Question: Use of SST 17-4 PH UNS S17400 material for NACE is listed in NACE MR0175/ISO 15156-3, Tables A.27, A.28, and A.30. Only Table A.27 contains limitations for partial pressure H2S and PH. Questions: (1) For surface safety relief valves with internal components made of SST 17-4 PH heat treated and hardness tested to limits specified, do the limits of Table A.27 or A.28 apply? Internal components are considered non-pressure retaining by definition 3.4 in Part 2. However, failure of an internal component can cause release of service fluid to the valve outlet. It is assumed for NACE applications that safety relief valves for NACE service would not be vented to atmosphere. (2) Does Part 3 Table A.28 only apply to subsurface equipment or does it apply to all valves?
The equipment user is responsible for defining the intended service environment and selecting materials in accordance with this standard.
This is in relation to NACE MR0175/ISO 15156-3 A.8.2, Table A.27, A.28 and A.30
Reference: ISO 15156 Maintenance Panel Inquiry #2011-17
Update April 2016: NACE MR0175 2015 – Technical Circular 1 has implications for 17-4PH. Contact us for more details.
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