PROJECT: Voisey’s Bay Paste Plant
PROJECT TYPE: N/A
LOCATION: Newfoundland and Labrador, Canada
SERVICE SCOPE: Technologies
The construction of the new paste plant at Vale’s Voisey’s Bay Mine site in Newfoundland and Labrador, required long-distance high-pressure tailings and water and paste pipelines to be constructed conveying water, thickened tailings material and paste material in pipelines for over 2 km in six dedicated pipelines.
These pipelines are exposed to environmental constraints, including changes in topography leading to a differential in elevations of 70 m, and variations of temperatures from -42 ºC to 33 °C, which significantly affect the pipe stresses due to expansion and contraction of the pipe materials.
The second type of constraint faced in this project was operational in nature. Parameters of the fluids transported in each pipeline were very different, presenting varying high pressures between 1.7-15 MPa, and high fluid velocities up to 4.5 m/s. Mitigation of settling of solids was another important consideration, as settled solids would cause blockages. Additionally, the slurries conveyed by these pipes are very abrasive. All these factors contribute to high stresses on the pipe design and materials to be used; if the stresses exceeded the maximum allowable, the pipes would fail, leading to rupture and/or spill, which would be an environmental catastrophe.
Finally, we were faced with an economic constraint. The designs had to accommodate an optimal cost for a minimum lifespan of 10 years, considering materials cost, installation cost, operation cost, and cost of replacement.
Halyard, with the aid of stress analysis software, was able to calculate static and dynamic stresses to specify the pipeline material.
We evaluated 7 wear resistant materials, which we hypothesized would satisfy the expected liner requirements for the tailings slurry pipeline. After numerous iterations, looking at more than 20 material combinations for the pipe and liner, we concluded that high strength steel pipe with a HDPE liner would be a suitable combination to increase the lifespan of the tailings slurry pipeline constructed with carbon steel material with a HDPR slip lined insert liner. We concluded that the paste pipelines that move abrasive paste in slow moving, high pressure means were to be Induction hardened carbon steel material pipes. All pipes were to be insulated with foam insulation and a hard HDPE casing.
Besides the specification of the piping materials, various design issues were overcome. We determined that the expansion/contraction forces were too large on pumps and diverter valves and hypothesized that we could improve the anchor design to relieve some of the stresses on these elements while maintaining their ability to control pressure. Stresses in these areas were increased by the compounding action of stresses down the pipe. Through iterative design and stress analyses we developed line stops that allowed a bit of differential between the concrete and steel which allowed some play to be had while maintaining structural integrity. To accommodate the range of loads exerted on anchors, we had to develop two different anchor designs (up to 50 kN and up to 100 kN).