NACE MR0175 Interpretation for Nickel-Based Alloys: Alloy 20 (UNS N08020)

Introduction

This page addresses an inquiry seeking a definitive interpretation of NACE MR0175 regarding nickel-based alloys. The inquiry specifically pertains to alloy 20 (UNS N08020), which has a Mo range of 2.0-3.0 according to ASTM/AMS/UNS composition listed in Table D3 on page 65.

Background

Section A.4 of MR0175 contains Table A.12, which lists the minimum Mo for solid solution nickel-based alloys at 2.5%. The inquiry seeks clarification on whether N08020 must have at least 2.5% Mo to be certified for MR0175 compliance and the reason behind this requirement.

Answer

The answer provided confirms that N08020 must have a minimum of 2.5% Mo to comply with Table A.12, material types 4a and 4c. Heats of N08020 not meeting this minimum may be acceptable as “”Highly alloyed austenitic stainless steels”” under the limits provided in Tables A.8, A.9, and/or A.11. The answer explains that the 2.5% Mo restriction for N08020 is similar to the PREN restrictions for Duplex Stainless steels. It also notes that the full chemistry ranges of the UNS numbers listed in the Annex D tables are for reference only.

Conclusion

This question pertains to NACE MR0175/ISO 15156-3 A.4, Table A.12, and the reference cited is ISO 15156 Maintenance Panel Inquiry #2011-07.