A PVC pipe is in no way a reasonable substitute for a cast iron plumbing pipe. Wall strength is far lower, hence it cannot contain major pressure before rupturing. This means the bomber was an idiot who knows nothing about pipe bomb making. An amateur. He was probably guessing that he could do damage to a train (and thereby get some satisfaction / attention ) but was incompetent. This maybe was just a nutcase and not a real terrorist or an FBI shill.

Ah, how I remember the good old days in the 50s when Popular Mechanics published tips on do it yourself pipe bombs.

A PVC pipe is in no way a reasonable substitute for a cast iron plumbing pipe. Wall strength is far lower, hence it cannot contain major pressure before rupturing. This means the bomber was an idiot who knows nothing about bomb making. An amateur. He was probably guessing that he could do damage to a train but was incompetent. This maybe was just a nutcase and not a real terrorist or an FBI shill.