A Failure Analysis and Remaining Life assessment of Boiler Water Wall tube

Patel Sunny Sanjay, Dr R. K. Mandloi

Boiler, Creep, Corrosion, Root Cause Analysis, Water wall tube, Failure, Life Estimation.

This paper presents failure investigation on the SA210GrC water wall tube by visual Site inspection, tube wall thickness measurements, chemical composition test, Hardness test and microstructure analysis with proper evidence collected to identify the exact cause of the failure. The water wall tube was failed with blister, bulging and creep cracks on outer surface located near to the Soot Blower. On-site wall thickness measurements were performed on some of the water wall tubes located at the same level of the ruptured tube. The tubes have significant wall thinning and erosion from outside. Mild corrosion deposition also seen in the inner side. Microscopic examinations on the failed rupture region and some distance away of the as-received tubes are also conducted in order to determine the failure mechanism and root cause. Failure mechanisms are also discussed and relevant data from few months back to the failure gathered to identify the failure reason. The failure mechanism is identified as a result of the combination of the significant wall thinning of water wall tube due to long term overheating and creep. Corrosion due to oxygen is also a cause of wall thinning. Root cause analysis identified that deaerator was not working efficient to remove dissolved gases was reason behind corrosion. Long term overheating was due to operating temperature above the design one. Finally all the parameters checked and rectified properly. Maintenance of Deaerator has been done to put it in the working condition.