Four key points to improve the welding operation level of pressure vessel

For important structures such as boilers and pressure vessels, it is required that the joints be welded through safely. However, due to the limitation of structural size and shape, it is sometimes impossible to carry out double-sided welding. It is a difficult operation skill in manual arc welding.


In vertical welding, due to the high temperature of the weld pool, under the action of gravity, the droplets formed by the melting of the electrode and the molten iron in the weld pool are easy to flow down to form weld bumps and undercut on both sides of the weld. When the temperature is too low, slag inclusion is easy to occur, and defects such as incomplete penetration and overlap are easy to form on the reverse side, which makes it difficult to form the weld. The temperature of the molten pool is not easy to judge directly, but it is related to the shape and size of the molten pool. Therefore, as long as the shape and size of the molten pool are carefully observed and controlled during welding, the purpose of controlling the temperature of the molten pool and ensuring the welding quality can be achieved.
According to Fu’s experience of more than ten years, this rule can be summed up in the following sentences:

The angle of welding rod is very important and the welding specification is indispensable

During vertical welding, the droplet formed by the electrode melting and the molten iron in the molten pool are easy to drip down to form welding nodules, and the welt on both sides of the weld is formed, which makes the weld forming worse. Master the correct welding specification and adjust the welding rod Angle and speed according to the change of welding condition. The Angle between the electrode and the weldment surface is 90° in the left and right direction, and the angle of the weld, the starting welding is 70° ~ 80°, the middle is 45° ~ 60°, and the ending is 20° ~ 30°. Assembly gap for 3 ~ 4㎜, should choose a smaller electrode diameter Φ3.2㎜ and a smaller welding current, backing welding for 110 ~ 115A, intermediate transition layer for 115 ~ 120A, cover layer for 105 ~ 110A. The current is generally 12% ~ 15% lower than that of flat welding, so as to reduce the volume of molten pool and make it less affected by gravity, which is conducive to droplet excess. Adopt short arc welding, shorten the distance of droplet to the pool, and form short circuit over.

Observe the weld pool, listen to the arc sound, and remember the shape of the weld hole

The base welding of the weld root is a key to ensure the welding quality. When the arc extinguishing method is used for welding, the arc extinguishing rhythm of vertical welding is slightly slower than that of flat welding, 30-40 times per minute. The arc burning is slightly longer at each welding point, so the welding flesh of vertical welding is thicker than that of flat welding. When welding, the welding starts from the lower end, and the angle of backing electrode is about 70 °~ eighty °, Two click penetration welding is adopted to ignite the arc on one side of the groove, preheat and melt along the spot welding point to the root, hear the “flutter” sound of the arc penetrating the groove, see the molten hole and form the molten pool seat, and immediately lift the electrode to extinguish the arc. Then re ignite the other side of the groove, and the second bath should press 1 / 2 ~ 2 / 3 of the first bath that begins to solidify, so that the whole weld can be obtained by left and right arc extinguishing breakdown. The flexibility of the wrist should be used to extinguish the arc cleanly every time, so that the molten pool has the chance of instantaneous solidification.
During arc extinguishing, it is obvious to see the weld hole formed by the broken blunt edge. The weld hole of vertical welding is about 0.8mm. The size of the weld hole is closely related to the back forming. If the weld hole is too large, it is easy to form a weld bead on the back. On the contrary, if there is no weld hole on the back, it is often not penetrated. It is required to keep the size of the weld hole uniform during operation, so as to ensure that the root of the groove has uniform penetration, the back weld bead is full, and the width is uniform. When backing and changing the welding rod joint, clean up the coating of the joint every time, ignite the arc in the groove, continuously weld along the formed weld about 10 mm, change the angle of the welding rod, extend into the weld center at 90 degrees, swing slightly left and right, and press down the arc at the same time, hear the arc sound, form the molten hole, and extinguish the arc immediately, so that the welding rod arc extends into the root of the weld, The arc is extinguished immediately. Then, the same as the first electrode backing welding method, the left and right alternate cycle arc extinguishing and breakdown, each action should be focused, pay attention to observe the contour of the molten hole and the melted gap on both sides, the molten gap at the root of the groove, only when the arc moves to the other side, it can be seen that the blunt edge is not fused well, and the next generation of arc is a little bit, in order to achieve good fusion, Each time the arc extinguishing time is controlled in the molten pool, there is still one-third of the non solidified arc starting again.
When stopping the arc, it should be noted that when each welding rod is only 80-100mm long, the welding rod will melt faster due to overheating. At this time, the arc extinguishing time should be increased to make the molten pool solidify instantaneously, so as to prevent the high-temperature molten pool from falling down and forming weld bead. When the welding rod is only 30-40mm, prepare to do arc extinguishing action, drop two or three times continuously on one side of the weld pool, so that the weld pool can achieve the purpose of slow cooling, so as to prevent shrinkage and crater cracks on the front and back of the weld bead.

