42" NB piping and vacuum piping

[jonesey]

We have a requirement for a 42" overhead line from a vacuum tower. Most of our pipe specs only go up to 36". Are there any special requirements to larger than 36" lines or can you just calculate the required wall thickness based on B31.3 calculations?
With respect to lines in vacuum service, design criteria is full vacuum. Am i right in assuming that wall thickness checks will need to made for these lines under full vacuum as wall thickness in our pipe specs are based on B31.3 with pipes under internal pressure.

 

[pennpoint]

jonesey
What is the critera that is forcing you to go to 42"?

 

[jonesey]

The vacuum tower is 50m high and approx 6m in diameter. Our Process dept. have sized the line based on process conditions. When we pump high temperature, high pressure process fluid into the vacuum tower, it 'expands' violently and they have decided a 42" line is required to allow the gases to escape.

 

[jte]

jonsey-

Check the index of B31.3 under "external pressure." Yes, you do need to account for it. The basics are in 304.1.3. It's not unusual for a vac tower overhead line to be in the 42" range. Ours is bigger.

jt