Presentation on theme: "Quality Control of Industrial Painting Operations"— Presentation transcript:
1 Quality Control of Industrial Painting Operations William D. CorbettKTA-Tator, Inc.This one-hour webinar describes the various procedures and instrumentation for controlling the quality of industrial painting operations.
2 Webinar Content Industry standards for coating application QC Developing a quality control plan for paintingNavigating a Technical (Product) Data SheetMeasuring ambient conditions and surface temperatureWitnessing mixing, thinning and application proceduresCalculation and measurement of wet film thicknessDry film thickness measurementPost-application testingCure/hardnessHoliday/pinhole detectionAdhesionIdentifying application defectsDuring this webinar, I will overview the industry standards commonly associated with quality control of coating application operations, including (list from slide)
3 Learning Objectives/Outcomes Completion of this webinar will enable the participant to:Describe the industry standards that pertain to coating applicationPrepare a Quality Control Plan for paintingDescribe the content of a Technical (Product) Data SheetMeasure environmental conditions and surface temperature prior to coating mixingEvaluate mixing, thinning and application proceduresCalculate and measure wet film thicknessMeasure dry film thicknessPerform post-application testingThere are eight learning outcomes or objectives for this webinar. Completing this webinar will enable you to:Describe the industry standards that pertain to coating applicationPrepare a Quality Control Plan for paintingDocument environmental conditions and surface temperature prior to coating mixingEvaluate mixing, thinning and application proceduresCalculate and measure wet film thicknessMeasure dry film thicknessPerform post-application testing, including cure and hardness evaluations, pinhole & holiday detection, adhesion and identification of coating film defects
4 Industry Standards for Coating Application SSPC-PA 1 Shop, Field and Maintenance Painting of SteelSSPC-PA 2 (frequency and tolerance of coating thickness measurements on steel)SSPC-PA 9 (frequency and tolerance of coating thickness measurements on concrete)ASTM E337 (use of whirling/aspirating psychrometers)ASTM D4414 (wet film thickness measurement)ASTM D7091/D6132 (dry film thickness measurement)ASTM D5402/D4752/D3363/D1640 (drying, curing, hardness)ASTM D5162/D4787 (holiday/pinhole detection)ASTM D3359/D6677/D4541/D7234 (adhesion)There are nine areas of quality control of coating application operations that have associated industry standards. These are listed on the slide. Note that three areas have multiple standards.SSPC PA 1 and PA 2 will be described in detail later in this webinar. SSPC PA9 describes a procedure for measuring coating thickness on concrete, and is used in conjunction with ASTM D6132.There are many ASTM standard test methods and practices that are invoked in project specifications related to quality control of painting operations, including use of psychrometers and wet film and dry film thickness gages, as well as assessing drying or curing properties, hardness, continuity and adhesion.
5 SSPC Paint Application Specification No. 1 (PA 1) Shop, Field and Maintenance Painting of SteelCommon specification referenceContains 14 Sections:Scope Shop CoatingDescription Field CoatingReferenced Standards Repair of Damaged CoatingsDefinitions Appl. Proc. For CoatingsPre-application Procedures Curing & HandlingFactors Affecting Application InspectionApplication Methods Safety & EnvironmentalSSPC Paint Application Standard No. 1 or PA1 covers procedures for the painting of steel surfaces, which is why you may see it referenced a lot in painting specifications. The scope of PA1 is rather broad, covering both specific as well as general requirements for the application of paint. It provides detailed coverage of the procedures and methods for application once the selection of the coating materials has been made. PA 1 is intended to be used for steel which will be subjected to corrosive attack, either from the weather or from the service environment, and where a high quality of cleaning and painting is essential. The standard contains 14 sections including those listed on the slide.
6 Purpose of a Quality Control Plan Provides QC Inspector with:A systematic inspection and testing plan that covers all phases of work in sequenceA written document that lists what to inspect, how to inspect and the acceptance criteriaA tool to enable an inspector to navigate through and extract inspection check points from the specificationMay be a required contract submittalHere’s a question: Why should a contractor prepare quality control plan, when all of the inspection requirements and acceptance criteria are already described in the specification?A thorough, well-organized quality control plan is a systematic tool that covers each phase of work in the general sequence in which it will likely be performed.In general, quality control plan is a written document that lists what must be inspected, how it is to be inspected and the acceptance criteria from the specification. Coating specifications are often complex documents and can describe both technical and legal or contractual requirements. The process of developing quality control plan provides the contractor with an opportunity to carefully navigate through the contract, extract the inspection check points and transfer them to a separate chart that can be referenced throughout the project to clearly understand and communicate the quality requirements of the specification.Some specifications require the contractor to develop a Work Plan and a Process Control Plan or PCP. The quality control plan is a component to the process control plan. These items are considered “submittals” and oftentimes must be submitted and approved before production operations are allowed to begin.
7 Benefits of a Quality Control Plan Coating specifications can be complex documentsSpecifications typically contain the quality requirements for a coatings projectGood inspection doesn’t happen by accident; it requires planningQC plans make specification compliance more streamlined and completeProvides a key communication tool between QA and QC inspection personnelCoating specifications can be very complex documents containing multiple parts, sections and items. The quality requirements for a coatings project are oftentimes contained in the Execution component of the specification, but may be scattered in other parts or sections as well.Quality doesn’t happen by accident. One of the many keys to quality inspection is careful planning, so that each check point is properly inspected using the techniques, instruments, standards, guides and test methods established by the industry to verify the adequacy of the work before proceeding to the next step.The development of a well-organized, thorough quality control plan prior to production activities commencing can help to verify that each of the specification requirements is being inspected. It is a key communication tool between contractor and facility owner that clarifies what will be inspected, how and when the inspection will take place and the quality requirements of the specification.
