Original Story: energyglobal.com
Thousands
of chemicals, petroleum products, and corrosive elements like salt
water brine are transported by tanker truck, railcar and distributors,
as well as processed in chemical storage tanks at facilities and refineries, every day.
In
these venues, carbon steel corrosion can require early tank replacement
and maintenance, as well as pose a safety risk in terms of potential
leaks, spills, and even fire and explosion, so effective corrosion
protection is a must.
“We clean just about any tank hauling
product or waste on the road or rail,” said Joe Svehlak, Facility
Manager at DFW Tank Cleaning, a Dallas-Fort Worth, Texas-based full
service tank cleaning facility that specialises in chemical cleaning.
“Protecting against corrosion is vital in such tanks, as it is in our
facility flush tanks.”
According to Svehlak, effective corrosion resistance is essential in the chemical holding tanks
because they hold the wastewater from the first flushes of tanks that
the company cleans, which can include residual chemicals, until it is
treated. This amounts to thousands of different residual chemicals held
in the flush tanks annually – from petroleum products and salt-water
brine to fluoride, caustic soda, and a variety of acids.
Against
such tank corrosion challenges, traditional polymer paints and rubber
type coatings have long been used as physical barriers to keep corrosion
promoters such as water and oxygen away from steel substrates. This
works until the paint is scratched, chipped, or breached and corrosion
promoters enter the gap between the substrate and coating.
However,
truck or rail tankers hauling waste, including sand and sediment, can be
particularly prone to scratches, chips, or breaches. Then the coating
can act like a greenhouse – trapping water, oxygen and other corrosion
promoters – which allows the corrosion to spread. While stainless steel
can be used for tanks to resist corrosion, it can be up to six times
more costly than carbon steel, as well as challenging to weld,
fabricate, and maintain.
Now a new generation of anti-corrosion
coating, called Chemically Bonded Phosphate Ceramics, is poised to stop
such corrosion, improve safety, and extend tank life in the
transportation industry and beyond while minimising maintenance and
downtime.
Rugged anti-corrosion protection
“Our corrosion
protection for our 10 000 gal. flush tanks has to be particularly rugged
because we mix the wastewater so it does not stratify, and sand, rocks,
and even metal shavings can be present from the waste trailers we
service,” said Svehlak. “The corrosion protection also has to withstand
the high-temperature, high pressure water we often work with.”
To control corrosion, the chemical storage tank cleaning
facility chose to have Ennis, Texas-based DC Metal Construction, a
privately owned company specialising in steel construction and
industrial plant building projects, coat the inside of two flush tanks.
The flush tanks were coated with a spray applied inorganic coating
called EonCoat® from the Raleigh, NC-based company of the same name.
EonCoat represents a new category of tough, Chemically Bonded Phosphate
Ceramics (CBPCs) that can stop corrosion.
In contrast to
traditional polymer coatings that sit on top of the substrate, the
corrosion resistant coating bonds through a chemical reaction with the
substrate, and slight surface oxidation actually improves the reaction.
An alloy layer is formed. This makes it impossible for corrosion
promoters like oxygen and humidity to get behind the coating the way
they can with ordinary paints. The corrosion barrier is covered by a
ceramic shell that resists corrosion, fire, water, abrasion, chemicals,
and temperatures up to 400°F.
Although traditional polymer
coatings mechanically bond to substrates that have been extensively
prepared, if gouged, moisture and oxygen will migrate under the
coating’s film from all sides of the gouge.
By contrast, the same
damage to the ceramic-coated substrate will not spread corrosion
because the carbon steel’s surface is turned into an alloy of stable
oxides. Once the steel’s surface is stable (the way noble metals like
gold and silver are stable) it will no longer react with the environment
and corrode.
Visible in scanning electron microscope
photography, EonCoat does not leave a gap between the steel and the
coating because the bond is chemical rather than mechanical. Since there
is no gap, even if moisture was to get through to the steel due to a
gouge, there is nowhere for the moisture to travel. The only spot that
can corrode is the scribe line itself, which eliminates the possibility
of the corrosion migrating.
“Unlike traditional methods, the
corrosion resistant coatings for mild steel have a double layer of
protection,” said Bobby Hobbs, a DC Metal Construction job foreman. “The
tough, outside ceramic coating will not chip like paint and takes
sandblasting to remove. The chemically bonded layer stops corrosion and
will not allow corrosion promoters to spread.”
“EonCoat has stood
up really well to everything from chemicals and salty brine to
abrasion, high-pressure water and heat,” added Svehlak. “I believe it
will double the life of our tanks while significantly lowering
maintenance costs and downtime.”
According to Svehlak, the
coating’s rugged anti-corrosion properties could also benefit a wide
range of transportation-related businesses.
“Tanker truck and rail
operations can benefit from the anti-corrosion coating’s reliability,”
said Svehlak. “Its abrasion resistance would be a big plus to wastewater
haulers or super sucker truck operators with vacuum tanks that may
encounter metal chips, glass shards, etc. when cleaning out sumps. It
would also resist tank corrosion when transporting petroleum products or
even used restaurant waste such as oil, fat, or grease.”
For
transportation companies looking to reduce costs, there are additional
advantages to CBPC coatings beyond corrosion resistance. This includes
quick return to service that minimises equipment downtime, as well as no
VOCs or HAPs, and a flame spread rating of zero which improves safety.
For
corrosion protection projects using typical polymer paints such as
polyurethanes or epoxies, the cure time may be days or weeks before the
next coat of traditional ‘three part systems’ can be applied, depending
on the product. The cure time is necessary to allow each coat to achieve
its full properties, even though it may feel dry to the touch.
In
contrast, a corrosion resistant coating for carbon steel utilising the
ceramic coating in a single coat requires almost no curing time. Return
to service can be achieved in as little as one hour. This kind of speed
in getting a tank, tanker truck, or railcar operating again can save
significantly in reduced downtime.
“After appropriate tank
preparation, we found that if we spray EonCoat in the morning the tank
can be returned to service the same day because it applies in one coat
and dries quickly,” said Hobbs.
EonCoat consists of two,
non-hazardous components that do not interact until applied by a plural
spray system like those commonly used to apply polyurethane foam or
polyurea coatings. Since the coating is inorganic, there are no VOCs, no
HAPs and no odour. This means that the coating can be applied safely,
even in confined spaces.
“Since the corrosion resistant coating
has no VOCs, HAPs or odour we were able to spray during work hours, so
work next to the tanks could continue while we coated them,” concludes
Hobbs. “For any tank, facility, or transportation-related operation with
corrosion issues, it is well worth considering.”
