Differences in coating inspection standards

Let’s Talk About Differences Between Coating Inspection Standards

KTA’s Certified Coating Inspector Forum Volume 3, Issue No. 5 – May 2024

William Corbett, COO

AMPP Senior Certified Coating Inspector & Certified Protective Coating Specialist

KTA’s Certified Coating Inspector Forum is designed to provide professional development/continuing education on standards, inspection practices, new instruments, and other topics to help keep certified AMPP and FROSIO coating inspectors current. It represents the views of the author and KTA-Tator, Inc. It may or may not represent the views of AMPP: The Association for Materials Protection & Performance, even though SSPC, NACE, and AMPP standards are frequently referenced in the content.


Introduction

We frequently hear it stated: “The World’s Getting Smaller & Smaller Every Day.” Most if not all coating Standards Development Organizations (SDOs) now reach internationally and publish standards that are designed to be referenced across the globe. While here in the North America we frequently reference legacy SSPC/NACE standards (or newly developed AMPP standards) and ASTM standards in coating specifications, other countries recognize those or ISO standards. As certified coating inspectors we are expected to know (or have access to) all coating industry standards, as we may be called to work anywhere in the world or may inspect based on coating specifications that were written in the US or in another land. Case-in point: The International Maritime Organization (IMO) Performance Standard for Protective Coatings (PSPC) references ISO inspection standards since most cargo and cruise shipbuilding occurs in European countries.

Duplicative standards can certainly add complexity. In recent years there has been some effort to ensure SSPC/NACE standards and ASTM standards are complementary and not duplicative, competing, or contradictive. For example, ASTM D7091[1] focuses primarily on gage use, while SSPC-PA 2[2] focuses on frequency and acceptability of measurements taken with the gages. Similarly, ASTM D4417[3] focuses on measurement procedures and number of readings per location, while SSPC-PA 17[4] focuses primarily on frequency and acceptability of location measurements. While there is information that is duplicative in each, it is not contradictory. Also, it is common for a standard to reference one or more standards from another SDO. For example, the SSPC Abrasive Standards (e.g., AB 1, AB 2, AB 3) all reference ASTM D4940[5] and D7393[6] for abrasive cleanliness, versus developing their own duplicative standards.

However, there are ISO standards that appear to address the same subject matter as that covered by SSPC/NACE or ASTM standards and vice versa. If ISO standards were considered “equivalent” to the legacy SSPC/NACE and ASTM standards it wouldn’t be as challenging. However, ISO standards frequently cover the same subject matter but invoke different inspection processes, procedures, and acceptance criteria. If an ISO standard is referenced in a coating specification and we assume equivalency to ASTM or SSPC/NACE (and vice versa), we may be inspecting and documenting incorrectly. This article highlights the primary differences between several common ISO and SSPC/NACE or ASTM inspection standards that may be referenced in coating specifications. I always recommend obtaining the latest version of the standards and reading them thoroughly to uncover any nuances not addressed in this article.

Primary Differences: ISO Versus SSPC/NACE or ASTM Standards

Table 1 lists nine categories of inspections and contains the ISO standard and the SSPC/NACE (now published by AMPP) or ASTM standard that address each of the subjects under the nine categories. The “Table” reference in column 1 corresponds to the tables 2-11 in this article that explain the primary differences. While Table 1 shows them side-by-side, it should never be inferred that these are equivalent standards. Note that in four instances there is no known standard for comparison, so they are not addressed in subsequent tables.


