Xiang Feng Zheng

Failure Analysis and Welding Repair for Reheater Tube Crack of 12Cr1MoV Steel

Through methods, such as microscope analysis, chemical analysis, hardness analysis, metallography examination etc, the causes resulting in reheater tube cracking of 300MW station boiler have been analyzed. The result indicates this reheater tube cracking is reheat crack. The higher sensitive temperature in operating, excessive welding residual stress are the primarily inducement of cracking. In welding repair, the measures , such as replacing the material ,lower welding heat input, preheat treatment and so on, were taken. The welding repair succeeded greatly.

Failure Analysis on Heating Surface Tube Crackof High Temperature Reheater in Station Boiler

Through methods, such as microscope analysis, chemical analysis, metallography examination and scanning electron microscope etc, the causes resulting in high temperature reheater tube cracking of station boiler have been analyzed. The result indicates the crack is reheat crack, and structure stress, higher hardness and excessive welding residual stress are the primary inducement of tube joint crack.

Research on NDT Technique for Thick-Walled Metal Parts of Power Stations

A NDT technique suited to inspecting thick-walled metal parts of power stations is comprised of time-of-flight-diffraction technique, Pulse-echo technique and magnetic particle inspection technique or dye penetrate technique. Flaw sizing accuracy and probability of detection can be improved greatly with application of the technique, and the risk of components` failure can be decreased greatly.

Analysis on Welding Crack of Subcritical Power Station Boiler Platen Superheater Header

Welding crack analysis was carried out on tee joint crack of boiler platen superheater header (12Cr1MoV) of subcritical power station applying finite element analysis,microanalysis, mechanical properties test, chemical composition analysis, metallography examination and SEM observation etc. Results indicated that the improper structure, the original welding defects, higher welding heat input, excessive welding residual stress and improper heat treatment led to cold crack and reheat crack ,then induced to the leakage failure while operating.the welding crack originated at the original defects, connected with reheat cracks during propagation and led to leakage finally.

Research on Welding Repair for Tee Joint Crack of Final Superheater Header of 300MW Station Boiler

Through methods, such as microscope analysis, metallographic examination, the crack located nearby the fusion line between tee joint and outlet steam pipe of subcritical power station boiler final superheater header is reheat crack (the main crack occurred in the heat affected zone and extended along the fusion line and grain boundary in HAZ. There are many small cracks paralleling with main crack). The base metal material (12Cr1MoV) and excessive welding residual stress are the primary inducement of crack. In repair crack, the measures of reducing residual stress, such as lower welding heat input, reducing thickness of welding layer, hammer blowing, assigning reasonably heat treatment power ,lengthening holding time and so on, were taken. The welding repair succeeded greatly.

Failure Analysis on Tube Socket Crack of Supercritical Boiler Water Wall Header

Through methods, such as microscope analysis, mechanical analysis, chemical analysis, metallography examination and scanning electron microscope etc, the causes resulting in lots of tube socket cracks of supercritical boiler water wall header (15CrMo) have been analyzed. The result indicates failure of the supercritical boiler water wall header tube sockets are the ductile fracture and belong to thermal stress crack. The unreasonable structure, excessive thermal stress between header and sockets are the primarily inducement of crack failure.

Research on Welding Repair for Tee Joint Crack of Subcritical Power Station Boiler Platen Superheater Header

Through methods, such as microscope analysis, metallography examination, the causes resulting in tee joint crack of subcritical power station boiler platen superheater header have been analyzed. The result indicates the tee joint crack originated in the original defects, expanded to connect with reheat cracking and leaked finally. In repair crack, the measures of reducing residual stress, such as lower welding heat input, reducing thickness of welding layer, hammer blowing, assigning reasonably heat treatment power ,lengthening holding time and so on, were taken. The welding repair succeeded greatly.

Research on Welding Repair for Reheating Hot Pipe Elbow of 325MW Station Boiler

Through methods, such as microscope analysis, metallographic examination, the crack located nearby the fusion line between reheating hot pipe elbow and blocking valve is reheat crack. The base metal material and excessive welding residual stress are the primary inducement of crack. In replacing pipe elbow, the measures of reducing residual stress, such as hammer blowing ,lower welding heat input, post welding heat treatment and so on, were taken. The welding repair succeeded greatly.

Failure Analysis of T91 Finishing Superheater Tube Bursting for Improper Initial Microstructure and their Life Evaluation

The failure analysis was performed for T91 finishing superheater bursting tube. It is concluded that improper initial microstructure resulted from non-standard heat treatment contributes to poor creep properties at high temperature and subsequent tube bursting. In addition, life evaluation was carried out on the basis of creep-rupture test result of experimental steel with similar improper microstructure. It is in accordance with the practical condition and provides significant guidance for safety and operation supervision.

Failure Analysis on Tee Joint Crack of Subcritical Power Station Boiler Platen Superheater Header

Failure cause analysis was carried out on tee joint crack of boiler platen superheater header (12Cr1MoV) of subcritical power station applying microanalysis, mechanical properties test, chemical composition analysis, metallography examination and SEM observation etc. Results indicated that the tee joint crack originated at the original defects, connected with reheat cracks during propagation and led to leakage finally. The improper structure, the original welding defects, overhigh welding heat input, and excessive welding residual stress resulted in the leakage failure.