Welding and testing

[Satsystem]

I have a 50 litre seamless gas cylinder with a 200 bar working pressure. I wish to cut a hole approx 50mm in the side midway along the cylinder and weld in a weld type fitting giving me a thread to connect too. I want to convert this to a buffer tank with a max pressure of 60 bar the gas medium will be a helium/oxygen mix. Would this be possible to weld and be safe at 60 bar? A 1.5 hydrostatic test and MPI what would be the best way to go with this concept? Weld procedure etc.
Satsystem

 

[metengr]

First off, since this is pressure retaining item it is probably fabricated under ASME Boiler and Pressure Vessel Code rules. For this type of work, I would strongly suggest you hire a boiler/pressure vessel repair contractor that has a valid National Board R-Certificate of Authorization to evaluate this option.

Do not attempt to perform this activity on your own.

 

[Satsystem]

Thanks for the responce but if I have derated from the original 200 bar WP. Go through a correct welding procedure and hydrostatic test to cover the 60 bar all would be ok?
I understand what you are saying its still acting as a pressure vessel.
I have done it before on a 200 bar 12 litre cylinder but cut into the orginal neck and welded a 1-1/2" NPT connection but the big differance it was only a buffer for 3 psi!
Its the 60 bar that concerns me.
Satsystem

 

[metengr]

You still need to have a NB Certificate Holder review your proposed design, perform the welding and subsequent testing. Someone needs to take responsibility for alterations to this vessel despite the fact that you are derating to a lower pressure. The 60 bar derated pressure is well within the ASME Boiler and Pressure Vessel scope for a Code vessel.

 

[weldtek]

I may be reading more into this than I should, but, if this is for human use there may be other considerations. If so, I would talk to a fabricator familiar with the
ASME-PVHO Code.

 

[Satsystem]

Safety Standard for Pressure Vessels for Human Occupancy
50ltr flask a bit small for a human?
All though I know the PVHO code.
It must Have been my name or oxy/Helium that brought you to that conclusion.
To put you more in the picture its a modification with a series of pressure reducing regulators for oxy/helium gas to get the pressure down to enter a HP gas compressor, for gas transfer. I want to fit a buffer bottle between an HP reducing regulator and an LP reducing regulator.

Satsystem

 

[stanweld]

Do you know the material and Design/Construction Code? Forged cylinders for gas are often made from AISI 4130 material and are governed by DOT.

 

[metengr]

stanweld;
DOT references ASME Section VIII, Div 1 Code of Construction.

 

[stanweld]

I was trying to address the weldability issues of SA-372 materials, dpending on grade, commonly used for forged cylinders. The requirements of UF-32 must be considered.

 

[weldtek]

Satsystem,
I was thinking of the requirements in ASME PVHO pertaining to piping systems for breathing air. Since you are familiar with the Code you have no doubt considered those if they're applicable in your case.