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RE: Bolt Tightening - Turn of the nut method

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"Turn of the Nut" method is not for "monitoring" bolt tension.  I always
write special requirements for the installation and inspection of bolts
using the turn of the nut method.  I actually modify all of the RCSC bolt
tensioning methods in my specification to some degree.  

Your supposition is not correct.  Of all 4 methods allowed by the RCSC
Specification only #4 (direct tension indicator) is indicative of a true
bolt tension.  Methods 1 (turn of the nut), 2 (calibrated wrench), & 3
(alternate design bolts) are all torque type methods that empirically
determine minimum bolt tension.  

Also of note is that all 4 methods in the RCSC require that the faying
surfaces be drawn into full contact prior to starting the bolt tensioning
process.  Once the faying surfaces are in full contact, the only element
that can deform to any significant degree is the bolt in tension, thus
flange flexibility is not relevant.

The object is not so much to have an "accurate" bolt tension, but to provide
a minimum bolt tension.  All 4 methods will accurately provide the minimum
bolt tension.  I personally have problems with method #2 and do not allow it
in my specifications.

On some critical bolt installations such as in the nuclear and petrochemical
industries bolts are installed using hydraulic tensioners.  And even those
bolts require calibration in a Skidmore.

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	K.S. Raghavan [SMTP:ksr(--nospam--at)bhelrnd.co.in]
> Sent:	Monday, October 08, 2001 4:28 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Bolt Tightening  -  Turn of the nut method
> 
> Hello all,
> 
> If the "Turn of Nut" method is adopted for monitoring the bolt tension is
> it
> not right  to say that
> the turn indicates the compression of the flanges rather than tension in
> the
> bolt ? In my opinion
> tension in the bolt will be in error depending on the flexibility of the
> flanges if the turn of nut is directly correlated with bolt tension.
> 
> Comments please.  ..  raghavan  (BHEL , India)
>  << File: Card for Dr. K S Raghavan >> 

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