Ductile Iron Pipes

DUCTILE IRON PIPES
- Application of 100% Solids Polyurethane Coatings

In June of 1993 a San Diego corrosion engineering firm, tested the corrosion protection system installed in 1991 on the 12", 6 mile, ductile iron pipeline known as Fiesta Island Replacement Project (Phase 1) in San Diego, California. The system uses 25 mils (625 microns) of a 100% solids polyurethane coating and sacrificial magnesium anodes. The consultant’s analysis15 showed that the coating system had an installed efficiency of 99.66% and the pipe had an actual current requirement (for corrosion protection) three times less than the design value.

The inspector said that, in his opinion, "this is outstanding performance for a coating on bell and spigot ductile iron pipe". The analysis goes further to report that, given the excellent condition of the polyurethane coating and the corresponding low rate of consumption of the anodes, the system will last 111 years.

In 1991, a start was made towards meeting the San Diego Clean Water Program’s water reclamation goals by building Phase 1 of the Fiesta Island Project. The line conveys digested sludge at high pressure from the Point Loma Wastewater Treatment to a new biosolids processing plant 19 miles away. The balance of the pipeline is to be completed by 1997.

Success of this first pipeline was (and still is) very critical. The pipeline route goes through a military base, a popular park and an affluent neighborhood. It also goes through an earthquake fault line and several heavily traveled business corridors. Corrosion survey reports indicated that the soil was very corrosive. Any sort of premature failure could mean political and functional disaster. The 100% solids polyurethane successfully met this challenge on all counts as the external corrosion resistant coating.

The applicator prefers to use the polyurethane system about conventional coal tar epoxies due to the many handling advantages of the technology. First, there is no concern over carcinogenic coal tar in the polyurethane system because the safer petroleum tar is used as an extender instead of coal tar. Secondly, the polyurethane is applied in one coat (no primer), directly to the blasted metal using an automatic spray gun and pipe conveyor at a rate of 20 feet of pipe per minute (6 meters/min). These production rates are at least 5 to 10 times of what is possible with coal tar epoxy.

The pipe installers and on-site inspectors reported that the pipe survived the installation and a 2000 mile trip from Birmingham, Alabama (where the pipe was made and coated) to San Diego with little or no coating damage; an ‘unheard-of‘ feat when dealing with coal tar epoxy or tape coatings.

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