ISO 13680 and NACE MR0175 have different hardness limits for solid solution nickel based alloys, which one to follow?

Question: NACE MR0175/ISO 15156 Table A.14 (Environmental and materials limits for annealed and cold worked, solid-solution nickel-based alloys used as any equipment or components) at the bottom indicates “The maximum hardness value for these alloys in these applications shall be 40 HRC.” 2. ISO 13680 Table C.27 (Example for PSL-2 product mechanical properties at room temperature) indicates Mean Hardness Number of 33 or 35 HRC depending on the grade (Category 3). These are vastly different values–I appreciate your thoughts.


The MP can only answer about NACE MR0175/ISO 15156 Standard. The maximum hardness values correspond to the maximum hardness values of the tested materials. The MP cannot comment on hardness values from other ISO standards like ISO 13680.

This question is in relation to NACE MR0175/ISO 15156-3 A.14

Reference: ISO 15156 Maintenance Panel Inquiry #2010-10

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