1.Fundamentals of stripe coatingFromJPCL,January 2014

More items forQuality Control

Paint failures on bolted connection that had not been stripe coatedPhotos courtesy of Corrosion Control Consultants and Labs, Inc.

Consider the following scenario, which points out one of the worst disappointments in the painting of steel structures.The owner carefully plans a project to include a well-written specification, careful material evaluation and selection, a qualified contractor, and thorough inspection of the work. The project is done on time, within budget, and with no claims for extra work. Two years later, visual inspection of the project reveals that 99% of the painting work shows no signs of failure. Yet, essentially every edge, bolt, and weld is rusting.What happened?The project specification did not require striping or stripe coating of all edges and welds during the painting work. Is this the problem? Maybemaybe not.What is Striping or Stripe Coating?A stripe coat is a coat of paint applied only to edges or to welds on steel structures before or after a full coat is applied to the entire surface. The stripe coat is intended to give those areas sufficient film build to resist corrosion.1Therefore, striping, as it is sometimes called, is the process of painting the edges of a surface or welds to give them extra protection. Striping is done before priming or before the application of a full coat of paint.1(In this article, the terms stripe coating and striping are used interchangeably.)SSPC-PA 1, Shop, Field, and Maintenance Painting of Steel, includes the following advice about stripe coating.2 If stripe coating is specified for a project, then all corners, crevices, rivets, bolts, welds, and sharp edges should receive a stripe coating with the priming paint before the steel receives a full coat of primer. The stripe coat should extend at least 1 in. (2 cm) from the edge. To prevent removal of the stripe coat by later application of the primer, the stripe coat should be allowed to set to touch before the full coat of primer is applied. (However, it should not be permitted to dry long enough to allow rusting of the unprimed steel.) Alternatively, the stripe coat may be applied after a complete coat of primer, especially if a long drying period for the stripe coat would allow the uncoated steel to deteriorate. Tinting of the stripe coat is advisable to promote contrast. Stripe coating is most effective on edges that are rounded by grinding.The specification notes that stripe coating is advantageous in preventing coating breakdown on edges, etc., in very corrosive surroundings, but it is an expensive operation and may only be justified when it is believed that the cost will be compensated for by extra service life of the coating system.Is Stripe Coating Necessary?Stripe coating of edges, bolts, and welds is often specified because liquid paints tend to flow away from these parts. This is a result of surface tension in the paint film and shrinkage of the paint film during curing.If this occurs, the paint film at or near the edges will be thinner than elsewhere on the painted surface, and the result can be early corrosion failure in these areas. This can become a critical issue when the paint is failing on the nuts, bolts, rivets, and welds, because these are the items holding the structural pieces together.

Edge failure on stiffener that was not stripe coated

Edge failure evident on yellow angle

The benefits of striping are two-fold. First, it tends to fill in small voids, laps, and irregularities in the substrate (such as porosity in welds). Second, if allowed to cure to the point of tackiness, striping tends to retard the next full coat of paint material from flowing away from edges.High-solids paints are less prone to thinning at edges than low-solids paints because they generally have faster setting time, higher viscosity, and lower surface tension.At one time, most structural steel painting work was done with low-solids, relatively slow-curing, oil-based (alkyd) materials. The fact that the industry has moved toward the use of faster setting, higher solids coating materials, which exhibit less tendency to flow away from edges after application, does not mean that stripe coating is not necessary.The corrosiveness of the environment will often determine whether stripe coatings are needed. Stripe coating is often considered most cost-effective in highly corrosive environments such as the insides of tanks and marine or chemical exposures. In moderately corrosive environments such as those frequently wet by fresh water, coating choice and good control of the application without stripe coating may be adequate to protect the structure cost-effectively. In mild environments such as those with low humidity or indoors, striping is not necessary.Stripe Coating TechniquesSince the original ATB on stripe coating was published in 2001, SSPC has issued SSPC-PA Guide 11, Guide to Protection of Edges, Crevices, and Irregular Surfaces. Published in 2008, the guide discusses the reasons for employing extra corrosion protection measures on edges, corners, crevices, bolt heads, welds, and other irregular steel surfaces, as well as various protection options such as edge grinding, chamfering, and application of stripe coats. Some details, including the advantages and limitations of specific methods of obtaining additional coating thickness by stripe coating, are described to assist the specification writer in assuring that the project specification will address adequate corrosion protection.While Guide 11 should be consulted for projects that may include stripe coating application, each specifier and paint applicator must interpret the necessity, means, and methods for stripe coating for each individual project.Therefore, the following information is provided for the reader, based on the authors experiences and interaction with various paint manufacturers, specifiers, and applicators. This information is not meant to be comprehensive; for more specific questions on stripe coating application, you should refer to Guide 11.When Should Stripe Coating be Specified?Stripe coating should be specified when the history of the structure indicates that edge failure of the paint system has been a problem. Consideration also should be given to specifying stripe coating in a severely corrosive environment, or if the paint manufacturer recommends stripe coating.Is Stripe Coating an Additional Coat of Paint?Owners and contractors have disagreed about whether stripe coating is an additional coat of paint. That depends on what the specification says. The need to cover a blast cleaned surface is paramount in corrosive environments. Therefore, the logical course is to apply the stripe coating after the primer. In this case, the stripe coating is clearly an extra step. On the other hand, in moderate environments or if there are not a lot of edges, it may be possible to apply the stripe coat just prior to the full primer. Then the contractor may have workers applying the stripe coat in front of workers applying the primer, and both of them using paint from the same cans. This process would not necessarily be considered an extra step.Which Generic Paints Warrant Consideration of Stripe Coating?For the most part, low-solids/low-viscosity paints (such as alkyds) tend to benefit from stripe coating. In general, fast-setting paints (such as inorganic zincs) and high-solids/high-viscosity paints (such as epoxy mastics) do not draw away from edges. However, striping does apply additional coating thickness to edges that might not have received enough paint originally.Which Coating Layers Warrant Stripe Coating?Keeping in mind that the primary benefit of stripe coating is compensation for possible reduced coating thickness at sharp edges and irregularities in the substrate, it is reasonable to conclude that only the primer should be striped. After application of the primer, substrate irregularities are covered.Applying stripe coats to all layers of paint can cause more harm than good. Too much paint increases stresses in a coating film, thereby causing cracking or peeling. The tendency of liquid paint to pull away from edges is reduced once a layer of primer has been applied. It is quite common to measure 750 micrometers (30 mils) of paint or more on a surface near edges where a three-coat system of 300450 micrometers (1218 mils) was specified with stripe coating of all three layers.Should Stripe Coating Be Applied Before or After the Full Coat of Primer?If a high degree of surface cleanliness is specified, such as SSPC-SP 10/NACE No. 2, Near-White Blast Cleaning (the equivalent of Sa 2 in ISO 8501-1), the applicator has only a short period of time, depending upon atmospheric conditions, to prime the steel substrate before flash rusting occurs. To preclude flash rusting, the entire substrate probably should be primed first and the stripe coating applied later. The stripe coat should then be tinted so that it is obvious where the stripe coat was applied and if any areas were missed.Is Thinning Required for the Striping Material?If stripe coating with a particular paint material is specified, the application data sheet should be consulted for thinning instructions for the application method selected. For instance, if the stripe coat is to be applied by brush, the thinning instructions for brush application should be followed. No extra thinning should be done. Too much solvent in the paint, especially when the stripe coat is applied before the primer, will require more time for the stripe coating to become tacky. Solvent entrapment, bubbling, or pinholing can occur.Should a Thickness Be Specified for a Stripe Coat?Since irregular surfaces are one of the places stripe coating is used, it may be difficult or impossible to get an accurate dry film thickness reading. Nevertheless, it is important to remember that if total dry film thickness is exceeded by applying both a stripe coat and a full coat, then film defects may result. To achieve a stripe coat that is not excessively thick, the specifier may require that the paint be applied to produce a visual color change on the affected areas and not specify a particular wet or dry film thickness. It should be noted that only a portion of the paint applied directly to an edge flows away, so only a small amount of additional paint is needed to bring the coating on an edge to the same thickness as on flat surfaces.What Application Methods Should Be Used for Stripe Coating?The specifier and applicator must first examine the required qualities of the stripe coating to determine the optimum method of application. In general, the required qualities of stripe coating are filling voids and other irregularities in the affected substrate areas; providing a tacky surface for subsequently applied full coats of paint to adhere to; and not exceeding the optimum dry film thickness for the stripe coat in combination with the full coat.Two application methods meet the requirements of these three qualities: brushing and spraying with conventional or air-assisted airless equipment. The specifier should permit all of these application methods for stripe coating, depending on specific job conditions. For instance, brushing can be used for stripe coating of small, complex shapes (such as lattice members and bolted connections), whereas conventional spraying is appropriate for the edges of large structural shapes.Application methods that can deposit relatively high volumes of paint (e.g., rolling with a heavy nap roller or airless spraying) should be avoided to prevent excessive dry film thickness and possible film defects. (This assumes that the stripe coating or full layer of primer is being applied while the underlying material is still tacky. More latitude in application methods can be allowed if a full layer of primer is applied and allowed to cure until its dry-to-recoat time. Then, the stripe coating can be thought of as an additional coat of paint being applied to the primer.)Edge Retentive CoatingsYou have probably also heard of edge retention coatings, which claim to have an edge coating thickness similar to that of a nearby flat plate. The question youre asking is, can I use one of these coatings, or do I still need to carry out stripe coating?The answer is simplestripe coating still needs to be carried out, as it serves more than one purpose. In addition to increasing the film thickness at the edge of plates or beams, stripe coating carried out by brush is better at wetting the surface and forcing the paint into cracks and crevices, over weld beads and bold heads, and other areas which are subject to premature failure.ConclusionStriping or stripe coating is used to extend the life of certain paint systems in corrosive environments. It compensates for liquid coatings that flow away from edges of steel structures, thus reducing the dry film thickness. For stripe coating to be beneficial and cost-effective, the specifier must consider the configuration of the structure to be painted and the type of paint system to be applied. Stripe coating should be limited to one coat of paint to avoid overly thick coating systems. Proper stripe coating application is needed to avoid defects in the paint film that can cause other problems besides early rusting, for which the stripe coating was applied.Editors Note: The original ATB on stripe coating was written by Jon R. Cavallo, P.E., of Corrosion Control Consultants and Labs, Inc. (Eliot, ME) for the May 2001JPCL. It was slightly updated for this issue byJPCLTechnical Editor Brian Goldie.

