ISO 15156 (NACE MR017): SULPHUR CONTENT ---CS BALL VALVES

[compo]

I was reviewing a few really top questions related to NACE and valves and well composed/experienced loaded responses by rneill, SJones and Thomas. Would especially appreciate feedback and guidance on this argument over interpretation inside NACE - trying to bottom out.

Reference to ISO 15156 (NACE MR0175) re sulphur content of carbon steel products (this case ball valves): Part 1 - General Principles for Selection of Cracking-resistant Materials - Terms and Definitions - Section 3.20 - stepwise cracking

“HIC/SWC leading to loss of containment has occurred only rarely in seamless pipe and other products that are not flat-rolled. Conventional forgings with sulphur levels less than 0.025 % mass fraction, and castings, are not normally considered sensitive to HIC or SOHIC. The equipment user shall consider HIC/SWC as defined in ISO 15156-1 when evaluating flat-rolled carbon steel products for sour service environments.”

1 . Could one take this interpretation being that this is HIC/SWC failure mechanisms occur in flat rolled products such as plates, strips, slabs, etc. Where ball valves manufactured from round products (rolled and forged bars) are concerned these are and not flat rolled products. Per ISO 15156 (NACE MR0175) Part I section 3.0, the definition of SWC is associated with low strength plate steels used in the production of pipes and vessels (not forgings). So the interpretation is these valves should not be applicable to this point in ISO 15156 (NACE MR0175)

Or

2. Could one take the interpretation as being simply, this is a general description of the terms applicable in the remainder of the standard highlighting that stepwise cracking is usually, but not exclusively, associated with plate materials?

This is given the liberally applied spec to be compliant with ISO 15156 (NACE MR0175)” and having CS valves ranging from 0.02 to 0.035 wt% sulphur content

3. Ref. ISO 15156 (NACE MR0175) - Part 2: Cracking-resistant Carbon and Low-alloy Steels, and the use of Cast Irons - Section 8 Evaluation of carbon and low alloy steels for their resistance to HIC/SWC

. “The probability of HIC/SWC is influenced by steel chemistry and manufacturing route. The level of sulphur in the steel is of particular importance, typical maximum acceptable levels for flat-rolled and seamless products are 0,003 % mass fraction and 0,01 % mass fraction, respectively. Conventional forgings with sulphur levels less than 0,025 % mass fraction, and castings, are not normally considered sensitive to HIC or SOHIC."

Is this to be interpreted as forgings with sulphur levels less than 0.025% should not normally be considered sensitive to HIC, and sulphur levels >= 0.025% HIC must be considered and Annex B strictly followed re test methods and acceptance criteria?

 

[SJones]

1.
Look at the definition of HIC in Part 1, 3.12 and see what you make of that. The quotation for SWC contains the word 'usually,' it does not say 'never'. Also, try using the 2009 version, where the definition differs from the one quoted.

2.
Correct. Forgings can most definitely fail HIC tests.

3.
Think of it this way: does the wording state that forgings with <0.025% sulphur need never be tested? Remember - it's all down to the end user's perception of risk and what the judge says in the court case!

Steve Jones
Materials & Corrosion Engineer

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