×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Measuring Bolt Torque

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

Some processes and hardware that we use to check bolt torque are: using strain bolts ($$$$$$$), Preloaded Indicating Washers, Ultrasound, and Deflection Method.  I appears that Ultrasound testing would work out for you.

Best Regards,

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 2.0 & Pro/E 2001
Dell Precision 370
P4 3.6 GHz, 1GB RAM
XP Pro SP2.0
NVIDIA Quadro FX 1400
      o
  _`\(,_
(_)/ (_)

(In reference to David Beckham) "He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right."  -- George Best

RE: Measuring Bolt Torque

Probably an easy way would be to mark the bolt position
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

i'd be more interested in how you know the bolt preload (unless that's just the drawing requirement).  Personally, i'd be more interested in measuring the bolt preload than carefully controlling the torque.  maybe look into preload indicating (PLI) washers.

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

(OP)
The bolts are existing, but the tightening procedure and preload are being questioned.  Background:  We used a 30-60-100-100 step procedure and have found that many of the bolts loosened.  Some question whether the procedure was fully applied.  Hence, we did a tightly "supervised" one and are going back in 3 weeks to check to see if the bolts are still tight.  

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

what's the vibration loading like ?

RE: Measuring Bolt Torque

(OP)
Its actually low.  This is drinking water piping that is still empty prior to operation.  We looked at thermal and  vibration and we didn't think anything was there.  We did wonder about pipe alignment and movement during installation.  This is partly why we are doing the test now -- after the pipe is in place.

RE: Measuring Bolt Torque

So there is a gasket being compressed?

RE: Measuring Bolt Torque

In automotive, the torque on bolted joints is audited by applying a torque in the tightening direction to rotate the fastener less than or equal to 5°ree;.  This is a quick, easy way to see if a joint has loosened.  It is best to use on a high-volume process that is in control.

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

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

RE: Measuring Bolt Torque

(OP)
To mintjulep, its a hard joint with a double o-ring.  

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

If it is a "hard joint", increasing the torque (thus tension) in one bolt should not effect the others.  However it will if the joint is soft.

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

(OP)
Byrdj,

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

Are you saying that the tension for the 2 inch bolt
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

The 27k being 30% of yeild is in agreement with my terminilogy, But 600 ft-lbs for a 2" diameter bolt is very low with my thinking

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

dimjim

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

Thanks!  I understand the 87K pounds and the 27K psi.

The 30-60-100-100 is still a mystery.  What does the second 100 imply?

RE: Measuring Bolt Torque

(OP)
I guess that is one good question.  The 27,000 lbs of tension on each bolt (~3 inch sq or 10k per inch) is sufficient to prevent flange opening during service loads.  It is low, but is it too low?

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

a bolt should not "feel" any operational events.  the bolt is like a spring and its initial loading should exceed any force applied to the flange.  if there is any overload where the flange force exceeds the bolt clamping, the flange will open and the bolts will then feel the load.

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

At that low of torque, I would expect the bolts would vibrate loose very easily.  are you using any locking method after torquing.

RE: Measuring Bolt Torque

I would like to understand your flange detail.
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

Please excuse my ignorance about the stregnth of B8N.  

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

(OP)
Yes, you are all pretty much understanding the situation...the second 100 percent is a check pass.  I generally followed EPRI Good Bolting Practices.  Yes, this is a soft bolt and the o-ring is likely completely compresssed in the groove.  We are not using any locking methods, but did mark the flats during the last bolt-up.  Using the "no nut rotation" as the confirmation of applied torque is a good idea.  

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

You mentioned this was "drinking water piping".  I was just curious is this by any chance 48" flanged joining? If so, are "Class 300 steel" per AWWA C207, F&D per ANSI B16.1 Class 250 iron, and/or some joining of both material types involved?  

RE: Measuring Bolt Torque

What you are seeing is the effects of "cross talk" where the later bolts are effecting the earlier bolts.  What you are describing is a common occurance in multibolt flanges.  The ideas of measuring stretch are the best method to accuratly measure the preload in the bolts (use a center drill and ball end mic to get accurate readings.
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

Myself and perhaps another poster or two have tried to get a little more information (no names nor places would be necessary, to get a little better feel from at least a technical perspective what is involved here to be able to provide more meaningful information).  This has not yet been forthcoming.  I will therefore go ahead and ask yet another question.  You mentioned that "many of the loose bolts had galling".  While I don't claim a lot of expertise in "soft" stainless steel bolting, is it possible that a whole lot of "investigation of torquing procedures" might not really mean a whole lot in the big scheme of things if the bolts have a tendency to "gall"?  Perhaps for that reason, I think at least some codes or authorities suggest other bolting material with minimal tendency for such.  In other words, is it possible a contractor could (and maybe even arguably in reasonably good faith?) put a whole lot of effort and "torque" on some types of bolts, but without that necessarily being accompanied my much if any beneficial tensile loading on the bolt (and flanged joint/gasket etc.)?
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

Yeah, this can be a problem, bolt torque and backoff of those in the immediate vicinity.  I see this all the time mounting blind flanges on valving in order to do pressure testing.

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

PeterHerman.
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

EvelRod...Sounds like a good tip, obviously from experience.  I'm going to try this, blind flange bolting on NPS 42 ANSI Class 900 Ball Valves.

Thanks!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources