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NACE MR0175/ISO 15156-2: 2009

NACE MR0175/ISO 15156-2: 2009

NACE MR0175/ISO 15156-2: 2009

(OP)
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.

http://uk.linkedin.com/pub/terry-roberts/28/a9a/a1...

RE: NACE MR0175/ISO 15156-2: 2009

Quote (enmax)

After all, aren't all these mechanisms a form of hydrogen cracking

Unfortunately, no they are not. HIC requires only hydrogen pressure to generate the crack driving force, hence it's other monicker: "hydrogen induced pressure cracking." That's why there are different qualification tests. If they were all the same, materials could be qualified with one test only. You could have an 'expectation' that an SSC resistant steel would pass the tests for the other mechanisms, but you would only prove that expectation by testing.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: NACE MR0175/ISO 15156-2: 2009

(OP)
Thanks Steve,

Your reply would suggest that all carbon and low alloy steels should always be tested for HIC whether they fall into Appendix A.2 criteria or not. This makes the clauses that say no additional testing is required is mis-leading since you always have to test for HIC (but not necessarily SSC).

Best wishes

Terry

http://uk.linkedin.com/pub/terry-roberts/28/a9a/a1...

RE: NACE MR0175/ISO 15156-2: 2009

I wouldn't go as far as 'misleading,' more like inviting the end user to answer the question: 'how lucky do you feel.' Does one accept the statements regarding risk of HIC with certain product forms, or does one test it all. Personally, I fall in the latter category as I have seen forgings fail HIC testing too many times.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

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