re-use of pretentioned bolts

[Struct71]

Hi,

In my business it is common practice not to re-use bolts that are pretentioned/torqued.

Now I have designed a clamp. The clamp uses 16 bolts of M36/1.5in size bolts. They are pretentioned to 40% of yield. Yes, it is a big thing.

The clamp needs to be re-used a dozen times. Following the general common practice, I would need 16 new bolts for every operation. This is not cost effective.

I have looked in the codes and standards in our bookshelf, I can't find anything about re-using pretentioned bolts. One could consider an inspection before re-use, but what kind would be suitable? MPI, DP, UT - not sure if they work on a bolt and if you can clean the bolt afterward.

Any advice? Experience? Codes I can refer to to justify new bolts? (or re-use)?

Regards

 

[civeng80]

IMHO it sounds like you have an important structure. I would just purchase 200 bolts in bulk and reuse them when appropriate. It sounds like an insignificant cost compared to the structure involved and would not risk using bolts that nave been stressed so heavily no matter what the literature says.

 

[hokie66]

What grade are the bolts? If they are only stressed to 40% of yield, I would have no fear about reusing them. But how do you know how much they are stressed?

 

[Struct71]

In my case bolts are 10.9 M36, loaded with 250kN

As for buying extra bolts - As an engineer I have to convince purchasing department, financial department, management etc. We are a project contractor, so naturally pennywise-poundfoolish, even if I don't like it.

So any handles to do one or the other are welcome.

 

[rb1957]

"for want of a nail, a battle was lost"

"don't be penny-wise, and pound-foolish"

(buy a fortune cookie if you want more ...)

there ain't no free lunch ... if you want to re-use the bolts, have someone either ...
1) crack-check them after removal (how much will that cost?)
or 2) anayze them to this usage. if you preload them to 40% fty, it would be reasonable to assume that the maximum service load is maybe 40% fty (no gapping), possibly 60% fty (gapping in-service). the fatigue spectrum would be (for the latter) a cycle 0-60% and multiple cycles 60%-40% ... doesn't sound too bad. a healthy safe-life factor would help.
and 3) analyze for a failed bolt

 

[IFRs]

Fatigue load a bolt at a lab to 40% for 5x the cycles. If they survive, OK. If not...

 

[dougantholz]

You have to decide for yourself, but I have no problem re-using any structural item that shows no signs of ware (no worn threads for instance) and stayed in the elastic range. If you don't want to re-use them whats the great loss? New bolts are probably cheaper to install then re-using old bolts.

 

[kelowna]

http://www.boltcouncil.org/Publications.html

The guides on that link contain a very good discussion on bolt re-use.

In a previous life, in a job I worked on, we were using a clamp to pull some cables. The clamp had 10xM25 bolts that were hand tighted (ot tensioned) and re-used. All was good until we lost one of the cables. Almost 1 week delay and a lot of money lost, never mind that we almost killed a few people (we were very, very lucky nobody got killed).

Hence, I do not like re-using bolts now.

Why do you have to convince the purchasing department? What you need is what you need, period! I assume is your name, not theirs, on the plans.

 

[dik]

Some bolts, like A325 can be re-used after being tensioned for slip critical (>40%). Others, like A490 cannot be reused.

I would suggest that re-use after tensioning 40% is not enough to cause any problems from a strength or from a fatigue issue.

You might get some local yielding as a result of the first installation, but subsequent installations should be completely elastic.

Dik

 

[ajh1]

The general rule for structural bolts is that while the RCSC spec mandates no reuse, if you can hand thread a nut onto the bolt all the way to the head, then the bolt has not been stretched during any previous tensioning and would be acceptable for reuse. If the bolt has been stretched previously, then it should not be reused.

 

[dicksewerrat]

Are you gong to inspect the bolts yu self? Or let the maint. staff decide when to re-use and when to replace? I would not re-use any bolt. It is your design, And your butt if something goes wrong.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Struct71]

No, I am not inspecting the bolts my self.

Yes, its my butt is something goes wrong.

And yes, I get the blame if we throw away expensive bolts that have been used for only a few hours.

So here I am looking for justification to waste money.

 

[civeng80]

A pity that we let accountants rule. I know what position your in but for such an important structure its nonsense to make savings on a few bolts.

 

[desertfox]

Hi eelco71

I think as others and yourself the best way is to replace but one thing to consider is:- what is the cost of inspecting/testing the old bolts in comparison with just using new ones.

regards

desertfox

 

[saplanti]

I guess you need to do a proper calculation for the fatigue that you mentioned.

If you use lower pretension value on the bolts than the fatigue stress value for the infinite cycle I do not see any problem of using them again. This does not include the damaged or corroded bolts. Your cycle counting values should include the unloading and loading cycles as well.

I guess if you can follow one of the B31 piping code (I recommend B31.1) rules for fatigue calculation and the code allowable (you may be able to find 10.9 material equivalent in ASME codes) for fatigue on bolts you are in the right direction. Doing a calculation will answer your own question and satisfy your client as well.

Hope it helps.

Ibrahim Demir

 

[MightyPirate]

The only thing I could think to add is that if you do reuse them make sure that the threads are oiled properly each time or it wont pretension properly with each re-use. I remember seeing this tip in an AISC magazine.

-MightyPirate, EIT