Limitations on Nozzle Reinforcement

[crosby84]

Hey everybody,

I'm analyzing a horizontal vessel with a large (24") tangential nozzle that is throwing the Div. 2 deficiency, referencing 4.5.2 which says that if the ratio is greater than 1.5 then you need to design by analysis. Therefore I'm doing FEA - but I'm still getting high stresses (~40 ksi) close to the nozzle even with a small repad modeled. The nozzle is pretty close to the head (~6 inches) so there's only so much room for more reinforcement.

My question is, does ASME (or API 510 for that matter) limit how close a reinforcement pad can get to a head-to-shell seam? What about just putting a rectangular plate on that section of shell, basically a big thick square repad?

Thanks in advance. I'm new to this forum and it's been super useful so far.

 

[pdiculous963]

What is the Code of construction? Are you analyzing a new design or a current one? You reference Div. 2, but you may just be using Div. 2 rules. Are you linearizing elastic stresses, or just looking at maximum stress values shown in your FEA? To qualify the nozzle elastically requires linearization and comparison to the allowable limits outlined in the hopper diagram (Figure 5.1). You note you are near a head, therefore you will have interaction between the discontinuity stresses at the head to shell junction and the discontinuity of the nozzle. Personally, I wouldn't want to try to classify elastic stresses in this situation. Given your previous question in another forum regarding hoop compression on a torispherical head, it appears you have limited experience in vessel design. Taking up a FEA analysis to qualify a design is a tough task.

To directly answer your question, no, I cannot think of any rules which limit extending the pad into a head, although I believe many would consider it to be poor practice. Generally, rectangular pads would not be considered a good alternative either, perhaps they could be shown to be acceptable with very generous corners. However, if it were my vessel I would first opt to relocate the nozzle, or if that was not possible, look to use an integrally thickened nozzle and/or insert plate. Optionally, the non-linear plastic collapse options in Part 5 such as limit load or elastic plastic analysis could be performed. Don't forget the other required checks in Part 5 (local failure, buckling, fatigue, and ratcheting).

 

[TGS4]

You've been given good advice already. I'll add to that advice: hire an expert. This is not something to be passing around with. There's so much more to this that meets the eye. And absolutely do not use rectangular reinforcement!