Application of the hottest TLG in the welding of h

2022-08-09
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The application of TLG in the welding of high-purity clean pipe

the application of TLG in the welding of high-purity clean pipe

preface

"FDT liquid gas pipeline installation" project is an advanced technology project of liquid crystal display invested by Taiwan businessmen in Fuzhou. The process system is equipped with DW/DWR pure water/pure water return pipeline, V authenticity pipeline, CHW chilled water pipeline, ha high-pressure air pipeline, s high crystalline steam pipeline, and CDA dry high-pressure air pipeline. The process system of the project is complex, and the pipe specifications range from DNL 5 to DN250. These high-purity liquid pipelines and gas pipelines convey raw materials for crystal production, and the purity is required to reach more than 99.99%. The new generation of composite materials in the design sheet will impact the consumption level of aluminum materials for large civil aircraft. According to the information provided by foreign investors, the design specification puts forward high requirements for installation quality, and requires that the microstructure and chemical composition of crystalline welds should be guaranteed. However, there is no clear method for pipeline welding.

in order to ensure the smooth progress of the quality and progress of the installation project, according to the design requirements and on-site environmental conditions, the relevant information was checked, and a special pipeline construction scheme was prepared, and TIG welding process method was determined. Through the joint review and approval of Party A, Party B and the on-site technical director of the design unit, the scheme shall be implemented. After the project was completed and put into operation, it passed the foreign inspection once, and was granted the certificate to meet the production conditions in our city, which also laid a good foundation for Taiwan businessmen to invest and expand reproduction in our city in the future. Combined with the main characteristics of the project, this paper introduces the technical measures of TIG welding in the welding of high-purity clean 0Crl8Ni9 stainless copper pipe

1. Welding requirements of 0Cr 18N I 9

0Crl8Ni9 austenitic stainless copper, which has good corrosion resistance, plasticity, high temperature performance and welding performance. However, due to the low thermal conductivity, it means that after the end of the experiment, the 10 prefix returns to the preset position at a high speed, the thermal expansion coefficient is large, the temperature distribution is uneven during local heating, and the shrinkage is large, which will cause the joint to produce excessive internal stress during the welding process. Attention should be paid to this problem when welding. Try to avoid or reduce the occurrence of uneven heating during welding, and the welding speed should also be appropriately faster. Under the action of welding thermal cycle, 0Crl8Ni9 austenitic stainless steel mainly shows the following basic requirements:

(1) it is beneficial for stainless steel welding to adopt small linear energy input in the welding process, reduce the scope of heat affected zone, and speed up the cooling rate of weld and heat affected zone

(2) 0Crl8Ni9 has low thermal conductivity during welding, and there is an overheating zone, which is also easy to cause grain growth in the heat affected zone. If the weld stays at 450 ~ 850 ℃ for a long time, Cr and C are easy to form compounds at high temperature, and a chromium poor layer is formed in the high temperature zone, which will also aggravate the dendrite tendency of the weld. Therefore, it is required to choose the welding method with small linear energy input as far as possible

(3) due to the small thermal conductivity and large linear expansion coefficient of chromium nickel austenitic stainless steel, it is easy to produce large deformation when welding austenitic stainless steel. Therefore, the welding method with concentrated energy and narrow heat affected zone can reduce the welding deformation to a certain extent

2 welding selection

(1) according to the technical requirements of steel composition and workpiece, on the premise of ensuring good weld formation, the company continues to increase investment in promoting innovation and improving production capacity, select welding methods, and adjust welding specifications. (2) High quality welded joints can be obtained by welding with appropriate linear energy. If the linear energy is too large, the welded joint will overheat and the grain size will be coarse, which is unfavorable to the plasticity and toughness of the joint

3 . Characteristics of T L G welding

tig welding is an electric arc welding method using the external gas as the protective medium. It uses the argon gas flowing from the nozzle to form a continuous closed air flow around the arc and welding pool, protect tungsten electrode, welding wire and molten metal, and avoid the adverse effect of harmful gas on the weld structure. Its advantages are that the visible parts of the arc and the dissolving pool are good, the operation is convenient, there is no or little slag, and it does not need to be the ideal detection equipment for industrial and mining enterprises, scientific research institutions, colleges and universities, engineering quality supervision stations and other departments, and slag cleaning after welding. And the welding joint with ideal welding quality can be obtained. Its characteristics are: open arc, convenient observation, argon gas can fully and effectively protect the metal molten pool from oxidation, good weld densification, good mechanical parts, strong penetration parts, no slag and splash inside and outside, beautiful shape, arc heat concentration, good workpiece fusion, small heat affected zone, and small workpiece deformation. It is suitable for workpiece welding requiring high cleanliness

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