RE: flange stud bolt replacement criteria.

From: <Steve>
Date: Thu May 05 2005 - 06:55:00 EDT

Thanks Chris

While we have no corpses, I would like to keep it that way. Our shutdown labour force quality is generally good but variable, so procedure and supervision must unfortunately take precedence over individual skill level.

Cheers

Steve

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From: <a href="/group/PipingDesign/post?postID=ox7mMRklDihte5YwAHWW9xELsxXxE08n6Fqydh_5zjM1atC_-SsZKxzflI3COtCUUMx5YXoXKvXO6k9UMJ85NtXd6D0">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=ox7mMRklDihte5YwAHWW9xELsxXxE08n6Fqydh_5zjM1atC_-SsZKxzflI3COtCUUMx5YXoXKvXO6k9UMJ85NtXd6D0">PipingDesign@yahoogroups.com</a>] On Behalf Of Christopher Wright
Sent: Thursday, May 05, 2005 1:55 AM
To: <a href="/group/PipingDesign/post?postID=ox7mMRklDihte5YwAHWW9xELsxXxE08n6Fqydh_5zjM1atC_-SsZKxzflI3COtCUUMx5YXoXKvXO6k9UMJ85NtXd6D0">PipingDesign@yahoogroups.com</a> Subject: Re: [PipingDesign] flange stud bolt replacement criteria.

On May 4, 2005, at 6:45 AM, Steve McKenzie wrote:

> Does anyone have any references to standard testing/rejection criteria

> for stud bolts?

I've never heard of any such, primarily because pre-loaded bolts really don't undergo cyclic stress if they're tightened properly. I can't imagine any way to come up with a generally applicable standard given the variation in service requirements for stud bolts.

The first thing I'd ask myself would be 'where are the bodies?' Have you had failures or near-failures that you could ascribe to worn-out bolting or some other cause? If not it's hard to know what you'd test for. Other than corrosion, the biggest problem I've found with bolts has been undertightening leading to loss of preload. There's no surer way to get a fatigue failure than not tightening a bolt properly. Your service testing might simply be training fitters in the gentle art of pre-loading bolts, followed by a system of random checks with a torque wrench, to make sure no corners are being cut.

I should add that 'Visual signs of distress' isn't such a great criterion, if only because it's almost impossible to determine significant over-strain. For example, 0.2% strain corresponds to yield which in a 3 inch long stud amounts to a change in length of 0.006 inch. Likewise cracks at the roots of threads are damn near impossible to see, unless you really work at it.

Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=WExn3fDT4pI4rbIVr1z54eNYyStDLbKBmaw1AmOYB8-N8r71TEfo3c-Oy7c5BsWvBGAYDwhvX6vc">chrisw@skypoint.com</a> | 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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