During drilling, a section of drill pipe unexpectedly failed. This pipe was a rental, and we were asked to determine what had happened.
It was immediately clear to us that the failed end had been highly heated. It had deformed before it failed and separated. This indicated to us that this was a pack-off failure.
A pack-off is a condition where the formation being drilled has a series of hard material layers with soft layers above them. The bore in the hard material is on gauge, and the bore in the soft material opens up larger. The harder cuttings escape into the larger soft bore and pack around the pipe, gripping the pipe and causing a friction stop. In this instance, the friction was enough that a weak section of piping fractured, causing the failure.
In this photograph, the twisting of the hot pipe before fracture is visible.