Nozzle Limit of Reinforcement on Torispherical Head

[Speckworm]

Good Afternoon,
Question #1: I cannot find in Section VIII what to use as the limit of reinforcement for a LARGE nozzle on a torispherical head. I have a 60in OD insert nozzle on an 81in OD ASME F&D head. My recently purchased design software defaults the limit on the reinforcement area to 2x the nozzle ID, which in this case is larger that the entire vessel OD. I have to manually enter a limit and I do not know if I should use the spherical portion of the head, the OD of the head or something else. If I leave the 118in which the software defaults to I am basically counting material that in not there. I have scoured UG-32, UG-36, UG-37, and App 1-4 with no luck of this particular situation.

Question #2: In this case (and assuming that I will need a re-pad), is the re-pad OD subject to the same limit?

Thank you very much.

 

[SnTMan]

Speckworm, see UG-37(a) for tr. When the opening and reinforcement are within the spherical portion, tr is calculated per Appendix 1-4(d). When not, tr is presumably calculated per UG-32(e), resulting in a greater tr. I'd try to stay within the spherical portion if I could. And yes, this applies to any pad as well.

Regards,

Mike

 

[Bmechz]

Hii Mr.Speckworm

Please refer Appendix 1-7 for large opening calculation.

If your software is PV elite then you can enter the limits of reinforcement manualy

Go to nozzle wndow of pv elite in which there is an option to enter the limits at the bottom of window.

Baijuz

 

[TomBarsh]

In ASME Code, openings in heads are not limited in size, see UG-36(b)(2). This means that there is no such thing as a "large" opening in a head, at least in terms of ASME Code rules...in other words, Appendix 1-7 does not apply to openings in heads (its title is "Large Openings in Cylindrical and Conical Shells").

SnTMan is right that if the opening and all its reinforcement is within the "dished" radius defined in the definition of "tr" given in UG-37(a) you'll get a benefit in that tr may be taken as for a spherical shell, which will be smaller than the required thickness for the head itself. Thus less reinforcing area is required, which eases the design burden.

UG-40(b)(1)&(2) define the limits of reinforcing parallel and perpendicular to the shell. The limits follow the contour of the shell surface. Thus the limits of reinforcing for a nozzle on a head follow the contour, or curvature, of the head surface. Conceivably they can even extend onto the adjacent cylinder and utilize that material. This situation is a bit tricky though. Whenever the nozzle limits extend onto an adjacent component, whether from head to cylinder, or cylinder to cylinder, the excess thicknesses (nominal - corrosion - required thickness) in the main shell component and the adjacent component may vary and should be accounted for if utilized. And that's not to say that spilling reinforcing from the head into the cylinder is a good idea from stress distribution view. It's likely better to try to keep all reinforcing within the head itself by using a reinforcing pad, increasing the head thickness, and/or increasing the nozzle neck thickness. Remember that the pressure vessel is like a big balloon, any geometric discontinuities want to round-out...try a thought experiment and try to imagine the distortions in the vessel with the relatively large opening in the head, then think of the best way to minimize this.

 

[SnTMan]

It might be more practical to increase head / nozzle thickness than to obtain a spherically dished pad. Might consider changing out the head for a cone. See UG-36(e).

Regards,

Mike

 

[Speckworm]

This is great information. Thank you very much for sharing your knowledge. I struggle with interpretation of the Code at times and it is great to have advice from experienced professionals.

 

[SnTMan]

(Don't tell anybody but I do too, at times)

 

[innovation2]

I agree with SnTMan. Go with a thicker head or try to use a cone. I would limit reinforcement to the head OD and check the box that "nozzle or reinforcement is outside of spherical portion" of the head.