ASTM D7091
Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals
Describes nondestructive magnetic and eddy-current gauge measurement of dry coating thickness on ferrous and non-ferrous metal substrates.
What ASTM D7091 specifies
ASTM D7091 is the standard practice for using electronic or mechanical gauges to measure dry film thickness without cutting the coating. Magnetic methods measure nonmagnetic coatings on ferrous substrates; eddy-current methods measure nonconductive coatings on non-ferrous conductive substrates. The practice addresses instrument verification, calibration adjustment, substrate effects, surface roughness, curvature, edge effects, probe positioning, and reporting. It does not create a universal acceptable thickness range; the coating or project specification provides nominal thickness and sampling acceptance. Multiple readings are needed because individual measurements vary with both the film and the substrate profile.
ASTM D7091 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Requirement / test |
|---|---|---|
Type 1 | Permanent-magnet pull-off instrument for nonmagnetic coatings on ferrous substrates | Instrument verification, adjustment, and repeated readings |
Type 2 | Electronic instrument using magnetic induction on ferrous substrates or eddy current on non-ferrous conductive substrates | Instrument verification, adjustment, and repeated readings |
Tests and the drawing call-out
Tests the document imposes
- Magnetic pull-off thickness
- Electronic magnetic-induction thickness
- Eddy-current thickness
- Gauge verification and calibration adjustment
How to cite it
Drawing call-out
MEASURE DRY FILM THICKNESS PER ASTM D7091; REQUIRED DFT <RANGE>; SAMPLING <PLAN>Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
ASTM D7091 — frequently asked
Does ASTM D7091 specify the required paint thickness?
No. It explains how to measure dry film thickness; the coating or project specification sets the required range.
Which gauge is used on aluminum?
A suitable eddy-current gauge measures nonconductive coatings on conductive non-ferrous substrates such as aluminum.
Why do DFT readings vary on blasted steel?
Surface profile changes the probe response and the local coating thickness. Calibration adjustment and multiple readings are required.
ASTM D7091 is copyrighted by ASTM International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