The Spiral Welded Pipe Line, End to End

Tengtian builds two classes: Φ219–820 × 3–12 mm and Φ219–1620 × 5–16 mm.

What Is a Spiral Pipe Mill?

Diameter is changed by changing the forming angle — anywhere between 39° and 80° — so one machine covers its whole band rather than needing a line per size. A spiral pipe mill — real designation Spiral Welded Pipe Equipment, forward-swinging type — is a complete line that turns coil into large-diameter welded pipe: uncoil, level, butt-weld coil to coil, edge-prepare, deliver and pre-bend, form helically over three rolls at a set angle, then weld inside and out by submerged arc and flying-cut to length.

Changing Bore Without Changing RollsThe angle range is 39 to 80 degrees, set by swinging the front bridge, and a diameter change on this line does not require a change of forming rolls.See the line →X-Ray, Hydrostatic and Ultrasonic, Station by StationOn the Φ820 grade the sequence is shorter: weld repair, X-ray, end facing, hydrostatic test, finished.See the line →What the Large-Diameter Tier AddsThree of those nine are worth expanding, because they are where this class differs from the smaller one and where most of the quotation difference sits.See the line →SSAW or HFWThe high-frequency line forms strip into a round or square shell and closes a straight seam with high-frequency induction heat and squeeze rolls.See the line →

The single most useful thing to understand about this technology is how it changes diameter. It does not change rolls. Maximum pitch is 1250 mm on the Φ820 class and 1900 mm on the Φ1620 class.

That is also why a plant needing Φ630 mm and above has no real alternative. High-frequency straight-seam welding covers Φ10–630 mm here and stops; large-diameter line pipe, water main and structural pipe above that ceiling are made by spiral submerged arc.

The line runs in nine stages, and each one has a specific thing it can get wrong — worth knowing before purchase rather than after: 1. Uncoiling (double-cone head) — a crane loads the coil, hydraulic cylinders raise the double cone heads into the coil bore, clamp it and centre it to the line, and an 11 kW main drive feeds strip into the leveller.

Cone centring that is off gives a wandering or slack coil, and the strip enters the line already displaced. 2. Clamping and levelling — a five-roll leveller straightens the strip. Feed rolls Φ210 × 1350 mm, levelling rolls Φ190 × 1350 mm, 42CrMo hardened to HRC52-58. It can run actively in step with the delivery machine or passively with the clutch disengaged.

Residual curvature here becomes forming-angle drift and edge mismatch later. 3. Shear and butt welding — a hydraulic shear (Φ320 cylinder) trims the strip ends and a submerged-arc butt-welding trolley (MZ-2000, sharing the welding power source with the inner welder) joins coil to coil so production continues across coil changes. 4.

Edge preparation — the Φ1620 class mills both edges to a bevel (Φ500 cutter head, 190 m/min, milling width 500–1250 mm, 2 × 22 kW variable-frequency climb milling); the Φ820 class uses a disc shear instead. Edge quality and width consistency decide the joint gap at the spiral seam. 5.

Delivery and guide-plate pre-bending — the delivery machine drives the whole line (planetary reducer, forged Φ360 42CrMo rolls, 2 × 15 kW), while guide plates with 42CrMo pre-bending rolls curve the strip edges before forming. Under-bending leaves a straight edge on the tube blank, and that shows up as out-of-round and mismatch at the seam. 6.

Three-roll spiral forming — the strip enters at the set angle (39°–80°) and rolls 1# to 7# bend it into a spiral tube blank at the required diameter, with external sizing holding shape. The front bridge swings to set the angle. This is the diameter-setting stage and the changeover stage at once. 7.

Inner and outer submerged-arc welding — inner and outer heads follow the spiral seam at 0.5–3 m/min, synchronised with delivery speed. Flux is dried and magnetically separated before it covers the weld zone, and recovered afterwards.

Current, voltage, travel speed and flux condition all have to stay matched, or the result is lack of penetration, slag inclusion, porosity or undercut. 8.

Flying cut-off and slag removal — a plasma cutting trolley (LGK-160 on the Φ820 class, LGK-200 on the Φ1620 class) cuts 8–12 m lengths while the mill keeps running; the pipe then passes a slag remover that cleans the inside seam. 9.

Finishing and inspection — on the Φ1620 class: slag removal, weld repair, pipe-end alignment, X-ray, hydrostatic test, off-line ultrasonic, end facing and bevelling. On the Φ820 class: weld repair, X-ray, end facing, hydrostatic.

The mill is forward-swinging, centre-located, and runs discontinuously. Forming is by three-roll bending with external sizing, which is what holds pipe shape at large diameter where thin wall wants to go out of round.

Range, Configuration and Output

Two classes. Φ219–820 mm × 3–12 mm, and Φ219–1620 mm × 5–16 mm. Two machine classes, three configuration levels, and a plant output that depends on which of each is chosen.

Pipe length 8–12 m. Single-pipe weight up to 3 t on the Φ820 class and up to 7.5 t on the Φ1620 class.

