalt concrete. The finalregulation will address severalenvironmental concerns, including
● Potential long-term leachate ratesand levels
• Responsibility and liability of theproduct manufacturers
• Expanded uses in other buildingproducts such as clay bricks
• Improved verification and recordkeeping requirements for manufacturers
● Development of specifications andstandards for the manufacture and use ofthe materials.
The HSWA Amendments to RCRA requireall hazardous waste generators to establishwaste minimization programs. Generatorsare required to sign a certification onmanifests for off-site shipment stating thatthey have a program in place to reducethe volume or quantity and toxicity of thewaste generated. Generators are alsorequired to submit biannual reports (FormR) describing waste minimization effortsand actual reductions in waste volumeand toxicity.
The use of recyclable steel grit as areplacement for non-reusable abrasiveswould go a long way toward satisfyingthis waste reduction requirement bysignificantly reducing the volume ofdisposable hazardous abrasive waste.However, waste from recyclable steel gritwould contain a more concentratedvolume of potentially toxic paint particles.The extent to which blasting only tankswith steel grit reduces a shipyard’s totalvolume of abrasive waste depends, ofcourse, on the percentage of tank blastingwork as compared to the total blastingwork load.
Late in 1992, EPA had proposedmodifications to RCRA to establish a newmaterial waste management system.Under this new system, certain wastesnow considered hazardous would be
16
downgraded to solid, or nonhazardouswastes, whereas other solid wastes may bedesignated hazardous. It is unclear if andwhen these new waste designations willbe implemented. This new proposal againunderscores the importance for shipyardsto remain abreast of changes inenvironmental regulatory issues.
6. GRIT BLAST AND RECOVERY TESTS
A number of options were looked at whenplanning the test program. Initially, actualtank blasting aboard a Navy orcommercial ship was investigated.However, at the time of the testing, theNavy had not fully approved the used ofsteel grit aboard Navy vessels. Also,because of the extent of the tests and thelength of time required to test the variousabrasive mixtures it was decided toconduct the tests on a fixed facility. Afterlooking at several alternatives, a 20 footlong Connex container was selected as asimulated tank configuration. The Connexbox chosen had been used for paintstorage and had built-in steel shelves. Theinterior of the Connex box is shown inFigure 6.1, and the overall test set up isshown in Figure 6.2.
Prior to testing, the Connex box was blastcleaned to white metal and repainted witha 3-5 mil coating of Navy Formula 150Epoxy. The total square footage of theConnex box interior, including shelves, is1043 square feet. A blast cleaningprogram was set up based on cleaning the1043 square foot Connex box and thefollowing data was recorded for each test.
Outline of Data Recorded
Blast Cleaning Test
• Abrasive ConsumptionŽ Nozzle Pressure• Blast Time• Abrasive Size Distribution Before
and After Blast● Blast Hose Size● Nozzle Size● Surface Cleanliness After BlastŽ Square Feet Blast Cleaned
Abrasive Recovery Test
● Type of Vacuum Used
17
● Vacuum Hose Length• Recovery Rate● Size Analyses of Recovered Products
The original test program was designed todetermine the advantages of using steelgrit compared to mineral grit abrasives.The program was set up as follows:
Standard 600 lb. pots were filled withknow weights of abrasive. The interior ofthe painted Connex box, described above,was blast cleaned completely with mineralgrit using air from NASSCO’S compressedair system. The same Connex box, afterblasting with mineral grit, was repainted.About four weeks after painting, theConnex box was reblasted completely withG-40 steel grit again using NASSCO’S airsystem. The same blasters and blast potswere used in both cases to keep the testsas similar as possible.
A decision was made at the conclusion ofthe mineral and steel grit tests to extendthe scope slightly by looking at two keyparameters that impact significantly onproductivity: nozzle pressure andabrasive particle size distribution. Thesetwo tests were conducted using theConnex box and blast cleaning set-upexcept that a separate compressed airsource was used to achieve the highernozzle pressures. The results of thesetests, although somewhat less complete,show that significant improvements inproductivity can be accomplished for bothmineral and steel abrasives by elevatingnozzle pressures. Productivity of steelabrasives can also be increased by using afiner sized abrasive mix.
The test parameters and results arediscussed in the following subsections.
Figure 6.1 Interior of Connex Box.
Figure 6.2 Typical Set-Up for the Blast Cleaning Tests. Thededicated compressor is on the left. Blast pot andsteel grit drums are in the center. Vacuumrecovery and steel grit cleaning station next tothe Connex Box on the right.
18
6.1 Test Parameters
Table 6-A describes the parameters for thetesting. The mineral grit used for the testsis a commercially available copper slagabrasive. The steel grits used for the testsare commercially available steel abrasives.The initial mineral grit and steel grit testswere conducted using yard nozzle airpressure of about 80 psi ± 1.2 psi. For thehigher pressure test, a dedicated 1350 cfmcompressor and an Ingersol Rand airdryer/after cooler were used to achieve 91psi k 0.5 psi at the nozzle. The blast hosesused were all 1¼ ID with 10 ft. long, 1 in.ID whip hoses for flexibility. The hoselength for the first test was 100 ft. of 1¼inch hose plus the 10 ft. whip. For thesecond test, the hose length was 60 ft.including the 10 ft. whip.
TABLTEST PAR
Nozzle Pressure I 80 psi I
Supply Pressure (psi) I 100 IHose Length (Pres. Potto Nozzle) I 110ft INozzle Size #7 I
Coating Thickness(Prior to Blast) 2 mils IType Blast Equipment 600 lb.
Connex boxArea to be Blasted 1043 Sq. ft.
Vacuum Type Liquid Ring, 75
Vacuum Recovery Hose 120 ft.
Vacuum Head 12” Hg
1
The same 600 lb. blast pots were used forall tests. The pots were weighed emptyand the weight recorded. The pots werethen filled with abrasive and re-weighed.This filled weight less the tare weight of thepot gave the weight of abrasive. At the con-clusion of the test the pot was re-weighed,the weight of the pot subtracted from thisweight giving the amount of abrasive stillin the pot. This weigh-in weigh-outmethod enabled an accurate determinationof abrasive consumption for each test.
The area blast cleaned was the interior of aConnex box as described earlier and shownin Figure 6.1. After each blast cleaning testthe Connex box was repainted withapproximately 3 -5 roils of epoxy. Thecoating was allowed to dry for three to fourweeks before being reblasted.
E 6-AAMETERS
80 psi I 90 psi 90 psi
100 I 120 I 120
60 ft 60 ft 60 ft
#7 I #7 I #7
2-3 mils 2-3 mils I 2-3 roils
~ 600 lb.
Connex box1043 Sq. ft.
hp IR AirVac
120 ft.
11.2 Hg 15’’ -18” Hg
9
Vacuum recovery was tested at thecompletion of each blast cleaning test. Theinitial vacuum recovery for the mineralgrit and steel grit tests were done usingNASSCOS water-vat recovery systems.Vacuum recovery after the higherpressure -90 psi-test was conducted usingan IPEC air-vat vacuum recovery system.The vacuum recovery results are discussedunder Section 6.4.
6.2 Screen Analysis Results
Table 6-B summarizes the size analyses ofall abrasive products tested before andafter blast cleaning. The sieve sizes usedfor the screen analyses are themanufacturers recommended sizes for theproducts used. It should be noted that thenew slag and steel abrasives havesignificantly different size distributions.Copper slag, because of its lower density,is significantly coarser that steel grit. 70%of the slag is coarser than a #18 screencompared to only 2% of G-40 steel grit.Finer slag particles — particles finer thana #40 sieve — have little cleaning valueand end up as dust. Steel grit, on theother hand, because of its density anddurability, is an effective abrasive even at#50 sieve size. Because of the inherentdifferences in the two abrasives, commonindustry practice sets the minimumeffective size for the copper slag at #40sieve and for G-40 steel grit at #50 sieve.For slag, particles finer than #40 sieve areconsidered too fine for blast cleaning. ForG-40 steel grit, the minimum size is #50.
Comparing the breakdown of slag abrasiveversus steel abrasives in Table 6-B, it isclear that slag abrasives lose a significantamount — almost 50% — of their particlesize after a single use. This disintegrationmanifests itself in excessive dustgeneration, as shown in Figure 6.3. Thisphoto was taken during the copper slagblast cleaning test. Compare Figure 6.3with Figure 6.4, which was taken during
9 n
the steel grit blast cycle. Little or no dustwas generated, and in contrast to the slagtest, the blasters used no lighting.
Analysis of steel grit after the blast testshowed that steel abrasive breakdown at80 psi was about 1% after initial impact.Compare the size analysis (Table 6-B) ofsteel grit before and after blast, at weightpercent coarser than #50 sieve. Steel grit is99% recyclable after one use and still 99%recyclable after two (2) uses. Thisdemonstrated durability of steel coupledwith the significantly lower dust levelsillustrates the advantages of steelcompared to slag abrasive.
Blast cleaning efficiency is a function ofthe amount of energy transmitted by theabrasive particle to the steel surface. Amajor portion of the energy of a mineralabrasive particle is expended in abrasiveparticle breakdown (50% size reduction onimpact) rather than cleaning the steelsubstrate. Steel, on the other hand, showsthat 99% of the energy is imparted to thesteel substrate (1% size reduction onimpact). Steel’s more efficient use ofenergy is apparent in the productivityresults shown in Table 6-C.
Figure 6.3 Dusty Blast Cleaning Environment when usingMineral Abrasive.
Figure 6.4 Blast Cleaning with Steel Grit. Note low level ofdust and excellent visibility well within theConnex Box.