References1. SSPC Protective Coatings Glossary (Pittsburgh, PA, USA: SSPC: The Society for Protective Coatings, 2011), p. 201.2. SSPC-PA 1, Shop, Field, and Maintenance Painting of Steel (Pittsburgh, PA, USA: SSPC: The Society for Protective Coatings, April 2000), p. 13.The Journal Of Protective Coatings & Linings2014 Technology Publishing Company

Comment from Michael Deaton, (2/26/2014, 7:03 AM)

After supervising the 1 million square foot Innerbelt project in Cleveland last year and dealing with the very intense inspection by Mr. Dave Nolan, owner of Quality Control Services, stripe coating was an essential part of the coatings application. There is over a half a million bolts on this project and the finish coat is white, therefore the stripe coat must provide a paint tight seal. Painters utilized 4" cigar or weeny rollers to apply 1st the organic zinc, then macropoxy 646 and finally the acrylic polyurethane to all bolts, edges, welds, etc. The finish coat only required striping where the airless gun could not access, but both the primer coat and the intermediate required full striping. This striping was very time consuming and should be factored into any bid.

Comment from Tom Selby, (2/26/2014, 12:49 PM)

It makes more sense to get all blasted surfaces covered with the first coat of paint so that there is no compromising of the quality of the initial blast. After that coat is dry a contrasting color can be used to stripe coat with a brush or weenie roller.

Comment from Billy Russell, (2/26/2014, 4:35 PM)

3.Testing adhesion of multi-coat system

When should the adhesion of an applied coating or lining multi-coat system be tested?From Karen Fischer Amstar of WNYAdhesion testing should be performed for one of two basic reasons: if the specification calls for it as a qualifying test for acceptance of the coating system, or if there is a failure or suspected failure in the coating system (material and/or methods) that cannot be evaluated (or fully evaluated) by non-destructive methods.One must always keep in mind that an adhesion test is a destructive test, so the resulting test area now becomes a repair that could, in itself, fail. This is especially important to keep in mind in the case of linings or any system that will be in immersion service, mechanical service, or a chemical/harsh environmental service. Because it may be necessary to perform adhesion testing in multiple areas (depending on the size of the suspected areas), there will be multiple repairs. Destructive testing should always be the last method employed, not the first method, when evaluating a coating for suspected or obvious failure.From James Albertoni CA Department of Water ResourcesSome good instances where a multi-coat system should be tested for adhesion include if the re-coat window is missed, if the topcoat is not specifically recommended by the manufacturer to be compatible with the basecoat, if the basecoat and topcoat are from two different manufacturers, or if it is suspected one of the coats was mixed slightly off ratio. Most importantly, the system should always be tested for adhesion if the spec calls for it.From Daniel Liu APCFirst, it will be up the specifier to decide if an adhesion test is required, and, if so, the specification should include not just the testing requirement but also the acceptance criteria and tester type. From my experience in the field of tank coating, this test is normally not required in the specification because it is a destructive method. Any repair area creates a weak point in the lining, so the more repair areas you have, the more weak spots you have.However, it is quite necessary to make a proper adhesion test recommended by the paint maker when application has or may have deviated from the specification, such as by exceeding the recoat interval, not maintaining the proper level of humidity, or using the wrong mixing ratio for plural-component coatings. Adhesion is quite important for tank coatings that are to be immersed in liquid. But passing the adhesion test does not mean the whole coating system is conclusively qualified for service. The test is only a reference.From Tom Swan M-TESTIts important to note that if an adhesion test is called for in the specification, the document should specify failure criteria as well as the pull tester to be. All pull testers pull at different rates, and, when I discuss pull tests with most people, they have no idea what the pass/fail criterion is or what adhesion tester to use.If you want to use adhesion testing for pass/fail testing, the specifications should specify the minimum pull required and what test instrument to use. Also note that if you stop the test before the coating fails, there is no guarantee that the pull fixture will not take off the coating when you try to remove the fixture, nor does passing the test guarantee that the adhesion or coating integrity was not affected by the pull.From Manpreet Singh Spiecapag Australia PTY LTDIf the clients specification calls for adhesion testing, the paint system should be simulated on a test specimen of the same material class, 100 mm2and 6 mm thick. ISO 4624 describes the method of performing the adhesion test. Acceptance criteria, unless specified by the end user, shall be a minimum of 7 MPA at 23 C, and, at 65 C, no more than 40% decrease from pull-off at 23 C.From Atanas Cholakov ACTAdhesion should be tested after the complete cure of the coating system. Information on curing can be acquired from the paint suppliers technical representative. In the product data sheet, curing is highlighted in a table in accordance with different ambient temperatures and other conditions.From Trevor Neale TF Warren GroupCritical service specifications typically call for adhesion testing, so I assume this question relates to field painting where weather and other delays are often unavoidable and formal adhesion testing is not part if the job/project specification. If there is any suspicion that adhesion may be compromised, then the appropriate form of adhesion testing is recommended to ensure the complete system integrity. This is simply a CYA procedure to avoid possible conflicts, or worse, premature failures.From Bryant Chandler Greenman-Pedersen, Inc.Adhesion testing on coatings must be done after the proper cure time at the correct temperature. This enables the coating to develop the full physical properties. If the coating is tested prematurely, the results often will not meet the specified minimum requirement. The test may or may not be destructive, depending on the thickness of the coating/substrate, and whether or not the test is continued until coating disbondment.As called for in ASTM D 7234 (adhesion testing of coatings on concrete), scoring around the dolly down to the substrate will require a repair even if the test does not go to failure and stops at the minimum test value; a thick coating system (>3040 mils) on a metallic substrate may require scoring if called for in the specification. If the test can be stopped at the minimum value specified without causing coating failure, than the dolly can be removed, often times by striking the dolly with a sharp blow from the side or carefully inserting a sharp 5:1 tool (putty knife) at the glue line and shearing off the dolly. Repairing the top surface may be required but is much better than having to repair the total coating system.When testing thermal spray coatings, always perform the adhesion tests before application of the seal coat. Tests performed after seal coat application will result in test values that are two to three times the value of virgin thermal sprayed coating.

The Journal Of Protective Coatings & Linings2013 Technology Publishing Company

4. The case ofbubbles, and pinholes, and blisters, oh my!FromJPCL,September 2013

JamesD.MachenPCS, KTA-Tator, Inc.James D. Machen is a Senior Coatings Consultant with KTA-Tator, Inc., a coatings consulting engineering firm and distributor of inspection instruments, where he has been employed for over 20 years. Machen is an SSPC-certified Protective Coatings Specialist, a NACE-certified Coatings Inspector Level 3 (Peer Review), and a Level II Inspector in accordance with ASTM D4537. He performs coating failure analyses, coating system recommendations, specification preparation, and major project management for a variety of clients in the transportation, water and waste, power generation, chemical processing, and marine industries. He holds a B.A. from the Pennsylvania State University.RichardBurgessKTA-Tator, Inc., Series EditorThis months Case from the F-Files describes the problem of bubbles, pinholes, and blisters in a polyurethane finish coat applied to new structural steel members at a coal-fired power generation plant. Many of the pinholes and bubbles were so small that they were difficult to detect with the unaided eye. Many of the largest blisters on the webs of structural members were very flat and shallow and also difficult to detect by eye. These conditions became more difficult to see overtime as thin layers of dirt from normal plant operating processes formed on the surface of the polyurethane finish coat. This case file illustrates that interacting variables, rather than a single cause, can combine to cause a failure.BackgroundThe specification required that the structural steel be blast cleaned in the shop in accordance with SSPC-SP 6/NACE No. 3, Commercial Blast Cleaning. Following blast cleaning, a two-coat system, consisting of a moisture cured urethane (MCU) zinc-rich primer and an aliphatic polyurethane finish, was shop-applied. The MCU primer was specified to be applied at a dry film thickness (DFT) of 2.5 to 3.5 mils, and the polyurethane finish was to be applied at a DFT of 4.0 to 5.0 mils. The total two-coat DFT was to be 6.5 to 8.5 mils.

