Requirements for Large-diameter Welded Flange
First, the level and technical requirements of large-diameter welded flange should comply with the relevant requirements of JB4726-4728.
1. Grade Ⅰ forging is allowed to use in carbon steel forgings and austenitic stainless steel forgings with nominal pressure among 0.25PM to 1.0MPa.
2. Forging, whose nominal pressure is among 1.6MPa to 6.3MPa, should comply with the requirements of grade Ⅱor above grade Ⅱ forging.
3. Meet one of the following circumstances, it should comply with the requirements of grade Ⅲ forging:
(1) Nominal pressure (PN)≥10.0MPa - flange forging;
(2) Nominal pressure (PN)> 4.0MPa - chromium molybdenum steel forging;
(3) Nominal pressure (PN)> 1.6MPa and working temperature≤-20 degrees - Celsius ferritic steel forging.
Second, usually with forging and rolling technology, large-diameter welded flange needs to meet these following requirements when using steel plate or profile steel as the material.
1. There should be non-hierarchical defect for welded flange after ultrasonic flaw detection.
2. Cutting steel strips along the rolling direction and steel plate is not allowed to directly be machined into welded neck flange;
3. Use full penetration welds to do the connection of ring;
4. After welding, the ring should do heat treatment and 100% ray or ultrasonic inspection, radiographic inspection.
Third. For large-diameter welded flange, the outer slope of its neck shall not exceed 7 degree.
Technical parameters of large diameter welded flange should be strictly controlled during the production and welding so that to ensure its valve can be fully played.