Construction company uses orbital welding on underground pipeline
November 21, 2002
Using orbital welding equipment led to productivity gains in one of the nation's first fusion-welded underground pipelines.
|A critical requirement of this underground pipeline was to build it directly to the bottling plant.|
The 8-inch-diameter 304L stainless steel Schedule 10 pipeline -- more than 1.5 miles long -- delivers spring water from a mountain borehole to a new bottling plant. A completely penetrating fusion weld with no interior reinforcement was necessary; this required tight control of parameters to make a uniform weld.
Using gas tungsten arc welding (GTAW) would have escalated the cost and made it impossible to meet the client's deadline. Instead, the engineering and construction contractor, KS Industries LP, Bakersfield, Calif., (www.kensmall.com) used orbital welding, in which a welding head rotor completes the joint by revolving around the pipe's circumference.
This approach reduced to less than an hour the time required to prepare and complete a weld and move the welder to the next joint.
"The use of orbital welding was critical to winning this job and completing it to the customer's satisfaction," said Craig Bonna, vice president of Ken Small Construction. "We believe this process has enormous potential and plan to use it on future projects in the oil and gas, food and beverage, water supply, wastewater, and other industries."
The bottling company originally ran water from the borehole down a short pipeline to a station where it was loaded onto trucks and shipped to a distant plant. When the company decided to build a plant near the water source, one of the critical requirements of the job was to build a pipeline directly to the plant.
The pipe was installed in a trench. Project planners required a totally fused weld, with the interior weld flush to the surface of the pipe. This presented the challenge of maintaining high welding quality standards in a tough desert environment where winds blow from 20 to 70 MPH, causing nearly continuous dust storms with the potential to damage the quality of the welds and the equipment.
Bonna said his company would not have been awarded the job using other methods.
"Using traditional manual gas tungsten arc welding methods, we would never have been able to meet the deadline using even two welders," Bonna said. "The number of man-hours required to do the job would have driven up the costs, reducing our competitiveness. Fortunately, we foresaw the technology shift to orbital welding and had first rented and later purchased equipment before we had our first job. When this project came along, we saw it as the perfect opportunity to really put this method to the test."
When the company decided to use orbital welding, it spent time investigating different suppliers and various equipment options.
"We didn't have a specific application at the time, so our key requirement was flexibility," said Rick Grove, manager, fabrication and machine for KS Industries. "Two things impressed us about Arc Machines [www.arcmachines.com]. First, the company's equipment was very versatile and was used in a wide range of industries, including all of our target markets. Second, Arc has invested a lot of effort into making their equipment easy to use. A technician without extensive welding experience was able to consistently produce quality welds after only a few days' training."
Ken Small Construction selected the model 227, a fully computerized, inverter-type GTAW power supply with 100- to 200-amp output and an internal memory that holds up to 100 multilevel, multifunction welding schedules. It also chose a model 15 large-diameter pipe weld head that handles all standard piping sizes from 3 in. up and has a zero-backlash gear drive for positive travel speed, consistent in all positions.
|Welders used a fully computerized, inverter-type GTAW power supply with 100- to 200-amp output and an internal memory that holds up to 100 multilevel, multifunction welding schedules for this project.|
"When we first got the equipment, Arc Machines brought in an instructor to provide classroom training," said Jim LeVasseur, project superintendent. "This class provided instruction in theory and programming and established an excellent road map of how to get started. When we won the water pipeline project, we used this knowledge to create a miniclass of our own for the technicians who would be doing the work. This was designed as a four-day, hands-on course to teach the technical aspects of making this particular weld.
"Within two days all of our technicians were able to meet the specification without any difficulties," LeVasseur said. "We used the rest of the class time to repetitively practice the weld and developed a level of confidence that we could meet the client's demanding specifications. That gave us a tremendous head start on the project."
Practicing the weld was especially important, considering other challenges of the job.
"Because conditions were so harsh, we used a portable structure consisting of a small tent to protect the welding operation from the elements," said Mark Green, construction foreman.
"The pipe wasn't square when it came in, so we precut every pipe before it was installed with a George Fischer [www.us.piping.georgefischer.com] saw," Green said. "Then we used Walhonde [www.walhonde.com] aligning equipment to fit the pipe into position for welding."
After this they prepped the pipe by brushing off and sanitizing the ends, pulling a purge plug into place for the argon backpurge, and tacking the joint. This process was completed while the orbital machine was making a weld at the previous joint.
Once the weld was completed, the equipment was moved to the next weld that had just been prepared. The welder clamped the weld head onto the pipe and started the operation by aligning the tungsten to the joint and centering the oscillation with the actual weld.
A remote pendant was used to start the weld sequence, and the welding head moved around the pipe to complete the weld. A heads-up display allowed the operator to view the welding and provided a display of welding current and other functions. The only cleanup required was brushing the weld to remove excess discoloration.
Green said that after a brief start-up phase, he had no difficulties in meeting production goals.
"The fact that only one welder was required helped to maintain our profitability on the project," Green said. "Despite the difficult and dusty conditions, the machines ran throughout the project without a single breakdown. Quality of the welds was also uniformly excellent. In the beginning we ran a test weld every morning that was inspected by the client's representative to make sure we met their requirements. If they found any problems, we would have had to redo the test weld, but that never happened. After a few weeks of looking at nothing but perfect welds, they told us we didn't need to do the test welds anymore."
While at first the company invested in orbital welding because it offered the opportunity to grow into new types of projects, Bonna also found that this particular application demonstrated the process's capabilities.
"This job was exactly what we had in mind, and I doubt that we would have had an opportunity to win the job unless we had invested in the equipment and had a chance to experiment with it before bidding on this project," Bonna said. "As it was, the project proved to be the perfect showcase of its capabilities.
"We were able to do the job in far less time and for much less money than would have been possible using conventional manual welding methods," Bonna said. "Most important, we were able to meet the client's quality and delivery date requirements without any difficulties. We believe our orbital welding capabilities position us well for growth in a number of promising markets."
Jerry Fireman is a technical writer for Structured Information Services, 350 N. Old Woodward, Suite 210, Birmingham, MI 48009, phone 248-540-5610, fax 248-540-3506, e-mail email@example.com, Web site www.strucinfo.com.