Rationale

ASTM B928 provides criteria for alloys in the H116, H321 and H128 tempers for passing an intergranular corrosion (NAMLT) test. This test is detailed in ASTM G67, which has recently been updated. One of the updates changed the nitric acid concentration of the test solution from 70-72% to 67-70%. A decrease in nitric acid concentration has been shown to increase the NAMLT result. This relationship was presented in the May 2019 G01.05 meeting where data was shown in which a 2% drop in nitric acid was shown to cause an approximate 9-10 point increase in NAMLT weight loss value (mg/cm2). Therefore it is necessary to change the pass/fail limits outlined in ASTM B928 to reflect the lower nitric acid concentration in the NAMLT test solution.