Analysis of Factors Affecting the Quality of Circumferential Welding of Petroleum Liquefied Petroleum Gas Bottles Zhao Wei 6, Mao Weinong 2 1. Department of Technology, Pearl River Steel Pipe Co., Ltd., Panyu 511450, Guangdong; 2. Tianjin Institute of Mechanical and Electrical Technology, Tianjin 300131 , Take timely measures to adjust the welding process parameters, so as to ensure the welding quality of each cylinder. This paper analyzes many factors that affect the quality of the seam welding of petroleum liquefied petroleum gas cylinders, introduces the causes of defects through intuitive judgment, and proposes solutions to the problems.
The shape and quality of the first layer of welding seam depends on the quality of the welding layer. The first layer of welding bead should be covered. The first layer of welding bead should cover both sides of the groove. The center of the welding bead is slightly lower and is semi-circular arc. ) Or flush with the edge of the groove).
The arc voltage directly affects the shape and quality of the weld, and the arc voltage fluctuation has a greater impact on the welding quality than the welding current. When the arc voltage is too high, the weld becomes wider, and the shape of the two sides is high and the middle is low. At the same time, the surface of the weld is too smooth, which is easy to cause internal undercut. When the arc voltage is too low, first of all, it is difficult to start the arc, resulting in a bad shape of the arc welding seam. At the same time, the weld seam is too narrow to fill the groove completely. The surface of the weld is uneven and uneven, and the welding slag is difficult to clean. Too low arc voltage causes a small width-to-depth ratio of the weld, which is not conducive to the smooth progress of the metallurgical reaction of the molten pool, and defects such as pores and slag inclusions appear.
In the production process of professional civilian 15kg petroleum liquefied gas cylinders, the welding process of cylinder girth welds is usually: single-wire double-layer submerged arc welding, first layer bottoming, second layer cover, welding wire selection H08A! 2.0mm, the flux is H431. According to the provisions of GB5842-1996, for every 50 steel cylinders produced, one steel cylinder should be randomly selected for 100A ray inspection. The purpose is to check the welding quality of the steel cylinder, monitor the working state of the welding machine, and check the welder ’s Operational situation. It is very important to ensure the stable and reliable welding quality of the liquefied petroleum gas cylinder girth welds. How to monitor the quality of other steel cylinders that have not been radiographically inspected, especially when the external conditions change, such as power grid voltage fluctuations, groove shape changes, and assembly Status), whether the welder can quickly make an intuitive judgment and adjust the process parameters according to the shape, color of the weld, and the sound of the arc burning, so as to ensure the welding quality of each cylinder is particularly important. The following describes how to make intuitive judgments from several aspects.
Appearance and shape of the weld seam 1.1 The shape of the arc starting point The slag inclusion at the arc starting point is the most common defect in actual production, which is mainly caused by the poor shape of the weld at the arc starting point. The shape of the welding seam of the arc starting point should be round head, wide and thin), if it is narrow and thick), it is not conducive to the removal of welding slag, and it will cause slag inclusion. There are two factors that affect the shape of the arc starting point. On the one hand, it is determined by the characteristics of the welding machine, on the other hand, it is related to the process parameters such as welding speed, groove shape, and front offset.
Weld shape and quality of the second layer Weld shape of the second layer should be full and smooth, with a certain width and height. At a certain welding speed, the main factors that affect the shape of the weld are: arc voltage, welding current and front offset. Increasing the arc voltage will increase the arc heating area, increase the width of the weld, reduce the residual height of the weld, and increase the pores on the surface of the weld.
When increasing the welding current will increase the volume of the weld, when reducing the arc voltage or reducing the welding current, the effect is opposite.
2 Factors affecting the quality of the weld 2.1 The effect of the front offset on the weld seam The front offset has the most obvious effect on the shape of the weld seam, followed by the deputy director of the weld pool deep penetration test laboratory.
Metallurgical structure: the weld is austenite matrix with ferrite and carbides distributed on it, hot oxygen and liquid nitrogen storage tank for welding. The mechanical properties of the welding test plates of all container products are affected by the austenite matrix, along the Carbide is distributed in the austenite grain boundary, the base material is austenitic to meet the technical requirements, especially the low temperature impact performance is higher than the technical index (31), and the compound is distributed in the form of strips on the matrix. Six of these vessels have been in use for one year so far, and the other 9 have also used 6 conclusions. 150-1998 steel pressure vessels and 1999 version pressure vessel safety technology monitoring 19 according to the process described in 2 above. The requirements of the P51 low-temperature liquid regulations require the correct installation of tsreserved.httP: //wwxnki.net welding wire. The greater the offset, the smaller the penetration, and the smaller the offset, the greater the penetration. The amount of offset depends on the diameter of the cylinder and the welding linear velocity).
