Q345B spiral pipes are prone to cracking during heat treatment and cooling. So, what aspects should spiral pipe manufacturers focus on during production to avoid the occurrence of cracks?
Tempering should be done promptly after quenching. Many spiral steel pipe cracks do not occur during quenching and cooling but rather appear after some time after being removed from the quenching medium, known as aging cracks. These are caused by high quenching stresses, which can be effectively prevented by immediately tempering the pipes after quenching.
For steels sensitive to cracking, self-tempering using residual heat from quenching can effectively prevent the formation of quenching cracks in spiral steel pipes.
Employing a lower quenching temperature and shorter holding time is recommended for high-alloy steels due to their poor thermal conductivity resulting from the high content of alloy elements. Sufficient preheating (once or multiple times) should be performed.
Vulnerable areas prone to quenching cracks (such as threaded holes, edges, grooves, etc.) should be packed with asbestos ropes or covered with iron sheets. During quenching, appropriate pre-cooling should be applied to prevent cracking of the spiral steel pipes caused by excessively fast cooling at weak points.
Select a medium that cools slowly. For spiral steel pipes undergoing oil cooling, avoid water cooling. Control the timing of removing the pipes from the cooling medium, typically by immediately removing them from the cooling medium when they are near the temperature for air cooling. To prevent cooling cracks during single-fluid quenching, a high-concentration nitrate or saline solution can be used as the cooling medium, which can eliminate the risk of quenching cracks in complex-shaped workpieces.