Fig. 1: Sections of newly-coated steel members at a coal-fired power plant displayed blistering and other signs of coating failure. Photos courtesy of James D. Machen, KTA-Tator, Inc.

Field touchup work was specified to be SSPC-SP 2, Hand Tool Cleaning, and/or SSPC-SP 3, Power Tool Cleaning, followed by the application of a coat of surface-tolerant epoxy mastic (4.0 to 6.0 mils DFT) and a finish coat of polyurethane (4.0 to 5.0 mils DFT).The steel was delivered to the project site for sequenced erection. In mid-summer, near the completion of the project, blistering and peeling were observed. At that time, the shop contractor mobilized a field team to make repairs. Repairs were reported to have been performed using low-pressure water cleaning (4,0005,000 psi), in conjunction with hand and power tool cleaning, to identify and remove defective areas, which were then touchup repaired.In the spring of the next year, additional coating defects were discovered and field touchup was again performed. However, the same problems reportedly continued to appear. As a result of the continuing problems, an independent investigation of the coating problem was undertaken.Field Investigation

Fig. 2: Close-up of typical concentrations of small, fine blisters in the polyureathane finish coat

The tests and inspections performed during the field investigation were those typically associated with failure investigations, and included the following. A visual assessment was performed to determine the degree and distribution of coating defects (in this instance bubbles, pinholes, blisters, and peeling). Total coating thickness was measured using a Type 2 electronic film thickness gage operated according to ASTM D7091, Nondestructive Measurement of Thickness of Nonmagnetic Coatings on a Ferrous Base. The number of coatings present and the thickness of each were determined using a destructive coating thickness gage as described in ASTM D4138, Standard Test Methods for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive Means. An integral portable microscope (50X) was used to observe a cross-section of the applied coating. The number of coating layers and thickness of each were measured. Further, evidence of intercoat contamination, voids, underlying rust, mill scale, and pinholes was recorded. Adhesion testing was conducted using Method A (X-Cut) of ASTM D3359, Measuring Adhesion by Tape Test. Method A involves cutting an X through the coating to the substrate using a razor knife. Pressure sensitive tape is placed over the X-cut, then rapidly removed. The amount of coating detached by the tape is rated in accordance with the ASTM rating scale. Ratings of 4A and 5A are considered to represent good adhesion, 2A to 3A represent fair adhesion, while 0A and 1A represent poor adhesion. The coating system was removed in small areas, and the substrate was examined for under-film corrosion or mill scale. Active under-film corrosion may be associated with the coating failure and may also contribute to a shortened life of the system.Coating samples at both failing and non-failing areas were removed for laboratory analysis, and digital images of the typical field coating conditions were obtained.Visual ObservationsThe structural steel consisted primarily of vertical and horizontal I-beam members. Both intact and fractured (peeling) blisters were observed. Blisters were observed on virtually all members inspected. Some of the blisters appeared to be fractured as a result of someone physically scraping the areas, while others appeared to have cracked and fractured on their own. Blistering ranged in size from concentrations of very fine blisters (approximately 1/64 to 1/128 of an inch in diameter) up to single blisters with diameters of approximately 2 to 3 inches. Both irregularly shaped and circular blisters were observed. The fine concentrations of blisters were located primarily on beam flanges and in the corner areas where the webs and flanges meet. Larger shallow blisters were generally located on the webs of the I-beams. The fine blisters and larger shallow blisters on the webs were more difficult to see, oftentimes becoming visible only when viewed at the proper angle with sunlight hitting the surface after the film of surface dirt and grime was removed.

Fig. 3: Blisters formed in the polyurethane finish coat on a flange

Upon scoring around the perimeter of the larger blisters or areas of concentrated fine blisters with a razor knife, the full blister area could be removed. Upon removal, a portion of the zinc-rich primer remained on the steel surface, and a portion remained attached to the backside of the removed blister (cohesive break within the zinc primer). Both faces of the split primer films contained a visible white powder-like residue.Areas that had been repaired by field touch-up were visible across the structure. Blisters were still visible in some touch-up areas. It was not apparent if the blisters had reoccurred in the touch-up area or if some of the blisters were not completely removed and touch-up material was applied over them.Coating ThicknessThe results of the total system thickness measurements from various locations on the structural steel are summarized below. Minimum DFT (mils): 6.3 Maximum DFT (mils): 15.7 DFT Average (mils): 13.2Destructive film thickness measurements most often identified two distinct layers of paint on the steel. In some instances where touch-up repairs had been made, additional coats were apparent, and three to five individual layers were evident. When two coats were present, the first coat was a metallic gray/green and ranged from 4 to 10 mils; the second coat was dark green and ranged from 3 to 7 mils.

Fig. 4: Blisters in the polyurethane finish coat on a lateral brace web

AdhesionAdhesion of the coating system in and immediately around blistered areas was rated poor (0A to 1A rating); however, adhesion of the coating system in blister-free areas was rated fair to good (3A to 4A rating). The adhesion test process consistently forced a break within or at the surface of the zinc-rich primer layer.Substrate ExaminationThe substrate was examined at destructive film thickness measurement areas and sample acquisition areas. Because a thin layer of zinc-rich primer remained adherent to the steel surface, a thorough inspection of the underlying substrate was not possible. However, under 50X power illuminated magnification of the destructive coating thickness gage, a roughened bright metal substrate was sometimes visible. This evidence suggests that the steel surface had been abrasive blast cleaned.Laboratory InvestigationThe laboratory investigation consisted of visual and microscopic examination, infrared spectroscopy and scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS). The test methods and results are described below.

Fig. 5: Formation of whitish-colored zinc salts on the surface of the zinc-rich primer, beneath areas where the blistered finish coat was removed

Microscopic ExaminationMicroscopic examination of the samples was conducted using a digital microscope with magnification to 200X. The samples had between two and five coating layers. Coating layer thickness measurements, obtained by laboratory microscopic methods, are inTable 1.

TABLE 1Coating Layer Thickness MeasurementsSample #Coating Layers and Thickness (mils)

Sample 1(Fine Blisters)Two LayersGreenTopMetallic GrayBottom3.06.93.87.3

Sample 2(Fine Blisters)Two LayersGreenTopMetallic GrayBottom2.24.42.33.6

Sample 3(Fine Blisters)Two LayersGreenTopMetallic GrayBottom3.86.05.27.2

Sample 4(Large Blisters)Two LayersGreenTopMetallic GrayBottom4.98.45.07.9

Sample 5(Non-Failing)Two LayersGreenTopMetallic GrayBottom6.98.52.63.9

Sample 6(Non-Failing Repair Area)Five LayersGreenTopLight GreenGreenGreenMetallic GrayBottom2.04.02.55.54.06.03.05.05.29.9

Sample 7(Non-Failing Repair Area)Four LayersGreenTopGrayGreenMetallic GrayBottom4.05.53.54.01.83.53.95.2

Sample 8(Single Blister)Three LayersGreenTopGrayMetallic GrayBottom2.95.83.16.83.98.0

Infrared SpectroscopyInfrared spectroscopic analysis revealed the following. The spectrum obtained of the green top-coat was consistent with a urethane. Water (moisture) and crystalline silica were also indicated. The spectrum obtained of the gray primer was most consistent with a zinc urethane. No distinct characteristic bands are associated with zinc coatings although the baseline noise appearance was consistent with a zinc coating (confirmed by elemental analysis).SEM-EDSSEM-EDS analysis revealed that the white powdery substance on the gray surface of the primer was primarily zinc. Other elements detected included magnesium, aluminum, and silicon.ConclusionsThe field investigation and laboratory analysis identified multiple variables that contributed to the blistering coating problems on the structural steel.

