ISO 19840:2012 PDF

Overview - ISO 19840:2012 (dry-film thickness on rough surfaces)

ISO 19840:2012 specifies a standardized procedure for verifying dry-film thickness (DFT) of protective paint systems on roughened steel surfaces. It defines how to adjust and verify film thickness gauges, select inspection areas and sampling plans, perform measurements with magnetic and eddy‑current instruments, and apply acceptance/rejection criteria. The standard supplements the ISO 12944 corrosion‑protection series and applies to nominal DFTs of 40 µm or greater.

Key topics and technical requirements

• Scope and definitions
  • DFT is defined as the coating thickness remaining above the peaks of a rough surface profile.
  • Applies to coatings on abrasive blast‑cleaned or otherwise roughened steel substrates.
• Measurement principles
  • Approved instruments: permanent magnet, magnetic induction (electromagnet) and eddy current types (eddy‑current mainly for non‑ferrous substrates).
  • Devices are adjusted and verified at zero and at a known thickness on a smooth surface before use.
• Probe handling and reading methods
  • Twin‑pole probes may require multiple pivoted readings (e.g., 0°, 90°, 180°, 270°) with the arithmetic mean used as the spot value.
  • Individual readings versus multiple‑reading methods are described; Annex B covers multiple readings and Annex A gives an alternative method of adjusting to known rough‑surface thicknesses.
• Correction value
  • Measurements on rough surfaces yield higher gauge readings; the correction value (instrument reading minus correction = individual DFT) compensates for profile influence.
  • Annex D provides a normative procedure for determining a specific correction value.
• Sampling plan and acceptance criteria
  • Defines inspection areas, number of readings and statistical treatment (mean, standard deviation) and sets acceptance/rejection rules based on nominal DFT.
• Reporting
  • Requirements for test reports and example forms are included (Annex E informative).

Applications and who uses ISO 19840:2012

• Practical uses:
  • Quality control and verification of protective paint systems on bridges, offshore structures, industrial plants, and other steel assets.
  • Establishing contractual acceptance criteria and audit evidence for coatings applied over blast‑cleaned surfaces.
• Typical users:
  • Coating specifiers, corrosion engineers, NDT technicians, inspectors, paint contractors, QA/QC personnel, asset owners and procurement teams.

Related standards

• ISO 12944 series (protective paint systems for steel structures)
• ISO 2808 (film thickness determination)
• ISO 8503‑1 (surface roughness/profile references)
• Use of ISO 19840:2012 helps ensure consistent, reproducible film thickness measurement and supports robust corrosion protection practices for steel structures.