What are the applications of straight-seam pipes?

　　 Straight-seam pipe It is a steel pipe welded in a straight, parallel fashion to its longitudinal axis. It is commonly referred to as a straight‑welded pipe or a longitudinal‑seam steel pipe. Straight pipes are manufactured by rolling long steel strips of specified dimensions into a cylindrical shape and then joining the edges with a longitudinal seam using high‑frequency welding. Pipe specifications are expressed in terms of nominal diameter and can be classified, based on wall thickness, into thin‑walled and thick‑walled types. They may also be categorized according to cross‑sectional shape, including round, square, or specially shaped pipes.

　　What are the standards and inspection procedures for straight-seam pipes?

　　Standards for straight-seam pipes: Straight pipes typically comply with GB/T 3091-2015 and GB/T 9711-2011.

　　Materials for straight-seam pipes: The materials commonly used for straight-seam pipelines include Q235A, Q235B, Q345B, 16Mn, 20#, Q345, L245, L290, X42, X46, X70, X80, 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, and 0Cr18Ni11Nb.

　　Quality inspection of straight-seam pipes: According to GB/T 3091-2015 “Welded Steel Pipes for Low‑Pressure Fluid Transport,” the pipe surface must be smooth, with no defects such as folds, cracks, delamination, or lap welds. Minor surface imperfections—such as laps, scratches, or welding irregularities—may be present, provided they do not exceed the negative wall‑thickness deviation. During welding, slight thickening of the wall and internal weld beads may occur. Mechanical property tests, flattening tests, and flaring tests must be conducted in compliance with the standard requirements. The pipe shall withstand a specified internal pressure; if necessary, a 2.5 MPa pressure test shall be performed and maintained for one minute without leakage. Eddy‑current testing may be used as an alternative to hydrostatic testing. Eddy‑current inspection is carried out in accordance with GB/T 7735-2004 “Eddy‑Current Testing Method for Steel Pipes.” In this method, the probe is mounted on a stand and positioned 3–5 mm from the weld seam; the pipe is rapidly conveyed past the probe to perform a comprehensive weld inspection. The eddy‑current signals are automatically processed and classified by the eddy‑current testing equipment, thereby achieving the inspection objective. Following inspection, the welded pipe is cut to the specified length using a flying saw and then passes through a turning lathe before being discharged. Both ends of the pipe shall be chamfered, marked with printed identifiers, and packaged in hexagonal bundles for shipment.

　　What are the applications of straight-seam pipes?

　　Seamless pipes are primarily used in municipal water supply projects, the petrochemical industry, the chemical industry, the electrical industry, agricultural irrigation, and urban construction. For liquid transport: water supply and drainage. For gas transport: coal gas, steam, and liquefied petroleum gas. For structural applications: pile‑driving pipelines, bridges, as well as pipelines for docks, roads, and building structures, among others.

　　The main manufacturing processes for straight-seam steel pipes are as follows:

　　Forging: A metalworking process that uses the reciprocating impact force of a forging hammer or the pressure of a press to shape a blank into the desired form and size.

　　Extrusion: A manufacturing process in which steel or other metals are placed in a sealed extrusion die; pressure is applied at one end, forcing the metal to flow through a predetermined die opening and forming a finished product of uniform shape and size. This process is commonly used to produce nonferrous metal materials.

　　Rolling: a pressure‑working process in which a steel billet is passed through the gap between a pair of rotating rolls of various shapes; as the rolls compress the material, its cross‑section decreases while its length increases. Drawing: a cold‑working process in which a previously rolled metal billet—such as wire, tubing, or other products—is pulled through a die opening, reducing its cross‑section and thereby shortening its length.