Sizing the Welder to the Pipe Diameter

Two points in that range are published; the rating for every other model step is sized against your actual diameter, wall and output.

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Technical Specification Table

Welder power range across the HG series: 150–1500 kW, stepped with diameter Published endpoint, smallest step: HG32, Φ10–32 mm → 150 kW Published endpoint, largest step: HG630, Φ325–630 mm → 1500 kW Welding process across the whole series: high-frequency induction welding Model steps in the series: twelve, HG32 through HG630, covering Φ10–630 mm Wall thickness across the series: 0.5–16 mm

The table shows the welder rating at the two ends of the series.

For the models in between — HG50, HG76, HG89, HG114, HG165, HG219, HG273, HG325, HG426 and HG508 — welder power is quoted per project.

Wall thickness, line speed and shift output are confirmed against your pipe size, material grade and cut length at quotation. Send us those three and we will state the figures.

Line Configuration and Scope of Supply

Upstream, the coil car and expanding-mandrel uncoiler tension the coil; a five-roller leveller flattens the strip; an automatic shear-welder joins coil to coil; and a spiral accumulator buffers strip so forming never stops for a coil change. The welder is one unit in a train of eight, and its rating only means something in the context of the units either side of it.

Downstream, a flying saw cuts to length at speed, and a PLC with variable-frequency drives ties speed, sequence timing and cut length together.

Three parts do the welding itself, and all three matter to the rating question.

• The high-frequency induction welder supplies the energy. Power is stepped with diameter, and it is the unit sized against the pipe range.
• The induction coil and impeder concentrate that energy at the seam through skin and proximity effect. They are wear parts, and their condition governs how tightly the energy stays focused; as they degrade, energy spreads, seam quality fluctuates and consumption rises.
• Post-weld cooling, matched to welding speed, stabilises the seam structure after the weld is made.

The physics behind the rating is worth one paragraph. High-frequency current does not spread evenly through the strip: skin effect drives it to the surface and proximity effect draws it towards the facing edges of the open tube, so it concentrates at the seam and heats that narrow band to welding temperature.

Squeeze rolls then press the two heated edges together and the weld is formed under pressure rather than by adding filler. Rating follows from that: more section to heat, and more metres per minute to heat it in, means more power at the coil.

The forming and sizing mill then bends flat strip progressively into an open tube, and after welding brings it to final diameter.

Size Change, Roll Wear and Running Cost

Changing pipe size changes the forming set, and on a conventional build that means a roll change; on a direct-forming square build a combined die set is adjusted by servo instead, with a roll saving above 90%. Welder rating is a capital decision, but the running cost around it is decided by three process variables and two wear parts. There is one exception: making 100 × 100 mm tube needs the upper roll on the final open stand changed.

Squeeze amount and seam alignment sit alongside them: too little or too much squeeze, or a seam that is not centred, produces weld offset, edge mismatch and burr. Post-weld cooling has to be matched to welding speed, or the seam structure is not what the weld parameters were chosen to produce.

The two wear parts are the impeder and the induction coil. Both wear according to welding hours rather than tonnage, and both are in continuous supply.

That continuous supply is what matters to an overseas buyer asking “can I still get these in three years”.

Two further consumables sit around the welding station: cooling water or emulsion, and hydraulic oil and grease. Specifications come from us; purchase is local.

A size change also affects the welding section.

The welding parameters have to be re-established afterwards — which is why parameter setting is a training requirement in its own right.

The three process variables are power, frequency and welding speed, and they govern seam fusion together rather than individually. Set them out of balance and the failure modes are specific: lack of fusion, cold welds, or burn-through — and a pipe that then fails pressure testing and inspection.

Applications and Output Examples

Buyers here measure weld pass rate first, then diameter and wall coverage, non-stop coil change, and energy and yield per tonne. Sizing a welder starts from the pipe, not from the machine, so the first step is to collect a few inputs from the buyer.

The two application families this equipment serves put different weight on those inputs.

Fluid transport pipe — carbon-steel welded pipe for oil and gas transport, municipal water and drainage, gas distribution, and chemical and heating pipework. Weld integrity is the binding constraint, so welder sizing is discussed before line speed.

Structural and scaffolding tube — square, rectangular and round sections for load-bearing steelwork, scaffolding and general machinery components. Buyers here measure corner definition and straightness, changeover efficiency, and electricity per unit. Throughput tends to lead the conversation, and welder sizing follows from the speed target.

Where the responsibility line falls matters most in welding, because that is where blame tends to land. The mill controls welding power, seam alignment and squeeze; that is the equipment side. Incoming strip grade, thickness tolerance and flatness, and the operating discipline around parameter setting, sit with the buyer.

Weld defects arising from out-of-tolerance strip are not a welder rating problem, and no rating solves them.

Two further outcomes sit on the equipment side once the welder is correctly sized, and both are worth naming because buyers often attribute them to welder power alone. Dimensional accuracy and straightness are set by sizing and straightening rather than by the weld, and incoming wall tolerance remains a buyer-side input.

Material yield of 93% or better is a line-design outcome, though achieved yield also depends on scheduling and operating practice.

Final inspection is a separate stage. In-line ultrasonic and eddy-current testing are part of the API line-pipe build; they are not standard equipment on a general HG line.

Four inputs decide the rating: target outside diameter, wall thickness, section shape, and the output the plant needs. Diameter and wall come from the finished-pipe specification; section shape matters because most model steps run round, square and rectangular; output converts into line speed, and line speed is what turns a heating problem into a power number.

Delivery, Installation and Training

Lead time is 50–90 days.

Of the five operating steps on a tube mill, welding needs the most training. Setting welder power, welding speed and squeeze, then starting continuous forming, welding and sizing while watching the process, requires professional process training rather than operator familiarisation.

The failure modes if it is done wrong — lack of fusion, burn-through, dimensional drift — are the same ones listed under running cost above. Coil loading and threading, and shear-welding a coil join in time with the accumulator, need operator training; setting a new size needs a trained change crew; cutting and collecting is routine.

After handover, support is a first reply through a single named point of contact, all-hours online support, on-site dispatch when required, and direct spare-part shipment — in the welding section, that mainly means impeders and coils.

Behind that sits an engineering team of twenty averaging twenty years each, working from an owned production base open to factory audit.

Certification: GB/T 19001-2016 / ISO 9001:2015 (quality management system, certificate No. 18524Q11269R2S). The product standard the finished pipe is made to depends on the destination market and the buyer’s specification; the equipment follows destination-market machinery-safety rules and that product standard.

Export packing is specified per item. The welder cabinet, impeders and induction coils travel in moisture-protected wooden cases with a spare-parts pack; heavy frames ship bare, braced on cradles with designated lifting points and rust protection.

High frequency welding steel

Wear Parts and Consumables