After the above WPS preparation, WPQR welding procedure qualification test shall be carried out to determine the WPS process reliability. For the sample with designed groove, after welding repair, the welding sample shall be sampled according to the position shown in Figure 1. The macro inspection of the welding test bar can judge whether the weld fusion performance is good. Through the test, it is determined that most of the fracture positions of the welding process test bar of nodular cast iron end cover are at the base metal (as shown in Fig. 2). The performance test results of the welding process qualification test bar are shown in the table.
Conduct appearance inspection on the samples of nodular cast iron castings after welding (as shown in Fig. 3). Firstly, visually inspect the weld appearance for defects such as pores and slag inclusion. Secondly, cross cut the weld and observe whether there are defects such as non fusion and pores in the cross section after corrosion. At the same time, conduct hardness inspection on the heat affected zone (HAZ) and weld zone (WM) of base metal (BM). If the test results of mechanical properties after sample preparation meet the requirements, it indicates that the welds of nodular cast iron castings are well fused and the weld properties meet the requirements of 80% of the base metal. Through the macro metallographic and mechanical property inspection of the weld, the welding process WPQR is qualified, and the corresponding WPS can meet the welding performance requirements.
Before welding, magnetic particle inspection rather than penetrant inspection is used to confirm whether the defects of nodular cast iron castings are removed. However, penetrant inspection (PT) rather than magnetic particle inspection (MT) is usually used to confirm whether there are welding defects after welding. Through the test, it is found that due to the difference between the base material QT500-7 of the welding end cover and the electrode enife CL material, when magnetic particle flaw detection is adopted, a similar crack defect will be formed at the weld (as shown in Fig. 4), which is easy to cause misjudgment, and the cost of ultrasonic and X-ray flaw detection is relatively high. Therefore, It is more suitable and economical to use penetrant flaw detection in the welding repair of nodular cast iron castings.
