Pressure vessel Leak on girth flange (R.T.J type)

[Alpec]

on the hydrotest occured leak on girth flange position.
below is detail,

D.P :10 bar
Hydrotest : 19.77bar
girth flagne : 316L, t150 X I.D900 X O.D1200 R.T.J type(with octagonal Sus gasket)
bolt : 1-1/8" Inconel 625 (bolt tighting performed 106 bar)

i'm not sure exactly why occured leak.

girth flange, gasket, bolt we already check dimension and detail. it is no problem.

could you please share experience??

 

[SnTMan]

Flange rotation, maybe?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[mk3223]

Also, it may be caused by improper bolting torque or incorrect tightening sequence.

 

[racookpe1978]

New gasket, or was an old one re-used?

 

[SnTMan]

Or ?? or ?? or ?? Really not much to go on, in the OP.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TGS4]

In my experience, you need to secure the services of a bolted flange joint expert to help you troubleshoot your problem. There are so many things that can go wrong, that you will likely need someone on-site.

 

[BJI]

Did you torque or tension at 106 bar, what was your target bolt stress? Even without knowing what equipment you used, I would assume the target bolt load is still too low. Was the bolt load selected in accordance with ASME PCC-1 Appendix O?

The first thing that seems odd for the pressure is the use of a RTJ gasket, most likely a better gasket choice could have been made. You also didn't say what ring number you used.

The biggest issue though would be the bolt size selected. If you compare this flange to standard B16.47 flanges then you will notice the bolt size is very small. Likely someone thought it would be a good idea to use more smaller bolts than fewer larger bolts, but this is not a recommended practice. Based on TEMA sizing recommendations I assume you have about 48 bolts, is that correct? The problem with small bolts is you can only take them up to yield then you are out of options, and you will most likely have to take the bolts as close to yield as you can get them.

You also never mentioned the operating temperature the flange was designed for. If the increase in flange thickness was for thermal effects then you may still have issues in operation even if you get it to pass the hydro.

I think the root cause is bad flange design. I also agree with TGS4s recommendations, and it is even better if you can assess the bolted joint integrity before you fabricate.