Chemical Engineering May 2021 - 41

Cortec Case History 668
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FIGURE 3. Spare valves should be neatly restored and preserved for future use while in storage so that
they are ready to go when needed
that the facility can be reopened or
the assets sold. If the valves are allowed
to rust, either in place or in
storage, there could be serious repercussions.
The equipment may
not work when it is put back into
operation, or there may be a sudden
failure down the road. Here,
the basic goal is the same as with
spares in storage - to preserve
pieces in good working order to
avoid loss of value.
Restoration and preservation
There are two key aspects to making
sure that valves are corrosionfree
and ready to go. The first is
restoration for valves that have already
rusted during the manufacturing,
shipping or storage phase. The
second is preservation of valves
that have either been restored or
have not yet rusted. Manufacturers
will also likely deal with hydrostatic
testing in the preservation process.
Restoration. There are different
ways to remove existing rust on
valves. A common method is abrasive
blasting or grinding, which
could be especially challenging on
intricate valve internals. Another option
is to use water-based or even
bio-based rust-remover concentrates
or gel. These can be applied
by dipping the valve into the liquid or
brushing on the gel, leaving it to sit
for 20 minutes to an hour (or even
overnight, depending on the severity
of the rust), then neutralizing and
rinsing it with an alkaline cleaner
that
contains
flash-corrosion
inhibitors
(Figure 4). Once the valve
is restored, it can be preserved or
installed as needed.
Preservation. Leakage is one of
the first preservation concerns that
valve
manufacturers
often
need
to address. Hydrostatic testing is
used to check for leaks. While this
procedure introduces moisture to
the valve, which can heighten corrosion
risks, appropriate corrosioninhibiting
additives can be used to
prevent this. Since disposal of the
hydrotesting water can present
challenges when levels of chlorides,
sulfates or other chemicals exceed
wastewater discharge limits, it is
important to evaluate the disposal
profile of the hydrotest additive
before adoption.
It is also beneficial to choose a
hydrotesting additive that can do
double duty for ongoing corrosion
protection. For instance, some filmforming
hydrotest additives leave
behind a corrosion-inhibiting film
that protects metals through direct
contact and also release corrosioninhibiting
vapors (also called vapor
corrosion inhibitors, or VCIs), which
offer added protection for metals
in hard-to-reach spaces inside the
intricate valve internals. VCIs offer
some advantages when compared
to standard methods of corrosion
protection, because the protective
chemistry is able to diffuse through
void spaces and adsorb onto metal
surfaces in an invisible protective
layer that interrupts the normal
corrosion reaction, yet naturally
evaporates when the enclosure is
breached, so that special removal
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