# ASTM D7091

Source: https://coatmentor.com/standards/astm-d7091/ · Updated 2026-10-14

Non-destructive DFT measurement with magnetic and eddy-current gauges.

**Publisher**: ASTM International

**Area**: Application and film thickness

ASTM D7091 covers how to use dry film thickness gauges. These are magnetic gauges for non-magnetic coatings on ferrous metals, and eddy-current gauges for non-conductive coatings on non-ferrous metals.

## Three different words

- **Calibration:** done by the manufacturer or a qualified laboratory, with a certificate.
- **Verification of accuracy:** done by the user with reference standards, at least at the start and end of each shift.
- **Adjustment:** aligning the gauge reading to a known thickness, for example with shims on the surface to be coated.

## Verification in practice

- If a gauge fails its check, treat every reading since the last good check as suspect.
- A Type 1 (magnetic pull-off) gauge is verified on certified coated plates, not on plastic shims. Shims suit Type 2 (electronic) gauges.
- On blasted steel, SSPC-PA 2 Appendix 8 adjusts a Type 2 gauge on the blasted surface or a blasted panel of similar steel, at one point or at two.

How many readings to take and how to accept them comes from SSPC-PA 2 or the specification.

**7** practice items in the members area mention ASTM D7091 (CIP 1: 4 · CIP 2: 3).

## Related

- **Concepts:** [Dry film thickness measurement](https://coatmentor.com/learn/dft-measurement/)
- **Standards:** [SSPC-PA 2](https://coatmentor.com/standards/sspc-pa-2/) · [ISO 19840](https://coatmentor.com/standards/iso-19840/) · [ISO 2808](https://coatmentor.com/standards/iso-2808/)

## About this page

This page describes the subject of ASTM D7091 in our own words; it does not reproduce the standard. For the full text, buy the current edition from ASTM International. Checked on 2026-10-14; errors go in the [corrections log](https://coatmentor.com/method/). CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.