8 Sample Quality Control Plan Inspection ItemTechnique/InstrumentFrequency of TestsStandard Test Method ReferenceSpec.Reference(mock)AcceptanceCriteriaVerify ambient conditionsElectronic psychrometerBefore mixing and every 4 hours; changing conditionsSSPC-PA 13.4.1Air: °FSurface: °FRH: <85%ST > 5°F DPVerify installation of protective coveringsVisualPrior to primer application3.4.2Properly installed & maintainedDry Film Thickness of PrimerCalibrated Type 2 gage verified for accuracyArea coated during the previous work shift, per SSPC PA2ASTM D 7091SSPC-PA23.4.73-5 milsHoliday DetectionLow voltage wet sponge detectorAfter topcoat applicationASTM D51623.4.10No pinholes or holidaysThis slide illustrates a portion of a quality control plan using a 6-column format. (GO THROUGH EXAMPLE OF 3rd ROW - DFT)
9 Product Data Sheets Prepared by the coating manufacturer An “instruction manual” for the coatingTechnical & marketing information about the coatingASTM F 718 provides a standard specification for marine paintsProduct data sheets or technical data sheets are prepared by the manufacturer of the coating. It should be considered an instruction manual for how to properly store, mix, thin, apply and cure the coating. These data sheets typically contain both technical data and marketing information which is used to sell product. Once the product is selected for use, the technical data is most important. Data sheets change as products modifications are made or as necessary. Coating manufacturer’s websites typically contain the latest version, and most manufacturer’s indicate the date of the latest version on the datasheet itself.ASTM F718 is a Standard Specification for Shipbuilders and Marine Paints and Coatings Product or Procedure Data Sheet. However, since an ASTM standard is not a regulation, coating manufacturers can place anything they want, anywhere they want. That is, there is no standard format or content for a data sheet.
10 Product Data Sheets, con’t. Typically contain:Brand name of the productGeneric type of the coatingWhen/where the coating can be usedCompatible coatingsProduct weight and volume solids contentTheoretical coverage rateCoating manufacturer’s product data sheets typically contain the brand name of the product and the product number, the generic type of coating, information on when and where the coating can be used, what products in the manufacturer’s line that it is compatible with, the weight and volume solids content of the mixed product and the number of square feet that one gallon will cover, based on the recommended thickness and volume solids content. The coverage rate typically does not address mixing and application losses or the effect of surface roughness on the primer coverage rate. These must be considered based on experience.
11 Product Data Sheets, con’t. Often contain:Recommended level(s) of surface preparationRecommended dry film thicknessVOC content of the coating (as manufactured)Adjusted VOC content dependant on amount and type of thinnerPerformance data (adhesion, abrasion resistance, etc.)Recommended methods of applicationMixing and thinning instructionsPot life, induction timeDrying times (dry to handle, dry to recoat)Cure timesRecoat timesMethod to verify cureProducts data sheets will often describe the recommended levels of surface preparation, dry film thickness, VOC content of the coating both as manufactured and when reduced, based on the type and amount of thinner added. Product performance data may be listed, and may be useful to those comparing manufacturers products.Coating applicators and quality control personnel will find recommended methods of application, mixing and thinning instructions, potlife, induction time, minimum and maximum drying or cure times, recoat times and methods that can be used to verify that the coating has cured.
12 Product Data Sheets Vs. Specification Requirements Product data sheets contain recommendationsWhen the PDS and the project specification differ, the specification is the governing document (contract)The specification may invoke the PDSQC inspector should note discrepancies/vague information and advise the owner at the bidding stage and at the pre-job meetingProduct data sheets cover a wide range of industries where the coating may be used. Therefore, most contain recommendations for the specification writer. When the information on a data sheet differs from the specification, you need to remember that the specification is the contract, not the data sheet. Occasionally the specification will invoke the information on the data sheet, so then it becomes part of the contract. The quality control inspector should note any such discrepancies or vague information so that the issues can be resolved pre-production.For example, the data sheet may recommend 4-6 mils thickness for mild environments and 8-10 mils for severe exposures. Without clear direction from the specification, the contractor has to assess the service environment and decide whether it is mild or severe. This is something that the owner should decide, not the contractor.
13 Environmental Conditions for Coating Application Air Temperature (min. & max.)Relative Humidity (min. or max)Dew Point TemperatureSurface Temperature [min.5 °F (3°C)] above Dew Point TemperatureWind Speed (max.)Achieving environmental conditions that conform to the specification and the manufacturer’s requirements is critical before mixing and during coating application. The project specification or the coating manufacturers product data sheet may invoke a minimum and maximum air temperature; a minimum or a maximum humidity, and a minimum and maximum surface temperature. Additionally, there may be a requirement for the surface temperature be a minimum of 5 degrees Fahrenheit or 3 degrees Celsius higher than the dew point temperature for coating work to begin or to continue. That is, there will not be a minimum or maximum dew point temperature restriction – only a requirement for the surface temperature to be higher than the dew point temperature. Finally, the project specification may invoke a maximum wind speed.
14 Significance of Conditions Air TemperatureToo cold or too hot can affect coating application & curingRelative HumidityToo damp or too dry can affect coating application & curingSurface TemperatureToo cold or too hot can affect application & curingSurface temperature at or below dew point temperature will result in condensationIf the air and surface temperatures are too hot or too cold, the coating application and curing processes may be adversely impacted. A high humidity or cold, damp conditions can cause an epoxy to form an exudate or blush on the surface, and high humidity can cause a urethane coating to down gloss during curing. Conversely, the curing process of a moisture-cure coating can be inhibited when there is insufficient humidity in the air.A surface temperature at or below the dew point temperature can result in surface condensation which may or may not be visible.
15 Significance of Conditions, con’t. Wind SpeedToo windy can affect application (dry spray) and cause overspray damageMixing/application of coatings under adverse weather conditions can void the manufacturer’s warranty and is considered a specification non-conformanceExcessive wind speed can cause the coating to dry during the atomization process, creating dry spray, and there is a potential for overspray damage to adjacent property or vehicles.Mixing and application of coatings under adverse weather conditions may void the coating manufacturers warranty and is considered a non-conformance if the specification invokes minimum and maximum temperatures, humidity or the requirement for a minimum increase of surface temperature over dew point temperature. Perhaps most importantly, it may result in a reduced service life of the coating system or catastrophic coating failure.
