Thread Tolerance/Repair

[ChristopherFehr]

The threads for the cover on our compressor heat exchangers have become worn to a point where if you turn the bolt in it can wiggle some. Is there an easy rule of thumb for determining if the threads should be repaired or best left alone?

Given that they on occasion use longer bolts through the cover into these threads to hold a lifting bracket for final placement is there an easy repair available that will guarantee a pullout strenght?

Thanks

 

[proinwv2]

You can purchase thread gages to see if the threads are within tolerance.

I would be wary of oversized/worn threads and I don't know of anyway to determine their strength other than a (unacceptable) test to failure.

There are inserts, such as Helicoil which might fit your needs. I suggest that you contact them and see if their product is suitable for you.

Also, new, larger threads can be tapped given adequate material, space, etc.

Paul Ostand

http://www.ostand.com

 

[abeltio]

to insert helicoils you need a good thread to begin with.

the fix would require to re-tap the threads to the helicoil size to use.

btw. wire inserts (helicoil) are the way to go on threaded joints contained in structural parts (like your cover) this allows to change the helicoil when worn without disturbing the structural member.

saludos.
a.

 

[diamondjim]

Is it the bolts or the threads that
are worn? Keenserts might work as
well if they are the threads.
Do not know what wall thickness you
have around the threads. That would
be a consideration as well.
I would also contact loctite to see if
any of their products would help.

 

[rmw]

If these are coded vessels and the cover you refer to is part of the pressure boundary, the bolting is integral to the code calculations and any changes would have to be considered in that light.

I don't deal with the calculations directly, but I often deal with the issue on HP coded vessels and refer it back to our engineers who are code literate.

I'll let the code experts on this site address the finer points regarding this.

If this is a code vessel, you may want to post the question in the ASME code issues forum.

rmw