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TABLE 6-BSCREEN ANALYSIS RESULTS
MINERAL GRIT, 80 PSI
NEW USED (1st USE)
SIEVE SIEVE CUMULATIVE CUMULATIVESIZES OPENING, IN. WT.% RETAINED WT.% RETAINED
12 .066 6 116 .047 45 4
20 .033 72 13
30 .023 90 28
40 .017 98 50
70 .008 99 83
Pan 100 100
G.40 STEEL GRIT, 80 PSI
NEW USED (1st USE) USED (2nd USE)
SIEVE SIEVE CUMULATIVE CUMULATIVE CUMULATIVESIZES OPENING, IN. WT.% RETAINED WT.% RETAINED WT.% RETAINED
18 .039 2 2 125 .028 36 27 22
30 .023 75 59 59
40 .017 99 94 94
50 .012 100 99 99
Pan 100 100 100
G-40/50 BLEND STEEL GRIT, 90 PSI
NEW USED (1st USE)
SIEVE SIEVE CUMULATIVE CUMULATIVESIZES OPENING, IN. WT.% RETAINED WT.% RETAINED
22
20 .033 6 6
25 .028 22 22
30 .023 48 42
40 .017 92 82
50 .012 99 98
Pan 100 100
Screen analyses were also run on theabrasives used at the elevated nozzlepressure and the finer sized steelabrasives. These analyses are included inTable 6-B. It is interesting to note that thefiner G-40/G-50 blend steel abrasiveshowed very little breakdown on impact atthe higher nozzle pressure of 90 psi (1%breakdown going from 99% coarser than#50 sieve for new abrasive to 98% afterone use). This demonstrates that even thefiner G-50 steel grit particles are tough, donot break down and are recyclable.
In addition to the recycled steel abrasiveproduct, the fines generated by thereclaiming system were also examined.These results showed that only traceamounts of usable steel abrasive werepulled out by the reclaiming system. The
TABLEMINERAL GRIT VS. STEE
Nozzle Pressure 80 Total Area Cleaned(square foot) 10Total Cleaning Time(hours) 5.Total Amount of Abrasive Applied(pounds) 79Volume Abrasive Applied(cubic foot)Rate Abrasive Applied(pounds/square foot) 7Rate of Cleaning(square foot/hour) 1Consumption(pounds/square foot non-reusable abrasive) 7Recovery Factor (PercentReusable Grit After Blast)P r o f i l e * ( m i l s ) 4Degree of Cleanliness SP1
● the high profile produced by the initial mineral grit absubsequent abrasive blasts. Thus the Testex profile
23
bulk of the fines generated by steel gritblast cleaning were made up of the coatingsystem removed from the Connex box.
No attempt was made to analyze theabrasives or residues for salt, oil, or othercontaminants. The interior of the Connexbox had not been exposed to any traceablecontaminant that would make suchanalyses meaningful. Contamination ofrecyclable abrasive is an important andcontroversial issue and should be includedin any future research.
6.3 Test Results
Table 6-C summarizes the data collectedduring the test phase of the program. Theprimary objective was to compare the
6-CL GRIT TEST RESULTS
psi I 80 pSi
43 1043
94 2.85
40 7020
69 26
.6 6.7
76 366
.6 0.1
o 99.2 4.1O SP5rasive will not be significantly reduced by results were all about the same.
cleaning rates of steel abrasive andmineral abrasive under essentially similarconditions. Cost analyses based on thetest results are discussed in Section 7. Itshould be emphasized that these testresults are based on removing a 3-5 roil,one-coat coating system; an easy job whichwould account for the excellent cleaningrates achieved. Production rates achievedduring this test may not reflect rates foractual field work, and should be used forcomparison of abrasives only.
The test results show some significantproductivity differences. For example, ittook more than twice as long, 5.94 hours,to clean the same area using copper slagcompared to the 2.85 hours needed whenusing steel grit. These same numbersshow up in the cleaning rate, with slagcleaning at a rate of 176 square feet perhour versus steel grit at 366 square feetper hour. The actual degree of cleanlinessafter blast was not the same. The sIagabrasive achieved an SP 10 (near white)compared to steel grit’s SP 5 (white metal).In discussing this cleanliness differenceand cleaning rate difference with theblasters, they said visibility was a problembecause of the dust generated by the slagmaking it difficult during blasting todetermine the degree of cleanlinessachieved. Also, copper slag left a residueon the surface, confusing the degree ofcleanliness.
Another significant difference betweenmineral abrasives and steel abrasives is theamount of abrasive applied. Compare inTable 6-C the slag and steel grit tests at 80psi. The results show that about 7,900pounds of slag and about 7,000 pounds ofsteel grit were used to blast clean the samearea. However, if we look at the volumeof material used there is a significantdifference. Copper slag required 69 cubicfeet of grit compared to only 26 cubic feetof steel grit. Steel grit, due to its higherdensity, offers a 62% reduction in thevolume of grit that must be handled.
Since blast cleaning is essentially amaterial handling operation, anything that
2
reduces the volume of material that mustbe handled will significantly reduce thecost of the operation. Steel abrasiverequires a little over 1/3 the volume ofmaterial compared to copper slag. Everycubic foot of material brought into the jobmust be picked up and removed, thusclean-up of steel grit with about ²/3 lessvolume, will be faster and less costly.Clean up costs are further discussed inSection 7.2.
A final important difference between slagand steel grit is abrasive consumption persquare foot; that is, the amount of non-reusable abrasive after each use. Sincecopper slag is not normally reused, the 7.6pounds per square foot used for blastcleaning must be picked up and disposedof. Compare this to steel abrasive whichhad 0.1 pounds of waste per square footblast cleaned for disposal. The waste forsteel is calculated by multiplying theabrasive application rate of 6.7 lbs/ft2&(from Table 6-C) by the 1% loss per cycle(from Table 6-B). The result is 0.067,which is rounded to 0.1 lb/ft2.
Steel grit offers a 99+% reduction in wasteper square foot blast cleaned compared tocopper slag. An earlier MARAD studydone in 1987 (Ref. 9) looked at recyclingmineral abrasives. The study proved thefeasibility of limited recycling, but as yetno shipyard has implemented the process.A more recent study by PittsburghMineral and Environmental Technology,Inc. (Ref. 11) attempted to demonstrate therecyclability of mineral abrasives. Theresults of this study indicated that about40% of first-use spent mineral abrasivecould be reused one additional time. Withsuch limited reuse potential, the costeffectiveness of mineral grit recyclingappears marginal at best. Steel gritcurrently offers the most economical andproductive solution to the regulatorymandate for waste minimization.
Since steel grit will be recycled, we lookedat the recovered steel abrasive to see howmuch change in size took place after oneand two bIast cleaning cycles. Table 6-B
4
Nozzle Pressure I 90 psi I 90 psi
Total Area Cleaned(square foot) 55 377
Total Cleaning Time(hours) 0.18 0.66
Total Amount of Abrasive Applied(pounds) 640 1583
Rate Abrasive Applied(pounds/square foot) 11.6 4.2
Rate of Cleaning(square foothour) 305 628
Consumption(pounds/square foot non-reusableabrasive) 11.6 0.05
Recovery Factor (PercentReusable Grit After Blast) o 99.9
Profile*(mils) 4.5 4.3
Degree of Cleanliness I SP1O SP5
● The high profile produced by the initial mineral grit abrasive will not be significantly reduced bysubsequent abrasive blasts. Thus the Testex profile results were all about the same.
shows the screen sizes after each of theseblast cycles. Note that there is very littlesize change and that 99% of the abrasive isrecoverable for reuse.
In addition to the comparison of mineralgrit and steel grit, tests were run toevaluate other parameters that affect blastcleaning. One test looked at the effect ofelevated nozzle pressures and the othertest looked at working mix particle size.These tests were initiated because manypainting contractors doing blast cleaningand painting of structural steel have foundthat blast cleaning at nozzle pressures of120 - 130 psi have resulted in markedincreases in productivity. In addition,when using these elevated nozzle
2
pressures, contractors have found that afiner abrasive working mix furtherenhances productivity.
Table 6-D summarizes the test resultsusing higher nozzle pressures and using ablended steel abrasive media. These testswere conducted to demonstrate the effectof nozzle pressure and particle size oncleaning properties. A more completestudy should be made to optimize thebenefits. These preliminary results arediscussed in more detail below.
Nozzle Pressure
Initially, a significantly larger difference innozzle pressure was planned, but because
5
of equipment problems only a 10 psidifference was achievable. However, evenwith this small increase in nozzle pressurethere was about a 70% increase in cleaningrate for both the slag and steel abrasives.Compare Rate of Cleaning in Table 6-Cwith Rate of Cleaning in Table 6-D. Thisdemonstrates dramatically that elevatingnozzle pressure can make a significantimprovement in productivity . The resultsare still significant even when consideringthat some of this increase may have beenthe result of the small areas being cleanedor blaster technique as the blaster becamemore familiar with blast cleaning theConnex box.
Working Mix Particle Size
These results are also summarized in Table6-D. Compare the amount of abrasiveapplied per square foot with straight G-40(see Table 6-C), 6.7 pounds versus 4.2pounds for G-40/G50 blend (see Table 6-D). By going to a finer particle size andelevating nozzle pressure there was a 37%reduction in the amount of abrasive usedto clean each square foot. This markedimprovement in abrasive consumption canbe explained by the increased coverageresulting from the finer particle size (G-50grit) introduced into the G-40 grit.
The advantages demonstrated by thesetwo tests emphasize the need for a morecomplete study of nozzle pressure,abrasive particle size and their relation-ship to cleaning rate. These were dem-onstration tests to examine otherparameters impacting blast cleaning andinvolved cleaning relatively small areas, 55square feet for mineral grit and 377 squarefeet for the steel grit blend. Limits onproject time prevented a more completestudy. A follow-up study should includeblast cleaning significantly larger areas tomore adequately demonstrate the effect ofnozzle pressure and abrasive particle size.This follow-up study would be included inthe proposed Phase II of this project.
