The successful and efficient production of a tube or pipe is a matter of optimizing 10,000 parts, including equipment maintenance. With many moving parts in every type of mill and every piece of peripheral equipment, following the manufacturer’s recommended preventive maintenance schedule is a challenge. Photo: T&H Lemont Inc.
Editor’s note. This is the first part of a two-part series on optimizing tubing performance. Read the second part.
Manufacture of tubular products is a challenging task even under the most favorable circumstances. Factories are complex, require regular maintenance and, depending on what they produce, competition is fierce. Many metal pipe manufacturers are under intense pressure to maximize uptime in order to maximize revenue while leaving little valuable time for scheduled maintenance.
The conditions in the industry today are not the best. Material costs are ridiculously high, and partial deliveries are not uncommon. Now more than ever, pipe manufacturers need to maximize uptime and reduce scrap, and getting partial deliveries means shorter production times. Shorter runs mean more frequent changeovers, which is not an efficient use of time or labor.
“Time is of the essence these days,” says Mark Prasek, North American Tubing and Tubing Sales Manager for EFD Induction.
Conversations with industry experts about tips and strategies for getting the most out of your venture reveal some recurring themes:
Running a plant at peak efficiency means optimizing dozens of factors, most of which interact with each other, so optimizing plant performance is not always easy. A famous quote from former The Tube & Pipe Journal columnist Bud Graham gives some insight: “A pipe mill is a tool rack.” Knowing what each tool does, how it works, and how each tool interacts with others is about a third of the way to success. Making sure everything is supported and aligned is another third. The final third is dedicated to operator training programs, troubleshooting strategies and specific operating procedures unique to each pipe or pipe manufacturer.
The number one consideration for efficient plant operation has nothing to do with the plant. This raw material, getting the most out of the rolling mill, means getting the most out of every coil fed to the rolling mill. It starts with the buying decision.
coil length. “Pipe mills thrive when coils are as long as possible,” says Nelson Abbey, director of Abbey Products at Fives Bronx Inc. Working with shorter rolls means handling more roll ends. Each end of the roll requires a butt weld, and each butt weld creates a scrap.
The difficulty here is that the longest coils may sell for more, while the shorter coils may be available at a better price. A purchasing agent might want to save some money, but that’s not the point of view of people in production. Almost everyone who runs a plant will agree that the price difference must be large to compensate for the loss of production associated with the extra plant shutdown.
Another consideration, Abby says, is the capacity of the decoiler and any other restrictions at the mill entry. It may be necessary to invest in more powerful input equipment to handle larger, heavier rolls to take advantage of buying larger rolls.
Cutting is also a factor, whether cutting is done in-house or outsourced. Slitter rewinders have a maximum weight and diameter that they can handle, so an optimal match between roll and slitter rewinder is critical to maximizing productivity.
Thus, it is the interaction of four factors: the size and weight of the roll, the required width of the slitter, the productivity of the slitter and the power of the input equipment.
Roll width and condition. It goes without saying in the shop that the rolls must be the correct width and the correct size to produce the product, but mistakes do happen. Rolling mill operators can often compensate for slight under or over strip widths, but this is only a matter of degree. Close attention to the width of the slit complex is critical.
The edge condition of the steel strip is also the most important issue. According to Michael Strand, president of T&H Lemont, consistent edge performance without burrs or any other inconsistencies is critical to maintaining a consistent weld across the length of the strip. Initial winding, longitudinal unwinding and rewinding also work. Coils that are not handled with care can arc, which is a problem. The forming process, developed by rolling die engineers, starts with a flat strip, not a curved one.
instrumental considerations. “Good mold design maximizes productivity,” says Stan Green, general manager of SST Forming Roll Inc., noting that there is no single tube forming strategy, and therefore no single mold design strategy. Roller tool suppliers vary and pipe processing methods vary, so their products also vary. The yield is also different.
