Reinforcement pad on top of existing reinforcement pad, Construction code: B31.8

[alsy]

Code: B31.8

Hello all,

Although not typical, is there any provisions restricting the placement of a repad on top of an existing repad to come up with the required area per 831.4 and appendix F, and as long as the additional area needed is within the reinforcement zone, and applicable provisions followed? The second pad would be smaller in diameter so achieving required fillet size and placement of fillet would not be an issue.

Background: The pads in question are on some large bore branch connections and was realized (after installed) that the incorrect working stress of the repad material was utilized in determining the proportionate area needed.

Thanks!

 

[BigInch]

Something's wrong if you need two pads to produce the required area.

I hate Windowz 8!!!!

 

[jte]

Agreed that one would ideally not use two repads. But then, ideally we wouldn't use repads at all, we'd just use insert plates.

However, stuff happens. I'm not particularly familiar with B31.8, but in general if you are looking strictly at area replacement, you could argue that a two pad arrangement is ok.

I've rerated vessels where the repads on nozzles were limiting. In order to increase the area we did a weld buildup over the existing pad to add 1/4 to 3/8". One reason to prefer a weld buildup is that you won't face fitup issues (get the pad to pad curvature just right!) and you can run the design as though it is a "normal" repad.

.

 

[alsy]

JTE,

I am coming to same conclusion that although not ideal, I cant find anything that would prohibit in either BPVC or B31.8(less stringent. We will probably back up the AR calcs with some FEA.

Thanks for your input!

 

[BigInch]

Lots of things arn't prohibited, but that doesn't make them a good idea.
Let's have a closer look at what you're doing. Why do you need so much replacement area? Cutting a very big hole?

I hate Windowz 8!!!!