ETD has recently carried out root cause failure analysis for a number of boiler tubes samples removed from oil & gas fired boiler units of two large power plants in Far East.
Several of the superheater tubes had ruptured after 100,000 hours in service, causing forced outages. The tube materials removed from the boilers were steel grades ASTM A213 T91 and also X20 CrMoV12-1. Analyses were carried out to identify the specific failure mode for respective tube samples, which involved the following:
Detailed visual and dimensional checks for signs of wall thinning, defects/ damage (cracking, corrosion etc.)
Metallurgical examination of the material microstructure condition, and Hardness tests evaluation – for assessment of overheating, creep damage etc.
Chemical composition analysis of the base material to check conformance with specification, and analysis of surface scale/deposits indicative of fireside conditions.
Measurement of effective tube operating temperatures based on established oxidation kinetics allowing comparison with the expected operating temperatures.
Assessment of the minimum wall thickness required according to design and operating conditions.
Remaining Life Assessment for any non-failed tubes (creep rupture life and corrosion rate evaluation).
Investigations showed that some tubes had failed due to the combined effects of fireside corrosion, steam side oxidation and long-term overheating. Drawing on extensive experience of boiler tube failures and T91 steel, ETD was able to recommend remedial measures to the plant operator on modifications to boiler design, operation and maintenance/replacement strategy, and continued condition monitoring.
ETD has established expertise in the failure analysis of the components for power plant boilers and turbines and process industry. For more information about our failure analysis services please click here.