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RE: Thermal props of high tensile bolts

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You mentioned that you lost tension in "torqued" screw.  Torque is not a
very good way to get an accurate predetermined tension.  If tension is
important, use a method that indicates tension.  

The thermal coefficients of various steels don't vary much.  Heating all
components of an assemblage uniformly (heat source, proximity to source,
thickness of materials, etc.) is almost impossible.

Harold Sprague

-----Original Message-----
From: Dave Meney [mailto:yenem(--nospam--at)]
Sent: Thursday, February 11, 1999 3:32 PM
To: seaint(--nospam--at)
Subject: Thermal props of high tensile bolts


Does anyone know whether the thermal coefficient of expansion for a high
tensile bolt (UTS=1050 MPa, yield stress = 945 MPa) is any different to that
for mild steel?

I have a problem where an argument has been raised regarding the loss of
pre-tension in a torqued screw, where the screw is high tensile and the
components are mild steel.  The claim is that after heating the assembly to
130°C (266°F) for a couple of hours, the thermal differences in the two
steels causes significant loss of prestress.

Any comments?

Dave Meney
Structural Engineer

Yenem Engineering Services
54 John Street

Phone  (08)9257 2695
Fax    (08)9257 2264
Mobile  0417 949 374