When it comes to pre-and post-weld heat-treating, many fabricators see it as a choice between resistance heating and flame heating or between ceramic heating elements and “weed burners” (flame torches). However, a leading provider of material and O.E.M. replacement parts for the nuclear power industry recently put away their weed burners in favor of two Miller ProHeat™ 35 Induction Heating Systems.
These systems induce heat electromagnetically and can bring a part to temperature up to four times quicker than by resistance or flame heat. With the ProHeat 35, induction coils are positioned on or near the part to be heated while thermocouples monitor the process and provide accurate, minute-by-minute recordings of the temperature. The induction coils remain cool.
By switching to the ProHeat 35, Energy Steel & Supply Co., Lapeer, Michigan:
• Eliminated the safety concerns with using flame or resistance heat, including reducing exposure to hot heating elements or open flames, as well as reducing the need to store flammable materials.
• Saved $400 to $800 per day in propylene and unproductive labor costs lost to waiting for a part to get to temperature or by using a skilled welder to do his own pre-heating. Combined with savings from perform
ing post-weld heat treatment in-house, the new machines quickly paid for themselves.
• Brings parts to temperature up to 400 percent quicker, allowing the company to better meet customer deadlines while keeping highly skilled welders doing what they do best: weld. In addition, they can maintain the preheat temperature for days or weeks, eliminating the need to repeatedly heat and cool a part, which could place unnecessary stress on the component.
• Eliminated the need for shipping multi-ton components to a post-weld heat-treating facility, saving transport and facility rental costs. Since a QA specialist no longer needs to travel with the component to monitor the heat-treating, it also saved significant labor costs.
• Made it easier to document that components meet the stringent QA standards required by the nuclear industry by being able to reach and maintain the pre-weld and post-weld temperatures and provide verification throughout the heating cycle.
Carving a Niche at the Top
“The nuclear power plants that were built 30 years ago don’t have spare parts lying on the shelf. When they need a replacement part, it needs to be fabricated from scratch. That’s when they turn to us,” says Patrick Siwa, fabrication department foreman, Energy Steel & Supply Co. (energysteel.com).
These components are often replaced during a scheduled shut down, a time when the plant goes off the grid and purchases power from another supplier. While missed deadlines can be very costly, there is absolutely no room for error, no sacrifice of quality for speed, no cutting corners. The standards and dedication to quality assurance, as well as the level of scrutiny, are unbelievably high. Lives are at stake.Of the few companies willing or able to take on the challenge of supplying material and O.E.M.-replacement parts to the industry, Energy Steel & Supply Co. has risen to the top.
Michael Mitchell founded the company in 1982 as a broker of raw steel. In 1996, with its increased knowledge of ASME codes and in response to an increased need for nuclear-qualified suppliers, the company decided to focus its efforts in that area. By 1998, the company expanded its capabilities and evolved into a value added supplier, having the capability to weld to nuclear code requirements and supply machined products.
In 2003, Lisa Rice (Michael Mitchell’s daughter) purchased the company, and under her leadership the company has continued to grow and expand its capabilities, becoming one of the top manufacturers of O.E.M. replacement parts to the nuclear power industry. The company is ASME accredited — most of its work falls under the requirements of ASME Sections III and IX — and holds the N, NPT, NS, and U Code Symbol Stamp and Certificates of Authorizations. It is also accredited by The National Board of Boilers and Pressure Vessel Inspectors and has been awarded the R Code Symbol Stamp and Certificate of Authorization. The company focuses on parts and components related to the safe operation and shutdown of nuclear facilities. Few other companies can equal Energy Steel’s wide range of services, from material supply to welding and machining, or can equal its expedited services.
“We take on the jobs that other companies won’t,” says Siwa. “When contractors call us, they know that they’ll get the highest quality product, documented under the most comprehensive QA program in the industry, and they’ll get it on time. Our people give up vacations and work on holidays to get a rush job out the door.”
One of the reasons Energy Steel has risen to the top is the forward-thinking Rice, who encourages her team to “not be afraid of change.” As an example, when the company recently moved into a new facility, Rice made sure the facility and its grounds could easily be expanded as the demand for nuclear energy and her company’s services grew. And with her support, Siwa was able to put away the flame torches used for heat-treating in exchange for two Miller ProHeat 35 induction heating systems. This change decreased consumable costs while increasing productivity, safety and quality assurance control.
An induction heating system, such as the ProHeat™ 35, induces heat electromagnetically in a metal part rather than by using a heating element to conduct heat, as does resistance heating, or an open flame. Induction heating systems employ non-contact heating. With induction heating, heat is induced in the part by placing it in a high-frequency magnetic field created by the induction heating coils. The induction coils can rest on or near the part and do not heat up themselves.
The magnetic field creates eddy currents inside the part, exciting the part's molecules and generating heat. Because heating occurs slightly below the metal surface, no heat is wasted.
