FAQ's

Interpretation of “As Close as Possible to the Fusion Boundary” in NACE MR0175

NACE Fusion Boundary

Introduction

An inquiry was made regarding the correct interpretation of NACE MR0175/ISO 15156-2, 7.3.3.3 regarding the placement of hardness impressions. Specifically, when welding dissimilar metals, such as corrosion-resistant overlays on low-alloy steels, does the phrase “”as close as possible to, but no more than 1mm from, the fusion boundary”” mean that the indentation should not be less than 3x the mean diagonal length of the indentation from the fusion boundary, as required in ISO 6507-1:1998? Note that ISO 6507-1:1998 is referenced by NACE/ISO 15156-2 in Section 7.3.3.2 (Hardness testing methods for welding procedure qualification).

Response

The response indicates that the ISO 15156 Maintenance Panel cannot provide an interpretation of ISO 6507-1:1998 with regards to the minimum distance of hardness indentations from the boundary between the base metal and the overlay weld. ISO 15156-2, 7.3.3.2, and ISO 15156-3, 6.2.2.2.2 allow hardness measurements to be carried out with a smaller indentation load, such as HV5 instead of HV10, in many cases, enabling compliance.

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