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# Bolt Torque to Pressure3

## Bolt Torque to Pressure

(OP)
I have a scenario of installing a circumferential clamp on a 12.75" OD pipe. I calculated that the max allowable external pressure is ~45 psi from ASME BPVC VIII UG-27.

The 2 bolts will be torqued to 30 ft lbs. How do I calculate the pressure the clamp will put on the pipe due to it being torqued?

The (SA-516 Gr 70) 12.875" OD clamp is 1.25" wide, with two 5/8-11 UNC Studs (SA-193 Gr B7) used to tighten against the pipe.

Mechanical Integrity Specialist (Year 1)

### RE: Bolt Torque to Pressure

What does the clamp need to do?

My first cut would be the force X the projected are of the clamp (12.875" OD clamp is 1.25" wide = 16.09 squinches ).

Then I'd start thinking how complicated it must really be with hoop stress and friction and if the pipe is horizontal each support probably needs a saddle and .............

### RE: Bolt Torque to Pressure

Unless the clamp is perfectly rigid or the pipe is very soft you have proposed a very difficult calculation.

Is the clamp pressure so limited to allow for thermal expansion of the pipe? Consider using a plastic or elastomer insert that allows the pipe to move.

Or, consider using springs compressed to a specific height instead of bolt torque which is notoriously innacurate.

### RE: Bolt Torque to Pressure

Please pick an image to explain what "circumferential clamp" means to you.

Regardless, pipe clamps are commodity things. Unless you are doing something really unique there shouldn't be a need to calculate anything.

### RE: Bolt Torque to Pressure

First convert bolt torque to axial load.

There are many calculators and approx figures out there e.g. https://shipbuildingknowledge.wordpress.com/2019/0...

Then apply that bolt force x 2 over the area of your clamp in contact with the pipe.

It really is pretty basic stuff here...

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

### RE: Bolt Torque to Pressure

Hi Earl

We need to see what the clamp is like first as MintJulep suggested and then we can go from there.

If it helps the pressure on the pipe would be the surface area of the clamp that’s in contact with the pipe and from the bolt torques once you get the bolt tension, divide the bolt tension force by the surface area of the clamp and you have the pressure approximately.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Bolt Torque to Pressure

(OP)
All, thank you for the responses. As requested, the design package from the vendor is attached

https://files.engineering.com/getfile.aspx?folder=...

We do tend to install clamps common to water service which I do not look into as much. When we purchase an engineered clamp for uncommon circumstances due diligence is needed for me to buy off.

In this case, a 50# steam header had a 1" branch severed at the weld olet. There are obstacles on the back side of the pipe forcing a unique design.

Mechanical Integrity Specialist (Year 1)

### RE: Bolt Torque to Pressure

What in holy gods name is that thing?

A cantilevered clamp?

I think you're into doing more damage than the original issue here.

Can't you plug the hole from the inside using internal pressure to seal and expanding plug?

This looks like some sort of unholy monstrosity, adding all sorts of forces, moments and huge risk of someone trying to tighten this thing until something snaps.

your original question bears no relevance to this thing IMHO.

got a photo? We all love looking at pictures of damaged equipment....

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

### RE: Bolt Torque to Pressure

(OP)
Haha! I knew when MintJulep shared google photos I was going to throw you all a curveball.

No, we cannot seal from the inside, and the vendors design these for a living so we have a bit of trust in them to design it correctly... No one here has any design software either so as far as doing some type of stress analysis would be very elementary.

These are photos as close as we could get.

https://files.engineering.com/getfile.aspx?folder=...

Mechanical Integrity Specialist (Year 1)

### RE: Bolt Torque to Pressure

The last time I saw something like that it was evidence photos from an event that killed several people. Time for a new pressure vessel and not for patching this one.

Even the clamp is sketchy - the other end of that teeter-totter could be much farther away, reducing the forces required or just add a second clamp on the other side to split the load in half.

Yeessh.

### RE: Bolt Torque to Pressure

Well you're a braver man than me trying to fix a clamp to that rusty old pipe.

please tell me you're not doing it whilst steam is p8ssing out of the hole.

For those that can't be arsed to download the attachments, here they are: NOTE - the second attachment has 17 photos in the pdf - this is just the first one.

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

### RE: Bolt Torque to Pressure

(OP)
well it is either install the clamp or shut the plant down for repair and that is not my call.

