Faster, more efficient high-frequency welding
High-frequency (HF) welding is how most steel tube and pipe is made: strip is formed into a round, an induction coil heats the open seam, and pressure rolls forge the edges together. The process is fast and continuous, but it is energy intensive, and the heating pattern at the weld seam depends on how well the magnetic field is controlled.
Fluxtrol’s soft magnetic composite (SMC) materials give engineers that control. In HF welding, the place they matter most is the impeder, the magnetic core inside the tube. For a deep dive on the impeder product, geometry and cooling, see our SMC impeder cores page . This page covers the welding process and where SMCs fit.
How HF tube and seam welding works
A metal strip is formed into a tubular shape, leaving a narrow gap between its edges. An induction coil generates a high-frequency electromagnetic field that heats those edges to welding temperature. Pressure rolls force the heated edges together, creating a solid longitudinal seam.
Because heat is generated directly in the material, induction welding offers:
- High production speeds for continuous manufacturing
- Heating focused along the weld seam
- Energy-efficient operation with little wasted heat
- Consistent weld quality and reduced scrap
- Easy integration into automated tube mill lines
The challenge: keeping current on the weld edges
Efficiency depends on how induced current flows in the tube. If too much current travels along the inside diameter (ID) instead of the weld edges, energy is wasted and heating becomes less efficient. In some cases, poor current distribution also causes weld quality problems.
The impeder limits that ID current. As solid-state IGBT power supplies make more power available, and as demand grows for lower-cost, higher strength-to-weight tube, the magnetic loading on the impeder keeps rising.
Why ferrite impeders hit a limit
Traditional impeders are made of ferrite, which has a low saturation flux density. Under heavy loading it saturates, and a saturated impeder lets more current flow on the tube ID. That means lower process efficiency and weld quality, and in some cases an inability to form a proper weld.
Ferrite struggles most in small-diameter tubing and thick-wall sections. Ferrite impeders also wear out quickly, so more frequent replacement slows production and adds cost.
How SMC impeders increase line speed
Fluxtrol SMCs offer higher saturation flux density than ferrite, so they hold effective magnetic control under demanding conditions. By guiding flux and improving current distribution, they put more of the heating energy where the weld forms. Fluxtrol’s research and field work report:
- Lower energy use at the same line speed
- Higher power density in the weld vee, supporting faster production
- Fewer impeder replacements and less unplanned downtime
- Stable weld conditions across tube sizes, since SMCs can be machined into many shapes
Fluxtrol’s December 2025 presentation, summarized in the newsletter, cites more than 30% lower welding current and nearly 40% lower welding power at the same line speed with maintained weld quality.
Where SMC impeders pay off most
Fluxtrol sees the best opportunities in:
- Small-diameter, heavy-walled steel tubes
- Small-tube lines where the welder is the bottleneck and the impeder is saturating
- Lines where impeders frequently fail from mechanical impact
- Designs with metallic components inside the impeder
- Applications with very short impeder life
Designing and validating SMC impeders
SMCs generate more heat than ferrite at high field levels, so the cooling water available must be balanced against magnetic loading. Fluxtrol builds this into the design workflow: 3D electromagnetic and 2D coupled thermal models predict current distribution and temperature, and physical test stands define the loading and cooling conditions a core can survive. A 2026 paper in MDPI Applied Sciences extends this into an off-line validation method, so new impeder designs can be assessed without interrupting production. See the technical library for the papers, and our simulation services .
Choosing a Fluxtrol grade
Fluxtrol A offers the highest permeability and lowest losses at low to intermediate frequencies in its favorable direction. Fluxtrol 100 has the highest thermal conductivity and saturation flux density in the family, with much less anisotropy, which helps with heat removal from the core. Fluxtrol 50 performs well over a wide frequency range. Fluxtrol’s customer trials above used Fluxtrol A, and the off-line validation study analyzed a Fluxtrol 50 impeder. Final grade selection depends on tube size, welder power and cooling, so it is made with Fluxtrol engineers during design.
Get started
If you run an HF welding line and want higher line speed, lower energy use or longer impeder life, contact Fluxtrol . To buy SMC stock, see ordering .
Fluxtrol SMCs for high-frequency tube welding
Field trials and research on SMC impeders
Prinz & Co. GmbH Stahlrohre: 15 mm steel tubing
Prinz & Co. in Germany compared ferrite and SMC impeders on 15 mm steel tube at the same line speed. Fluxtrol reports that the SMC impeders cut energy use and greatly extended impeder life, which reduced changeover time and scrap.
- 40% energy savings
- 5x greater impeder life
- 4-5x reduction in changeover time and scrap costs
- 87 tons of CO2 emissions prevented
Sartid Fahop d.o.o.: larger, thicker tube
Fahop in Serbia tested Fluxtrol A impeders against TDK ferrite and local impeders on 21-27 mm OD steel tube with a 2.6 mm wall. The SMC impeders outperformed in every case, at each line speed tested.
- 30-50% energy savings
- 5x longer impeder life
Simulation: ferrite vs. SMC impeders
A COMPEL paper modeled tube welding in 2D and 3D to compare impeder materials. Simulation results suggested upwards of 25 percent system power savings with an SMC impeder instead of ferrite.
- 3D current distribution along the weld vee
- 2D coupled electromagnetic-thermal heat-affected-zone models
Validating impeders off-line
Fluxtrol and university partners published a method that pairs 3D electromagnetic-thermal modeling with test-stand work, so SMC impeder designs and cooling can be checked without a live mill trial.
- Identified a thermal hotspot in a Fluxtrol 50 impeder near the inductor position
- Reduces the need for costly industrial testing