It was hoped that this project wouldprovide an opportunity to evaluate
26
abrasive cleanliness. Unfortunately,because of the type of coating system usedon the Connex box there was no heavymetal element that would be easilytraceable in the reclaimed abrasive. Aheavy metal could be detected analyticallyif it had been picked up by the steel grit.Sieve analyses on the cleaned, recycledabrasive (see Section 6.2) showed less than1% minus #50 sieve (0.0177”) material inthe cleaned abrasive mix, indicating thatthe abrasive cleaning station was removingthe dust and fines horn the abrasive. Inaddition, the fines that remained in therecycled abrasive were essentially finermetallic abrasive particles, not paint chips.For future tests, a test cycle should be runthat would allow 5-10 recycles to fullyevaluate abrasive cleanliness in terms ofpaint, oil, grease, salt, and other potentialcontaminants.
6.4 Vacuum Recovery
Abrasive recovery, whether for recyclingor just abrasive removal after blastcleaning, is a major labor cost when blastcleaning. This study looked at vacuumrecovery rates for both mineral abrasiveand steel grit abrasive. Extensive vacuumrecovery tests were not run because of theshort blast cleaning cycles. However,these limited-scope tests demonstrated thefollowing
● Vacuum recovery of steel abrasivescan be accomplished with the same equip-ment used for mineral grit abrasive.
● Vacuum recovery time is moresensitive to volume than to density of theabrasive media.
● Blow-down after blast and recoverytakes almost twice as long with copperslag as with steel grit.
The parameters for the vacuum recoverytests are summarized in Table 6-E. Thesame 75 hp liquid ring CAB vacuumrecovery unit was used for both tests. Noproblem was experienced in vacuuming
steel grit even though it is almost threetimes heavier than copper slag abrasive.The major difference in vacuum recoverybetween slag and steel abrasives was inthe time required to clean up the spentabrasive. Almost three times as much slagby volume was needed to clean the testareas as compared to steel grit. Thisresulted in approximately 40% longervacuum clean up time for the slag.
TABLEVACUUM REC
(After 80 psi
P A R A M E T E R
Type EquipmentVac Hose Length IRecovery Rate IClean Up Time IVacuum Head (inches Hg)Blow-down Time (after blast and recovery)
* Pounds of abrasive applied (Table 6-C) = 7940 lbRecovery Rate (Table 6-E) = 2600 l
● * Pounds of abrasive applied (Table 6-C) = 7020 IRecovery Rate (Table 6-E) =3240 lb
27
An additional difference noted was inblow-down time after blasting andrecovery. The excessive dust generated bymineral grit required almost twice as longto blow-down the blasted surfacecompared to steel. These preliminaryrecovery trials show a potential labor costsavings on cleanup and recovery of about33% when switching from mineral grit tosteel grit. Section 7.2 further discussesrecovery and clean up costs.
6-EOVERY TEST Blast Test)
Liquid Ring, 75 hp Liquid Ring, 75 hp120 ft. I 120 ft.
2600 lbs/hr 3240 lbs/hr3.1 hours* I 2.2 hours**
12 in. 11½ in.30 minutes 17 minutes
s.bs./hr
=3.1 hours
bs. =2.2 hourss./hr
7. ECONOMIC ANALYSIS
This section addresses the economics oftank blasting with recyclable steel grit ascompared to commonly used disposableabrasives. Copper slag was chosen as arepresentative disposable abrasive,although other types of slag and mineralabrasive are also used around the country.Cost and performance of most of thesenon-metallic abrasives, when compared tosteel, will not vary significantly. Ifdesired, cost data for other abrasive typescan be substituted for copper slag in anyof the analyses in this section to make thecomparisons more meaningful for aparticular shipyard.
The cost comparisons in this section areprimarily based on the project test resultsas discussed in the previous section. Asmentioned, the scope of the testing waslimited since actual on-board productiontesting could not be arranged. Therefore,the data collected during the simulatedtank test is considered to be somewhatlimited, but still representative of aproduction situation.
TABLCOST SUMMARY FR
Note: Cost Values Shown are in Dollars per Square
Abrasive CostBlast Cleaning Labor Cost
Vacuum Recovery Labor Cost*
Disposal CostRecycling Cost
Total Cost per Square Foot Blast Cleaned
* includes blow-down time The followinLabor atAverageCost per
CoppG-40
2
Table 7-A summarizes the cost dataobtained by analyzing the test results. Thecost categories are then discussed in moredetail in this section. To allow meaningfulcomparisons, all cost values are given indollars per square foot of area cleaned. Acomparison of the total cost per squarefoot at 80 psi indicates that steel abrasivecosts are about one half the costs usingcopper slag.
Using the data from Table 7-A, overallcosts can be projected for a typicalshipboard tank blasting job. The totalsurface area for a small tank (40’ x 20’ x20’) would be about 5000 &, including a30% allowance for stiffeners and otherstructural members. A typical large tank(60’ x 40’ x 40’) would contain a b o u t16,000 &. Projected total job costs forthese tanks, including material, labor,waste disposal and recycling costs, areshown in Table 7-B.
E 7-AOM TEST RESULTS
Foot Blast Cleaned
STEEL GRIT (G+40)
0.26 0.0250.20 0.10
0.124 0.0860.19 0.003
o 0.170.774 0.384
g assumptions were made to develop this cost summary: $36/hour including fringes abrasive landfill disposal at $50 per ton including hauling ton of abrasives (all prices FOB NASSCO):er Slag-$ 69 per ton Grit-$500 per ton
8
7.1. Abrasive Costs
The abrasive cost information discussedbelow is taken from the project test data.For comparison and addit ionalinformation, a cost analysis of steel gritand slag abrasives, provided by the IPECCompany of Rhode Island, is also includedas Table 7-C. This analysis indicates thatthe typical annual cost of using slagabrasive is about seven times higher thanthe cost of using recycled steel grit.
The test results in Table 6-C (80 psi test)show that approximately equal weights ofsteel and slag abrasives were used duringthe test. However, due to the muchhigher density of steel (2.5 to 1), thevolume of steel abrasive used is about onethird the slag volume. Also, steel grit isapplied at a lesser rate (6.7 lbs/ft2) thanthe slag (7.6 lbs/ft2), so steel gains anadvantage from the start. The obviousmajor advantage in material cost with steelgrit is reusability. Although typical steelabrasive cost is nearly seven times higherthan slag, when recyclability is factored in,the steel cost drops to a fraction of the slagcost.
Table 7-A shows the slag and steelabrasive costs per square foot blasted to be$0.26 and $0.025 respectively. The costsare calculated as follows (using data fromTable 6-C):
TABLEPROJECTED TANK
STEELGRIT I 5.000 0.384 1,920
29
7.6 lb/ft2 (Consumption Rate) x $69/ton(Slag Cost) ÷ 2000 lb/ton = $0.26/ft2
Steel grit cost per square foot blasted
0.1 lb/ft2 (Consumption Rate) x$500/ton (Steel Grit Cost) ÷2000 lb/ton = $0.025/ft2
This comparison shows that, based on testdata, the cost of actual material consumedfor steel abrasive is about one tenth of thecopper slag cost. Total abrasive costs forthe test area are
SLAG:$ 2 7 1 . 1 8
STEEL GRIT$ 2 6 . 0 8
7.2 Recovery and Clean-Up Costs
Recovering and cleaning up spent abrasivecontributes a significant cost to theabrasive blasting operation. In manycases, the labor cost involved in cleaningup spent abrasive exceeds the labor cost ofapplying the abrasive. This is trueregardless of the type of abrasive used,although costs can vary depending onabrasive type and recovery method.
7-BBLASTING COSTS
.00 16,000 0.384 6,144.00
TABLE 7-CCOST COMPARISON
STEEL GRIT VS. SLAG ABRASIVE
This analysis is based on the following:
Number of Blast Nozzles 1Nozzle Size l/2tfBlasting Pressure (nozzle) 100 psiAir Consumption 300 cfm
Abrasives Appaer HourSlag 1,500 pounds @ $ 50.00/tonSteel Grit 3,500 pounds @ $450.00/ton
Non-Recycled Slag vs. Steel Grit
Calculating abrasive costs per year and assuming six manhours (M. H.) per day and 250 blasting days peryear
6 hrs, x 250 days = 1,500 manhours of blasting per year per operator
For slag abrasive, the yearly consumption is calculated as follows:
1,500 ibs/M.H. x 1,500 M.H. = 2,250,000 ibs. per operator per year, or
2,250,000 ibs = a yearly consumption of 1,125 tons of slag per operator2,000 ibs/ton
For steel abrasive, the yearly consumption is calculated as follows:
3,500 Ibs/hr. x 1,500 hrs. per year= 5,250,000 ibs. per operator per year.
5,250,000 ibs = 2,625 tons of steel grit per year2,000 ibs/ton
if properly utilized however, steel grit can be recycled up to 150 times (cycles), thus:
2,625 tons = a yearly consumption of 17.5 tons of steel grit per operator.150 cycles
Material Cost per year for slag would be:
1,125 tons/yr. x $50/ton =$56,250.00 per operator
Cost of steel grit for actual consumption would be:
17.5 tons/yr. x $450/ton = $7875 per operator
Data supplied by IPEC Co.
30
Vacuum recovery is the most commonmethod for spent abrasive collection. Theprimary vacuum types are liquid ring andair induction and positive displacement(PD) pumps. Liquid ring vacuums usecentrifugal water flow to generate avacuum head, while air induction and PDsystems generate negative air pressure toproduce a vacuum.
With mineral or slag abrasives, blastingand waste clean-up are separate operationsusing separate equipment. Spent abrasiveis usually collected in storage hoppers andeventually sent out of the shipyard fordisposal or reprocessing. Steel gritrecovery systems, however, are complete,closed systems in which spent abrasive isvacuumed, cleaned, reclassified and storedfor reuse. The small amount of unusablewaste generated (dust and fines) iscollected for disposal.