Table 1: ISO and SSPC/NACE (or ASTM) Standards by Category and Subject

Category/TableSubjectISO StandardSSPC/NACE or ASTM Std.
Abrasive Cleanliness (Table 2)Oil ContentNo known standardASTM D7393
 Water Soluble ContaminantsISO 11127-6ASTM D4940
Compressed Air Cleanliness (Table 3)Oil & Moisture Detection in AirISO 8573ASTM D4285
Surface Profile (Table 4A-4C)Visual ComparatorsISO 8503-1, 2ASTM D4417; A
 Depth MicrometerNo known standardASTM D4417; B
 Replica TapeISO 8503-5ASTM D4417; C
 Portable Drag StylusISO 8503-4ASTM D4417; D
Surface Cleanliness (Table 5A, 5B)Solvent CleaningNo known standardSSPC-SP 1
 Hand ToolISO 8501-1, St 2 & St 3SSPC-SP 2
 Power ToolISO 8501-1, St 2 & St 3SSPC-SP 3
 Brush-off Abrasive BlastISO 8501-1, Sa 1SSPC-SP 7/NACE 4
 Commercial BlastISO 8501-1, Sa 2SSPC-SP 6/NACE 3
 Near-white Metal BlastISO 8501-1, Sa 2 1/2SSPC-SP 10/NACE 2
 White Metal BlastISO 8501-1, Sa 3SSPC-SP 5/NACE 1
 Pictorial GuidesISO 8501-1SSPC VIS 1
  ISO 8501-1SSPC VIS 3
 Surface DustISO 8502-3No known standard
Surface Soluble Salt Detection (Table 6A, 6B)ExtractionISO 8502-6SSPC Guide 15 (4.2.2)
 AnalysisISO 8502-9SSPC Guide 15
Coating Thickness (Table 7, 8)Wet Film ThicknessISO 2808ASTM D4414
 Dry Film ThicknessISO 19840SSPC-PA 2/ASTM D7091
Holiday/Pinhole Detection (Table 9)Low and High Voltage DetectionISO 29601ASTM D5162/ASTM G62/ NACE SP0188
Adhesion (Table 10A, 10B)Tensile (pull-off)ISO 4624ASTM D4541
 Tape/KnifeISO 2409ASTM D3359, B
Hardness (Table 11A, 11B)Pencil HardnessISO 15184ASTM D3363
Durometer HardnessISO 7619ASTM D2240

Table 2: Differences in Abrasive Cleanliness Standards

ISO 11127-6ASTM D4940
Applies only to non-metallic abrasivesApplies to metallic and non-metallic abrasives
Requires that a “representative sample” be tested (per ISO 11127-1)Obtain 2 – 1-Liter samples at random from different packages (lot, batch)
Requires use of minimum Grade 2 purity water (ISO 3696)Requires use of Type IV purity water (ASTM D1193)
Requires use of a balance (0.1 g accuracy)Does not require the use of a balance
Abrasive to Water Ratio – 100 g of abrasive to 100 ml of waterAbrasive to Water Ratio – 300 ml of abrasive to 300 ml of water
Extraction Process: Shake for 5 min., stand for 1-hour, shake for 5 min, allow fines to settleExtraction Process: Stir for 1 min., Stand for 8 Min., Stir for 1 min.
Filter only if liquid is not clear. No requirement for filter paper type or to discard any filtrate.Filtering Required: Filter Paper Type 1, Class C (per ASTM E832). Discard first 10 ml of filtrate.
Does not address calibration or standardization of conductivity cellRequires periodic check of the conductivity cell using a predetermined Constant
Calculations based on 20°C solution temperatureCalculations based on 25°C solution temperature
Reporting: Identification of product tested, Reference to ISO 11127-6, Test results, Deviations from procedure,Test anomalies, Date of test, Name of inspectorReporting: Material being tested,Calibration:Measured valueCell Constant (solution)DateName of individualTemperature from the conductivity meter,Date of test,Test results and mean in µmho/cm,Name of inspector
Duplicate results invalid if they differ more than 10%Two results, each the mean of two tests is suspect if they differ more that 5% relative

