With any large construction project, almost everyone involved can expect to be challenged in one way or another in the struggle to complete the project on time and on budget. This is the story of one such challenge involving a large construction project and its corrosion-resistant solution.
The Eastside Reservoir in Los Angeles area is an extraordinarily large project. Scheduled for completion in fall 1999, the reservoir covers nearly 4,500 acres and will hold more than 260 billion gallons of water. Its location at 1,750 feet elevation will allow water from the lake to be distributed by gravity flow throughout most of the Metropolitan Water District of Southern California service area.
The reservoir stretches over 4.5 miles through the Diamond and Domengigoni valleys, about 100 miles east of Los Angeles. Three dams of earth/rock construction will contain the water.
The West Dam, now completed, is 285 feet high, 1.7 miles long and 1,200 feet wide at the base. Through the base of the dam runs the P1 Pressure Tunnel, which will feed water from the reservoir to a pumping plant nearby. The tunnel is actually a pipeline ? 2,800 feet of steel pipe 16 feet in diameter.
The Problem
The project originally called for lining the pipe with a cement-mortar lining, but problems with that system were encountered. The contractor decided instead to line the pipe with a sprayed (painted) application of an epoxy resin coating prior to installing the pipe.
The Problem
The problem was that most epoxy resin pipe coatings in the industry provide a thickness of only about 7 mils per coating pass. To sufficiently line the inside of the P1 Tunnel, the coating would have to be applied to a thickness of at least 30 mils, meaning that the pipe would have to be sprayed four or five times to sufficiently coat it. That many applications meant that it would be impossible to line the tunnel on time and on budget.
The Problem
J.L. Manta Company of Hammond, IN, won the bid to coat the pipe, but it became clear that there was another problem. The contract was to line the pipe in pieces, before it was installed. Manta?s engineers knew that painting the 48-foot sections before they were put in place and welded together meant that time-intensive seam repair after installation severely increased the amount of time and labor to finish the job.
The Problem
Manta selected an epoxy coating from 3M™. The coating, Scotchkote™ brand 306 Liquid Epoxy Coating, is an ambient temperature cure liquid epoxy coating designed to protect metal, concrete and other surfaces from corrosion and deterioration. Mixed 1 to 1 by weight, it would be possible to maintain the right mix on a consistent basis for the entire job. The mix also could be applied to a thickness of 16 mils; meaning that the tunnel could be fully lined in only two passes, saving time and money.
The Problem
The chemical characteristics of the Scotchkote 306 coating are engineered for optimum protection of metal, even in the harshest environments: saltwater, wastewater, petrochemicals and corrosive gases. The coating protects against soil stress, bacteria and fungus attack, soil acids, alkalis ? all the corrosive elements associated with underground or underwater use. It requires very low levels of cathodic protection, even after extended periods of time.
The Process
The Manta work plan involved an automated post-erection solution, with the actual lining process taking place after the pipe was in the ground. Coating the pipe after installation meant that the lining would be continuous, with no seams, and no repairs or touch-ups needed.
The Process
A 3M customer service representative coordinated getting approximately 300 epoxy kits shipped to a storage facility near the construction site. A day?s worth of product was then taken to the work site and stored in a refrigerated trailer.
The Process
Working during the night, crews used a custom-built ?spin blaster? on a rolling platform to abrade the steel and prepare it for the lining. During the day, scaffolds were erected on the same rolling platform, from which work crews sprayed on the epoxy. Large fans above the entrance enclosure were used to create negative air, so that work crews didn?t require respirators. The abrasive was blended and recycled daily to keep production up and dust and costs down. A Bobcat was used to scoop abrasive into a modified front-end loader. The scoop was modified to the contour of the pipe and fitted with a protective plastic edging.
The Process
By the end of the allotted five weeks, the job had been completed on time and within budget limitations.
