+44 (0) 114 4000850   |   US toll-free 877-399-1010


Is UNS N08020 listed in NACE MR0175 / ISO 15156?

Viewed 5048 Times

Question: I am looking for a definitive interpretation of NACE MR0175 concerning nickel-based alloys. My company produces alloy 20 (UNS N08020). The standard ASTM/AMS/UNS composition is listed in Table D3 on pg. 65 showing a Mo range of 2.0-3.0. Section A.4 of MR0175 contains Table A.12–Materials types of solid solution nickel-based alloys. This table does not list any specific alloys, but it does list the minimum Mo (which I assume is for compliance with the standard) at 2.5%. Does that mean that in order to certify our 20Cb3 to MR0175 the heat must have at least 2.5% Mo, even though the acceptable Mo range is 2.0-3.0? If so, what is the impetus behind requiring a higher Mo range than is standard for the alloy?


You are correct, a minimum of 2.5% Mo is required for N08020 to be compliant with Table A.12, material types 4a and 4c. Heats of N08020 not meeting the 2.5% Mo 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 2.5% Mo restriction for N08020 is similar to the PREN restrictions for Duplex Stainless steels. The full chemistry ranges of the UNS numbers listed in the Annex D tables are for reference only.

This question is in relation to NACE MR0175/ISO 15156-3 A.4, Table A.12

Reference: ISO 15156 Maintenance Panel Inquiry #2011-07

At Oil & Gas Corrosion we can support you with materials selection and NACE MR0175 compliance.


With a wealth of experience in the oil and gas industry, we provide independent materials and corrosion consultancy to help companies reduce risk, save money and apply best practice in their oil and gas businesses.

Find out more by getting in touch – you’ll get an answer from a qualified, experienced materials engineer every time.


USA toll-free


US: 877-399-1010 (toll free)
UK: +44(0)1144000850

66 Eldon St
S1 4GT
United Kingdom


Was this answer helpful ? Yes / No