When the offset is large, the arc weld is thin, and the offset is small and the weld is thick. For the second pass, when the offset is small, the weld is sharp and high. The smaller the offset, the sharper and higher the weld, which is turtle-shaped (when the offset is large, the weld is flat) , When the offset is too large, the welding seam will appear low in the middle and high on both sides, that is, the weld seam overflows).
Judging the size of the current according to the sound produced by the arc burning Under the appropriate welding current, the sound produced by the arc burning is crisp and rhythmic, continuous and stable. When the current is too large, the sound made becomes very rapid and ambiguous; when the current is too small, the sound made has no strength.
Influence of welding wire extension length If the welding wire extension length is too short, it will cause insufficient weld seam height, and it is easy to burn out the conductive sheet; if the welding wire extension length is too long, the weld seam height will increase greatly, and it will cause Poor arcs make the arc burning unstable, resulting in welding defects. Generally speaking, the welding wire extension length should be 20-25mm.! Judge the size of the heat input based on the color. The color on both sides of the weld. When the welding heat input is moderate, there is a dark blue circle at about 20mm on both sides of the weld. If the blue part is far away from the weld and the color becomes darker, then the welding heat input is too large. On the contrary, the heat input is too small.
Weld surface color When the welding heat input is appropriate, the surface of the weld seam is black and bright.
The color of the back of the weld seam is welded, and immediately look into the bottle through the valve seat hole. The back of the weld seam should be red, the temperature is about 800-850 /, and there is a small amount of oxide on the surface. If the color of the back of the weld is white and there is too much oxide, it means that the heat input is too large; if the color of the back is red and there is no oxide, it means that the heat input is too small.
The size and shape of the flux bowl should be moderate, the taper should be small, the diameter of the large end of the flux bowl is about 80mm, the diameter of the small end is about 60mm, and the height is 55mm. If the flux bowl is too large, the flux is too thick, it will increase The pressure of the molten pool is not conducive to the rise of the welding slag and the formation of the welding seam, and the pitting on the surface of the welding seam increases; if the flux bowl is too small, the amount of the welding flux is insufficient, and the molten pool cannot be well protected. The edge of the solder bowl and the cylinder should be as close as possible to the cylinder. The opening height of the back of the flux bowl should be moderate. If the opening height is too low, the surface of the welding seam is not well protected, and a large number of surface pores are generated. In severe cases, the shape of the welding seam will be changed and the welding seam will be scratched.
The position of the welding wire in the flux bowl The welding wire should be in the center of the flux bowl. If the welding wire is too forward, the molten pool is not well protected, the arc is exposed, which is not conducive to the welder's operation; the welding wire is too far behind, the molten pool is too short in the flux bowl , Not conducive to the metallurgical reaction of the molten pool.
Requirements of conductive splint and conductive sheet The semicircular grooves of the upper and lower conductive sheets installed on the conductive splint should be coaxial, otherwise it is not easy to straighten the welding wire, the semicircular groove should not be too deep, the conductive sheet should be higher than the conductive plywood after installation 1- 2mm, and the two planes of the upper and lower conductive plates are aligned and parallel to the plane of the conductive splint, which is not only convenient for clamping the welding wire, but also uniformly wears the upper and lower conductive plates, which not only helps to extend the service life of the conductive plates, but more importantly Conducive to starting the arc, avoiding firing when starting the arc ", and at the same time ensuring the stability of the arc voltage during welding.
5.2 Requirements for the conductive sheet The surface of the conductive sheet should be smooth, the semi-circular surface coincides with the semi-circular groove of the conductive splint, and the contact is good. The depth of the welding wire guide groove should be moderate. Too shallow is not conducive to guidance. Causes severe fever. The depth of the guide groove should be (1 / 3-1 / 2! G is the diameter of the welding wire)).
The state of the welding wire in the conductive sheet is directly related to the welding quality. If it is not installed properly, it will cause arcing, "arc breakage, and severe heating of the conductive splint. Too tight, and the lower conductive piece should clamp the welding wire, and the upper conductive piece must not clamp the welding wire too tight and the lower conductive piece is too loose, which will cause the welding wire between the upper and lower conductive pieces to become hot, red, or even unable to Smooth arc starting and welding. The method to check whether the welding wire is installed correctly is to shake the welding wire by hand, and the welding wire should not shake. When the wire is jogged, the welding wire will not drive the conductive splint, and the welding wire can be fed smoothly.
Conclusion According to the changes in the appearance shape and color of the weld, correct visual judgments and appropriate measures can be taken in time to avoid batch welding quality problems, monitor the overall welding quality, and meet the requirements of the specification.
The effect of welding quality is a compound result of superposition of many factors. Different reasons can cause different results, but the same result can be caused by different reasons. This requires dialectical analysis, comprehensive analysis, and comprehensive solutions. The advantage of a certain factor neglects its disadvantage. Only in this way can the weld be formed well and the mechanical properties are excellent, so as to ensure the overall quality of the welding of petroleum liquefied gas cylinder products. Therefore, the quality of the welder is the key, and must pass rigorous training before they can pass the examination.
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