Digging the Heat: Miller Engine Drives Provide Reliability at Mississippi Refinery
Fluor® Corporation one of the world’s largest engineering, procurement, construction and technical services companies, has roots in the Fox Valley region of Wisconsin. Coincidentally, so does Miller Electric Mfg. Co. These leaders in their respective industries shared something more in common when Fluor used the Miller Du-Op™ and a Big Blue® 400-amp welding generator for its on-site maintenance and contracting operation at Chevron Corporation’s Pascagoula, Miss. facility.
Fluor ranked No. 2 ($2.3 billion in revenues) in the 2005 Engineering-News Record (ENR) Top 500 Design Firms survey, for the second year in a row. ENR consistently ranks Fluor among the top three performing companies on the "Top 500 Design Firms" list and the "Top 100 Contractors by New Contracts" list.
For more than 20 years, Fluor has assisted Chevron in obtaining a competitive advantage by delivering an unmatched level of service. One of the nation’s largest oil refineries, the Pascagoula facility processes hundreds of thousands of barrels of crude oil per day, turning it into products such as gasoline, diesel and aviation fuels and chemicals. Fluor ’s on-site employees ensure that repairs are made in a timely fashion and that new projects stay on schedule. Typical work includes repair on, or construction of, reactors, piping, heat exchangers, fractionation columns and storage tanks.
Blake Senseney, Fluor’s manager for quality assurance at the refinery, understands why Chevron continues its partnership with his employer. “We use the best equipment to provide the best service,” he says.
Gouging Two Acres of Steel
One of the biggest projects at the Pascagoula refinery is the repair of petroleum and chemical storage tanks. The tanks range in size from 100 ft. to more than 200 ft. in diameter, covering up to an acre and holding more than 10 million gallons.
Fluor removes worn plate from the bottom and shell (sides) of the tank by air carbon arc gouging. Before work can begin, they cut a door sheet in the shell to allow for the excavation of the old steel and installation of new plates. Other than the door sheet, tank access requires crawling through valves no bigger than a manhole. The welders can spend much of their day working in a surreal blend of darkness and light (see photo).
|Fluor welders can gouge out the bottom of this tank without worry about high temperature shutdowns because Miller tests and rates the output of its engine drives and welders at 104 degrees F.|
The first cut on a tank, which separates the bottom plate from the shell, creates an annular ring. These rings average 5 to 20 ft. wide and 20 ft. long. The rest of the tank bottom, constructed of 1/4 in. to 3/8 in. thick carbon steel, is a compilation of sheets 10 ft. wide by 40 ft. long. Air tuggers and trucks remove the old rings and sheet through the door sheet, then bring in new rings and sheet.
Welding of the bottom (fillet welds for joining the annular ring to the shell and butt joints for the bottom plates) usually requires at least two passes. Fluor uses an E-6010 for a deep penetrating root pass, and then caps it with an E-7024 (this electrode provides a high deposition rate and is easier to clean up). A concrete berm supports the outside shell of the tank, while the bottom plate has sand pumped under it for support.
Gouging out the old plate and welding new plate can take anywhere from two weeks to more than a month, depending on the size of the tank and the amount of repair. This fatiguing work requires welding and gouging machines that work non-stop for an 80- or 10-hour shift without overheating and shutting down. What Fluor experienced with its current welding generators during the hot summer was quite the opposite.
“A tank valve is not very conducive to travel, so no one wants to crawl in and out to re-crank an engine drive,” says Jerry Betts, salesman, Welding Engineering Supply Co. Inc. (WESCO). “I saw an opportunity to solve Fluor ’s problem with the Big Blue welding generator. Miller rates the output of all its machines at 104°F. That might seem extreme, but in a Mississippi refinery, 104°F can be a real-world condition. In fact, the temperature reached nearly 100°F every day last week.”
This Big Blue model works well for gouging because it features a maximum output of 600 amps and has a 100 percent duty cycle rating at 400 amps.