• Three configuration levels (this is where quotations differ most, and where two suppliers’ prices stop being comparable):
• Mill only — the base machine
• Mill plus finishing — slag removal, weld repair, end facing, hydrostatic test, X-ray
• Full — adds off-line ultrasonic and, on the Φ1620 class, an edge miller

Output. Roughly 62 tonnes per 8-hour shift on the Φ820 class, roughly 120 tonnes per 8-hour shift on the Φ1620 class.

Incoming strip is a stated requirement, not an assumption. Strip width 400–1050 mm (Φ820 class) or 500–1250 mm (Φ1620 class), width tolerance within ±5 mm; coil OD Φ1200–1800 mm, coil ID Φ508–760 mm, coil weight up to 15 t / 20 t. Width drift outside that window forces repeated forming-angle correction and shows up as diameter drift and mis-matched edges at the seam.

Steel grade sets the wall-thickness ceiling. A capacity table gives the maximum wall for each diameter by grade — Q235B, Q355C, L360. Grade is decided before wall thickness, not after.

• What the finished pipe is for narrows the configuration further. The line serves four downstream uses:
• Oil and gas transmission line pipe — Φ820–1620 mm produced to GB/T 9711 or API 5L, every pipe X-rayed, hydrostatically tested and ultrasonically inspected before release. A missed defect here is a claim, which is why the inspection chain is the order threshold rather than a feature.
• Urban gas and low-pressure fluid pipe — from Φ219 mm up, where weld soundness and uniform wall matter and delivery has to hold against a municipal project schedule.
• Water supply and drainage pipe — project-batch orders cut to 8–12 m. Large diameter at thin wall wants to go out of round, and external sizing is what holds it.
• Industrial structural pipe — where the grade-to-diameter-to-wall relationship has to be settled first, because the maximum wall differs by grade.

Key Parameters: Size Range, Wall Thickness, Line Speed and Welder Power Band

Key roll materials, since they decide how long the geometry holds: pressure rolls GCr15 hardened to HRC56-60; feed, levelling and pre-bending rolls 42CrMo at HRC52-58. Feed rolls Φ210 × 1350 mm, levelling rolls Φ190 × 1350 mm; the delivery machine drives the line through forged Φ360 42CrMo rolls at 2 × 15 kW.

Key bought-in components on the Φ1620 class are listed by brand so a buyer can price and check them independently: Lincoln welding power sources, Siemens PLC and motors, Delta drives, Schneider (partly CHINT) electrical components, Jiangsu Guomao cycloidal reducers, Jiangsu Tongli planetary reducers, Harbin or Wafangdian bearings, Beijing Huade hydraulic valves.

How to Choose the Right Model

Anything above Φ820 mm requires the Φ1620 class outright. Three inputs decide the class: the largest outside diameter to be sold, the heaviest wall at that diameter, and the steel grade it will be made from.

Diameter first. Below it, both classes reach the diameter and the decision moves to wall and grade — the Φ820 class stops at 12 mm wall, the Φ1620 class carries to 16 mm.

Then the inspection requirement, which is often what actually decides it. If the finished pipe must be certifiable to API SPEC 5L, that is the Φ1620 class — the Φ820 class is built against GB/T 9711 and GB/T 5037.

Then the plant itself, because a spiral line has real building requirements: workshop 32 × 18 m with a 20 t crane at 7 m hook height for the Φ820 class; 36 × 24 m with a 32 t crane at 6.5 m for the Φ1620 class. Supply 220 / 380 V 50 Hz, compressed air 0.6 MPa. Feed direction can be set left or right to suit an existing workshop.

Scope of Supply, Installation and Commissioning

Consumables deserve early attention on this technology, because spiral submerged arc consumes them continuously: welding wire and flux by tonne of steel, plasma cutting tips and milling inserts by cutting and milling volume. Scope is quoted at one of the three configuration levels above, and what sits inside each level is written out rather than implied.

Shipping is planned into the scope. Large-diameter Φ1620 lines ship as bare heavy units — forming machine, the 1200-tonne hydrostatic frame, test-bay bases and roller tables — strapped to reinforced frames with designed-in lifting points and rust-protected. Test-bay bases number 195 sets, driven roller tables 47 sets, idle roller tables 45 sets, with 45 suction units.

Installation, commissioning and operator training sit inside the after-sales scope; engineers are dispatched to site and support continues online after handover. Rolls and key wear parts are machined at the works on its own CNC equipment, which is what makes continuous roll supply possible years after handover.

Acceptance is defined rather than left open: continuous production of two different pipe sizes is the basis on which the line is signed off — not a single demonstration run at one diameter, which would prove nothing about the changeover that the whole forming-angle design exists to make possible.

One last note for plants replacing an existing spiral line rather than adding a first one: the usual reason for switching is that the incumbent line cannot produce certifiable pipe because its inspection configuration is incomplete — no X-ray, or no ultrasonic.

That is a configuration problem, and it is worth checking against the three levels above before concluding the mill itself needs replacing.

Flux drying, magnetic separation and recovery units are part of the supply scope rather than an accessory.

Spiral pipe mill with X-ray and hydrostatic test

Spiral pipe mill with ultrasonic inspection