Pipe flanges for small diameter pipe
Pipe flanges for small diameter pipe
(OP)
Many engineering pipe specifications will specify the use of 300# flanges for pipe diameters of 3" and below for pipe classes specified for 150# service. Does anyone know the basis of this? I havve heard it is to provide the smaller pipe more structural strength and resistance to vibration issues.





RE: Pipe flanges for small diameter pipe
"Many engineering pipe specifications will specify the use of 300# flanges for pipe diameters of 3" and below for pipe classes specified for 150# service. "
In my more than 45 years in Process Plant Piping Engineering and Design I have NOT found this to be true.
Unless it is something very, very special these sizes and ratings have all used "Unions" for removal assembly joints.
RE: Pipe flanges for small diameter pipe
Pennpiper is correct,
Your company is an exception in pipespecs.
Maybe it is done for later upgrading of process systems.
150# specs use 150# flanges for all sizes by other companies.
Greetings
RE: Pipe flanges for small diameter pipe
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pipe flanges for small diameter pipe
RE: Pipe flanges for small diameter pipe
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pipe flanges for small diameter pipe
Thanks. Great information. When I see these types of changes in specifications, I scratch my head and say why did they do this. As you said I see no advantage to going to the higher class to to provide more available bolt load for seating stress. Typically at these smaller flanges there is plenty of bolt load available to seat the gaskets and have a leak free joint.
RE: Pipe flanges for small diameter pipe
We permit no unions in alloy piping systems and if one is used in CS it is on a case by case basis.
I know of two other very large chemical companies that have very similar piping specifications.
RE: Pipe flanges for small diameter pipe
One problem not mentioned is with Class 150 flanges, especially in SS, mechanics have been know to roll or cup a flange and when using a Teflon gasket you have problems.
RE: Pipe flanges for small diameter pipe
RE: Pipe flanges for small diameter pipe
I've seen this anti-150# prejudice before but never understood it. I don't know if anyone has calculated the cost versus the benefit of such a spec, pushing every flanged valve or instrument in the line up to 300# etc. Personally I have no hesitation using a 150# flange set at any size in a 150# line. We experience no problems with these flanges with spiral wound gaskets either.
Avoiding unions in alloy service? That I can understand. The only unions we permit are in CS, and then only with a brass seating ring. Even after lapping, alloy unions are a 1st order PITA.
RE: Pipe flanges for small diameter pipe
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pipe flanges for small diameter pipe
RE: Pipe flanges for small diameter pipe
I prefer resolving such situations via notes and markings on the drawings that identify the off-spec flange pair.
I have seen some clients express a preference for 300# flanges in small lines in order to achieve what they perceive to be better joint tightness in hot lines such as heat medium glycol or heat medium oil, which tend to be difficult services to seal once a leak path develops.
To me, the best answer is in proper fit-up and alignment and adequate regard for piping displacements and supports to ensure that a 150# flanged joint maintains its integrity throughout the operating range. We have probably all seen situations where the "solution" was "get a bigger snipe and yank that sucker together and really reef on those nuts.". It does work, but one has to think that there's a better way.
Regards,
SNORGY.
RE: Pipe flanges for small diameter pipe
RE: Pipe flanges for small diameter pipe
**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Pipe flanges for small diameter pipe
rmw
RE: Pipe flanges for small diameter pipe
It may also have something to do with the whole issue that most spiral wound gaskets don't meet code calcs in class 150 since you either exeed the allowable stress of the bolting or you have insufficient seating stress on the gasket. The manufacturers make low stress 150 spiral wound gaskets but these are rarely used and we almost always look the other way on this issue. Perhaps they have done some analysis and determined that this is a signficant problem on the small bore flanges and they want the additional bolt load area ?