In power plants (especially thermal and nuclear power), welding heat treatment is the lifeline to ensure the long-term safe operation of high-temperature and high-pressure equipment. Its applications are concentrated in key components such as boiler heating surfaces, main steam pipelines, steam drums, turbine cylinders, and high-pressure rotors. These devices typically operate at temperatures exceeding 500 ° C and pressures of tens of megapascals, requiring extremely high durability, creep resistance, and tissue stability of the materials.
Industry characteristics:
The core goal of welding heat treatment in power plants is to ensure the long-term stability of materials under high temperature and high pressure. Compared with other industries, its most significant feature is the emphasis on optimizing the high-temperature performance of materials through post weld heat treatment (PWHT), rather than just stress relief. For example, for martensitic heat-resistant steels such as P91 and P92, PWHT is a necessary process to obtain the necessary toughness and high-temperature strength.
Key points to note:
Preheating before welding: Preheating is crucial for thick walled pipelines and alloy steels. The temperature must be uniform and sufficiently high (e.g. 200-300 ° C for P91 steel) to prevent cold cracking and reduce welding residual stress. The preheating range should be greater than 3 times the wall thickness on both sides of the weld and not less than 100mm.
• Hydrogen removal treatment: For high-strength steel thick walled components, post heat hydrogen removal during or immediately after welding is the standard practice. Usually, the weld area is heated to 250-350 ° C and kept warm for more than 2 hours to allow sufficient time for diffused hydrogen to escape, fundamentally avoiding the occurrence of hydrogen induced cracking (HIC).
Post weld heat treatment:
1. Heating control: The heating rate must be strictly controlled (usually ≤ 150 ° C/h), especially when passing through the phase transition temperature range, it needs to be slower to prevent deformation of the workpiece and the generation of new internal stresses.
2. Temperature and time: The temperature selection should be precise, achieving the purpose of tempering and softening martensite, improving toughness, and not being too high to cause excessive decrease in material strength. For example, the PWHT temperature of P91 steel is usually 760 ± 10 ° C.
3. Cooling control: The cooling rate also needs to be controlled (usually ≤ 150 ° C/h), and can only be air-cooled below 300 ° C to ensure uniform temperature of the workpiece and avoid secondary stress.
Product Application
The core of heat treatment in power plants is precise temperature control and uniform heat distribution to ensure optimal creep strength and toughness of materials. Our company's high-temperature flexible ceramic heater, with its temperature resistance of up to 1200 ° C, excellent insulation performance, and flexibility to tightly adhere to complex pipe walls, ensures the temperature uniformity of thick walled pipeline circumferential welds throughout the insulation period, completely eliminating the risk of local overheating or undercooling. At the same time, our multi loop intelligent heat treatment temperature control machine monitors and controls temperature in real time through dozens of K-type thermocouples, strictly following the specific process curve of P91/P92 steel (such as 760 ° C ± 10 ° C) to automatically perform heating and cooling. Its ± 1 ° C accuracy and complete data recording function provide a solid guarantee for quality traceability of nuclear power and ultra supercritical thermal power projects