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D-1 Training: Remediation of Soluble Salt Contamination A P P E N D I X D REMEDIATION OF SOLUBLE SALT CONTAMINATION This presentation covers issues related to remediation of soluble salt contamination on steel highway structures. It includes several inter-related sections. The reader should be familiar with the introduction to soluble salts training before viewing this material.
D-2 Key Learning Objectives This Training Addresses the Following Questions â When Should Soluble Salts be Remediated on Steel Bridges? â How Effective are Different Methods of Soluble Salt Remediation? â What Issues are Important to Consider During Remediation? â What are the Economic Benefits of Soluble Salt Remediation? â What are the Recommended Best Practices for Soluble Salt Remediation?
D-3 WHEN TO REMEDIATE? Situations calling for Salt Detection and Remediation Good spot to ask people when they have remediated surfaces, for what reasons During Surface Preparation for Coating Before any surface preparation process â Pressure wash salts and other debris prior to mechanical surface preparation â Ensure salt on prepared surface doesnât exceed acceptable levels for coating This may require reworking areas before painting During full coating removal projects â Able to use more effective remediation methods such as: Dry abrasive blasting to an SSPC-SP 10/NACE No 2 condition Wet abrasive blasting SSPC-SP 10 (WAB)/NACE WAB-2 condition Ultra-high pressure water-jetting to an SSPC-SP WJ-2/NACE WJ-2 condition â Rework may involve pressure washing in conjunction with the specified surface preparation method â Soluble salt levels in the range of 5 to 10 Âµg (Cl or salt per ISO 8502-9)/cmÂ² are reasonable expectations During spot coating removal projects â Higher levels of power tool cleaning are more effective (e.g., SSPC-SP 11 is more effective than SSPC-SP 3) â Light pressure wash after power tool cleaning is effective Allow surface to fully dry prior to painting â May be difficult to achieve the same cleanliness as with full removal methods
D-4 Seasonal Remediation of Salts from Bridge Surfaces Areas subject to winter snow conditions may require seasonal salting for safety â Springtime washing of these salts can prolong steel life â Remediation is typically performed with low pressure water methods May be subject to local environmental restrictions â Visual surface inspections may be appropriate for determining reduction in salt levels Quantitative testing may periodically be used in conjunction with visual inspection to address specific issues In conjunction with washing, areas requiring further remediation and repainting should be identified During Subsequent Coats of Paint Remediate primer and intermediate coats of paint when soluble salt contamination of coating is observed â Pressure wash, low pressure water, or washing with a wet cloth are effective methods Consider soluble salt testing between coats, especially in marine environments, or where primer/intermediate coats are exposed for extended periods of time â Rusted areas may require mechanical preparation
D-5 METHODS TO REMEDIATE SOLUBLE SALTS Ways to Efficiently Remove Rust and Salts from Steel Surfaces Mechanical Methods Power Tool Cleaning SSPC-SP 3 SSPC-SP 11 Media Blasting SSPC-SP 10 SSPC-SP 10 (WAB)
D-6 Power Tool Cleaning With Rotary Bristle Tool SSPC-SP 11 âPower Tool Cleaning to Bare Metalâ Cuts through scale and surface rust Pneumatic tool operated at 90psi spins brush head with needles 3500rpm against surface Difficult to use in tight areas or complex geometries Achieves new surface profile Surface appears visibly cleaned of rust Power Tool Cleaning with Needle Gun SSPC-SP 3 âPower Tool Cleaningâ Quickly remediates heavy scaling on surfaces Pneumatic tool operated at 90psi forces metal pins (needles) back and forth against the surface to remove rust and salts â May require additional dust or vacuum shroud Achieves new surface profile Tightly bonded rust and staining remains on the surface after use Not recommended as only step in remedia on of soluble salts due to leaving the surface contaminated Can be useful in ht, complex areas as first step
D-7 Power Tool Cleaning Comparison SSPC-SP 3 Needle Gun Remediates well around bolts, crevices, complex and small areas Only remediates loosely adherent rust or chlorides Surface may be visibly dirty after completion SSPC-SP 11 Rotary Bristle Tool Good on flat surfaces but difficult to use around bolts and in tight crevice areas Little to no visible surface rust or chlorides after Both used for spot surface preparation during maintenance and touch up work Media Blast to an SSPC-SP 10/NACE No.2 - Near White Metal Blast Commonly used media used: Aluminum Oxide, Steel Shot, Garnet Abrasive media is propelled against the surface, removing scale and surface rust and re-finishing the surface â Substrate and material used will affect remediation time and final surface profile Final surface shall be 95% free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter. â Surface may contain light shadows in 5% of each 3-inch by 3-inch surface area When viewed without magnification shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter of at least 95% of each unit area. Staining shall be limited to no more than 5 percent of each unit area, and may consist of light shadows, slight streaks, or minor discolorations caused by stains of rust, stains of mill scale, or stains of previously applied coatings. Unit area shall be approximately 3 in. x 3 in. (9 sq. in.).
