The main functions of API 5L X52 seamless steel pipe welding preheating include the following aspects:
Prevent cracks: Preheating can reduce the cooling rate of the welded joint, which helps the escape of diffused hydrogen in the weld metal, thereby avoiding hydrogen-induced cracks. In addition, preheating can extend the cooling time of the heat-affected zone in the temperature range of 800-500`C. During the cooling process of the welded joint from the high temperature just solidified to room temperature, the metallographic structure will change. Austenite will begin to transform from 800℃. When cooling is slow, it will transform into ferrite and pearlite or troostite, thus avoiding the occurrence of martensite hardening structure, improving the crack resistance of the welded joint, and thus avoiding welding cracks.
Reduce welding stress: Preheating can reduce the temperature gradient between the welding zone and the entire weldment, thereby reducing welding stress and reducing the occurrence of welding cracks. Preheating can also reduce the welding strain rate, which is conducive to avoiding welding cracks.
Improve welding quality: Preheating can remove factors that affect the quality of the weld, such as oil and moisture, promote the escape of hydrogen in the weld, and prevent the generation of defects such as pores, thereby improving the welding quality.
Adapt to environmental changes: When welding in a low temperature environment, preheating can prevent the weld and heat-affected zone from producing hardened structures, thereby avoiding the generation of cracks. Preheating is particularly important for API 5L X52 low-carbon steel pipes with a thickness of more than 20mm.
API 5L Grade X52 PSL2 Carbon Steel Seamless Pipes