Table 3: Differences in Compressed Air Cleanliness Standards

ISO 8573ASTM D4285
Laboratory methods for quantifying the amount of oil aerosol (Part 2) and liquid water content (Part 9) in compressed airField methods for verifying the cleanliness of compressed air used for abrasive blast cleaning, dust removal and air-atomized paint spray methods
Purity classes vary and are listed in Part 1Qualitative check for visible water/oil on collector
Primarily focused on protecting equipment that operates using compressed airPrimarily focused on preventing contamination of prepared surfaces and paint

Table 4A: Differences in Surface Profile Standards – Visual Comparators

ISO 8503-1,2ASTM D4417; A
Type G (Grit) and Type S (Shot) comparators onlySand (S), Grit/Slag (G/S) and Shot (SH) comparators available
Qualitative assessment (i.e., Grade: Finer than Fine; Fine; Medium; Coarse; Coarser than Coarse)Quantitative assessment (mils/microns)
Visual or tactile examinationVisual examination only
No precaution about touching blast cleaned steel with an unprotected handPrecaution about touching blast cleaned steel with an unprotected hand
For frequently used comparators, it is recommended to compare to an unused similar comparator at a three-monthly intervalNo verification interval provided
Record Disc Type and Grade, not Segment No., the rust grade before cleaning, and abrasive type usedRecord Disc Type and Profile Depth

Table 4B: Differences in Surface Profile Standards – Replica Tape

ISO 8503-5ASTM D4417; C
Requires adjusting the zero point on the analog micrometer to -2 mils.Analog micrometer can be set to 0 or -2. If 0, manual deduction of 2 mils is required.
Reporting Requirements: Identification of sample tested, Reference to ISO 8503-5, Replica tape batch no. and date of manufacture, Profile readings and location measurement (average of 2), Micrometer calibration date Date of most recent accuracy check,Project name/work site ID, Date of test, Name of inspectorReporting Requirements: Type of instrument used (manufacturer, model, serial no., date of calibration),No of locations measured and approximate total area covered,Average of each pair of replica tape readings
Does not specifically address the need to remove dirt, dust, abrasive debris prior to measurement.Addresses removal of dirt, dust, abrasive debris prior to measurement.

Table 4C: Differences in Surface Profile Standards– Portable Drag Stylus Gauge

ISO 8503-4ASTM D4417; D
Primarily focused on verifying the accuracy of the ISO comparator discs but can be used on blast cleaned steel.Primarily focused on measurement of prepared steel substrates prior to coating application.
Requires removal of dust followed by washing with commercial grade petroleum spirit to remove grease/oil.Requires removal of dust/abrasive debris by dry brushing.
Requires a minimum of 10 evaluation lengths uniformly distributed over the test area to calculate the grand mean. No more than 4 sets of readings in any one direction.Requires 5 evaluation lengths to calculate the grand mean (initial trace measurement [2 parameters], then four additional trace measurements taken in the compass directions from the original measurement and about 1 in. away.)
Measure maximum peak-to-valley height (Ry) onlyMeasure maximum peak-to-valley height (Rt) and peak count (optional)
Reporting: Identification of steel substrate tested, Reference to ISO 8503-4, Evaluation length & no. of lengths measured, Sampling length, Test results – average reading, standard deviation, maximum reading,Deviations from procedure,Test anomalies, Date of test, Name of inspectorReporting: Type of instrument used (manufacturer, model, serial no., date of calibration),No of locations measured and approximate total area covered,Sampling length,Evaluation length, Values of the five trace measurements for each parameter measured (Rt and Rpc) and their averages for each location.Whether a skidded or non-skidded instrument was used.

