A mining company I sometimes work for uses (shouldered) Victaulics extensively; both on steel and on PE. The PE joints can give trouble on long overland lines; probably due to thermal expansion. For most new overland lines I use flanged joints on 50m pipe lengths. In the plant area victaulics have worked fairly well. Most failures have been associated with one of the following:
Damage to the gasket sealing faces, normally from rough handling of the pipe. Dressing the sealing faces with a file normally works.
Failure to lubricate and install the seals properly. Normally the pressure test will pop a poorly installed seal into place. But not always.
Poor pipe alignment. Because Victaulics absorb a limited amount of misalignment, it is easy to abuse this feature by forcing poorly aligned pipes into place and clamping up the coupling. It is easy to then overstress when operating loads and deflections come into play. Care during fabrication/installation avoids this.
Use of alternative coupling brands. While some alternative brands are at least equal to Victaulics, other brands are not. I have had problems with distortion and coupling shoulder failure on inferior brands. This is often a result of a purchasing officer trying to save money. Make sure you get what you specify.
Cheers
Steve McKenzie
-----Original Message-----
From: SubrataP_Saha@ril.com [mailto:SubrataP_Saha@ril.com]
Sent: Thursday, October 17, 2002 1:22 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] viclaulic coupling
"Couple of things. Don't assume that allowable deflection is the same as allowable stress or allowable load. Deflection will govern how seals perform, but allowable loading will affect fatigue behavior in the undercut pipe. People tend to assume that fatigue isn't a problem because most piping codes and Section VIII-1 don't require fatigue analysis. That doesn't mean that fatigue failures can't happen."
The problem was found to be in the seals. The lines were not subject to vibrations and since the temperatures were low thermal cycling was also insignificant. For vibrating lines of course the fatigue is checked . The worst affected are the fillets at the small bore branches. We had repaired numerous of them in our plant.
Texas Flange - a good source for information on industrial flanges, all they
ask is for referrals for designs they help with.
877-610-8924.
www.texasflange.com
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Received on Wed Oct 16 16:38:00 2002
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