Hot Tap Testing?!

[jseag]

I'm confused with the testing of piping hot taps in B31.3 piping, please help clear it up for me! I'm hearing all kinds of different opinion as to what the welds shall be tested at prior to cutting out the coupon in any scenario- whether it is a split tee or weldolet branch connection.

API RP2201 states you should test at 1.1x the current operating pressure in parent pipe so that you do not buckle the parent piping. However, if you do that, the welds are below what B31.3 states is the min hydrotest pressures required (1.5x design pressure x stress ratio). If this is done, would there not need to be additional NDE (100% radiography) done in order to certify those welds per B31.3?

Others say to test at B31.3 min pressure after running a crude buckling calc to verify it won't buckle.

And others say to take it further to the flange rating and test at 1.5x flange limit after running a crude buckling calc. This would certify the welds to absolute max that system could ever see.

Any thoughts?

 

[LittleInch]

See this.

http://www.eng-tips.com/viewthread.cfm?qid=417146

The problem comes when your "crude" calculation (I haveno idea what this is) results in damage to the inner pipe . You're also in danger of applying loads to the tee it won't see in service and damaging the fillet welds.

Feel free to do more than anyone else does for no benefit but more risk. If you're that uncertain or inexperienced then appoint a competent contractor and consultant. And listen to them.

Hot taps are not for learning on from first principles.

The only way I know to check on the max differential pressure is by FEA.

Good luck and tell us what you decide.

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Also: If you get a response it's polite to respond to it.

 

[jseag]

LittleInch, thanks for replying! I guess what I'm trying to gather is what is everyone else doing? You say I can do more than anyone else does, but what is it that everyone else does?

I'm simply just gathering info, we let the experts do what they do, but it seems we hear from the hot tapping contractors and various pipe owners their approach is different from one another in the way I initially explained. The philosophies on test pressures they want to use are all over the place.

 

[LittleInch]

I would go with what is written as an international Recommended Practice on the matter and ask anyone who wants to do anything different to justify it using the relevant sections of B 31.3. and an FEA - there is no such thing I am aware of as a "crude buckling calc" for the complex geometry of a hot tap. Using a version of something like a subsea calculation is simply not valid. Ask someone to prove by FEA or physical testing whether their "crude calc" is actually valid and accurate and then don't hold your breath waiting. Many people will offer an opinion until you ask them to commit it to writing and take responsibility....

A hot tap, almost by definition, is a modification or repair, otherwise you would take the pipe out of service, cut a hole and weld in a weldolet or a tee. As such using original specs for test pressure is accepted as being impractical in many circumstances.

You need to examine the welds in the best possible manner, but hydrotesting to a pressure > 110% of actual pressure in the main line at the time of the hydrotest is often not possible due to the collapse issue. Therefore other suitable inspection techniques need to be used and specialist experienced contractors used for the welding as the flowing fluid in the original pipe can cool the weld very rapidly if you don't use the correct equipment and techniques.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jseag]

I follow you. So if you follow RP2201 and hydro at a max of 1.1x operating, to certify welds per B31.3 you'd need to utilize other NDE means.

 

[LittleInch]

Yes

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.