Standard · Surface preparation and conditions
ASTM D4940
Soluble salt contamination of blast abrasives, by conductivity.
ASTM D4940 checks blast abrasive for soluble salts before they reach the steel. It measures the electrical conductivity of water that has soaked the abrasive.
The procedure
Mix equal volumes of abrasive and deionized water, 300 mL each. Stir for a minute, let it stand for 8 minutes, stir again, filter and measure the conductivity of the filtrate.
Points to remember
- Conductivity shows all the dissolved salts together. It does not say which ions they are, so it is not a chloride test.
- D4940 is a test method only. The limit comes from the abrasive standard: the SSPC abrasive standards allow at most 1,000 µS/cm. A meter that shows mS/m reads that limit as 100 mS/m.
Not the ISO method
ISO 11127-6 also uses conductivity, but with a different ratio and a longer soak, and ISO 11126 sets its own, lower limit for new slags. A result by one method cannot be judged against the limit of the other, so the specification names the method together with the limit.
1 practice item in the members area mentions ASTM D4940 (CIP 2: 1).
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This page describes the subject of ASTM D4940 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. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.