The costs associated with operating therecycling equipment required for a steelgrit system must be included in the overallcost comparison of steel and mineralabrasives. These costs do not occur formineral abrasives, since they are normallynot recycled. The cost summary in Table7-A indicates a recycling cost of $0.17 persquare foot, which is determined asfollows:
2000 lb/ton x $50/ton (Recycling Cost) +0.99 (Recovery Factor)
The Application Rate and Recovery Factorused above are taken from Table 6-C, TestResults. The Recycling Cost represents atypical average cost including labor,operation, and maintenance expenses forrecycling equipment.
Abrasive blasting in tanks often results inincreased recovery and clean-up costs dueto accessibility problems. Tank access iscommonly available only through anopening in the tank top. Vacuum hosemust then be run from the equipmentlocation on deck to the bottom of thetank — often over 100 feet. To minimize
31
flow resistance, large diameter vacuumhoses (3-6” I.D.) are normlly used. Ifpossible, a temporary access opening canbe cut near the bottom of the tank to alloweasier grit removal. Mechanical methods,such as a screw conveyor, may also beused to more effiaently remove steel grit.
The results of the vacuum recovery testperformed in this project (see Table 6-E)show that the spent abrasive clean up timefor copper slag was 3.1 hours as comparedto 2.2 hours for steel grit. Recovery andclean up labor costs are discussed inSection 7.5 Labor Costs. The difference inclean up time indicates a savings of about30% when using steel grit. However, sincethis test was not performed in a tank on-board a ship, the results must be taken atface value for the test conditions.Conclusions cannot be drawn for actualon-board applications based on this testdata, as conditions and costs may bedifferent in tanks.
Steel grit does have a distinct advantageover other abrasives in the clean-upprocess. Slag and mineral abrasivesproduce large amounts of dust duringblasting. This dust normally adheres to allexposed tank surfaces, such as bulkheads,stiffeners and overheads. Dust must beremoved prior to painting to preventpotential coating failure. Removal of dustby brushing, sweeping or blowing downwith air is labor intensive, especially incomplex tanks. Since steel grit producessignificantly less dust than other abrasives,dust clean-up time is reduced and costsavings are realized.
Dust blow-down time was measuredduring the NASSCO test as shown inTable 6-E. The time for blow-down afterblasting with copper slag was about twiceas long (30 minutes) as the time for steelgrit (17 minutes). While this differencemight seem insignificant for a small testarea, the savings with steel grit would besubstantial for a typical tank cleaning job.
7.3 Waste Disposal Costs
Abrasive waste disposal costs can have asignificant impact on the total job cost,particularly if the waste proves to behazardous. (See Section 5.3 for adiscussion of hazardous waste disposal.)Disposal costs will vary based on themethod of disposal. Probably the mostexpensive method currently is landfilldisposal. For example, the southernCalifornia 1992 fees for solid, non-hazardous (Class 2 or D) grit wastedisposal were $65/ton plus a 10% localsurcharge. Typical hauling charges canadd $25/ton, resulting in a total cost ofabout $100/ton.
If the grit waste tests hazardous (Class 1or C), landfill fees increase to $85/ton andthe total cost becomes nearly $125/ton.Thus, landfill disposal costs in Californiacan amount to almost double the rawmaterial cost of slag abrasives. Fees forlandfill disposal will vary by state andlocality. Also, landfill disposal willbecome a limited and more expensiveoption for many states in the future ascurrent disposal sites fill and new sites arenot readily available.
Alternative methods to landfill disposal,such as those discussed in Section 5.3, canresult in greatly reduced grit wastedisposal costs. In some cases,manufacturers of building materials suchas concrete, asphalt or bricks will buy (ata small price) spent abrasive fromshipyards to use in their products. Mostcommonly the shipyard pays a nominalfee ($20 - 30/ton) to have the wastehauled to the manufacturer’s facility.
In California, grit waste is also being usedas a cement additive. Fees to haul thewaste to a state approved cement kiln run$20-30/ton, plus a processing fee of about$20/ton. Alternative methods of wastedisposal, where available, are becomingmore popular as a way to lower disposalcosts and reduce the landfill overcrowdingproblem.
3
A comparison between potential wastedisposal costs for slag and steel abrasivescan be made based on the project testresults. Table 6-C data shows that, sinceslag is not recycled, all of the 7940 lbs.used during the test has to be disposed of.For the steel grit, approximately 100 lbs. ofwaste residue was left in the dustcollection drum after the test. All othermaterial was reusable. Using a nation-wide average landfill disposal charge of$50/ton for non-hazardous waste(includhg transportation), disposal costsper square foot are calculated in Table 7-Aas follows
SLAG:
2000 lb/ton x $50/ton
STEEL
$50/ton
If the slag waste is useable as a buildingmaterial additive, disposal cost could be
times higher than the steel grit disposalcost.
Conditions for tank blasting on board willvary from the project test conditions.However, the comparative differencesbetween slag and steel abrasive are validand demonstrate the major savingspossible in waste disposal costs whenusing steel abrasive.
7.4 Equipment and Operating Costs
This section offers a comparison of thecosts associated with the purchase,operation and maintenance of equipmentrequired for tank blasting with steel grit ascompared to slag or other mineralabrasives. There are a number ofmanufacturers and suppliers around thecountry that can supply a wide range ofequipment for use with either steel ormineral abrasives. Appendix B providesinformation for several suppliers.
2
Equipment used for abrasive blasting withdisposable abrasives such as slags is lesscomplex and thus somewhat less expen-sive to purchase initially. A basic systemwould include the following components:
● Air compressor (por tab le orstationary)
. Blast pot (to hold abrasive)
. Air dryers and after coolers
● Moisture and oil separators
● Blast nozzle and hoses
● Ventilation and dust collectionequipment (for tank blasting)
● Vacuum equipment to collect spentabrasive
Costs for such a system would vary basedon equipment type and manufacturer, and
TABLE EQUIPMENT, OPERATING AND
WITH AND WITHOU
(1300 cfm Portable) $70,000Blast Pot
(Pressure Type) $15.000Air Dryers and After CoolersMoisture and Oil Separaors I
‘$ 2;000------- $1,000
Hoses I(Hoses last approximately $600two months) (200 ft (@ $3/ft)
Nozzles (two)(Nozzles last approximately $300two months) (2@ $150 each)
Dust Collector(24,000 cfm) $79,000
Vacuum(PD Air Pump) $51,000
Abrasive Recycling Unit $30,000
TOTAL - Without Recycling $218,900With Recvcling $248,900
1
● Where applicable annual operating or maintenance CIW were divided by 2000
33
size of system required. Typical costs aresummarized in Table 7-D. For compari-son, a similar system with abrasive recycl-ing is also included. Note that the sameequipment is used for both systems, exceptthat for recycling with steel grit there is theadded cost of an abrasive recycling unit.Recycling with steel grit, therefore, addsabout 15% to the initial equipment cost.
The individual components for arecyclable abrasive recovery system maybe purchased separately, but the morecommon approach is to buy a completeunitized system, designed and engineeredby an abrasive equipment manufacturer.These complete systems, which allowclosed loop blasting and recovery, areavailable from several suppliers aroundthe country. Section 8 describes a typicalsystem. While recovery systems are usedmost effiaently with steel grit, they maybe modified to process other reusableabrasives, such as aluminum oxide andgarnet.
7-D MAINTENANCE COSTST RECYCLING
(Full Power) $1.57
N/A N/A$1.40 $0.05
N/A $0.20
$1.80 N/A
$0.90 N/A$6.00 (fuel)
$1.00 (filters) $0.10$1.00 (fuel)
$0.21 (filters) $0.10$0.14 $0.10
$38.59 $202$38.73 $212
hours to come up with an houriy cost value. N/A Not Applicable
Typical operation and maintenance costsfor equipment components are also shownin Table 7-D. Total operation andmaintenance costs for a complete systemwithout recycling would amount to about$41 /hour or $82,000/year based oncontinuous operation of 2,000 hours peryear. These costs, when using recycledsteel grit, would remain basically thesame, since operating the recycling unitadds only pennies per hour.
7.5 Labor Costs
Labor is the largest cost element associatedwith an abrasive blasting job andsubsequent clean up. This factor is, inturn, dependent on the prevailing wagerate of the particular area of the country.Labor costs to apply abrasives are alsodirectly related to the production rate thatcan be achieved for the job. In otherwords, the faster an area can be blastcleaned, the lower the incurred labor cost.Production cleaning rate is a function ofseveral variables, including operator skill,degree of cleanliness reqired, equipmenttype, surface condition, type of abrasiveand nozzle pressure. As previouslydiscussed, all other variables being equal,higher production rates can usually beachieved with steel abrasive.
Test results in Table 6-C show a cleaning
Assuming an average labor rate of $36/hr(including fringes), the labor cost factor forabrasive application is calculated asfollows:
SLAG:
STEEL
The clean up times for spent abrasive(from Table 6-E) were 3.1 hours for copperslag and 2.2 hours for steel grit. Dust
34
blow-down time must also be included inthe total labor cost, since this is anecessary part of the clean up operation.Adding in the 30 minutes for slag and 17minutes for steel grit, the total timesbecome 3.6 hours for slag and 25 hoursfor steel grit. Therefore, the recovery costfactors are
SLAG:
STEEL
The total labor cost factor is calculated bycombining the application and recoveryfactors
SLAG:
STEEL
Thus, the total labor cost for blast cleaningthe test area would be
SLAG:
STEEL
This comparison indicates that the totallabortimes
COSts using a slag abrasive arethe costs using steel abrasive.
1.7
8. RECOMMENDED PROCEDURES FOR TANKBLASTING WITH RECOVERABLE STEEL ABRASIVE
8.1 Current CommercialSpecifications
Tank blasting currently involves the use ofnon-recyclable mineral abrasives, whichare purchased according to the SteelStructures Painting council (SSPC)specification SSPC-AB-1, Mineral and SlagAbrasives, June 1, 1991. In addition, mostmineral abrasive suppliers provide aspecification sheet with their abrasiveproduct giving sizing limitations,chemistry, heavy metal and free silicavalues. Since mineral abrasives aregenerally not recycled there are no limitson durability or recyclability.
