Flanges or Butt-Welding 2

[carletes]

Dear all!

I am specifying some pressure vessels for a power plant. In some of them I am thinking of designing butt welding nozzles instead of flanged nozzles, since I don't mind that welding is a not removable joint. But I am worried about the pressure testing of the connecting pipes: how can I isolate the vessel from the pipes? I don't want the vessels to be tested with pipes. Is it usual to use in those cases plugs or similar?
Moreover, I suppose that testing of pipes must be performed after welding them to vessels to test that joint, so the plug should be installes from the indside part of the vessel. Is it possibble not to test that joint and carry out i.e ultrasonic inspection instead?

thanks a lot for ay help

 

[metengr]

Are these new pressure vessels or existing pressure vessels being moved to an new location? If you are purchasing new pressure vessels, have the completed vessels hydrotested at the fabrciation shop BEFORE field installation. Once the pressure vessel has been hydrotested per ASME B&PV code, the field pipe connection welds can be subjected to NDT using radiographic testing (RT) to meet the requirements under the NBIC (if this is the code in your Jurisdiction).

 

[bmoorthy]

Why do you want to welded connection in the first place. Is it because of cost saving or is it because purchase of flanges(Timely) is a hazzle?

It is advisable to have flangd joint so that you have easy maintenence and you do not brush the local law/code.

In any case, if you are going for a welded joint and you do not have strict local law , Radiography will do instead of Hydro.

If hydro is a must (You boss is insisting but local law/code does not address this situation), then try offering this solution,

weld 2 rings from outside parallel to the joint, With the joint in between and than box it up with a cover plate, perform hydro from outside in the anular space.

I do not know, where you are and whether NBIC is applicable. If it is applicable, i doubt whether the local inspector will agree for this.
If he agrees then you are lucky.

But i will always bet on Flanged connections.


Good Luck

 

[carletes]

Hello,

I am thinking of using welded connections because of several reasons. In general because of the cost saving. In some pressure vessels because they may work with vacuum and finally, because with high pressure/tempearature services (i.e steam 50 bar, 500 C) I am afraid of leaks through the flanges.

The dode I am following is B31.1 as it is a power plant.

best regards,

 

[arto]

Thaxton Plugs for Hydrotesting pipes:

http://www.hy-techinc.com/pages/thaxton.html

 

[unclesyd]

I have seen where the nozzles in the vessel were purposely made long and capped for testing then cut off and prepped for field erection. Whether this would be applicable in your case would depend on the jurisdiction and AI.

On all test plugs make sure you have a chain/safety stop attached to the plug. We have put several plugs in orbit.

In line with arto post here is another supplier of test plugs.

http://www.expansionseal.com/index.htm

 

[tickle]

What are the vessels to be used for?

What design code are the vessels being made to? Is there a requirement for the future isolation and inspection of these vessels. A flanged joint allows you to isolate the vessel and add a blind.

Are there valves attached to the vessels? Are the valves going to be flanged? And if not, how will you service the valve when it goes wrong?

Are you sure that they are going to be suitable now and in the future. The cost of flanges are likely to be cheaper than buying / hiring plugs to allow you pressure test, not forgetting the cost to install them etc.

Australian Standard 4041 (piping code) states that all welds should be pressure tested, unless it cannot be then it must be subject to some other form of inspection (X-Ray or Ultra sound or pneumatic) YOU NEED TO READ THIS YOUR SELF AND NOT USE MY WORDS AS GOSPEL. There is a thread on EngTips that explains that hydrotesting is not testing the welds but offering some stress reliefing of the heat effected zone. It is worth you searching.