“The radius of the roller surface is constantly changing, so the rotational speed of the tool changes over the entire surface of the tool,” he said. Of course, the pipe passes through the mill at only one speed. Therefore, the design can affect the yield. He added that poor design wastes material when the tool is new and only gets worse as the tool wears.
For those companies that do not provide training and maintenance, developing a strategy to optimize plant performance starts with the basics.
“Regardless of the type of plant and what it produces, all plants have two things in common – operators and work procedures,” Abbey said. Operating the facility with the greatest possible consistency depends on standardized training and adherence to written procedures, he said. Inconsistency in training leads to differences in setup and troubleshooting.
To get the most out of the plant, each operator must use consistent setup and troubleshooting procedures, operator to operator and shift to shift. Any procedural differences usually involve misunderstandings, bad habits, simplifications, and workarounds. This always leads to difficulties in the effective management of the enterprise. These problems can be homegrown or occur when a trained operator is hired from a competitor but the source is irrelevant. Consistency is key, including operators that bring experience.
“It takes years to develop a pipe mill operator, and you really can’t rely on a generic, one-size-fits-all program,” Strand said. “Every company needs a training program tailored to its own plant and operations.”
“The three keys to efficient operation are machine maintenance, consumables maintenance and calibration,” said Dan Ventura, president of Ventura & Associates. “This machine has a lot of moving parts – whether it’s the mill itself or the peripherals at the inlet or outlet, the dance table or whatever – regular maintenance is important to keep it in top condition.”
Strand agreed. “It all starts with a preventive maintenance program,” he says. “This gives the best chance for a profitable operation of the plant. If a pipe manufacturer only responds to emergencies, it is out of control. It depends on the next crisis.”
“Every piece of equipment in the plant has to be adjusted,” Ventura said. “Otherwise the factories will kill each other.”
“In many cases, when rolls exceed their useful life, they harden and eventually break,” Ventura said.
“If the windrows are not kept in good condition with regular maintenance, the day will come when they will need emergency maintenance,” Ventura said. If tools were neglected, he says, two to three times more material would have to be removed to repair them than otherwise. It also takes longer and costs more.
Strand noted that investing in backup tools can help prevent emergencies. If a tool is frequently used for long runs, more spare parts will be needed than for a tool that is rarely used for short runs. The capabilities of the tool also affect the level of expectation. The ribs can break off from the ribbed tool and the welding rollers give in to the heat of the welding chamber, problems that don’t bother forming and calibrating the rollers.
“Regular maintenance is good for equipment, and proper alignment is good for the product it makes,” he said. If ignored, factory workers will spend more and more time trying to catch up. Time that could be spent on creating a high-quality product that is in demand on the market. These two factors are so important, but often overlooked or overlooked, that Ventura believes they provide the best opportunity to get the most out of a plant, maximize productivity, and minimize waste.
Ventura equates maintenance of mills and consumables with maintenance of vehicles. No one is going to drive a car tens of thousands of miles between oil changes and blow a tire. This will lead to costly repairs or accidents, also for poorly maintained plants.
Periodic checks of the tools after each launch are also necessary, he said. Inspection tools can reveal problems such as microcracks. Identifying such damage immediately after the tool is removed from the machine, rather than before it is installed for the next pass, allows more time to manufacture a replacement tool.
“Some companies have been operating normally during scheduled shutdowns,” Greene said. He knew it would be difficult to meet scheduled downtime during such times, but noted that it was very dangerous. Shipping and trucking companies are either overloaded or understaffed, or both, so deliveries are not made on time these days.
“If something breaks at the factory and you have to order a replacement, what are you going to do to get it delivered?” – he asked. Of course, air delivery is always possible, but this may increase the cost of delivery.
The maintenance of mills and rolls is not only about following the maintenance plan, but also about aligning the maintenance plan with the production plan.
