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What is the NACE MR0175 hardness limit for 17-4PH?

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Question: We have a requirement to supply NACE-compliant control valves for the oil and gas industry. One of our internal components is a part made from UNS S17400 (17-4 PH), details of which are described in Table A27 of Part 3 of the standard. NACE MR0175/ISO 15156-3 states this material should have a maximum hardness of 33 HRC, after one of the following heat treatment processes: HEAT TREATMENT (DOUBLE AGE-HARDENING PROCESS) 1) – SOLUTION-ANNEAL AT 1040±14°C AND AIR COOL OR LIQUID-QUENCH TO BELOW 32°C; – FIRST PRECIPITATION-HARDENING CYCLE AT 620±14°C FOR 4 HRS MINIMUM AT TEMPERATURE, THEN AIR-COOL OR LIQUID-QUENCH TO BELOW 32°C; – SECOND PRECIPITATION-HARDENING CYCLE AT 620±14°C FOR 4 HRS MINIMUM AT TEMPERATURE, THEN AIR-COOL OR LIQUID-QUENCH TO BELOW 32°C 2)- SOLUTION-ANNEAL AT 1040±14°C AND AIR COOL OR LIQUID-QUENCH TO BELOW 32°C; – FIRST PRECIPITATION-HARDENING CYCLE AT 760±14°C FOR 2 HRS MINIMUM AT TEMPERATURE, THEN AIR-COOL OR LIQUID-QUENCH TO BELOW 32°C; – SECOND PRECIPITATION-HARDENING CYCLE AT 620±14°C FOR 4 HRS MINIMUM AT TEMPERATURE, THEN AIR-COOL OR LIQUID-QUENCH TO BELOW 32°C. Ultimately we are trying to establish if these components are still compliant and if not, what we can do to rework the parts. Other materials such as 316 state an annealing process, but there is not one for UNS S17400. In addition, the components are “delicate” in design so post-machining heat treatment is probably not desirable due to component distortion. What does the hardness of 33 HRC refer to, wrought bar or finished component? What, if anything, can we do to rework these parts if the hardness value refers to the finished (machined) condition?

Answer

The 33 HRC max. hardness is applicable to the finished component. The MP does not provide consulting service for material processing issues.

This is in relation to NACE MR0175/ISO 15156-3 A.8.2, Table A.27

Reference: ISO 15156 Maintenance Panel Inquiry #2011-16

Update April 2016: NACE MR0175 2015 – Technical Circular 1 has implications for 17-4PH. Contact us for more details.

Are you using 17-4PH (UNS s17400) as a material for sour environments? We can provide support in 17-4PH metallurgy to safeguard the integrity of your asset. 

 

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