45-degree cut on Open Pipe 10

[UKCats]

Does anybody have a scientific reference (or test data) to why the end of an open pipe is often cut at a 45 degree angle. My recollection is a straight cut could build up harmomics (standing waves) and reduce capacity. If you notice, organ pipes, and many automobile exhaust pipes are cut at an angle.

You don't see it on smoke stacks, etc so I think it's a phenomia that occurs at high velocities.

 

[Gator]

No. Am I wrong?

 

[UKCats]

ASME B31.1, Appendix ??? shows the benefit of cutting the end of a pipe to change the force vector and reduce bending moments on the boiler nozzle. I notice a bending moment symbol on your sketch, so I put 2 and 2 together...

What is your input on why the pipe is beveled at 45-degrees?? Is your application steam???

 

[Gator]

OK, gotcha - II-2.3.1.2

Thanks.

 

[Gator]

I knew I had seen comments on this somewhere and I just tracked it down (mind you, these were written by piping designers, not stress engineers):


"Pipe exhausting to atmosphere is cut square, not at a slant as formerly done, as no real advantage is gained for the cost involved."

Piping Guide
PP 94
David R. Sherwood
1973-1991
ISBN 0-914-08219-1

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"There is a very old myth among piping designers that calls for a 45 degree bevel on relief valve tail pipes discharging to the atmosphere. This myth has been handed down from generation to generation and in almost every plant today the beveled tail pipe is seen. The idea proposed by the myth is that beveling will direct the outlet velocity away from a platform or building. The squared cut end shown in Figure 5-12 will direct the discharge upward, away from platforms, etc., and will do it at the minimum cost. The 45 degree bevel is more expensive to cut and results in extra waste pipe. The real falacy [sic] of this myth is seen when observing the actual installation where bevels have been cut, which, in effect, direct the velocity toward operating platforms! This is caused by improper orientation of the bevel. the square cut end design eliminated all orientation problems."

Process Piping Design Volume 1
PP 90
Rip Weaver
1973-1979
ISBN 0-87201-759-1

 

[NozzleTwister]

Thank you for your valuable post Gator.

NozzleTwister
Houston, Texas