Breadth and depth of experience is important in all three areas – operations, troubleshooting and maintenance. Warren Whitman, vice president of T&H Lemont’s Die and Die business unit, says companies with only one or two pipe factories for their own use usually have few people to maintain the mill and die. Even if maintenance personnel are knowledgeable, small departments have little margin of experience compared to larger maintenance departments, putting smaller employees at a disadvantage. If the company does not have an engineering department, the service department must troubleshoot and repair on its own.
According to Strand, the training of operations and maintenance employees is now more important than ever. The wave of retirements associated with the aging baby boomers means that much of the tribal knowledge that once helped companies navigate their ups and downs is being dwindled. While many pipe manufacturers can still rely on the advice and guidance of equipment suppliers, even this experience is not as great as it used to be and is dwindling.
The welding process is as important as any other process that takes place in the manufacture of a pipe or pipe, and the role of the welding machine cannot be underestimated.
Induction welding. “Today, about two-thirds of our orders are for retrofits,” Prasek said. “They usually replace old, problematic welders. Right now, throughput is the main driver.”
According to him, many people fell behind eight balls because the raw came out late. “Usually, when the material finally arrives, the welder leaves,” he said. A surprising number of pipe and pipe manufacturers even use machines based on vacuum tube technology, which means they use machines that are at least 30 years old. Knowledge in the maintenance of such machines is not great, and it is difficult to find replacement tubes themselves.
The problem for tubing and tubing manufacturers who still use them is how they age. They do not fail catastrophically, but degrade slowly. One solution is to use less welding heat and reduce the speed of the rolling mill to compensate, which can easily avoid the capital cost of investing in new equipment. This creates the illusion that everything is in order.
According to Prasek, investing in a new power source for induction welding can significantly reduce the power consumption of the facility. Some states, especially those with large populations and congested grids, offer generous discounts after purchasing energy efficient equipment. He added that the second motivation for investing in new products is the potential of new manufacturing capabilities.
“Often, a new welder is much more efficient than an old one and can save thousands of dollars by delivering more welding power without power upgrades,” Prasek said.
The alignment of the inductor and resistor is also critical. John Holderman, general manager of EHE Consumables, says that a properly sized and installed telecoil has an optimal position in relation to the welding wheel and requires proper and constant clearance around the pipe. If set incorrectly, the coil will fail prematurely.
The blocker’s function is simple – it blocks the flow of electricity, directing it to the edge of the strip – and like everything else in a rolling mill, positioning is critical, he says. The correct location is the tops of the weld, but this is not the only consideration. Installation is critical. If it is attached to a mandrel that is not strong enough, the position of the bollard may shift and it will actually pull the ID along the bottom of the pipe.
Taking advantage of trends in welding consumables, split coil concepts can have a significant impact on plant uptime.
“Large diameter mills have been using split serpentine designs for a long time,” Holderman said. “Replacing the built-in induction coil requires cutting the pipe, replacing the coil, and re-cutting it on a milling machine,” he said. The two-piece split coil design saves all that time and effort.
“They were used in large rolling mills out of necessity, but to apply this principle to small coils required some fancy engineering,” he said. Manufacturers simply have nothing to work with. “The small, two-piece reel has special hardware and a clever mount,” he said.
Regarding the impedance cooling process, pipe and pipe manufacturers have two main options: a central cooling system for the plant, or a separate dedicated water supply system, which can be costly.
“It’s best to cool the resistor with clean coolant,” Holderman said. To this end, a small investment in a special rolling mill coolant impedance filtration system can significantly increase the life of the impedance.
Coolant is commonly used on impeders, but coolant can pick up fine metal. Despite all attempts to trap small particles in the central filter or use the central magnetic system to trap them, some of them got through and got into the blocker. This is not the place for metal powder.
“They heat up in the induction field and burn through the resistor body and ferrite, causing premature failure followed by shutdown to replace the resistor,” Haldeman said. “They also build up on the telecoil and eventually cause arc damage.”
Post time: Jan-15-2023