Here is a closeup of the flange joint - or were you looking for a detail drawing? Also, the joint immediately to the south slipped - the joint restraint did not hold. Sure seems like this leverage on the stick of pipe between the elbows would be the culprit.
Thank you everyone for your feedback- most helpful. I spoke with the pipe supplier further and he still contends the failure was an air pocket issue. I am supposed to get some data from them explaining the issue - will certainly share what I find out.
On a project I worked on, a section of 12" C900 fire line completely burst while undergoing a pressure test. The attached image shows the length of pipe that blew up between two 45 degree elbows. Due to changes during construction, a high point existed at the elbow on the right, without an air...