Too high local temperatures cause the tube's metal to become plastic and internal pressure results in so-called high-temperature creep causing the tube to expand and bulge.
But please do check /analyze data of crude flow through the tube as if for any reasons minimum cooling media flow was not ensured at all times through operation(by mistake or intentionally; which usually results in starvation/ localized hot spots),
then adequate controls and stringent operating practices need to be in place to eradicate recurrence possibilities.
I came across a situation several years ago on a high pressure firetube boiler. The problem was that the heat exchanger that was heating up the bunker C oil developed a leak and the oil seeped into the water space of the boiler and nicely coated the furnace; amazingly, the check valves did not stop the reverse flow of the bunker C oil into the boiler. I don't remember if the furnace was corrugated or plain but being a high pressure boiler, it was probably corrugated. A new boiler was purchased instead of an expensive repair.
Sometimes the resonance on the tubes in addition the creep can cause bulge. However this type failure should start with noise in the furnace that you may/may not hear.
