Ultrasonic flaw detection mainly detects the near surface and internal quality of steel castings, and the internal quality of steel castings is mainly guaranteed by casting technology. Ultrasonic flaw detection is generally based on the requirements of GB / t7233-2009 ultrasonic flaw detection methods and ratings for steel castings and appendix 7b in Chapter 7 of the guidelines for ship welding inspection (2015) and approved drawings of China Classification Society.
According to the requirements of the Chinese Classification Society for the inspection of the parts of the pouring mouth and the parts of the riser that are likely to bear the force (see Appendix 7b of the drawings of the ship Surveyor in 2015).
If the grain size is determined to be coarse due to no low wave or serious low wave attenuation in ultrasonic flaw detection, RE heat treatment is allowed. If the ultrasonic flaw detection is still after re heat treatment, it shall be judged as unqualified.
Due to the limitations and near-field blind area of longitudinal wave straight probe, it is recommended to use double crystal probe or angle probe to detect defects within a certain depth range (within 50mm) on the near surface of steel castings.