Measuring Bolt Torque
Measuring Bolt Torque
(OP)
I am involved in an investigation of torquing procedures and we need to measure the torque of some 2" b8m bolts in a 40 hole flange. The tension was 27 kips, and the torque using the Sidmore was roughtly 600 ft-lbs. Question is: how do I measure torque? If I go around using the sequqnce, won't I affect the later bolts? Should I check in the tightening or loosening direction? Is there a digital readout wrench this large?





RE: Measuring Bolt Torque
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RE: Measuring Bolt Torque
then turn it backwards one flat and then retighten it to its marked position and check the torque. This would only be a rough measurement but maybe close enough if you are averaging the readings for the 40 bolts.
I think almost no one recommends turning torques for bolts larger than 1 1/8 inches. Let us know your results.
Curious why you are doing this.
RE: Measuring Bolt Torque
agreed, tightening later bolts was an effect of the previously tightened bolts, so when you're installing the bolts you tighten they up gradually (each one a bit at a time) and then go round the joint one more time checking.
personally i don't think a digital readout would help much. if you've set the torque wrench up properly, it'll give you the torque you want.
witness marks (like dimjim is suggesting above) allow you to readily inspect the joint, to see if the bolts are lossening up.
RE: Measuring Bolt Torque
I am interested in the "one flat, then retorque" suggestion...also the ultrasound (?)
On another topic, we noticed that many of the loose bolts had galling. However, the extent of galling was large. I was trying to understand, by examining the galling, what rough percentage the applied torque was lost. Any guidance?
This forum is great, by the way. Thanks for your earlier replies!
RE: Measuring Bolt Torque
RE: Measuring Bolt Torque
RE: Measuring Bolt Torque
RE: Measuring Bolt Torque
A better method for checking bolted joint quality is to measure the preload (instead of torque). Ultrasound (or even using a micrometer if you have access and can find one large enough) is the best method for this. You measure the initial length in the strained condition, loosen the bolt, then remeasure the length. The change in length plus the fasteners stiffness gives you the preload.
Regards,
Cory
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RE: Measuring Bolt Torque
To corypad, 5 degrees in the tightening direction...this is probably what we will do, but I am still worried that it will affect the rest of the bolts.
RE: Measuring Bolt Torque
where did the 600 ft-lbs give 27k come from though
My handy dandy cheat sheet says 2" 8TPI should be about 2200 ft-lbs to get 30K
Not having all the data about oring size and durometer, but experance with flexatalic gaskets 600 ft-lbs would not compress the gasket completely and the joint would be soft.
RE: Measuring Bolt Torque
27 kips per inch...on a 2" bolt I think this translates to roughly 30 percent of yield (bolt is 314 ss).
The durameter is like 70, and its 1/4" dia. But the flange has a raised face (on the non-grooved side) and the "overhand" towards the outer circumference (where the bolt holes are) flex ever so slightly.
RE: Measuring Bolt Torque
is 27000 pounds. I do not understand the 27000 pounds per inch. Does this mean that the 2 inch bolts has 54000 pounds tension?
As to the 30-60-100-100 step procedure, I have heard of
tightening in 1/3 and then 1/3 and then 1/3 step method
ie if the full torque was 600 ft-lbs you would tighten
first to 200 ft-lbs all around, then 400 ft-lbs the second time around and then 600 ft-lbs the last time around.
Sorry to be so dumb.
RE: Measuring Bolt Torque
I'm not familiar with orings, so I cannot calculating the force required to compress o-ring till the flange joint goes "metal to metal". but i recall 600 to 800 ft-lbs the torque required to fully compress a flexatilice gasket so joint is metal to metal for the flanges I deal with
when I can not measure the actual strech of the bolt being tighten (something like 0.001" per active lenght of bolt gives 30K, but very material related), I use nut rotation to approxamate the desired elongation. for example if the bolts are 15" active length, and the desired elongation for 30K is 0.015", and the bolt is 8TPI, it would be rotated 1 flat. However, accounting for having the joint hard must be considered.
