After competitively winning the TC Energy bid to fabricate pipe for their 670-kilometer Coastal GasLink Pipeline, located in Kitimat, British Columbia, the project team was challenged with a new opportunity to problem solve and innovate.
The fabrication job required fabricating almost 100 3D elbows with bends varying from 15 to 90 degrees on primarily 48-inch-diameter, large-bore pipe and a one-meter piece of pipe had to be welded to either end of every elbow. The completed elbow assemblies weighed upwards of 17,000 pounds each.
Instead of welding the joints with the elbows placed statically, Fabrication Shop Superintendent Pedro Mendes dug deep to find a process to perform the welds that would save the client significant time and money.
“Being able to roll 48” welds allows the shop to execute the work a lot more safely,” says Mendes. “Welders aren’t on their hands and knees in uncomfortable positions for hours. Instead they’re on subarc welding positioners with proper ergonomics.”
Traditionally, when welding elbows onto small-bore pipe, rotational pipe positioners are used to spin the elbows during welding. This technique, however, had never been used for pipe elbows of the considerable size and weight TC needed.
Pedro reached out to PCL’s in-house engineering team to help fabricate a solution, a challenge they quickly took up. A number of challenges emerge when attempting to rotate elbows of this size: the eccentric center of gravity causes a large rotational torque while the heavy weight of the spool extends significantly from the pipe stands that support the spools. The elbow clamp must be positioned to line up exactly with the centerline of the elbow so that it does not wobble as it rolls, and the weld can be made from a static position.
“We love when our project teams give us unique construction problems to help solve,” explains Travis Zubick, assistant manager of Construction Engineering. “The design of the elbow clamp required using both traditional structural engineering principals and computational finite analysis calculations to ensure it structural integrity. It also meant working closely with the pipe fitters and welders in the shop to deliver them a usable tool.”
The engineered design for the elbow clamp featured a rigid connection between the pipe elbow and the clamp so that it would remain immobile as the pipe was rolled for welding. For the clamp to fit properly on the varying degree of elbow bends, two different sizes of the elbow clamps were fabricated. For the larger radius bends, custom extensions to the pipe stands were also built to raise the elbows higher from the floor, as the elbows were up to 21 feet long.
Using a traditional static position weld, each weld of this size would take two welders 20 labor hours to complete. For a weld of this type and size the pipe is set up in a static position in the shop and one welder works on each side of the pipe. As the welders progress towards the top and bottom of the pipe they must either position themselves underneath the pipe or use a work platform to access the top of the pipe. Welding in these positions can be ergonomically challenging for the welders and more care and control are required to make a safe and high-quality weld.
Using submerged arc welding machines in the shop and elbow clamps to secure and rotate the pipe for welding, each weld took one welder just eight hours to complete, more than half the traditional time. Using this process was also much less physically demanding for the welders and greatly reduced the risk of injury from strains due to worker positioning. It also led to a higher-quality weld.
In total, three elbow clamps were fabricated to complete 194 welds. Overall, the labor hours needed to complete each weld were reduced by 80%, and the time needed to complete each weld was 60% less than using the traditional method. The rolling with elbow clamps helped our weld quality and reduced possible weld repairs. This increased customer satisfaction and securing future work as well.
When PCL takes on a challenge, we look at it with an owner mindset. We don’t see problems or issues; we see opportunities to solve. The development of our elbow clamp welding solution is just another example of this mindset.