I'm not sure "the manual" is always the best or right answer on bolt
torque..
Often its just cut and paste from god knows where? and unreliable, wrong, or
maybe even right. You dont know.
Personally i think in these non "run of the mill" (Deliberately not defined)
cases , you need to independently check the bolt torque for each and every
case along with all the other variables, because its one of all the many key
variables. Who can say the manual knew the right answer or got it from the
right source. eg the guy who did the original calcs (if they were done at
all) .
I have always advocated that the guy who designs the joint or the equpt
should issue bolt torque data with the equpt and the process should require
verification that the inputs data were followed/adhered to. Otherwise too
many things to go wrong. Why design a joint then leave all the key
executions up to someone else , an ill defined design basis and lacking in
design detail instruction. And then on top of it all, an ill conceived or
uncertain follow-up execution process.
Sometimes it happens, but because its not mandated as with structures , the
compliance is highly spotty and suspect.
Oddly we see bolt torque signoff on buildings and structures,from design
right through to QA. But not necessarily equpt. The ASME Vessel , piping
and pipeline codes are all
peculiarly silent on the issue, but not the european codes.
The importance is really well recognised and understood in that industry , seems to me pressure equipment is even more important... but then the same goes with structures getting Eng/Installation signoff and designer involvement right through ....but not with pressurized "structures". Its a weird world. Maybe a hangover from rivetting days and welding which thereby lets bolted joints slip under the radar.
I think the wide ranging responses have indicated the dilemnas/issues. (Multiple opportunites for system breakdown). Lack of a cookie cutter "easy to apply" solution (to replace the old m & Y factors) demonstrates the issue complexity.eg PVRC hasnt sisued their long awaited "answer". I think the whole "process" has to be addressed. I suspect thats part of the stumbling block. Cost for benefit.
There have been attempts to remedy this but industry cheapness hasnt helped. Fugitive emissions regulations started down that road but on this issue got knocked on the head (major opposition) and left up to non-prescriptive and non-enforced , after the fact discovery control. Structures are considered a public safety issue and get govt regulation and code enforcement in bolting.
> Hi Alejandroperezposada
>
> have you tried carrying out a warm and hot torque in addition to the
> initial torque?
> We use this on some process equipment with good results.
> Are the maintenance guys using a proper bolt torquing pattern? If the
> guys are simply working their way around the flange, then portions of
> the gasket may become overloaded and not recover properly, resulting in
> loose bolts.
> Have you checked the torque against whats in the manual? It would pay to
> check this as manuals sometimes have bad numbers in them.
> It would pay to check you are using the correct gasket; sometimes an
> alternative has been used which may not perform.
>
> In 90% of cases, I find a loose bolt was never tightened properly in the
> first place.
>
> Is this a new problem, one that has always existed or one that may have
> existed for some time but has only now been found?
>
>
> The likely causes of loose bolts are: inadequate torquing, nut backing
> off in service, insufficient gasket recovery/overcompression, bolt
> permanent stretch.
> It would pay to identify which of these is causing your problem.
>
> I suggest you confirm that the joint is being assembled properly before
> worrying about alternative bolts to those originally specified.
>
> Cheers
>
> Steve
> -----Original Message-----
> From: <a href="/group/PipingDesign/post?postID=14U1biC4FT8jk-cYU4f4iDzyiJAQLe4IhEsqgobnzmrMZTaxh3d__cdCchTnhJ2fK7heVN2fIIYWx6e4CJcEXlXi1ftXWg">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=14U1biC4FT8jk-cYU4f4iDzyiJAQLe4IhEsqgobnzmrMZTaxh3d__cdCchTnhJ2fK7heVN2fIIYWx6e4CJcEXlXi1ftXWg">PipingDesign@yahoogroups.com</a>]
> On Behalf Of Christopher Wright
> Sent: Wednesday, May 18, 2005 8:50 AM
> To: <a href="/group/PipingDesign/post?postID=14U1biC4FT8jk-cYU4f4iDzyiJAQLe4IhEsqgobnzmrMZTaxh3d__cdCchTnhJ2fK7heVN2fIIYWx6e4CJcEXlXi1ftXWg">PipingDesign@yahoogroups.com</a>
> Subject: Re: [PipingDesign] Re: Bolting Loose
>
>
>
> On May 17, 2005, at 11:56 AM, alejandroperezposada wrote:
>
> > Is there a posibility in replace the ASTM A-193
> > GR B7 stud with a Machine Bolt Grade 8?
> why do you think you need to replace the bolt? You shouldn't be
> guessing about this. First, you *must* use ASME specifications for
> bolts anyway. Nylock bolts probably won't
>
> What are your bolting calculations telling you about the adequacy of
> the bolt?
> What does the joint look like?
> What size are the bolts and how long are they?
> Is there a gasket involved?
> I gather your loads are cyclic. Have you done any calculations to see
> if the temperature excursions are high enough to relax the preload in
> the bolt?
> What is the temperature and pressure range?
> How long does it take for the bolts to loosen (in terms of the load
> cycle time)?
> Have you set the preload?
> How certain are you that the bolts are tightened properly? Have you
> checked?
>
> Christopher Wright P.E. |"They couldn't hit an elephant at
> chrisw@skypoint.com | this distance" (last words of Gen.
> .......................................| John Sedgwick, Spotsylvania
> 1864)
> <a href="http://www.skypoint.com/~chrisw/">http://www.skypoint.com/~chrisw/</a>
>
>
>
>
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Received on Wed May 18 03:41:00 2005
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