ASME B31.3 minimal thickness calculation came out to be 0.081" based on the pressure and material. The minimal measured thickness is 0.201" with a corrosion rate of 0.000845"/yr
MAWP calculations is 547 PSI based on a circular shell in Section VIII UG-27. Reversing the t-min calc from B31.3 to solve for pressure using the minimal measured thickness is 373 psi.

The maximum allowable external pressure is 45 PSI from UG-27(the reason I asked how to determine pressure applied through bolt torquing)

Yes this will be installed with 50# steam blowing out, PPE, permitting, safety, etc. is determined from a group risk analysis and MOC process

Mechanical Integrity Specialist (Year 1)

### RE: Bolt Torque to Pressure

"Yes this will be installed with 50# steam blowing out, PPE, permitting, safety, etc. is determined from a group risk analysis and MOC process" ... oh please, god no ! The mere fact that we're talking about this suggests to me that your "group risk analysis" is going to be a "yes" session with the boss.

If your tag line is right and you're just out of school/uni ... please listen to the (other) experienced professionals here.

If that corroded out "piece of cr@p" is truly your PV, then no good will come of this. It looks like it hasn't been maintained since delivery. Possibly the only thing killing people in the neighbourhood alive now is a "leak before burst" design that would never have envisioned this level of disregard (contempt) for the PV.

Where is this (which country) ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

### RE: Bolt Torque to Pressure

OPs profile says OH. Staying away, Far away :)

Regards

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

### RE: Bolt Torque to Pressure

Have you looked at furmanite? Or other similar services.

They seem to have been bought out by Team https://www.teaminc.com/services/mechanical-servic...

Clamping that 24" "vessel" is just a recipe for disaster. I can't work out where that sealing clamp is going and how it will actually seal the leak. Do you want to keep the 1" line operational?

That looks like a might big crack in a very difficult place to seal.

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

### RE: Bolt Torque to Pressure

you're no reacting (or over-reacting as I am be) about he general corrosion seen. Is this "typical" ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

### RE: Bolt Torque to Pressure

(OP)
TEAM and COLT Group are the two vendors we use for these situations; colt had designed this one.

The clamp is on a 12" steam header and the corroded 1" pipe will be severed and covered. This is not a pressure vessel either strictly pipe.

The corroded piece of crap is 100% the truth for the 1" branch - the 12" steam header has seen 60 years of service with a loss of 0.049". Not a corroded piece of crap...

The seal also will not be a metal-on-metal circumstance and will be filled with sealant rated for the pressure and temperature.

Mechanical Integrity Specialist (Year 1)

### RE: Bolt Torque to Pressure

time to scrap it all and start over, even giving advice here is risky

### RE: Bolt Torque to Pressure

Hi Earl

A very rough calculation based on the info you have posted:-

Surface area of half clamp roughly 25.28 sq inch from (12.875 x pi/2) x 1.25

Tension from torque on stud 2851 lbf

Two studs therefor 5702 lbf

Pressure 5702/25,28 = 225.5 psi

The clamp has grooves machined within it which means the area of the clamp in my calculation is higher than what it should be.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Bolt Torque to Pressure

(OP)
Thank you for answering my question desertfox! I will give it a no-go.

Mechanical Integrity Specialist (Year 1)

### RE: Bolt Torque to Pressure

So you chop the 1" pipe off before you place that sealing pad over it? So 50 psi steam jetting out of your 1" hole?

With that clamp structure connected beforehand I guess. Then fit something in the hole in the clamp?

Still looks too high risk to me and only a 5mm thick 24" piece of pipe to boot.

There is a significant risk that you will collapse the 24" pipe or "crimp" it when you tighten up those clamp bolts as you first described.

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

### RE: Bolt Torque to Pressure

Hi Earl

You’re very welcome.
I also have concerns about the corrosion etc but others. Are giving you good advice on that.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Bolt Torque to Pressure

would be unacceptable to tighten the bolts to 6 ft.lbs ? (20% torque = 20% pressure = 45psi)
or maybe 3 ft.lbs ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

### RE: Bolt Torque to Pressure

#### Quote:

How do I calculate the pressure the clamp will put on the pipe due to it being torqued?

You don't, the supplier provides test data showing the boundary conditions under which their product functions. You verify the boundary conditions.

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