The formula that I have seen, for the relationship between torque and tension,
T = (0.20*F*D)/12 = 0.167*F*D
where: T=torque (ft-lb)
However, I agree that DTI's are the best method for tensioning bolts.
"c2" <jimmycccccc(--nospam--at)email.msn.com> wrote:
>I am well aware of the requiments of RCSC pertaining to the proper
>tensioning of A325/490 bolts. I found it prudent to read the same materials
>that field inspectors do a long time ago. It would have been like a battle
>of wits with an unarmed man if I did not.
>It is my understanding that research has established a direct relationship
>between bolt tension and torque values. As a matter of fact there is a
>formula (which I wish I could recall) reliabily predicting approximate bolt
>tension based upon thread pitch, bolt diameter and applied torque. If I
>remember correctly the proper torque value for a 3/4 inch A325 bolt is 225
>foot pounds. This WILL induce the correct amount of bolt tension when the
>bolt is installed with a hardened washer under the turned element.
>Likewise, so will the practice of turning the nut from a snug tight
>condition some 1/3 to 1/2 turn more. As a practial matter in the field the
>bolt is usually turned somewhat less than a full turn..
>My considerable experience with Skidmore calibrated wrenches, obstinate
>ironworkers and incompetent field inspectors leads me to say that this
>method is somewhat less than satisfactory under any circumstances less than
>near laboratory conditions. That which works well in the lab often fails
>miserably under field conditions. I have previously enumerated some of the
>many variables that affect the desirability of utilizing this method, the
>paramount one being the lack of inspector confidence level and mutual
>satisfaction that the bolts have been uniformly correctly tensioned.
>Direct tension indictors have the unique characteristic of being the only
>method by which an ironworker and a inspector have the same simple tools by
>which to gauge the quality of work being performed. One can furnish an
>ironworker with a feeler gauge to check his work with as he goes along and
>he soon develops the "hang" of the operation without having to recalibrate
>his tool every two hours. When the worker gets through he knows that the
>inspector will be using the same thickness of feeler gauge that he used.
>This aside from the fact that an inspector can check a far greater quanity
>of bolts in a given period of time than by any other method. The confidence
>level on both ends just soars.
>The name of the game is to produce a properly tensioned connection with
>maximum efficiency to the mutual satisfaction of all parties. As I have
>said "a tensioned bolt is a tensioned bolt".
>I see you missed my attempted humor in offering pre-flattened tension
>indicating washers to the steel industry. <g>