Gussets and their use?

[reades]

To all,

What is the recommended use for gusset plates? Can they be used on elbows for both "in-plane" and "out-plane" bending? If so.. what would be the change in the Stress Intensification Factor for the elbow? Is there any way to calculate it or must it be done by experimentation? Any help would be greatly appreciated.

Steve R.
Mechanical Engineer

 

[MJCronin]

reades,

Why do you want to add "gusset plates to elbows ? I hope that you are not trying to "strengthen" the elbow or change it's flexibility characteristic. This is not necessary in a properly designed piping system.

Are they for some type of pipe support attachment ?

In thiry years of piping/mechanical experience, I have never seen a plate attachment on the intrados of a piping elbow.....

In answer to your question, yes, the addition of gusset plates (or "support lugs" or trunions or any welded attachment) all affect both the flexibility factor and the stress intensification factor for the elbow.

In my opinion, the only legitimate welded attachment to a piping elbow would be in a high-temperature, high pressure boiler application ( such as a main steam/reheat steam system) at the top of a long heavy riser. I have analyzed this type of application and know that the addition of a "support lug" at this location is the lesser case of other evils.

My opinion only....


MJC

 

[KernOily]

Oooh, good question. I would love to see the SIF for this. If you read the Markl et al. papers you will see how they came up with the original SIFs. Today you could estimate it using FEA. If you do it, I want to see the results! Methinks not only will this affect the SIF but your modeling software, e.g. CII, will no longer be accurate since it uses the beam-column model to do its analyses. An elbow stiffened in the manner you mention excludes it from the assumptions inherent in the beam-column method. Pete

Thanks!
Pete

 

[Hench]

Reades,

If you are trying to stregthen an elbow, try increasing the schedule/wall thickness of the fitting. The fitting could then be taper bored to match the remaining piping. This would be much easier than adding gussets and trying to calculate their resulting effects to the fitting.

Good Luck!

Hench

 

[MJCronin]

to all,

"Hench" is correct if your problem somehow is an elbow that is not designed for the pressure of the system ( but if the adjoining piping is of the same schedule, it too will be undersized for the pressure)

I suspect that you are trying to "stengthen" the elbow for some other reason....Perhaps the failure of the elbow in a computerized stress analysis code check ???

If this is so, the correct solution is to evaluate the piping system flexibility and/or pipe support locations to get an acceptable system....

By modifying the elbow, you simply make the system impossible to evaluate using conventional "beam-type" programs such as CAESAR-II and AUTOPIPE....

Steve, what are you trying to do ?????

My opinion only

MJC