To be competitive in the world of designing and manufacturing vacuum and heat transfer equipment, lead time is critical. Projects often run eight months to two years or more for large energy projects, with vacuum and heat transfer equipment installed near the end.
For companies such as Graham Corporation, a world leader in engineered-to-order vacuum and heat transfer equipment, achieving customer satisfaction the first time and every time means delivering components on or ahead of time. One element of reducing lead time involved adding 14 welding systems that feature RMD™ and Pro-Pulse™, which are advanced MIG welding processes developed by Miller Electric Mfg. Co. and featured on Miller’s PipeWorx® Welding System. Graham added 10 of these units.
The PipeWorx System’s Stick, TIG, MIG, RMD, Pro-Pulse and Flux Cored processes have been optimized specifically for pipe welding. Switching between the processes is almost instantaneous, with no need to manually switch polarity, cables or hoses. Up to four programs can be stored for each process, and processes can be shared among different machines via an SD memory card. The front panel is clearly labeled, easy to use and provides only the controls necessary for the task at hand.
In the eyes of Kim Denton, Graham’s manufacturing engineering manager, the number one benefit of the PipeWorx is that, “The RMD and Pro-Pulse processes reduce rework, and that contributes significantly to reducing lead time. As of September 2010, we have reduced rework as a percent of total hours to an average of about 1.3 percent, down from about 3.2 percent in January of 2009.”
Graham Corporation (NYSE Amex: GHM) is a global designer, manufacturer and supplier of custom-engineered ejectors, pumps, condensers, vacuum systems and heat exchangers. Since 1936, Graham has built a reputation for top-quality, reliable products and high standards of customer service. Sold either as components or complete system solutions, the principal markets for Graham’s equipment are energy, including oil and gas refining and electrical power generation, chemical/petrochemical and other process industries. Graham’s equipment can be found in diverse applications, such as metal refining, pulp and paper processing, shipbuilding, water heating, refrigeration, desalination, food processing, pharmaceutical, heating, ventilation and air conditioning.
Graham’s 2010 annual report states that the company has reduced production hours on its large steam surface condensers and ejector systems by about 20 percent compared to three years ago. It has accomplished manufacturing efficiency and productivity improvements through the attention placed on quality, the resulting reduction of rework and through investments made in new equipment.
Denton notes with 20 to 30 continuous improvement projects implemented every year, attributing a specific improvement percentage to the PipeWorx systems alone is impossible. However, Denton unequivocally states that PipeWorx contributes to the solution. Overall, she says the PipeWorx, RMD and Pro-Pulse helps Graham in five major ways:
1. Reduced rework by improving first-pass weld quality.
2. Faster travel speeds.
3. Reduced set-up and process change-over time.
4. Eliminating the need for a backing gas in some stainless steel applications.
5. Greatly reducing or eliminating the need to compensate for distortion.
A Different Kind of MIG
RMD is a modified short circuit transfer MIG welding technology that promotes stable metal transfer, prevents excess puddle agitation and lowers heat input, allowing it to overcome less-than-ideal fit-up (gaps) and potentially eliminates the need for a hot pass.
Ron Halpenny, Graham’s weld technician and instructor, says that, “I’ve been welding for 37 years. Conventional short circuit transfer (SCT) was always a tough sell and still is in the energy and other process sectors that weld open-root joints. However, RMD and short circuit are two different animals. The control that RMD provides eliminates the trouble with traditional short circuit. Once people have been exposed to RMD, they’ll realize the difference.”
Halpenny states that RMD creates a softer arc, and that the metal transfer is more stable. RMD provides, “A lot better control. You can manipulate the puddle and see the joint more clearly. Having that control allows you to watch the fusion at the edges. You can actually take your time, control your arc and control the quality of the weld you’re putting in.”
With traditional MIG, the short circuits occur at erratic intervals and with varying intensity. As a result, the weld puddle experiences a great deal of agitation.
Brian Garvey, the Praxair territory manager supporting Graham, notes that, “With short circuit transfer, it looks like you have penetration. Then you shoot it (X-ray the weld) and realize that the force of the short circuit caused the weld puddle to splash and freeze on the sidewall of the pipe, creating cold lap. Conversely, RMD provides consistency, and that promotes good fusion.”
As part of proving this point, Garvey worked with Denton to place a demonstration unit in production settings and encouraged eight to 10 welders to use the RMD process.
“Always get the skeptics on it first,” advises Garvey. “Those guys are hard to sell, but they’re always eager to try new stuff.”
Jeff Schenck, a first shift welder at Graham with 31 years of experience, notes that, “Sometimes you think new things aren’t going to work out very well. It took a few minutes to get used to the PipeWorx, but once I got the hang of it, I really liked it. It’s simple, and it’s a lot quicker than TIG. RMD fills an open root joint really well.”
By substituting the continuous RMD process for TIG on root passes, Graham makes longer, continuous welds. This reduces the number of arc starts and stops and the number of tie-ins, which are the most common spots for incomplete fusion or inclusions.
Further, “Weld bead placement is a lot easier with RMD,” says Halpenny. “It’s just a matter of holding the gun steady when we can roll the weldment, or holding a steady travel speed when welding out-of-position. The operator only has to concentrate on the gun, not on holding a torch in one hand, feeding filler rod with the other and also working a foot pedal.”
