huangyhg

a325 bolts
i have an inspector who is checking some a325 bolts in slip critical connections that i designed. the bolts are supposed to be tensioned to 19 kips. the inspector is useing a torque wrench to check the bolts. what is the required value that he should be looking for(ft-lbs)?...i found a method of calcing the torque but it requires a "torque coeeficient"...(k)..that i cannot find. my bolts are a325 5/8" diameter...galvinized.
also i'm not sure that his method is correct in checking the torque. the bolts have been installed for about 2 months and from what i read some relaxation of the connection and elongation in the bolt will effect the tension...if anyone has any comments or input i would like to hear some....thanks
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he, the inspector, should be using a skidmore-wilhelm testing machine to calibrate the torque wrench. in doing so he will be checking the actual lot of bolts (so as to consider galvanizing etc) to a specific tension level - the torque wrench can then be calibrated on that or the reading taken so as to note when the actual field bolts are checked.
levelrod is the expert on this...rod, where ya at?
generally there is about 20% loss due to relaxation and elongation for galvanized bolts.
danny_m (visitor)9 jul 02 7:24
sorry, i made a mistake
the nut factor(you call it "torque coeeficient") for unlubricate galvanized bolts is 0.2.
par060...qshake is right on target. the skidmore-wilhelm device should be used as a field correlation measure of torque value showing on the wrench to tension value achieved in the bolt.
analytical relationships have been tossed about for years and sometimes they are relatively close to actual values, but not reliably and consistently so.
the s-w device is a hydraulic load cell that allows you to place a bolt and nut sample directly into the device and tighten the bolt with a torque wrench. as the bolt is tightened, the tension is the bolt shows on a gage on the s-w device. the scale on the gage is marked by bolt size and tension. once the required tension in the bolt is achieved (in your case 19k), the torque value on the wrench is read. several of these are done and an average "job torque" is determined for that day with those bolts. this should be done routinely, as there are quite a few variables that change the job torque value.
your inspector 'should' have a skidmore and if he does not, he will have access to one. any bolt up job that is critical should re calibrate the torque wrenches/impacts each morning. the problem is in setting up the skidmore. it requires a much longer bolt for testing purposes than you will normally find in use on the job (generally, but not always, of course). i normally ordered extra long bolts just for testing while in the refineries. testing and checking the calibration of our impacts was done weekly there, but is often done more frequently depending on the job, bolt size changes, etc.
if your job is 'super critical', just set the skidmore up on a column and you can retest in a matter of minutes any time you wish . any combination of dry, oiled, waxed bolts/nuts/load indicators etc. can be tested in the field with very little effort.
i am not sure what part of the world your in, but any bolt up job in l.a. starts with calibrated torque wrenches. if there is any doubt, they must be re-calibrated. often testing extends several months after the job is completed. i am not aware of any changes in standards due to that brief timespan. i have been out of the loop for four years now, but i doubt things have changed much.
rod
as a ps---ts bolts will not wrench torque to the same values as conventional bolts after installation. they generally will turn at a somewhat lower value (a 3/4 a-325 conv. say at--- 355ft/lbs and ts at 325ft/lbs. not totally accurate numbers, just a referance, ok?)

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