dished end thickness 1

[Ap734]

dear all,
can you tell me what is thickness tolerance for dished end (claded or plain)of pressure vessel.

thanks

PAUL A.

 

[SnTMan]

Ap734, best to ask the manufacturer. It can vary. Some will publish minimums.

IIRC for 2:1 heads a good rule of thumb is 1/16" for 1" and under, 1/8" up to about 2", and 1/4" over that. Use at your own risk

Regards,

Mike

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

 

[JStephen]

Don't confuse tolerances with thinning allowances. But you might check Appendix 32.

 

[SnTMan]

Yes, I was speaking of forming allowance, separate from plate tolerance and other head dimensional tolerances.

Regards,

Mike



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

 

[Ap734]

JStephen,
Appendix 32 of what code / specification / documents?

regards,
PAUL A.

PAUL A.

 

[JStephen]

Just to clarify-
I'm not sure there IS a tolerance on thickness, actually.
By which, I mean that if you have a calculation showing minimum formed thickness of 0.8920" or whatever, are you allowed anything under that? And just glancing through, I didn't see a specific tolerance for underrun below that- maybe I'm overlooking it somewhere.
However, that Appendix 32 of Section VIII Div 1 of the ASME Boiler and Pressure Vessel Code relates to localized thin spots- so if you just have one little section of a head that underruns the thickness, you can evaluate it by this appendix.

On the forming allowance, heads are commonly referred to by the nominal thickness, which is the thickness of the flat plate they start with. But it's understood there will be some thinning in the process, so it's customary to specify a forming allowance or a minimum thickness after forming. So you might specify a 0.625" nominal head, and the formed thickness is actually 0.5625" minimum or something like that.

 

[Don56]

Take it from an old head maker. Make your life simple. Tell the head maker you minimum required thickness & let him figure out the nominal. If you are using clad materials let him know both the minimums, the clad requirement & the backer. If it is a welded head let him know if the clad is part of your design strength calculations or only for corrosion protection. With deepest apologies to the lady head makers.

 

[SnTMan]

Yes

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

 

[JStephen]

Actually, that makes your life simpler but complicates mine a little. Normally, there is some difference between the required thickness and the minimum thickness available, and that can be used in the reinforcement calculations to help eliminate repads. The thickness furnished also figures into some of the detailing, required weld sizes, impact test exemption, weights, etc.

 

[racookpe1978]

Yet using a standard metal thickness (already available from stock or from a certified supplier) may save tens of thousands by NOT specifying an arbitrarily calculated but "precise" thickness.