Overheated pipe due to scale: Field failure investigation and finite element analysis

Through a field failure investigation and finite element analysis, a study on overheated pipe due to scale was performed. The field failure samples were collected from primary reformer convection tube made of material based on ASTM A 335 grad P91 modified specification. The type of the object was a fin tube coil. The tube shows rupture with the shape of fish mouth accompanied by bulging. The analysis performed using finite element mimics the actual field conditions. It was discovered that long term overheating due to scale both at the outside and in the inside of the tube hinders the smooth heat transfer process. This consequently leads to poor heat transfer and violates the original design philosophy. Metallurgical evaluation proves this verdict. Furthermore, the finite element analysis also supports the conclusion.