THE BACKGROUND
Strained fresh water resources in Chile's arid north, where most of the Andean nation's copper mines are concentrated, and projections for decreased precipitation due to the effects of climate change have prompted mining companies to increasingly turn to ocean water to supply their operations.
Chile's state copper commission, Cochilco, said in a report that seawater consumption is expected to reach 10.7 cubic meters per second in 2026 and reaches 4.3 times more than the current expected amount. All seawater used for mining will first be desalinated in desalination plant built close to sea and be transported to mines through long-distance pipeline. It is estimated that by the year 2026, half of the fresh water for mining will be from desalination seawater.
PROBLEMS OF TRANSPORTING DESALINATION SEAWATER
Corrosion rate of desalination seawater is double higher than seawater
Total dissolved solids of seawater is approximately 36000mg/L which will be decreased to less than 800mg/L after desalination. Numerous studies show that steel corrosion rate by desalinated water using the first pass reverse osmosis is even higher than the common seawater with results reaching up to 1.3mm/a, which could be classified as severe corrosion and the corrosion rate of desalination seawater is almost double higher than seawater to the transporting carbon steel pipeline.
Huge elevation drop(3000-3500 meters) produces negative pressure to pipeline internal coating
In order to provide anti-corrosion protection against severe corrosion from desalination seawater, internal PE liner or liquid epoxy coating was used as internal protection for such transporting pipelines. However, due to the special geography of Chile, produced desalination seawater is transported to copper mines at elevation level of 3500m through transporting pipelines.
But when using traditional internal anti-corrosion method, though PE liner or liquid epoxy coating provides good resistance to corrosion from seawater/desalination seawater, there's almost no adhesion between PE liner and carbon steel pipe and low adhesion of liquid epoxy coating is not enough to resist the strong negative pressure during backflow caused when water transporting stops occasionally, which had collapsed the PE liner and peeled off internal epoxy coating.
SOLUTION: INTERNAL PRIMED FBE COATING
Antofagasta Minerals had long been seeking for a proper pipeline internal coating solution which is able to long-term transporting desalination seawater with stable and high adhesion to resist the negative pressure.
In order to provide a suitable internal coating protection with strong adhesion working in wet environment to project desalination seawater transporting pipeline, Tyhoo has proposed to Zaldivar copper to use internal primed FBE coating with external 3LPE coating as a suitable solution.
The primed FBE coating consists a phenolic primer applied onto the steel substrate with post-curing FBE as top layer. It is applicable to be used for transporting sea water, desalinated seawater, pulp, crude oil, raw natural gas and other corrosive medium. The coating has much higher cost performance compared with internal rubber liner, internal high density polyethylene liner or injection of liquid epoxy coating.
The FBE coating with liquid phenolic primer is cured for long period by high temperature oven (about 1 hour for primer and 2 hours for FBE coating), so as to achieve a uniformly, gently and fully cured coating, of which inside stress fully released and ensure that the cured modified-phenolic FBE coating reaches high crosslink density and stable wet Tg and provide strong and stable adhesion between FBE coating and pipe internal surface, thus to ensure the pipeline service life on the condition of ensuring the coating's integrity and thermal aging resistance ability.
