For Hardness (vickers HV), What is NACE MR0175 retesting criteria?
Question: Typically, when an indentation fails the micro hardness test several additional indentations are made and measured in the same area as the suspect indentation on the same weld test coupon. The results are then averaged. If the additional indentations average is acceptable, the survey is considered acceptable. This is in line with the NACE MR0175 Part 2 Section 7.3 “Hardness” paragraph 7.3.2 “Parent Materials” which allows additional hardness readings in the adjacent areas of a failed hardness reading. Logically, the same testing methodology would apply to welds, even though it is not specifically stated in the standard and subsequent paragraphs of Part 2. I would like to clarify if the above is acceptable with regards to Vickers HV 10 micro hardness testing / re-testing requirements for welds while conforming to NACE MR0175 Section 7.3.3 Welds.
Maximum acceptable hardness values for carbon steel, carbon-manganese steel and low-alloy steel welds are given in Table A.1.
No individual readings above these limits are acceptable for welds.
Reference: ISO 15156 Maintenance Panel Inquiry #2014-07