I have a sewage tank environment that operates at ambient temperature,
contains human waste and a special microbe, which I believe is the BZT
product from United Tech, Inc.
http://www.united-tech.com/wd-ww-urinescale.html. The fluid operates
at a pH between 6-8.5.  It had a coal tar epoxy coating on it that has
since worn out, and they are having pinhole leaks at locations of
coating failure.  Some sodium hypochlorite (probably in the ppm range)
is added to the discharge of the tank for cleaning of the microbes.

I have been asked to recommend a potential thermal spray coating that
would appropriate for this application.  Some choices proposed have
been aluminum and hastelloy C-276 (may be overkill).

My question has several parts:
(a)has anyone tried to thermal spray coat a tank in this type of
environment , and if so,
(b)what coating material was used,
(c) what was the resulting performance (did the coating peel,
crack,etc) and (d) what was the type of coating applied (wire arc,
HVOF), etc.

I am looking for case study information.  I do not need general
articles on corrosion resistance of thermal spray coatings. I don't
need references to applicators that might have applied thermal
coatings in general.

Hi:
This is the first time I've used Google Answers.  I saw your question
posted and thought I'd comment.  I have over 30 years experience in
thermal spray, with OEM equipment and powder/wire manufacturers.  I
did product and process development.  Thermal spray, when properly
applied, is likely the best choice for corrosion resistance
applications.  The best corrosion resistant coatings are applied with
either HVOF or some materials can be satisfactorily applied with high
velocity arc spray systems.  As you outlined in your question,
corrosion of the base metal will start at any pin hole through any
coating.  Base material, surface prep, bond strength, residual stress
(coating), coating material, coating sealer material, among other
factors, play a synergistic role in a successful corrosion resistant
coating.  Proper selection, along with proper execution of each
parameter, determine success.  Case studies may reveal information,
but will not ensure success.  The material selected may not be nearly
as important as the process and methods of implementation selected. 
Operator experience as it relates to coating uniformity (which is a
major variable to coating success)is also important.
There are a lot more factors, to decide the economics/payback of a
thermal spray coating for your application, to consider also.
Bob