With its lush greenery and old-growth trees, the Pacific Rim Rainforest is a beautiful place to visit. But it can be a difficult place to work: annual precipitation is among the highest in the world, and the terrain can be steep and uneven.
Canoe Creek Hydro Company Ltd. faced this situation during construction of its 5.5-MW run-of-river facility on Vancouver Island, British Columbia, Canada. Development of this facility called for installation of a 2-km-long penstock on terrain up to 84% grade. Construction was set to reach peak activity in the winter, when rainfall is the heaviest. These factors, combined with safety and labor considerations with regard to welding the penstock joints, created significant challenges. Victaulic, a manufacturer of mechanical pipe-joining systems, worked with project manager Barkley Project Group, as well as engineer Amnis Engineering and contractor Hazelwood Construction, to provide a solution that would reduce costs with minimal impact on the project schedule.
Canoe Creek, 45 km northwest of Port Alberni, is located in the UNESCO Biosphere in Clayoquot Sound and is majority owned by the Tla-o-qui-aht First Nations. The facility was built in response to the BC Hydro Standing offer Program and generates clean electricity for use by the nearby communities of Ucluelet and Tofino.
Construction crews knew they would face significant challenges during penstock construction, which was scheduled to begin in October 2009. The plan was to join the more than 150 sections of the 36-inch-diameter penstock using welding, but this would be challenging due to the method’s lengthy installation process (which involves preparation, setup, testing and teardown), combined with the difficulties imposed by the terrain and elements. Welding in heavy rain requires weld tents and preheating the pipe, which increases installation time. During dry periods, forest fire hazards can result in restrictions or temporary prohibitions on industrial activities, including welding, adding risk to the construction schedule.
|The use of mechanical couplings rather than more traditional welded joints when installing the penstock at the 5.5-MW Canoe Creek facility saved time and money and provided a safer environment for workers.|
In addition, field repair of the penstock coatings would have introduced safety hazards. Once a welded joint is completed on lined pipe, coatings must be hand-applied on the burn path or uncoated areas. The process requires one or more workers to tie off to the penstock and be lowered into the pipe, giving rise to confined space entry procedures and personal protective equipment considerations. Pipe coatings produce toxic fumes, requiring the use of respirators and increased ventilation, and are also extremely flammable.
The project was designed around welding, but Victaulic presented another solution to the project engineers: using mechanical couplings rather than welded joints.
A grooved mechanical joint comprises four elements: grooved pipe, gasket, coupling housing, and nuts and bolts. The groove in the pipe end is made by cold forming or machining. A gasket is wrapped around two abutted pipe ends, then enclosed in the coupling housing, the key sections of which engage the grooves. The bolts and nuts hold the housing segments together and are tightened using a socket wrench or impact wrench. In the installed state, the coupling housing encases the gasket and engages the grooves around the pipe circumference to create a leak-tight seal in a self-restrained pipe joint. The completed joint is visually inspected; metal-to-metal bolt-pad contact confirms proper assembly.
Victaulic personnel explained how the use of mechanical couplings would offer several advantages: installation in any weather, elimination of the safety concerns associated with welding and confined space entry, and optimization of the labor force by reducing the number of specialized trades required on the job site and enabling employment of more of the local labor force. Project managers were hesitant at first because welding is a traditional and widely recognized joining method, but they soon came to understand how these benefits could help keep the project on schedule and on budget.
The pipe to be used for the penstock was already on site, so Hazelwood workers grooved and re-coated the pipe, then sent it up the narrow single-lane logging road to be assembled.
Use of the couplings proved advantageous in several ways. First, assembling the coupling does not affect the coatings, so confined space entry for re-coating was unnecessary. Second, despite the rainy weather, the couplings were installed on time and with no special requirements. No flame or heat is required to assemble a coupling on a joint, so crews were able to work in downpours and snow showers. Third, the excavation, bell holing (widening of a trench over a given distance) and dewatering that would have been required with welding were dramatically reduced. The trench was narrowed to 6 meters from the original 13 meters. Eliminating a majority of the welding significantly decreased safety risks on the jobsite.
Construction finished in May 2010, and the facility went into service in June, on time. Use of Victaulic couplings minimized site labor-hours required to complete the work and increased jobsite productivity. A total of 154 couplings were installed for the project. Barkley Project Group estimates welding would have taken four to six hours per joint. Using mechanical couplings, contractors were able to install three to five joints per day, with each coupling taking about 10 to 20 minutes to install.
Use of mechanical couplings also resulted in cost savings. Although the material cost of the couplings was higher than the material cost for welding, the significant reduction in labor time and costs slashed the total installed cost of the penstock.
Another noteworthy feature of the project is the minimized construction footprint and environmental benefits gained. Welding the 154 pipe joints would have produced about 37,422 kg of CO2 emissions using a diesel-powered welding machine and 8,779 kg of CO2 using an electric machine. Grooving and coupling that same run of pipe would produce about 58 kg of CO2.
Use of couplings also reduced the amount of X-raying of welded joints to ensure joint integrity, which emits radiation into the environment. Project managers extrapolated that the use of Victaulic couplings at Canoe Creek significantly reduced emissions of particulate matter, carbon dioxide and radiation, as well as electrical energy use. The green benefits of the couplings mirrored the clean energy goals of the facility and supported the provincial movement toward green projects.
The use of Victaulic mechanical pipe-joining products at Canoe Creek changed the way all parties think about welding. Hazelwood reports that it will employ the method wherever possible on future projects, and site supervisor Brian Cross said, “If I never have to do another welded joint again, that’ll make my life a lot easier.”
-By Scott McDonald, power specialist, Victaulic, and Iain Cuthbert, president, Barkley Project Group