The cracks are easily occurred on tube sections at weld joints of sealing plates in boilers due to the working stress of tube proper

the thermal stress resulted from different superimposed thermal expansion coefficients

and additional tension stress caused by sway of tube rows

and the said cracks can't be effectively detected by using other detection methods

such as liquid penetrition inspection

magnetic powder detection

and magnetic memory method etc.

and only the ultrasonic detection can be used for this purpose.The selection of ultrasonic probe

the operation method

and the evaluation of defects in ultrasonic detection have been presented.The ultrasonic detection can provide detection basis for diagnosis of early cracks occurred at weld joints of the sealing plates.