Table 5A: Differences in Surface Cleanliness – Written Standards

ISO 8501SSPC/NACEPrimary Differences
ISO St 2/St 3SSPC-SP 2/SP 3ISO St 2 and St 3 depict two levels of surface cleanliness (thorough and very thorough cleaning) using either hand or power tools, while SSPC-SP 2 and SP 3 have the same definitions of surface cleanliness, but SSPC-SP 2 focuses on hand tools and SP 3 focuses on power tools. ISO St 2 and St 3 do not require the use of a dull putty knife, while SSPC-SP 2 and SP 3 do.
ISO Sa 1SSPC-SP 7/NACE 4ISO Sa 1 does not require the use of a dull putty knife, while SSPC-SP 7 does.
ISO Sa 2SSPC-SP 6/NACE 3ISO Sa 2 requires that most of the mill scale, rust, paint coatings and foreign matter be removed, and allows any residual contamination to remain provided it is firmly adhering, while SSPC-SP 6/ NACE 3 only permits staining to remain and cannot exceed 33% of each 9 sq. in. of prepared steel.
ISO Sa 2 1/2SSPC-SP 10/NACE 2Both standards only allow staining to remain, however ISO Sa 2 ½ does not quantify the amount of staining, while SSPC-SP 10/NACE 2 does (maximum of 5%).
ISO Sa 3SSPC-SP 5/NACE 1While the wording in the definitions varies, both standards have essentially the same requirements.

Table 5B: Differences in Surface Cleanliness – Pictorial Guides/Standards

ISO 8501-1SSPC VIS 1 and VIS 3
Contains only 4 uncoated initial conditions (Rust Grades)Both visual guides contain 4 uncoated and 3 previously coated initial conditions
Post-cleaning photos represent ISO surface cleanliness definitions, not SSPC/NACE surface cleanliness definitions (see differences in Table 4A)Post-cleaning photos represent SSPC/NACE surface cleanliness definitions, not ISO surface cleanliness definitions (see differences in Table 4A)
Photos are approximately 3” x 4”Photos are approximately 3” x 3” to match basis for definitions (9 sq. in.)

Table 6A: Differences in Surface Soluble Salt Detection Standards – Extraction

ISO 8502-6 (Bresle Method)SSPC Guide 15 (Method 4.2.2)
Requires Grade 3 water purity per ISO 3696, but notes that distilled water with a conductivity <5 µS/cm meets this requirementRequires Reagent Water (conductivity <5 µS/cm)
Cell cleanliness via a “Blank Test” for each batch of cells is requiredCell cleanliness testing not required
Volume of water needed is variable depending on patch compartment size. Record volume of water used.Use 3 mL or other designated water quantity
Specifies to insert the needle into the patch at about a 30° angleOnly specifies to insert the needle through the perimeter of the patch
No requirement to evacuate the air from the cell prior to water injectionRequires evacuation of the air using the syringe prior to injecting the water
Water can be withdrawn and reinjected 4 times, or the patch can be massaged to agitate the sampleWater should be withdrawn and reinjected into the patch at least 4 times
Requires a minimum 10-minute dwell (extraction) timeUnspecified dwell (extraction) time, but references ISO 8502-6
Requires measurement and recording of surface temperatureNo requirement to measure/record surface temperature
Includes procedure for extraction using pre-filled sleeveMethodology for extraction using pre-filled sleeve in Method 5.2.5 of Guide 15
Reporting: Reference to ISO 8502-6, Type/size of extraction cell used (patch or sleeve), Type of water used, Total volume of water used, Total dwell (extraction) time,Surface temperature, Manufacturer batch no. of patch or sleeve used,Date of testNo reporting requirements since it is a Guide and contains multiple extraction and analysis procedures that have varying reporting requirements

