Hydro Testing of Slip-On Flanges

[JakeR82]

I recently argued with my QA department about hydro testing Slip-On flange to a pipe. It is my understanding that all welds must be hydro tested, even though the slip-on flanges partially cover the pipe and one of the welds isn't a boundary weld, while the other is a fluid boundary weld. (We use two fillet welds for a slip on flange, one on the inside of the pipe to the flange, and another on the outside of the pipe to the flange). My QA department argues that it isn't a pressure containing weld, so there is no reason to test them, primarily because it isn't a butt end weld.

UG-99 (ASME VIII) indicates that all permissible points should be hydro tested.

I would appreciate any clarification on the issue that can be given.

 

[btrueblood]

Is this part of a pressure vessel? Wouldn't then the flange need to be capped with a blank to allow pressure to be applied to the rest of the vessel? Sorta doesn't matter, as ASME B31 would have you hydro test the flanges as well.

"My QA department argues that it isn't a pressure containing weld"

Can't fathom that arguement. The internal fillet weld is most certainly a pressure containing weld.

 

[pennpiper]

It sounds to me like your QA department is trying to "Comb Frog hair".
Ask them how you are supposed to get the hydro-test water into the cavity and how you are supposed to get any trapped air out? Then after the test you need to drain out the water and dry the cavity.

Then ask them if these NDE steps might be acceptable?
- VT of each pass, PT of each pass and MT the final weld.

prognosis: Lead or Lag

 

[JakeR82]

@Btrueblood: "ASME B31 would have you hydro test the flanges"

The way I read this statement means that all flanges are required to be hydro tested. Is this correct?

 

[btrueblood]

My wording may not be correct, but the intent is that under B31 you would hydro test the entire piping system, blanking any open flanges where necessary, using suitable gaskets. The way I read your question is that the QC person is trying to tell you that you don't need to hydro the flange, which is part of the device you are hydro-testing, so my reply is along the lines of "how the heck will I cap this pipe without putting a blind flange on it?"

Reading what pennpiper wrote...are your QC types trying to say they can't verify integrity of the external fillet weld, because it won't see pressure during hydro test? Kind of nonsense, as the external weld, as you noted, is not (normally) a seal weld, and the stresses it would see in use are simulated by the hydrostatic test.

 

[JakeR82]

I just called our typical code AI about the issue. The entire piping system includes any flanges. It is also a pressure weld, and I drew it out to explain. Typically what they do is weld another cap on it that has a hole to put the water in the system with a air valve to the side. The unit is hydro tested, and after completion of the test they cut the 'test' cap off.

The problem becomes with the actual fabrication of the unit, which is why they don't want to hydro the flange. I needed the engineering reason to say 'Yes, you must hydro' and have the code back it up.

Thank you for your help.

 

[pennpiper]

You wrote: "what they do is weld another cap on",
They weld the cap on to what? and Where? please try to be very specific.
A sketch would help.

prognosis: Lead or Lag

 

[Kiwi2671]

I think I understand what JakeR82 is saying.
Say we are fabricating piping from Vessel A to Vessel B.
When a large spool is fabricated and it is going to be installed in a plant somewhere else it is quite often left with a loose flange (slip on or weld neck)and what we call (in the Southern Hemisphere) "green" or a bit of extra length where it connects to the vessel.
This is to allow for any mistakes that were made with the vessel installation. Location, squareness of flange, orientation of holes etc.
If you fully weld the last connecting flange perfectly square,level, and with holes in the perfect orientation and go to install and the flange on the vessel is not perfectly square, level or holes are not perfectly aligned you have a major problem.
This is what we call "field fit" - trial fit with flange loose, bolt the two flanges together, tack the flange to the pipe, remove and weld out then re-install a spool that perfectly matches the existing flange.
Back to the original question - how do we hydro all the welds in the spool with no flange on the end ?.
A cap is welded on the one end of the spool (in lieu of the flange)and hydro is performed, the cap is then cut off and a fully hydrotested spool (minus 1 x flange weld) is sent to site.
The closure weld (the flange closest to the vessel) is then treated in accordance with B31.3 Clause 345.2.3 (c) and no additional hydrotest is required,
Regards,
Kiwi