RE: Measuring Bolt Torque
I'm use to the bolt loading being expressed as a percent of the yeild strenght of the material. thus if yeild is 90k pounds per square inch, and the % desired is 30%, then the desired loading is 27k psi. This doesn't care what size the bolt is, only what the material is.
Now if a 2" diameted bolt is loaded to 27K the actual force will be 27K over the bolt area. not accounting for threads, the area of a 2" diameter bolt is 3.14 square inches. thus expected load would be 85K
RE: Measuring Bolt Torque
The 30-60-100-100 is still a mystery. What does the second 100 imply?
RE: Measuring Bolt Torque
However, I though the whole preload question was more complicated...like, the percentage of the force felt by the bolts during an operating event (say water hammer) was dependant on the ratio of the stiffness of the bolt & flange metals, and actually the flange absorbs a good deal of this force (so that the bolts feel, say, 60 or 70 percent of the load).
RE: Measuring Bolt Torque
as far as repeating 100%. when i just want to compress the gasket, that torque (calculated by gasket compress psi x gasket area per number of bolts) is used and the pattern repeated untill there is no nut rotation. then the final torque is applied
If 10K is 30% of yield, they are some mighty soft bolts
RE: Measuring Bolt Torque
RE: Measuring Bolt Torque
The O ring should be totally compressed in the groove
and you should be having metal to metal contact for
the bolts to be in tension. The Yield for these bolts
are listed at 30000 psi. Most grooves that I have designed for o rings had an area exceeding the cross
section of the o-ring. The intent is to compress the
o-ring in the groove to seal any leakage. I assume this
is a static seal design. I think the o-ring groove height
was like 80 percent of the size of the diameter of the
o-ring. I may not understand your seal design however.
RE: Measuring Bolt Torque
My earlier post assuMEd they were much stronger than 30K yeild. Thus the 600 ft-lbs is a more reasonable torque for that soft of material. If anyone thinks my replies should be deleted, please red flag.
I am sorry if I added any confussion.
RE: Measuring Bolt Torque
ht
RE: Measuring Bolt Torque
Again, I am debating between using the "turn it back a flat and retorque" or the "less than 5degree movement" approaches, both applied in the tightening direction.
I will let you know how this all turns out!
RE: Measuring Bolt Torque
RE: Measuring Bolt Torque
If you can't do that, you might want to try multiple passes at the final seating torque to eliminate the loose parts. Also make sure that you are using a criss-cross pattern when tightening, and don't repeat the pattern each time (offset the starting point by a few bolts).
RE: Measuring Bolt Torque
Of course, if specifications would require a certain minmum amount of tensile loading regardless of bolting material, I would think this could be confirmed in initial installation by some methods other than measurements of torque (as explained by others in this thread), but I suspect most of these methods would require advance knowledge/planning and probably also some additional installed cost to the Owner.
RE: Measuring Bolt Torque
I rent a bolt tightening machine. They are indeed, big bucks to purchase and ridiculously expensive to rent. It is perhaps the best method I have used to tighten bolts to a specified level acceptable by the industry.
I have used a bucket of water on the end of a wrench with a pipe of known length welded to the end. Simply fill up the bucket with water, measure the volume of fluid and given the density of water as 62.5 lbm/ft^3, you pretty much have what you are looking for, torque.
Extremely crude, an excellent conversation piece over a few beer, but not my professional recommendation as a practice.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Measuring Bolt Torque
Please excuse me if I smile a bit, having tightend about a "million" bolts/nuts on beams and flanges. The problem is not at all uncommon, but can easily be rectified with the proper tightening sequence. I tend to 'do' the pattern skipping every other bolt and rotating the sequence. Sneak up on the final torque no matter which device you use, torque wrench/multiplier or hydraulic. For a 2" bolt, the hydraulic 'wrench' is nice, but time consuming. Typically on large dia flanges, eg. the heat exchangers on a co-gen unit, I had the initial torque value set with a Skidmore but came back and did a std. retorque after all bolts met that tq. By std. retq. I mean, back off each bolt/nut a 'flat' and retighten to the prescribed tq. Never had a failure that I can recall.
Rod
RE: Measuring Bolt Torque
Thanks!
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada