Definition & Manufacturing:
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Butt-weld fittings primarily refer to pipe fittings connected via welding.
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Manufacturing typically follows two paths:
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Path 1: The fitting manufacturer uses welded pipes conforming to standards as raw material. These are formed into the required shapes (e.g., elbows, tees) through cold/hot forming processes (e.g., pushing, pressing, bending). This forming process itself does not include welding operations; the welding refers to the final connection to the piping system.
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Path 2: The fitting manufacturer uses steel plates or strips. After cutting and forming (rolling, pressing), critical longitudinal or circumferential welds are performed in-house to create fitting blanks or finished products (e.g., large-diameter butt-weld elbows, reducers). This path inherently includes necessary welding operations.
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Weld Neck Flanges are a prominent type of butt-weld flange, requiring the neck to be butt-welded to the pipe.
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Heat Treatment:
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Heat treatment requirements are dictated by the specific fitting product standard (e.g., GB/T, ASME, JIS) and material specification (e.g., ASTM, GB).
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Heat treatment is NOT mandatory for all formed fittings.
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Primary objectives of heat treatment:
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Eliminate work hardening induced by the forming process.
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Relieve residual stresses.
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Improve or restore metallurgical properties altered by deformation.
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Achieve mechanical properties (e.g., strength, toughness) or corrosion resistance mandated by standards.
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Primary Types & Functions:
Elbow: Changes pipeline direction. Common angles: 45°, 90°, 180° (Return Bend).
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Tee: Facilitates fluid branching or combining. Types: Equal Tee, Reducing Tee.
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Reducer: Connects pipes of differing diameters. Types: Concentric Reducer, Eccentric Reducer.
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Cap: Welded to pipe ends to provide sealed closure.
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Cross: Connects four pipes at a single junction.
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