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: <a href="/group/PipingDesign/post?postID=vwCkwhSrNoZSwuQPyXRFDgKlRPvSXBKByePboO49LsB-1KJGLdozuC2qaMYZHGzz41XgUXf9p51XKwmQxFYfMZT0tmg">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=vwCkwhSrNoZSwuQPyXRFDgKlRPvSXBKByePboO49LsB-1KJGLdozuC2qaMYZHGzz41XgUXf9p51XKwmQxFYfMZT0tmg">PipingDesign@yahoogroups.com</a>]
On Behalf Of George McKinney
Sent: Tuesday, May 17, 2005 10:05 AM
To: <a href="/group/PipingDesign/post?postID=vwCkwhSrNoZSwuQPyXRFDgKlRPvSXBKByePboO49LsB-1KJGLdozuC2qaMYZHGzz41XgUXf9p51XKwmQxFYfMZT0tmg">PipingDesign@yahoogroups.com</a>
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
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)
<a href="http://www.skypoint.com/~chrisw/">http://www.skypoint.com/~chrisw/</a>
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