Table 6B: Differences in Surface Soluble Salt Detection Standards – Analysis

ISO 8502-9 (Conductivity)SSPC Guide 15
Only describes conductometric measurement, i.e., the use of an immersion-type or a direct measuring conductivity meterVarious methods of analysis are available and may be ion specific (e.g., chloride, sulfate, nitrate, ferrous ion) or non-ion specific (conductivity)
A detailed formula is provided to report the surface density of soluble salts in mg/m2Conductivity is reported as µS/cm
Requires: Calibration of the conductivity meterWater & equipment “Blank” testRecording of amount of dilution water used (if needed for immersion-type conductivity metersCalculating the corrected water volume when dilution is usedRecognizes that probe-type conductivity meters can be used, but does not provide specific instructions on their use to determine surface soluble salt concentrations
Reporting: Reference to ISO 8502-6 and -9,Measuring range of conductivity meterMeasured conductivity of the “Blank,”Type/size of extraction cell used (patch or sleeve), Type of water used, Total volume of water used (for the extraction and dilution, if diluted) and temperature of solution,Total dwell (extraction) time,Surface temperature, Manufacturer batch no. of patch or sleeve used,Calculated surface density of salts,Test deviation and/or anomalies,Date of testNo reporting requirements since it is a Guide and contains multiple extraction and analysis procedures that have varying reporting requirements

Table 7: Differences in Wet Film Thickness Measurement Standards

ISO 2808ASTM D4414
Addresses mechanical (comb, wheel, dial gauges), gravimetric and photothermal methodsAddresses only notch gauges (square, rectangular, circular). Wheel-type gauges are addressed in a separate method (ASTM D1212)
No formal reporting requirementsReport: Mean and range of readings,No. of readings,Smallest graduation of gauge used
No number of measurements specifiedSpecified to take measurements in at least 3 locations on a film

Table 8: Differences in Dry Film Thickness Measurement Standards

ISO 19840SSPC-PA 2
Specifically for measurement of paint systems applied to roughened steel surfacesDoes not distinguish between rough and smooth surfaces in the Scope.
Requires verification to zero using an uncoated, smooth test plate as well as verification below and above the specified coating thicknessDoes not require verification of zero.Does not require a two-point adjustment. A one-point adjustment is acceptable
Allows the use of shims/foils or certified coated plates for verification of accuracyDoes not allow the use of shims/foils with Type 1 (magnetic pull-off) gauges.Allows use of shims/foils for Type 2 (electronic) gauges provided they are certified shims and are placed on a smooth zero plate.
Provides sampling plan based on “inspection areas.” Unless the structure is divided into smaller inspection areas, the whole structure is considered the inspection area (unless > 1000 m or m2, when subdividing is recommended).Frequency of inspection areas based on the size of the coated area (i.e., the area coated during the previous work shift).No. of Spot Measurements (5/area) and Gauge Readings (min. 3/spot) are the same for each inspection area.
Inspection area may be in lineal meters or square metersInspection area in square feet or square meters
Sampling plan contains minimum no. of measurements based on the size of the inspection area.Total no. of gauge readings and spot measurements are based on the no. of inspection areas. No. of Spot Measurements and Gauge Readings are the same for each inspection area.
Sampling plan contains maximum no. of measurements allowed to be repeated (i.e., replaced) based on the size of the inspection area.No restriction on the number of gauge reading that can be repeated/replaced. Gage readings are unrestricted.
Incorporates “Correction Values:” Measured from the prepared, uncoated steel, orSelected from a table based on surface profile as assessed per ISO 8503-1 (Fine, Medium, Coarse), orIf unknown, assumed to be 1 milType 1 (magnetic pull-off gauge): Minimum of 10 base metal readings (BMR) averaged and subtracted from the measured coating thickness.Type 2 (electronic gauge): Certified or measured shim placed on the prepared, uncoated metal and the gauge adjusted to match the shim thickness, or if unavailable,Selected from a table based on surface profile as assessed per ISO 8503-1 (Fine, Medium, Coarse)
Acceptance Criteria: Arithmetic mean of individual measurements must be greater than or equal to the nominal DFT.Individual measurements shall be within 80% of the nominal DFT.Individual measurements between 80% of nominal DFT and nominal DFT are acceptable, provided they represent <20% of the total no. or measurements obtained.All measurements must be less than or equal to the maximum DFT.Acceptance Criteria: Based on Coating Thickness Restriction Level Table (5 levels for specifier to choose from). If Level is unspecified, Level defaults to 3.Gage Readings: UnrestrictedSpot Measurements: Higher or lower than specified thickness range by 20% maximum.Area: Must conform to specified thickness range
No requirement to determine the magnitude of any nonconforming inspection area(s)Requires determining the magnitude of the nonconforming spots/area(s) by radiating out in 8 directions until 2 consecutive spot measurements conform to the specified range
Reporting: Reference to ISO 19840,Identity of paint/paint system,Identity of substrate,Identity of substrate surface preparation,Identity of inspection area,Instrument used and serial no.,Method of adjustment,Correction value used,No. of repeated measurements,Measurements,Whether or not measurements met the acceptance criteria,Ambient and surface temperatures,Supplemental information,Name of inspector,Date of measurementsReporting: Instrument used (manufacturer, model, serial no., date of calibration),Type of certified standard used to verify gage accuracy (manufacturer, model, serial no., thickness values),Thickness of measured shim used for adjustment,Average BMR (if used),Spot and Area Measurements,Name of inspector,Date of measurements