“Our other machines would cut out when we gouged too long with them. Not only that, it seemed like the carbon wanted to jump off the plate,” says welder Tommy Langley. “With the Miller, I gouged hard all day in 98°F heat and never had a shutdown. We were running 3/8 in. carbons, then stepped down to 5/16 in. carbon for some other work, and the Big Blue burned both of them fine.”
Aaron McDaniel, another welder, adds that, “You can really dig with that Miller. We need to take out as much metal as we can with as little resistance possible. It makes my life easier if I can gouge out all the trash out in one pass.”
McDaniel and Langley also report that the Big Blue creates a very consistent arc with E-6010, E-7024 and E-7018 electrodes.
“It is a smooth burning machine, and the smoother the arc is, the better the weld bead is,” says Langley. “The Big Blue starts out hot, where I want it, and stays steady on its heat all day. One of my main gripes with some other engine drives is that they fluctuate. Running to cold or too hot creates porosity, so I’d have to crawl out of the tank and turn the machine up or down.”
|Fluor welders report that the Miller Du-Op maintains a consistent arc throughout the entire day, eliminating the need to return to the machine to make adjustments.|
Dual Arcs, One Engine
Fluor is now constructing a new pipeline in the refinery that will consist of approximately 8,000 ft. of 6-in. schedule 40 steel carbon pipe welded with an E-6010 root pass and an E-7018 for the fill and cap.
Perhaps no other type of operator is more sensitive to arc quality than a pipe welder making an open root bead. Because the pipe carries potentially hazardous fluids, each weld must pass x-ray or ultrasonic inspection. Any unacceptable welds must be removed by grounding or gouging and re-welded. Too many imperfections can cost a welder his or her job.
For the oil recovery line, Fluor decided to try another type of engine drive in addition to their traditional DC generators: the Miller Du-Op, the first U.S.-designed and -built dual-operator engine driven welding-generator. Originally designed for a petrochemical contractor working in Middle East, the Miller Du-Op allows two operators to weld independently of each other using a single machine. That is, one dependable Deutz engine powers two high performance arcs. Operators can make independent process choices (Stick, DC-TIG, MIG) and verify output parameters on their own digital voltage and amperage meters.
“Our old DC generator machines broke arc too easily, but the Miller Du-Op’s been working real well,” says welder Mike Moore. “We’ve had two people welding with it, putting in a root pass at the same time with the same amperage setting. We’ve put in 32 joints this week and haven’t made a repair. That’s because it doesn’t break arc, so there’s less chance for a bad weld to occur.”
“I thought we would have some variation in the amperage while one person is welding and the other person is starting and stopping the arc, but we haven’t had any problems,” adds welder Alton Robichaux. “We’ve even had two grinders running off the auxiliary power while Mike’s been welding, and like he just said, the arc doesn’t fluctuate.”
Blake Senseney also notes that, “A lot of our procedures call for a TIG root and then an E-7018 fill and cap. With the Miller Du-Op, we can set one welder up to put in the root pass and set another welder up to come along behind him to fill and cap without losing time to swap machines.”
The Miller Du-Op has an output range of 15 to 300 amps per side (40% duty cycle at 275 amps). A switch on the machine parallels both outputs to a single side for double the amperage output (maximum paralleled output is 600 amps), typically required for air carbon arc gouging or running larger SMAW electrodes.
The number of men and machines required for some of Fluor ’s work — sometimes as many as 1,400 employees provide support during scheduled maintenance shutdowns — means that work sites become very congested. To concentrate 12 arcs in small area (such as the “tank farm”), Fluor uses a flat bed trailer to transport two multi-operator grids, a diesel generator and a fuel tank. This permanent set-up mobilizes 3,000 amps of CC welding power. However, large-scale projects such as storage tank repair often require up to six or eight additional welding machines, typically engine drives.
In these instances, “The Du-Op can really save us a lot of time and space in the field,” says Senseney. “We only have to transport, fuel and maintain one machine. When we’re mobilizing for a project, that’s half the number of machines to move. That’s half the time for a cherry picker or truck to be tied up, and that’s premium time.”
Time is money in refineries. In situations such as this, engine driven welding generators that halve transportation time, maintain consistent arcs and gouge all day without stopping truly help Fluor deliver an unmatched level of service for its client.