16 Ambient Conditions & Surface Temperature Measuring InstrumentsSling Psychrometers*Battery-powered Psychrometers*Electronic PsychrometersAnalog, Thermocouple-type & Non-contact Surface ThermometersInstruments used to measure the prevailing environmental conditions and surface temperature include sling and battery-powered psychrometers, electronic psychrometers, and surface temperature thermometers, which can be analog, thermocouple or non-contact infrared type. Sling and battery-powered psychrometers that measure dry and wet bulb temperatures are used in conjunction with psychrometric charts or calculators to determine the relative humidity and dew point temperatures.* Used in conjunction with psychrometric charts or calculators
17 The sling psychrometer consists of a housing containing two bulb thermometers. The thermometers are identical, except that one contains a woven cotton filament or wick over one end. Since this wick will become saturated with water, we refer to this as the wet bulb thermometer. The other thermometer indicates the air temperature and is called the dry bulb thermometer. The thermometers are available in Fahrenheit or Celsius and are available from several manufacturers.Sling Psychrometer
18 Using Sling Psychrometers ASTM E337Verify wick cleanlinessSaturate wick and/or fill reservoir with DI waterWhirl second intervals until wet bulb stabilizes (2 readings within 0.5o)Record wet & dry bulb temperaturesThe sling psychrometer is ventilated by a whirling action. The standard governing the use of these types of instruments is ASTM E 337, which is the standard test method for measuring humidity with a psychrometer.To use the sling psychrometer, verify that the wick is clean. If it is dirty the pores may be clogged, preventing water contact with the bulb. Additional wick is provided in the capped reservoir on the end the device, and replacement wick can be purchased.Saturate the wick with deionized or distilled water, or fill the reservoir with the water. Verify the wick is thoroughly saturated, not just dampened. Whirl the instrument through the air, away from the body, at a rapid speed for 20 to 30 seconds, then stop and read the temperature of the wet bulb. Without rewetting the wick, whirl the instrument for an additional 20 to 30 seconds and take a second reading of the wet bulb thermometer. Repeat this process until two readings of the wet bulb thermometer are within one-half degree of one another, indicating that the wet bulb has stabilized at the lowest point. Read the temperature from the dry bulb thermometer last. Record the readings of the dry bulb and wet bulb thermometers.
19 Using Psychrometric Charts Locate Chart (relative humidity or dew point)Verify Barometric Pressure (e.g., 30.0 in.)Intersect air temperature with wet bulb depression (Ta-Tw)Calculators (bottom image) can also be usedThe relative humidity and dew point temperature can be determined using psychrometric charts or calculators. The United States Weather Bureau published a book of relative humidity and dew point temperature look-up tables in the early 1900’s. These are still used today. There are three steps to take when using these charts. First, locate the desired chart, relative humidity or dew point temperature. Second, select the chart based on the prevailing barometric pressure, typically 30 inches.Intersect the dry bulb or air temperature with the difference between the dry and wet bulb temperatures, known as the depression of the wet bulb or Ta minus Tw, to determine the relative humidity or dew point temperature.
20 Electronic Psychrometers Measure/Record:Air TemperatureSurface Temperature (ST)Relative HumidityDew Point Temperature (DP)Spread betweenDP and STFeaturesAuto-logging allows for automatic data collectionMagnetic surface probeData graphing and Blue Tooth uploadingAudio/visual alarmElectronic psychrometers are a welcome alternative to sling and battery-powered psychrometers. These devices do not use wet bulb temperature to determine relative humidity and dew point temperature and therefore do not require water. Once powered-up and allowed to stabilize for a few minutes, the air and surface temperatures, relative humidity and dew point temperature are all displayed. Most of these devices calculate the spread between the dew point and surface temperatures. Depending on the manufacturer and model, automatic data collection, even surface temperature using a magnetic holder is possible. Data graphing and uploading is possible using software and some devices can be programmed to alarm if conditions are outside of the specified parameters.
21 Measuring Surface Temperature Dial-Type ThermometerPosition & stabilize for minimum of 2 minutesThermocouple-Type ThermometersStabilize quicklyInfrared (non-contact) thermometersWatch distanceWhen sling or battery-powered psychrometers are used, the surface temperature must be measured using a separate thermometer. The surface temperature can be measured using dial-type thermometers shown in the top image, thermocouple type thermometers like the one shown in the left image and non-contact infrared thermometers like the one shown in the bottom right image. Dial type thermometers will need to stabilize for at least two minutes before they are read and the distance the non-contact thermometer is held from the surface should conform to the capability of the device.
22 Assessing Wind Speed Analog wind meters Digital wind meters Rotating Vane AnemometersAir flow inside containmentWind speedIf the project specification invokes a maximum wind speed, then a wind meter will need to be used. Analog wind meters are inexpensive but are typically more difficult to use than the digital wind meters. Rotating vane anemometers that are used to measure air flow inside containment can also be used to measure wind speed. While air flow inside containment is typically measured in terms of feet per minute, many anemometers can also display air movement in miles per hour, or kilometers per hour, which are better values to use relating to measurement of wind speed.
23 Documenting Ambient Conditions and Surface Temperature DataDate2/15/12Time0900 hoursDry Bulb Temperature (DB)16oC (60oF)Wet Bulb Temperature (WB)13oC (55oF)Depression (DB-WB)3oC (5oF)Relative Humidity73%Dew Point Temperature11oC (51oF)Surface Temperature15oC (59oF)Wind Speed11 km/Hr (7 mph)Measurement LocationWest side of tank, ground levelDocumentation of environmental conditions and surface temperature is very important. While electronic psychrometers have the capability of storing and uploading the data for reporting, other devices will require you to document the values. An example of the type of information that is typically documented is shown on the slide.