“What really sold us on the ProHeat,” says Siwa, “is the person who came to demonstrate it wrapped the blanket around the pipe and brought it up to temperature in 15 minutes, something that would have taken flame torches an hour to do. Once the unit was switched off, the coils were cool enough to be removed by hand.”
Prior to adapting the ProHeat induction heating systems, Energy Steel used weed burners, wands with open flames fueled by propylene. A direct comparison between the two systems is difficult, since the ProHeat allows Energy Steel to do much larger projects than before, but Siwa attempted to put it into perspective.
“Prior to using the ProHeat, welding on the discharge head (see Fig. 1), would have taken three people,” Siwa says. “Two people with flame torches would hold the pre-heat temperature while the other guy welds. Then the welder would back away and the other guys would keep it warm. If those are contract workers running the flame torches, it’s costing between $13 and $15 an hour each.”
At those prices, it would have cost $208 to $240 per day just for the contract workers; however, this is a conservative amount and doesn’t include the time to reach the preheat temperature. Either the contractor workers have to start two hours before the welder arrives, or the welder has to wait until the part is brought up to temperature.
“On one project, the welders did their own preheating,” Siwa says. “So, instead of welding the whole time they’re here, they would have to stop, heat the joint and then continue welding. On big jobs, we could have 10 people with flame torches heating up a part. Since switching to the ProHeat, I no longer need workers for preheating and my welders can concentrate on welding. Plus, the ProHeat can bring a large part to temperature about four times faster than with a weed or burner.”
The costs of a highly skilled welder not welding quickly add up—almost as quickly as the costs of the propylene. At $70 per bottle, a company could go through between two and eight bottles per shift ($140 to $560).
As an example of how induction heating has changed the workflow, Energy Steel recently began work on a hot-leg for a steam generator. When finished, it will carry steam at 12,000 psi from the generator. Prior to cladding with 308L and 309L stainless steel, two plates, 4-in. x 96-in. x 120-in. were welded back to back to cut down on warpage. The Energy Steel team laid the induction cables in a circular pattern on top of a plywood platform. The coils were then covered by 1 inch of insulation to protect the cables from the heat given off by the plates. The plates rested on stops just above the insulation to prevent damage to the cables from the weight. While the company’s prototype submerged arc welder laid down a 60mm strip of cladding on one side, the ProHeat maintained heat from the other side.
“We used the ProHeat to heat up that eight inches of metal to 250 degrees (F) and hold it there continuously for a week,” Siwa says. “If we had to do that with flame torches, it would have taken four to six weeks and we would have gone through four or six bottles of propylene a day. Plus, every time we flipped the plates, we’d add another hour of preheating to our time (using four flame torches) before we could start welding again. Without the ProHeat, I would have either had to have somebody keeping it hot with flame torches during the night so we could start welding right away in the morning, or we would have been down two or three hours each day warming it back up again ”
The Savings Heat Up
The cost of four welders using four bottles of propylene a day for six weeks is enough to pay for a ProHeat system. But that’s only half of the savings. The other half comes in post-weld heat-treating. Prior to using the ProHeat, Energy Steel would ship components to a heat-treating facility accompanied by a QA expert who would hook up thermocouples to the part and monitor the part temperature. Now the part is heated in the shop, saving transportation costs, and the information is gathered by the ProHeat’s thermocouples and stored on a digital recorder and can be downloaded to a computer and shared with others via USB drive or Ethernet connection.
“We’re on a schedule at the heat-treating facility,” adds John “Jay” Kelly, lead welder. “We have to reserve that furnace time. If for some reason we’re held up and we miss our window, they’ll go ahead and put the next job in there and we’ll have to wait, which will delay delivery of our job. So by us being able to do it whenever we’re ready is going to save us money. We’re also saving shipping charges of a semi trailer sending it there and bringing it back again.”
These levels of cost and efficiency improvements would be enough for most companies to justify the purchase of a ProHeat induction heating system; however, just as important, if not more so, is the level of quality and quality assurance Energy Steel provides its clients.
The ProHeat heats everything evenly,” says Siwa. “You’re never going to get that with a handheld torch. It’s going to get hot in one spot. It’s not going to be even throughout the part. But with the ProHeat, you can check the temperature at any point across the part and it will be picture perfect.”
“That’s important because we have to hold a certain temperature for a certain amount of time,” says Kelly. “If we miss it by a few minutes, we have to do the heating all over again. We would have had to notify the customer that they were going to lose five hours on their part or whatever. So, by getting it right the first time, it saves life on the part, and it saves us 12 to 24 hours depending on how long the hold time is. Plus, our parts are built with a specific amount of time for post-weld heat treating. If we exceed that time, we have to start over with a new part.”
