Dear All,

We are going to connect new lines to existing headers. Tie-In is either tee or welded branch depending upon piping spec and size of lines. Isolation valves are some time far away from header as per requirement of client and there are several weld joints in between isolation valve and Tie-in. Now we have to define the hydrotest limit. We cannot isolate the portion in between last isolation valve and header and neither we can do hydrotest of exisitng header.
Can any body guide me what to do with that portion of piping. Currently we are asking client to do 100% radiography of those joints. is it appropriate?

I know the question is not related to stress analysis but as there are many helpful seniors here and I have learnt great deal of experience from them, I expect that you people will help me.

Suggestion;
1, Make your Tie-In to the existing line and install a pair of flanges minimum distance from the tie-in (fitting to fitting if Tee. etc).

2, Install a Spec-Blind (closed position) between the pair of flanges.

3, Do the hydro-test on the "New" side of the spec blind. Drain the water from the line after the test.

4, Do extra NDE (as required) on the "Old" side of the Spec-blind.

5, When ready for start-up change the spec-blind to the open position.

Thanks Jop for your valueable suggestion.