The Effect of Elemental Sulfur and Surface Condition on Stress Corrosion Cracking of High Nickel Alloys under Hot Sour Environments

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Abstract
Two variables, elemental sulfur and surface condition, which can affect the crack resistance performance of C-276 and I-825 were investigated by using a slow strain rate test (SSRT) method. Several methods of introducing elemental sulfur (charging) to the test environments were assessed to establish the validity of the laboratory test results. Stress corrosion cracking (SCC) was prevented on specimens showing marginal susceptibility to SCC when the surface was given a near-metallographical finish. The SCC susceptibilities for both alloys were dependent not only upon the amount of elemental sulfur, but also on the charging method. Both alloys exhibited higher cracking susceptibility with an increase in the amount of elemental sulfur charged. Among the four different charging methods tested, sulfur charging using a sleeve promoted the most aggressive SSC on the alloys. These test results imply that better control of elemental sulfur during materials evaluation could improve the reliability of laboratory data. Such data have resulted in more conservative recommendations for alloys in sour service and tend to make the test environments more aggressive than actual service conditions.

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