Fig. 6: Close-up of zinc salt formation on the zinc-rich primer surface, beneath the removed blistered finish coat

The zinc-rich primer used on the project was a MCU material. MCUs react with moisture (atmospheric humidity or other moisture source) to cure. During the curing reaction with moisture, carbon dioxide gas (CO2) is liberated as a reaction product. The CO2gas escapes from the coating film in a process commonly referred to as out-gassing. When a lot of moisture is available, MCUs cure at an accelerated rate, and CO2formation and out-gassing increase. When an additional paint layer is applied while the MCU is still out-gassing, the release of CO2from the MCU can be inhibited. The gas must now pass out of the MCU and through the newly applied layer. Depending on the state of drying and curing of the newly applied layer, some CO2gas may escape, and some may become trapped in the new film. The CO2that escapes produces pinholes or craters when the topcoat has begun to gel, while CO2that is trapped creates sufficient pressure to form bubbles through the cross-section and at the surface of the new film.Laboratory microscopic examination of the paint samples consistently revealed that pinholes and bubbles were present in the green topcoat layer applied over the MCU primer. This evidence indicates that the MCU zinc-rich primer was top-coated with the polyurethane before the primer had sufficiently cured.Infrared spectroscopic analysis of the green polyurethane finish coat identified bound moisture within the film. In order for moisture to become bound within this layer, the moisture would have had to have been present on the MCU zinc-rich primer layer over which the polyurethane finish was applied. This evidence indicates that the surface of the MCU zinc-rich primer where defects occurred (i.e., bubbling, pinholes) was damp when the polyurethane was applied.Field thickness measurements and laboratory microscopic measurements revealed that the MCU zinc-rich primer was often applied above the specified DFT range of 2.5 to 3.5 mils. Destructive thickness measurements and laboratory microscopic measurements indicated DFTs of up to 7 mils and 9.9 mils respectively. Excessive primer thickness prolongs the dry and cure time of the primer; as a result, the CO2out-gassing is also prolonged, serving to increase the likelihood of pinholes and bubbling.The polyurethane finish coat was also applied above the specified DFT range of 4.0 to 5.0 mils, with measurements up to 8.7 mils in some instances. These thicker films could slow the escape of the CO2or trap it, possibly contributing to increased bubble and pinhole formation.The white powdery residue on the backside of the detached blister area and on the substrate was identified as zinc oxide in the laboratory. Zinc oxide (white rust) is produced as the zinc dust in the primer oxidizes. This finding indicates that the MCU zinc-rich primer layer was performing as designed: providing galvanic/sacrificial corrosion protection to the carbon steel substrate. Moisture (rain, condensing moisture) was gaining access to the MCU zinc-rich primer through the voids (i.e., pinholes, fractured bubbles) in the polyurethane finish coat. The moisture served as the electrolyte, allowing the MCU zinc-rich primer to oxidize. Moisture condensing on the steel was likely contaminated with sulfides from the coal-fired power generating station. Water-soluble salts such as sulfides, in combination with moisture, increased the corrosivity of the exposure environment.RecommendationsThe defective areas (i.e., bubbles, pinholes) were identified and removed by high-pressure water cleaning. Industry experience has shown that water pressures in excess of 4,000 psi are usually effective for revealing and removing defective coatings. However, because each individual project is unique, some experimentation is needed to arrive at the optimal cleaning pressure. It was ultimately determined that the best removal method involved the use of a zero-degree, rotating tip on the pressure washer gun, with careful observation to maintain the equipment manufacturers gun-to-work-piece distance and dwell times. In areas where pressure washing was not entirely effective, supplemental mechanical cleaning with power tools (i.e., power sanding) was used. Once the defective coating was completely removed, any coating that remained was probed with a dull putty knife as described in SSPC-SP 2 and SSPC-SP 3, Hand Tool and Power Tool Cleaning, respectively. Remaining coating that passed the dull putty knife test criteria was considered tightly adherent for touchup repairs. The periphery of touchup areas was feather-edged to provide a smooth transition from the repair area to surrounding intact coatings.Once surface preparation was accomplished, touchup proceeded using the field touchup system, consisting of a coat of epoxy mastic followed by a matching green polyurethane finish coat.The Journal Of Protective Coatings & Linings2013 Technology Publishing Company

5. Measuring Dry Film Coating Thickness According to SSPC-PA 2FromJPCL,April 2013

William D. CorbettPCS, KTA-Tator, Inc.

WilliamD.CorbettPCS, KTA-Tator, Inc.Bill Corbett is the Vice President and Professional Services Group Manager for KTATator, Inc., where he has been employed for 33 years. He chairs SSPC committees C.3.2 on Dry Film Thickness and C.6 (Education). He is an SSPC-approved instructor for four SSPC courses, and he holds SSPC certifications as a Protective Coatings Specialist, Protective Coatings Inspector (Level 3), and Bridge Coatings Inspector (Level 2). He is also a NACE Level 3-certified Coatings Inspector. He was the co-recipient of the SSPC 1992 Outstanding Publication Award, co-recipient of the 2001JPCLEditors Award, recipient of SSPCs 2006 Coatings Education Award, and recipient of SSPCs 2011 John D. Keane Award of Merit.Coating thickness shall be measured in accordance with SSPC: The Society for Protective Coatings Paint Application Standard No. 2 (SSPC-PA 2) is a simple enough statement, yet this common specification requirement is often misinterpreted or regarded as a document that simply states how to measure the dry film thickness (DFT) of coatings, something we already profess to know how to do. Yet the requirements of SSPC-PA 2 regarding gage calibration, verification of gage accuracy and adjustment procedures, the number of measurements to obtain, and the tolerance of the measurements are complex and should be fully understood by the specification writer before invoking PA 2 in a contract.

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On more than one occasion, I have heard the question, When did SSPC-PA 2 and dry film thickness measurement become so complicated? In fact, when you take a close look, measuring DFT isnt that complex. We have allowed it to become more technologically complex while making the data easier to analyze. We can gather hundreds of gage readings in a relatively short time; batch the measurements; print the data or upload it to a computer for graphing; report the highest, the lowest, the mean, and standard deviation of the collected data; incorporate digital images of the structure or coated area; and even program the gage to produce an audible signal if a spot measurement is outside of the tolerance range. I am no doubt leaving out other bells and whistles, but my point is that while we are able to do a lot with the readings obtained, measuring DFT involves four or five basic steps. Step 1: Instrument Calibration Step 2: Verification of Gage Accuracy on Certified Coated Standards or Certified Shims Step 3: Base Metal Reading Acquisition or Gage Adjustment (using certified or measured shims) Step 4: Measurement of Coating Thickness Step 5: Correction for Base Metal Reading (if acquired).After a brief review of the history of SSPC-PA 2, this article will describe each of the five steps, based on the 2012 edition of SSPC-PA 2. Special attention will be given in the article to how PA 2 addresses the required number of coating thickness measurements; the acceptability of gage readings, spot measurements, and area measurements; nonconforming thickness; measuring DFT on coated edges; and measuring DFT on pipe exteriors.Some HistorySSPC-PA 2 was originally published as a temporary standard 40 years ago in 1973 (73T) as Measurement of Dry Coating Thickness with Magnetic Gages. The standard referenced gages like the one shown inFig. 1, which are now all but obsolete. The standard has been updated on multiple occasions. Until 2012, the most recent technical changes were published in May 2004, with a minor editorial revision in 2009 to one of the appendices (regarding measurements on test panels). The SSPC Committee on Dry Film Thickness Measurement began revising and updating the 2004 version in 2007. The revisions took five years to complete. The latest edition of the standard (Procedure for Determining Conformance to Dry Coating Thickness Requirements) is dated May 2012 and was made available to the industry in July 2012.

Fig. 1: One type of magnetic gage referenced in original SSPC-PA 2 for measuring dft Figures courtesy of the author except where otherwise indicated

In nearly the same timeframe, the 2005 version of ASTM D7091, Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to NonFerrous Metals was being revised and updated. It, too, was published in 2012. The most current version of the ASTM standard focuses on proper gage use, while SSPC-PA 2 focuses primarily on the frequency of measurements and the acceptability of the acquired measurements. References to the frequency of measurements were removed from the ASTM standard. The two documents are designed to be used together. It is important to note that both documents address the measurement of the DFT of coatings on ferrous and non-ferrous metal substrates. Before 2012, SSPC-PA 2 addressed measurement of coatings only on steel, a ferrous metal. (The sidebar onp. 32in this article summarizes the key changes made to PA 2 in 2012.)Summary of Changes to SSPC-PA 2: 2004 Version and 2012 Version20042012

Measurement of Dry Coating Thickness with Magnetic GagesProcedure for Determining Conformance to Dry Coating Thickness Requirements

Addressed measurement of coatings on steel onlyAddresses measurement of coatings on ferrous and non-ferrous metal surfaces

No referenced standards sectionASTM D7091 and SSPC Guide 11 included by reference

Definitions section included Calibration; Verification; Adjustment; Coating Thickness Standard; Shim (foil); Dry Film Thickness Reference Standard; Accuracy; Structure.Definitions section includes Gage Reading, Spot Measurement and Area Measurement only. All definitions related to gage calibration, accuracy and adjustment are incorporated by reference in ASTM D7091. Spot measurement definition was expanded.

No. of Area Measurements based on the size of the structureNo. of Area Measurements based on the size of the area of coated surface

Isolation of nonconforming areas required measurement of each 100 square foot area painted during the work shift.The magnitude of nonconforming thickness assessed by obtaining spot measurements in eight equally spaced directions radiating outward from the nonconforming area

Recommended specifying minimum & maximum thickness range; if no range was specified, thickness value was considered minimum (with no maximum)If a single value is specified and the coating manufacturer does not recommend a range, the minimum and maximum thickness range is established at 20% of the stated value

Contained a minimum gage accuracy requirement to qualify for useNo minimum gage accuracy requirement to qualify for use

Conformance to Specified Thickness:Gage Readings: UnrestrictedSpot Measurements: 20% of specified rangeArea Measurements: Per SpecificationConformance to Specified Thickness:Five different Coating Thickness Restriction Levels established. If no Restriction Level is specified, default is based on 2004 conformance requirement.