The weld quality can be improved by controlling the bath temperature well

The welding wave of intermediate layer is required to be level. The middle two layers are based on the diameter of welding rod φ 2 mm, the welding current is 115-120a, and the electrode angle is about 70 °~ eighty °, The temperature of molten pool is controlled by the angle of electrode, the length of arc, the welding speed and the residence time of both sides in the groove. The two sides are fused well and the shape of oblate molten pool is ensured.
During the welding of the third layer, do not damage the edge of the groove, and leave a depth of about 1 mm to make the whole filler bead smooth. The edge of the groove above the depth is taken as the reference line to lay the foundation for the cover surface. Generally, the left and right swing is adopted. The two sides of the groove stop a little more to make the edge of the groove melt 1-2mm, and the temperature of the molten pool and both sides of the groove is balanced. The shape of the molten pool is mainly observed, and the molten pool is controlled into crescent shape. The more side of the molten pool stays less, and the less side stays more, Calculate the weld height and width while welding. Because the welding flesh of vertical welding is thicker than that of flat welding, pay attention to observe the shape of molten pool and the thickness of welding flesh. If the lower edge of molten pool protrudes from the flat edge, it indicates that the temperature of molten pool is too high. At this time, shorten the arc burning time and extend the arc extinguishing time to reduce the temperature of molten pool. The crater must be filled before replacing the welding rod to prevent crater cracks.

The welding seam can be formed only when the method of transporting strip is correct

During cover welding, the saw tooth or crescent shaped strip transportation method can be adopted. The strip transportation should be stable, the speed in the middle of the weld bead should be a little faster, and the edge on both sides of the groove should stay a little. The process specification is electrode diameter φ 2 mm, the welding current is 105 ~ 110A, and the angle of welding rod should be kept at 80 ° The welding rod swings left and right to make the edge of the groove melt 1-2mm, and vibrates slightly up and down when both sides stop. But when the electrode is from one side to the other side, the arc in the middle is lifted slightly to observe the shape of the whole molten pool. If the weld pool is flat and oval, it means that the temperature of the weld pool is appropriate and the weld surface is well formed after normal welding. If it is found that the bulging belly becomes round at the bottom of the molten pool, it indicates that the temperature of the molten pool is slightly high. The method of transporting the welding rod should be adjusted immediately, that is, the residence time of the welding rod on both sides of the groove should be increased, the intermediate transition speed should be accelerated, and the arc length should be shortened as far as possible. If the molten pool can not be restored to the flat elliptical state, and the bulge increases, it means that the temperature of the molten pool is too high, so the arc should be extinguished immediately to give the molten pool cooling time, and the welding can be continued after the temperature of the molten pool drops.
When covering, make sure that the weld edge is good. If the undercut electrode is found to move slightly or stay more to make up for the defect, the surface can be smooth only if it is excessive. When the cover joint starts to weld, the temperature of the weldment is too low, which is easy to produce defects such as poor fusion, slag inclusion, joint disjointed and too high, so the quality of the cover directly affects the surface forming of the weld. Therefore, the preheating method is used to weld the joint. At about 15 mm above the welding end, the arc is ignited from top to bottom by scratching method, and the arc is lengthened by 3-6 mm to preheat the welding seam. Then lower the arc and swing 2-3 times at 2 / 3 of the original arc pit to achieve good fusion and then switch to normal welding.
Although the position of the weld is different, they also have common rules. Practice has proved that by selecting the appropriate welding process parameters, maintaining the correct angle of the electrode and mastering the three actions of good luck, strictly controlling the temperature of the molten pool, excellent weld quality and beautiful weld formation can be obtained when welding vertical welding.

Source: Network Arrangement – China Pressure Vessels Manufacturer  www.secmachinery.com

www.secmachinery.com is one of the leading china filtration equipment & sanitary stainless steel pressure vessels manufacturer, with professional factory. We focus on the sanitary pressure vessels, filtration equipment research and development, manufacturing, sales and service since the company been established. Our products is widely used on bio-pharmaceutical, food and beverage, fine chemical industry. 

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