RE: hand wrench and sledge hammer

torquing is more of an art than science. why? we'll lets consider the equation from Motosh and Farr (i prefer it over api).

torque = fLd^2 / (8.8d - 1.4*.001^f)
f is of course the coef. friction and L the bolt load.

Fel-Pro graphite based lubricant , f=.086 Jet-Lube gives an f avlue of 0.143
Other Gen. purpose graphite lubricant about 0.117 (if its not grpahite, i dont know).

Ok now lets throw in poor alignment of flanges holes, imperfection of threads, burrs, inconsistent lubrication, manufacturing tolerance for bolts/nuts, dirt (as most have mentinoned), techniques for tightening,thread engagement not full, etc. and the calculated torque values is now more of guess work (equivalent to the millwright "fell"). surebolt (they have a website) test indicated values of torque measured varying from 30 to 50%.

ok. now lets have a look at the bolt stress which is normally around 15 to 30% of the smys. hey plenty of room there.

conclusion. same as steve observation and that for critical service, Measuring bolt stretch rather than torque makes more sense since the application of the preload result in tensioning of the bolt (stretch = preload*bolt lenght/A*E). One thing ive learn about measuring bolt elongation is that in some cases you may actually have to increase the torque over the published values (call it standard) to ensure that the preload is greater than the operating load.

-----Original Message-----
From: Steve McKenzie [mailto:Mechproj@xtra.co.nz] Sent: 26 March, 2002 10:24 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] hand wrench and sledge hammer

Hi Davis

I think you can trust a good fitter a little more than your table suggests. If we are talking about the main cooling water pump on a PWR, I would not, in a pink fit, rely on feel. Nor would I use torque. Bolt extension and gasket compression is the appropriate method in this application.The gasket compression is used as a crosscheck on the bolt extension. Received on Tue Mar 26 23:50:00 2002