Chamfering-free pipe row welding technology of ultra-supercritical boiler high-temperature screen type overheater

Abstract

The invention discloses a chamfering-free pipe row welding technology of an ultra-supercritical boiler high-temperature screen type overheater. Compared with the prior art, the chamfering-free pipe row welding technology is characterized in that firstly, the thickness of flat steel is reduced to 6 mm, and the restraint intensity of welding lines is reduced; secondly, an alkaline soldering flux is adopted, and plasticity and tenacity of a connector are improved; and thirdly, small-standardization parameters are adopted for strict welding. On one hand, the heat input amount is reduced, and the high temperature standing time of a welding pool is shortened; and on the other hand, the crack resistance of the connector is improved. The double-layer single-pass welding is adopted, firstly, the fracture surfaces of all the welding lines of the welding connector can be reduced, the cooling speed can be increased, the one-time crystallization condition is improved, the sequential thermal treatment action is achieved among all layers of welding lines, and accordingly a secondary structure is improved; and secondly, the position of welding line metal crystallization lines is changed. Improving of the strength of the connector is the final purpose. In addition, the thermal treatment parameters of corner welding lines are reasonably adjusted, the standard post-welding thermal treatment of 730-760 DEG C*1 h is carried out, and accordingly the hardness value of the corner welding lines is obviously reduced.

Description

technical field [0001] The invention relates to the technical field of boiler equipment, in particular to a non-groove tube row welding process for a high-temperature panel superheater of an ultra-supercritical boiler. Background technique [0002] The boiler high-temperature panel superheater is used in the boiler industry. The superheater is installed in the furnace. The main function of the superheater tube row fillet weld is heat transfer, while the traditional ultra-supercritical boiler high-temperature panel superheater SA213-T91 tube row adopts OE -S1CrMo2Φ2.0 welding wire / S-777MXT flux is used for submerged arc welding. This type of welding method has longitudinal cracks in the center of the reverse weld seam, and the crack length is long. After enlarged inspection, intermittent longitudinal cracks are also found in the center of the front weld seam. Cracks, and most of the cracks appear immediately after welding, so the traditional welding process has thermal cracks...

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Problems solved by technology

[0002] The boiler high-temperature panel superheater is used in the boiler industry. The superheater is installed in the furnace. The main function of the superheater tube row fillet weld is heat transfer, while the traditional ultra-supercritical boiler high-temperature panel superheater SA213-T91 tube row adopts OE -S1CrMo2Φ2.0 welding wire / S-777MXT flux is used for submerged arc welding. This type of welding method has longitudinal cracks in the center of the reverse weld seam, and the crack length is long. After enlarged inspection, intermittent longitudinal cracks are also found in the center of the front weld seam. Cracks, and most of the cracks appear immediately after welding, so the traditional welding process has thermal cracks and crystallization cracks, and the thermal cracks directly affect the heat transfer coefficient of the fillet weld of the superheater. Secondly, the crystallization during the welding process The phenomenon is serious, and it is found in the actual welding process that the flat steel is thick and narrow, and the welding stress after welding cannot be adjusted by the flat steel, resulting in a large degree of weld restraint, which is the main cause of the longitudinal crack in the center of the weld. The low shape coefficient of the weld seam is also the main reason for the crack on the crystallization line in the center of the weld seam. The flat steel is narrow, two torches are close to each other during the welding process, and the fillet welds on both sides are easy to overlap after welding, and the mutual influence between the weld seams is large. The secondary main cause of longitudinal cracks in the center of the weld after welding is that the plasticity and toughness of the joint after welding with acidic flux is worse than that of the joint after welding with alkaline flux, so it is not suitable for Φ51×8T91 pipe row submerged arc welding and welding

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