24 Significance of 5°F (3°C) Theoretically, a small (<1°F) increase (surface temperature over dew point) will preclude moisture formationMinimum increase of 5°F (3°C) compensates for:Instrument tolerancesVarying conditionsChanging conditionsTheoretically a slight increase in surface temperature over dew point temperature, even 1 degree, will prevent moisture in the air from condensing on the surface. However the industry has adopted a general rule that the surface temperature should be atleast 5 degrees Fahrenheit or 3 degrees Celsius above the dew point temperature, and rising, to account for instrument tolerances as well as changing conditions and varying conditions across the surface. Specifications may deviate from this general rule and may require a greater difference for critical environments, while other specifications may allow a smaller difference.
25 Location and Frequency of Data Acquisition Dictated by where the work is being performed (e.g., inside vs. outside of a containment; balcony of elevated storage tank vs. ground level)If interior, with ventilation in operationShops: Blast or Paint bay areaFrequencyPrior to mixing of coatingsFour-hour data collection intervals is commonMore frequent measurement if conditions are changingAmbient conditions and surface temperature data should be acquired where the work is to occur, not where it is convenient like stepping outside the project office. Conditions should be assessed prior to mixing the coatings and at four hour intervals thereafter; more frequent if conditions are changing
26 Inspecting Mixing Procedures Verify components are within the manufacturer’s shelf life (and stored properly)Check PDS for mixing instructionsMeasure coating temperature after all components are thoroughly blendedStraining required?Thinning required/allowed?Induction time required?Pot life monitoringOne of the most commonly overlooked quality control checkpoints is verifying that the mixing procedures employed by the crew conform to the manufacturer’s requirements. Unfortunately this is where there is significant potential for errors and costly rework. Until the quality control inspector has confidence that the mixing crew is competent, they should witness the mixing process, which includes:1. Verifying that the shelf life has not expired and that the components are stored according to the manufacturer’s requirements.2. Reading the mixing instructions on the product data sheet and verifying that the instructions are followed by the mixing crew3. Measuring the temperature of the mixed coating, as this temperature dictates the length of the induction period, when required, and the length of the pot life.4. Considering whether straining of the coating is required or necessary5. Considering whether thinning is permitted, and if so, the type and amount of thinner that can be added to the mix.6. Considering whether an induction time is required by the manufacturer, and7. Monitoring the elapsed time of application to assure that the mixed coating is not used beyond its pot life
27 Inspecting Thinning Procedures Verify:Correct type of thinner is usedCalculation of thinner quantity is accurateGraduated containers are used to measure thinnerConsider impact on local VOC regulationsQuality control of the thinning procedures includes verifying the correct type of thinner is on-site and that the amount that is allowed to be added is calculated properly. Graduated containers should be used to measure the amount to be added, since pouring thinner directly into the mixed product may result in over thinning. Adding excessive thinner can result in application problems, solvent entrapment and violation of local environmental regulations.
28 Calculating the Target Wet Film Thickness Sometimes the wet film thickness will be listed on the PDS (many times it is not)Arriving at the target wet film thickness is necessary to arrive at the specified dry film thicknessMust be adjusted based on the amount of thinner addedWhile the wet film thickness is typically monitored by the coating applicator, quality control personnel may have to help calculate the target wet film thickness. In some cases, the target wet film is listed on the product data sheet, but frequently it isnt. Without properly calculating and verifying the applied wet film thickness, the resulting dry film thickness may not conform to the specification requirements. Since thinner is part of the wet film but not the dry film, the wet film thickness target must reflect thinner addition.
29 Calculating a Target Wet Film Thickness Calculating Target Wet Film ThicknessWFT = Target DFT% solids by volumeExample: 5 mils DFT68% solids by volume (0.68)Target wet film thickness: 7-8 milsThe formula and example shown on the slide is based on no thinner addition. Simply divide the target dry film thickness by the volume solids content of the coating, which is located on the product data sheet to arrive at the target wet film thickness. The application of 7-8 mils of a product that contains 68% volume solids will yield 5 mils dry film thickness.
30 Calculating a Target Wet Film Thickness Effect of Thinner Addition on WFT TargetWFT = Target DFT% solids by volume100% + % thinnerThe formula and example shown on the slide is based on thinner addition. In this case, there are two calculations – one to adjust the volume solids content and another to calculate the target wet film thickness using the adjusted volume solids value.First divide the volume solids content of the coating by 100% plus the percentage of thinner added. For example, if one gallon of thinner is added to 10 gallons of mixed coating, the denominator is 110%, since 10% thinner was added to 100% of what is already in the can. This effectively reduces the calculated volume solids content of the coating. Once the adjusted volume solids content is calculated, the target wet film thickness can be calculated by dividing the target dry film thickness by the adjusted volume solids content.
31 Calculating a Target Wet Film Thickness Effect of Thinner Addition, continuedWFT = 5 mils DFT0.68100% + 20% thinner5 mils DFT 5 mils DFT68 = = 9 mils WFT120For example, if 20% thinner is added to the coating that originally contained 68% volume solids content, the adjusted volume solids becomes 57%. This value is derived by dividing the original volume solids content, 68% by 120% The application of 9 mils of the reduced product will yield 5 mils dry film thickness.
32 Measuring Wet Film Thickness ASTM D 4414 – “Practice for Measurement of Wet Film Thickness by Notch Gages”Place gage into wet coating immediatelyWithdraw gage and read highest wetted step (e.g., 5 mils)Immediately clean coating from gageASTM D4414 describes the proper use of a notch-type wet film thickness gage. This gage should be used by the coating applicator during application. To measure the wet film thickness, insert the gage into the wet coating immediately after application. Withdraw the gage from the wet coating and read the highest wetted step on the gage. In the lower photo on the slide, the wet film thickness would be read as 5 mils. The wet coating should immediately be wiped from the gage so that it does not dry.
