Sensitization is a critical degradation mechanism in austenitic stainless steels, occurring when chromium carbides precipitate at grain boundaries during welding or heat treatment in the 450-850?C range. This chromium depletion leaves the grain boundaries susceptible to intergranular corrosion, especially in corrosive environments.
Per ASTM A262, the standard practices for detecting susceptibility to intergranular attack include the Strauss test (Practice E) and the Huey test (Practice C). The Strauss test exposes a specimen to boiling copper sulfate-sulfuric acid solution for 15-24 hours, followed by a bending test to reveal cracks. The Huey test uses boiling 65% nitric acid for five 48-hour periods, measuring weight loss as corrosion rate.
For austenitic grades like 304L and 316L, controlled carbon content (max 0.03%) or stabilization with titanium or niobium (grades 321, 347) prevents sensitization. In NACE MR0175 sour service, ferrite number control between 3-8 FN is also required to avoid selective attack.
Understanding and qualifying these tests is essential for welding engineers specifying stainless steel fabrications for chemical, petrochemical, and hydrogen service. The Huey test is particularly stringent and is often specified for nitric acid service.
Source: ASTM A262
How do you select between Strauss and Huey testing for your stainless steel weld qualifications?