Re: Bolting Loose

From: <George>
Date: Tue May 17 2005 - 11:04:00 EDT

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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[Non-text portions of this message have been removed] Received on Tue May 17 11:04:00 2005