33 Measuring Dry Film Thickness Three common standards that address the nondestructive measurement of coating thickness :Ferrous and nonferrous metals: ASTM D 7091Steel only: SSPC-PA 2 (2004)2012 version will address ferrous and nonferrous metalsNon-metal surfacesASTM D 6132SSPC-PA 9There are three common industry standards and test methods that address the use of dry film thickness measurement gages. ASTM D7091 describes the proper use of magnetic pull-off and electronic coating thickness gages for measuring the thickness of coatings over both ferrous, or steel and non-ferrous metal substrates like aluminum, copper, brass and high grade stainless steel. SSPC Paint Application Standard No. 2, or PA2 currently addresses measurement of coating thickness on steel only; however the new version, which is expected to be published this year will address both ferrous and non-ferrous metal substrates. This next section will focus primarily on SSPC-PA2.Acquisition of coating thickness data from non-metal surfaces like concrete is conducted according to the procedures described in ASTM D6132 and SSPC Paint Application Standard No. 9 or PA9.
34 Measuring Dry Film Thickness Standards provide procedures for:Calibration (gage manufacturer/approved lab)Frequency of verifying gage accuracy (user)Frequency of measurements (number of measurements to obtain based on the size of the structure)SSPC-PA 2 places limits on spot and area readings vs. specified thicknessBoth the ASTM and the SSPC standards for coating thickness measurement provide the user with procedures for calibration of the gages, which must be performed by the gage manufacturer or an approved laboratory, typically annually, under controlled conditions of temperature and humidity. The standards also describe methods and frequency for verifying gage accuracy, which is done prior to and after each period of use, and prescribe the number of measurements to acquire based on the size of the structure.SSPC-PA2 prescribes limits on the tolerance of the spot and area measurements, in order to determine conformance to the project specification.Later this year, an SSPC/JPCL webinar titled “The New PA2” will be delivered, so be on the lookout for that.
35 Measuring Dry Film Thickness (SSPC-PA 2) Requires calibration by manufacturer (typically annual)Certificate of calibration traceable to a National Metrology Institute requiredVerification of accuracy (by user) before and after each period of useTwo types of nondestructive coating thickness gagesMagnetic pull-off (Type 1)Electronic (Type 2)As we defined earlier, gages must be calibrated by the manufacturer or a qualified lab. A Certificate of Calibration or other documentation showing traceability to a national metrology institute is required. There is no standard time interval for re-calibration, nor is one absolutely required. Calibration intervals are usually established based upon experience and the work environment. A one-year calibration interval is a typical starting point suggested by gage manufacturers.The gage type is determined by the specific magnetic properties employed in measuring the thickness of the coating and is not determined by the mode of data readout, for example digital or analog.Type 1 gages are considered magnetic pull-off and Type 2 gages are considered electronic
36 Verifying Type 1 Gage Accuracy Use calibration blocksNIST TraceableProprietary from gage manufacturersVerify accuracy:In range of useBefore and after each period of useMust correct for surface roughness (BMR)To verify the accuracy of Type 1 magnetic pull-off gages, measure the thickness of a series of reference standards covering the expected range of coating thickness. These can be traceable to the National Institute of Standards and Technology, or NIST; or they can be proprietary standards supplied by the gage manufacturer. To prevent acquiring measurements with an inaccurate gage, the gage is checked at least at the beginning and the end of each work shift with one or more of the reference standards. If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy must be rechecked.The specified dry film thickness of each coating layer is measured from the tops of the peaks of the surface profile. However, most coating thickness gages must reach down into the surface roughness to satisfy the magnetic properties of the gage. As a result, the effect of the surface profile on the thickness gage must be measured and subtracted from the coating thickness measurement. This in known as a base metal reading or BMR.Once the Type 1 thickness gage is verified for accuracy, the next step is to measure and record the Base Metal Reading or BMR. This is accomplished by placing the gage magnet on the prepared, uncoated substrate and obtaining a measurement. The BMR will vary widely, ranging from 0.1 mil to over 1 mil. Therefore, the user should take several measurements of the base metal and calculate the average. The average BMR is subtracted from the thickness of each coat, in order to assess the thickness of the coating film above the peaks of the surface profile.
37 Verifying Type 2 Gage Accuracy Use calibration blocks or shimsVerify accuracy in range of useMost can be adjustedFollow gage manufacturer’s instructions (vary)Similar to Type 1 gages, the user must verify the accuracy of Type 2 gages before and after each period of use. The step-by-step procedures for verifying gage accuracy vary widely between gage manufacturers. It is beyond the scope of this webinar to describe each; however the user should carefully follow the manufacturers instructions when verifying gage accuracy and when making adjustments to the gage. Most Type 2 gages can be verified for accuracy using reference standards or plastic shims. Use of plastic shims is more economical, as most gage manufacturers supply a set of shims with their gage. If needed, calibrated shims are available from many gage manufacturers. These are sold separately.
38 Verification of Type 2 Gage Accuracy If smooth reference standards are used (A), user must correct* for surface roughnessIf shims (foils) are used (over the prepared steel; B), no correction is needed*Via Base Metal Reading (BMR)If the gage manufacturer permits the use of reference standards to verify gage accuracy – as shown in (A) on the slide, the user must then acquire a base metal reading and deduct it from each coating thickness measurement, since the gage was verified for accuracy on a smooth surface but the coating was applied over a roughened surface. Conversely, if shims or foils are used to verify gage accuracy – as shown in (B) on the slide, and the shim is placed over the prepared, uncoated steel, then no correction for base metal is required, since the gage has been adjusted to the shim thickness resting on the peaks of the surface profile.The application of a base metal correction is tied to the type of reference material used to verify gage accuracy, reference test blocks versus shims, and not the type of gage. This is a common misunderstanding in our industry.AB
39 Measurement Frequency Terminology:Gage Reading: A single reading at one locationSpot Measurement: The average of at least 3 gage readings made within a 1.5” diameter circleArea Measurement: The average of 5 spot measurements made within a 100 square foot areaSSPC PA 2 prescribes a frequency for coating thickness measurements. Some of the terms relating to frequency are reviewed here. A gage reading is a single reading at one location, and a spot measurement is the average of at least 3 gage readings made within a 1.5 inch or 4 cm diameter circle. An area measurement is the average of the 5 spot measurements made within a 100 square foot or 10 square meter area on a structure.
