Pipe Caps as vessel heads - reinforcement

[Ronin609]

Hello,

Possibly a basic question for the forumites. ASME is not the standard I use most frequently for unfired pressure vessels, and there are a few subtle differences between ASME and the Australian Standard.

I am working on re-rating an ASME BPVC Sec VIII Div I designed vessel for a slightly higher design pressure. Originally 9.28 MPa, re-rate to 9.77 MPa. The heads are ASME B16.9 pipe caps (20") Sch 80. I am aware of the UG-44 rule to calculate thickness/ pressure for pipe fittings "as for straight seamless pipe in accordance with the rules for this Division" - "Division" referring to ASME BPVC Sec VIII, Div 1.

Does that also mean that shell thickness "t,subscript(r)" in the UG-37 nozzle calculation is the thickness "as for seamless pipe" without making use of either; the rule for torispherical heads, or that for ellipsoidal heads?

Is it also correct to keep factor F as 1.0 since the nozzle has a reinforcing ring and assess the area removed in the opening as being an arc? The fabrication drawing shows that a template was made to check the internal radius of the caps, so that should be a suitable basis for calculating the geometry.

Thanks,

James

 

[TomBarsh]

James.

(1) The F factor does not apply to openings in heads... for heads, F always equals 1.0

(2) In my opinion, once a nozzle has been put into a "standard pipe cap" the head is no longer a "standard pipe cap" under UG-44, and the head should be analyzed as an ellipsoidal head.

 

[SnTMan]

Does that also mean that shell thickness "t,subscript(r)" in the UG-37 nozzle calculation is the thickness "as for seamless pipe" without making use of either; the rule for torispherical heads, or that for ellipsoidal heads?

No. See UG-27(a), definition of tr, (c). If meeting the 80% limit, the calculation of tr is as given. If not, tr is calculated as an elliptical head as per UG-32(d) if semi-elliptical, or Appendix 1, 1-4(c) if not.

Unfortunately B16.9 does not seem to specify semi-elliptical form, only "ellipsoidal". It seems you'd have to make either measurements or assumptions

Regards,

Mike

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