Intergranular Corrosion Testing: An Overview of ASTM A 262

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Intergranular Corrosion Testing: An Overview of ASTM A 262

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Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

ASTM A 262 intergranular corrosion testing is the standardized set of practices for detecting susceptibility to intergranular attack in austenitic stainless steels — evaluating whether sensitization caused by chromium carbide precipitation at grain boundaries has reduced corrosion resistance to the point where preferential grain boundary attack will occur in corrosive service environments. ASTM A 262 defines five distinct test practices covering oxalic acid etch screening, ferric sulfate-sulfuric acid immersion, nitric acid immersion, nitric-hydrofluoric acid immersion, and copper-copper sulfate-sulfuric acid immersion — providing stainless steel producers, pressure vessel fabricators, chemical process equipment manufacturers, and quality engineers with standardized sensitization detection methods for material qualification, weld procedure verification, and heat treatment assessment programs.

Scope, Applications, and Benefits

Scope

ASTM A 262 evaluates intergranular corrosion susceptibility in austenitic stainless steels by exposing specimens to aggressive corrosive media under defined conditions and assessing grain boundary attack through metallographic examination, weight loss measurement, or bend ductility evaluation — detecting sensitization resulting from carbide precipitation during heat treatment, welding thermal cycles, or elevated temperature service exposure.

ASTM A 262 intergranular corrosion testing evaluates:

Sensitization susceptibility in austenitic stainless steel wrought products, castings, and weld deposits
Chromium carbide precipitation effects on grain boundary corrosion resistance after thermal processing
Weld heat-affected zone intergranular attack susceptibility in stainless steel fabrications and pressure vessels
Heat treatment and solution annealing effectiveness for restoring corrosion resistance in sensitized stainless steel
Compliance against intergranular corrosion susceptibility requirements per stainless steel product and fabrication specifications

Applications

Austenitic stainless steel plate, sheet, pipe, and bar products requiring sensitization verification per material specifications
Pressure vessel and heat exchanger fabrications requiring weld and base metal intergranular corrosion qualification
Chemical process equipment components requiring stainless steel corrosion resistance verification for aggressive media service
Nuclear and pharmaceutical industry components requiring documented intergranular corrosion test certification
Stainless steel supplier qualification and incoming inspection programs requiring ASTM A 262 sensitization testing data

Benefits

Provides reliable sensitization detection data for stainless steel material qualification and product release
Supports the weld procedure and heat treatment qualification against intergranular corrosion resistance requirements
Identifies sensitized stainless steel materials before fabrication, assembly, and corrosive service deployment
Delivers traceable intergranular corrosion test records for design submissions and regulatory filings
Reduces in-service intergranular attack risk by verifying stainless steel corrosion resistance before equipment commissioning

Test Process

Practice Selection & Specimen Preparation

Applicable ASTM A 262 practice selected per specification requirements; specimens prepared and surface-finished per standard requirements.

Corrosive Exposure

Specimens immersed in the specified corrosive reagent solution under defined temperature and time conditions per the applicable practice.

Post-Exposure Evaluation

Specimens evaluated by metallographic examination, weight loss measurement, or bend ductility test per applicable practice acceptance criteria.

Data Analysis & Reporting

Intergranular attack susceptibility assessed against acceptance criteria and documented for material compliance result.

Technical Specifications

Parameter	Details
Applicable Materials	Austenitic stainless steel wrought products, castings, weld deposits, and heat-affected zones per ASTM A 262 scope
Test Practices	Practice A (oxalic acid etch), Practice B (ferric sulfate-sulfuric acid), Practice C (nitric acid), Practice D (nitric-hydrofluoric acid), Practice E (copper-copper sulfate-sulfuric acid)
Evaluation Methods	Metallographic grain boundary structure rating, weight loss per unit area measurement, and 180° bend ductility evaluation per practice
Exposure Conditions	Boiling reagent immersion at defined concentrations and exposure durations per each ASTM A 262 practice procedure
Measured Outputs	Etch structure classification, corrosion weight loss (g/m²/h), bend ductility result, and intergranular corrosion susceptibility determination

Instrumentation Used for Testing

Reflux immersion apparatus with boiling reagent solution for controlled corrosive exposure per ASTM A 262 practices
Metallographic preparation equipment for specimen sectioning, mounting, and polishing for grain boundary examination
Optical microscope for etch structure classification and intergranular attack assessment per Practice A criteria
Analytical balance for pre- and post-exposure weight measurement per Practice B and C weight loss determination
Bend test fixture for 180° bend ductility evaluation per Practice E acceptance criteria

Results and Deliverables

Etch structure classification results and photomicrographs for Practice A oxalic acid screening examinations
Corrosion weight loss values and acceptance determinations for Practice B, C, and D immersion test specimens
Bend ductility evaluation results and crack assessment for Practice E copper-copper sulfate test specimens
Accept or reject compliance determination for each tested specimen per applicable ASTM A 262 practice criteria
ASTM A 262 intergranular corrosion test report

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Frequently Asked Questions

ASTM A 262 is the standardized set of practices for detecting sensitization and intergranular attack susceptibility in austenitic stainless steels — using corrosive immersion, etch examination, and bend testing to evaluate grain boundary corrosion resistance.

Practice A is an oxalic acid etch screening; B uses ferric sulfate-sulfuric acid immersion; C uses nitric acid; D uses nitric-hydrofluoric acid for molybdenum-bearing grades; E uses copper-copper sulfate-sulfuric acid for weld and wrought products.

Sensitization results from chromium carbide precipitation at grain boundaries during welding or heat treatment — depleting adjacent zones of chromium and reducing localized corrosion resistance to intergranular attack in corrosive environments.

ASTM A 262 evaluates standard austenitic grades including 304, 304L, 316, 316L, 321, 347, and other austenitic stainless steel wrought products, castings, and weld deposits requiring intergranular corrosion susceptibility assessment.

Specimens are electrolytically etched in oxalic acid solution and examined metallographically — classifying grain boundary etch structure as step, dual, or ditch to screen for sensitization before selecting confirmatory immersion practice testing.