Flat oval pipes

Welded steel pipe is a seamed steel product manufactured by bending steel strip or steel plate into round, square or other shapes and then welding. Its raw materials are steel sheets or strips. With the development of strip rolling, welding and inspection technology, welded pipes have richer specifications and more reliable quality.

Nickel and chromium are key elements for anti-corrosion performance. Higher nickel content provides stronger resistance against acid environments such as sulfuric acid and hydrochloric acid. Adding chromium alone can also effectively prevent corrosion.

Poor edge condition of steel strip, irregular shape and dimensional deviation at the head and tail of uncut steel strip will lead to hard bending of the strip and further cause weld misalignment. This defect may result in product downgrade.

General technical requirements and inspection rules follow GB3092 Welded Steel Pipes for Low-Pressure Fluid Transmission. Hydrostatic test complies with relevant pressure regulations, and eddy current flaw detection is implemented according to GB7735 Steel Tube Eddy Current Flaw Detection Inspection Method.

Defects like folds, cracks, delamination and lap welding are strictly prohibited. Minor scratches, weld misalignment, burns and scars that do not exceed wall thickness negative deviation are acceptable. Wall thickening and inner weld beads at welding seams are also permitted.

Welded pipes shall undergo mechanical property test, flattening test and flaring test. They must withstand a 2.5Mpa hydrostatic pressure test for 1 minute without leakage. Eddy current flaw detection can be used as an alternative to hydrostatic test.

Qualified pipes are cut to fixed length by flying saw, then transported via turning frame. Both pipe ends are chamfered and flattened, marked clearly, and finally bundled into hexagonal bundles for delivery.

The weld seam of straight seam steel pipe is parallel to the pipe longitudinal direction. It can adopt narrow blanks to produce large-diameter pipes, and the same-width blanks can make pipes of different diameters. Its disadvantage is longer weld seam and lower production efficiency compared with spiral welded pipe.

There are four mainstream processing methods: Forging, Extrusion, Rolling and Steel Drawing. Forging uses impact or pressure to shape steel; Extrusion is widely used for non-ferrous metal pipes; Rolling reduces cross-section by roller compression; Steel Drawing is mainly applied to cold working to narrow pipe diameter and extend length.

Surface quenching and tempering generally adopt induction heating or flame heating. Local quenching can also be realized by induction heating for parts requiring partial high hardness.

Vickers hardness tester is commonly used. Rockwell hardness tester is also available: use HRA scale when hardened layer thickness is 0.4-0.8mm, and HRC scale when thickness exceeds 0.8mm. For shallow hardened layers, superficial Rockwell hardness tester with HRN scale is recommended.

Yes. Vickers, Rockwell and superficial Rockwell hardness values can be converted to one another. Corresponding conversion tables are provided in ISO, ASTM and GB/T standards.