Pipe-Tube Heating Systems With Induction

Category: Pipe and Tube Tags: induction annealing, induction heat treatment, induction heater, induction heating, induction heating coils, Induction Heating equipment, Induction Heating Machine, induction heating system, induction pipe bending, induction pipe heating, induction stress relieving, induction tube heating machine, induction tube heating system, induction welding preheating, pipe end heating, pipe heating, pipe heating system, pipe induction heater, pipe induction heating, pipe preheating, pipeline induction heating, RF heating tube machine, tube annealing machine, tube heating, tube heating system, tube induction heating

Brand: HLQ

Description

Pipe and Tube Heating Systems with Induction for Production Lines

Quick Answer

Induction pipe and tube heating systems heat the pipe wall directly with an encircling or end-heating coil. The pipe either passes through the coil on a conveyor or sits with its end inside the coil.

Range: HLQ MF-25 to MF-500 systems (25–500 kW, 0.5–30 kHz) cover pipe from Ø20 to Ø1500 mm and walls from 2 to 100 mm, up to 1250 °C.
Uses: Quench and temper, annealing, end upsetting, bending, coating cure, stress relief and weld preheat.
Sizing rule: Power = throughput × enthalpy ÷ efficiency. For example, 1 t/h of steel heated to 1000 °C needs about 290 kW. Choose a lower frequency for thick walls and a higher frequency for thin tubes.

HLQ induction pipe and tube heating system with encircling coil and roller conveyor — HLQ induction pipe heating system with an encircling coil and roller feed.

What is the Pipe and Tube Heating System with Induction?

Pipe and tube induction heating is the most energy-efficient and controllable way to apply heat during the production of tubular products. Processing pipe and tube involves drilling, threading, welding and other mechanical deformation, which may require heat treatment to harden the metal or to remove residual stresses. In addition, tube and pipe ends are often heated and then upset (formed) to increase or decrease the diameter or wall thickness, so that pipes can be joined end to end.

An HLQ system combines an IGBT medium-frequency power supply, a matched capacitor bank, water-cooled coils, pyrometers and a PLC with recipes. It can be built into a continuous line or used as an end-heating station. For an overview of all pipe heating uses, see induction pipe and tube heating applications.

Pipe heating with induction coil on a production line — Pipe heating with an induction coil on a production line.

Heating type	How it works	Used for
Through (in-line) heating	The pipe moves through one or more encircling coils	Quench and temper, annealing, coating cure, billet pre-heating
End heating	A set length of the pipe end sits in the coil	Upsetting, swage-end stress relief, tool-joint preheat
Narrow-band heating	A short heated zone moves along the pipe	Hot bending
Zone heating	A fixed band of the pipe is heated	Weld preheat, PWHT, de-bonding

Key Applications

HLQ induction pipe and tube heating systems are designed for a range of applications, including:

Application	Typical temperature	Heating type
Heat treat quench and temper of tubing and pipe	850–920 °C / 550–700 °C	Through heating
Upset processing for heat treating	850–920 °C	End heating
Pre-heating for upsetting; heating rod upsetting	1150–1250 °C	End heating
Swage-end stress relieving	550–650 °C	End heating
Preheating tool joints	200–400 °C	Zone heating
Curing and pre-heating of coatings	180–300 °C	Through heating
Swivel-joint bending; pipe bending	850–1050 °C	Narrow-band heating
De-bonding of rubber	150–250 °C	Zone heating
Continuous coiled-tube processing	Per process	Through heating
Seamless mill billet pre-heaters; seamless finishing taper re-heaters	1200–1280 °C	Through heating
Solution annealing; bright annealing (stainless)	1040–1100 °C	Through heating (protective gas for bright annealing)
Hot reduction; hybrid gas/induction lines	900–1250 °C	Through heating

Application cases

HLQ medium frequency pipe heating unit with encircling coil — Pipe heating unit: MF power supply with an encircling coil.

Induction heating for hot bending of large steel pipe — Narrow-band induction heating for hot bending. See the induction pipe bending machine.

Induction preheating of large diameter pipe before welding with flexible cable coil — Large-diameter pipe preheated with a flexible cable coil before welding.

For field welding, see induction preheating before welding for pipelines and the induction post weld heat treatment machine.

Suitable Materials

Material	Magnetic?	Typical processes	Note
Carbon and low-alloy steel pipe (API 5L, ASTM A106/A53)	Yes, below ≈ 770 °C	Q&T, normalising, bending, upsetting, coating	Very efficient to the Curie point; less efficient above it
OCTG casing and tubing (J55, N80, L80, P110)	Yes	Q&T, end upsetting, stress relief	Tight hardness bands, so pyrometer control is needed
Cr-Mo alloy pipe (P11, P22, P91)	Yes	Bending, PWHT, tempering	Respect the Ac1 limit for P91
Austenitic stainless tube (304, 316)	No	Solution and bright annealing	Bright annealing needs H₂ or N₂/H₂ atmosphere
Duplex stainless	Partly	Solution annealing	Fast quench to avoid sigma phase
Copper and brass tube	No	Annealing, brazing	Low resistivity, so higher frequency is needed
Aluminium tube	No	Annealing, coating	Low resistivity, so higher frequency is needed

Working Principle

Principle diagram of induction pipe and tube heating with encircling coil, pyrometer and skin depth by frequency — Principle diagram: encircling coil, eddy currents in the pipe wall, and skin depth by frequency.

