1.Magnetic particle inspection
The statistical results of magnetic particle flaw detection are given in the table. Four crack defects are detected in zg-03 and zg-08; Three crack defects were detected in zg-09; One crack defect was detected in ZG-10.
| Node number | Type of defects | Number of defects |
| ZG-03 | crack | 4 |
| ZG-08 | crack | 4 |
| ZG-09 | crack | 3 |
| ZG-10 | crack | 1 |
Due to the limitation of magnetic particle flaw detection method, only surface or near surface defects can be found. In 24 test samples, only three kinds of defects, i.e. incomplete fusion defect, crack defect and shrinkage cavity, can be found, and other types of defects can not be detected. The cast steel joints with incomplete fusion defects accounted for 41.67% of the total samples; The cast steel joints with shrinkage defects accounted for 8.33% of the total samples; The number of cast steel joints with crack defects detected in R zone accounts for 30.77% of the total number of cast steel joints in R zone. According to the statistical results of magnetic particle flaw detection, the probability of non fusion defect of brace in cast steel joint and crack defect in R area of cast steel joint are large.
2.Ultrasonic flaw detection
Visual inspection and magnetic particle flaw detection are used for surface or near surface defect detection, and ultrasonic flaw detection is used for internal defect detection of castings.
For the ultrasonic flaw detection of 24 steel castings, refer to the standard GB / t7233 1-2009 ultrasonic testing of steel castings Part 1: general purpose steel castings. The general defect indication types are given in this specification. For the defects that still have doubts, other verified and effective nondestructive testing methods can be used for inspection, such as radiographic inspection. If no conclusion can be reached, the supplier and the demander can handle it through consultation. The instrument for ultrasonic flaw detection of steel castings shall comply with the relevant provisions in ZBY 230-84 general technical conditions of type a pulse reflection ultrasonic flaw detector [42]. The ultrasonic testing instrument used in the test is pxut-320c digital ultrasonic flaw detector. The probe adopts longitudinal wave bicrystal probe, the probe frequency is 2.5GHz, and the coupling agent is paste. The reference block adopts ZGS reference block for longitudinal wave bicrystal probe.