Spherical tank assembly welding process and quality control

1) Welding sequence. The principle of spherical tank welding sequence is to reduce the welding residual stress as much as possible. Generally, the equatorial belt is welded first, then the electrode plate is welded. First weld longitudinal seam, then weld ring seam; First, weld one side of the big groove (the outside side), and then weld the small groove side (the inside side) after the inner side root cleaning, grinding and penetration testing is qualified. The upper and lower pole belts are also made of longitudinal seam and then circular seam. The longitudinal seam of the equatorial belt is divided into five sections, and the backwelding method is carried out first on the top and then on the bottom. Ring seam welding pole belt square ring first, then welding equatorial belt and pole belt big ring seam, ring seam section for rear-end welding. 2) Welder layout. There are 20 longitudinal joints in the equatorial belt. The welding method is segmented upward vertical welding. 10 welders are arranged between the joints and carried out simultaneously. The pole belt small vertical seam up and down 4, by 4 welders welding respectively; Two longitudinal plates of the upper and lower poles are welded by 4 welders respectively. The upper and lower plate square rings are divided into 8 sections and welded symmetrically by 8 welders. Equatorial belt and upper and lower plate 2 large ring joints, each ring joint is divided into 20 sections by 10 welders section symmetrical welding; It conforms to the principle of symmetrical welding of spherical tank, ensuring the geometric size of spherical tank and reducing stress and deformation. 3) Preheating temperature and interlayer temperature. For spherical tanks, it is necessary to choose appropriate preheating temperature and interlayer temperature. If the preheating temperature is too high, the welding condition of the welder will deteriorate, the first pass rate of welding will be reduced, and the toughness of the welded joint will be reduced. The preheating temperature is too low, the welding joint is easy to produce cold crack. Liquefied petroleum gas is used for preheating before welding. Preheating temperature ≥100, heating width of each side from the weld center of 125mm range; The temperature measuring point is 50mm away from the weld center, and the temperature measuring point of each weld shall not be less than three. The temperature between the welding layers should not be lower than the preheating temperature before welding, and the highest temperature should not exceed 180℃, otherwise the low temperature impact toughness of the welded joint will be affected. 4) Welding environment. The welding of spherical tank belongs to the field operation, and the field of spherical tank is set up with windproof and rainproof shed, as shown in the figure. The welding environment shall be measured within the range of 500 ~1000mm from the surface of the spherical tank according to the NB/T 47015-2011 standard. 5) Welding of spherical tank. Before welding, the welding slag, oxide scale, rust, oil and dust on both sides of the groove within a range of 50mm should be strictly removed; When welding, try to avoid the arc in the non-welding place, so as not to cause arc scratch and produce microcrack, to accidentally cause arc scar or arc pit, are polished to eliminate, all polished place by measuring thickness must meet the relevant process requirements, and qualified by the surface detection. The weld metal of cryogenic steel spherical tank is sensitive to the amount of welding heat transfer, so the welding current and welding speed should be strictly controlled, and the amount of welding heat transfer should not exceed the maximum value in the welding process evaluation report. Welding using a short arc operation, in the groove welding, must avoid the middle of the welding bead, both sides of the depression shape, as shown in the figure; Weld head back arc method is used, that is, each electrode welding arc 10 mm before beginning of solder joints, then quickly back to the beginning of solder joints for welding, arc extinguishing guoquan method will fill arc crater, the next electrode arc as quickly as possible, as far as possible to reduce time interval, in case the weld cooling and produce welding defects, the layers of the joint between the staggered over 50 mm, prevent per layer, the accumulation of arc a little weld defects and defects in excess of the section form, each layer after welding, welding slag are cleared. After welding the outer welding seam of the spherical tank, the root is cleared by carbon arc gouging on the back, and the weld metal formed by positioning welding must be completely removed. After the root is cleared, the grinding wheel is used to show the metallic luster, and the groove shape is U-shaped. Then, the surface penetration detection is carried out, and the results shall meet the requirements of Grade I of NB/T 47013-2012 standard. The point thermometer is used to measure and control the preheating temperature, interlayer temperature and post-thermal dehydrogenation temperature before welding. After inspection, the actual preheating temperature in the welding process is above 100℃, the interlayer temperature is basically controlled within the range of 100-180 ℃, and the temperature of post-thermal dehydrogenation treatment is controlled between 200 ~-250℃, which meets the requirements of the Technical Conditions. The welding parameters of the spherical tank body are recorded according to the welder’s steel seal number, weld code and date. The data are complete and detailed, and all the welding parameters are basically in accordance with (Welding Procedure Specification).铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods