The purpose of SSAW steel pipe preheating

Preventing Hydrogen-Induced Cracking:

Slows Cooling Rate: Preheating slows down the cooling rate after welding, allowing hydrogen to diffuse and escape from the weld metal. This prevents hydrogen-induced cracking.

Reduces Hardening: It decreases the degree of hardening in the weld and heat-affected zones, enhancing the crack resistance of the welded joint.

Reducing Welding Stress:

Temperature Gradient Reduction: Uniform partial or overall preheating reduces the temperature gradient in the welding zone. This helps to lower welding stress and the welding strain rate, thereby preventing welding cracks.

Improving Weld Integrity:

Bonding Reduction: Preheating decreases the degree of bonding with the welded structure, particularly in corner joints, which reduces the occurrence of cracks.

Higher Preheating Temperature: Increasing the preheating temperature further enhances these effects.

Factors Affecting Preheating Temperature and Interpass Temperature:

Material Composition: The chemical composition of the steel and welding rod.

Structural Rigidity: The rigidity of the welding structure.

Welding Method: The specific welding technique being used.

Environmental Conditions: Ambient temperature and other environmental factors.

Importance of Uniform Preheating:

Thickness Direction Uniformity: The uniformity of preheating temperature through the thickness of the steel is crucial for maintaining uniformity in the welding area and reducing welding stress.

Local Preheating Width: The width of the local preheating should be proportional to the restraint degree of the weld, generally three times the wall thickness around the weld zone, and not less than 150-200mm.

Avoiding Uneven Preheating: Uneven preheating can increase welding stress rather than reducing it.

By carefully selecting and maintaining the appropriate preheating and interpass temperatures, weld quality and structural integrity can be significantly improved, reducing the risk of cracks and enhancing the overall performance of the SSAW steel pipes.