Welding technology of liquefied gas storage tank

Liquefied gas is a flammable and explosive dangerous gas. The liquefied gas storage tank is a special equipment for containing liquefied gas and belongs to special equipment. Its quality requirements are very strict. The main structure of the liquefied gas storage tank is composed of head and cylinder. The welding process runs through the whole manufacturing process. The quality of the welding technology directly affects the quality of the product.

Q345R steel plate with yield strength of 265-345mpa is selected as the material of liquefied gas storage tank. It is a special plate for pressure vessel, which has good comprehensive mechanical properties and process properties. The phosphorus and sulfur content of Q345 (16Mn) steel is slightly lower than that of Q345 (16Mn) steel, which is a low-alloy high-strength steel. In addition to improving the tensile strength and elongation, it is also required to ensure the impact toughness. It is the most widely used and most used steel plate for pressure vessels in China.

Welding of carbon steel for pressure vessels:

Carbon steel is based on iron and carbon is the alloy element, and the content is generally not more than 1.0%. In addition, the manganese content does not exceed 1.2%, the silicon content does not exceed 0.5%, and Si and Mn are not used as alloy elements. Other elements, such as Ni, Cr, Cu, etc., are controlled within the residual limit, and are not alloy elements. S. As impurity elements, P, O, N, etc. are also strictly limited according to the variety and grade of steel. The main pressure components of pressure vessels are carbon steel, mainly limited to low carbon steel. It is specified in the capacity specification that "the carbon content of carbon steel and low alloy steel used for welding the main pressure components of structural pressure vessels shall not be greater than 0.25%. Under special conditions, if the carbon content of steel is more than 0.25%, the carbon equivalent shall not be greater than 0.45%. The manufacturer shall obtain the consent of the user, obtain the approval of the general technical director of pressure vessels of the manufacturer, and go through the approval procedures according to relevant regulations".

1、 Welding points of low carbon steel

1. In submerged arc welding, if the welding line energy is too large, the grain size in the coarse grain zone of the heat affected zone will be too coarse, and even the widmanstatten structure will be generated, which will reduce the impact toughness and bending property of the zone and lead to unqualified impact toughness and bending property. Therefore, when submerged arc welding is used, especially when welding thick plates, welding shall be conducted in strict accordance with the welding line energy qualified by the welding process evaluation.

2. When welding, welding thick or rigid welds at low temperature on site, the tendency of cold cracks increases due to the rapid cooling rate of the welded joints. In order to avoid welding cracks, measures such as preheating before welding shall be taken.

Welding of carbon steel for pressure vessels:

Carbon steel is based on iron and carbon is the alloy element, and the content is generally not more than 1.0%. In addition, the manganese content does not exceed 1.2%, the silicon content does not exceed 0.5%, and Si and Mn are not used as alloy elements. Other elements, such as Ni, Cr, Cu, etc., are controlled within the residual limit, and are not alloy elements. S. As impurity elements, P, O, N, etc. are also strictly limited according to the variety and grade of steel. The main pressure components of pressure vessels are carbon steel, mainly limited to low carbon steel. It is specified in the capacity specification that "the carbon content of carbon steel and low alloy steel used for welding the main pressure components of structural pressure vessels shall not be greater than 0.25%. Under special conditions, if the carbon content of steel is more than 0.25%, the carbon equivalent shall not be greater than 0.45%. The manufacturer shall obtain the consent of the user, obtain the approval of the general technical director of pressure vessels of the manufacturer, and go through the approval procedures according to relevant regulations".

1、 Welding points of low carbon steel

1. In submerged arc welding, if the welding line energy is too large, the grain size in the coarse grain zone of the heat affected zone will be too coarse, and even the widmanstatten structure will be generated, which will reduce the impact toughness and bending property of the zone and lead to unqualified impact toughness and bending property. Therefore, when submerged arc welding is used, especially when welding thick plates, welding shall be conducted in strict accordance with the welding line energy qualified by the welding process evaluation.

2. When welding, welding thick or rigid welds at low temperature on site, the tendency of cold cracks increases due to the rapid cooling rate of the welded joints. In order to avoid welding cracks, measures such as preheating before welding shall be taken.