DFT acceptance: ISO 19840 and SSPC-PA 2

Use the standard your specification names. Paste the readings and the calculator applies its acceptance rules and its sampling plan.

This tool is a reference aid. Before you act on a result, check it against your specification and the product data sheet.

How the rules work

ISO 19840 judges individual readings, corrected for surface profile: 10 µm for a fine, 25 µm for a medium and 40 µm for a coarse ISO 8503-1 profile, and 25 µm when the profile is unknown. The minimum number of readings depends on the inspection area: 5 up to 1 m², 10 up to 3 m², 15 up to 10 m², 20 up to 30 m², 30 up to 100 m², and 10 more for every further 100 m² or part of it. Split areas above 1,000 m². It applies to nominal DFTs of 40 µm and above.

SSPC-PA 2 judges spots and areas. Up to about 30 m² (300 ft²), measure every 10 m² (100 ft²) area; from 30 to 100 m² (300–1,000 ft²), three random areas; above that, three areas in the first 100 m² plus one for each further 100 m² or part of it. If the specification gives only one value, the default range is ±20 % of it.

Worked examples

ISO 19840: 25 m², nominal 250 µm, so 20 readings. The mean must be at least 250 µm, no reading below 200 µm, and no more than 3 of the 20 between 200 and 249 µm.

SSPC-PA 2: 200–300 µm, Level 3, 450 m² (about 4,800 ft²): seven areas, 35 spots, at least 105 readings. Each spot between 160 and 360 µm, each area average between 200 and 300 µm.

Traps

• Do not deduct the profile twice: if the gauge was adjusted on the blasted surface, no correction value applies.
• Under PA 2, 120 % applies to spots; area averages must still sit inside the range.
• Under ISO 19840, one reading below 80 % fails the area, however few there are.

Related: SSPC-PA 2 vs ISO 19840 guide · Standard: ISO 19840 · Standard: SSPC-PA 2.