miter joints

[dman25]

I have been trying to find information on miter joints. CFR 192.233 only allows up to 3 degree miter joints but can't locate any info as to why they are not allowed. Can someone explain why not?

 

[boo1]

All bends embody geometric characteristics that tend to concentrate stresses due to internal pressure or external bending moments, but miter bends contain more acute stress concentrating features than an analogous smooth bends. This can make miter bends more susceptible to fatigue from pressure cycles or thermal expansion cycles than smooth bends. They may contain initial defects that reduce their tolerance for operational cycles: cracks due to workmanship defects in the miter bend welds. You can review ASME B31.8.

§ 192.233 Miter joints.
(a) A miter joint on steel pipe to be operated at a pressure that produces a hoop stress of 30 percent or more of SMYS may not deflect the pipe more than 3°.
(b) A miter joint on steel pipe to be operated at a pressure that produces a hoop stress of less than 30 percent, but more than 10 percent, of SMYS may not deflect the pipe more than 12 1?2° and must be a distance equal to one pipe diameter or more away from any other miter joint, as measured from the crotch of each joint.
(c) A miter joint on steel pipe to be operated at a pressure that produces a hoop stress of 10 percent or less of SMYS may not deflect the pipe more than 90°.

 

[MikeHalloran]

I'm not sure how I'd word it better, but 'deflect' sure seems like the wrong word to use there, especially in the same sentence with 'stress'.



Mike Halloran
Pembroke Pines, FL, USA

 

[boo1]

§ 192.233 is the CFR code.

I think of "delfect the pipe", as change in piping direction though a fabricated elbow.

Cheers

 

[vesselfab]

THAT amount of deflection is for each segment of a miter.

3* means 30 joints in a 90* bend.