ASTM A262 Intergranular Corrosion Test (IGC) | Practices A, B, C, E, F Explained
ASTM A262 is a standard test method used to evaluate the susceptibility of austenitic stainless steels to intergranular corrosion (IGC). It includes Practices A, B, C, E, and F, which assess sensitization and corrosion resistance under different test conditions.
What is Intergranular Corrosion (IGC)?
Intergranular corrosion (IGC) is a localized attack that occurs:
- Along grain boundaries of stainless steel
- Due to chromium carbide precipitation
- Causing chromium depletion zones
This leads to loss of corrosion resistance and potential failure.
What is ASTM A262?
ASTM A262 defines several test methods to:
- Detect sensitization in stainless steels
- Evaluate resistance to intergranular corrosion
- Verify material performance after welding or heat treatment
Applicable Materials
- 304 / 304L
- 316 / 316L
- 321 / 347
- Duplex: UNS S31803 / S32750
Overview of ASTM A262 Practices
| Practice | Test Type | Purpose |
|---|---|---|
| A | Oxalic Acid Etch | Rapid screening |
| B | Ferric Sulfate–Sulfuric Acid | Weight loss |
| C | Nitric Acid (Huey) | General corrosion |
| E | Strauss Test | Grain boundary attack |
| F | Cu–CuSO₄–H₂SO₄ | Severe IGC |
Practice A – Oxalic Acid Etch Test
- Microscopic screening method
- Electrolytic etching in oxalic acid
Result Interpretation:
- Step structure → acceptable
- Dual / ditch structure → sensitized
Fast and suitable for screening, but not sufficient for final acceptance.
Practice B – Streicher Test
- Ferric sulfate + sulfuric acid solution
- Boiling test for 24–120 hours
Purpose:
- Quantitative evaluation via weight loss
Used for:
- 321 / 347 stainless steels
- Nickel alloys
C – Huey Test
- 65% nitric acid
- 5 cycles × 48 hours
Purpose:
- Evaluate corrosion resistance
- Detect chromium depletion
Used for strongly oxidizing environments.
Practice E – Strauss Test
- Copper sulfate + sulfuric acid solution
- Followed by 180° bend test
Evaluation:
- No cracks → pass
- Cracks → fail
Most commonly used method for IGC detection.
Practice F
- More severe than Practice E
- Used for highly critical applications
Key Differences Between Practices
| Practice | Speed | Severity | Use Case |
|---|---|---|---|
| A | Fast | Low | Screening |
| B | Medium | Medium | Weight loss |
| C | Slow | Medium | General corrosion |
| E | Medium | High | Standard IGC |
| F | Medium | Very High | Severe |
When is ASTM A262 Testing Required?
Testing is required when:
- Stainless steel is welded
- Heat treatment may cause sensitization
- Used in corrosive environments
- Required by project specifications
Applications
- Chemical processing
- Oil & gas industry
- Power plants
- Heat exchangers
- Pressure vessels
Quick Summary
- ASTM A262 = IGC testing standard
- Detects grain boundary corrosion
- Practice A = screening
- Practice E = most commonly used
- Practice F = most severe
FAQ
What is ASTM A262 used for?
To detect intergranular corrosion in stainless steel.
Which practice is most commonly used?
Practice E (Strauss test).
What is the fastest method?
Practice A (Oxalic acid etch).
Is ASTM A262 always required?
No, but required in critical applications.