Its no wonder the boys (& girls)who write standards have steered clear of
defining this one.
--- "SARE, RALPH H." <SARERH@YANPET.SABIC.com> wrote:
<HR>
<html><body>
<tt>
torquing is more of an art than science. why? we'll lets consider the<BR>
equation from Motosh and Farr (i prefer it over api).<BR>
<BR>
torque = fLd^2 / (8.8d - 1.4*.001^f)<BR>
f is of course the coef. friction and L the bolt load.<BR>
<BR>
Fel-Pro graphite based lubricant , f=.086<BR>
Jet-Lube gives an f avlue of 0.143<BR>
Other Gen. purpose graphite lubricant about 0.117 (if its not grpahite, i<BR>
dont know).<BR>
<BR>
Ok now lets throw in poor alignment of flanges holes, imperfection of<BR>
threads, burrs, inconsistent lubrication, manufacturing tolerance for<BR>
bolts/nuts, dirt (as most have mentinoned), techniques for
tightening,thread<BR>
engagement not full, etc. and the calculated torque values is now more of<BR>
guess work (equivalent to the millwright "fell"). surebolt (they have
a<BR>
website) test indicated values of torque measured varying from 30 to 50%.<BR>
<BR>
ok. now lets have a look at the bolt stress which is normally around 15 to<BR>
30% of the smys. hey plenty of room there.<BR>
<BR>
conclusion. same as steve observation and that for critical service,<BR>
Measuring bolt stretch rather than torque makes more sense since the<BR>
application of the preload result in tensioning of the bolt (stretch =<BR>
preload*bolt lenght/A*E). One thing ive learn about measuring bolt<BR>
elongation is that in some cases you may actually have to increase the<BR>
torque over the published values (call it standard) to ensure that the<BR>
preload is greater than the operating load. <BR>
<BR>
<BR>
<BR>
-----Original Message-----<BR>
From: Steve McKenzie [mailto:Mechproj@xtra.co.nz]<BR>
Sent: 26 March, 2002 10:24 AM<BR>
To: PipingDesign@yahoogroups.com<BR>
Subject: Re: [PipingDesign] hand wrench and sledge hammer<BR>
<BR>
<BR>
Hi Davis<BR>
<BR>
I think you can trust a good fitter a little more than your table suggests.<BR>
If we are talking about the main cooling water pump on a PWR, I would not,<BR>
in a pink fit, rely on feel. Nor would I use torque. Bolt extension and<BR>
gasket compression is the appropriate method in this application.The gasket<BR>
compression is used as a crosscheck on the bolt extension.<BR>
<BR>
</tt>
<br>
<!-- |**|begin egp html banner|**| -->
<table border=0 cellspacing=0 cellpadding=2>
<tr bgcolor=#FFFFCC>
<td align=center><font size="-1" color=#003399><b>Yahoo! Groups
Sponsor</b></font></td>
</tr>
<tr bgcolor=#FFFFFF>
<td align=center width=470><table border=0 cellpadding=0 cellspacing=0><tr><td
align=center><font face=arial size=-2>ADVERTISEMENT</font><br><a
href="http://rd.yahoo.com/M=217097.1884387.3412360.1261774/D=egroupweb/S=1705083\
319:HM/A=999859/R=0/*http://service.bfast.com/bfast/click?bfmid=29150849&siteid=\
39282504&bfpage=account"
target=_top><img
src="http://us.a1.yimg.com/us.yimg.com/a/ne/netstock_direct/300x250_green_ira_a.\
gif"
alt="" width="300" height="250" border="0"></a></td></tr></table></td>
</tr>
<tr><td><img alt="" width=1 height=1
src="http://us.adserver.yahoo.com/l?M=217097.1884387.3412360.1261774/D=egroupmai\
l/S=1705083319:HM/A=999859/rand=333053275"></td></tr>
</table>
<!-- |**|end egp html banner|**| -->
<br>
<tt>
_____________________________________________________<BR>Unsubscribe: PipingDesign-unsubscribe@yahoogroups.com</tt>
<br>
<tt>Your use of Yahoo! Groups is subject to the <a
href="http://docs.yahoo.com/info/terms/">Yahoo! Terms of Service</a>.</tt>
</br>
</body></html>
This archive was generated by hypermail 2.1.8 : Mon Oct 27 2008 - 20:23:56 EDT