Sub-Arc Metal-Cored Wires Help Increase Production And Reduce Rework
EP Editorial Staff | September 2, 2006
Use of these wires in a company’s buildup/overlay processes is optimizing the quality of final welds on pressure vessels around the globe.
Alloy Cladding Company, LLC of Fort Myers, FL, is the world’s oldest running company in the business—the business of overlay welding and rebuilding pressure vessels used in the paper, pulp and chemical industries. True to its name, Alloy Cladding specializes in cladding or rebuilding the interior of these structures using custom-made submerged arc welding (SAW) platforms.
Because chemical and mechanical action steadily corrodes and erodes the interior of the vessels, they must be inspected annually to ensure they meet strict American Society of Mechanical Engineers (ASME) guidelines.When there’s a problem—whether it’s cracking or thinning of the interior walls— project manager, Steve Buckmeier and the Alloy Cladding team are among the first to be called.
Time to change
For many years, Alloy Cladding used SAW solid wire on the first pass of the buildup/overlay process.Unfortunately, that wire was not without its problems. Given Steve Buckmeier’s penchant for tinkering with machines, he adjusted his power sources and submerged arc platforms in hopes of optimizing the process. Eventually, however, the feeding and porosity problems caused by the solid wire began to add up—both in frustration and costs. That’s when the company began looking for a way to optimize the submerged-arc process and the quality of the final weld. The solution it discovered came in the form of sub-arc metal-cored wires.
Since Alloy Cladding switched from the 5/32 SAW solid wire to Tri-Mark® Metalloy EM12KS 1/8-diameter metalcored SAW wire from Hobart Brothers, the company has increased its deposition rates by 10 lbs. per hour, as well as reduced problems with porosity and its corresponding rework. Even better, the improved operating efficiencies have helped the company assure quality and safety for its clients, and reduced operating and labor costs in the process.
Meticulous work extends life
Alloy Cladding has pioneered its specific method of buildup/overlay welding on pressure vessels to ensure the structural integrity of these special structures in countries around the world—including the U.S., Canada, Chile,Mexico, Brazil and Australia. Each project varies in size (some pressure vessels can be 250 ft. tall) but the overall goal is the same: line the inside of the unit with new steel—one weld bead at a time—to extend the service life of the vessel and to prevent failure.
Maintenance Repair Operator (MRO) teams at the companies often perform smaller repairs that are found during the annual inspections of vessels to confirm that they are still meeting the minimum thickness and structural requirements determined by the ASME. But, when a vessel needs a complete build-up and overlay, these teams turn to Alloy Cladding. This process may be performed once every 12-20 years (depending on the pressure vessel’s application) and is used on modern and older vessels alike—some date back to the early 1900s—with the company mostly encountering repairs on wall thicknesses ranging from 3/4″ to 2″.
As a first step in the repair process, Alloy Cladding professionals inspect the inside of each pressure vessel to determine the amount of wear. According to Buckmeier, the inside often looks like it has divots and craters as a result of corrosion and erosion that has slowly eaten away at the steel. Rough areas are carbon arc gouged and small manual welding repairs are made before grinding down and grit blasting the inside of the vessel surface to prepare it for automatic welding.
The crew then assembles two welding rigs inside of the vessel, each consisting of Miller Electric’s Dimension 1000 or SR1500 power sources and an automated SAW configuration that propels each welding unit around the inside of the vessel. Once each rig is constructed, welding operators preheat the carbon steel to 300 F to prevent cracking and the welding process begins.
Switching wire switches on savings
The SAW process is similar to other welding processes in that it creates the coalescence of metals by heating them with an arc between the base metal and an electrode that is deposited into the weld. The difference is that the process does not require an external shielding gas, nor can it use a self-shielded welding wire. Instead, the arc and molten metal are submerged” and shielded by a blanket of granular, fusible material called flux.
To complete the repairs, two custom designed welding rigs sit on either side of a platform inside of the vessel. One is elevated two feet above the other, allowing each platform to create a continuous 4-ft. band around the inside of the vessel simultaneously. Every time the rig goes around the tank, it automatically indexes itself upward to lay a bead directly above the previous bead. Once each rig has reached the end of its section, the entire platform is raised up on scaffolding to lay the next 4-ft. section. The rigs repeat this process until they reach the top of the vessel and the entire structure has been built up. This process is usually carried out twice, depending on the remaining thickness of the vessel’s steel. The first pass is done using a single, Tri-Mark Metalloy EM12KS 1/8-diameter sub-arc metal-cored wire. The second pass is done using twin 1/8 309 or 312 stainless steel electrodes, depending on the vessel’s use, as a protective overlay to battle corrosion.
