ASTM G48 is the standard laboratory test for pitting and crevice corrosion resistance of stainless steels and related alloys. A sample is immersed in an aggressive ferric chloride solution for 24 to 72 hours, then assessed for weight loss or pitting. A good result shows zero corrosion, reported as 0g/m2.
How does the test work?
ASTM G48 is the "Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution". The test uses an aggressive ferric chloride solution. This medium is rarely seen in day-to-day operations, but it partly replicates the conditions found within a corrosion pit in chloride-containing environments, which is why it has become a recognised benchmark.
The standard includes several formats, including the use of a crevice-forming device to artificially simulate an undesirable feature. All of them follow the basic approach of Method A: a sample is immersed in the acidic ferric chloride solution, typically for 24 to 72 hours, and then assessed either for relative weight loss or for the presence of pits.
What test temperature applies to each alloy?
The test temperature is set according to the alloy:
| Alloy | Test temperature |
|---|---|
| 2205 duplex (1.4462, F51) | 25°C |
| SAF2507 (1.4410, F53, S32750) | 50°C |
| S32760 (1.4501, F55, Zeron 100®) | 50°C |
| Ferralium® 255 (1.4507, F61, S32550) | 50°C |
A good result shows zero corrosion, reported as 0g/m2 of the test piece. This indicates an optimised microstructure, with a balance of austenite and ferrite achieved through appropriate solution annealing and quenching.
Which ASTM G48 test do I need?
The choice depends on the alloy and on whether you are assessing pitting or crevice corrosion. The available methods are:
- Method A - ferric chloride pitting test
- Method B - ferric chloride crevice test
- Method C - critical pitting temperature test for nickel-base and chromium-bearing alloys
- Method D - critical crevice temperature test for nickel-base and chromium-bearing alloys
- Method E - critical pitting temperature test for stainless steels
- Method F - critical crevice temperature test for stainless steels