Etch structure classification or commonly known as oxalic acid etch test or sodium hydroxide etch test is performed as a screening test on austenitic and duplex stainless steel respectively prior to corrosion resistance test.

The oxalic acid etch test is a rapid method of identifying austenitic stainless steel sample that is essentially free of susceptibility to intergranular attack associated with chromium carbide precipitates. These specimens will have low corrosion rates in certain corrosion tests and therefore can be eliminated (screened) from testing as “acceptable.”

The sodium hydroxide etch test may be used for the acceptance of duplex stainless steel material but not for rejection. This test method may be used with other evaluation tests to provide a rapid method for identifying those specimens that are free of detrimental intermetallic phases as measured in these other tests.

LMATS is NATA accredited to perform etch structure classification in accordance with ASTM A262 and ASTM A923.