D-8 Water Remediation Methods Four SSPC/NACE standards address water remediations: â SSPC-SP WJ-1/NACE WJ-1 âWaterjet Cleaning of Metals â Clean to Bare Substrateâ â SSPC-SP WJ-2/NACE WJ-2 âWaterjet Cleaning of Metals â Very Thorough Cleaningâ â SSPC-SP WJ-3/NACE WJ-3 âWaterjet Cleaning of Metals â Thorough Cleaningâ â SSPC-SP WJ-4/NACE WJ-4 âWaterjet Cleaning of Metals â Light Cleaningâ Does not produce a new profile, but instead exposes previous abrasive blasted profile on the steel â If pitting has occurred following corrosion of the original substrate, the exposed surface will be pitted All wet methods of bare steel remediation are susceptible to flash rust Specified by visual and non-visual standards of surface cleanliness Visual Near White Metal Blast Cleaned Examples Examples of varying initial surface conditions being remediated to an SP-10 surface, curtesy of SSPC-VIS 1 Dry Abrasive Blast Cleaning
D-9 Water Remediation Specifications Descriptions WJ-1 â Surface shall be free of all previously existing visible rust, coatings, mill scale, and foreign matter and have a matte metal finish WJ-2 â 95% of surface shall adhere to WJ 1 â 5% may contain only rust staining, coatings, and foreign matter WJ-3 â 66% of surface shall adhere to WJ 1, with the exception of mill scale â 33% may contain only rust staining, coatings, and foreign matter WJ-4 â Surface shall have all loose rust, loose mill scale, and loose coatings uniformly removed Not to be confused with differences in water pressures Water Pressures used in Remediation LP WC â Low Pressure Water Cleaning â 3,000 to 5,000 psi â Can be used without damaging adherent coating â Recommended for seasonal & partial salt remediation HP WC â High Pressure Water Cleaning â 5,000 to 10,000 psi â Will remove all but tightly adherent rust and coating from the surface UHP WJ â UltraHigh Pressure Water Jetting â >25,000 psi â Highest level of remediation achieved through water methods HP WJ â High Pressure Water Jetting â 10,000 to 25,000 psi â Will remove most coatings, rust, and staining from the surface Not to be confused with WJ-1 through WJ-4 classifications
D-10 Non- Visual Specifications of Water Remediated Surfaces SSPC SC-1 â Surface Cleanliness 1 â Surface shall be free of all detectable levels water-soluble chlorides, iron- soluble salts, and sulfates measureable at the field level SSPC SC-2 â Surface Cleanliness 2 â <7 g/cm2 chloride contaminants â <10 g/cm2 soluble ferrous ion salts â < 17 g/cm2 sulfate contaminants SSPC SC-3 â Surface Cleanliness 3 â < 50 g/cm2 chloride or sulfate contaminants SSPC non-visual standards Visual Cleanliness Examples Visual examples of a panel cleaned from WJ-4 through WJ-1 from SSPC-VIS 4 Water Jetting Visual examples of original panel cleaned from WJ-4 through WJ-1
D-11 Solvent Cleaning Methods SSPC-SP 1 Solvent Cleaning â Removal of all oil, grease, soil, drawing and cutting compounds, and other soluble contaminants from the surface â Often termed as a âSolvent Wipeâ with acetone or another paint thinner â Solvents remove non-salt contaminants on surfaces as well Addition of Chemicals to low pressure wash water â Acidic and alkaline solutions when added in low concentrations to low pressure wash water can help to dissolve salt ions from the surface Natural Methods Surface salt concentrations can be reduced through natural methods Soluble salt measurements are necessary to determine whether natural methods are reducing salts enough to merit no further remediation Examples include: â Entering into a wet season in certain climates â Spring snow melt
D-12 Geometry Effects on Remediation Surface geometry can make it difficult to remediate soluble salts with power tool methods â Corners, crevices, and tight spacing are examples of areas that are difficult to clean with most methods â HEPA vacuum shrouds are often required that limit the ability of tools to clean around obstructions â Crevices may retain water used during remediation with wet methods The location of the contaminated surface may inhibit remediation â Working with power tools may be unsafe â Full containment of the area (e.g., for abrasive blasting) may not be possible â Chemical and/or water run off (e.g., during waterjetting) may be an environmental concern ISSUES AND CONCERNS Troubles with Salt Remediation
