Ultrasonic inspection of a reactor pressure vessel from outside surface

Welds are one of the main objects in inservice inspections of reactor pressure vessel (RPV). Circumferential core region weld is most critical for RPV integrity and therefore complementary ultrasonic inspection from the outside surface is found necessary. In reactor pressure vessel inspection, there are some factors that have an effect on the ultrasonic inspection. It is important to know the temperature of outside vessel wall during inspection. Temperature changes the angles of incidence and affects on the detection capability of defects. The state of cladding is important also for detection of the defects at the interface between cladding and base material. The basic inspection techniques and the measurement of transducer contact will be discussed in this overview. It is very important to have similar noise level in the validation block as in the cladding of the component. By this way, the best verification of the technique for real situation will be achieved. The crack detection is depending on orientation, skew and tilt angle of the crack. The optimisation for detection of smaller defects requires certain angle of incidence. Noise from the cladding can enlarge the size of detectable defect. These factors are handled in the qualification of ultrasonic inspection of pressure vessel at Loviisa NPP performed from the outside surface.