reinforcing pad? 4

[shahdadf]

hi dear friends,
how many types of reinforcing pad we have and when they shall be used?
how the outside diameter of them shall be calculated??
are there any differences between saddle and pad???
thanks a lot for your answers

 

[gr2vessels]

1. Please read ASME VIII-1, clause UG-37.
2. Yes, the wrapper plate for saddle supports is diferent from openings reinforcing plate and for this, please read ASME VIII-1, Appendix G.

Cheers,

gr2vessels

 

[deanc]

gr2vessels has pointed the way.

Just don't cheat and make a small pad extra thick.

 

[JoeTank]

deanc
Why would it be cheating to make a pad smaller in diameter and slighlt thicker? I've done it numerous times when good practice could not be followed for toe-to-toe weld spacing. Although Code is silent on this, weld spacing is important.

Joe Tank

 

[TomBarsh]

For what it's worth, the European Code doesn't permit any pad to be more than 1.5 times the shell thickness. If the pad is "too thick" it will create a hard spot on the vessel and may be more susceptible to a fatigue failure.

 

[deanc]

I knew someone would say so. Like to start discussions.

Say you have a 6" nozzle in a 1/2" shell. Lets say per UG-37 you would need a 1/2" pad 3" wide. But I have seen things like a 2 1/2" pad 1" wide with 1/2" fillets. Ugly.

One can debate the meaning of UG-37(c)and I believe the Code intent is described in Appendix L. Then one asks,how about a forged nozzle with an extra heavy wall?

Need good engineering for the same,justify your extra thick pad. Plus I like things to look right,Just picky.

 

[shahdadf]

Thanks dear friends,
but what about the difference between saddle and pad????

 

[TomBarsh]

"Saddle" can refer to a support for horizontal vessels, such as analyzed by Zick analysis.

"Saddle" can also refer to the nozzle reinforcing plate or pad, due to its "saddle" shape. This usage is less common in the United States, more common in Europe, etc. This usage comes from the similarity in shape of the nozzle reinforcing pad to a horse's "saddle". The word is also used in mathematics in study of topology of surfaces for same reason.

 

[gr2vessels]

shahdadf,

The saddle you've mentioned is a complex structure required for the support of the horizontal vessels. The saddle plate is a rectangular plate of similar quality as the pressure vessel, which is shaped to wrap itself around the vessel shell. It is welded on the outside of the shell and is required to provide distribution of the saddle support reaction on the shell, due to the dead and live loads, in order to minimise the stresses generated in the shell by the mentioned loads.
In opposition to the role of the saddle plate, the reinforcing pads are welded around the holes cut in the shell for nozzles required to be be reinforced, due to the loss of shell material. There are rules for the design of those compensation (reinforcing) pads, which are included in the book called ASME Section VIII Division 1. Refer above comments for the specific clause.

Best of luck,

gr2vessels

 

[OwaisGillani]

I agree with "deanc". I dont like extra thick repads on nozzles. It is something that I am not comfortable with.

And there are other ways to provide reinforcement for nozzles besides using extra thick and less wide repads.

 

[AravindSujay]

Hi gr2vessels,

Thanks for your Info. But, should we use the same material of the shell for saddles. I think, need not be. If shell is SA-516 70, we can go for SA-36 for saddle material. Correct me, if Iam wrong.

Regards,
Aravind Sujay

 

[SnTMan]

AravindSujay, you should be OK to do that, however it is good practice to separate the two with a SA-516-70 pad. It is often done that SS vessels, lo chrome vessels, etc use CS supports with an appropriate pad between.

Considered "good practice" to weld to the pressure boundary only the same material, or in some cases higher alloys.

Regards,

Mike

 

[doct9960]

AravindSujay,

If your vessel is installed in a cold climate (say -45C), you may want to consult with a material specialist.

 

[zjliang]

Here below is some experiences about the stress distribution around a reinforced nozzle based on the FE study.

Pad or repad, often used to increase the available area as per UG-37, is essentially introduced to redistribute the local bending stress due to the internal pressure or piping loading. However, as some codes recommended, the size needs to be limited. The reason is, increasing the width within some limits, the peak stress is relocated from the inner conner of nozzle to shell, to the pad and shell (in some cases, the peak stress moves to the edge of the pad), and the stress magnitude drops.

However, beyond the limit, there is little impact on the stress magnitude.

So I think that's why the size of pad needs to be limited.

 

[deanc]

zjliang

Very interesting. Did you in the course of the study find a "sweet spot ratio" for diameter versus thickness?

 

[cmryu]

Hi

Reinforce pad calculation in pressure vessel will be figured at following website.

http://www.pes21.com

 

[zjliang]

deanc,

The so-called study was actually repetitive work on the local stress analysis around attachments when the piping loading changed again and again from the layout. So I did glean some rules of thumb through FEA though, they were not generalized at all.

However, as we know, unless around hillside and/or inclined nozzles, the pure pressure-induced stress around a normal nozzle is always symetrical and a 1/4 model can show enough info. If you are intterested, a parametrical model can definitely give you a sweet ratio. Good luck.

Thanks,