huangyhg

cathodic protection for pier
i've got a client with a 1/4 mile pier into a brackish (salt and fresh water mix) river.
over time, the painted steel pipe piles have started to corrode. the plant currently uses an impressed current and sacraficial anodes to protect (or reduce) the pile corrosion but this does not appear to be enough.
my initial reaction is a ndt program, and clean and paint; with concrete jacketing on the piles with excessive reduction in thickness.
any other thoughts?
any experience out there with other types of repairs?
as always, thanks for the help.
jjf
if an impressed current system cannot handle the problem, i doubt if other measures will be successful. many years ago i had the opportunity to do some field work with an authority on impressed current systems. as the system works and the sacrificial anodes do their job (i.e. vanish), the applied voltage has to be adjusted (increased) to compensate. we made field measurements of the voltage at various locations on a buried natural gas pipeline network. then based on his experience he adjusted the cathode voltage to maintain protection. of course, over time, the anodes will become so deteriorated that they must be replaced.
suggest you call in a specialist on impressed current systems to check out the present conditions.
on pipelines, i have always used sacrificial anodes until the pipeline is complete. these are then removed and the impressed current switched on. otherwise the two systems fight each other. of course all elements of the structure would have to be electrically connected.
i would agree that a specialised cp company is a definite.
on a recent pipeline, the local dc motor commuter trains were pushing out 1500v onto a leaking negative return rail and the potential on the pipeline was changing by a volt every second. we were collecting hydrogen gas off the line at one stage! could this be a factor?
other thoughts
cement rich concrete may protect the steel without the need for paint, although you may have to remove any salts first.
we have had special paint applied to bare steel underwater by divers.
guys, thanks for the feedback.
stephena - you bring up an interesting point. my pier is handling crude oil in and finished gasoline out. i know they got grounding cabling in differnet areas, but i wonder if they've tested the potential differences during operation.
jjf

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