CRA cladded pipe welding purging gas

[bernoullies123]

Hi Peers,

I have a specification requirement that requires the purging gas to remain on until the completion of the weld. (CRA cladded pipe weld)

Now I would concur with purging for the root and hot pass and maybe even a couple of filler runs. But I do not understand why the gas would need to remain on for the full duration of the weld.

I wanted to turn off the gas after about 30% (5-8 layers) of the weld was completed but unfortunately I wasn't granted this request by the specification owner.

Appreciate any feedback as to your thoughts about any benefits for keeping the internal purge on until the joint is 100% welded.

I note that AWS D10.11 clause 6.3 says that it is normal practice to maintain the purge for the 2nd and 3rd layers.

The continuous purge will have significant implications as I'm assure you already understand (cost of gas, HSE, no in-process inspection internally etc.)

Thanks in advance.

 

[Duwe6]

Seems a little unreasonable to me too. Might switch from argon to nitrogen after the 3rd layer and save a little $$.

However, as long as his/her checkbook is open, the customer is always right.

 

[metengr]

bernoullies123;
I would concur with your approach that purging gas should not be required/needed once "x" thickness of weld is deposited.

The only technical reason I can think of for having such a specific requirement is to ensure no surface oxidation or other surface contamination of the weld region CRA cladding occurs from the heat of welding.

 

[bernoullies123]

Thanks, I was hoping I wasn't alone on my thinking.

Unfortunately since it is in the spec, we are faced with the cost and not them. Thanks for the N2 tip, may have to investigate that one quickly, as the pallet of argon will run out quickly at 300 L/h.

 

[metengr]

Be careful here because nitrogen can be a contaminant for certain grades of CRA. Stick with welding grade Argon.

 

[bernoullies123]

Thanks metengr.

Spec only allows industrial grade argon (< 50 ppm O2), and noted that nitrogen will probably cause weld metal porosity in the grade of CRA.