Large-diameter stainless steel cylinders play a critical role in heavy-duty equipment such as boilers and nuclear energy vessels. These components require high-quality welding due to their structural complexity and strict performance requirements. For example, a large-diameter stainless steel cylinder is fabricated from 06Cr19Ni10N steel with a plate thickness of 22 mm. The inner diameter of the cylinder is 12 meters, and its height reaches approximately 17.6 meters. After welding, the verticality and ellipticity of the cylinder must not exceed 10 mm, making the manufacturing process highly demanding.
The cylinder is composed of 11 separate sections. Each section is machined using a planing machine, then rolled by a coiling machine to achieve the required dimensions and shape accuracy. The main challenges in producing these large-diameter cylinders include controlling the ovality and verticality of the final structure, as well as ensuring the quality and tightness of the welds.
To maintain precision, the cylinder is assembled and welded using a vertical assembly method. The first section serves as the reference plane. To ensure high-quality welding, several control measures are implemented throughout the process.
First, the ellipticity of the cylinder is carefully controlled. During welding, it's essential to balance the lateral shrinkage on both the inner and outer sides of each longitudinal weld. This can be achieved by welding large, stiff П-shaped plates to the inner, outer, and upper, middle, and lower parts of the weld. Additionally, the groove is designed as an asymmetrical X-shape, with a larger opening on the inside. The inner side is first welded with back-capping and second-layer welding, followed by deep-rooted welding on the outer side. Once the outer side is fully welded, the inner side is completed. By controlling the welding sequence and layer thickness, the deformation on both sides is kept balanced. Finally, the П-shaped plates help equalize the inner and outer corners, keeping the ellipticity below 10 mm.
Second, the lateral shrinkage of the longitudinal seams is strictly managed. To ensure the cylinder remains vertical, the amount of lateral contraction on both the top and bottom of the vertical joints must be uniform. This requires that the top and bottom surfaces of each cylinder section are parallel and lie on horizontal planes. With proper alignment and welding techniques, the verticality of the 17.6-meter cylinder can meet design specifications.
During the initial welding phase, each vertical joint is divided into four or five equal parts. Both the inner and outer sides are welded using a top-down, segmented back-welding technique to minimize upper-side contraction. Starting from the third layer, bottom-up through-welding and symmetrical welding are applied to increase upper-side contraction. This compensates for the contraction that occurred during the initial welding. Combined with rigid fixation using II-plates, this approach ensures even lateral contraction across all welds.
Third, the lateral contraction of the circumferential seams is also tightly controlled. In addition to managing the full-length contraction of the longitudinal seams, the contraction of the annular joints between sections must be precisely regulated. This is done by placing rigid shaped panels at regular intervals along the entire length of the weld. Eight welders work simultaneously using identical parameters—such as welding current, speed, rod diameter, thickness, and direction—to perform segmented jump welding. This method ensures consistent lateral contraction across the entire circumference, keeping the center of each ring in a horizontal plane.
By combining the II-plate rigid fixing method, optimized welding sequences, and tailored groove designs, the verticality and ellipticity of the cylinder are maintained within acceptable limits. These measures ensure that the final product meets both design specifications and operational requirements.
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