One Leak, Two Solutions
The City of Dayton, Ohio Tackles Water Main Rehab Using Multiple Methods
Jayne Bringer Apr 04, 2012
Sometimes you need more than one product to get the job done. The Department of Water for the city of Dayton, Ohio, recently used two complementary technologies from Insituform Technologies LLC and Corrpro Companies to tackle a variety of pipe problems on a 10-in water line running along Guthrie Road on the outskirts of the city.
Being near a public golf course and water treatment plant, the pipe needed to increase its capacity to withstand heavy loading due to heavy truck traffic that hauled daily loads of trash to and from another nearby waste facility.
Several point repairs had already been made to address previous water main breaks, and personnel from the water treatment plant had also identified cracks in the cement and mortar — lined pipe. City engineers chose to line the pipe to protect it from internal corrosion. For that, they applied a process known as cathodic protection to prevent corrosion throughout the entire system.
The liner chosen for the project was a fiber reinforced cured-in-place pipe (CIPP) product known as InsituMain. The InsituMain System was chosen as it has been proven in both field and lab testing to provide a fully-structural, standalone solution. It was installed by water inversion using a specialized torpedo launcher – different from the traditional upright inversion unit used by many CIPP contractors. Benefits of the torpedo launcher included a smoother, quicker installation for the crew.
The 4,700-ft project was completed in just 12 shots in the same number of pits, and four individual service connections were reinstated. Taking advantage of the already excavated pits, Corrpro Companies installed a sacrificial anode system to provide additional corrosion protection.
During the project, magnesium anodes were welded onto the ductile iron tie-in pipe in each pit to prevent a reaction between the different types of potable water lines. This is because each different type of metal has its own unique “potential” ranking in the Galvanic Series of Metals. Metals with more negative potentials corrode first, as the release of energy coincides with the degradation of the metal into its natural state.
A cathodic protection system uses this basic energy principle to prevent corrosion. By attaching a lower energy metal (cathode) to a higher energy metal (anode), degradation of the “cathodic” metal can be prevented. For instance, to prevent the corrosion of a steel pipe, you could connect it to a higher energy metal such as magnesium. The transfer of energy causes the magnesium anode to corrode first while preserving the steel pipe.
Since the system had both ductile iron and cement mortar lined pipe, the sacrificial magnesium anode helped to prevent corrosion with its lower energy ranking. Over time, the anode degrades, or is “sacrificed,” while the pipe stays in good condition. A total of 12 magnesium anodes were installed - one for each open installation pit.
An electrical connection between the anode and cathode was achieved using a wire connecting the anode to the existing pipe. In large cathodic protection systems where a galvanic anode may not provide adequate protection, this connection is regulated using a transformer-rectifier. A rectifier converts AC power to a DC output, ensuring that there is enough current to provide complete corrosion protection to large assets.
Water pipelines are not the only assets that can benefit from cathodic protection. Cathodic protection systems are used for a variety of different materials and applications in the industrial and oil and gas industries as well. Fuel tanks, water tanks, offshore structures, marine vessels and concrete structures with metal rebar can all be preserved using the process.
The project in its entirety was completed in just a four-week period with an average of two to three installations per week. Once the InsituMain System had been installed and the anodes welded to each subsequent section of the pipe, the system was bacteria tested, flushed and connected back to the rest of the system. The project was a prime example of how municipalities can take advantage of one project to implement two solutions at the same time.
Jayne Bringer is a Senior Marketing Specialist with Aegion Corp. She has over 5 years of experience in the trenchless industry and has been published in multiple trade journals. Bringer has a Master’s in Strategic Communication from the University of Missouri School of Journalism.