Thread lenght requirements ( after torque) 1

[woodman90]

I am needing help on codes that address, Threads showing
through nut after torque,on ASTM A325 and A490 bolts.
I have always used 2t-3t, after torgue as rule of thumb.
Any clarification would be appreciated

 

[CWIC]

Good question.

I have found the project specifications determine this dimension. Or, it may be a proponent specification. Typically "full thread engagement" (FTE) is all that is required UNO.

When I worked for ARAMCO, their specification was 3 threads. Anything less had to be evaluated by the inspector and approved by the Project Engineer. Please note this applied to all connections whether a pressurized system or structural application. Another client of mine had the same 3 thread requirement, but it was for a dynamic/cyclic application (amusement devices).

I have in my collection of noncompliant materials a 1-1/2" dia. nut that was cut in half (I only needed one) for an A 325 galvanized fastener. The contractor claimed they had FTE. I rejected all of these connections as quickly as I could write. They should have reversed the installation of the bolt and there would not have been any problems. Replacing these with nuts that were not modified and reversing the installation cost them plenty in manhours.

 

[rmp319]

Woodman,
AISC Specifications for Structrual Joints using ASTM A325 or A490 bolts Par 2(b) "The length of bolts shall be such that the end of the bolt will be flush with or outside the face of the nut when properly installed"

This specification usually applies if you are dealing with Structural Building Issues ie: Specifications call out for building in accordance with ICBO/ICC - which refers to AISC for bolting and other issues. This information is from the Manual of Steel Construction ASD Ninth Edition Section 5.

You can also download the most recent version from AISC.org website.

RMP

 

[Rjeffery]

Rpoche is exactly correct. The best rule of thumb is if you can catch your (thumb) nail on a portion of the bolt's thread at the face of the nut then there is full thread engagement. That thread need be only long enough to catch the nail.

As for 'Torqueing' the same manual does not recognize torque values. If you have to do the arbitration inspection, someone fell down on the job... Just MESHO... []

 

[CoryPad]

There is more information on this subject in this thread:

thread725-57019





Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Kenneth]

... and still more at thread725-37409...

 

[evelrod]

To add my usual touch of realism---Mobil Oil, Torrance Facility c.1993, "several" A-325 galved bolts found in non compliance even though thread projection was "visibly" correct. It appeared that a "Texas based non union contractor" had "pulled" the threads a bit by severe overtorquing. I have always been aware of cheating but, this was a first for me in, at the time, 32 years! Thankfully the problem was located and corrected before the bents were loaded. This was a "mile long" three tiered pipe rack. I would have liked to have seen the contractor sent packing but that did not happen, unfortunately as they tried to re use the nuts---that did not happen either!
By the time I retired in '98 I am told that most bolted connections were using TS bolts. That would seem to solve this particular problem.

Rod

 

[unclesyd]

I agree with the thumb nail approach and have used it all my career. I think the 2t/3t approach is for easy verification at a distance. We based our 1t approach on the fact that only the first and second threads carry the major part of the load in most assemblies. Extra exposed threads can and did cause problems in disassembly. The extra threads were a particular problem with moderately loaded S/S fasteners that required periodic disassembly. I have never seen a case where extra threads contributed any thing to the integrity of a bolted joint