CS and SS welding

Dear gpsvn, Thanks For your Reply.

Yes this vessel working pressure is 200barg, The Upstream of PSV Ratting is 1500# SS, Downstream of PSV Ratting is 300#.

1. I asked the Qustion because is Flange (CS) already purchased.

Thanks,

Happy New Year...

So the 300# is on the outlet (downstream) of the PSV. The design pressure of 200 barg is applicable to the inlet (upstream) of the PSV only. The outlet (downstream) of the PSV should be designed for much lower pressure, similar to the flare header pressure, that's why the 300# was specified.

1. I think the system integrity should be considered rather than a flange costs a few dollars to replace.

Dear GPSVN,

I don't know the flare header pressure, but it was accepted by the Client,
Anyway i will check with Process Group.

Ya.. i modified with Stainless steel flange and carbon steel vale like what you suggested earlier.

Thanks for your all answers. Keep it up.

I guess your P&ID looks like this, I haven't CAD so I used Word to draw.

Yes My friend you are right...

Is possible to weld Carbon Steel flange with Stainless Steel Pipe?
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Yes. Using a qualified WPS following the rules of ASME B&PV. Let me qualify my answer. A CS steel pipe can be welded directly to a SS pipe succesfully and will maintain its in-service integrity within the limit of its process requirement . Basically we call it welding of dissimilar metals.