Welding repair of gas tank cracks Zhao Qiaoliang\Wang Yongqiu 2 (1. Zhejiang Industrial Vocational Technical College, Shaoxing 312000, Zhejiang; 2. Zhejiang Sanhua Co., Ltd., Zhejiang Xinchang 312500) The sequence and welding direction, auxiliary preheating, afterheating, Made a good repair effect.
A C-0.6/3.0 medium-pressure gas storage tank is shared by two air compressors in a factory. The material is Q345R and the thickness is 12mm. The air compressor of No.1 air compressor is directly connected with the gas transmission pipe flange of the gas storage tank. The gas pipe of No. 2 air compressor is vertically connected to the 90. elbow of the air compressor of No. 1 air compressor. On August one day in August 2008, the head near the leg of the gas tank was again found to have cracks. The outer surface was 80 mm long and the inner surface was 110 mm long, which was horizontally distributed.
The cracks in the gas tank legs are described below.
1Cause analysis The compressed air in the air compressor of No. 2 air compressor impacts the air pipe of No. 1 air compressor and generates lateral thrust to the gas tank, and the air flow pulse in the tank causes the gas tank to shake left and right, resulting in the left side of the lower head. Cracks in the head casing of the gas tank caused by long-term fatigue damage at the legs. Due to the effect of the primary membrane stress in the internal pressure of the gas tank, the inner surface of the crack is slightly longer than the outer surface.
2 Weldability analysis (3) Preheating: The heating width of each side of the groove shall not be less than 23 times the thickness of the weldment and not less than 100mm. The infrared crawler type preheating 100150 (1) shall be used to determine the welding specification: in order to avoid the coarse grain of the weld Granular structure causes a drop in impact toughness, requiring small gauge welding and strict control of heat input. Small-size welding rods, small swings, thin weld layers, and multi-layer multi-pass welding are used. The specific process parameters are shown in Table 1. Table 1 Welding repair process parameter table Welding rod welding level welding current / A welding power supply interlayer temperature / Â°c underlying filling layer DC reverse connection cover layer (2) Welding sequence and direction: according to the table 1 Process parameters Firstly, the single-sided welding double-sided forming welding of the bottom layer is completed by arc-extinguishing method. Secondly, the welding current is slightly larger than the bottom layer, and the filling layer is welded by a small zigzag moving strip method. Finally, two welding beads are designed to complete the surface. The welding and welding layer layout is as shown, avoiding large current, slow welding speed and wide swing of single bead to bring large heat input to reduce the plasticity and toughness of the superheat zone. It is required that each layer or weld bead is welded by means of symmetrical welding, and finally the crack holes at both ends are filled.
Polishing the middle layer (3): Grinding with a sander along the direction of the tearing force line.
(4) Post-weld heat treatment: immediately after welding, use infrared crawler type to heat to 300400 Â°C for 12h, and the required temperature rise and fall speed should not exceed 220 Â°C / h, and not lower than 55 Â°C / h. 3.2.3 Note Matters (1) The number of repeated repairs in the same part of the weld shall not exceed 2 times. The undercut depth of the weld surface shall not exceed 0.5 mm, and the cumulative length shall not exceed 11 mm. (3) It is not allowed to arbitrarily arc the gas storage tank body outside the weld. 3.2.4 Post-weld inspection (1) Immediately after welding, the welding slag and splashes on the surface of the cylinder are cleaned, and the weld is polished to make a smooth transition with the base metal. No defects such as cracks, pores, slag inclusions, and unfusion were observed on the surface of the weld by a 10x magnifying glass. Weld seam 100% PT and 100% UT flaw detection, in line with JB/T4730 "Non-destructive testing of pressure equipment" ä¸¨ grade standard.
(2) Hydraulic test after non-destructive testing. Slowly increase to a test pressure of 3.75 MPa (1.25 times the design pressure), maintain no leakage for 30 min, then reduce to a design pressure of 3.0 MPa, no abnormality in the pressure check, and the water pressure test is qualified.
4 Conclusion After the welding repair, the air compressor tank not only meets the GB150 "steel pressure vessel" standard, but also stores compressed air and stabilizes the pressure of the air source, so that the compressed air passes through the gas storage tank to have certain drop, water removal and decontamination. The initial treatment effect has been good for 5 years.
(Continued from page 228) 5 Conclusion Cross-welding in the construction of hull sections is one of the more difficult to grasp in various welding positions. Through the various types, probabilities, positions and causes of common defects in such joints, After comprehensive analysis, a process improvement method for eliminating major defects is proposed. On the basis of many experiments, the non-destructive testing of the welded products before and after the process improvement was carried out with reference to the industry testing standards. Through the comparison of the results, this method can effectively control the defects such as unmelting in such welds.
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