D-13 Solubility of Salts Some salts are not soluble in water, thus they are more difficult to remediate with wet methods â These salts will not be detected in methods which require the dissolution of salts on the surface being tested â Insoluble salts may or may not affect coating performance If they are visible (e.g., ferric salts) they should be remediated as required to meet the visual requirements of the surface preparation specification Remediation Within Pits or Tight Crevices High levels of pitting will complicate the remediation process Pits tend to trap both corrosion product and salts â Narrower and deeper pits will be more difficult to remediate than wide and shallower pitting â Pitting creates a non-uniform surface which may cause pre-mature coating failure if not remediated Due to this, pits and tight crevices will require extra attention when remediating, similar to the extra attention needed when making salt measurements
D-14 Economic Benefits Remediation of Salts Before and during Coating Application â Ensuring a clean and salt free surface will decrease the chance of failures in the coating adhesion, blistering, or through film corrosion in the coating â Increases in the lifetime of the coating and reduces maintenance costs Seasonal Remediation of Salts â Remediation allows visual inspection to parts of the bridge which would otherwise not be available for inspection â Can prolong coating lifetime by reducing salt buildup ECONOMIC BENEFITS OF SOLUBLE SALT REMEDIATION
D-15 RECOMMENDED REMEDIATION PRACTICES Full Remediation to Bare Steel 1. Remove corrosion product from heavily corroded areas using mechanical methods such as shipping tools 2. Pressure wash salts and other debris prior to mechanical surface preparation 3. Able to use more effective remediation methods such as: â Dry abrasive blasting to an SSPC-SP 10/NACE No 2 condition â Wet abrasive blasting SSPC-SP 10 (WAB)/NACE WAB-2 condition â Ultra-high pressure water-jetting to an SSPC-SP WJ-2/NACE WJ-2 condition 4. Ensure salt on prepared surface doesnât exceed acceptable levels for coating â Soluble salt levels in the range of 5 to 10 Âµg (Cl or salt per ISO 8502-9)/cmÂ² are reasonable expectations 5. Rework may involve pressure washing in conjunction with the specified surface preparation method
D-16 Remediation Without Coating Removal Low pressure (e.g., 100 psi) wash with water is recommended for salt remediation without coating removal â Pressure washing (e.g., 2000 psi) may remove coating, offsetting the advantages of removing the salts In smaller areas where low pressure washing is not economical, a water or chemical rinse and wipe with a clean cloth will remove salts from the surface If pressure washing removes coating, consider spot maintenance painting to slow corrosion Partial Remediation to Bare Steel 1. Remove corrosion product from heavily corroded areas using mechanical methods such as shipping tools 2. Pressure wash salts and other debris prior to mechanical surface preparation 3. Perform Power tool cleaning to the specified requirement 1. Higher levels of power tool cleaning are more effective (e.g., SSPC-SP 11 is more effective than SSPC-SP 3) 4. Washing surface after power tool cleaning is effective at reducing soluble salt levels 1. Allow surface to fully dry prior to painting 5. Ensure salt on prepared surface doesnât exceed acceptable levels for coating 1. This may require reworking areas before painting 2. May be difficult to achieve the same cleanliness as with full removal methods; soluble salt levels in the range of 10 to 50 Âµg (Cl or salt per ISO 8502-9)/cmÂ² are reasonable expectations 3. Rework may involve pressure washing in conjunction with the specified surface preparation method
Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACIâNA Airports Council InternationalâNorth America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing Americaâs Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation
TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED 4804377803099 ISBN 978-0-309-48043-7 90000 N O N -PR O FIT O R G . U .S. PO STA G E PA ID C O LU M B IA , M D PER M IT N O . 88 G uidelines for D etection and Rem ediation of Soluble Salt Contam ination Prior to Coating Steel H ighw ay Structures N CH R P Research Report 912 TR B