ANSI/NACE MR0175/ISO 15156 states that the risk Hydrogen Induced Cracking (HIC) needs to be evaluated, and testing as per NACE TM0284 should be considered to demonstrate a specific materials are HIC resistant.
Question: We are trying to interpret the NACE/ISO requirements for pressure vessel plate material. The NACE/ISO standard leaves the option of HIC testing with the client, as it appears. In accordance with the standard, the condition in which the HIC testing becomes mandatory should be based on some criteria other than H2S partial pressure. We would appreciate it if you can guide in giving the other conditions if sulfur and phosphorous content are controlled in accordance with NACE/ISO. Does HIC become mandatory due to non-uniformity of sulfur and phosphorous in the material due to steelmaking process even if the limit of these elements are maintained? Are there other reasons such as chloride environment?
Answer:
The statements in ISO 15156-2, 8 “Evaluation of carbon and low-alloy steels for their resistance to HIC/SWC” are based on the extensive experience of the experts who drew up the requirements of the standard.
They serve as a warning to the equipment user that damage to products from some flat-rolled carbon steel types due to HIC has been common and the risk of attack must be considered when selecting such materials for sour service. (See ISO 15156-1, 3.19 for definition of sour service in this context.) They also provide some indications of the types of flat-rolled carbon steel likely to give satisfactory resistance to HIC.
The overall aim of ISO 15156-2, Clause 8, is to ensure that materials that give satisfactory HIC performance in sour service can be selected. It is not the intention of this Clause to provide detailed information that can lead to the qualification, without testing, of HIC-resistant steels.
If, in accordance with NACE MR0175/ISO 15156:2, Clause A.2.2.2, Paragraph 3, the HIC resistance of flat-rolled plate is uncertain then the equipment user can elect to carry out HIC testing, possibly for use in an application-specific environment. Testing in accordance with Annex B.5 is proposed as a means of qualifying the material to ISO 15156-2.
Testing is not necessary if the equipment user can document that he has evaluated the risk of HIC failure of his equipment and considers the risk acceptable.
This question is in relation to NACE MR0175/ISO 15156-2 Clause 8
Reference: ISO 15156 Maintenance Panel Inquiry #2005-04
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