Measuring Bolt Torque

[PeterHerman]

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?

 

[byrdj]

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.

 

[byrdj]

I did find a site with charts that provides the force required to compress the o rings

http://www.chemraz.com/85256D3C0038D8DA/vwContentByKey/N25S7NQJ541ELETEN

 

[PeterHerman]

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!

 

[rconner]

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?

 

[Screwman]

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).

 

[rconner]

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.

 

[Cockroach]

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

 

[evelrod]

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

 

[Cockroach]

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