Does NACE MR0175 require PWHT of overlay weld inconel 625?
Question:We have weld overlays (Inconel 625 filler metal with SAW process) applied to low-alloy ferritic steel valves (ASME/ASTM A 352 Gr LCC). The steel valve is used on wet gas wellhead production platform with operating temperatures at 93°C, operating pressure of 145 bar with vapor fraction of H2S (177 kg-mol/h) and CO2 (877 kg-mol/h). Hardness tests were performed on the as-welded condition. The results achieved were well below the 250 HV criteria of Table A.1 of NACE MR0175/ISO 15156-2. Since the hardness results complied with the requirements of Table A.1 of NACE MR0175/ISO 15156-2, we believe and understand that the valve does not require postweld heat treatment after the weld overlay. Having met the hardness criteria after overlay we believe that we met the requirements of the following paragraphs of NACE MR0175/ISO 15156-2: -Paragraph A.2.1.5 and -Paragraph A.2.1.4 Question: Is our interpretation of Paragraphs A.2.1.5 and A.2.1.4 of NACE MR0175/ISO 15156-2 correct based on the above-stated specific application and conditions and that the valves overlayed with Inconel 625 consumables do not require postweld heat treatment?
Paragraph A.2.1.4 states (in the third sentence):
“As welded carbon steels, carbon manganese steels, and low-alloy steels that comply with the hardness requirements of Table A.1 do not require postweld heat treatment.” Paragraph A.2.1.5 states: “Overlays applied by thermal processes such as welding . . . are acceptable if they comply with one of the following: (a) The heat-treated condition of the substrate is unchanged, i.e., it does not exceed the lower critical temperature during application of the overlay. (b) The maximum hardness and final heat-treated condition of the base metal substrate comply with A.2.1.2 and, in the case of welded overlays, A.2.1.4.
Therefore, your interpretation is correct. Provided your weld procedure qualification complies with the hardness requirements in A.2.1.4 and A.2.1.5, no postweld heat treatment is required.
This question is in relation to NACE MR0175/ISO 15156-2 Annex A.2.1.4 and A.2.1.5
Reference: ISO 15156 Maintenance Panel Inquiry #2004-11
UPDATE 2018-06-04: A recent Technical Circular brings relevant updates on NACE MR0175 and 625 weld overlays: https://ogcenergy.com/nace-mr0175-iso-15156-technical-circulars-for-part-2-and-3-published-2018-06-01/