1. Appearance characteristics
Cracks generally appear in the hot joints and structural abrupt parts of the forging valve body, such as the root of the flange and the convex surface of the outer wall of the valve. The depth of the crack is shallow, and it is generally dominated by hairline. The shape of the hot crack is irregular and irregular, the gap is wide, the section has severe oxidation, no metallic luster, cracks occur along the grain boundary and develop. The cold crack is generally straight, and the metal surface of the crack is not oxidized, and the crack often extends through the grain to the entire section.
2. Inspection methods
Cracks on the exterior of the valve can be detected by magnetic powder or by impregnation, in addition to visual inspection.
3. Identification of defects
The presence of cracks reduces the cross-sectional area of the valve load, and the crack ends form sharp notches, the stress height is concentrated, and it is easy to expand and cause damage. Cracks that are generally visible are not allowed, regardless of their position and size, which are judged to be unacceptable. After the crack is found, it can be ground with a grinding wheel. If it is confirmed that the crack has been eliminated and the appearance of the valve is not damaged, the thickness is not significantly reduced, and it can be judged as qualified, otherwise it is processed according to the return.
