This is one of my favourite topics, since I had a large number of systems piping failures related to stress, mostly external.
One of the flange connections of the fire main systems on board a ship, couple of bolts used to break at the head frequently; more often if the ship had done some high-speed manoeuvres. Initially, we used to change the bolt and live with it, but a nagging doubt came into our minds and we did a root cause analysis. What we finally found was that, the last pipe that fitted into the system was a little oversized and had been forced into its slot using a chain pulley, thus leading to a stressed piping section. Whenever high vibrations occurred, the stress used to increase, thus resulting in the flange securing bolts at one end shearing.
I came across a nice article on the topic. Please read and be enlightened on the topic.