Steel abrasives, on the other hand, aremuch more closely specified. Steelabrasives are purchased to a strict sizingspecification as defined by the proposednew SSPC specification for steel abrasives(see Appendix C) and must also meet thedurability standard that is included in thissame specification.
8.2 Current U.S. Navy Specification
The Navy has a specification for non-metallic abrasives, MIL-A-22262A (SH),which is currently being revised. Thisspecification is primarily concerned withsetting limits on heavy metals and freesilica, both of which could create ahazardous environment when blasting.Friability of abrasive is also addressed butonly to the extent that the abrasive meetsthe California Air Resources Board (CARB)limits for dry abrasive blasting.
The Navy specification does not addressperformance of mineral abrasive. Theshipyards therefore, should have ways ofevaluating whether or not a given mineralgrit will perform and thus meet the job
35
requirements. There is a need for a goodperformance specification for non-metallicabrasives.
For steel abrasives, the Navy referencesseveral specifications, most of which arerelated to performance. The primaryNavy specifications are General ServicesAdministration (GSA) Commercial ItemDescription (CID) AA-1041B Steel Grit andAA-1042B Steel Shot. These specificationsdefine abrasive sizing, durability andchemistry. In addition to these speci-fications, t h e N a v y should beincorporating the new SSPC performancespecification as well as the SSPCRecyclable Abrasive CleanlinessSpecification.
8.3 Recommended Procedures for BlastCleaning and Recovery
The test results reported in this study havedemonstrated that a recyclable steelabrasive offers the greatest opportunity forsignificant productivity improvements intank blasting. Steel abrasives alsominimize environmental impact becausethey are recyclable, minimize dust andcontain no hazardous elements. Thediscussion that follows outlines a typicalproduction scenario using a steel gritrecycling system. Recent discussions withshipyard personnel as well as others inrelated industries have contributed to thedevelopment of this scenario.
In addition to the systems descriptionsbelow, Appendix D provides a sampleProcess Control Procedure (PCP) formatthat was developed for tank blasting withsteel abrasive aboard U.S. Navy ships.This sample PCP is intended to be used asa guide to assist any shipyard indeveloping their own process procedures.
Although the format was developed tomeet Navy requirements, it can be easilyadapted to serve as a process controldocument for commercial tank blasting aswell.
For tank blasting, abrasive blasting andrecovery cannot generally occursimultaneously if the tanks are small andconfined. Therefore, a holding tank ortanks should be set up to hold sufficientsteel abrasive to support a full complimentof blasters for a single shift. Air dryers,dehumidification and dust collectorsshould also be integrated into the systemto eliminate moisture in the blast pots,rust-back of the blast cleaned surface andexcessive dust during blasting. A typicalset-up is shown schematically in Figure8.1. To take full advantage of steelabrasive’s productivity, high pressurecompressors capable of up to 150 psinozzle pressures should also be utilized.After blast cleaning, abrasive recovery isbest accomplished using a vacuum pickupsystem and collection tank as shown inFigure 8.2. If the tanks being blasted areof sufficient size however, it may beadvantageous to incorporate somemechanical recovery system while blastcleaning, such as conveyors and augers.(See Appendix B for recommendedsuppliers.)
Following is a generalized outline of thetype of equipment needed for an effectivesteel grit blast cleaning recovery andrecycling system. All componentsdescribed are currently available “off-the-shelf” items. Included in this outline arethe key performance requirements to meetthe needs of the job. A list of thesuppliers of each component is given inAppendix B.
Blast Cleaning
Initial blast cleaning can be accomplishedby any of the currently available shipyardblast pots. Large capacity, 10 - 20 ton
36
pressurized pots are preferable since theywill allow continuous blasting by two ormore blasters for an entire eight hour shiftwithout having to refill the blast pot.Blast cleaning equipment capable ofoperating at 150 psi is recommended totake advantage of the increased blastcleaning efficiencies when blast cleaningwith 120 - 150 psi nozzle pressures. Tomaintain productivity, regular additions ofnew abrasive should be added to theworking mix. A good “rule of thumb” is:after every 10- 20 cycles add 1 - 2% ofnew abrasive.
Air Compressors
As noted above, compressors capable ofoperating to produce 120-150 psi nozzlepressures are preferable. However,conventional yard air or compressors canalso be used as long as the compressed airsource generates nozzle pressures of 90-100 psi.
Dust Collectors
Although steel abrasive itself generateslittle dust, dust is generated during tankblasting by paint, rust and scale beingremoved from the steel surface. Tomaximize worker safety and productivityand improve visibility, large capacity(10,000 -20,000 cfm) dust collectors shouldbe used for dust removal during blasting.Maintaining air flows in the tank of 50-100 ft/min are generally recognized asoptimum for dust control.
Dehumidification
The high humidity environments of mostshipyards causes condensation on the blastcleaned steel surface, which can lead toflash rusting. Dehumidification is recom-mended to assure a rust free and dry blastcleaned surface for subsequent painting.The most common dehumidificationsystem for shipyard use is the dryhoneycomb desiccant wheel system. A
Figure 8.1 System Schematic
Schematic layout of a steel abrasive blast and recovery system with dust collector.
37
9,000-10,000 cfm unit is large enough andportable for most shipyard applications.For energy conservation, the clean airdischarge from the dust collector can besent through the dehumidifier and backinto the tank This essentially recirculatesthe dry air.
Abrasive Recovery
After blast cleaning, abrasive recovery isusuaIly accomplished using some type ofvacuum system connected to a suitabledust collector. There are currently threetypes of vacuum systems:
● Liquid ring vacuums
● Positive displacement (PD) vacuumpumps
● Compressed air eductor vacuums
For efficient vacuuming, the recoverysystem should include the following:
● Hoses 3 - 6“ I.D. vacuum hosesfitted with 1/2” screens over the ends. Thescreens will prevent sucking up trash,large pieces of rust scale and paint chipsthat could plug the abrasive recoverysystem.
● Collection Tank This tank acts as adrop-out chamber for the vacuumedabrasive and as a holding tank, and allowsmetering of the recovered abrasive to theabrasive cleaning station. This collectiontank could be any existing large abrasivetank
● Abrasive Cleaning Station: Thecleaning station design is the most criticalportion of the abrasive recovery systemand must contain two major componentsa magnetic drum separator to removepaint chips and non-magnetics, and anairwash system to remove dust and fines.These two components should be
38
integrated to process five to ten tons ofreclaimed abrasive per hour.
Dust Collector: A small 500-1000cfm dust collector to collect dust and finesremoved by the airwash.
● Cleaned Abrasive Storage TankAfter the abrasive has been run throughthe abrasive cleaning station, the cleanedabrasive is returned to an abrasive storagetank or hoppers for reuse.
All the equipment noted above is currentlyavailable and being used in abrasiverecovery and recycling systems. AppendixB lists most of the manufacturers currentlyin the abrasive recovery and recyclingbusiness. A system setup at PhiladelphiaNavy Shipyard, using the componentsdescribed above, is shown in Figure 8.3.Note that the system is skid mounted tofacilitate movement to and from the jobsite.
39
9. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
Mineral abrasives, used once anddiscarded, historically have been theabrasive of choice for a major portion ofshipyard blast cleaning. Shipyards todayare faced with a changing workplace thatrequires more efficient use of materials,waste minimization, and the use of high-tech coatings to mention a few. Thesechanges are causing the industry torethink current methodologies and lookfor ways to meet the strict environmentalrequirements and the need for higherproductivity to remain competitive. Basedon the results of this project, recyclablesteel abrasive appears to fit the needs ofthis new workplace.
This project explored and compared thevarious aspects of tank blasting withdisposable mineral abrasives andrecyclable steel grit. Project researchincluded a survey of abrasive blastingmethods at various shipyards around thecountry, as well as a look at currentblasting practices in the bridgemaintenance industry. An overview ofenvironmental, health and safety issues,including waste disposal, was alsopresented.
Production testing was conducted tocompare abrasive application and recoveryusing copper slag and steel grit in asimulated tank environment. Aneconomic analysis based on the test resultswas performed to compare the variouscost factors for a typical tank blasting job.The study also describes recommendedequipment and procedures for tankblasting with recyclable steel abrasive.
The primary conclusion resulting from thisstudy is that tank blasting with steel grit isan economically and environmentallyviable replacement for the current practiceof blasting with disposal mineralabrasives. Several environmental and
4
health issues can be favorably addressedwith the use of recyclable steel grit, suchas improved air quality through reduceddust generation and the significantminimization of solid and hazardouswaste. Based on the project test results,the economic advantages of using steelgrit also appear to be substantial.Although the testing was performed in asimulated tank rather than on board aship, valid performance comparisons werepossible. Significant findings can besummarized as follows:
● Overall job costs using steel grit,including material, labor and wastedisposal, are about one-half the costs forcopper slag.
● Blasting and clean up labor costs forsteel grit are about 60% of the costs forslag.
● The biggest savings with recyclablesteel abrasive are in the material cost (onetenth the cost of slag) and waste disposalcost (less than 2% of the slag cost).
● The largest single cost factor forcopper slag is material cost, which is aboutone third of the total job cost.
● The largest single cost factor for steelgrit is the cost to operate and maintain therecycling equipment, which is almost onehalf of the total job cost.
This study has also led to conclusions andrecommendations with respect to currentspecifications and procedures for tankblasting with recoverable steel grit. TheU.S. Navy does not currently have anapproved Process Control Procedure (PCP)for the use of steel grit in tanks. This wasthe primary reason that production testingfor this project could not be conductedaboard a Navy ship, as originally
0
intended. At the time of this writing, aperformance specification and a PCP werebeing developed by NAVSEA and areexpected to be issued sometime in 1993.The authors of this report would highlyrecommend the incorporation of thenewly-drafted Steel Structures PaintCouncil (SSPC) performance andcleanliness standard for steel abrasive intothe Navy specification.
