Discussion on quality evaluation standard of cast steel joints:
(1) For the flaw detection of castings, special attention can be paid to the specific area of cast steel joints. For example, the cast steel joint nozzle in the weld affected area is the area that should be paid attention to. The casting defects in the weld affected area should be paid special attention, because the casting defects may be more dangerous under the action of welding residual stress. For special-shaped cast steel joints, it is difficult to judge the specific location of high stress area. If there are special requirements, the flaw detection area can be combined with finite element analysis.
(2) NDT can focus on specific casting defects. A single inclusion may have a great impact on the fatigue performance of high-strength and high purity steel, but it has a limited impact on the cast steel joints bearing general static load. In engineering practice, more attention can be paid to cracks, shrinkage porosity and other dense casting defects with serious bottom wave attenuation.
(3) The actual casting process mainly depends on the casting manual and the experience of engineers. For large castings with special requirements, unified casting simulation and finite element analysis of castings with defects can be carried out.
(4) Cast steel joints are allowed to be evaluated after repair welding twice, but the impact of multiple and multiple welding on cast steel joints is unknown. Especially for the nozzle where stress concentration and residual stress coexist, butt welding shall be carried out with other steel pipes after repair welding. The two welding areas may interact and adversely affect the performance of castings.