The new and old specifications of steel castings in China, methods for ultrasonic flaw detection and quality assessment of steel castings GB7233-87 and ultrasonic testing of steel castings Part 1: general purpose steel castings GB7233 1-2009。
In terms of defect classification, GB7233-87 divides defects into plane defects and non plane defects, and evaluates the quality grade of steel castings according to the defect size in the evaluation frame. Non planar defects need to measure the size of the defect in the thickness direction of the steel casting, which is obtained from the upper and lower boundaries obtained by ultrasonic testing in different directions, so as to obtain the percentage of the size of a defect in the thickness direction of the steel casting in the whole thickness. However, it is difficult to realize such detection in actual operation. During flaw detection, only the approximate position and depth of defects are recorded, and then unified repair welding is carried out. In addition, GB7233-87 is directly rated as grade 5 for components with cracks in the detection area. It is difficult to find cracks in the actual operation process, because the direction of cracks is often perpendicular to the surface of steel castings. At this time, it is necessary to combine angle probe to detect.
GB7233-09 retains the concept of planar defects and non planar defects, and further changes the classification of volumetric defects to point defects (defects whose size cannot be measured) and extended defects (defects whose size can be measured) following the practice of Germany
There are two categories. For the above two types of defects, 6dB method, i.e. half wave height method, is used to determine the size.
The improved GB7233-09 classifies each grade of steel castings according to the wall thickness, which reflects the requirements that steel castings of different sizes have different defect thresholds. Generally, the larger steel castings can withstand more defects. Unlike GB7233-87, all steel castings, regardless of size (1t steel castings or 30t steel castings), are evaluated according to the same defect tolerance. 09 specification also divides the steel casting into three areas along the wall thickness direction, the outermost layer and innermost layer are the edge part, and the middle layer is the core part.