Notes section contained principles of gage operation and various substrate/surface conditions that may affect measurements; overcoating; and correcting for low/high thickness.Notes section includes Overcoating and Correcting for Low/High Thickness only ASTM D7091 describes principles of gage operation and various substrate/surface conditions that may affect measurements.

Contained 6 appendicesContains 8 appendices. Six appendices from 2004 version included. Added two: Method for Measuring DFT of Coating on Edges Method for Measuring DFT of Coated Steel Pipe Exterior

Gage TypesSSPC-PA 2 addresses two types of DFT gages, both of which are supplied by a variety of manufacturers. Magnetic pull-off gages are categorized as Type 1 (Fig. 2).

Fig. 2: Example of magnetic DFT gage categorized as Type 1 in SSPC-PA 2

These gages were designed in the 1950s. While their use has declined, they are still readily available and used by some. For these gages, a permanent magnet is brought into direct contact with the coated surface. The force necessary to pull the magnet from the surface is measured and converted to coating thickness, which is displayed on a scale on the gage. The operating principle is simple. Less force is required to remove the magnet from a thick coating, while more force is required to remove the magnet from a thinner one. The scale is not linear, as will be discussed below.Electronic gages are categorized as Type 2 (Fig. 3). These gages use electronic circuitry to convert a reference signal into coating thickness and are more popular than Type 1 gages. They are typically regarded to be faster, more accurate, and easier to use.

Fig. 3: Example of electronic DFT gage categorized as Type 2 in SSPC-PA 2

Gage Calibration, Accuracy Verification, and AdjustmentTo help assure the reliability of the coating thickness measurements, ASTM D 7091 describes three operational steps that must be performed before taking the measurements. These steps are (1) gage calibration, (2) verification of gage accuracy and (3) gage adjustment. The steps are incorporated by reference in SSPCPA 2 and are completed before obtaining coating thickness measurements to determine conformance to a specified coating thickness range. The steps to verify the accuracy of the gage are based on the principle thatyou check the gage by measuring a known thickness before you use the same gage to measure an unknown thickness.Verification of gage accuracy is typically performed using certified coated thickness standards (for Type 1 or Type 2 gages) or certified shims (Type 2 gages). Adjustment of Type 2 gages to compensate for substrate characteristics (described later) is typically performed using certified shims. Measured shims (individually labeled with a stated thickness value) commonly supplied with Type 2 gages can also be used for gage adjustment.Dry film thickness gages are calibrated by the equipment manufacturer, its authorized agent, or an accredited calibration laboratory (under controlled conditions). A test certificate or other documentation showing traceability to a national metrology institution is required. While there is no standard time interval for re-calibration, an interval can be established based on experience, the work environment, and/or the internal equipment calibration procedures of the company using the gage. A one-year calibration interval is a typical starting point suggested by gage manufacturers.Verifying Gage AccuracyTo guard against measuring with an inaccurate gage, SSPC-PA 2 requires that gage accuracy be verified (at a minimum) at the beginning and end of each work shift according to the procedures described in ASTM D 7091. If a large number of measurements are being obtained, the user may opt to verify gage accuracy during measurement acquisition (for example, hourly). If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy should be rechecked.Verifying the Accuracy of Type 1 GagesThe accuracy of Type 1 (magnetic pull-off) gages is verified by placing the gage probe onto a certified coated thickness standard (Figs.4and5). A one-point or two-point accuracy verification procedure can be performed; typically, the two-point verification provides greater accuracy. If a one-point verification procedure is adopted, the coated standard should be selected based on the intended range of use. For example, if the intended use is between 4 and 6 mils, then a five-mil coated standard is appropriate. Using the same example, if a two-point verification procedure is adopted, then a two-mil and an eight-mil set of coated standards (slightly below and above the intended range of use) is appropriate.

Fig. 4: (top) and 5 (bottom) Verifying the accuracy of Type 1 gages using certified coated thickness standards

The final step in the process is to obtain a set of base metal readings (BMRs) to compensate for substrate characteristics including (but not limited to) substrate metallurgy, geometry, thickness/thinness, and roughness (Fig. 6). These readings represent the effect of the substrate conditions on the coating thickness measurement device. SSPC-PA 2 states that a minimum of 10 (arbitrarily spaced) locations should be measured (one reading per location) and then averaged. This average BMR is then deducted from subsequent coating thickness measurements to remove any effect of the base metal surface and its conditions.

Fig. 6: Obtaining base metal readings with Type 1 gage

Because Type 1 gages cannot be adjusted, some gage operators believed that a correction value could be applied to the coating thickness readings to compensate for the inaccuracy of the gage. For example, if a gage reading was 5.7 mils on a five-mil coated standard, a 0.7-mil correction value could be deducted (by the gage operator) from subsequent coating thickness measurements. However, because Type 1 gages are non-linear, one cannot assume a linear (mil-for-mil) correction value across the full range of the gage. While the gage may be out of tolerance by 0.7 mils at 5 mils, it may be out of tolerance by more or less than 0.7 mils at a different thickness. Accordingly, SSPC-PA 2 states that the practice of using a linear correction value is not appropriate.However, Note 6 in the standard states,A correction curve can be prepared by plotting the actual gage readings against the stated values on the (coated) test blocks (standards). Subsequent coating thickness measurements can be corrected by plotting the measurements along the correction curve. The correction curve may or may not cover the full range of the gage, but should cover the intended range of use. The Base Metal Readings (BMR) described in 6.1 may also need to be plotted on the correction curve.This requirement makes Type 1 gages very difficult to use. While some gage operators may simply subtract a fixed amount (for example, 0.5 mils) from any reading, such a practice is not in compliance with SSPC-PA 2.Verifying the Accuracy of Type 2 GagesThe accuracy of Type 2 (electronic) gages can be verified by placing the gage probe onto a certified coated thickness standard (described for Type 1 gages) or certified shims (Figs.7and8). The certified shim should be placed onto a smooth, uncoated metal surface to remove any effect of the surface roughness during this process. A one-point or two-point accuracy verification procedure can be performed (as described earlier for Type 1 gages).

Fig. 7: Verifying accuracy of Type 2 gage on a certified coated standard

Fig. 8: Verifying accuracy of Type 2 gage using a certified shim

Adjusting Type 2 GagesThe final step in the process is to adjust the gage on the surface to which the coating will be applied. Adjustment is accomplished by placing a certified or measured shim (or shims) onto the prepared, uncoated metal surface and adjusting the gage (when feasible) to compensate for substrate characteristics including (but not limited to) substrate metallurgy, geometry, thickness/thinness, and roughness (Fig. 9). The gage reading is adjusted to match the thickness of the shim, which effectively removes any influence from the underlying surface.

Fig. 9: Adjusting Type 2 gage using a measured shim on the surface to which the coating will be applied

This step sounds reasonably straightforward but poses several hidden challenges. First, once the surface is coated (for example, with a primer), an uncoated surface may no longer be available for subsequent gage adjustments, so the user may want to have a similar uncoated surface prepared and reserved for future gage adjustments on a given project. Naturally, this surface must be representative of the metallurgy, geometry, thickness/thinness, and roughness of the actual surface, which can be a challenging requirement.Second, some Type 2 gages cannot be adjusted. In such cases, the user will need to obtain BMRs from the prepared, uncoated substrate (described earlier for Type 1 gages). While many Type 2 (electronic) gages have a zero-set function, the gages should never be adjusted to zero unless the surface is smooth.Required Number of Coating Thickness MeasurementsThe section of SSPC-PA 2, Required Number of Measurements for Conformance to a Thickness Specification, causes many users confusion, which can result in either under- or over-inspection. Arguably the most critical section in the document, Section 8, describes how many areas to check, the size of the areas, the number of measurements to obtain in each area, and the steps to take if spot or area measurements do not conform to the specification.SSPC-PA 2 contains three definitions that are critical to understanding this next area of discussion. Gage Reading: A single instrument reading. Spot Measurement: The average of at least three gage readings made within a 4-cm (1.5-inch) diameter circle. Acquisition of more than three gage readings within a spot is permitted. Any unusually high or low gage readings that are not repeated consistently are discarded. The average of the acceptable gage readings is the spot measurement. Area Measurement: The average of five spot measurements obtained over each 10 m2(100 ft2) of coated surface, or increment (portion) thereof.An area is defined as approximately 100 square feet. Within each area, five randomly spaced spots are selected. Each spot consists of a 1.5-inch diameter circle. A minimum of three gage readings is obtained in each spot, culminating in a minimum of 15 gage readings within an area. Unusually high or low gage readings that cannot be repeated consistently are discarded. The average of the three acceptable gage readings is the spot measurement; the average of five spot measurements is the area measurement.Figure 10, from Appendix 1 in SSPC-PA 2, depicts an approximate 100-square-foot area containing gage readings and spot measurements.