Table 9: Differences in Holiday Detection Standards

ISO 29601ASTM D5162[7]/ASTM G62/NACE SP0188
Low voltage detection is performed at either 9v (coatings up to 12 mils) or 90vLow voltage detection is performed at < 100 volts.
No requirement for Verification of Output Voltage on High Voltage DetectorsRequirement for Verification of Output Voltage on High Voltage Detectors prior to use
Voltage settings (in kV) for High Voltage Spark Testing are selected from a Table and are based on the mean DFT (in µm) as a range (4-mil range per voltage setting)Voltage settings (in kV) for High Voltage Spark Testing are selected from a look-up able and are based on the mean DFT (in µm and mils)
The basis for voltage settings in Table 1 of the standard is not stated. Voltage settings (compared to ASTM and NACE standards) are lower below 140 mils, align between 140 and 160 mils, then are higher above 160 mils. Max. DFT in Table is 315 mils (30.0 kV setting)Voltage settings are based on formulas listed in standards, which are based on current science (Paschen’s Law – incorporating the dielectric strength of air in the calculation). Look-up tables based on the calculated voltage setting are provided for convenience. Max. DFT in Table is 268 mils (34.3 kV setting)
The number of discontinuities must be reported; however, the standard does not describe methods of demarcating locations of the discontinuities for repairRequires operator to demarcate the location of the holiday/pinhole using a removable product such as chalk or painter’s tape.
Reporting: Reference to ISO 29601,Identity of area inspected,Identity of protective paint system inspected,Test method and voltage used,Name & serial no. of detector used, Details of wetting agent used (low voltage only)No. of discontinuities,Test deviation and/or anomalies,Date of test,Inspector nameReporting (from ASTM G62): Identity of area inspected,Identity of protective paint system inspected,Test method used,For high voltage detection, test voltage used and dielectric strength of coating (if known)    

Table 10A: Differences in Adhesion Testing Standards – Tensile (Pull-off)

