Materials & Welding: Which NACE MR0175 table applies to 718 (regardless of heat treated condition)?

Wednesday, June 27, 2018

Which NACE MR0175 table applies to 718 (regardless of heat treated condition)?

If a Nickel alloy does not have any age / precipitation-hardening heat treatment applied to it, does this not make it a solid-solution type alloy, and therefore should be covered by Tables A.12 to A.16 of the NACE standard instead?

Regarding precipitation hardened Nickel based alloys, Tables A.31 to A.34 all have the heading ‘Environmental and materials limits for precipitation-hardened nickel based alloys used…….’. The heading gives the impression that all materials listed in the Tables A31. to A.34 are precipitation hardened type Nickel based alloys only, however in the notes sections in the Tables, the alloys are allowed to be in other conditions i.e. in Table A.32, wrought UNS N07718 is allowed to be in four different heat treated conditions including a solution-annealed condition, and a hot-worked condition (both of these conditions do not involve any age / precipitation-hardening).
If a Nickel alloy does not have any age / precipitation-hardening heat treatment applied to it, does this not make it a solid-solution type alloy, and therefore should be covered by Tables A.12 to A.16 of the NACE standard instead?

Question: If UNS N07718 precipitation hardened nickel base alloy in NACE MR0175/ISO 15156-3 is in the solution annealed condition, is this Table A.32 still applicable or should it be considered a solid solution nickel base alloy and Table A.14 would be applicable?

Answer: UNS N07718 is considered to be a precipitation hardened nickel base alloy regardless of the heat treated condition; Table A.32 is the applicable Table as opposed to Table A.14.
This question is in relation to NACE MR0175/ISO 15156-3 A.9 Table A.31
Reference: ISO 15156 Maintenance Panel Inquiry #2016-08