MINING: Canadian all-stainless steel building used in U.S. copper mine

Copper mining creates a highly caustic environment that challenges the structures that house its processes. In 2001, Phelps Dodge, a copper producer based in the United States, found a unique answer to this challenge through the combined efforts of three Canadian companies.

Phelps Dodge’s Morenci Mine is located in Morenci, Arizona, 200 miles due east of Phoenix, and is the largest source of copper in North America. The mine is an open pit operation where the process begins with raffinate solution being applied over ore to leach out copper. The resulting pregnant leaching solution (PLS) is combined with reagents in a settler building where it is separated to yield an electrolytic solution. This solution is then pumped to a tankhouse, where the copper attaches to starter sheets and 99.99 per cent pure copper plate is formed.

Previously the settler buildings were rigid frame, epoxy-painted carbon steel, with wall panels of the same material or fibreglass reinforced plastic (FRP). Colony Management, a building supply company of Vancouver, was bidding to supply some new buildings. However, Marian Podlovsky, P.Eng., manager of the civil/structural/architectural department of Fluor Daniel Wright of Vancouver, B.C., consulting engineers for the project, was aware of a frameless convex building that Colony supplied which might be suitable. He approached Colony’s president, David Thompson, and provided him with all the relevant data on mechanical aspects and functional constraints.

In turn, Thompson contacted Behlen Industries of Brandon, Manitoba regarding a pre-engineered frameless building system in stainless steel. The company had previously engineered a stainless steel building to combat corrosion at a composting facility. What would be unique about the structure at Morenci was that all components would be stainless steel.

Behlen’s general manager, Craig Downey, explains: “We regularly manufacture pre-engineered structural panel systems in the form of convex buildings that don’t require a conventional frame. In this case we were looking at every single component being stainless steel, from struts and gussets down to nuts and bolts. Here our challenge was working with so many different gauges of stainless steel — 12, 14, 16, 18, 20 ga. — and it took us about six weeks to engineer the parts.”

The challenge for Colony, Thompson says, was “to design custom windows fabricated with special opening mechanisms, fibreglass panes, and stainless steel frames allowing both ventilation and access.”

Podlovsky adds: “An advantage of the frameless convex building for this application is that of evenly distributed load along the length of the building, rather than a point load where columns occur. The main advantage though is cost.”

Sam Maldonado, senior engineer with Phelps Dodge at Morenci, is “extremely pleased” with the results: “We’ve saved money not only through reduced downtime to repair the traditional settler buildings, but also the cost of the structure compared to our other buildings.”

By Robert Fletcher. Article supplied by Behlen Industries.