ISO 4624 (Method B)ASTM D4541
Appears primarily written for laboratory use (references to specific ambient conditions and preparation of test panels)Written for laboratory or field use
Requires cutting (scoring) through the coating to the substrate unless otherwise specifiedDiscourages cutting (scoring) through the coating to the substrate unless required
Rate of pull is less than 1 MPa/second so that the break occurs within 90 seconds on the initial loading. Not required to record actual rate of pullRate of pull is less than 1 MPa/second so that the break occurs within 100 seconds on the initial loading. Required to record actual rate of pull
Minimum of 6 replicatesMinimum of 3 replicates
No requirement to secure dollies in place while adhesive driesRecommends that loading fixtures be secured in place while adhesive cures
Testing shall be performed at 23 +/- 2°C and 50 +/-5% RHReport actual air temperature and relative humidity
Results reported in megapascals (MPa)Results reported in megapascals (MPa) or pounds/sq. in. (PSI)
Separate protocols for Pass/Fail and Test to Fracture not providedProtocol 1: Test to Fracture (no established pass/fail value). Protocol 2: Pass/Fail (pre-established pass/fail value).
No requirement for retesting if glue fails and minimum adhesion value isn’t specifiedProtocol 1: Retesting required if glue break represents ¼ or more of the loading area.Protocol 2: Retesting required if glue break represents 5% or more of the loading area and value is below the pre-established pass/fail value
Information on operation of each instrument type not provided.Five annexes describing proper instrument use (based on type) included
Record Location of “Failure”Record Location of “Fracture”
Reporting: Reference to ISO 4624 and method used (A, B, or C),Test panel preparation details,Adhesive and curing conditions,Length of time/conditions between assembly (gluing) and testing,Instrument used and diameter of dolly,Type of cutting tool used to score coating,Test results,Deviations from test method/anomalies,Date of test  Reporting: Date, location, testing agency,General nature of test (field/lab),Temperature and relative humidity,Description of adhesion tester (manufacturer, model, calibration date, loading fixture type/dimension…),Substrate type/orientation, thickness, preparation and coating system,Glue used and cure time; Method used to secure fixture during adhesive cure,Rate of pull,Test results,Location(s) of fracture, per Protocol 1 or 2Any correction to results made/results omitted (e.g., low/high),Scoring, if performed,Deviations from test method

Table 10B: Differences in Adhesion Testing Standards – Tape/Knife

ISO 2409ASTM D3359 (Method B)
Method is applicable to hard (metal) and soft (wood/plaster) substratesMethod is applicable to metal substrates only
Method can be used on coatings up to 10 mils (250 µm) thickMethod B (cross-cut) can only be used on coatings up to 5 mils (125 µm) thick
Coatings more than 10 mils (250 µm) – use X-cut (ISO 16276)Coatings more than 5 mils (125 µm) – use X-cut (Method A)
Spacing: Up to 2.4 mils (60 µm): 1 mm (6 cuts)2.4-4.7 mils (61-120 µm): 2 mm (6 cuts)4.8-10 mils (121-250 µm): 3 mm (6 cuts)Spacing: Up to 2 mils (50 µm): 1 mm (11 cuts) 2-5 mils (51-125 µm): 2 mm (6 cuts)
Incision length is unspecifiedIncision length: 20 mm (¾-in.)
Tape is an option for removing loose paint, not for delaminating adherent coatingPressure sensitive tape is used as part of the testing procedure
If using tape, specifies to remove by pulling at a 60° angleSpecifies to remove tape by pulling it over itself at a 180° angle
Frequency: Routine Testing – 1 determinationHigher Precision – 3 determinationsFrequency: 3 determinations
One grid per Test Result Classification provided in Table 1Two grids per Test Result Classifications 1, 2, 3 are provided in Figure 1
Classifications: Rating of 0 represents no detachment; Rating of 5 represents >65% detachmentClassifications: Rating of 5 represents no detachment; Rating of 0 represents >65% detachment
Allows for the optional use of a 3x magnifier for visual inspectionAllows for the optional use of a 10x magnifier for visual inspection
Reporting: Reference to ISO 2409, Test panel preparation details,Temperature and RH,Type of cutting tool used and operation (manual or motor-driven),Method used to remove loose paint,Test results,Deviations from test method/anomalies,Date of testReporting: Substrate type, coating, method of cure,No. of tests, results, mean, range,Adhesion strength of pressure sensitive tape per ASTM D3330 (or manufacturer, product no., lot no.),Estimate of primary location of detachment  