Fig. 10: Approximate 100-square-foot area containing gage readings and spot measurements, as depicted in Appendix 1 of SSPC-PA 2. Courtesy of SSPC

The number of areas that must be measured for coating thickness varies, depending on the size of the coated area. There are three categories of coated area: less than 300 square feet; 300 to 1,000 square feet; and greater than 1,000 square feet. For areas containing less than 300 square feet of coated surface, every 100-square-foot area must be measured for coating thickness. For areas of coating 300 to 1,000 square feet, three random areas are selected and measured. For areas of coating exceeding 1,000 square feet, three random areas are selected from the first 1,000 square feet, along with one additional area for each additional 1,000 square feet.Because areas of coating often exceed 1,000 square feet, our example will be based on this third tier (>1,000 square feet). Lets assume that the total coated area (perhaps the area coated during a work shift, although SSPC-PA 2 does not equate coated area with work shift) is 12,500 square feet. A total of 15 areas must be measured (three in the first 1,000 square feet and one additional area in each of the 12 remaining 1,000-square-foot areas or portions thereof). This culminates in a total of 75 spot measurements (15 x 5) and a minimum of 225 gage readings (15 x 5 x 3). If spot measurement variances result in area measurements that do not meet the specification, then additional spot measurements are acquired (radiating outward in eight directions from the nonconforming area) to determine the magnitude of the non-conforming thickness. This process is described later in this article.Acceptability of Gage Readings, Spot Measurements, and Area MeasurementsWhile individual gage readings that are unusually high or low (and cannot be repeated consistently) can be discarded, there are limitations on the thickness values representing the spot measurements (the average of three gage readings). A minimum thickness and a maximum thickness are normally specified for each layer of coating. However, if a single thickness value is specified and the coating manufacturer does not provide a recommended range of thickness, then the minimum thickness and maximum thickness for each coating layer are established by SSPC-PA 2 at 20% of the stated value. For example, if the specification requires 3 mils DFT and the coating manufacturer does not provide any additional information regarding a recommended thickness range, then, by default, the specified range is established as 2.43.6 mils. Because the coating may not perform at the lower thickness, it is important for the specifier to indicate an acceptable range for each coating layer. To assist the specifier, the 2012 edition of SSPC-PA 2 incorporates a Restriction Level Table (Fig. 11). The Table enables the specifier to select from five different restriction levels related to spot and area measurements.

Fig. 11: Coating Thickness Restriction Levels (as shown inTable 1of SSPC-PA 2, Section 9)Courtesy of SSPC

Level 1 is the most restrictive and does not allow for any deviation of spot or area measurements from the specified minimum and maximum thickness, while Level 5 is the least restrictive. Depending on the coating type and the prevailing service environment, the specifier can select the DFT restriction level for a given project. The specifier may also invoke a maximum thickness threshold for Level 5 Spot or Area Measurements for a generic product type and/or service environment that will not tolerate an unlimited thickness. If no Restriction Level is specified, then the default is Level 3, which is based on the 2004 version of SSPC-PA 2 (what many users of the standard have become accustomed to).For the purpose of final acceptance of the total DFT, the cumulative thickness of all coating layers in each area must be no less than the cumulative minimum specified thickness and no greater than the cumulative maximum specified thickness.For example, assume that the specification requires a four- to six-mil application of primer. The actual minimum and maximum spot and area thickness requirements are shown inFig. 12for each of the five restriction levels.

Fig. 12: Coating Thickness Restriction Levels Based on a Four-to-Six-Mil RequirementDerived using the 2012 edition of SSPC-PA 2, Table 1, Coating Thickness Restriction Levels

Determining the Magnitude of Nonconforming ThicknessAnother change in the 2012 version of the standard is the procedure for identifying nonconforming areas (Fig. 13). In the 2004 edition, if spot or area measurements were out of conformance, each 100-square-foot area coated during the work shift had to be measured, and nonconforming areas had to be demarcated. On a larger structure with multiple applicators, the measurement and documentation process could be extensive, so the approach was changed in the 2012 revision. If a nonconforming area is identified, spot measurements are made at five-foot intervals in eight equally spaced directions radiating outward from the nonconforming area, as shown inFig. 13.

Fig. 13: Depiction of procedure for identifying nonconforming areas, as described in the 2012 edition of SSPC-PA 2.Courtesy of SSPC

If there is no place to measure in a given direction, then no measurement in that direction is necessary. Spot measurements are obtained in each direction (up to the maximum surface area coated during the work shift) until two consecutive conforming spot measurements are acquired in that direction, or until no additional measurements can be made. Acceptable spot measurements are defined by the minimum and maximum values in the contract documents. No allowance is made for variant spot measurements (for example, 20%), which is consistent with the practice followed when determining the area DFT.On complex structures or in other cases where making spot measurements at five-foot intervals is not practical, spot measurements are taken on repeating structural units or elements of structural units. This method is used when the largest dimension of the unit is less than 10 feet. Spot measurements are obtained on repeating structural units or elements of structural units until two consecutive units in each direction are conforming or until there are no more units to test.Non-compliant areas are demarcated using removable chalk (or another specified marking material) and documented. All of the area within five feet of any non-compliant spot measurement is considered non-compliant. For a given measurement direction or unit measurement, any compliant area or unit preceding a non-compliant area or unit is designated as suspect, and, as such, is subject to re-inspection after corrective measures are taken.Appendices to the StandardThere are eight appendices in the 2012 version of SSPC-PA 2. Two of the eight appendices were added in 2012 (the remaining were in the 2004 edition) and are highlighted below. The appendices to SSPC-PA 2 are not mandatory but may be invoked by contract documents.Appendix 6: Method for Measuring the Dry Film Thickness of Coatings on EdgesFor decades, the industry was cautioned about taking coating thickness measurements within one inch of an edge, let alone on an edge. However, several Type 2 (electronic) gage manufacturers offer a variety of probe configurations, some of which are less affected by proximity to edges and are designed to better measure the thickness of coatings on edges (Fig. 14). Obviously, the gage operator should consult the gage manufacturers instructions before measuring coating thickness on edges.

Fig. 14: One of a variety of Type 2 gage probe configurations designed to better measure DFT of coatings on edges

Before measuring coating thickness on edges, the user should verify the gage and probe for accuracy by placing a thin, flexible shim (certified or measured) onto the prepared, uncoated edge. Adjustments to the gage may or may not be required. This procedure also verifies that the probe configuration will accommodate the edge configuration before acquiring coating thickness data.Once verification of accuracy and adjustments are made, a minimum of three gage readings are taken within 1.5 linear inches of coated edge. The average of the gage readings is considered a spot measurement. The number of spot measurements along the edge will vary, depending on the total length of the coated edge.Appendix 7: Method for Measuring Dry Film Thickness on Coated Steel Pipe ExteriorAppendix 7 was added to accommodate pipe coaters that need to determine coating thickness conformance on non-flat (or non-plate) areas, including smaller pipe sections on a cart or rack and longer pipe spools.Pipe sections loaded onto a cart or rack can be considered a complete unit (Fig. 15). The total number of spot and area measurements is based on the total square footage of pipe on the cart or rack. The square footage is calculated as shown onp. 35.

Fig. 15: (top and bottom): Appendix 7 of the 2012 edition of SSPC-PA 2 describes a method for measuring DFT on non-flat steel, such as pipe sections that can be loaded on racks or carts. Photos courtesy of Turner Industries Group, L.L.C.

Some carts may have several small pipe sections, and the total coated surface may exceed 100 square feet. In this case, a Pipe DFT Frequency Factor shown below may be invoked. Pipe DFT Frequency Factor 2 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 2 Pipe DFT Frequency Factor 3 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 3 Pipe DFT Frequency Factor 4 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 4 Pipe DFT Frequency Factor 5 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 5 Pipe DFT Frequency Factor 6 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 6Based on the example above, if Pipe DFT Frequency Factor 4 was invoked, 20 spot measurements would be taken (5 spots x Frequency Factor 4)Pipe spools that are not loaded onto a rack or cart are typically measured individually (Fig. 16). The number and locations of spot measurements are based on Appendix 7s Table A7 (Fig. 17). Three sets of four circumferential spot measurements should be obtained on pipe spools less than 10 feet in length.

Fig. 16: DFT of pipe spools not loaded on cart or rack are typically measured individually.

Fig. 17: Number and Locations of Spot MeasurementsPipe Spools (Table A7 from 2012 edition of SSPC-PA 2, Appendix 7)Courtesy of SSPC

ConclusionSSPC-PA 2 has undergone significant changes in an attempt to make it more complete; more in concert with ASTM D7091; easier to use in the shop and field; and more flexible in providing the specifier with options for coating thickness restrictions based on the type of structure, the coatings to be applied, and the service environment. SSPC-PA 2 and ASTM D7091 are both undergoing additional technical and editorial changes to bring them into even greater alignment with one another.Get the Latest Standards on Dry Film Thickness of CoatingsThe 2012 edition of SSPC-PA 2, Procedure for Determining Conformance to Dry Coating Thickness Requirements, is available from the SSPC: The Society for Protective Coatings throughsspc.org, under the Standards tab at the top of the home page.The 2012 edition of ASTM D7091, Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to NonFerrous Metals, is available from ASTM International throughastm.orgunder the Standards at the top of the navigation bar on the site.

