The construction of modern ships involves the splicing of a large number of thick steel plates (up to 80mm) to form a massive hull structure. The main task of welding heat treatment here is to control welding deformation and ensure the toughness of the joint under dynamic loads.
Industry characteristics
The biggest challenge in shipyard heat treatment is how to effectively regulate the stress of large ship segments or sections. The focus is not only on the microscopic weld performance, but also on the macroscopic control of the ship's hull shape. Improper stress distribution can cause the bow and stern of the ship to warp (keel warping) or local unevenness, affecting navigation performance and structural strength.
Key points to note
Preheating before welding: For thick plate joints of ship high-strength steel (such as AH36, DH36), especially T-joints and corner joints, preheating is a standard requirement to prevent root cracks.
• Hydrogen elimination treatment: For deep fusion and high restraint welds in key parts of the ship's hull (such as stern columns and rudder handles), as well as when using high hydrogen welding rods (now rarely used) or in extremely high environmental humidity, post weld hydrogen elimination treatment must be carried out to ensure navigation safety.
Post weld heat treatment:
1. Local stress relief: Overall heat treatment is not feasible, so local flame correction and local electric heating stress relief are commonly used. By controlled heating and cooling of the deformation area, induced shrinkage stress is used to correct deformation and reduce existing stress.
2. Process discipline: The heating temperature, speed, and range of local heat treatment must strictly comply with the process regulations. Excessive heating or improper heating sequence may backfire, introducing new deformations or damaging material properties.
3. Segmented heat treatment: For some large and important segments (such as bulbous bows), they can be sent to a super large heat treatment furnace for overall PWHT after manufacturing is completed. This is the most effective method to ensure quality, but the cost is high.
Product Application
On the dock and slipway, our company's flexible ceramic heaters and portable temperature control machine demonstrate unparalleled advantages. The heater can be applied to complex parts such as the large closure seam and stern hub of the ship according to the shape, for local stress relief or heat treatment after flame correction. Our temperature control box is designed to be sturdy and can adapt to the harsh environment of dampness and vibration in shipyards. Its clear operating interface and stable performance ensure that construction personnel can strictly follow the process requirements to complete the operation, effectively control the hull shape, and improve the fatigue resistance of key parts.