Spray-on Epoxy Provides Solution for Aging Cast-Iron Pipe
Underneath Pier 33 and 35 in the historic Embarcadero Waterfront of San Francisco, California, lays 3,200 ft of 48-in. cast-iron pipe submerged in the Pacific Ocean. The pipeline carries stormwater away from the city and into the San Francisco Bay.
As the pipes neared the end of their useful life, the city contracted JDH Corrosion Consultants to perform a condition assessment and provide a rehabilitation plan for the system. The condition assessment involved sending scuba divers through the interior of the pipes for visual inspection. The divers noted the condition of the interior cement liner, the presence of any visible corrosion, and identified the locations of the most severe corrosion pits. The most corroded areas were tested on the pipe’s exterior with a calibrated ultrasonic thickness tester to measure the wall’s thickness.
The wall thickness of the cast-iron pipes was in a range of 0.98 to 1.65 in. These thicknesses were deemed by the condition assessment team to be structurally satisfactory for continued operation. The divers inspecting the interior of the pipe noted it was evident corrosion was actively occurring but had not yet severely damaged the pipes. The interior mortar lining was found to be in poor condition and did not cover the full interior of the pipe. Divers found a 6-in. wide strip of mortar was missing from the crown of the pipe for the entire length.
The condition assessment and engineering team recommended removing the existing interior mortar lining and installing a 100 percent solid, high-build epoxy liner in its place.
The city considered many factors when selecting a product for this challenging environment. Due to the waterfront’s constant cruise and tourism activity, it was essential that the specified product perform in an array of conditions within a timely manner. The Warren Environmental coating system was ideal for its ability to complete the work in a single application and for its rapid cure time.
It was also decided that any products used would need to be free of volatile organic compounds (VOCs) and styrenes, or solvents. These components produce hazardous fumes and unpleasant odors that could potentially impact the pier vendors. Once again, Warren Environmental’s epoxy was the perfect product as it produced no noticeable odor nor contained any of the hazardous products commonly used within the spray coating industry.
Finally, it was vital to the city that they make the most responsible choice for the delicate marine ecology of the San Francisco Bay. The Warren Environmental epoxy coating system was the only option that passed standardized testing proving it will not harm aquatic life. This attribute was critical to the city as the pipes emptied into the San Francisco Bay.
Divers installed engineered plugs to isolate work areas, the interior motor lining was removed, and Warren Environmental’s local approved applicator, F.D. Thomas, was awarded the coatings work.
A strict schedule was set to minimize the impact on the surrounding area with F.D. Thomas’ crews implementing three shifts around the clock. Sandblasting was completed at night, and the epoxy coating was to be applied during the day. The crews were required to be flexible with their work plan to accommodate constant stoppages that had to occur for cruise ship docking.
A skilled team of certified National Association of Corrosion Engineers (NACE) inspectors oversaw the project. The inspectors ensured all conditions were correct for the coating application, verified the quality of the surface preparation. and coating installation.
As work began, NACE inspectors identified that the previously-prepared cast-iron surfaces where wicking moisture from the extremely wet and humid environment. The moisture caused the surface to change colors overnight indicating corrosion and was deemed unsuitable for coating. Dehumidification equipment was used and ran 24/7 to stop the substrate from changing color. However, it did not remove all presence of moisture in the pipe. Fortunately, the Warren Environmental system’s capability to adhere to damp surfaces made coating still possible. F.D. Thomas workers dabbed standing water from the surface of the pipes ahead of the robotic spray equipment.
As the project progressed, another problem arose. Levels of salt in the substrate were significantly exceeding what was allowed by the specification despite preparation methods. It was feared that the high levels of salt would create blistering in the coating which would then lead to delamination. After multiple attempts to reduce the high salt levels, the team was unsuccessful, and the project was stopped until all parties could agree on a path forward.
Warren Environmental recommended applying test patches to the four areas exhibiting different conditions. They were confident that if they could achieve exceptional adhesion despite the surface conditions, then delamination or blistering defects would not occur. Warren Environmental’ s single-coat, high-build epoxy possesses a much lower water vapor transition rate than its competitors. This attribute combined with its superior adhesion inhibits the growth potential of any small buried corrosion cells. Adhesion tests were performed on each of the test patch sections and all achieved over 800 PSI. Based on these results, Warren Environmental submitted a formal manufacturer’s written recommendation to continue with the project.
F.D. Thomas returned to work and the pipes were coated with the Warren Environmental 301 epoxy system. F.D. Thomas’ crew robotically spin casted 96 ft of pipe with ⅛ in. of the epoxy. An additional 6 ft of pipe that exhibited severe corrosion and pitting was coated with 1⁄4 in. or more in a single pass of by the sprayer. Coating mix ratio, temperature, application pressure, film thickness and adhesion were monitored and recorded by on-site NACE inspectors to ensure a quality installation.
To preserve movement of the pipes, the joints were cut open after the epoxy lining was complete. Leaving the joints open would allow for stray currents traveling through the interior of the pipe to cause severe corrosion. F.D. Thomas closed the open joints using a highly flexible specialty epoxy manufactured by Warren Environmental specifically for this purpose.
During the final inspection, NACE inspectors tested for adhesion of the coating system to the pipes and searched for any pinholes in the coating finish using a high-voltage spark tester. The overall average of the adhesion tests performed in the pipe was 1,200 psi. Inspectors were surprised to find that the section coated with ¼ in. of epoxy had no pinholes present while also exhibiting the best pull test results. In the end, the rehabilitation was a huge success due to the constant collaboration between all stakeholders to overcome the tremendous challenges presented throughout the project.