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Coating thickness (ISO 2808, ISO 19840 vs SSPC-PA 2) and ISPM 15 export crating

How dry-film thickness is measured and accepted under the two main coating standards, and what to check on export crates, flange protectors and bore preservation before the valves leave the factory.

Standards Comparisons2026-11-148 min read

ISO 19840SSPC-PA 2ISO 2808ISPM 15DFT

Short answer: ISO 2808 describes how to measure dry-film thickness. ISO 19840 and SSPC-PA 2 describe whether the thickness is acceptable, and they do not use the same rule. ISO 19840 applies an 80/20 rule to individual corrected readings against a nominal DFT. SSPC-PA 2 judges spots and areas against a specified min/max, with Level 3 as the default. Name one of them in the purchase order, and have the gauge checked with a reference foil on site before the first official reading.

By Kevin Lyu (吕中国), ValveWitness Inspection, Ningbo · Published 2026-11-14

In our sample report: Section 11 measures DFT with a magnetic gauge per ISO 2808, verified with a 125 µm reference foil. Acceptance is described as “in the spirit of ISO 19840”: each reading at least 80% of the 120 µm minimum, and the average at least the minimum. Sample S3 averaged 113 µm and is not conform. Section 5 records ISPM 15-marked wooden cases, flange caps and bore preservation. See the sample report.

Measuring versus accepting DFT

ISO 2808 is the method standard for measuring paint film thickness. A magnetic or electromagnetic gauge used on a steel valve body is one of those methods. Before official readings, the inspector (or the factory, watched by the inspector) should verify the gauge with reference foils or certified shims covering the thickness range of interest, on a suitable substrate, and record the foil value, the reading and the gauge identification. A colour check against a RAL card (RAL 5015 in the sample) is a separate visual comparison; it is not a thickness measurement.

Acceptance is not in ISO 2808. It comes from the coating specification, which should name ISO 19840, SSPC-PA 2, or a written project rule.

ISO 19840’s 80/20 rule versus SSPC-PA 2 spots

Both standards require a calibrated gauge and a method for dealing with blast-profile roughness. Their acceptance arithmetic is different. The edition named in the contract governs; the summary below is the commonly applied default logic, not a reproduction of the standards’ tables.

TopicISO 19840SSPC-PA 2 (AMPP)
What it is forAcceptance of dry-film thickness on rough (blasted) steel, used with ISO 12944 paint systemsProcedure for determining conformance to a specified dry coating thickness; widely used on US-specified work
What is judgedIndividual (corrected) readings, against a nominal DFT (NDFT)Spot measurements (the average of at least three gauge readings in a small circle, about 4 cm / 1.5 in) and area averages (typically five spots)
Gauge checkVerification at zero and with foils or certified plates; a correction value is deducted for the blast profileAccuracy verification and adjustment following ASTM D7091. Type 2 electronic gauges may be adjusted with certified shims; base-metal readings correct for the substrate
Default acceptance ruleThe 80/20 rule: the mean of all individual readings ≥ NDFT; every reading ≥ 80% of NDFT; fewer than 20% of readings may fall between 80% and 100% of NDFT; no reading above a specified maximumFive restriction levels. If the level is not stated, Level 3 is the default: each spot ≥ 80% of the specified minimum and ≤ 120% of the specified maximum; each area average within the specified range. Individual gauge readings are not themselves limited at Level 3 — they are averaged into the spot
SamplingA minimum number of readings based on the size of the inspection areaA number of inspection areas based on the coated area, with five spots in each area

Worked example: sample S3 in the sample report

Specified minimum DFT: 120 µm. Sample S3 readings (µm): 118, 104, 110, 121, 112. Average: 113 µm.

  • 80% of 120 µm is 96 µm. Every individual reading is above 96 µm.
  • The average, 113 µm, is below the 120 µm minimum (or NDFT, if that is how the specification is written). The sample already fails a “mean ≥ specified DFT” rule, which is the first limb of ISO 19840 and is also the rule stated in the sample report.
  • Under the full ISO 19840 80/20 rule, readings between 80% and 100% of NDFT must also be fewer than 20% of the readings. Here most of the five readings are below 120 µm, so the sample would fail that limb as well.

The low DFT is reported as a specification deviation, not as a visual AQL defect (see ISO 2859-1 vs ANSI/ASQ Z1.4). The lot can be within AQL for workmanship and still be PENDING or FAIL on coating.

ISPM 15 export crating, and what paint can hide

ISPM 15 is the IPPC standard for wood packaging used in international trade. Solid wood cases and pallets should be made of debarked wood, treated (heat treatment, HT, is the treatment almost always seen now) and marked with the IPPC wheat stamp: country code, producer code and treatment code. Missing, incomplete or unofficial marks are a common reason a shipment is stopped at destination. Plywood and some processed wood are treated differently; the mark applies to the solid-wood components that ISPM 15 covers.

Check (sample report, Section 5)What “conform” looks like
End protectionFlange faces covered with plastic or wooden caps, so the serration is not damaged in transit
Valve position for shippingAs specified — a gate valve is commonly shipped closed
Internal preservationBore and machined surfaces dry, with rust preventive applied
Packing materialWood packaging marked to ISPM 15 (typically the IPPC wheat-stamp with country code, producer code and treatment, for example HT), plus a moisture barrier where specified
Shipping marks and packing listMarks match the PO (client, PO number, case number, weights, dimensions, destination); the packing list matches case contents and serial numbers

Paint and crates also hide earlier work. Once a valve is coated and the flanges are capped, a PSI can no longer see as-cast surfaces, unmachined heat marks under a heavy film, or a flange face that was already scratched. That is one reason to combine a DUPRO or a test-witness hold point with the final pre-shipment visit, rather than booking only a packed-lot PSI.

What to write into the purchase order

  • The coating system, colour (for example a RAL number) and the specified DFT — as a nominal DFT (ISO 19840) or as a min/max (SSPC-PA 2).
  • The acceptance standard and edition (ISO 19840 or SSPC-PA 2, and the restriction level if you use SSPC-PA 2 and do not want the Level 3 default).
  • That the DFT gauge is verified with a reference foil or certified shim on site, and that the foil value is recorded.
  • ISPM 15 marking of solid-wood packaging, flange-face protection, bore preservation, and the shipping-mark layout.

Sources

  • ISO 2808, Paints and varnishes — Determination of film thickness — iso.org (ISO 2808:2019)
  • ISO 19840:2012, Paints and varnishes — Corrosion protection of steel structures by protective paint systems — Measurement of, and acceptance criteria for, the thickness of dry films on rough surfaces — iso.org
  • SSPC-PA 2, Procedure for Determining Conformance to Dry Coating Thickness Requirements — AMPP (formerly SSPC)
  • ISPM 15, Regulation of wood packaging material in international trade — IPPC / FAO
  • Our sample valve PSI report (fictitious data), Sections 5 and 11.

We report facts from the samples inspected. Standards named in these guides are public standards we work to, not certifications or accreditations we hold. We do not issue product certificates or accreditation marks. Test pressures, durations, leakage rates and acceptance numbers must be read from the licensed edition named in your purchase order; we do not reproduce copyrighted tables from the standards.

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