Change is never easy. Communicating the new requirements of this standard to the industry is challenging but essential. One conduit is through training and education. For example, SSPC offers a short course, Using SSPC-PA 2 Effectively, that was recently updated to reflect changes made to the standard. Free webinars are available through SSPC/JPCLfor those who cannot participate in instructor-led training. Updates to SSPC and other industry-provided inspector training and certification courses (and the associated instructor education) will be critical to fully understanding and effectively communicating the requirements of this highly regarded industry standard.The Journal Of Protective Coatings & Linings2013 Technology Publishing Comp

6.Testing the cure of IOZFromJPCL,April 2013Is the MEK rub test a conclusive test to check the cure of inorganic zinc coatings?From Rob Francis ConsultantThe solvent rub test for cure of ethyl silicate inorganic zinc (IOZ) coatings, as described in ASTM D4752, is the accepted test for checking if such a coating is cured. This is especially critical before overcoating, but even a single coat system can dry without curing if applied under low humidity conditions. Other tests that are used include scraping with the edge of a coin (the Quarter test in the USA) or simply a fingernail. If significant zinc powder is produced with either test, the coating is considered uncured. However, these tests are considered more subjective than the solvent rub test.An uncured coating will result in considerable zinc removal with a few double rubs, while a cured coating will be little affected with the 50 double rubs required. It should be noted that even a fully cured coating will show some zinc discoloration on the white rag. While as with any test, it may be possible to get ambiguous results, this test, in most situations, will be definitive, and certainly superior to any other simple field test. If there is any doubt regarding the cure, leave the coating (if the humidity is high enough) or water mist it and retest.From Simon Hope BIS Salamis (M&I)The MEK rub test is only subjective as proof of cure for IOZ coatings. The test is only valid for the actual area tested and can be applied to the whole item only by extrapolation of the result.Confidence in the result can vary wildly, depending on time, humidity, and temperature, because the curing mechanism of IOZ is totally dependent on the integration of water into the silicate precursor to create the matrix to support the metallic zinc. Hence, the best advice is that once touch dry, fresh water washing enhances the cure mechanism. High humidity and water washing will give confidence, and MEK rub then gives verification.From Gary Hall ConsultantI am answering the question about the MEK test as it relates to testing a coating in the field.The ASTM test method that pertains to measuring cure of inorganic zinc coatings/primers by solvent resistance is ASTM D4752, Standard Practice for Measuring MEK Resistance of Ethyl Silicate (Inorganic) Zinc-Rich Primers by Solvent Rub. This method has been shown to correlate well with the results obtained with an analytical chemical test called diffuse reflectance infrared spectroscopy, by which the degree of cure of inorganic zinc (IOZ) primers can be accurately determined. It should be noted that the results of D4752 might not indicate when full cure has been achieved because the coating may become resistant to MEK before full cure occurs.A hardness test may also be used if the coating manufacturer can provide the appropriate hardness data. One such test is ASTM D2240, which uses a Shore durometer. The Shore durometer test gives the amount of indentation made by a specific needle. Because the ASTM D2240 test will deform the coating surface under the needle, this type of test is best performed on a companion piece of substrate coated and cured in the same manner as the coating on the substrate on the actual project.Problem Solving Forum questions and answers are published inJPCLand its sister daily electronic publication,PaintSquare News. Upcoming questions inJPCLinclude the following. Whose responsibility is safety on a bridge coating site? If an inorganic zinc (IOZ) coating has not fully cured because of low humidity, can water be sprayed onto the IOZ-coated surface to accelerate the cure? What action should be taken if an inorganic zinc coating fails the MEK (methyl ethyl ketone) rub test? What causes amine blush in epoxy topcoats? Do water treatment processes to stop the transfer of invasive marine species in ballast water affect the performance of ballast tank coatings? How soon does metallizing need to be sealed after it is applied to concrete on bridges?Responses toJPCLquestions can be submitted tokkapsanis@paintsquare.com. Readers may also propose questions.Readers can also respond to PSF questions posted onPaintSquare Newsand can propose questions onPaintSquare Newsatpaintsquare.com/psf.

7. Basics of corrosion of steel for applicatorsFromJPCL,January 2013JoePikasA good coating job requires the right steps to be performed to achieve the protection needed. It is important to know why things are done, as well as how the various steps are performed. A primary reason for using protective coatings is corrosion protection.For the purposes of this series, corrosion of steel is defined as the destruction of steel by an electrochemical process that is characterized or recognized by the formation of rust or pits. To understand how protective coatings protect a steel surface, the nature of corrosion must be understood why it occurs and how it can be prevented.Steel is manufactured by taking the mined ore and adding a large amount of energy to it in the blast furnace. This produces an unstable metal. Nature does not like all that energy stored in the steel. So upon exposure to the atmosphere, especially moisture and oxygen, this energy is released, and the iron returns to its natural stable stateiron ore. Rust, therefore, is nothing more than a pure form of iron ore (oxides). Protection of steel from corrosion involves methods to retard this natural release of energy (Fig. 1).

Fig. 1: One approach to slowing the natural corrosion of steel and appearance of rust is the use of protective coatings.Courtesy ofJPCL

To understand how coatings protect steel, we must understand the four conditions required for corrosion to occur. Unless all four of these conditions are present, corrosion will not occur. These four conditions are: a positive pole (a cathode), a negative pole (an anode), an electrical conductor, and an electrolyte.The terms anode and cathode have technical definitions in electrochemistry, but for our purposes, we will use them to refer to areas on a substrate or materials of different electrical potentials. The electrical conductor is a means of conducting electricity, similar to the copper wiring in your house. An electrolyte is a liquid solution (usually water) that also can conduct electricity.To help illustrate these terms and how corrosion happens, lets look at the dry cell (battery). A battery represents a beneficial use of corrosion, though the process is the same as corrosion that occurs with steel.A battery has two terminals. Typically, one is connected to a carbon rod running down the center of the battery, while the other is connected to the outer casing, which is made of zinc. These are the two dissimilar materials of different electrical potential, which serve as cathode and anode. If you have ever taken a battery apart, you would have seen that there is a pasty material between the casing and the carbon rod. This substance is the electrolyte.If you wanted to use the battery, you would connect the wires to something such as a flashlight. The wires are the electrical conductor. Once the wires are connected, the flashlight will keep on glowing until the battery has become corroded. In the battery, it is actually the zinc casing that is consumed and corroded.How does this example of a battery relate to corrosion of steel? You would see that steel is not a smooth, uniform material if you looked at it under high magnification (Fig. 2). It actually consists of very small grains or grain boundaries. This means that steel has spots on it with slightly different electrical potentials.

Fig. 2: Peaks and valleys of profiled clean steelCourtesy of KTA-Tator

Adding stresses to the steel also creates areas of different electrical potential. This normally occurs by such processes as differential heating of the steel during treatment, bending or cutting the steel, or even hitting it with a hammer. Any of these processes adds small amounts of energy to the steel. So by its very nature, steel contains spots of different electrical potential, or anodes and cathodes.What about the electrical conductor? This was the wire in the example of the battery.Does steel conduct electrical current? It certainly does, so wires are not needed. As you can see from this explanation, steel contains anodes and cathodes, and is an electrical conductor. It already contains three of the four conditions necessary for corrosion.The fourth condition needed is the electrolyte or liquid that can conduct electricity. Where does it come from? Normally, atmospheric moisture that condenses on the surface serves as an electrolyte. It can be in the form of rain, dew, or simply humidity in the air. Some structures either are used to hold water or are used in water. They are constantly exposed to an electrolyte.Our atmosphere is laden with moisture at all times, even in desert areas, although to a esser degree. Most steel surfaces are exposed to dew at night and water vapor during the daytime hours in addition to the normal rainfall. In highly industrial areas such as Houston, Los Angeles, and New York, airborne chemical contaminants contain substances called ions.The point to be made is that steel (like most other manufactured metals) contains three of the four conditions needed for corrosion. The most common way to slow down corrosion is to isolate the steel from the electrolyte. Therefore, the major function of the coating is to keep moisture off the steel. Some coatings, such as zinc primers, perform other functions, which will be discussed in subsequent Bulletins.There are a few common forms of corrosion that a painter will see regularly: general corrosion, galvanic corrosion, pitting corrosion, and crevice corrosion. General corrosion takes place fairly evenly over the metal. Usually, it begins as spots or freckles and becomes progressively worse.Galvanic corrosion occurs when dissimilar metals are in contact. The more active metal (the anode) corrodes to protect the less active metal (the cathode). For example, if a brass valve were connected to a steel pipe, the steel would corrode to protect the brass. The steel at the fitting would be consumed rather quickly, first appearing as a thinning of the metal and ultimately resulting in penetration. Another example of galvanic corrosion is mill scale on steel. Steel is more active than mill scale, so when corrosion conditions are present, the steel will corrode to protect the mill scale.Pitting corrosion occurs when the corrosion forces are concentrated in a small area. Metal loss is into the steel rather than over the surface. The rust pits that form have serious consequences because the pits represent metal section loss. This can result in perforation if the structure is a tank or a vessel, and loss of structural integrity no matter what the structure is.Crevice corrosion (Fig. 3) is another common form seen on structures, and occurs when there is a small space between structural elements, be they metal-to-metal or metal-to-non-metal. Examples of places where crevice corrosion can occur are back-to-back angles, where steel plates overlap, around rivets and bolts, near tack welds, and any other place where a small opening is present. What happens is that moisture gets into the crack and completes the corrosion circuit. The moisture gets trapped in the crevice and accelerates the corrosion compared to the surrounding area. The corrosion reactions are greatest at the bottom of the crevice, so metal loss is concentrated in that area.

