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