Power conversion: An IGBT inverter converts 3-phase mains into medium-frequency current (0.5–30 kHz), tuned by a capacitor bank.
Induction: The water-cooled copper coil creates an alternating magnetic field. Eddy currents flow in the pipe wall and heat it from within.
Depth control: Frequency sets the current depth δ = 503 · √(ρ / (μr · f)). A lower frequency heats thicker walls through; a higher frequency suits thin tubes.
Temperature control: Pyrometers measure the exit temperature, and the PLC trims power or line speed to stay within ±3–5 °C.

Thermal image of an induction heated pipe end — Thermal image of an induction-heated pipe end.

Background: how induction heating works.

Skin depth of carbon steel by frequency

Frequency	Cold steel (μr ≈ 100)	Above Curie (μr = 1)	Suitable wall thickness
1 kHz	0.64 mm	17.4 mm	> 25 mm
3 kHz	0.37 mm	10.1 mm	12–25 mm
10 kHz	0.20 mm	5.5 mm	6–12 mm
30 kHz	0.12 mm	3.2 mm	3–6 mm
100 kHz	0.06 mm	1.7 mm	≤ 3 mm

Cold: ρ ≈ 1.6 × 10⁻⁷ Ω·m. Above the Curie point (≈ 770 °C): ρ ≈ 1.2 × 10⁻⁶ Ω·m.

Technical Specifications

Model	Power	Frequency	Pipe Ø	Wall	Heating length	Temperature	Cooling
MF-25	25 kW	10–30 kHz	20–100 mm	2–10 mm	100–300 mm	100–1000 °C	Water
MF-50	50 kW	5–25 kHz	50–200 mm	3–15 mm	150–500 mm	100–1100 °C	Water
MF-100	100 kW	3–20 kHz	100–400 mm	5–25 mm	200–800 mm	100–1150 °C	Water
MF-200	200 kW	1–15 kHz	200–800 mm	8–40 mm	300–1200 mm	100–1200 °C	Water
MF-500	500 kW	0.5–10 kHz	400–1500 mm	10–100 mm	500–2000 mm	100–1250 °C	Water

Performance

Parameter	Specification
Inverter efficiency	92–98 %
Coil-to-pipe efficiency	65–85 %
Overall efficiency	60–83 %
Temperature control	±3–5 °C with pyrometer feedback
Circumferential uniformity	±10–20 °C
Coil-to-pipe air gap	3–15 mm
Duty cycle	100 %, continuous operation
Power supply	380–480 V, 3-phase, 50/60 Hz
Control	PLC with HMI and programmable recipes
Cooling water	10–50 L/min, closed loop
Protection rating	IP54–IP65
Ambient temperature	−10 to +45 °C

Power for continuous through heating (steel, η 0.65)

Throughput	To 650 °C (0.11 kWh/kg)	To 1000 °C (0.19 kWh/kg)
0.5 t/h	≈ 85 kW	≈ 146 kW
1 t/h	≈ 169 kW	≈ 292 kW
2 t/h	≈ 338 kW	≈ 585 kW
5 t/h	≈ 846 kW	≈ 1462 kW

P = ṁ · Δh / η. The enthalpy values include the Curie transformation of steel.

Recommended Model Selection

Pipe and job	Recommended	Reason
Small tube Ø20–100 mm, wall ≤ 10 mm, coating or annealing	MF-25	High frequency for thin walls
Tube Ø50–200 mm, end heating or tempering	MF-50	5–25 kHz covers 3–15 mm walls
Pipe Ø100–400 mm, Q&T or bending	MF-100	Balanced power and depth
Pipe Ø200–800 mm, thick wall, upsetting	MF-200	Low frequency for through heating
Large pipe Ø400–1500 mm, billets, high throughput	MF-500 or multiple units	0.5–10 kHz, deep heating
ERW tube welding	HF solid-state welder	See the high frequency tube welding machine

Process Workflow

Induction pipe and tube heating process flow chart from loading to induction heating, quench, temper, cooling and inspection — Process flow chart for an in-line pipe and tube heating line.

