Weld Geometry Defect Influence On Boiler Tube Structural Integrity

Abstract

Damage of boiler tubes is a very serious problem in many utilities worldwide, including even in the most advanced countries. Preserve of boiler tube integrity present major part in maintenance programs centered to achievement of high levels of availability and reliability of thermal power plants. This is due to a very specific and complex interconnection of design and operating characteristics of the boiler unit. Based on the results of numerous boiler tube damages investigation performed on domestic thermal power plants it is concluded that the initiation of different damage mechanism was strongly influenced by tube weld geometry defects. In this paper particular attention was dedicated to this not well documented problem. Structural integrity of the boiler tubes are greatly affected by the weld excessive root penetration (melt-through) on the tube inner surface. This type of weld geometry defect, which occured often on boiler tubing system, present local flow disrupter and also very strong stress riser. In the vicinity and donwnstream of excessive root penetration type disrupter initiation of different damage mechanisms (erosive and corrrosive wear, underdeposit corrosion, stress corrosion, corrosion fatigue) occured due to working fluid nucleate boiling destabilization (eveporator), or due to turbulent flow (superheater and reheater), followed by intensive suspended solids deposition.