ASTM A262: Practices for Detecting Susceptibility to Intergranular Attack

ASTM A262 at a glance

Full title: Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels (designation A262). It is not a material specification. It is a family of test methods that a purchaser calls up on top of a product standard such as ASTM A240 plate or ASTM A312 pipe, to prove a heat is not sensitized.

The target failure mode is intergranular corrosion (IGC), often seen as weld decay. When an austenitic grade is held in the sensitizing range, chromium carbides precipitate at the grain boundaries and strip the adjacent metal of the chromium it needs to stay passive. A262 puts the steel into an aggressive medium that attacks those chromium-depleted zones first, so a susceptible heat shows itself quickly.

At Nandini Steel, we supply austenitic stainless to the major product standards and can have IGC testing per ASTM A262 run as a supplementary requirement. Every order ships with an EN 10204 3.1/3.2 mill test certificate.

Why intergranular attack happens: the sensitization link

Sensitization is the root cause A262 exists to catch. When grades like 304 or 316 sit between roughly 425–815 °C, carbon diffuses to the grain boundaries and combines with chromium to form chromium carbides (Cr23C6). The thin band beside each boundary drops below the ~11% chromium needed for passivity, and that depleted path corrodes preferentially. Welding is the usual culprit, since the heat-affected zone passes through the sensitizing range, which is why the damage is nicknamed weld decay.

Three routes keep a heat out of trouble, and A262 is how you verify them:

• Low-carbon "L" grades such as 304L and 316L, with carbon held at ≤0.03%, leave too little carbon to form damaging carbide networks.
• Stabilized grades 321 and 347, where titanium or niobium ties up carbon as stable carbides before chromium can.
• Solution annealing, which redissolves the carbides and quenches fast enough to keep them in solution. See solution annealing and our guide on how to prevent sensitization.

The five ASTM A262 practices

ASTM A262 contains a screening test and four quantitative corrosion tests. Practice A is a fast electrolytic etch used to screen out clearly acceptable material; the acid-immersion practices (B, C, E, F) then confirm the result by weight loss or by a bend test. A practice is chosen to match the service medium and the grade, especially whether the grade carries molybdenum.

A262 also historically listed Practice D (nitric-hydrofluoric acid), which has been dropped from the current edition. Order against the practice your project specification names, and confirm the edition on the mill certificate.

Practice A: oxalic acid etch (the screen)

Practice A is an electrolytic etch in 10% oxalic acid, examined under a microscope. The grain-boundary shape sorts the sample into a step structure (no carbides, acceptable), a dual structure (some ditching, borderline), or a ditch structure (boundaries fully surrounded by carbides). It is fast and cheap, so it is run first. A clean step structure can accept the heat outright; a ditch structure sends it on to an immersion test for a quantitative verdict.

Practices B, C, E, F: the immersion tests

These put the specimen into a boiling acid that attacks sensitized boundaries. Practices B, C and F report a corrosion rate from weight loss over the test period, so they give a number you can hold against an acceptance limit. The Strauss test, Practice E, instead bends the specimen after exposure and inspects for cracks under magnification, a straightforward pass/fail. The Huey test, Practice C, is the most severe and the one usually tied to nitric-acid duty.

Which practice for which grade

The grade, and specifically whether it carries molybdenum, steers the choice. Molybdenum-free grades behave differently in the ferric sulfate and copper sulfate tests than Mo-bearing grades do, so the standard pairs practices to grades.

Low-carbon and stabilized grades are specified precisely because they pass these tests after welding. For the welding side of the story, see how to weld 304L, how to weld 316L and weld decay and filler selection.

How ASTM A262 fits with the product standards

A262 never travels alone. It rides on a product standard that governs the plate, sheet, pipe or bar itself, and the purchase order calls up the practice as a supplementary requirement.

The result lands on the mill test certificate as a recorded supplementary test, alongside the chemistry and mechanicals. For the wider inspection picture, see testing, MTC, NDT & PMI.

Where IGC testing matters most

IGC testing is specified where the service medium would exploit a sensitized boundary. That means acid and high-purity duty above all.

• Chemical and acid processing, where boiling acids find any depleted grain boundary. See chemical processing and sulfuric-acid resistance.
• Pharmaceutical and hygienic systems, where surface integrity is non-negotiable; see pharmaceutical.
• Pulp and paper, with hot bleaching and digester chemistries; see pulp and paper.

Across these, the question is usually whether to upgrade from 316L, which 304L vs 316L and our austenitic stainless steel reference help answer.

How to specify ASTM A262 on an order

1. Name the product standard first, A240/SA-240, A312, A276 or A479, with grade and UNS.
2. Call up A262 as a supplementary requirement, state "IGC test per ASTM A262."
3. Name the practice, A, B, C, E or F; do not leave it as "A262" alone, since the practices test different things.
4. State the acceptance basis, the maximum corrosion rate (for B, C, F) or a no-cracks bend result (for E).
5. Specify the condition tested, as-received, or sensitized/as-welded, if the test is to represent the fabricated part.
6. Set the MTC level, EN 10204 3.1 (mill) or 3.2 (third-party witnessed).

For reading the finished document, see how to read a mill test certificate and material traceability.

Frequently asked questions

Order austenitic stainless with ASTM A262 IGC testing

Nandini Steel has operated as an ISO 9001:2015-certified stockist and supplier of corrosion-resistant steel since 2003, more than 20 years (Cert No. 1283438, Unitas Certification Services, valid through 11 January 2028). The record stands at 307+ projects, 260+ clients and shipments into 36+ countries. We supply austenitic stainless to the major ASTM and ASME product standards, cut from genuine mill material and held ex-stock for immediate dispatch, with IGC testing per ASTM A262 arranged as a supplementary requirement. Every order ships with an EN 10204 3.1/3.2 mill test certificate. Pricing is quoted live against your enquiry, not fixed in a catalog.

Send your grade, form, dimensions, the A262 practice and MTC level for a quotation.

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