Which material are required back purging for GTAW?

Hello,

I need a help back purging gases for GTAW, which material are required back purging and where to refer?

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API RP 582 2016 edition,
Please refer para. 7.3:

7.3 Back purging is required for the GTAW and GMAW processes for welding materials having a nominal chromium content greater than 2-1/4 %, unless the joint is ground or back gouged to sound metal. For GMAW-S variations, see 5.2.3 e).

a) When a back purge is used, the WPS shall state the gas used, including composition of the gas mixture and the flow rate.

b) Whenever a back purging gas is selected to prevent oxidation or scale formation on the underside of the weld, the purge shall be maintained until at least 1/4 in. (6.5 mm) depth of weld metal has been deposited.

c) For socket, seal, and any other attachment welds on base materials less than 1/4 in. (6.5 mm) thick, the back purging shall be maintained throughout the welding operation.

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Thanks for your sharing, @Lin.D.Wan

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