Working capacity of the elbow joint

The working performance of an elbow is closely related to its stress state. Both theoretical calculations and on-site measurements of the operating stresses in pipe fittings reveal that the arc‑starting point of the elbow is particularly sensitive to external loads. Apart from internal pressure and self‑weight, the primary external loads arise during pipeline startup—namely, thermal expansion of the pipe metal, pipeline vibrations, and abnormal behavior of supports and hangers. A push‑forming machine employs a horn‑shaped mandrel or core rod that gradually widens from the tip toward the base. The forming process involves diameter expansion combined with bending, with rear support provided to maintain stability. For stainless steel pipe fittings, the blank pipe section is slipped over the mandrel, while a gantry frame secures the mandrel at the rear. A carriage positioned between them may be driven hydraulically or mechanically.

The performance of an elbow is closely related to its stress state. Both theoretical calculations and on-site measurements of the working stresses in pipe fittings reveal that the arc‑starting point of the elbow is particularly sensitive to external loads. Apart from internal pressure and self‑weight, the primary external loads arise during pipeline startup—namely, thermal expansion of the pipe metal, pipeline vibrations, and abnormal behavior of supports and hangers. A push‑forming machine employs a horn‑shaped mandrel or core rod that gradually widens from the tip toward the base. The forming process involves diameter expansion combined with bending, supported by a rear backing device. For stainless steel pipe fittings, the blank section is slipped over the mandrel, which is secured by a gantry frame at the rear. A carriage moves forward; some carriages are driven hydraulically, while others use mechanical transmission via a leadscrew. As the carriage advances, it pushes the tube along the mandrel. An induction coil surrounding the mandrel heats the tube. Once heating is complete, the carriage pushes the tube off the mandrel, yielding a finished bend. Immediately after forming, the elbow must be straightened while still hot, since improper handling can cause distortion, which is unacceptable. Moreover, because welds are present, nondestructive testing is required, and residual welding stresses necessitate heat treatment. Compared with push‑formed elbows, welded elbows involve two additional steps—nondestructive testing and heat treatment—while all other processes remain identical.

The widespread use of pipe fittings abroad

Steel prices on the international market are volatile.

The widespread use of pipe fittings abroad

Steel prices on the international market are volatile.

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