A study of the nitric acid corrosion rate results as determined by ASTM A-262 Practice C on TP-304-L tubular products

Basic metallurgical factors affecting the corrosion behavior of wrought TP-304-L tubular products in the ASTM A-262 Practice C (Nitric Acid) corrosion test is reviewed. Over l00 heats of TP-304-L were selected statistically to provide a range of variables within ASTM tubular product specifications. Significant factors identified as affecting the corrosion rate were carbon, chromium, nickel, ferrite phase and molybdenum with the ferrite phase. Maintaining carbon and nickel concentrations constant small increases in the chromium content greatly influence the formation of ferrite. A small amount of residual ferrite--l to 5%-significantly reduces the corrosion rate in nitric acid. However, residual ferrite in conjunction with molybdenum concentrations over 0.25% increases the corrosion rate.