Plasma systems save time and money in pipeline construction

Paul Boughton
Paula Flanders looks at how plasma technology is being used on the Ruby Pipeline project in the US.

It is early November and 6000 feet up in the Wasatch Mountains near Ogden, Utah, USA. Wet snow has turned the already rough dirt road to half-frozen mud. Although grey skies are promising more snow, Kenny Glaze, member of Pipeliners Union Local 798, is on his way to repair a porous weld bead on Associated Pipe Line Spread 1B, part of the Ruby Pipeline project.

Construction on the Ruby began on July 31, 2010. The approximately $3billion project includes laying roughly 680 miles of 42-inch natural gas transmission pipeline on a right-of-way through parts of four states: Wyoming, Utah, Nevada, and Oregon. By the time the pipeline is fully operational, it will carry 1.5billion cubic feet of natural gas per day and any delays beyond the target completion date will cost considerable time and money.

A 20-year pipeline veteran, Glaze has worked on numerous projects throughout the United States. This is the first one where he has used plasma to repair welds though. "Before plasma, I had to use a grinder to access the repair area. That generally took 45 minutes or more of hand grinding. But now that I'm using a Powermax45 plasma system, I can gouge down to the repair area in a third of the time."

Hypertherm plasma systems, like the Powermax unit Glaze used, can remove 6.2 pounds of metal per hour. Another time saving benefit is that the plasma leaves behind a weldable edge, and for Associated Pipe Line Contractors, hired to build sections of the line, every minute saved helps keep the project on its tight schedule and under budget. For the welders though, time saved is just the beginning.[Page Break]

Valve noise

Fatigue and safety come into play as well. The grinder is heavier and harder to hold than the plasma torch and grinding presents safety hazards, such as eye injuries, from flying debris. There are other options, but unfortunately, they aren't much better. For instance, carbon arc gouging presents a problem because the carbon winds up puddling on the pipe and must then be ground off. On the other hand, the plasma system Glaze is using is highly portable, light weight and can cut 0.5-in mild steel with ease.

Once the path for the pipeline has been cleared and prepared, sections of pipe ranging from 40 to 80 feet long and varying in diameter and coating thickness based on their specific location, are laid out along the path in a process called 'stringing the pipe'. The pipes are welded together, contoured, coated, inspected, and tested. The inspection and testing phases may turn up defects in pipe welds that have to be repaired. For example, misalignment of the pipes can lead to inadequate weld penetration in a section of the weld seam. Another common problem is porosity in the weld. Porosity can be scattered, cluster, or hollow-bead, but all types are defects and must be repaired. There are a lot of causes for porosity, which occurs when gas bubbles get trapped in the weld bead as it solidifies. During outdoor projects such as pipelines, windy conditions can cause the shield gas to be blown away while the welding is taking place, resulting in high porosity.

While repairing weld defects adds time and cost to a project, the consequences of not repairing them would be far more severe. In fact, inadequate penetration and high porosity in welds, along with other issues, are actually the suspected cause of a September 2010 pipeline explosion in San Bruno, California. Federal investigators say they found dozens of substandard welds on the pipe; welds that could have been easily repaired with plasma.

Another advantage of using plasma is the increased visibility of the repair area. When making a repair, the goal is to remove the weld bead without touching the pipe section.

"This is where plasma really pays off for the welder doing the job," says Glaze. "The welder can see very precisely what he is doing." A wrong move while gouging or grinding can require the removal of a complete section of pipe at a cost of $60000 or more.[Page Break]

Pipeline construction

Pipeline construction is a highly technical and regulated industry. Companies like Associated, which has been building pipelines for more than 50 years, have to meet stringent quality demands. In addition, Associated specializes in working in difficult terrain. The company prides itself on its innovative approach and willingness to use new technology to meet these challenges. "New technology makes the industry much more efficient and works to eliminate hazards, such as those associated with the use of old hand grinders," states Sonny Weems, Superintendent of Associated Pipe Line Contractors.

Although gouging was the first application Associated found for plasma, they are finding other uses for the cutting method. One such use is for the actual cutting of pipe. The crew has discovered that using another Hypertherm product, the slightly larger Powermax65, with a mechanized torch and a pipe beveller, speeds up the process of cutting pipe for bends and preparing ends of pipe sections for fitting. With a recommended 0.75-in cutting capacity, the system can run at full capacity off of a 15kW engine-drive generator or at lower amperage off of a 12kW engine drive.

These cuts were traditionally done with oxyfuel, but the faster cut speeds of plasma reduce the amount of time the tie-in crews spend standing around waiting for the pipe to be prepped. Kevin Berryman, the tie-in foreman for Associated, has also found that the cut quality of plasma has reduced or eliminated the need for grinding the weld area after the cut - another time savings.

Better cut quality and smoother cuts results in easier 'fit ups' of the pipe, which in turn results in better welds and fewer field repairs needed. "Plasma is all about time and efficiency in our line of work," says Berryman.

Paula Flanders is with Hypertherm Inc, Hanover, NH, USA.

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