Averaging HV Values in NACE MR0175/ISO 15156

The inquiry questions whether averaging HV values is allowed when using the HV5, HV10, or HRC 15N scales in NACE MR0175/ISO 15156, as the document is silent on this issue. The ASTM E140 conversion chart shows that there is a 16HV difference that equates to 2 HRC, or 8 HV points for every 1 HRC point.

It appears illogical to reject a weld procedure for being off a few HRV points, which equate to less than 0.5 HRC points, and the inquiry asks whether there is anything preventing someone from averaging HRV values currently and if a formal ballot would be necessary to address this issue.

Response

The standard does not currently address the averaging of HV values for proving out hard readings. A successful ballot would be required to add this into the standard. This inquiry pertains to NACE MR0175/ISO 15156-2 7.3.2 and 7.3.3. The reference is made to the ISO 15156 Maintenance Panel Inquiry #2016-10.

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