Table 11A: Differences in Coating Hardness – Pencil

ISO 15184ASTM D3363
Test instrument with pencil holder and level applies a constant force to the pencil tip and holds the pencil at the specified anglePencil is held in the operator’s hand. Device similar to the one specified by ISO is referenced as optional
Hardness scale range: 9B to 9H (20 pencils)Hardness scale range: 6B to 6H (14 pencils)
Gouge hardness is reportedGouge and scratch hardness are reported
Reporting: Reference to ISO 15184, Test panel preparation details,Temperature and RH,Magnification of lens, if used,Test result,Deviations from test method/anomalies,Date of testReporting: Gouge and scratch hardness,Manufacturer, lot no. and grade of lead/pencil used,Deviations from standard conditions  

Table 11B: Differences in Coating Hardness – Durometer

ISO 7619ASTM D2240
Covers A and D durometer types, and two specialty scales (AO and AM)Covers 12 durometer types, included A and D
Specifies a test timer of 3 or 15 seconds depending on material typeSpecifies a 1 second test timer
Calibration section is comparatively less detailed and contains only 3 subsectionsCalibration section is comparatively more detailed and contains 9 subsections
Reporting: Reference to ISO 7619, Sample details,Test Details:             -Temperature and RH,             -Instrument type,             -Time lapse – preparation to             measurement, Test results (incl. mean, min/max),Time interval of each reading (if not 1 s),Deviations from test method/anomalies,Date of testReporting: Date of test,Temperature and RH,Manufacturer, type, serial no. of durometer,Whether a maximum indicator or timing device is present,Date of last calibration and calibration due date,Means of testing (i.e., handheld or other),Sample details,ID of material tested,Hardness value obtained and method of calculation (e.g., arithmetic mean),Time interval of each reading (e.g., 1 s),             – Can record result as e.g., D/75/1             (type, hardness value, time interval)

Summary

Project specifications frequently reference industry standard test methods, practices, and guides to communicate requirements. While there are similarities between standards developed by various organizations, they are often not a duplication. As certified coating inspectors we are expected to know and follow referenced standards. This article described the primary differences between several common ISO and SSPC/NACE or ASTM standards but is not to be considered comprehensive. Any time a standard is referenced in a project specification (and you are not familiar with it), it is prudent to obtain a copy, read, and comprehend the content prior to performing an inspection. If the standard is unclear, gain clarification in advance of the inspection.


[1] Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to NonFerrous Metals

[2] Procedure for Determining Conformance to Dry Coating Thickness Requirements

[3] Field Measurement of Surface Profile of Blast Cleaned Steel

[4] Procedure for Determining Conformance to Steel Profile/Surface Roughness/Peak Count Requirements

[5] Conductimetric Analysis of Water Soluble Ionic Contamination of Blast Cleaning Abrasives

[6] Indicating Oli in Abrasives

[7] As of this writing, a revision of ASTM D5162 is being balloted within ASTM to align with ASTM G62 and NACE SP0188. ISO 26901 is also in the process of review and updating with the same voltage recommendations as other standards.

6 thoughts on “Let’s Talk About Differences Between Coating Inspection Standards”

  1. Gordon Kuljian

    Bill thank you for putting together this exhaustive comparison between ISO and US standards.
    That took quite a lot of work on your end. This is surely a lifetime reference for any high-level coating inspector and/or specifier.
    Gordon.

  2. Thank you for the first rate list of ISO and SSPC, NACE, and AMPP standards and Primary Differences
    As performance requirements for protective coatings become ever more stringent , the need to control the quality of the application process becomes ever more obvious and the standards referenced in a project specification should be clearly understood and clarified in advance of the inspection.

  3. Thank you to Bill for an excellent document on the differences between Standards for Coating Inspection. All too often we see specifications for subjects such as surface preparation where the author states “dry abrasive blast to ISO 8501-1 Sa 2 1/2 or NACE No. 5 or in Australia / New Zealand AS 1627.4.
    Your document points out that while the standards are similar, they are not the same. I have been advising specifiers and contractors for years that when the pre-start meeting is called, one of the first items they need agreement on is which standard will be used for the entire project. This can avoid arguments between the owner, inspector and contractor over differences of opinion bewteen standards when disputes arise.

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