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Development and application of CTOD process for DH36 marine steel plate at -20°C

Offshore engineering blocks and jackets are typical large-scale welded structures. Due to their harsh working environment, complex structure, high degree of stress concentration, and the influence of welding defects and uneven joint structure and performance, they are very difficult to withstand external loads. prone to brittle failure. Especially when the thickness of the DH36 marine steel plate increases, the influence of the residual stress of the welded joint on the structure is more obvious. Therefore, the general standards and project specifications require post-weld heat treatment for DH36 marine steel plates to reduce welding residual stress.

In recent years, with the continuous deepening of research, more and more standards and specifications stipulate that when the CTOD performance of welded joints in the welded state is qualified, the post-weld heat treatment process of DH36 marine steel plates can be omitted. Based on this, the heat treatment-free CTOD welding process has been applied in more and more engineering projects, and the adoption of CTOD process has great significance for reducing construction cost and construction period. However, the design temperature has reached -15°C or even lower, which puts forward higher requirements for the CTOD process.

Temperature is the most important factor affecting the toughness of materials, and materials are prone to brittle fracture at low temperatures. There are researches on CTOD welding process both at home and abroad, but there are few studies on low-temperature CTOD, especially the CTOD performance of DH36 marine steel plate below -20°C, and the CTOD performance is getting lower and lower with the decrease of temperature. It is becoming more and more difficult to achieve the qualified value. The impact temperature of DH36 marine steel plate that can guarantee toughness is only -20°C. Therefore, to ensure CTOD performance at a lower temperature, higher requirements are put forward for the process.

The material of DH36 marine steel plate adopts the flux cored gas shielded welding process, and the welding joint can pass the test of CTOD test at -20 ℃ by selecting appropriate process parameters. The CTOD process test results show that the CTOD process has stronger adaptability. The successful development of the CTOD process under this temperature condition not only reduces the construction procedures in the project, reduces the work intensity of the construction personnel, but also saves a lot of costs and shortens the It will be more and more widely used in the welding of DH36 marine steel plates.