Step	Action	Control point
1	Define OD, wall, material, temperature and throughput	Power and frequency sized
2	Load pipes from the rack onto the roller conveyor	Straightness, clean surface
3	Feed and centre through pinch rolls at the recipe speed	Concentric in the coil
4	Induction heating in one or more coils	Exit temperature by pyrometer
5	Process step: quench, upset, bend, coat or anneal	Process parameters
6	Second heat (tempering coil) if required	Tempering temperature
7	Cool on the cooling bed or in controlled air	Cooling rate
8	Inspect and unload; log the recipe and temperatures	Hardness, dimensions, NDT

Typical line layout

Layout diagram of an in-line pipe and tube induction heating line with conveyor, coils, quench, temper coil, chiller and PLC — Layout diagram: loading rack, conveyor, heating coils, quench, temper coil, cooling bed, chiller and PLC.

HLQ induction pipe heating machine with coil station and roller table in workshop — HLQ pipe heating machine with a coil station and roller table.

Common Problems and Solutions

Problem	Likely cause	Solution
Uneven temperature around the pipe	Pipe off-centre in the coil; ovality	Centre with guide rolls; reduce the air gap variation
Surface overheats, core stays cold	Frequency too high for the wall	Lower the frequency or add a soak zone
Power drops above ≈ 770 °C	Curie point: steel becomes non-magnetic	Use a second coil tuned for the hot stage
Hot ends or cold ends	End effect as the pipe enters and leaves the coil	Adjust speed at the ends; use butted pipes for continuous feed
Hardness scatter after Q&T	Temperature or quench variation	Closed-loop pyrometer control; check the quench flow
Coil damage	Insufficient cooling water or pipe contact	Check flow and temperature; fit coil guards
Coating defects	Wrong cure temperature or dwell time	Set the exit temperature to the coating datasheet; see induction pipeline coating heating

Engineering Selection Guide

Factor	Question to answer	Guideline
Wall thickness	How thick is the wall?	Select the frequency from the skin-depth table
Throughput	How many t/h or pieces per hour?	Size the power with P = ṁ · Δh / η
Temperature	Below or above 770 °C?	Above the Curie point, plan two stages or a lower frequency
Heated zone	Full length, end or band?	Through, end-heating or narrow-band coil
Diameter range	How many sizes?	Each coil covers a range; plan coil changes
Atmosphere	Bright surface needed?	Use a protective gas muffle for stainless bright annealing
Fluid heating	Heating the fluid inside, not the pipe?	See the induction thermal fluid pipeline heater

Advantages and Limitations

Advantages	Limitations
Heats only the pipe; no furnace losses (60–83 % overall efficiency)	Coils are matched to diameter ranges
Fast start-up, 100 % duty cycle	Higher investment than a gas furnace for low volumes
±3–5 °C control and data logging	Lower efficiency above the Curie point
Compact in-line footprint	Needs closed-loop cooling water and a strong power supply
Clean, flame-free, little scale	Bright annealing still needs protective gas

Why Choose HLQ?

Strength	What it means for you
25–500 kW MF range	One supplier from small tube to large pipe
Engineered coils	Encircling, end-heating and narrow-band designs
Line integration	Conveyors, pyrometers, quench and PLC recipes
Continuous duty	100 % duty cycle with closed-loop cooling
Application testing	Process proven on your pipe before delivery

HLQ induction pipe and tube heating system installed in a fabrication workshop — HLQ induction pipe and tube heating system in a fabrication workshop.

10 Core FAQs

1. What is an induction pipe and tube heating system?

A power supply, coil and controls that heat the pipe wall directly by electromagnetic induction, either in-line or at the pipe end.

2. Which frequency should I choose?

Choose by wall thickness: 30–100 kHz for walls up to 3 mm, 10–30 kHz for 3–6 mm, 3–10 kHz for 6–12 mm, 1–3 kHz for 12–25 mm, and 0.5–1 kHz for thicker walls.

3. How much power do I need?

P = throughput × enthalpy ÷ efficiency. For example, 1 t/h of steel heated to 1000 °C needs about 290 kW at 65 % efficiency.

4. What pipe sizes can be heated?

The standard MF-25 to MF-500 range covers Ø20–1500 mm and walls from 2 to 100 mm. Larger sizes are built to order.

5. How accurate is temperature control?

±3–5 °C with pyrometer feedback, with the PLC adjusting power or line speed.

6. Why does heating slow down above about 770 °C?

Steel loses its magnetism at the Curie point, so the skin depth grows and coupling drops. A second coil or a lower frequency handles the hot stage.

7. Can the system heat only the pipe end?

Yes. End-heating coils heat a set length for upsetting, swage-end stress relief, threading or tool-joint preheat.

8. Is protective gas required?

Only for bright annealing of stainless steel. Most other processes run in air.

9. Can the same system bend pipe?

Bending uses a narrow-band coil and a bending machine. See the induction pipe bending machine.

10. Is induction more efficient than a gas furnace?

Usually, yes. Overall efficiency is 60–83 % with no furnace wall losses, starts are instant, and only the required zone is heated.

HLQ-Pipe-Tube-Heating-Systems-Induction-Brochure