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What are the NACE MR0175 limits for alloy 718 (UNS N07718)?

Title: Understanding ISO 15156-3 Table A.32: Maximum Temperature for Low H₂S Applications

Introduction

This page provides an answer to a question concerning the interpretation of ISO 15156-3, Table A.32, particularly the maximum allowed temperature for applications with less than 30 psi partial pressure of H₂S.

Understanding ISO 15156-3 Table A.32

The answer states that ISO 15156-3, Table A.32 does not qualify UNS N07718 for use at temperatures higher than 450°F. The limits on temperature, H₂S, Cl-, pH, and sulfur defined in some of the tables of ISO 15156-3, Annex A apply collectively and reflect the knowledge available, usually from laboratory tests, at the time the standard was published. There were no available data related to the use of UNS N07718 at any temperature higher than 450°F.

Qualification and Use of Materials Outside ISO 15156-3 Limits

ISO 15156 allows the qualification and use of materials outside the limits stated in the tables, to meet an equipment user’s requirements. This is detailed in ISO 15156-3, Figure B.1, Column 2. A qualification to define an alternative temperature limit for UNS N07718 for a partial pressure of less than 30 psi H₂S may be possible with appropriate testing and documentation.

Conclusion

In conclusion, ISO 15156-3, Table A.32 sets a maximum temperature limit of 450°F for UNS N07718 in applications with less than 30 psi partial pressure of H₂S. However, alternative temperature limits may be possible with appropriate qualification testing and documentation.

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