Good point George. I don't want to make too much of this "technique". Most of my
experience is field related in plants on standard pipe flanges and gaskets.
Typical grade used is B-7. It is definitely a very informal and imprecise method
for checking stud bolt integrity. But I've seen it employed by some pipefitters
and is far better than doing nothing.
Davis:
Would be cautious on that one. Whether the nut threads or not can also be a
function of the thread class. Some will have so much clearance that they will
thread on with gross elongation (consider an Acme type thread, with large
backlash clearance). You would have to be near failure point that you would
have so much elongation that they would bind up.
George McKinney
I have a reprint of a great article in the Sep/Oct '96 issue of "American Fastener Journal". I've looked for it on the internet but it doesn't seem to be available anywhere. It's titled: "When is a Bolt Suitable for Reuse?". The author is Dr. Joe Greenslade. He is described as "President of Greenslade & Co. located in Rockford, ILL. His firm specializes in providing manufacturing tooling and inspection equipment to suppliers of bolts, screws, rivets, and nuts throughout the world". I'll quote the pertinent passages:
"...the question arises as to whether...bolts are suitable for reuse or not. The answer to this question is: when a bolt has not been stressed past its yield point it can be reused. This answer brings to mind two more logical questions: what does it mean that a bolt has been stressed past its yield point? A bolts yield point has been exceeded when the bolt does not return to its original length when the assembly stress is removed from it...How can one easily determine if a bolt has yielded? Simply screw a nut on the previously used bolts threads to the head on a fully threaded bolt or to the thread run-out on a bolt with a full diameter body. If a nut will not screw on the entire bolt thread length, the bolt has yielded and it is not safe to reuse."
O Learned Ones
I do some work at a plant which has many flange stud bolt connections;
some of which are dismantled quarterly. Short cycle fatigue is not an
issue during operation, but perhaps there is a need to replace stud
bolts after a certain number of retensionings. At present studs are
replaced only if they show visual signs of distress, but this approach
seems somewhat arbitrary. Flange classes are 150# thru 600# studs are
typically low alloy steel with a few exotics thrown in and temperatures
are moderate; up to 250C.
I could revert to first principles, calculate bolt stresses and work
out fatigue life, but feel countless people will have done this before.
Does anyone have any references to standard testing/rejection criteria
for stud bolts? If so a reference would be appreciated.
Cheers
Steve
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[Non-text portions of this message have been removed] Received on Mon May 09 10:37:00 2005
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