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inspectionboss (Structural) (OP)
25 Feb 05 9:07
I need to know how many threads are required for proper engagement of a nut. I was told it must be full thread value to meet manufatures spec. any one know whrer i can find it in writing.
Thanks Inspectionboss
Helpful Member!  donf (Chemical)
25 Feb 05 9:47
When time allows, I'll try to track down some specific references and reply.

In the meantime, regardless of the physical requirements (one reference I recall allowed the end of the bolt/stud to be one thread "shy" of the face of the nut. Perhaps we'll hear more from other forum members), I recommend at least one thread projecting past the face of the nut.

As the piping QA/QC inspector who shared this tip with me said, "I can verify one thread sticking out from ten feet (or more) away. To see flush or one thread back, I need to be within ten inches."

Donf
metengr (Materials)
25 Feb 05 10:38
Here is good reference material on bolted connections regarding bolt or stud length that can be downloaded for free,
Specifications for Structural Joints Using ASTM A325 and A490 Bolts by the Research Council on Structural Connections

www.boltcouncil.org/download/RCSC Specification 6-23-2000.pdf
deanc (Specifier/Regulator)
25 Feb 05 12:11
See ASME SecVIII Div1 UG-43(g)
Mb17 (Automotive)
1 Mar 05 15:21
Try this..

I think it answers all of your questions.

http://www.engineersedge.com/thread_strength/thread_minimum_length_engagement.htm

Regards,

M-J
Kenneth (Aerospace)
6 Mar 05 0:10
Helpful Member!  TBP (Mechanical)
6 Mar 05 15:17
Take a look at the shots Wayne Kirsner has up on his website.

http://www.kirsner.org/pages/forensicResAlt.html

There's one of a Class 150 flanged joint failure where the nuts have been stripped off the studs by the water hammer event, and the operator was killed. If I was tangled-up in that investigation, I'd hate to be involved in the "one thread back of the nut and/or flush with the nut is OK" VS. the "one thread past the nut is required" arguement. I'd rather be able to say that the proper size & grade of studs & nuts were used, and ALL of the available threads were fully engaged.
TBP (Mechanical)
28 Mar 05 10:08
I just came across this in the ASME B31.1 Power Piping Code:

108.5.1 says in part: "Bolts and bolt studs shall extend completely through the nuts."
Weldmedic (Mechanical)
29 Mar 05 14:53
While many specs require flush with the face of the nut, this will not provide full engagment with the threads. Examining the leading end of the bolt or stud reveals a partial starting thread. In order for there to be full engagement a full thread crossection must exist for there to be full engagement. This will result in a 1-2 thread protrusion past the face of the nut. At my last refinery t/a we had to replace a lot of studs which did not meet min engagement.

Steve
TGS4 (Mechanical)
29 Mar 05 15:24
The typical reason that the bolt is specified to be flush with the nut face is that corrosion on the bolt can cause sever problems removing the nut.  In that case, the bolt would have to be cut off and replace if the bolted joint needs to be disassembled.  In a turn-around, that extra time can be a real problem.

TBP - That's an interesting picture (I also like to see goo dfailure pictures).  However, simple calculations, such as that shown by Mb17 would conclusively answer whether the failure woudl have occured regardless of thread engagement.

Mb17 - I have used that calculation in the past.

Since this is an engineering forum, has anyone performed any engineering calculations on typical ASME B1.1 bolts/nuts found in refinery/powerplant applications.  I've just about had enough of these hand-waving arguments regarding thread engagement.

SHOW ME THE MATH!
TBP (Mechanical)
29 Mar 05 20:43
TGS4 - I'm interested in seeing the math as well, but at the end of day, if the applicable code calls for it, then everybody involved ought to make sure it gets done. If somebody feels that they have a legitimate case for doing otherwise, then they should take it before the code committee, and see if they can get the requirements changed. Otherwise, if it's a B31.1 application, buy or cut your studs long enough to have the threads extend completely through the nuts. To do otherwise is to leave an installation in a non-code compliant state.
Helpful Member!  unclesyd (Materials)
29 Mar 05 21:57
Here is some of the math.

http://www.hexagon.de/dose/dose1e.htm
TGS4 (Mechanical)
30 Mar 05 11:11
unclesyd - excellent link!  Thank-you!
jte (Mechanical)
30 Mar 05 12:46
And then one day the time comes to isolate some piping for hot work or equipment for entry. The crews grab a bunch of slip blinds to slip in between the flanges to accomplish the isolation. Oh, wait, the studs are too short. Go get new sets of studs and nuts just to be able to throw in a slip blind. That argument alone justifies our policy of three threads beyond the nut on each side of the stud. When you are installing hundreds for a turnaround, you don't need that headache. We tend to not get severe corrosion on the studs; must be a location/environment thing.

jt
unclesyd (Materials)
31 Mar 05 12:36
TGS4, et all

Here is an analysis that has a lot of information, a little different and very simple, on thread pull out. Look at 3.2 on page 11. (Hard-Link}

wind.nrel.gov/amestest/StressAnalysisDocument.pdf


This report has a very good format for the newer engineer.

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