Why no miter joints allowed in DOT 195?

[KernOily]

Another pipeline new guy question here. Does anyone know why DOT 195 does not allow miter joints greater than 3°? Even B31.4 allows miters up to 12.5°.

I'd also like to hear why, in general, most owners do not allow miter joints at all. My guess is that it is because it is more difficult to control root gap with a handmade miter, and hence quality of the weld joint, vs. a regular forged fitting. Any comments?

Or is it due to the Bourdon /pressure stiffening effect at the bend? Perhaps the stress concentration and distribution at a sharp discontinuity like the inside of a miter weld has cause cracks in the past. A miter weld would be a musch greater stress riser and much poorer stress distribution than a factory-made forged elbow. Comments?

Thanks for your time. Thanks!
Pete

 

[11echo]

Well... as it was "painfully" explained to me, the labor it takes to properly do a miter joint tends to get way pass what a "store bought" fitting would cost! At least tell you get up into the real big stuff & exotic materials. Good Luck! ...Mark

 

[MJCronin]

74,

Well, it is my experience and opinion that most MBA owners do not have the engineering smarts to understand pressure stiffening or any of the other subtle stress issues associated with mitered pipe.

However, these same guys like to take a walk through the finished plant and look at pipe racks and ganged routing of piping systems.... stare at the empty expressions reflected back in the shiny new jacketed insulation.

Large (>3 degrees) miters can look awful ugly to these guys as they look down the systems. With a 12.5 degree miter, things are much easier for the fitters and piping contractor..... but may be ugly for the owner...

Just my thoughts...

MJC