Failure Analysis of Superheater Tube of Boiler
To investigate the cause of pre-mature failure of boiler superheater tube and suggest suitable remedial measures.
Metallurgical investigation has been carried out to ascertain the cause of failure of superheater boiler tube, installed in Boiler#5, of M/S Hindalco Aditya Aluminium Lapanga (HALL), Sambalpur. The tube has failed in a short span of nine months of service compare to its expected service life of 10 years. The material of the tube belong to SA213-T22 grade. The material failed due to intergranular fracture triggered by creep voids coalescence along grain boundaries leading to creep followed by rupture under hoop’s stress.Estimation of operating temperature based on steam side oxide scale thickness was made. It was concluded that overheating during the operation led to creep and subsequent failure within a short period.
The evidences found were enough to infer that the material has been exposed to higher operating temperatures. The SA213-T22 material is designed to withstand metal temperature up to 540oC (BHEL Journal, vol.27, No.-2, Sept. 2006). So corrective measures were suggested as,
- To keep operating parameters such that tube metal temperature does not exceeds 540oC
- Inspection of other tubes in the final superheater zone of boiler#5, to assess their structural health condition, so that this kind of failure can be avoided in near future.
Corrective measures suggested were accepted by the customer. Further instances of failure has not been reported by the customer.