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Discussion Forums - The Hendrix Group
HomeHomeDiscussionsDiscussionsMaterial Select...Material Select...Failure of PTFE Coated B7 Stud Bolts - PipingFailure of PTFE Coated B7 Stud Bolts - Piping
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11/13/2006 9:00 AM
 
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hey guys, i recently received the same powerpoint presentation outlining the failures discovered in these B7 studs and decided to turn to the internet to do some extra digging. what exactly caused the failure in these studs? the only transverse defect i know of in bar stock is "cupping" caused during the extruding or drawing process when the outer material moves through the die quiker than the inner material causing internal stresses and rupters. i haven't witnessed this first hand but the pictures i;ve seen of cupping all show chevron shaped defects, which do not look like these SUN stud defects. if anyone knows what the defect is then let me know or email me at Nick.Ferguson(at)asc.com.au Cheers, Nick
 
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11/13/2006 9:00 AM
 
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Sorry, I don't think I replied to this correctly the first time??? I may not be getting the attention of MJCronin, therefore posting again. Yes, my company had the exact same problem. Attached is a portion of a warning my company distributed 4 November regarding same topic and same manufacturer. I also have a power point presentation on this but I don't know how to attach it. I can forward to you if you provide your email address. "Please be aware of a failure with PTFE coated B7 Studs. Bolts broke while tightening at a Dow Chemical plant at Sarnia, Ontario, Canada. Other similar failures have occurred at a Valero refinery, Lake Charles, La. Manufacturer is reported to be Sun Fasteners located in Ningbo, China."
 
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11/17/2006 9:00 AM
 
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I'm currently looking for a corrosion resistant bolt to use in piping systems that are almost always moist from condensation. We've been using standard carbon steel and get short useful life, even coating with never sieze. The maintenance crew discourages the use of SS due to galling, as they commonly use air driven tools to tighten and remove nuts and studs. Any recomendations? I've seen Teflon coated bolts that corrode after some time as the teflon layer is scratched upon installation. Thanks,
 
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11/20/2006 9:00 AM
 
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Jeff, The technology exists to solve your problem..... 1) Consider hand tightening teflon-coated bolts in selected locations. Teflon coated studs, bolts and nuts have been used for many years in all types of service, iincluding some fair high temperature petrochemical service...... The fact that your maintenance crews "don't like them" tells us more about them than the quality of the bolts 2) Find a suitable combination of stainless steel bolt/stud and nut material. Not all combinations will gall. (Did you learn this information from the same group as in 1) above ? -MJC
 
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11/21/2006 9:00 AM
 
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Any recomendations on specific combinations of nuts/studs that do not gall. Thanks for the information. This is very helpful. Jeff
 
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