Question on NACE spec MR0175-3, Table D.3 Inco 625 Alloy Chemistry

This page presents a question related to the interpretation of NACE spec MR0175-3, Table D.3 Inco 625 alloy chemistry. The inquiry seeks clarification on whether the specified Nb max weight % 3.15 to 4.15 in the table is a typo, as industry standard spec ASTM B446 chemistry for Inco 625 bars specifies Nb + Ta as 3.15 to 4.15% instead of Nb only. The question also asks whether there is any technical reason why Tantalum would not be accepted as part of standard Inco 625 chemistry.

Answer on NACE spec MR0175-3, Table D.3 Inco 625 Alloy Chemistry

The answer states that ISO 15156 specifies material requirements for specific material groups or UNS numbers, established by international standard organizations that maintain the UNS.

Annex D Chemical Composition Data

Table D.3 in Annex D only lists chemical composition data using the values and elements defined by UNS. It is emphasized that the compositions listed in Annex D have no effect on the normative composition limits in Table A.12.

Tantalum Not Included in Annex D

The scope of the MP is limited to interpretation of wording in ISO 15156. As the standard adopted the UNS chemistries for UNS N06625, Tantalum is not included in Annex D.

Reference

This question pertains to NACE MR0175/ISO 15156-3 Table D.3, and the reference cited is ISO 15156 Maintenance Panel Inquiry #2013-01.