RMD also reduces rework because it simplifies operator training. As an example, Halpenny notes that he began training three welding operators on the RMD process on a Monday. By Thursday afternoon, they were ready to take their weld tests.
“The technology inside PipeWorx helps inexperienced welders learn faster,” he says. “With RMD, they can put down as good a quality weld as if they’d been under the hood for 15 years. Their welds meet codes such as ASME Section 9, AWS D1.1, API 1104 and those from TEMA, the Tubular Exchanger Manufacturers Association.”
Fast Travel, Quick Set-up and Change-over
As a continuous process, RMD offers welding travel speeds of 6 to 12 inches per minute (ipm), with travel speeds tending to increase with larger diameter weldments. Comparatively, Stick welding produces travel speeds of 3 to 8 ipm, while TIG welding produces speeds of 3 to 5 ipm (all speeds given are for welding in the fixed position).
“We do a lot of open root joints,” says Halpenny. “One of the reasons we looked at the RMD process was to try to cut back on manual TIG welding, which is labor intensive. A majority of our welds require full penetration, and RMD allows us to control penetration while being more productive.”
In the time study Denton conducted as part of the PipeWorx capital expenditure process, RMD demonstrated a 22 percent improvement over manual TIG welding. RMD also eliminates the need for a hot pass in many applications because it creates a root pass weld with a 1/8- to 1/4-in. throat, which is sufficient to support the heat input requirements of a fill pass made with Pro-Pulse, Flux Cored or Sub-Arc.
While RMD saves considerable time, Denton notes that, “The effective weld time differs from job to job based on complexity. Also, because our customers often specify welding processes, it was tough for us to capture how often we would be able to use the RMD and Pro-Pulse processes.”
Fortunately, even when used for conventional welding, the PipeWorx’s multiprocess output and one-touch weld set-up functions reduce lead time.
“The advantage of the PipeWorx is that it’s an all-in-one machine,” notes Steve Doty, second shift welder/lead at Graham. “Instead of a guy having to find a TIG welder, find a Flux Cored machine or change Flux Cored to a bare wire (hence changing the gas, too), the guy has one machine. It can save up to an hour per shift.”
Ron Halpenny confirms that there’s almost no changeover time, saying, “I have one power source that does everything that I need to do. I can run TIG. I can run Stick. With the dual feeder system, I can have stainless on one side and carbon on the other side. I can have several Flux Cored wires. With a simple touch of the gun or hitting a button, I go from one process to the other. It’s just such a user-friendly machine because it can pretty much handle anything that’s out there. We use it for a lot more than I think it was ever designed it for.”
With conventional welding systems, a single weld process change often takes 10 minutes. Activities can include changing wire types, changing wire diameters, changing shielding gases, switching the work cable and welding lead to change polarity, setting new parameters and fine tuning the welding arc prior to welding.
In addition to eliminating the time spent changing consumables and processes, the PipeWorx’s memory function eliminates the time required to set and fine tune to the welding arc. The system can store and recall four weld procedures for each process, and programs can be transferred between machines using an SD card.
“I found that the PipeWorx runs so consistently that I can take an SD card to any machine on the floor, upload the program, and there’s very little, if any variance,” says Halpenny. “There’s no individual machine characteristic like there is with conventional welders.”
Savings on Stainless
“We use RMD on both stainless and carbon, but the best features are on stainless. We’ve had excellent results with X-rays, and the time savings of welding without a back purge are huge,” says Halpenny. “We don’t have to prepare for the purge. We don’t have to tape the joint off. We don’t have delays, which can be hours as some of our units are four feet in diameter. And in cases where we used to have a second operator running a purge wand, that operator now stays productive on other tasks.”
“After putting in the RMD root,” he says, “I can hit the button for the Pro-Pulse process and for the fill passes.”
Reduced Heat Input
While faster welding speeds, faster set-up and faster processes all reduce lead time, the biggest advantage of RMD and Pro-Pulse (after reducing rework) is that they reduce distortion by reducing overall heat input.
“Heat input is a huge issue in the industry. The industry is crying for less heat input,” he says. “Pro-Pulse and RMD cut down our lead time tremendously because now we don’t have to anticipate distortion. We don’t have to hold off on certain steps of the fabrication process where we would weld a certain amount, check our tolerances, readjust and then weld again to try to compensate for distortion or shrinkage. Now we can build our unit to dimension and weld it without any second guessing.”
RMD and Pro-Pulse provide greater control compared to alternative processes. RMD lowers overall heat input compared to conventional MIG, Stick or TIG; Pro-Pulse lowers overall heat input compared to conventional spray transfer, conventional Pulsed MIG or Flux Cored welding.
Worth the Effort
As a manufacturing engineer, Denton knew that changing welding systems and developing new weld procedures would require patience and time to gain acceptance from operators, end-users and management approval for a capital expenditure.
However, with Graham’s focus on reducing lead time, “We are going to pursue any technology or product that prevents X-ray failures or rework. Weld lab qualifications and jobs where RMD and Pro-Pulse have been utilized since July 2008 have all had positive X-ray results. We are crushing our rework objectives, and RMD and Pro-Pulse are contributing.”