Weird sounds during pneumatic test 2

[ElCidCampeador]

Hi, a friend of mine who works in a workshop has told me about a strange fact happened during a pneumatic test of a stainless steel "transition piece".

This transition piece is a short section of pipe (lenght about 1m) with 2 flanges ad the end, but at small end both section and flange are circular (O.D about 200mm) and at large end both flange and section are rectangular (about 500x700mm), something like this one below:

https://www.grainsupply.com/wp-content/uploads/2020/10/Square-to-Round-Transition..-225x300.jpg

Flanges at both sided were connected to other flanges with classic bolts+nuts.

What is really weird was that happened during the phase of pressurization of this piping: when pneumatic pressure overcome 0,5 bar, this piece started to "bang", making sounds of blows or something like that, with a slight deformation of the external wall. At 0,7 bar he decided not to continue and vent out the vessel. Please notice that vessel wall (3mm thickness) returns in a as welded original state, without permanent deformation.

Do you think it's normal? What causes these sounds? There were no air leaks but they were all scared of these banging sounds...

Thank you

 

[3DDave]

It depends on how well secured the item is. One case is the entire item takes off and does damage, no fragmentation required. One might calculate the stored energy in the gas volume at the pressure differential and see what velocity would result if it all went to propelling the device.

It's really not often that flat sided items are a good idea to retain pressure.

 

[ElCidCampeador]

Update

My friend told me that he cut all welds and then re-welded but the sounds still persisted. There were significant vibration/displacement of the surface on the surface as the pressure increased, without plastic deformation. As before he stopped before reaching final pressure of test.
Now he has just finished welding a plate, at half height, parallel to the flanges plane, hoping to stiffen all the structure and solve the problem.
I've suggested him at least to put this piece in a separate place with protective shields around...

 

[LittleInch]

Well you can lead the horse to the water....

Or in this case the horse refuses to move.

Thanks for the update. A pity the message didn't seem to have got home.

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

 

[DriveMeNuts]

The shell is too thin me thinks.
The weld distortion and shinkage is creating undulations in the flat sides which are popping and buckling like a dented oil can being inflated. You might get lucky by rewelding it.

 

[chicopee]

The picture shown in the original post is more in tune with air handling systems than with pressure vessel designs. As a former fired and unfired pressure vessel NB inspector I have never seen such item shown in the picture associated with pressure vessels.

 

[chicopee]

The sounds that one hears is probably due to the metal distorting during the pneumatic pressure test.