40 Measurement Frequency The figure shown on the slide was extracted from SSPC PA 2. It illustrates three gage readings taken in each of 5 spots in an area of approximately 100 square feet or 10 square meters. The average of the three gage reading in each of the 5 spots has been calculated.
41 Dividing Structures into Test Areas If the structure is less than 300 square feet, each 100 square feet is measuredIf the structure is between 300 and 1000 square feet, select 3 random 100 square foot test areas and measureFor structures exceeding 1000 square feet, select 3 random 100 square feet testing areas for the first 1000 square feet, and select 1 random 100 square foot testing area for each additional 1000 square feetThe number of areas that are measured is based on the size of the structure being coated.For structures not exceeding 300 square feet or 30 m2, each 100 square foot or 10 m2 area is measured. As a result, the maximum number of areas to be measured will be 3.For structures greater than 300 square feet but not exceeding 1000 square feet or 100 in area, three 100 square foot or 10 m2 areas are arbitrarily selected and measured.For structures exceeding 1000 square feet or 100 m2 in area, three 100 square foot or 10 square meter areas are measured in the first 1000 square or 100 m2. For each additional 1000 square feet or portion thereof, one additional 100 square foot or one 10 m2 area is arbitrarily selected and measured.Other size areas or number of spot measurements may be specified by the owner in the job specifications for the size and shape of the structure to be coated.
42 Example: Structure Size: 55,000 square feet No. of Areas: = 57 areasNo. of Spots: 57 Areas x 5 Spots/Area = SpotsNo. of Gage Readings: 285 Spots x 3 Readings/Spot = Gage ReadingsFor example, lets say that the total area of the structure is approximately square feet. Three 100 square foot areas are arbitrarily selected and measured in the first 1000 square feet, then one additional 100 square foot area is arbitrarily selected and measured in each additional1000 square foot area, for a total of 57 areas . This culminates in the acquisition of a minimum of 855 gage readings acquired from 285 spots.
43 Coating Thickness Tolerance (SSPC-PA 2) Individual readings (averaged to create a spot measurement) are unrestrictedNon-repeating low or high readings can be discardedThe spot measurement (the average of 3) must be within 80% of the minimum thickness and 120% of the maximumArea measurement must be within specified rangeIndividual gage readings that are averaged together to create a spot measurement are unrestricted. That is, readings that are unusually high or low within the spot that cannot be repeated are discarded. The average of the individual gage readings is a spot measurement. The spot measurement must be within 80% of the minimum specified thickness and 120% of the maximum specified thickness. Stated differently, spot measurements can be high or low by as much as 20%; while individual gage readings can overrun or under-run by a greater amount.The average of the spot measurements must fall within the specified coating thickness range. That is, the 20% allowance only applies to the spot measurement and not the area measurement.
44 Assessing Intercoat Cleanliness Airborne dust and/or abrasive may be deposited on coated surfacesProblematic if surface is to be recoatedRequires visual or tactical (touch) examination of the surfaceIt is very common to perform a blow down or brush off of surfaces after surface preparation and prior to primer application. However, dust and surface debris may also become deposited between coats. This can be quite problematic if it is not detected and removed prior to application of subsequent coating layers. Surfaces should be carefully examined for dust or debris between coats; otherwise application defects and adhesion problems may arise.
45 Verifying Recoat Times and Temperatures Coating materials may have a minimum and/or a maximum recoat timeVerify:Coating has been allowed to dry or cure the minimum amount of timeThe next coat is applied before the maximum recoat time has been exceededMost coating materials have a minimum recoat interval and some have a maximum recoat time. Quality control personnel should record the date and time when the application is completed, so that the coating is allowed to properly release the solvent vapors as appropriate, and dry or cure before the next layer is applied.For some coatings, it is important to apply the next coating layer before the previous coat has cured too long, in order to attain intercoat adhesion. The coating manufacturers product data sheet will usually indicate the minimum and maximum recoat intervals, which are typically based on the prevailing conditions of temperature and humidity.
46 Detecting Pinholes and Holidays Definitions:Holidays – skips or misses in the coating/lining systemPinholes – tiny voids in the coating or liningStandards:ASTM D5162 and D4787; NACE RP01-88Conducted:After final coat has been applied, but before it has achieved complete cure (touch-up)Specifications may require holiday testing after the application of each coatMay cause intercoat contaminationHoliday or pinhole detection is typically performed on coating and lining systems that are hidden during service. That is, we cannot easily assess whether the coating or lining is protecting the steel, so we want to verify that there are no breaches in continuity when the coating is installed, prior to placing it into service. Examples include the lining of a potable water storage tank, a railcar lining, the interior of vessels and buried pipe and storage tanks.A holiday is a skip or a miss in the coating or lining system, while a pinhole is a tiny void in the coating or lining which may or may not be visually evidentThere are three common industry standards associated with holiday detection; two published by ASTM International and one published by NACE International.Holiday detection is typically conducted after the final coat has been applied but before it has achieved complete cure, in case touch-up is required. For example if a lining system is required to cure a minimum of 10 days prior to immersion, it may be inspected for pinholes after a couple of days curing so that all of the solvents have an opportunity to escape. Some specifications will require holiday testing after each coat. This practice can result in intercoat contamination and should be carefully considered by the specifier.
47 Rules for Holiday Detection Coating must be nonconductiveSubstrate must be conductiveHigh voltage (spark) testing requires voltage setting100 to 125 volts/mil of coatingObtain recommended test voltage from coating manufacturerExcessive voltage can damage coating filmIn order for holiday detection to be effective, the coating must be non-conductive and the substrate must be conductive. Performing holiday detection on a zinc primer or an aluminum filled coating, or on a coated plastic substrate would be ineffective. High voltage holiday testing, commonly known as spark testing or jeeping, requires that the voltage be set to prevent damaging the lining. While the coating manufacturer will typically recommend a voltage setting, the general rule-of thumb is volts per mil of coating.
