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For NACE MR0175 compliance of carbon steels, what’s the maximum hardness after PWHT?

Question:

A.2.1.4 Welding, Paragraph 6 states: “Carbon steel and low-alloy steel weldments that do not comply with other paragraphs of this subclause shall be stress-relieved at a minimum temperature of 620 °C (1 150 °F) after welding. The maximum weld zone hardness, determined in accordance with 7.3, shall be 250 HV or, subject to the restrictions described in 7.3.3, 22 HRC.” This particular paragraph does not refer to Table A.1 (Maximum acceptable hardness values for carbon steel, carbon-manganese steel and low-alloy steel welds), which states that weld cap hardness can be 275 HV with limitations. Could NACE please clarify if Table A.1 should or should not be applicable for stress-relieved weldments. Which hardness value 250 HV or 275 HV shall be applicable for weld cap hardness of stress-relieved weldments?

Answer

Table A.1 gives maximum acceptable values for carbon steel, carbon-manganese steel and low alloy steel weldments. It is applicable to welds whether they have been post weld heat treated or not.

This question is in relation to NACE MR0175/ISO 15156-2 Annex A.2.1.4

Reference: ISO 15156 Maintenance Panel Inquiry #2011-01

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