Solving the problem
Despite Alloy Cladding’s ingenuity with equipment, SAW solid wire never performed up to the company’s expectations. It never fed really well.We’d change the equipment around and try to do it the best we could,” explains Buckmeier. But our biggest complaint was that it was easy to get porosity.And we really prep the vessel surface. I’m not trying to run through rusty old metals. I’ve got nice clean metals and when we used sub-arc solid wire, we’d still get porosity.”
Given the stringent requirements of ASME codes, porosity is a costly defect that compromises weld integrity and leads to countless hours of rework.After discussing the complications with his local welding distributor and representatives from Hobart Brothers, Buckmeier decided to try the Metalloy EM12KS metalcored sub-arc wire in conjunction with Tri- Mark’s HPF-A95 flux.
For the work that we do,” states Buckmeier, the metal-cored sub-arc is the most forgiving welding wire we’ve ever had on our machines. It’s almost impossible to have a porosity problem with it.”
Metalloy EM12KS sub-arc wire is designed specifically for use in SAW applications. This composite metal-cored wire consists of a metal sheath and a core of various powdered materials that provides distinct advantages over Alloy Cladding’s previous solid wire, including higher deposition rates and faster travel speeds.
The sub-arc metal-cored wires also have improved Alloy Cladding’s arc starts through easier feeding and higher current densities. That’s because metal-cored wires focus the current through the outer sheath, whereas a solid wire focuses the current through its entire cross section. At equal diameter, with the same amperage, electrical stick-out and flux,Metalloy submerged arc electrodes provide higher deposition rates than SAW solid wires. Their penetration patterns are also broader than SAW solid wires, making it easier to bridge fit-up gaps; and higher current levels can be used on the root passes and thin materials without burn through.
Since making the switch to metal-cored wire, Alloy Cladding has been able to increase its voltage from 23 to 25 (at 500 amps) and run approximately 85″-90″ of welding wire per minute. Such efficiencies have increased deposition rates from 60 to 70 lbs. per hour. Interestingly, SAW metal-cored wires also have the advantage of reducing contact tip and liner wear. As a result, the company has reduced maintenance time and costs for replacing wire feeder components since switching to the Metalloy wire.
The HPF-A95 flux also has provided benefits. As an active flux, it includes components that help protect the bead from outside contaminants to help eliminate porosity in the final weld (Fig. 1.) In addition, the HPT-A95 offers more resistance to rust and mill scale. Most importantly, it helps cut down on the clean-up time required between the initial and secondary passes with the stainless steel wires.
“That’s another feature (we like),” explains Buckmeier. With some sub-arc welds, the flux gets stuck and you have to beat it off with hammers. This stuff (the HPF-A95) is selfpeeling. You just keep running and it falls out of the way.”
The finished product
Once finished, the vessels go through various tests (ultrasonic, dye-penetrant, magnetic particle, etc.) to ensure that Alloy Cladding has met ASME codes with its welds. If flaws are found, they are ground out and reworked. Since it’s begun using metal-cored wires, however, Buckmeier states that the company has far fewer flaws to deal with—approximately 24 man-hours less of rework time for every 1,000 square feet.
Equally important is the quality of the work Alloy Cladding has been able to provide to its customers. “When we finish a vessel, we quite often have added 15 to 20 years to its life,” says Buckmeier. There will be some small routine maintenance annually, but they won’t go through a total rebuild for a long time.” Summing up Alloy Cladding’s experience, Buckmeier smiles. We’ve run the same basic machinery for 50 years,” he says, I guess it’s about time we discovered this wire.” MT
Dennis Foster and Jon VanPelt are district managers with Hobart Brothers and Miller Electric, respectively. Both companies are business units of ITW. E-mail : firstname.lastname@example.org and email@example.com
Today, Hobart Brothers is still based in Troy, where it manufactures premium welding filler metals, including stick electrodes and solid and tubular (flux cored and metal cored) wires under the brands Hobart®, McKay®, Tri-Mark® and Corex®. All filler metals are sold through welding distributors and meet or exceed the specifications of the American Welding Society (AWS) and other regulatory classifications. To learn more, visit Hobartbrothers.com or www.ITW.com