New branch in a Steam Header

Hi,

We are planing to make a new branch connection(hottap) in a medium pressure steam header (145 oC).
We are concerning about how to performe the test in the new nozzle because of temperature, PT is not possible and water could be a problem.
I'll appreciate your comments or experiences in this kind of work.

Oh! the branch size is 2".

 

[petern1]

I am unsure as why water would be a problem - unless there is a leak in the line or nearby line or you are working in a pipe chase/vault or underground.

Anyway, dry magnetic particle in-process examination is a method we would use to verify the integrity of the root pass/hot pass of the weld-o-let or nozzle to the main pipe. The final cap of the weld would also be magnetic particle examined. Good visual examination of the welding in-process will also give indications of whether or not the welder is doing a good job. (in many cases with hot taps, coffins/leak boxes you have to rely on the welder skill and visula examination as the situation does not lend itself to thorough examination - if this is a permanent installation you will want to do some better inspection though.)

You can also consider welding on your hot-tap fitting complete with flange, and performing a pneumatic test prior to cutting the hot tap. This must be monitored carefully on the test with very slow pressure addition as the high temperature will affect the air pressure.

Not sure of your joint configuration, but shear wave UT can be done at these temperatures (I have had it done on much higher temperature lines than this) and may give you good results. Check with a good shear-wave qualified UT tech, may even want to test on a mock-up.

 

[Seldom]

From my experience, I agree with Petern1.
I'd make sure I have sombody on hand to VT the fit-up, subsequent passes, and MT the root bead and cap. Since you'll have a compressor there for the hot-tap machine anyway, do a final pneumatic proof test.

 

2 NPS branch hot tap is not big deal on a MP steam header. 2 inch and under are basically selfreinforcing, youll be OK with a stub-on nozzle.
the concern during the hot tap is actually burn-thru. welding on a live line one has to ensure you have sufficient meat on the header. next is to ensure that you got a good metal by doing a lamination check.

im not quite sure on how a pneumatic test be conducted on a hot line. i'll go with the hydro (select a fluid that will not of course vaporized) prior to cutting the coupon.

 

[kstaylor]

We often use steam as the pressure test medium for hot taps on steam lines.

 

wouldnt this qualify as pneumatic. if it is, then test pressure is 1.25x mp steam and then stabilize load say at 1/2 hour. Source should then be a steam higher than mp or high pressure steam line requiring a pressure reducing valve to bring it down to the req'd test pressure. sounds comlicated -this is on the assumption that the source can be found near the hot tap location. we've use light oil or glycol.