2001 Planning — Co-winner 1
Town of Beausejour, Manitoba
Retrofitting to control corrosion in metallic water mains
The Town of Beausejour has solved its problem with metallic water main breaks by using a procedure that many waterworks industry experts have dismissed as a "black art." The town is retrofitting its existing metallic water main distribution system using cathodic protection as a cost-effective alternative to conventional water main renewal. Initiated in 1993, the program has reduced the frequency of water main breaks, lowered the operating and maintenance costs of the community's water distribution system, and extended the lifespan of the protected water mains by 40 years — for approximately 10 to 15 per cent of what it would have cost to replace them. The program has also reduced greenhouse gas emissions and the consumption of non-renewable petrochemical resources by cutting down on the town's water consumption and avoiding the purchase of new water mains.
Experts have long recognized that external corrosion — caused when dissimilar metals come in contact with each other — is a major cause of early failure of metallic piping systems buried in the soil. For example, in 1985, Beausejour had to renew a section of ductile iron water main that had been destroyed by external corrosion in less than 10 years.
In 1991, the town attacked the problem by using cathodic protection on selected hot spots along its water mains. Cathodic protection creates an electrochemical process that controls corrosion in metals, such as water mains. Through cathodic protection, an underground water main is protected when it is connected to a metal anode, and an electric current is passed between them through the soil. The process focuses corrosion at the anode, the more electrically active metal, and away from the water main. In the end, the process corrodes the anode and protects the water main. There are two methods of cathodic protection: one in which the electric current is applied through a sacrificial anode, the other in which the current is applied through an impressed current system.
Beausejour municipal works staff attached sacrificial zinc anodes to the pipeline's hot spots — namely water main break sites or any other excavated sites where workers identified corrosion (The works department has since improved on this method and, in 1995, started using magnesium anodes, which offer two and a half times the protection coverage of zinc anodes). These measures, however, did not control corrosion on large sections of existing water mains.
In 1992, the town embarked on an extensive street reconstruction and resurfacing program. The project gave the works department an opportunity to replace most of the town's corroded water mains; it knew its water mains were in trouble and that the situation would have to be addressed sooner or later. But the town faced a difficult decision: could it afford to reconstruct streets and replace water mains at the same time? When it became obvious that the replacement would be far too expensive, Beausejour considered expanding its use of cathodic protection.
- By retrofitting existing metallic water mains with cathodic protection, Beausejour did not have to undertake a major water main renewal program. By keeping the installation process in-house, the works department ensured that it would be able to reproduce the results whenever necessary. Moreover, workers benefited from learning new skills and gaining experience in a new field of technology. They have also avoided interfering with other buried utilities.
- With cathodic protection, the town has reduced the number of water main breaks from eight to 10 per year to one to two per year. The breaks that do occur happen in areas where cathodic protection has not yet been applied. Since there are fewer interruptions to its water service, the town better serves the public. Furthermore, the town has reduced the potential health risks associated with water main breaks.
- The overall unaccounted for water loss in the town has decreased by five per cent, from 20 to 15 per cent of the water that the community consumes. This helps to preserve the groundwater on which the town depends, saves $16,000 a year in pumping costs and reduces associated greenhouse gas emissions from electricity consumption.
- The town has extended the life spans of these water mains by 30 to 40 years for 10 to 15 per cent of what it would have cost to replace them. The money it has saved on the interest charges has almost paid for the cathodic protection program.
- This approach reduces the environmental footprint that would otherwise be caused by a water main renewal program. Water main renewal uses large excavating and earth moving equipment, which disrupts the landscape and burns fossil fuels, while cathodic protection causes little surface damage. In addition, water main renewal requires manufacturing new plastic replacement pipe, which consumes additional fuels, lubricants and other raw materials.
- Beausejour has helped ensure the growth of its population and economy by preserving and maintaining its infrastructure by the most economical means possible. Beausejour will continue to allocate money saved through cathodic protection to expand and upgrade its water distribution system.
- During the first phase of the Beausejour cathodic protection project, municipal works staff prepared trenches for header cables by using a machine that opens the ground from the surface. This resulted in a heavy investment in labour, time and equipment. In the second and third phases, staff ploughed in header cable conduits using a viber plough, which ploughs conduit pipe directly into the ground without opening a trench. (Staff then pulled the header cable through the conduit pipe.) Staff were able to use cheap, polyethylene water pipe as a conduit, making it possible to install as much as 600 metres per day. This new ploughing method caused little surface damage, which helped to keep costs down.
- The activities involved in the construction process, such as anode drilling, conduit laying, cable pulling and anode lead splicing, do not have to be carried out concurrently. Staff can finish one activity, leave the project to work on something else, and pick up later where they left off. This allows for flexible scheduling, which is an important consideration for a small staff.
- The original DICCAP design placed individual DC rectifiers at 100-metre intervals along the water main route, with streetlight circuits providing power. Research showed that Manitoba Hydro considered each location a separate service and would apply a $17 service charge to each one every month. Since supplying power to each rectifier costs only five dollars a year, the works department considered the service charges prohibitive. Staff decided to modify the design by grouping the rectifiers in a central location where a single hydro service could power several rectifiers in a group. To save even more money, staff placed rectifier groups, whenever possible, in publicly owned buildings where hydro services already existed.
- Small towns with few staff can aspire to innovative solutions. Despite the reputation of cathodic protection as a "black art," Beausejour's six public and waterworks employees have grasped the difficult science of the procedure and applied it very successfully.