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RE: Design for anchor bolt corrosion in refineries, etc

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I have typically used a 1/8" corrosion allowance for anchor bolts.
Simply size the bolt and then add 1/8" to the diameter. The bolt is
sized for tension and shear per AISC allowables based on the shank or
nominal diameter. The tensile stress area is used for post tensioning
calculations.  

Landon Anderson
office: 970-945-1006
home: 970-984-3949
email: landon(--nospam--at)oddogws.com


-----Original Message-----
From: Tom Barsh @ Codeware [mailto:tom(--nospam--at)codeware.com] 
Sent: Thursday, May 12, 2005 2:55 PM
To: seaint(--nospam--at)seaint.org
Subject: Design for anchor bolt corrosion in refineries, etc


What is the recommended practice, if any, for accounting for corrosion
acting on anchor bolts for industrial equipment (say, in a refinery,
chemical plant, paper mill, water towers, etc) and the effect this may
have on the bolt ("anchor rod") size?

When selecting connection bolt size for buildings and similar structures
the size is based by determining the tensile stress acting on the shank.
But in this sort of application corrosion seems to be of little concern.

Unlike anchor bolts for most building structures, those for industrial
equipment (and I am thinking specifically of tall pressure vessels and
stacks in refineries) are often subject to large tensile forces. For
industrial equipment subject to large amounts of corrosion the threaded
portions of the rod may also corrode, so it seems reasonable to size the
bolt based on the thread root area in the corroded condition.

I have seen a conflicting opinions in various published references.
Maybe not so conflicting, 'structural' references address sizing anchor
bolts by stress on the shank but do not mention anything about
corrosion, texts that address design of ASME pressure vessels size the
bolts based on root area and generally mention that corrosion is a
factor.

So, what is practiced? apply a corrosion allowance to the threads and
size the bolt based on the corroded root area? size the bolt based on
the corroded shank area? Or ???


Thanks!
Tom Barsh, P.E.



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