Fig. 3: Severe corrosion is seen at a weld seam.Courtesy of KTA-Tator

There are many other forms of corrosion that a painter may see, including microbiologically influenced corrosion (deep isolated pitting as shown inFig. 4), cavitation corrosion, or erosion corrosion, to name a few. In most of these cases, the corrosion reaction is accelerated by another factor beyond the general corrosion reaction explained above.

Fig. 4: Microbiologically influenced corrosion on piece of steel pipeCourtesy of the author

To stop corrosion, all that is needed is to eliminate one of the factors that produce the reaction. It is impossible to eliminate the environment, and it is cost-prohibitive to make steels that corrode at a slow rate. Therefore, coatings are often used to prevent corrosion by eliminating contact between the environment (electrolyte) and the steel substrate. Coatings are therefore a barrier material.A coating may also be applied to enhance appearance. However, to protect against corrosion for a period of time, it is necessary for coatings to possess features that make them effective barriers.By isolating steel from the electrolyte, a good protective coating can prevent corrosion for extended periods of time. The better the application, the longer the coating will serve its useful purpose.On the other hand, a poor coating job may lead to the expense of premature failure, which requires reblasting and recoating. On large projects, such premature failure can cost hundreds of thousands of dollars or more. Good coating work can also save steel structures from unnecessary and costly deterioration. It is estimated that the cost of corrosion in the U.S. each year runs in the billions of dollars. Your work as an applicator can help significantly to reduce these losses.Upcoming Applicator Training BulletinsThe following are among the upcoming Applicator Training Bulletins.Basics of Corrosion and Coatings How Coatings Protect Steel Basics of Concrete Deterioration for Applicators How Coatings Protect ConcreteSurface Preparation Why Surface Preparation Is Important Introduction to Surface Preparation of Concrete Mechanical Methods of Preparing Concrete Chemical Cleaning of Concrete Power Tool Cleaning for Steel Using Paint Strippers on Steel and Concrete Setting Up Air Abrasive Blasting Systems Techniques of Air Abrasive Blasting Containing Dust and Debris during Air Abrasive Blasting Setting Up and Operating Wet Blasting Equipment Using High Pressure WaterjettingApplication Product and Application Data Sheets Mixing and Thinning Paint Basic Training in Brush and Roller Application The Basics of Conventional Air Spraying Using High Volume, Low Pressure Spray Equipment Using Airless Spray Equipment Introduction to Plural Component Spraying Applying Two-Pack Epoxies and Polyurethanes Applying Zinc-Rich Coatings Applying Water-Borne Coatings Applying High Solids Coatings Applying Polyureas Applying Floor Coatings and Toppings Special Concerns about Applying Coatings in the ShopQuality Control The Effects of Weather on Cleaning and Coating Work Conforming with Job Requirements Records of Work and Working Conditions Why Good Housekeeping Is Important Assessing Surface Cleanliness and Profile Assuring Quality during Abrasive Blasting Assessing Quality of Wet Methods of Surface Preparation Computing Film Thickness and Coverage Measuring Dry Film Thickness Measuring Adhesion of Coatings Recognizing and Correcting Paint Application Deficiencies Quality Control in Coating ConcreteSafety and Health Safety Considerations for Abrasive Blasting Anticipating Job Hazards Respiratory Protection: Hazards and Equipment Fit Testing Procedures for Respirators Job Hazards during Climbing and High Work An Introduction to Confined Spaces Identifying and Controlling Job Hazards When Working around High Voltage Using Lighting Safely Protection against Worker Exposures during Hazardous Paint Removal Safety for Applicators Working near Process Equipment Safety with Solvents and Paint Strippers Where To Get Help in Safety and HealthEditors Note:This article marks the return of JPCLs Applicator Training Bulletin, a series first published from 1988 to 1992. The series was intended to help industrial contractor firms train blasters and painters. The original series was developed and written by the Coatings Society of the Houston Area in collaboration with SSPC, and Lloyd Smith edited it. The series was subsequently collected in one volume. From 1992 to 1993, a separate series on safety was developed and written under the direction of KTA-Tator. In 1997, the series was updated and expanded. Beginning this month, the series will again cover the basics of corrosion, surface preparation, application, quality control, and safety. The series will be updated and expanded where necessary. Because the basic theory of corrosion, how coatings protect steel, and the importance of surface preparation have changed little since 1988, some of the original articles will also appear with minor revisions, including this first one on what applicators need to know about corrosion. Written by Joe Pikas, with Transco Corporation at the time, the article was first published in the July 1988 JPCL, then updated and re-published in the April 1997JPCL.

8. Can in-process QC prevent premature coating failures?FromJPCL,January 2013

William D. Corbett, PCS, KTA-Tator, Inc.

PCS, KTA-Tator, Inc.Bill Corbett is the Professional Services Business Unit Manager for KTA-Tator, Inc., where he has been employed for 31 years. He is an SSPC-approved instructor for three SSPC courses, and he holds SSPC certifications as a Protective Coatings Specialist, Protective Coatings Inspector, and Bridge Coatings Inspector. He is also a NACE Level 3-certified Coatings Inspector. He was the co-recipient of the SSPC 1992 Outstanding Publication Award, co-recipient of the 2001JPCLEditors Award, recipient of SSPCs 2006 Coatings Education Award, and recipient of SSPCs 2011 John D. Keane Award of Merit.RichardBurgessSeries Editor, KTA-Tator, Inc.For decades we have heard that the incidence of premature coating failure would decline by explicitly requiring the contractor to control the quality of workmanship (via contract document language) using properly trained (and equipped) quality control personnel. In this Case from the F-Files, well take a brief look at five case history failures and assess whether quality control inspection of the work as it proceeded could have prevented the failure from occurring, or whether it would have happened despite the efforts of knowledgeable quality control personnel.Defining Quality ControlThe ISO definition states that quality control is the operational techniques and activities that are used to fulfill requirements for quality.1 This definition could imply that any activity, whether serving the improvement, control, management, or assurance of quality could be a quality control activity. Quality control is a process for maintaining standards and not for creating them. Standards are maintained through a process of selection, measurement, and correction of work, so only the products or services that emerge from the process meet the standards. In simple terms, quality control prevents undesirable changes in the quality of the product or service supplied. The simplest form of quality control is illustrated inFig. 1. Quality control can be applied to particular products; to processes that create the products; or to the output of the whole organization, by measuring its overall quality performance.

Fig. 1: The generic control processFigure and photos courtesy of KTA-Tator

Quality control is often regarded as a post-event activity, that is, a means of detecting whether quality has been achieved and taking action to correct any deficiencies. However, one can control results by installing sensors (e.g., inspection check points) before, during, or after the results are created. It all depends on where you install the sensor, what you measure, and the consequences of failure.1The Joint Certification Standard for Shop Application of Complex Protective Coating Systems (AISC SPE/SSPC-QP 3 420-10) defines quality control as the inspection of work. Inspection includes but is not limited to confirming that procedures are met; workers are properly qualified; equipment is appropriate and in acceptable working order; and the proper materials are used and are in compliance with inspection criteria.Lets take a look at a few case studies to see whether implementation of a quality control program using trained, properly equipped inspectors makes a difference.Case Study No. 1:Mirror, MirrorBackground:A contract was awarded to remove and replace the existing coating system on a large riveted structure. The specification required abrasive blast cleaning to achieve a Near-White blast (SSPC-SP 10/NACE 2), followed by two coats of a polyamide epoxy (standard gray) and one coat of polyurethane topcoat. Six months after the contract was completed, corrosion was observed (Fig. 2).

Fig. 2: Corrosion products on the back sides of the rivets and edges after six months service

Cause:Corrosion products remained on the back side of the rivets that were not subjected to direct impact by the abrasive stream during blast cleaning. The coating was also applied from one direction, causing thin areas of coating on the back side of the rivets and the adjacent flat areas of the steel plate. Inadequate attention was given to the coating along the edges.Avoidance Through Quality Control Inspection?The QC inspector should have carefully examined the difficult access areas after surface preparation and application of each coating layer