SUS316 Corrosion Resistance Test Standards: ASTM A262, G48, B117, and ISO 3651 Explained

Why Test Standards Matter for SUS316

SUS316 stainless steel is specified across chemical equipment, marine components, and food-processing systems because of its 2-3% molybdenum content, which resists chloride pitting and crevice corrosion far better than SUS304. But a grade name alone does not guarantee performance: corrosion resistance depends on composition, heat treatment, surface condition, and fabrication quality. Standardized corrosion tests let buyers verify that delivered material meets the intended service capability. This article explains the test methods most commonly called up for SUS316 and how to interpret their results.

ASTM A262: Intergranular Corrosion (IGC) Testing

ASTM A262, Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels, is the primary IGC test family. The practices most relevant to SUS316 are:

Practice E, the copper/copper sulfate-sulfuric acid (Strauss) test: exposes the sample to boiling copper sulfate-sulfuric acid for 15-24 hours and then bends it; cracking indicates sensitization. This is the standard acceptance test for welded SUS316 pipe and sheet.

Practice C, the nitric acid (Huey) test: five 48-hour boiling periods in 65% nitric acid, with weight-loss measurement. More aggressive, used for high-chromium and higher-carbon service conditions.

SUS316 with controlled carbon (0.08% max, or 0.030% for SUS316L) and proper solution annealing normally passes IGC testing, because no significant chromium-carbide network remains at grain boundaries.

ASTM G48: Pitting and Crevice Corrosion Testing

ASTM G48, Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Alloys by Use of Ferric Chloride Solution, is the industry benchmark for localized corrosion. Method A exposes the specimen to 6% ferric chloride at a controlled temperature for 24 hours and records the critical pitting temperature (CPT), the highest temperature at which no pitting occurs. For SUS316, CPT values typically fall in the 22-28 C range, and Method B (crevice assembly) is used when crevice geometry, such as gasketed joints, is part of the service. Higher molybdenum and nitrogen contents raise the CPT, which is why higher-alloy grades achieve 35 C and above.

ASTM B117: Neutral Salt Spray (NSS) Testing

ASTM B117 runs a continuous 5% neutral salt fog at 35 C and records the hours to first rust or failure. It is a comparative test for atmospheric and coating performance rather than a design-life predictor. For bare SUS316, NSS results commonly range from several hundred hours to more than 1500 hours depending on surface finish, with smoother passivated surfaces performing best. Because real environments differ from the constant salt fog, NSS hours should be used to compare surface treatments and suppliers, not to calculate service life.

ISO 3651-1 and ISO 3651-2: European IGC Methods

ISO 3651-1 and ISO 3651-2 are the European intergranular corrosion test methods for stainless steels. ISO 3651-1 (Method A) uses boiling nitric acid, and ISO 3651-2 (Method B) uses boiling sulfuric acid with copper sulfate, with metallic copper added as a cathodic depolarizer. They serve the same purpose as ASTM A262 Practices C and E and are commonly required for European pressure equipment documentation (EN 10204 3.1 certificates). A common misunderstanding is calling these high-temperature corrosion tests; they detect sensitization, not hot-gas attack.

Composition and Mechanical Properties of SUS316 (JIS G4304)

Chemical Composition (% by mass)

Element	SUS316
C	0.08 max
Cr	16.00-18.00
Ni	10.00-14.00
Mo	2.00-3.00
Mn	2.00 max
Si	1.00 max
P	0.045 max
S	0.030 max

Mechanical Properties (plate, typical minimums)

Tensile strength	520 MPa min
Yield strength (0.2% proof)	205 MPa min
Elongation	40% min
Hardness	200 HBW max (typical)

Reading Test Reports: What to Check

Verify the test method and edition are the ones called up in your specification (e.g., ASTM G48 Method A, 24 h, 6% FeCl3).

Check the test temperature and the measured result: for G48 Method A, the CPT or the pass temperature; for A262 Practice E, pass/fail on bend cracking.

Confirm the sample origin: test coupons should represent the same heat and heat-treatment batch as the delivered material.

Look for the material identity, heat number, and certificate reference so the report is traceable to your order.

Remember that a single test result is a snapshot: corrosion performance in service depends on media, temperature, crevices, and surface condition.

FAQ

Which standard tests intergranular corrosion of SUS316?

ASTM A262 (Practices C and E) and the equivalent European methods ISO 3651-1 and ISO 3651-2. Practice E (Strauss test) is the most common acceptance test for welded SUS316 pipe and sheet.

What is the critical pitting temperature of SUS316?

In the ASTM G48 Method A ferric chloride test, SUS316 typically pits in the 22-28 C range. Higher-alloy grades such as duplex or 6% molybdenum super-austenitic types reach substantially higher temperatures.

Is the salt spray test a reliable life predictor for SUS316?

No. ASTM B117 is a comparative test for coatings, finishes, and material lots. Use it to compare suppliers and surface treatments; do not convert NSS hours directly into service life.

Does SUS316L need different corrosion testing than SUS316?

The same test methods apply. SUS316L (0.030% max carbon) will more reliably pass the IGC tests after welding, which is why welded equipment is usually specified in SUS316L and tested to ASTM A262 Practice E.

What documents should I request to verify SUS316 corrosion performance?

Request a mill test certificate referencing JIS G4304 or G4303 for composition and mechanical properties, plus corrosion test reports for the specific methods in your specification: ASTM A262, ASTM G48, or ISO 3651. PMI (positive material identification) confirms composition on delivered parts.