In addition to establishing the feasibility oftank blasting with steel grit, this projecthas identified several key parameters andvariables for future study. Preliminarytesting at elevated nozzle pressure andfiner steel grit particle size indicate thatthese two parameters may have thepotential to significantly increaseproductivity. Additional testing would berequired to quantify the optimum nozzlepressure and particle size combination tomaximize productivity without sacrificingrecyclability.
41
One of the main issues to be addressedwith respect to using a recyclable abrasiveis ensuring the cleanliness of the abrasiveduring the recycling process. For arecycling system to be truly effective, theabrasive being recycled must have acleanliness close to that of new abrasive.The abrasive must be basically free ofcontaminants such as moisture, oil, saltand paint residue. To demonstratecleanliness, the abrasive should be runthrough several blast and recoverycycles — at least ten — with a follow-upcleanliness test after each cycle. The newSSPC abrasive cleanliness standard forrecycled steel abrasive can be used for thisanalysis. Since the test scope of thisproject did not allow for multiple recycles,future testing should incorporate a largertest area to permit numerous recycles.
A Phase II follow-on project has beenproposed as part of the 1994 NSRPprogram to address the aboverecommendations.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
10. REFERENCES
Bureau of National Affairs, Environment Reporter,WASTE CONTROL ACT, May 1992.
CALIFORNIA HAZARDOUS
Michelle C. Coyle, SUMMARY OF THE CLEAN AIR ACT AMENDMENTS OF 1990,EPA Publication, November 1990.
ENSR Consulting and Engineering, AIR QUALITY HANDBOOK, June 1988.
Society of Naval Architects and Marine Engineers, Panel O-23, TANK COATINGGUIDE FOR BALLAST TANKS OF ALL VESSELS AND CARGO TANK OFPETROLEUM TANKERS, Technical and Research Bulletin 4-23, March 1991.
Steel Structures Painting Council, GOOD PAINTING PRACTICE, 2nd ed., 1989.
Steel Structures Painting Council, SYSTEMS AND SPECIFICATIONS, 6th ed., 1991.
K. A. Trimber, KTA-Tator, Inc., INDUSTRIAL LEAD PAINT REMOVALHANDBOOK, 1991.
U.S. Department of Transportation, Maritime Administration, PROCEDUREHANDBOOK FOR SURFACE PREPARATION AND PAINTING OF TANKS ANDCLOSED AREAS, September 1981.
U.S. Department of Transportation, Maritime Administration, PROTOTYPEMINERAL ABRASIVE RECLAIMER SHIPYARD OPERATION, March 1987.
U.S. Navy and National Steel and Shipbuilding Co., DETERMINATION OFPARTICULATE AND DUST CONCENTRATION DURING SHIPYARD DRYDOCKSANDBLASTING OPERATIONS, NSRP #0365, September 1992.
T. E. Weyand and W. F. Sutton, Pittsburgh Mineral and Environmental Technology,Inc., IDENTIFICATION OF ACCEPTABLE/BENEFICIAL REUSES FOR SPENTBRIDGE PAINTING BLAST MATERIAL, July 1990.
42
APPENDICES
43
APPENDIX ASAMPLE SHIPYARD SURVEY FORM
44
SHIPYARD QUESTIONNAIREBlast Cleaning Operations
shipyard Person Interviewed
Phone No.
Plates and Shapes:Abrasive used (steel, mineral slag, other)Type (shot, grit)Method of blast cleaning (centrifugal wheel, nozzle)Profile (mils)Degree of cleanliness: (SP6, 10,5)If abrasive recycled
method of recoverymethod of abrasive reclamation
Coating systems: (thickness and type)
SubassembliesAbrasive used (steel, mineral slag, other)Type (shot, grit)Method of blast cleaning (centrifugal wheel, nozzle)Profile (mils)Degree of cleanliness (SP6, 10,5)If abrasive recycled
method of recoverymethod of abrasive reclamation
Coating system(s): (thickness, type)
Aboard-Ship Blast CIeaningAbrasive usecd: (steel, mineral slag, other)Type: (shot or grit)Method of blast cleaning: (nozzle, vacublast, other)Profile (mils)ContainmentVentilation: (cfm)Abrasive recovery methodAbrasive reclamation methodCoating systems (thickness and type)
45
APPENDIX BEQUIPMENT MANUFACTURERS DATA
46
EQUIPMENT MANUFACTURERS DATA
Following is a list of manufacturers of the equipment noted in Section 8.3, RecommendedProcedures for Blasting and Recovery. This is only a partial list of manufacturers and ispresented as a guide. The manufacturer’s address, phone number and contact person arealso given.
Dehumidification Conveyors and Augers
Enviro-Air Control Corporation TETKO, Inc.J.G. Systems, Inc. FMC CorporationMunters Moisture Control Service
Dust Collectors
Environmental Containment SystemsIPEC Advanced Systems, Inc.J.G. Systems, Inc.
Vacuum Recovery Equipment
BMSI, Inc.IPEC Advanced Systems, Inc.Vacuum Engineering CorporationVacmasters of Denver
Air Dryers
Van Air Systems, Inc.Deltech Engineering, L.P.
Blast and Recycling Systems
Advanced Recycling Systems, Inc.IPEC Advanced Systems, Inc.Clemco Industries Corporation
Environmental Containment SystemsSurface Preparation Machinery, Inc.
Abrasive Collection/Storage Bins
J.G. Systems
47
INDEX TO MANUFACTURERS
Advanced Recycling Systems, Inc.1089 N. Hubbard RoadLowellville, OH 44436-9737216-534-3330
American Welding Inc.P.O. Box 119Maumee, OH 43537Ted Weaver800-537-3370
BMSI, Inc.P.O. Box 410Seahurst, WA 98062Neil MacKinnon206-433-6947
Clemco Industries CorporationOne Cable Car DriveWashington, MO 63090Patti Roman314-239-0300
Deltech Engineering, L.P.P.O. BOX 667New Castle, DE 19720Bob Simons302-328-1345
Enviro-Air Control Corporation1523 North Post Oak RoadHouston, TX 77055Charles H. Wyatt713-681-3449
Environmental Containment SystemsP.O. BOX 58763Houston, TX 77258Marshall Seavey713-4743734
FMC CorporationMaterial Handling Equipment Div.Homer City, PA 15748412-479-8011
48
IPEC Advanced Systems, Inc.9 Spinnaker StreetNorth Kingstown, RIGerald McNamara800-822-IPEC
J.G. Systems, Inc.P.O. BOX 840247Houston, TX 77284Bob Jellerson713-466-4233
Munters Moisture Control Services79 Monroe StreetAmesbury, MA 01913W. Craig Fillman508-388-4900
Surface Preparation Machinery, Inc.708 North First Street, Suite 331Minneapolis, MN 55401Brian Williams800-800-7761
TETKO, Inc.333 South Highland Ave.Briarcliff Manor, NY 10510914941-7767
Vacmasters of Denver, Inc.6114 West 55th AvenueArvada, CO 80002-2704Richard Roatch303-467-3801
Vacuum Engineering Corporation3374 West Hopkins StreetMilwaukee, WI 53216Scotty Johnstone4144444010
Van Air Systems, Inc.2950 Mechanic StreetLake City, PA 16423Sharon Mleczko814-7742631
APPENDIX C
DRAFT OF PROPOSED SSPC SPECIFICATIONFOR STEEL ABRASIVES
(NOTE The new SSPC specificationis targeted for release priorto year end, 1993. Copieswill be available from theSteel Structures PaintingCouncil.)
49
Draft #lASSPC-AB X2X
March 22,1993
STEEL STRUCTURES PAINTING COUNCILABRASIVE SPECIFICATION SSPC-XAB2X
Cast Steel Abrasive
1. Scope
1.1. This specification covers the requirements for granular, cast steel abrasive foruse in cleaning either coated or uncoated steel surfaces for the removal of rust, mill scale,paint or other surface coating systems and for general blast cleaning applications utilizingsteel abrasive.
1.2. The abrasives covered by this specification are primarily intended for use inrecycling systems.
2. Description
2.1. This specification covers two types of cast steel abrasive steel shot and steelgrit.
2.2. Each type of cast steel abrasive has the following size classification:
Steel Shot S460, S390, S330, S280,S230, S170, S110, S70
Steel Grit G14, G16, G18, G25, G40,G50, G80
2.2.1. The requirements for each size classification are given
3. Reference Standards
3.1. SSPC Standards
SSPC-SP 5 White Metal Blast Cleaning
3.2. ASTM Standards
in Section 4.3.1.
A 370 Standard Test Methods and Definitions for Mechanical Testingof Steel Products
C 128 Test Method for Specific Gravity
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C 136 Test Method for Sieve Analysis of Fine Sand and CoarseAggregates
E 29 Standard Practice for Using Digits in Test Data to DetermineConformance with Specifications
E 350 Standard Test Method for Chemical Analysis of Carbon Steel,Low-Alloy Steel, Silicon Electrical Steel, Ingot Iron andWrought Iron
Application for copies of ASTM Standards should be addressed to ASTM, 1916Race Street, Philadelphia, PA 19103.
4. Requirements
4.1. General Physical and Chemical Properties.
The abrasive shall meet all the requirements of Sections 4.2 through 4.5 (SeeNote 7.1.).
4.2. Manufacturing Cast Steel Abrasive.
Cast steel abrasive shall be newly manufactured or remanufactured as definedbelow.
4.2.1. Newly Manufactured. These are abrasives manufactured for virgin rawmaterials (recirculated or used show or grit is not permitted).
