leak sealing clamp design for piping

[NovaStark]

Hi,

I am trying to understand the design of clamp for an application of a leak sealing clamp on a pipe with a defect on it.

The clamp would be an enclosure around the leak and then bolted then injected with sealant. However going through the calculation sheet given, I am not sure that I understand some of the numbers obtained.

In the cover thickness, the value given is 1.125 inches, however I am not seeing this value anywhere on the drawing.

Similar to the working load per stud, for the area, no matter what dimensions I think are used, I don't get that value for the area.

And I am not sure of the purpose of the blind circular plate end thickness as then wouldn't that make the cover thickness calculation incorrect?

I attached the drawing and calculation sheet if anyone is willing to try to explain this to me.

 

[LittleInch]

S far aI can see, the design is using a tube approach with the minimum thickness of the block used. The thickness at the thinnest point says 4.75". Biggest ID is 7.25, so half shell thickness 3.625,so min weakness 1.125".

Bolt area seems to allow 0.1" for the threads.

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[NovaStark]

S far aI can see, the design is using a tube approach with the minimum thickness of the block used. The thickness at the thinnest point says 4.75". Biggest ID is 7.25, so half shell thickness 3.625,so min weakness 1.125".

Bolt area seems to allow 0.1" for the threads.

Right, but in the formula it was OD = 9.5 inches and I don't understand where that comes from as I am working under the assumption that before they do the drawing, they do the calculations to make sure that they have at least the min. thicknesses.

 

[LittleInch]

Err 4.75" x 2 = 9.5" ??

As I said, they are doing it really quite simplistically and ignoring the actual shape of this box, which I'm not sure is actually correct. An FEA model would do a better job and might point out some stress concentrations, but considering the sheer mass of metal there, this seems to be a conservative approach.

I think they've designed it first as a big strong box and then done the calc to make sure, which is why it say min required thickness is 0.7xx", actual min is 1.1.

given that this thing relies on being filled with "sealant", I don't think the issue is with the mechanical integrity, but the sealent.

My bigger concern would be having this no inconsiderable weight imposed on a 1 1/2 " pipe...

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Also: If you get a response it's polite to respond to it.

 

[NovaStark]

Thanks for the help, yes I understand the 9.5" thing. So this means that they'd basically measure a box to cover the entire area and then do calculations to show that it satisfies min. requirements.

Also the clamp was to have an additional support installed on it due to its weight and the 1.5 inch piping it would have been installed onto.

If they were using a box approach, then for the working load per stud, from what I understand, the area would have been (bore) 6.99 * (7.83+1.75) = 66.96 in^2.

However they have a value of 57.36 in^2.

Any idea how they got that value?

 

[LittleInch]

inside area of the circular hole inside the thing is my understanding

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[NovaStark]

Much thanks, that get's near the value given.

However while the FEA would be the best solution, would using ASME BPVC to design a rectangular pressure vessel be better to use for quicker hand calculations (as these clamps are usually made on an emergency basis so FEA would be a bit time consuming for safety reasons)?

 

[LittleInch]

Don't know.

I think the lots of metal technique seems to the option to use and circular things are inherently better for internal pressure.

Of course removal or cut out would be a lot better, but there are other options, wraps, split sleeves etc, but I guess you're looking at something which includes an elbow?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[NovaStark]

Yeah the defect was on the weld of a flange so they designed one to go over the nearest elbow.

Thanks for your help though.