Bolting Loose last choice

From: <aluser2>
Date: Tue May 17 2005 - 15:25:00 EDT

these are really good and valuable answers (advice) from competent professionals and everything George, Bruce and Chris have said is correct.

I would add checking the choice of gasket by analysing the bolted joint very carefully
under all the conditions and scenarios. As Stated elsewhere Bickford (up to the latest edtn is great for this) and flange analysis methods will allow you to investigate gasket seating and opreating options. Experience and gut feel pluys understanding of the problem and issues helps with any sort of analysis right up to Ansys or other modelling.

Without knowing all the design conditions its hard to say but another option is to switch gasket choices in combination with the other options described for the bolting. This often surprisingly works, but takes care and skill, and is difficult to get a surefire answer on. This doesnt make managers and owners happy, who want guarantees, to what are actually complex problems with many variables (often lacking good information).

This is a widespread problem and eventually after exhausting these options you may likely have no choice but to lock it up completely, either the joint with Joint sealants
which become essentially permanent (have to be broken off later for maintenance or removal- furmanite is one) and or loctite (or equivalent competitor custom product) on the bolts once set to best leak minimized seal (or both bolt and joint sealing - last choice) . Sometimes it ends up coming to this to stop the leak, but exhaust the other options first, this is a last resort.

Good luck. Keep us posted.
Al

> I would emphasize the bolt and nut temper (grade). Often this is
> overlooked. Go with at least a grade 8 nut and bolt. Also consider
> double nutting (a backup nut tightened against the primary, torqued,
> nut), along with PMs to check nut torque. The frequency of the PM will
> be a function of the thermal cycle frequency and system vibration.
>
> ... Bruce D. Bullough ...
> Sebesta Blomberg & Associates, Inc.
> 2381 Rosegate
> Roseville, MN 55113 USA
> + 651-634-7344
> www.sebesta.com
>
>
> -----Original Message-----
> From: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com]
> On Behalf Of George McKinney
> Sent: Tuesday, May 17, 2005 10:05 AM
> To: PipingDesign@yahoogroups.com
> Subject: Re: [PipingDesign] Bolting Loose
> [bcc][faked-from][mx][spf][bayes]
>
> Another consideration:
> Depending on the temperatures you are running with the heat exchanger,
> you can be doing annealing and softening, either on the bolts, washers
> or gasket material. I have had the experience of using a copper sealing
> ring between steel flange and body - you tighten the bolts and
> everything is sealed, and works well as it is heated up and operates.
> But the copper ring anneals and flows slightly. Then, when you shut
> down and cool, the bolts are loose and the gasket leaks. So, tighten
> the bolts and OK again, until the next shutdown, and it repeats. After
> a period of time, the copper gasket had essentially extruded. Solution,
> soft iron gasket with same coefficient of expansion as steel.
>
> Recommendation, look at the whole closure system, bolt torque and temper
> (grade), gasket material, and washers. Personally, I like the
> castellated locking nuts.
>
> George McKinney
> ----- Original Message -----
> From: Christopher Wright
> To: PipingDesign@yahoogroups.com
> Sent: Tuesday, May 17, 2005 10:57 AM
> Subject: Re: [PipingDesign] Bolting Loose
>
>
>
> On May 17, 2005, at 9:18 AM, alejandroperezposada wrote:
>
> > I'm having some problems with the heads of a Heat Exchanger related
> > with the bolts. The Bolts are loosening in operation.
> Typically bolts loosen because they aren't tightened properly. When
> the
> bolt is subject to cyclic loading the joint slips and the nut loosens.
>
> There are lots of reasons why bolts won't maintain a preload, from
> bolts that are too short or flanges that squash out over time or poor
> understanding of the actual loading. Bellevilles and those worse than
>
> useless split washers won't maintain a preload. Depending on the
> circumstances, you might have some luck with thread locking compounds
> or special locking threads. Nylock nuts sometimes work. As a last
> resort you can stake the threads, but you can't reuse the bolt and
> it's
> a bear getting it loose.
>
> Christopher Wright P.E. |"They couldn't hit an elephant at
> chrisw@skypoint.com | this distance" (last words of Gen.
> .......................................| John Sedgwick, Spotsylvania
> 1864)
> http://www.skypoint.com/~chrisw/
>
>
>
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Received on Tue May 17 15:25:00 2005

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