48 Holiday DetectorsLow voltage (wetted sponge) – coatings that are less than 20 mils thickHigh voltage (spark tester) – coatings that are greater than 20 mils thickMove wand/electrode maximum of one foot/secondThere are two general categories of holiday or pinhole detectors, including low voltage or wetted sponge detectors, which are used for coatings less than 20 mils thick and high voltage or spark tester, which are used for coatings greater than 20 mils thick. In either case, the speed of detection or the rate at which the wand or electrode is passed over the surface should not exceed one linear foot per second
49 Inspecting OAP Coating Systems “Visual” pinhole/holiday detectionOptically Active Pigments (OAP) added to coatings during formulationInspection performed using UVA-340 lightProcess described in SSPC TU 11Inspector training recommended if inspections not previously performedVisual pinhole detection using optically active pigments or OAP that are added to the coating during formulation provide an alternative to low and high voltage holiday detection. In this case, an ultraviolet light source is used to perform pinhole and holiday detection visually. The process is described in SSPC Technology Update 11. The UV light inspection can reveal a variety of defects that may or may not be pinholes or holidays, so special training is recommended prior to performing these types of inspections.
50 Assessing Coating Drying/Cure Pencil Hardness (ASTM D3363)Solvent Resistance (Solvent Rubs; ASTM D5402) for convertible coatingsSolvent Resistance (Solvent Rubs; ASTM D4752) for ethyl silicate inorganic zinc primersImpressor HardnessBarcol Hardness (ASTM D2583)Durometer Hardness (ASTM D2240)Dry Time Testing (ASTM D1640)There are a host of tests that can be conducted to assess the degree of drying or curing of an applied coating. One or more of these tests may be conducted by the quality control inspector to verify the coating has dried or cured adequately prior to application of subsequent coats, or prior to placing the coating or lining system into service.ASTM D3363 describes a test where pencils containing various hardness of lead are used to attempt to either scratch or gouge the film. The coating manufacturer or the specification would have to indicate a minimum pencil hardness value for this test to be meaningful, as there is no standard pencil hardness.There are two solvent resistance tests that can be used to assess the degree of coating cure; one is used on organic convertible coatings and the other is for use on ethyl silicate-type inorganic zinc-rich primers. Both employ the use of a solvent saturated cloth and finger pressure to conduct a series of double rubs. Resistance to the solvent rub is an indication of the degree of cure.Thick film coatings are typically assessed for the degree of cure using impressor or indentor-type instruments. These include the Barcol harness tester and durometer hardness. In both cases, hand pressure is used to push an indentor probe into the coating. The coating’s resistance to this action is displayed on the gage dial in hardness units. Fiberglass reinforced plastic or FRP linings may be assessed for degree of cure using a barcol hardness tester, and a pipe coating may be assessed for durometer hardness prior to backfilling the ditch.Finally, dry time testing may include dry-to-touch, dry-to-handle, dry-through, and dry-to-recoat, which are all described in ASTM D1640
51 Measuring Adhesion Adhesion is destructive testing Testing should not be conducted unless requiredTypes of coating adhesion:The adhesion of the coating to the substrateThe adhesion of the coating layers to each otherThe inner-strength of each coating layer (cohesion)Adhesion testing is considered a destructive test and should not be performed unless it is required by the project specification. When tested, there are three primary adhesion planes that are evaluated, including the bond of the coating system to the substrate, the bond of the coating layers to one another and the inner-strength of the coating layers.So why test the adhesion of a coating or lining system if it is destructive?The painting specification may invoke a requirement for a minimum adhesion value or rating prior to placing the coating or lining into service. In this case, as long as the adhesion of the coating exceeds the minimum specified value or rating, the actual adhesion value is not critical. Also, the SSPC/NACE/ASW Tri-Society Coating Specification for thermal spray coatings invokes a requirement for tensile bond measurements using a self-aligning adhesion tester, and provides minimum tensile bond requirements based on the type of wire.
52 Adhesion Test Methods Standard Title D 3359 A Adhesion by Tape Test (>5 mils DFT)D 3359 BAdhesion by Tape Test (≤5 mils DFT)D 6677Knife AdhesionD 4541D 7234Pull-off Strength of Coatings Using Portable Adhesion TestersPull-off Strength of Coatings on Concrete Using Portable Adhesion TestersPrior to performing an adhesion test, you must select a test method. The project specification should indicate the required method, as the various methods can generate very different results. There are three primary ways to test the adhesion of a coating system, including knife and tape, knife only and pull-off. The three methods are described in four ASTM standard test methods. The chart on the slide lists the methods that are commonly used to test the adhesion of industrial coatings.
53 Tape Adhesion (D 3359) Method “A” (> 5 mils) SCRIBE AN “X” INTO COATING TO SUBSTRATEMethod A in ASTM D3359 employs knife and tape, and is used to evaluate coatings that are greater than 5 mils thick. To perform method A, mount a new razor blade in a utility knife. Use a straight edge and make a 1.5” long cut through the coating system down to the substrate then make a second 1.5” long cut across the first cut to form an “X”. The legs at the top and bottom of the “X” should be approximately 1” apart. The intersection of the “X” should be a 30-45o angle. Remove any debris from the “X” area using a soft brush.Remove two complete wraps of adhesive tape and discard it. Carefully remove a 3” piece of the adhesive tape and apply it to the “X” area. Because the tape and the “X” cut area are both 1” wide, the tape should cover the entire X-Cut.Use a soft pencil eraser to rub the tape over the X-Cut. Sixty to 120 seconds after applying the tape, remove it from the X-cut smoothly and rapidly, 180o back across the X-Cut. Do not pull the tape upwards.REMOVE TAPE QUICKLYAPPLY TAPE AND RUB ONTO SURFACE
54 Tape Adhesion (D 3359) Method “A” (> 5 mils) RatingDescription5ANo peeling or removal4ATrace peeling or removal along the incisions3AJagged removal along the incisions up to 1/16” on either side2AJagged removal along the incisions up to 1/8” on either side1ARemoval of most of the coating from the area of the “X” under the tape0ARemoval of coating beyond the area of the “X”Examine the X-Cut area for coating delamination. Since there will be shavings of coating down in the grooves of the cuts, it is not a good idea to rate the adhesion based on what appears on the tape since the tape will almost always have coating debris on it. Instead, look at the X-Cut area on the coated surface and rate the condition of it according to the rating scale in the ASTM standard, which is shown on the slide. A rating of 5A indicates excellent adhesion, while a rating of 0A indicates very poor adhesion.If possible, the location of break should also be recorded as adhesion, which is a split between two layers or between the substrate and first layer; or cohesion, which is a split within a single coating layer.
