Welding of pressure vessel nozzles and reinforcement rings

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The key elements in the design of welded structures are fillet welds and lap welds, which are the main methods used to connect pipes to shells and reinforcement rings; the structural design of these welds has a direct impact on the safety performance of the equipment. During design, factors such as medium properties, operating pressure, temperature conditions, and material characteristics must be taken into account comprehensively; particular attention should be paid to key parameters such as groove shape and weld penetration. For small-diameter nozzles of medium and low-pressure vessels, the basic structural form of the plug-type nozzle welding technique is typically a plug-type design with a gap control of ≤3 mm. Typical applications include: single-sided welding without grooves (suitable for non-reinforcement applications); double-sided welding without grooves (providing both sealing and reinforcement functions); fully penetrated structures with single-sided grooves (suitable for low-temperature conditions). For thick-walled containers with large-diameter nozzles in special operating conditions, a U-shaped groove design is recommended: the groove angle ranges from 45° to 50°; a single-sided groove ensures weldability; the pipe ends should have rounded transitions (with R≤δ/4 and ≤19 mm). Key points regarding the welding process for reinforcement rings include ensuring triple sealing: an inner groove with a large gap and a small angle, a root penetration layer, and an outer stepped lap weld. Quality verification methods include airtightness testing by injecting compressed air at 0.4–0.5 MPa through M10 test holes, as well as soap solution leak detection for simultaneous inspection of inner and outer welds. After testing, threaded plugs with sealant are used for sealing. Key parameter specifications are as follows: the stacking height should be ≥1/2 of the nozzle wall thickness and ≥6 mm; the lap welding height should be δ, or 0.7δ if δ > 8 mm; the testing pressure should be 0.4–0.5 MPa of compressed air; the radius of curvature should be ≤δ/4 and ≤19 mm. Practical recommendations include drawing detailed welding diagrams for critical joints, specifying heat treatment requirements when welding different steel types, using overall reinforcement structures in environments subject to fatigue, and being careful to avoid crevice corrosion in corrosive environments