Myths and Facts of Seamed vs. Seamless Flux Cored Wires
By Neil Farrow, Global Product Manager – Cored Wires, ESAB | April 12, 2022
ESAB introduced gas-shielded flux cored wires in 1957 and we have more experience than anyone else in the world in developing and manufacturing electrodes.
Flux cored wires come in seamed or seamless versions, and ESAB offers both. In recent years, some manufacturers of seamless wires have propagated myths about seamed vs. seamless wires. This article sets the record straight, then illustrates how ESAB seamed wires provide increased deposition rate of up to 20% and superior low temperature toughness when compared with some seamless types
The traditional cored wire manufacturing process starts by slitting sheet steel into strips and feeding the strip into a series of rollers that bend the strip into a U-shape. As the strip moves down the line, the core is filled with flux (a mixture of alloys and deoxidizers). Closing rolls form the strip into a tube and tightly compress the granular core material. Drawing dies and reduction rolls then reduce the tubular wire to its final diameter.
Seamless wires are produced a few different ways. Some competitive manufacturers fold an empty strip and use high-frequency or laser welding to form a tube, anneal it and draw it to filling diameter. They then pack the tube with flux, anneal it a second time, draw it to final diameter and add a copper coating.
There is some mis-leading information with regards to the technical differences between seamed and seamless which needs to be clarified.
Myth #1: Seamless wires have superior resistance to moisture pick up.
There is no dispute that seamless wires combat moisture absorption in extremely humid environments (e.g, Dubai, Singapore, Texas). Even after extended exposure, low hydrogen seamless wires retain their properties.
However, there’s also no disputing that all offshore grades of flux cored wire stay below the lowest EN ISO classification (H5) 5ml, of diffusible hydrogen per 100g of deposited weld metal after 14 days exposure at 20ºC and 80% relative humidity. Note that raw wire components can be specially processed to either not absorb moisture or to pick it up at a lower rate. The results? As the tests below prove, it doesn’t matter whether the wire is seamed or seamless when it comes to moisture pick up — all good offshore cored wires will maintain an EN ISO H5 designation if they are used within 14 days! of opening the package.
Myth #2: Seamless wires don’t require special storage.
In a typical industrial application, a manual welder will deposit about 6 kg of wire per day, thus consuming a 16 kg spool of anywhere in about two-and-a-half to three days. The storage issue is relatively moot because all offshore grades maintain H5 properties for 14 days.
For unopened spools of wire, as long as the packaging remains intact, wire integrity is not an issue. After more than 30 years of experience with products such as FILARC PZ6113 (E71) and FILARC PZ6138 (E81), ESAB can confidently report that there have been no issues with diffusible hydrogen pick up when users adhere to proper procedures.
If the wire is not used for several days, such as over the weekend, wire manufacturers recommend removing the wire from the feeder and storing it in a dry location. As a related side note, ESAB’s RobustFeed enclosed (IP54 rated) wire feeder comes with an optional built-in heater kit to drive off moisture, further preserving wire integrity during use.
Myth #3: Seamed flux cored wires tend to suffer more from hydrogen-induced cracking.
One claim is that moisture and impurities from drawing lubricants can be extruded onto the seamed electrode and collect in the weld pool, leading to more instances of hydrogen-induced cracking with seamed wire. For any quality flux cored wire, this claim is simply outrageous.
Approval from such respected bodies as ABS, Lloyds, BV, DNV, and VdTUV ensure conformance to EN ISO and SFA/AWS standards. If the wire carries an H8, H5 of H4 designation, users can be assured that it will provide matching low hydrogen performance upon opening a sealed package ESAB’s process lubricants have been developed to contain minimal levels of hydrocarbon, therefore minimizing hydrogen contribution. Further, flux cored wire undergoes rigorous third-party evaluation.
Myth #4: The copper coating on seamless wire provides better corrosion protection.
As one of the highest volume manufacturers of premium electrodes, we know that coated and non-coated wires eventually corrode when exposed. All the copper coating does is hide the rust because of their similar colors. If the wire shows rust, it means you’re not storing it properly.
The truth is that a copper coating was originally applied to ensure good current transfer between the wire and the contact tip and not — as is often claimed — to reduce tip wear or protect against rust. Since current transfer determines a large part of the actual feeding force needed, the copper coating primarily enhances wire feedability.
However, this benefit comes with a tradeoff. The copper coating flakes off during feeding and clogs the gun liner and contact tip. If too much debris clogs in the liner (because it is not cleaned or changed regularly), increased drag on the wire may cause erratic feeding. Build-up of flakes in a contact tip can also lead to micro-arcing, an erratic arc and burnback of the wire to the contact tip.
ESAB ensures excellent feedability of its non-copper coated wires with the use of a sophisticated lubrication system during wire manufacturing. To evaluate its feeding performance and related variables, ESAB encourages fabricators to conduct their own side-by-side evaluations.
Fact #1: ESAB seamed flux cored wires improve productivity.
To protect the flux during the sealing process, seamless wires require a thicker sheath. Thus, for a given wire diameter, seamed wires have a higher fill ratio. Because the alloys inside a tubular wire contribute more to deposition rates than the sheath, seamed wires from ESAB, such as FILARC PZ6113, improve productivity compared to a seamless equivalent.
In addition, the welding current concentrates in the sheath because the solid metal strip conducts electricity better than the powdered core. A thinner sheath concentrates the current density in a smaller area, so seamed wires have faster burn-off and higher deposition rates.
In fact, head-to-head tests prove that using a seamless wire means sacrificing productivity — by up to 20% in some cases.
To illustrate the real-world benefit of using seamed flux cored wires, ESAB conducted side by side tests welding a 20 mm plate (butt joint with 5 mm root gap and 60-degree included angle) in the vertical up position using E71 and E81 seamed and seamless wires.
A seamed wire filled the joint in seven passes. Because of its greater deposition rate, the seamless wire required nine passes. On a 1-meter weld made by hand, the seamed wire reduced arc-on time by 15 minutes and yielded a total production cost savings of 11%. If the calculation had been made with a 5-meter weld and a welding tractor, the savings would amount to 29%.
Fact #2: ESAB seamed flux cored wires offer superior low-temperature toughness.
To finally drive the point home about the benefits of seamed wire, the deposition rate tests also evaluated mechanical properties. They revealed that competitive seamless wires cannot handle higher heat levels because their Charpy V-notch toughness suffers significantly. Thus, they can’t compensate for lower deposition rate with higher parameters.
Seamed wires can be more operator friendly.
Concentrating the welding current in a thinner sheath (coupled with a good formulation) yields a more “forgiving” wire. A wire is said to be forgiving if the operator can obtain good results:
• Running at both the low and high end of the operating ranges.
• Welding out of position using a higher top-end current level.
• Welding at the high end to maximize travel speeds.
• Running at the low end but still have enough arc energy to prevent spatter.
ESAB offers a broad portfolio of thin sheath wires that have earned a reputation as the most forgiving wires in the industry.
In these side-by-side comparisons, we have demonstrated ESAB seamed wires meet the same H5 low hydrogen standards over a 14-day period, offer greater deposition rates and superior mechanical properties.