enmax
Materials
- May 17, 2007
- 51
My question concerns the use of carbon and low alloy steels in H2S-containg environments. The H2S in my case is low - 10ppm - and conditions fall into Region 0 of Figure 1. Therefore Clause 7, Option 1 applies, and it covers SSC, SOHIC and SZC (from the clause title).
Clause 7.1.1 of the NACE/ISO standard says that normally, no special precautions are required for steels used under these conditions with respect to SSC only. Other cracking mechanisms are covered in 7.2. Clause 7.2.1.3 reinforces 7.1.1 with regard to carbon and low alloy steels - "no precautions are required" although there are some precautionary caveats added for consideration. Again, this only deals with SSC. For SOHIC and SZC, Clause 7.2.2 says these have to be considered but are rare. HIC/SWC is covered in Clause 8 which says that even a few ppm H2S can be harmful, particularly for flat-rolled products. However, this clause is headed "Evaluation of carbon and low alloy steels....". Unlike Clauses 7.1.1 and 7.2.1.3, there is no dispensation to use cracking resistant steels with no special/additional precautions.
I now get to my question. If you've taken the trouble to read up to here - many thanks!
Since there are steels resistant to SSC for regions 1, 2 and 3 of Figure 1 and defined in A.2 with much higher levels of H2S than my 10ppm, could I consider these same steels (in the prescribed metallurgical condition and hardness <22HRC) as being resistant to the other cracking mechanisms (SOHIC, SZC, HIC, SWC)? After all, aren't all these mechanisms a form of hydrogen cracking - a steel resitant to SSC should be suitable for HIC, etc. provided the steels complies with A.2.
I look forward to any comments.
Clause 7.1.1 of the NACE/ISO standard says that normally, no special precautions are required for steels used under these conditions with respect to SSC only. Other cracking mechanisms are covered in 7.2. Clause 7.2.1.3 reinforces 7.1.1 with regard to carbon and low alloy steels - "no precautions are required" although there are some precautionary caveats added for consideration. Again, this only deals with SSC. For SOHIC and SZC, Clause 7.2.2 says these have to be considered but are rare. HIC/SWC is covered in Clause 8 which says that even a few ppm H2S can be harmful, particularly for flat-rolled products. However, this clause is headed "Evaluation of carbon and low alloy steels....". Unlike Clauses 7.1.1 and 7.2.1.3, there is no dispensation to use cracking resistant steels with no special/additional precautions.
I now get to my question. If you've taken the trouble to read up to here - many thanks!
Since there are steels resistant to SSC for regions 1, 2 and 3 of Figure 1 and defined in A.2 with much higher levels of H2S than my 10ppm, could I consider these same steels (in the prescribed metallurgical condition and hardness <22HRC) as being resistant to the other cracking mechanisms (SOHIC, SZC, HIC, SWC)? After all, aren't all these mechanisms a form of hydrogen cracking - a steel resitant to SSC should be suitable for HIC, etc. provided the steels complies with A.2.
I look forward to any comments.