Hydroelectric, O&M, Renewables

Giant hydro gates on the Niagara require 3-stageface-lift for tourists

Issue 6 and Volume 99.

Giant hydro gates on the Niagara require 3-stageface-lift for tourists

Corrosion from constant mist and humidity of Niagara`s Horseshoe Falls along with ultraviolet damage and aesthetic considerations forced Ontario Hydro to perform rigorous protective maintenance on one of its two control gates along the Niagara River in Niagara Falls, Ontario, Canada.

Moisture and sun exposure can wreak havoc on steel gates, weakening structural components. The damage also makes the gates, which stand close to six stories tall and 48 feet wide, less than attractive. “They`re quite visible,” said Jim Schacht, Ontario Hydro`s maintenance and technical service leader for the Niagara Plant Group. “Because they are situated along the Niagara Parkway, the main tourist track, we tend to pay a little more attention to them. There`s minimal mechanical maintenance, but appearance-wise, we want to keep them looking good.”

Recent work performed on the Sir Adam Beck No. 2 South Control Gate was the first in approximately 20 years, which Ontario Hydro says is the average cycle for such protective maintenance.

The Niagara River is one of the world`s greatest sources of hydroelectric power. Water was first diverted from the Canadian side for electricity generation in 1893 when a small 2,200-kW plant was built just above the Horseshoe Falls to power an electric railway between the communities of Queenston and Chippawa.

Today the river provides the driving force for almost 2,000 MW of electricity from a number of power plants on the Canadian side. The three largest are Ontario Hydro`s Sir Adam Beck-Niagara Generating Stations No. 1 and No. 2 and a nearby pumping generating station. The Beck control gates, built in the 1950s, regulate the flow of water to these three generating stations and serve as a safety dam.

While the gates are capable of stemming the rushing flow from the river into the 5.5 miles of underground tunnels leading to the stations in an emergency, they haven`t been used for that purpose and are only closed annually for routine mechanical maintenance.

The right program

Keeping the gates looking new demands stringent maintenance and intensive, effective maintenance requires application of a sturdy and attractive protective coating. Ontario Hydro and the painting contractor, C.H. Heist Ltd., of Hamilton, Ontario, together selected Sherwin-Williams Surface Tolerant Epoxy Primer, Surface Tolerant Epoxy and Hi-Solids Polyurethane because of the products` “good history” in steel maintenance jobs in terms of price and service, along with technical specifications for the damp conditions and low temperatures.

The epoxy primer offers corrosion protection, strong adhesion, toughness, high build capability and proven performance. The epoxy, a self-priming finish coat for marginally prepared surfaces, was selected for its chemical/moisture barrier properties and tolerance of damp or moist surfaces. The polyurethane was selected for its corrosion and abrasion resistance along with its color and gloss retention properties.

Maintenance in progress

Before the coating system could be applied, the painting contractor first had to properly prepare the surface, a complicated task since the previous coating contained lead. To comply with lead abatement regulations, contractors had to enclose both sides of the gate with a protective tarp to catch any lead.

Under the tarp, a system of scaffolds covered either side of the gate`s steel interior. The front side was scaffolded with a 24-foot, custom-made stage system with an electric motor. On the back, eight levels of scaffolds climbed up the structure.

A second consideration in surface prep was protecting the gate`s roller wheels and pockets from potentially damaging sandblasting grit. The roller wheel areas were masked off and protected during the blasting, according to Ray Martino, C.H. Heist estimator. Rollers were cleaned with solvent in accordance with the Steel Structures Painting Council (SSPC) Surface Preparation Specification No. 1 (SP-1) to remove all visible grease and contaminants from the steel surface. Roller wheel pockets were water blasted at 3,000 pounds per square inch to remove additional grit and dirt.

The remaining 20,000 square feet of gate surface was prepared by a team of six Heist painters who removed the previous coating with abrasive blasting per SSPC SP-10, which covers requirements for near-white blast cleaning of steel. Workers then hand cleaned areas near the roller wheel pockets to assure all grit was removed.

Next, the epoxy primer was applied, followed by the epoxy. Each was applied at a dry film thickness (DFT) of five-to-six mils per coat. The polyurethane finishing coat was then applied at a DFT of three-to-four mils. All coatings were applied by airless spray.

The process took eight weeks to complete. “We`re hoping to get 25 years of protection out of this coating system, and we`re confident the coating system we used will help us achieve that.”

Circle 141

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Technicians completed the stripping and three-stage protective coating of the Sir Adam Beck control gates on the Niagara River in approximately eight weeks. The coating is expected to protect the steel gates, erected in the 1950s, for another 25 years.