Maintenance and repair on in-service pipelines introduces different challenges into the equation compared to other types of pipeline welding.
In-service work might require an emergency repair of a crack or, more typically, scheduled maintenance for upkeep and upgrades on pipelines in the field. This maintenance work often includes replacing pipe coatings or fixing pipe corrosion.
Learn some tips for optimizing weld repairs on in-service pipelines and how industry leader Enbridge significantly improved productivity with a change to welding processes for pipeline repairs and tie-in projects.
Tips for In-Service Repairs
Welding in-service pipelines can present additional safety risks due to the oil or gas inside the pipe, making it critical to monitor safety during the welding process. (For more information on safety when performing in-service welding or hot tapping, see API RP 2009, “Safe Welding, Cutting and Hot Work Practices in the Petroleum and Petrochemical Industries” and API RP 2201, “Safe Hot Tapping Practices in the Petroleum and Petrochemical Industries.”)
The presence of liquid inside the pipe also affects how the material reacts during welding — introducing challenges for setting proper parameters to achieve high-quality welds.
The gas or liquid inside in-service pipe cools the weld puddle very quickly. Whether it’s an oil or gas line, the material inside is much colder than the weld metal so it pulls heat away, resulting in a smaller heat-affected zone. This requires some adjustments on the part of the welder to compensate for the fast puddle cooling.
Preston Ri’chard, president of Pipeliners Union 798, has more than 40 years of experience as a pipeliner welder. His most recent work involved fabricating pumping stations for Line 3 and the Keystone XL pipeline in Minnesota on a project with TC Energy and Enbridge. Ri’chard, who often trains welders on in-service pipeline jobs, offers three tips for optimizing results with this type of welding.
- Make adjustments during testing.
When welders are tested for in-service pipeline work, they test with water running through the pipe to mimic welding on a pipe filled with oil or gas. Don’t put a sleeve on the pipe during testing. This helps operators see how quickly the puddle cools — so they understand which amperage levels are necessary for these welds. It often takes 40% to 50% higher amperage for in-service welds, so operators must understand how to adjust the amperage enough that they can fuse the metal but not burn through it.
- Understand the parameters for the wall thickness.
The ultrasound testing (UT) of a pipe’s wall thickness is critical for in-service repairs. If the wall thickness in the weld area is too thin, the operator must extend the sleeve area on the pipe. The ability to safely weld the pipe also depends on the pressure the line is running; pressure is often lowered for repair work. Pipeline owners have different protocols for different wall thicknesses. They have predetermined the interpass temperatures and pipeline pressure measurements and what wall thicknesses can be safely welded.
- Focus on butter passes.
For in-service pipe welding, a butter pass is used in place of a root pass. Buttering is a term that refers to adding weld material to build a part up. A butter pass adds a layer to an in-service pipe to help prevent burn-through. This builds up the pipe wall, making it thicker so the operator can add more weld metal to it. It’s best to carry a light puddle for the butter pass. Running two butter passes should allow the welder to tie-in to the sleeve under the long seam. Operators may prefer different angles for this pass. A butter pass is required as part of the in-service weld test, which helps operators hone technique.
Switching to Wire Processes
Understanding the best practices for welding in-service pipelines can help optimize results. But companies should also consider more holistic changes to processes and equipment that can also save time and money while maintaining high weld quality.
It’s becoming more common — and even a mandate on some jobsites — for contractors to switch from traditional stick welding to wire welding processes for new pipeline construction, though the process change has been slower to take hold for in-service repair work since many of those jobs are one-off projects.
The move away from cellulosic stick in pipeline welding is driven by the process’s higher risk of hydrogen cracking, which results in more time and money spent on rework and repair. Ri’chard reports laying a lot of major pipelines with automated welders that use wire for every pass.
“I haven’t used wire welding for in-service repair yet, but I think it’s coming,” Ri’chard says. “Wire processes help promote stronger welds through higher tensile strength than what’s achieved with cellulosic stick welding.”
Paul Spielbauer, weld engineering manager with Lake Superior Consulting in Duluth, Minnesota, sees more contractors and holding companies making the switch from cellulosic stick to wire processes for new construction of transmission and distribution pipeline.
“Absolutely there is a trend toward adopting more and more wire-feed processes, whether it’s semi-automatic or mechanized,” says Spielbauer, who advises pipeline holding companies on welding best practices and oversees procedure qualifications in the field.
The move is not solely about increasing productivity. It’s also about weld quality.
“It’s an increased push from the pipeline owning companies to move toward better welding practices that reduce hydrogen in the weld during construction,” he says. “So obviously moving to a wire process allows that to happen for the contractor, and then simultaneously gives them the benefit of improved construction speeds.”
In addition to high weld quality and productivity benefits, wire processes can also help reduce operator fatigue by reducing the number of passes required, and they allow for easier implementation of higher strength consumables, which is a growing trend in the industry.
Enbridge Sees Success with a Switch
Industry leader Enbridge Inc., recently made a change to the welding processes used for pipeline repairs and tie-ins on several of its sites, switching from traditional stick welding to advanced wire processes. Productivity improved significantly — with weld time reduced by 40 percent — allowing Enbridge to meet timelines and complete more projects while maintaining its high safety standards.
In-service repair welding is a critical part of the operation across Enbridge’s entire U.S. system of pipelines — with the company using up to 300 welders in a given construction season.
Wire welding processes were not traditionally used in the field, but the company believed a process change could improve productivity to meet demanding timelines while also meeting the low hydrogen requirements that are critical for pipeline welding.
The company converted from stick welding to advanced wire processes for some of its pipeline repair and tie-ins, using pulsed GMAW and Regulated Metal Deposition (RMD) processes with XMT 350 FieldPro power sources and Smart Feeders from Miller Electric Mfg. LLC.
With RMD, a modified short-circuit GMAW process, the welding system anticipates and controls the short circuit, then reduces the welding current to create a consistent metal transfer. Precisely controlled metal transfer provides uniform droplet deposition, making it easier for the operator to control the puddle. Advanced welding processes, such as pulsed GMAW or modified short-circuit GMAW, are also more forgiving to variations in stickout and result in a calm stable arc, which makes it easier to control.
Enbridge leaders said the addition of wire welding to the company’s maintenance program resulted in timelines becoming more flexible and arc time decreasing, while still meeting safety standards. That efficiency allowed the company to conduct more projects in a given year.
They also stressed that the productivity gains happened without an impact on weld quality.
Optimizing In-Service Welds
Welding in-service pipelines can present different challenges compared to other types of pipe welding. It’s important to understand the best practices that can help optimize results for in-service repairs.
As the pipeline industry in general moves toward using wire welding processes more frequently, this is a change that can also offer benefits for in-service welding.
A change in welding processes and investing in new technologies helps companies like Enbridge boost productivity and efficiency — without sacrificing safety or quality on pipeline jobsites.
Tags: Pipe Repair, pipeline repair, September October 2020 Print Issue, Welding
Bill England, CWI, is a welding engineer at ITW Welding.