Question: Is UNS N08825 resistant to sulfur without limitations on pH, temperature, pH2S and chloride? In the remarks column in Table A.13 the following is stated: “…some combinations of the values of these parameters might not be acceptable”. How should this be interpreted?
Table A.14 currently states that Type 4c alloys including UNS N08825 are resistant to sulfur under any combination of conditions up to and including 132°C (270°F). Note that recent discussions in the Maintenance Panel have highlighted that the term “sulfur resistant” is not adequate (conservative) in itself and there is activity currently underway defining levels of resistance that are determined through three different test techniques and resultant 3 groups (#1 where successful tests were conducted using 1 g/l dissolved sulfur, #2 where there is direct exposure to solid sulfur – applicable below 110°C and #3 direct exposure to liquid sulfur – applicable for temperatures above 110°C). The user is cautioned that even though there are no environmental limits currently defined below 132°C for UNS N08825, there could be some combinations of parameters including elemental sulfur form (i.e. physically dissolved, solid or liquid) that may not be acceptable.
This question is in relation to NACE MR0175/ISO 15156-3 A.4, Table A.12
Reference: ISO 15156 Maintenance Panel Inquiry #2015-08