4.2.2. Re-Manufactured. In accordance with Section 4.2, the term“remanufactured” means materials which have been collected or recovered from solid wasteand reprocessed to become a source of raw materials as opposed to virgin raw materials.None of the above shall be interpreted to mean that the use of used or recirculated productsare allowed under Section 4.2 where “newly manufactured” or “remanufactured” isspecified.
4.3. Physical Properties
4.3.1. Size Classification. The abrasive size classification shall meet the sizerequirements for cast steel shot in Table 1 and cast steel grit in Table 2.
4.3.2. Appearance. Using a 10X microscope or magnifying glass, the steelshot shall be predominantly rounded particles. Steel grit shall be a mixture of irregularshaped and angular steel particles in accordance with paragraphs 5.2 and 5.3.8.
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March 22,1993
4.3.3. Specific Gravity. When tested in accordance with Section 5.3.3, thespecific gravity of the steel abrasive shall be not less than 7.0 g/cc.
4.3.4. Hardness. The average steel abrasive hardness shall be between C 35and C 50 on the Rockwell scale.
4.3.5. Durability Performance. When tested in accordance with 5.3.6, the steelabrasive shall conform with the durability requirements shown in Table 3, Steel Grit andTable 4, Steel Shot.
4.4. Chemical Properties
4.4.1. When tested in accordance with 5.3.6, the steel abrasive shall conformwith the following limitations.
Iron 97.00%, minimumCarbon 1.50%, maximumManganese 1.20%, maximumPhosphorus 0.05%, maximumsulfur 0.05%, maximumSilicon 1.50%, maximum
4.5. Cleanliness
When tested in accordance with Section 5.3.8, the steel abrasive shall be freeof dust, oil, grease, corrosion, and other contaminants. Corroded or rusted steel abrasiveshall be considered unacceptable.
4.6. Cleaning Performance
When tested in accordance with 5.3.7, the abrasive shall conform to theperformance requirements as shown in Table 5 for shot and grit. If agreed upon bypurchaser and supplier, an alternative cleaning performance criterion may be used. (SeeNote 7.3).
5. Quality Assurance Provisions
5.1. Lot Formation
For purposes of inspections and testing a lot shall consist of all shot or gritproduced utilizing the same feed lot of raw materials. (See Note 7.2).
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Draft #lASSPC-AB X2X
March 22,1993
5.2. Visual Examination
The sample steel abrasive media shall be examined for rust. The presence ofrust in excess of a slight red rust coloring of the abrasive particle shall be cause for rejection.
5.2.1. Frequency of Examination. The examination described in Section 5.2shall be performed on a lot-by-lot basis.
5.3. Procedures
5.3.1. Frequency of Testing. Unless otherwise specified in the contract orpurchase order, testing for size, durability and cleanliness shall be performed on each lot ofabrasive. Testing for density, chemical composition, hardness and extraneous material shallbe performed initially to establish conformance and thereafter anytime that the source of rawmaterial changes. In the event multiple sources of raw material are used, material from eachsource shall be tested.
5.3.2. Size. The abrasive sizing shall be tested in accordance with ASTMC 136.
5.3.3. Specific Gravity. Specific gravity shall be determined in accordancewith ASTM C 128.
5.3.4. Chemical Composition. Chemical composition shall be determined inaccordance with ASTM E 350.
5.3.5. Hardness. Hardness values shall be obtained in accordance with ASTMA 370 utilizing a microhardness tester with a 500 gm load. Measurements taken in Knoophardness numbers shall be converted to Rockwell C Scale. (See Note 7.4).
5.3.6. Durability Test. The following mechanical shot and grit durability testuses the complete breakdown or 100% replacement test method. (See Note 7.5).
5.3.6.1 Procedure
1. Using a calibrated* standard durability test machine (see Part 2-Calibration Procedure), weigh out 100 grams (± 0.1 g) of new abrasive.
2. Place 100 g sample in test machine and run for 500 passes.
3. Remove sample from test machine and screen sample on appropriatetake-out screen (see Table 1).
4. Hand screen sample on take-out for approximately 3 minutes.
53
Draft #lASSPC-AB X2X
March 22,1993
5. Weigh material remaining on take-out screen and record weight.
6. Add sufficient new abrasive to abrasive remaining on take-out screento again makeup 100 g sample and place sample back in test machinefor an additional 500 passes.
7. At the conclusion of 500 passes, repeat steps 3 through 6. Continuerepeating steps 3 through 6 until the cumulative loss is 100 g or more.
8. Interpolation of the end point or total passes required to equal 100%Life Test is as follows:
500 Pass Per Run 100 - Cumulative Cumulative Passes
Wt. Loss Iast Run x before 100% Loss before 100% Ioss
9. Record end point value and compare with standard values show onTable 1. Durability of test abrasive should meet or exceed valueshown in Table 1 for the same size and type of abrasive.
* Use manufacturer’s test for calibration. Calibration should be performed onceevery 20 durability tests.
5.3.6.2 Apparatus. Durability tests shall be performed using an ErvinIndustries Inc.* or equivalent shot/grit test machine, properly calibrated in accordance withthe manufacturer’s instructions.
5.3.7. Performance Test Procedure. Using a standard Ervin Durability TestMachine or equivalent (as defined in Section 5.3.6.2), remove the bell housing plus andreplace the plug with the alrnen strip holder. Before inserting the strip holder, mount on the
ASTM Grade A 283. The holder with test strip is inserted into the Ervin Test Machine BellHousing along with 20 g of new abrasive media to be tested. The test is then run for thespecified revolutions (cycles) of the beater housing as shown in Table 5 for specific abrasivesize being tested. After each test the test bar is removed and evaluated for degree ofcleanliness base on SSPC SP 5, White Metal Blast Cleaning. The abrasive media used for thetest is also removed. If the surface is not cleaned to white metal, the abrasive fails to meetthe cleaning performance standard.
5.3.8. Abrasive Cleanliness. First separate all magnetic particles from a 100gram sample using a magnet and calculate and record the percentage by weight of non-magnetic matter remaining. Discard the non-magnetic matter. Next, partially fill a cleanglass or plastic jar or beaker with potable water. Place the magnetic particles obtained in thejar or beaker using a clean spoon. Cover the containers and shake contents vigorously.Observe the surface of the water and container:
54
Draft #lASSPC-AB X2X
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Accept sample if Less than or equal to 0.2% by weight ofnon-magnetic matter and clouding or discoloration of thewater, but no oil film or slick on the surface of the water.
Reject sample(s) W More than 0.2% by weight of non-magneticmatter and/or oil film or slick on the surface of the water andsides of the container.
6. Disclaimer
6.1. While every precaution is taken to insure that all information furnished inSSPC specifications is as accurate, complete, and useful as possible, SSPC cannot assumeresponsibility nor incur any obligation resulting from the use of any materials, paints ormethods specified therein, or of the specification itself.
7. Notes
7.1. Disposal of abrasives should be in compliance with all applicable Federal,State, and local regulations. It should be noted that the spent abrasive may containhazardous paint and other foreign matter.
7.2. The importance of properly obtaining a sample cannot be over emphasized.All subsequent analyses performed on the selected sample are likely to be affected by particlesize, so it is imperative that every reasonable effort be made to select the sample in a waythat will assure proper representation. Therefore, it is important to select the propersampling location and to use proper techniques to select the sample. The followingguidelines should be kept in mind when deciding on a sampling method:
7.2.1. If possible, the sample material to be tested should be sampled whenit is in motion, such as at a conveyor transfer point or a discharge chute.
7.2.2. Several small samples of the entire product stream should be takenrather than one large sample.
7.3. Very limited data is currently available regarding this procedure. The SSPCAbrasive Committee is seeking data from other laboratories and planned SSPC laboratorytesting.
7.4. Metallic abrasives sometimes contain internal shrinkage or voids which remainundetected beneath the surface in a mounted and polished sample. These hidden cavitiescause a non-uniform hardness indentation and false hardness reading. These indentationsmust be ignored when testing for hardness.
55
Draft #lASSPC-AB X2X
March 22,1993
SCREEN SCREENNO. SIZE
10 0.078712 0,066114 0,055516 0,046918 0.039420 0.033125 0.028030 0.023235 0,019740 0,016545 0,013850 I 0.0117
TABLE 1STEEL SHOT SIZE SPECIFICATIONS
SHOT SIZE
460 I 390 I 330
all pass
5% maxI
all pass I5% max I all pass
all pass
5% max all pass
85% min I 10% max
96% min I 85% min I
I 97% min I 850% min
I I 97% min
Screen opening sizes and screen numbers with maximum and minimum cumulative percentages allowed oin I
Draft #lASSPC-AB X2X
March 22,1993
TABLE 2STEEL GRIT SIZE SPECIFICATIONS
SCREEN SCREEN GRIT SIZE
NO. SIZE G14 G16 G18 G25 G40 G50 G80
10 0.0787 all pass
12 0.0661 all pass14 0.0555 80% all pass
16 0.0469 90% 75% all pass18 0.0394 85% 75% all pass
25 0.0280 85% 70% all pass
40 0.0165 80% 70% all pass
50 0.0117 80% 65%
80 0.0070 75% 65%
120 0.0049 75%
Screen opening sizes and screen numbers with maximum and minimum cumulative percentages allowed oncorresponding screens.
5 7
Draft #lASSPC-AB X2X
March 22,1993
TABLE 3STEEL GRIT- - - - - - - - - -
STEEL MINIMUM DURABILITY TAKE-OUTABRASIVE CYCLES TO COMPLETE SCREEN
SIZE BREAKDOWN SIZE
G14 2000 40 mesh
G16 2100 40 mesh
G18 2200 40 mesh
G25 2300 50 mesh
G40 2300 50 mesh
G50’ 2000 70 mesh
G80*
* Abrasive sizes G50 and G80 cannot be accurately testeddue to limitations of the test apparatus in retaining thesesizes.
