Chloride stress corrosion cracking resistance of 6% Mo stainless steel alloy (UNS N08367)

The UNS N08367 (ALdXN (R)) alloy was designed to be a seawater resistant al loy and has been successfully used in a multitude of marine and offshore ap plications including process piping systems, heat exchanger equipment, dril ling platforms, and desalination systems. Although the N08367 alloy has imp roved resistance to chloride stress corrosion cracking (CSCC) it is not com pletely immune to this mode of failure. This investigation exposed U-bend s pecimens to various chloride bearing solutions to better define cracking th reshold of the N08367 alloy. Samples were exposed in an autoclave using sta tic solutions and no effort was made to either aerate or dearate test solut ions. Measurements in solutions with chloride concentrations of 0.02 to 2.0 wt% mixed from ASTM D-1141-52 sea salt, readily produced cracking at tempe ratures of 260 degreesC. The threshold temperature for the onset CSCC in st raight NaCl solutions was found to increase as the chloride concentration d ecreased. In the range of 0.02 to 15.8 wt% chlorides the threshold temperat ure in degreesC for the onset of cracking can be defined as follows. T-SCC = 190.05 - 47.42log [CI]. The results of this testing indicate that it is u nlikely to stress corrosion crack this alloy in presence of chlorides at te mperatures in the range of atmospheric boiling (approximate to 100 degreesC ). At temperatures greater than 120 degreesC cracking can be initiated depe nding on the chloride content of the environment.