To ensure this accuracy, the ProHeat 35 uses a patent-pending, multiple-control-thermocouple input, which allows four control and two monitoring thermocouples to be used simultaneously. The controller reads the control thermocouples and regulates the heat rise based on the hottest thermocouple and the cooling based on the coolest thermocouple. This ensures that heating and cooling rates are not violated during the procedure. Separate displays indicate the temperature of each thermocouple and indicate which are being used to control the heating process.
A digital recorder records time vs. temperature from the thermocouples. Data is encrypted and stored on USB flash drives for transfer to a computer for further analysis, storage, printing of hard copies or transferring files by e-mail.
Regardless of the heating source, precise tracking is mandatory for the type of work Energy Steel does. While checking pre-heat temperature could be done in shop, as noted above, when Energy Steel sent a component out for post-weld heat-treating a QA person would accompany it.
“Then he’s got to hook up the data recorder on site,” says Kelly. “The biggest problem you have with these ovens is a thermocouple could break as it rolls in and you don’t know it until it’s too late. We don’t have that problem with the ProHeat. It’s all done here out in the open.”
“We have to supply charts to prove we got a part up to the temperature specified in the procedure and that we held it for so many hours,” says Siwa. “The ProHeat System does that automatically. It collects data on a memory card, which I can then download to my computer and share with others. I can show minute-by-minute temperatures; I can do it every five minutes, every ten minutes, every hour, depending on what is required, and then e-mail it to our customers.
“Another plus to the ProHeat, is that we don’t want the parts to repeatedly cool and heat because there’s a chance of stress cracking,” he explains. “By running the ProHeat during the night we keep the part at the temperature we want, so when we walk in the door in the morning, we just start welding again.”
“When we first used the ProHeat to heat the plates, we had the [inductance coils] sitting on top of plywood and the plates on top of that,” says Kelly. “When we did, everybody from the front office came to watch, saying, ‘You’re going to burn the shop down.’ Everyone was used to the old resistance method where the coils get hot. But once we explained it to them and showed them how it worked, the concerns went away.”
Because the ProHeat 35’s induction heating coils do not heat up themselves or need to be in direct contact with the part being heatedâŽ¯ Induction coils can be one to two inches away from the material and still induce heatâŽ¯Energy Steel can use plywood frames to hold the coils without presenting a safety hazard. To achieve and maintain the proper temperature on a pipe while their subarc machine clad the inside, the team built a plywood frame. The inductance coils were wrapped around the outside of the frame, while the pipe rotated freely inside. (See FIG 1. IMG. 7175.jpg.)
“It [the ProHeat 35] has made our job a lot safer,” says Kelly. “With a weed burner, you have a three-foot wand with an open flame coming out the end of it. All it takes is one moment of somebody not paying attention for a moment or not be aware of his surroundings to present a potential safety hazard. The ProHeat eliminates that.”
Fuel tanks presented a storage issue, also, Siwa adds. They had to keep enough on hand so they didn’t run out in the middle of a job, but they had to be stored safely, away from any oxidizers.
In addition to the added safety, the ProHeat 35 induction heating system provides a more comfortable working environment and improves communication by eliminating the noise associated with flame torches, says Kelly.
“When you’re picking up 30,000 pounds ten feet in the air, you want to be safe about it,” Kelly says. “You want to be able to hear everything, so you can’t have a lot of background noise.”
The Heat is On
“Many of the nuclear suppliers entered the industry at the same time,” says Waylon Waters, sales manager, Energy Steel, “We’ve added capabilities and have expanded our business in ways that others have not. The added value of fabricating an entire component through material supply, machining and ASME Code Welding is very special in the Nuclear Power Industry. In addition to that, we have always been able to accommodate expedited work. Energy Steel is available 24 hours a day 365 days a year, including Christmas Day, Thanksgiving Day and New Year’s Day to meet our customers’ needs.
Waters cites the company’s size and structure with its ability to quickly adapt to tight deadlines.
“If we have a rush job, I can call a meeting and within minutes I can have every one of our employees available and ready to tackle any task at hand. The attention to detail and quality assurance is very intense at Energy Steel, but these are the things that set us apart from the competition. We can’t afford to make mistakes”
The change to induction heating fits in well with these company values.
“There are very important benefits to using the ProHeat 35,” he says. “We have confidence in this equipment. The fabricators know that they can come in the morning and start welding immediately. We get accuracy with this product, not only from a quality assurance perspective, but it allows us to be more accurate with out bids and timing for estimates. It helps in every aspect of our scheduling, it saves money and other resources within the company, and it eliminates the safety concerns associated with the burners. All those things are positive when you look at it from a sales and productivity perspective. The best part is that we can pass those benefits on to the customer. We work very hard to stay ahead of our competitors by continuing to improve our skill levels and equipment in every aspect of the business. The economy affects everybody and being able to win as many bids as we can and make safe, on-time delivery of top quality products is very important to us.”