Reverse polarity in TIG and stick welding
Repairing a massive power plant boiler is a job that can span two or three months for NAES Power Contractors — and one that requires adhering to a strict timeline and stringent quality standards. Staying on schedule is especially critical when the job involves an emergency, unplanned boiler outage.
“There's usually liquidated damages associated with these contracts. We're waiting for the plant to get done with their lockout/tagout so we can get in to do our work,” says Mike Geyer, president of NAES Power Contractors. “And there's usually electricians and maybe some other contractors waiting for us to get done, so they can get in and work following behind us. It’s very schedule-driven, and you have to be on top of your game.”
The XMT® 350 FieldPro™ with Polarity Reversing welding system allowed NAES welders to complete three times as many welds per shift on a recent project by allowing them to easily change welding polarity with the push of a button.
While boiler repair has traditionally been the focus for NAES Power Contractors, the full-service mechanical contractor based in Cranberry, Pennsylvania, also has chimney and stack and nuclear cask divisions. In addition, the company is diversifying into gas-fired power plant projects and broader pipe work for fossil fuel customers.
With liquidated damages, missing deadlines or quality targets costs NAES money. During a boiler outage, NAES welders are inside the boiler to repair or replace tubing or duct work. A typical project can involve replacing 50 to 150 boiler water wall panels — with hundreds of people working inside the boiler, running two shifts six or seven days a week.
A log of boiler outage jobs completed by NAES Power Contractors in the past five years shows the company put in one million labor hours and completed about 20,000 inspected welds — recording less than five welds that required rework.
“That speaks to our quality, that speaks to the equipment we use, and that speaks to our planning — our execution from the beginning to the end,” says Geyer. “If you have to go back and repair a weld, you’re blowing your budget. We aim to get it done right the first time as efficiently as possible.”
Because of the demanding schedule of boiler outage work, NAES Power Contractors is always looking for ways to improve productivity — without compromising quality or welder safety. The XMT 350 FieldPro with Polarity Reversing system fit that bill, saving hours per day on a recent project.
“We exceeded the ROI that we calculated,” says Project Manager John Dudo. “We’re easily saving an hour to two hours per man every day.”
Hours spent tracing welding leads
Depending on the size and scope of the boiler, the work can be difficult to reach. The boilers may be 400 megawatts or 900 megawatts, but the work completed inside is often similar from job to job. Welders may have to climb into the boiler through a 24-by-24-inch hole and, once inside, climb through additional crawl spaces or up scaffolding to reach the pipes to be repaired.
The welding may involve lying on their backs or at a sloped angle to complete an overhead weld. Despite the difficult positions and small spaces, the welds must meet high quality standards and are often subject to X-ray, radiographic or hydrostatic testing.
“Failure could be catastrophic, so everything has to be right,” says Don Cessna, NAES quality manager. “At the end of the day, we’re judged on our reject rate.”
The company welds a lot of SA213 T11, which is 1-1/4-inch chrome boiler tube, with wall thicknesses ranging from 238 millimeters to 1-1/2 inches. NAES welders most frequently TIG weld the root pass and stick weld the remaining passes.
There may be 100 welders or more inside the boiler during a job, and they could all be running the same type of welding power source. This can result in a tangle of welding leads, making it hard for operators to determine which lead and machine is theirs when they want to switch polarity or make parameter changes. Going from the TIG root pass to the stick passes requires the welders to trace the lead, find their machine — which often is outside of the boiler — and switch the cables to go from straight polarity (TIG) to reverse polarity (stick). This process could happen up to a dozen times per day per welder.
“Their leads end up being like a weave of spaghetti going up through the scaffold,” Cessna says. “It could take anywhere from a half hour to an hour to trace his leads up, get the machine switched over and climb back in.”
This not only takes time and impacts productivity, it also increases slip, trip and fall hazards for welders climbing in and out of the boiler.
In this situation, it’s also not uncommon for a welder to accidentally change parameters on the wrong machine, which results in frustrated welders and the potential for blown welds or porosity if the operator begins welding in the wrong polarity or with incorrect parameters.
“Sometimes we have people employed full time, and their job is tracing leads all day,” Dudo says. “That just takes a lot of time.”
Change polarity with the push of a button
NAES Power Contractors eliminated these wasted hours with the XMT 350 FieldPro with Polarity Reversing welding system from Miller Electric Mfg. LLC. The machine allows NAES welders to simply push a button on the Stick/TIG Remote to switch processes and polarity — without leaving the spot where they’re working or switching leads at the power source.
The productivity gains were immediate for NAES welders. Operators using the polarity reversing system completed 10 to 14 welds per shift, compared to the four to five welds completed per shift by welders not using the system.
“It was phenomenal,” says Jesse Yourich, a welder with Boilermakers Local 154 in Pittsburgh. “You do everything right there. It definitely saves a lot of time, and it just makes life a lot simpler.”
Welders no longer have to leave the boiler to swap leads at the power source to change polarity, and NAES also saved time in cable setup and management, since there are fewer welding leads needed inside the boiler.
The system also prevents any changes from being made at the power source once the Stick/TIG Remote is connected — eliminating the chance of another welder accidentally adjusting parameters or changing processes on the wrong machine.
“It takes away frustration from guys if they’re in the wrong polarity,” says Chris Darnell, NAES project manager. “It takes away the repairs to be made on the tube work. It saves time and money.”
Optimized arc performance
NAES Power Contractors greatly improved productivity, efficiency and operator safety on the jobsite while still producing the high-quality welds necessary for boiler code work. The optimized stick and TIG performance of the system is specifically designed to meet the needs of open root pipe welding.
The system’s arc starts maintain the root opening and prepared edge, while the stops limit arc marks outside of the heat-affected zone.
“It’s definitely a lot easier to start the arc. You don’t stick the tungsten, and the control was there as soon as you lit up,” Yourich says. “The TIG arc control is very precise.”
In stick welding, the easy arc starts and stops help reduce porosity at the start and stop locations and also allow NAES welders to reuse more stick electrodes — saving money in consumables. When using other welding systems, the stick rods typically go in the stub bucket after one use.
NAES welders can also adjust parameters without stopping the arc because the system has Adjust While Welding (AWW™) technology. This capability is especially handy because the company does a lot of “brother-in-law” welding, where two operators weld around the same pipe, trading off the arc on the same stick welding pass.