Required thickness for bolted bonnet

[STBish]

In designing various pressure relief valves we typically use a welded flange on one end of a weld tee. We then machine a bonnet that bolts to this flange (see attachment).

My question is, to determine the thickness of these two components, can you adapt ASME Section VIII Div 1 Appendix 2 for this configuration? With the use of o-rings between the 2 parts there is no gasket seating to calculate and the fact that the bonnet is exposed to the full pressure governed by the end flange inside diamter. Since it is not a typical flange design, I have looked at calculating the bonnet thickness similar to a unstayed flat head per UG-34. But in doing this I am still not sure how to calculate the corresponding end flange thickness since all of the stress on the bonnet will be transferred to the end flange through the bolting.

If I need to explain something better please ask for clarification. Just been at a loss on calculating these two thicknesses...

 

[prex]

You can calculate the bonnet per UG-34 and the flange per App.2 by using G=B (and of course m=0 y=0).
However to get the lightest design you could go with App.Y 'Flat face flanges with metal-to-metal contact outside the bolt circle'

prex

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[saplanti]

You may need to consult the following two books for your design of flange calculations in case your case does not fit the code formulation as Prex suggested:

1. Roark's Formulas Stress and Strain, Warren C. Young, Richard G. Budynas
2. Formulas for Stress, Strain, and Structural matrices, Walter D. Pilkey

You need to go through stresses and displacement calculations and heck rotation in case O-ring is between the faces of the flanges.

By looking at your assebly drawing I see that you are considering the theorical thickness of the pipe for the Tee. Depends on the manufacuring style you may find the Tee thickness is larger than the pipe, only the ends are machined to suit he pipe thickness. You need to check the Tees for the thickness first before designing.

There is a plate inserted between welding flange and pressure containing pipe. If thisplate is not forged and properly design for the load transfer between flange and pressure containing part may cause split under a couple cycles. So you need to be careful. We all rely on the PSV manufacturers and do not check their design when we buy it, so we trust youto design valves for the applications properly.

I might say the same for the discharge side. I guess that side is more lucier than intake.

Think about it.

Regards,

Ibrahim Demir

 

[STBish]

I appreciate the feedback.

Under larger sizes and higher pressures are what we are trying to get a handle on. We have had some instances where the impact upon opening has domed the bonnet. We had never had a failure where the end flange attaches to the body.

And in response to the inlet side of the valve, the pipe to plate is welded both inside and outside and the flange is attached with a full penetration weld. This has never been a problem area either since the ratings on the flanges and tees are much lower than the rating on the pipe.