55 Tape Adhesion (D 3359) Method “B” (< 5 mils) SCRIBE A CROSS-CUT PATTERN INTO COATING TO SUBSTRATEMethod B in ASTM D3359 also employs knife and tape, but is used to evaluate coatings that are less than or equal to 5 mils thick. To perform method B, mount a new razor blade in a utility knife. Use a guide or template to make a series of 6 or 11 parallel knife blade cuts through the coating system down to the substrate. The number of cuts and the amount of space between the cuts is based on the total thickness of the coating system, as we described earlier. Alternatively, a cutter blade with pre-determined spacing can be used. Turn the guide or template 90o and make a second series of parallel knife cuts over top of the first set of cuts, but make them perpendicular to the first set to form a grid, cross-hatch or “Cross-Cut” pattern.Remove any debris from the “Cross-cut” area using a soft brush.Remove two complete wraps of adhesive tape and discard it. Carefully remove a 3” piece of adhesive tape and apply it to the “Cross-cut” area.Use a soft pencil eraser to rub the tape over the cross-cut area. This will help ensure good contact between the tape and the coating. Within 60 to 120 seconds, grasp one end of the tape and remove it from the cross-cut area smoothly and rapidly, 180o back across the grid. Peel the tape back, do not pull upwards.APPLY TAPE AND RUB ONTO SURFACEREMOVE TAPE QUICKLY
56 Tape Adhesion (D 3359) Method “B” (< 5 mils) Rating%Description5B0%Edges of cuts completely smooth4B<5%Small flakes of coating detached at intersections3B6-15%Small flakes of coating detached along edges & at intersections2B16-35%Coating flaked along edges and parts of squares1B36-65%Coating flaked along edges in large ribbons and whole squares detached0B>65%Flaking & detaching worse than 1BExamine the cross-cut area for coating delamination and rate the condition according to the scale in the ASTM standard. The standard also provides a corresponding chart that illustrates the various percentages of delamination.A rating of 5B indicates excellent adhesion, while a rating of 0B indicates very poor adhesion.
57 Tensile (pull-off) Adhesion Testing ASTM D 4541 measures the resistance to a perpendicular pullRequires the attachment of “loading fixtures”Pulling mechanisms include:SpringPneumaticHydraulic (shown)Record psi (Mpa) and location of breakASTM D4541 describes the procedures associated with evaluating tensile or pull-off adhesion of coatings applied to metal substrates. There are five annexes in the standard describing the apparatus and procedures for one fixed alignment tester and four self-aligning test devices, including three hydraulic devices and one pneumatic device. All of these testers require the attachment of a loading fixture to the coated surface using an adhesive. The loading fixture is detached from the surface by applying a perpendicular load to the fixture. The tensile force in psi or megapascals is recorded along with the location of break, which is recorded as adhesion, cohesion or glue.ASTM D7234 addresses pull-off adhesion of coatings applied to concrete.
58 Illustrations of Various Locations of Break 12345Image 1 on the slide illustrates a 100% adhesion break between the topcoat and the primer.Image 2 illustrates a glue break, while image 3 illustrates a cohesion break within the primer layer.Image 4 illustrates an adhesion break between the substrate and the primer, while image 5 illustrates a cohesion break within the topcoat.
59 Identifying Coating Application Defects Multitude of defect typesIdentifying type, causes and remedies is challengingAcquire a pictorial reference guideSources:ASTM standardsFitz’s Atlas 2™ (shown)There are potentially dozens of coating defects and identifying the type of defect that has occurred and the cuase and remedy can be very challenging. However, a quality control inspector may be asked to identify and capture, using digital photography any defects that occur, so that the specifier or coating manufacturer can determine what if any repairs should be undertaken. There are some very useful visual guides containing images of coating defects, their potential causes and remedies. Some ASTM standards provide black & white images of defects, such as ASTM D714 for blistering. A handbook of defects known as Fitz’s Atlas 2 may also prove helpful in diagnosing coating defects in the shop or field.
60 Summary During this webinar, we have described : Industry standards for coating applicationDeveloping a quality control plan for paintingNavigating a Technical (Product) Data SheetMeasuring ambient conditions and surface temperatureWitnessing mixing, thinning and application proceduresCalculating and measuring wet film thicknessDry film thickness measurementPost-application testingIdentifying application defectsIn summary, we have described:The industry standards for coating applicationThe benefits of developing a quality control plan for paintingHow to navigate your way through a Product Data SheetHow to measure ambient conditions and surface temperatureThe importance of witnessing mixing, thinning and application proceduresHow to calculate and measure wet film thicknessHow to measure dry film thicknessA variety of post-application testing procedures including intercoat cleanliness assessments, pinhole or holiday detection, hardness and adhesionand finally, ways in which we can identify application defects on-site.
61 Quality Control of Industrial Painting Operations THE ENDWilliam D. CorbettKTA-Tator, Inc.Thank you for attending this one-hour webinar on quality control of industrial painting operations, sponsored by DeFelsko Corporation. I believe we have time for questions which our moderator will manage.
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