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The manufacturing processes of seamless pipes, straight seam welded pipes and spiral welded pipes

Steel pipes are very important in our production, including round pipes, square pipes, special-shaped pipes, and various other types.

Many structural products require various steel pipes, and different needs require us to use different steel pipe manufacturing processes. We can provide customers with solutions for various pipe materials, from material customization, cutting, heat treatment, cold drawing, laser cutting, etc

Seamless pipe, straight seam welded pipe, and spiral welded pipe are the three main types of steel pipes, and their characteristics and manufacturing processes determine their different application fields.

Let's take a look at how these different types of steel pipes are produced.

Comprehensive manufacturing of steel throughout the entire process

1. Seamless steel pipe

Core feature: There are no seams along the entire circumference. It is made by piercing solid steel billets.

Seamless pipe manufacturing (Mannesmann rolling method)

Seamless pipe manufacturing (hot extrusion - hot hollow forging)

Main manufacturing process:

1. 1Hot rolling (hot extrusion) process (main method):

Step: Round solid tube blank → Heating to plastic state in heating furnace → Perforation by perforating machine (forming hollow tube) → Rolling by pipe rolling machine (extension, thinning, sizing) → Finishing by sizing machine/reducing machine → Cooling → Straightening → Cutting → Inspection.

Representative processes: Mannesmann perforation method, oblique rolling perforation, etc.

Features: High production efficiency, capable of producing large-diameter thick walled pipes, is the mainstream process.

1.2. Cold drawing (cold rolling) process:

Steps: Using hot-rolled tubes as billets → acid washing to remove oxide scale → phosphating/saponification lubrication → cold drawing machine through mold drawing or cold rolling machine rolling → heat treatment (to eliminate internal stress) → straightening → finishing.

Features: High dimensional accuracy, good surface finish, superior mechanical properties, but high production cost and low output. Commonly used for small diameter, precision, or thin-walled pipes.

Advantages:

Uniform mechanical properties: no welds, uniform organization in the circumferential and longitudinal directions, strong pressure bearing capacity.

High pressure resistance and corrosion resistance: suitable for high pressure, extreme temperature, and corrosive environments (such as boiler pipes and hydraulic cylinder barrels).

Diverse cross-sectional shapes: can produce complex cross-sections such as circular, square, elliptical, etc.

Disadvantages:

High production costs: complex process flow, high energy consumption, and high metal loss (low yield).

Difficulty in controlling the uniformity of wall thickness: especially for thick walled pipes, there may be eccentricity and surface defects on the inner wall.

Limited size specifications: Due to limitations in raw materials and processing equipment, the length and maximum diameter of a single piece (usually ≤ Φ 660mm) are limited.

Typical applications:

Petrochemical (high temperature and high pressure pipelines), power plant boilers, hydraulic systems, bearing sleeves, gun barrels/barrels, high-precision mechanical structural components.

2. Straight seam welded pipe

Core feature: The weld seam is a straight line parallel to the axis of the steel pipe. Made by welding rolled steel plates or strips.

Resistance welded pipe

Thermal resistance welded pipe

Main manufacturing process:

2.1. Straight seam high-frequency welded pipe:

Process: Continuously forming the steel strip (coil) → utilizing the skin effect and proximity effect of high-frequency current to instantly heat the edge of the weld to a molten state → achieving solid-state welding under the pressure of the extrusion roller (without the need for welding wire).

Features: Fast speed, high efficiency, and low cost. The heat affected zone of the weld seam is small.

Common standards: ASTM A500 (for structural purposes), JIS G3444 (for mechanical structures).

2.2 Straight seam submerged arc welded pipe:

workmanship

JCOE forming: First, pre bend the steel plate edge, then gradually form it into a cylinder through J-shaped, C-shaped, and O-shaped multi-step compression molds, and finally expand the diameter.

UOE forming: First, pre bend the edge of the steel plate, then press it into a U shape, and then press it into an O shape. After welding, expand the diameter. Large equipment investment, suitable for large-scale production.

Welding: Submerged arc welding is used inside and outside the formed straight seam (the arc burns under the flux layer, with high automation and good weld quality).

Features: It can produce steel pipes with large diameters (up to Φ 1620mm or more) and large wall thicknesses, and has strong pressure bearing capacity.

Typical applications:

High frequency welded pipes: building structures (scaffolding), furniture, low-pressure fluid transportation, automotive transmission shaft pipes.

Submerged arc welded pipes: oil and gas long-distance pipelines, offshore platform structural pipes, urban pipeline networks, wind power towers.

Advantages:

High production efficiency and low cost: especially for high-frequency welded pipes, continuous high-speed production can be achieved.

High dimensional accuracy and good surface quality: using pre processed boards, uniform wall thickness, and good appearance.

Strong flexibility: Steel pipes of different diameters can be produced by changing the width of the raw materials.

Disadvantages:

There is a longitudinal weld seam: the weld seam is a potential weak link that requires extremely high welding quality.

Diameter limited by plate width: The diameter of steel pipes generally cannot exceed π times the width of the steel plate (due to equipment limitations).

3.Spiral welded pipe

Core feature: The weld seam is in a spiral shape surrounding the pipe body. Also made of rolled and welded steel plates/strips.

Argon arc welded pipes and pipes (SAWH pipes produced by spiral process)

Main manufacturing process:

Forming and Welding:

Continuously roll a steel strip (roll) of a certain width at a specific helix angle (forming angle) to form a tube.

During the forming process, double-sided submerged arc welding technology is used to weld the inner and outer spiral seams.

By changing the width and helix angle of the steel strip, steel pipes of different diameters can be produced using the same width of steel strip.

Subsequent processing: cutting to length, weld inspection, hydrostatic testing, expansion (optional), etc.

Advantages:

Multiple diameters of steel pipes can be produced using the same width of strip steel, with extremely high flexibility.

Weld seam avoids the direction of principal stress: The spiral weld seam forms a certain angle with the direction of principal stress, so that the bearing capacity of the pipe body in that direction is relatively balanced.

Weld defects are not easily penetrated and extended: the spiral shape makes the crack propagation path longer.

The equipment investment is relatively low, suitable for producing medium to large diameter pipes.

Disadvantages:

Weld seam length: 30% to 100% longer than straight seam pipes, which increases welding workload and instability factors.

The dimensional accuracy and geometric shape (roundness, straightness) are usually inferior to straight seam welded pipes.

High internal stress: The internal stress generated during the forming and welding processes is more complex.

The production speed is relatively slow.

Typical applications:

Low pressure fluid transportation (water, gas), pile pipes, pipe piles, structural supports (especially large diameter thin-walled), and some onshore oil and gas transportation.