Burst Cause Analysis of the High Temperature Steam Pipe in Heavy Oil Well

The high temperature steam pipe used in one heavy oil well in China burst. This failure pipe was investigated and analyzed by macroscopic analysis, material tests (including chemical composition, metallurgical analysis & mechanical property) and fracture surface scanning electronic microscopy (SEM) analysis. Then it can be concluded that the mechanical properties of the burst pipe accord with related standards, and that the fracture surface is a typical brittle fracture. The herringbone stripes were found on the fracture surfaces and pointed to a fracture source where there were over 1.6mm deep mechanical damages on the pipe surface. After micro hardness testing near mechanical damage area and the nearby substrate, it was found that the toughness of mechanical damage area was low. The expanding diameter of the burst pipe was also investigated. Because the residual water in the pipe was pushed by high temperature steam when the steam was turned on, the speed of water was very fast, and the stress caused by water hammer were higher than yield pressure of the pipe, which is the internal pressure in the pipe and which could produces a maximum hoop stress in the pipe equal to the yield strength of the pipe material, the pipe would be expanded. The fracture surface is a typical brittle fracture. There are two mechanical damages on the fracture source, and the pipe burst because of the mechanical damages and huge impact of water hammer.