TABLE 4STEEL SHOT_.— —— _..—
STEEL MINIMUM DURABILITY TAKE-OUTSHOT CYCLES TO COMPLETE SCREENSIZE BREAKDOWN SIZE
S460 2200 40 mesh
S390 2300 40 mesh
S330 2400 50 mesh
S280 2550 50 mesh
S230 2550 50 mesh
S170 2550 50 mesh
S110* 2000 70 mesh
S70’ ● ●
Abrasive sizes S110 and S70 cannot be accurately testeddue to limitations of the test apparatus in retaining thesesizes.
Draft #lASSPC-AB X2X
March 22,1993
TABLE 5CLEANING PERFORMANCE STANDARDS
CYCLES REQUIRED TO ACHIEVE WHITE METAL (SP 5) SURFACEFOR VARIOUS SIZED STEEL SHOT AND GRIT MEDIA
ABRASIVE SIZE WEIGHT NUMBER OF DEGREE OFGRIT SHOT ABRASIVE CYCLES CLEANLINESS
G14 S460 20 gm 90 SP-5
G25 S330 20 gm 70 SP-5
G40 S280 20 gm 60 SP-5
G50 S230 20 gm 40 SP-5
G60 S i l o 20 gm 60 SP-5
59
APPENDIX D
SAMPLE FORMAT FOR PROCESS CONTROLPROCEDURE (PCP) FOR TANK BLASTING WITHSTEEL ABRASIVE ABOARD NAVAL VESSELS
60
SAMPLE FORMAT FOR PROCESS CONTROL PROCEDURE (PCP)FOR TANK BLASTING WITH STEEL ABRASIVE ABOARD NAVAL VESSELS
1.O SCOPE
This document specifies the procedures by which [Insert Name of Shipyard] willcomply with the requirements for abrasive blasting of shipboard tanks interior metalsurfaces utilizing cast steel grit materials.
1.1 TITLE: CAST STEEL GRIT ABRASIVE BLASTING
2.0 REFERENCES
2.1 NAVSEA Standard Item 009-09; Process Control Procedure.
2.2 NAVSEA Standard Item 009-32; Cleaning and Painting Requirements.
2.3 Commercial Item Description (CID) No.s 1041B and 1042B, regarding SteelGrit and Steel Shot performance utilization for general blasting purposes,respectively.
2.4 ASTM D-4940-89; Standard Test for Conductimetric Analysis of Water SolubleIonic Contamination of Blasting Abrasives.
2.5 Mil Spec - MIL-A-22262A, dtd 14 Feb 1989, “Abrasive Blasting Media ShipHull Blast CIeaning”
3.0 REQUIREMENTS
3.1 Submit a Process Control Procedure to the cognizant Supervisor for review.
3.1.1 Ensert Name and Address of Shipyard]
(Contractor’s Name and Address)
3.1.2 Use of Cast Steel Grit Materials for Abrasive Blasting of ShipboardTanks Interior Metal Surfaces
(Process Title)
Ensert Shipyard’s PCP Number]
Process Control Procedure No.
(Process Number)
Revisions:
(Date Developed)
61
3.1.3 PROCESS DESCRIPTION
In preparing the interior surfaces of tanks to undergo painting, the Contractor willuse a lot mix of steel grit abrasive blasting materials commensurate with the job athand, in accordance with reference (2.2).
A.
B.
c .
D.
The cast steel grit/shot mix, Type 1,2, or 3, with Rockwell/C of C-40to C-SO hardness, in accordance with ref. (23), will be used as theabrasive blasting material to clean the tank interior metal surfacesbeing prepared for painting / preservation per reference (21).
The Contractor wilI institute a rigorous testing program in which itwill observe and test the quality of the steel shot/grit characteristicsand cleanliness for further reclassification on an ongoing basisthroughout the tank cleaning process. This will ensure optimum gritquality and cleanliness. The grit after inspection will be returned,along with any necessary replenishment of “Make-up Grit to the gritblasting source. This degree of testing and control will ensure thequality of grit being utilized.
Blast Equipment & Recovery Systems
Ensert name and description of abrasive blast machines to be used bythe shipyard.]
[Insert name and description of vacuum recovery and reclassifiersystem to be used.]
Applicable data sheets and instructions for blast equipment andrecovery systems are included as an enclosure to this Process ControlProcedure.
Method & Type of Equipment to be Used for Testing Cleanliness ofRecycled Grit
Prior to commencement of blasting operations, the Contractor will,through a series of tank cleanliness preinspections, ensure thatsalt/chemical contamination is controlled.
The Contractor fully recognizes that abrasive materials must be clean,otherwise contamination on the abrasive will be transferred to thesurface being blasted. The most dangerous contaminates on abrasivesare water, oil, grease, and chloride (or sulfate containing salt). Any ofthese contaminants, once transferred to steel being worked, couldcause premature failure of the coatings applied over them. At leastone inspection method will be used to detect oil and grease. Anabrasive material sample will be placed in a clean glass jar containingclean water. The contents will be vigorously shaken and observed.If a film of oil appears on the surface of the water, then the abrasiveis not clean enough for continued blasting utilization. The steel grit
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lot will then be reclassified and retested further to ensure it passes thetest for oil content as contained in reference (2.5). A periodicsampling/visual inspection of this will be conducted at the beginningof an abrasive cleaning effort, throughout the blasting operation, andbefore adding reclassified grit back to the blast supply source.Concurrent with this process, a visual inspection will be accomplishedto determine if the source abrasive material used in the blastingprocess is dry, and for the presence of any other possiblecontaminants.
A conductimetric analysis for salt contamination may be conductedon-site with a minimum of field equipment and process disruption.The Contractor intends to require the use of the test method outlinedin ASTM-D-4940, wherein a slurry of equal amounts by volume (300roil) of pure water and abrasive is agitated, the agitated solution isfiltered, and then checked for conductivity with a commercialconductivity bridge and conductivity cell as specified in ASTM-D-4940.
(microsiemens) indicates a high level of ionic contamination, and, a
the conductivity testing process substantiates a determination of a highlevel of contamination, the Contractor will elect to reduce thecontamination to an acceptable “further use” level by adding amountsof new, clean unused abrasive, by subjecting the currently examined“in-use” lot of abrasive material with new material.
Clean, or pure water, as used in the preceding paragraphs relative toconductimetric (flushing, testing, cleaning) is defined as “deionized”water so as to preclude false test results. The water to be used is TypeIV reagent water, as specified in reference (2.4).
E. Surface Profile
Surface profile recording shall be accomplished by Testex Press-O-FilmReplica Tape, which will provide a reverse replica of the surfaceprofile, or by visual determination as required to ensure proper profile.Surface will be evaluated to the required coating system.
F. Envtionmental Monitoring
(1) During grit blasting, dehumidifiers will be used as required tokeep humidity acceptable limits. Testing of tempera-ture/humidity will be conducted at commencement of shiftand at mid-shift break ensure acceptable limits are maintained.
(2) Coatings shall not be applied below 40 degrees F, or when thetemperature of the metal surface is less than 5 degrees F abovethe dew point of the ambient air. Readings are taken before,during, and upon completion of application of each coating,and recorded on [Insert name and number of Shipyard’s
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3.1.4
3.1.5
3.1.6
relevant inspection form.] Readings will be taken a minimumof every two hours and the results entered in the HumidityReading Log maintained for the contract.
G. Paint Applications
Paint Coating System shall be in accordance with NAVSEA StandardItem #O09-32.
H. Inspection Systems
Inspections shall be conducted in accordance with NAVSEA StandardItem #009-04, and [lnsert name and number of relevant inspectwnform.]
(1) Acceptability in meeting customer contractual requirementsand specifications shall be prepared on [insert name andnumber of relevant test acceptance record.] formalizing theacceptability of surface preparation.
L Contamination Protection
Contamination Protection shall be in accord. with NAVSEA Std ItemW09-06.
J. Safety
All abrasive blast operators and spray paint applicators shall wear air-supplied positive pressure full face respirators and protective clothing.Constant ventilation shall be maintained during all blasting operationsin accordance with OSHA/CAL OSHA requirements.
Employee Qualifications
[Insert names, titles title experience levelsDepartment supetvison] personnel.]
of shipyard’s Paint and Sandblast
Employees are assigned to jobs commensurate with experience-to-date, andability. Employees in training start at clean-up jobs, masking, and other lowskilled duties, and progress to the Journeyman level.
Inspection and Documentation
All work is inspected by a Supervisor prior to final acceptance in accordancewith paragraph 3.1.3.H.
Acceptance and Rejection Criteria
Conduct abrasive blasting to the required specifications in effect.
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3.1.7
3.1.8
3.1.9
3.1.10
Knowledge of Procedure Requirement
Contractor will print copies of the specifications, Process Control Procedures,and the Manufacture’s application instructions for each item. These aresubmitted to the Supervisor prior to each job. A pre-job conference with theSupervisors and the technical representative is called if any potential problemsare foreseen.
Hazardous Material
Material identified as hazardous waste under this PCP during the blast gritreclamation procedure will be set aside and disposed of in accordance withFederal, State, and local environmental regulations.
Method of Process Control Procedure (PCP) Control
The Procedure itself and on-site Supervision and Quality Assurance Inspectionprovides for feedback as to the continued satisfactory performance under thePCP.
Approval signature and title of the Sub-Contractor’s Representative, asapplicable, and the date of submission.
Date Title - Department
Date Title - Department
Date Title - Department
4.0 ENCLOSURES
[Include all required equipment operating instructions and samples of allrelevant shipyard forms and records.]
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Additional copies of this report can be obtained from the National ShipbuildingResearch Program Coordinator of the Bibliography of Publications and Microfiche Index,You can call or write to the address or phone number listed below.
NSRP CoordinatorThe University of Michigan
Transportation Research InstituteMarine Systems Division
2901 Baxter Rd.Am Arbor, MI 48109-2150
Phone: (313) 763-2465Fax: (313) 936-1081
