〠Abstract】 After repeated research, a dynamic automatic wire feeding and hot wire TIG semi-automatic welding process was tested. Through the dynamic stirring of the welding pool and the preheating of the welding wire, the welding quality is higher and the welding speed is faster. The welding process is used to carry out on-site installation of LNG inner tank wall panels, which can improve work efficiency and quality, reduce costs and shorten construction period.
With the rapid development of China's economy, the demand for clean energy is becoming more and more urgent, and the demand for Lliquefied Natural Gas (LNG) is increasing year by year. LNG storage tanks are mainly made of 9% Ni steel, which has high welding requirements. Up to now, all domestic LNG projects that have been built or under construction, such as Shanghai LNG, Dalian LNG, Shandong LNG, Jiangsu LNG, Zhuhai LNG, etc., are currently mainly equipped with electrode arc welding (except for submerged arc welding of circumferential seams). The welding process is known to be similar in foreign countries.
Electrode arc welding is a traditional manual welding process. The welding workload is large, the welding efficiency is low, the working conditions are poor, the strength is high, the welding quality is not easy to guarantee, the amount of consumables is large, and the cost is high. In order to improve the capacity of engineering construction, it is necessary to carry out research on core technologies and continuously improve the level of technological innovation. To this end, our company organized 9% Ni steel welding technology research work, through the welding process test, analysis and optimization of the welding process, and finally determined the advanced dynamic automatic wire feeding and hot wire TIG semi-automatic welding process.
1. Analysis of weldability of 9% Ni steel
(1) Chemical composition and mechanical properties of 9% Ni steel Take A553Type1 as an example. The supply state is quenching + tempering (QT) state. After the material is quenched, the fine grained martensite structure can be obtained. The tempering treatment (580 °C) transforms the martensite structure into ferrite and fine precipitated carbides, and at the same time, a small amount of dispersed austenite is obtained, so that the toughness of the base metal is greatly improved, and the metallographic structure is as shown in the figure. 1 is shown.
(2) Welding cold cracks 9% Ni steel itself has good cold crack resistance, and generally does not produce cold cracks under normal welding conditions. However, if the welding process conditions are not correct, there will be some cold cracking sensitivity. In particular, when the first layer of weld is welded, the cooling near the root is fast, and the restraining stress is large, and cold cracks may occur.
For more details, please refer to the attached content or read the relevant contents of the 20th issue of Metalworking (Hot Processing) magazine.
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