Missing / broken stud in 8"x600 # flange joint 4

[David19]

Hi;
One of the cap screw's threads got ripped off during final torqueing of 8"x600# Butterfly valve between flange joints. Can this piping system be operated with remaining 11 studs. What is the gasket seat force required to maintain the flange joint integrity ?

Thanks in advance,

 

[LittleInch]

And the reason you can't simply replace it is....?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[geesamand]

The preload on the adjacent bolts is now elevated, is it not?

What caused that first bolt to let go - will it "zipper" around the flange?

 

[racookpe1978]

No. It cannot be used. I'm disappointed you even asked.

Remove the stripped bolt, REMOVE THE VALVE and replace the remaining bolts and studs: usually this kind of valve will have 4x bolts who gave you "cap screws" from what supplier and what grade of materiel are they ?)

Check the threads in the valve. If bad - and they may or may not be bad, retap or drill out and use a thread repair insert. Replace the gasket with a new one.

How did you torque the bolts and studs?
What tightening pattern did you use?
What was the calibration date on the torque wrench? Hint: I'll bet donuts tomorrow morning that the crew CANNOT show you the torque wrench (that they didn't use ... Hint, hint.)
What intermediate torque values did they use at 30%, 70%, 90 and 100% levels?

 

[David19]

LittleInch - We can't replace it simply, since spare valve is not availalbe and threads that got ripped are in valve body.

geesamand - Yes, the preload shall increase on all remaining studs and more specifically to adjacent nearbuy studs. This is 8"x600 # butterfly valve with four threaded holes (two each on top and bottom) for alignment with piping flanges. Screws are tightened with adjacent piping flange and rest seating force is applied by eight studs of the adjace piping flanges. During torqueing, threads of one of the holes inside the valve body got ripped off and hence that side of the valve is left with three screws + eight studs.

racookpe1978 - I wouldn't have asked if we could have replace that damaged valve that easily. Damaged threads inside the valve body is beyond repair. We need to continue with the situation for a while until we get spare valve and the purpose is to understand hazards with such operation with one missing fastener. Final torque value for this size of the stud per our internal spec is 630 Ft-Lbs and manual, calibrated torque wrench was used for torqueing. Torqueing was carried out in three passes, first at 30%, second at 60% and final pass at 100%. Torqueing is done in legacy pattern per ASME PCC-1 and after the third pass, fourth pass in circular pattern is carried out at the same final torque value, i.e. 630 Ft-Lbs. Threads got damaged during final pass of the torqueing. 3.2 mm thick SS 316 Spiral wound gasket with grafoil filler is being used and stud-bolt/nut is A 193 Gr7 with A194 Gr 2H heavy hex nuts. Jet lube nikal paste is used as thread lubricant on studs for torqueing (friction factor - 0.15)

 

[europipe]

Put a clamp on the flange on the bolt location.

 

[LittleInch]

If I read this right, why can't you drill out the tapped hole which you've managed to strip and replace with a stud, all the way through.

Also we live in a world where anything can be obtained in short time if you pay enough, clearly you just don't want to, but not using one bolt is not an acceptable option.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[ornerynorsk]

If a bolt popped during torqueing, I would immediately worry about the source of the bolts and suspect the remaining 11. Would a catastrophic failure be less expensive to mitigate than simply getting it done correctly before placing in service?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[LittleInch]

Do you have a drawing of this thing or can sketch it out and upload.

I've not seen tapped holes in a butterfly valve like this before and am curious as to whether there are two tapped holes either side or what. Normally the whole point about butterfly valves is that they sit inbetween two flanges without any other attachment. The holes at top and bottom are normally just to rest the valve on the studs during assmebly not be part of the structural element.

Did the valve arrive with tapped holes or did you tap them?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Latexman]

Some lug-style butterfly valves have threaded inserts on both sides. They can be used for end-of-line service and this facilitates blind flange removal and drainage.

Good luck,
Latexman

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[LittleInch]

But then surely all or none of the lugs should be tapped, not just 4 out of 12. Something doesn't quite add up here for me, hence the request for a drawing or sketch. I did a quick search and couldn't see anything exactly like what the OP has described.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Latexman]

I've seen big wafer type butterfly valves like the OP described. 4 threaded inserts on the body and the rest drilled through for threaded rod. Makes installation much easier. Here's one:

http://www.gaonengvalve.com/showprd-20424/Wafer-type-Butterfly-valve.html

If this is similar to the OP's valve, I can see why they don't want to drill through the body and put threaded rod. They might hit something important!

David19, that drawing or sketch sure would help.

Good luck,
Latexman

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[JJPellin]

Keen-sert or heli-coil.A skilled machinist could fix it in a few hours.

Johnny Pellin

 

[Latexman]

Yes they could! A star for you Johnny!

Good luck,
Latexman

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[Gator]

Flange/wafer butterfly assemblies with many bolts typically have threaded bolt (stud/cap screws) holes at top and bottom because of the shaft running though the valve body. There's not enough room between bolts for the shaft.

Paul

Piping Design Central

http://www.pipingdesign.com

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