The setting
Municipal water treatment plant serving a regional population. The chlorine contact basins — large open tanks where disinfection happens — sit under covers that are supposed to contain the chlorine off-gas and keep operators safe during routine sampling. It's a wet, chemically aggressive atmosphere that doesn't give materials an easy ride. Chlorine vapour is relentless.
What was going wrong
The original aluminum covers were failing after about four years in service. The problem was galvanic corrosion at the fastener points — dissimilar metals plus chlorine vapour created a battery effect that ate through the panels around every bolt hole. Operators were carefully navigating around visibly weakened sections during sampling rounds. A cover panel collapse here would be a reportable safety incident, not a maintenance inconvenience.
What we installed
We fabricated new covers using FRP grating panels with integral covers and a resin formulation chosen specifically for continuous chlorine vapour exposure. The support framing underneath was built with pultruded FRP C-channels — chemically inert to the off-gas that destroyed the aluminum. Same footprint and access hatches as the original covers, so no tank wall modifications were needed. Just a material that doesn't react with chlorine.
What changed
Bottom line: The four-year aluminum replacement cycle has been eliminated. Based on the degradation rate measured in annual inspections so far, the FRP covers are projected to exceed 20 years in this service — five replacement cycles avoided. The operators no longer worry about where they step during sampling rounds.
Cover replacement interval projected from 4 years to 20+ years. Zero galvanic corrosion observed across all panels since installation.
How it compares
Aluminum covers in chlorine service fail at the connections first — galvanic corrosion at fasteners, then progressive panel loss, replacement every four years. Over a 20-year plant life, that's five procurement, fabrication, and installation cycles. The FRP alternative costs more upfront per panel, but the total cost of ownership flips in its favour before the second aluminum replacement would have been due.
When the operating environment is the enemy, material choice is the only real solution. See our corrosion prevention overview for more on this principle. Similar municipal applications are covered under FRP in water and wastewater treatment.