HYDROCARBON
ENGINEERING
78
Apart from the curing speed itself, another feature that
can assist in enabling the fast return to service of a lining is
the ability for it to be applied in a single coat. Good painting
practice would suggest that the likelihood of having low
areas of DFT would be minimised by being applied in two
coats, the theory being that should a low area be applied
during the first coat, the second coat is likely to be able to
cover this and build up this area to an acceptable thickness.
With recent advancements in lining technology, good lining
systems with a flexible DFT range have been developed to
enable the system to be applied in one coat. This helps to save
application time and avoids overcoating issues such as
maintaining the cleanliness between the coats, and applying the
second coat too soon or at the other end of the spectrum, too
late. The use of linings, which have no added solvents in the
formulation, help as this reduces the chances of pinholes or
voids being formed, and also prevents the risk of solvent
entrapment. As always, a good inspection regime and attention
to quality should help ensure that a defect-free film is achieved.
Safe and sound
One of the key properties is to be able to apply the coating to
the specified thickness without the risk of any sags or runs
forming. This allows the applicator plenty of scope for
over-application without causing any defects caused by a high
film thickness. It would then go without saying that such a
coating must be able to be applied at high film thickness and
still be able to perform successfully in its given environment
and conditions. A higher film thickness does not necessarily
equate to better or longer performance, as some coatings
become more brittle at higher thickness with the potential to
crack, particularly under onerous conditions. A ‘flexible DFT’
single coat lining system has to tackle this challenge providing
adequate film flexibility and cohesiveness even at higher dry
film thicknesses.
Another issue to consider is of safety, particularly with
tanks or vessels, which would be classed as ‘confined spaces’
by health and safety legislation. The use of solvent-borne
coatings is becoming less desirable due to the extra
precautions and measures that must be put in place to deal
with this, and so the use of ‘solvent-less’ or ultra high solids
products is becoming the norm. A few of these ultra high
solids products have the added benefit of providing
inherently better edge coverage due to the naturally higher
viscosity than traditional solvent-borne products. The higher
the film thickness on the edges, the more durable the coating
would be expected to be in these areas and subsequently
better longevity of the coating should be seen.
Conclusion
In order to simultaneously respond to the changing needs
described above, owners and operators of storage tanks
and vessels are turning to coatings manufacturers.
The use of glass and ceramic particles in conjunction
with a novel phenolic novolac resin system has led to a
new formulation platform for coatings that is capable of
withstanding higher pressure, higher temperature, a
broader range of cargoes and enabling quick curing single
coat application for faster return to service.
As well as providing a better barrier (or a more
‘tortuous path’) for any moisture or chemical present in the
cargo to migrate through the film, the ceramic and glass
particles help to provide toughness and moderate the
mismatch in the coefficient of thermal expansion with
steel substrates. The novolac resin system is a key element
in providing the additional film cohesiveness and film
forming quality, with its fast curing, user friendly and
compatibility with a single coat application.
The coatings industry is working hand in hand with the
asset owners and applicators to ensure that these coatings are
able to satisfy the needs and requirements of all concerned.
This new technology platform is now being translated
in real products. The first of such next generation linings
have been well received by process vessel operators, and it
is thought the same platform could also be translated over
to the demanding subsea process arena.
Such linings give numerous benefits: flexibility of cargo,
speed of cure, which results in reduced downtime during
maintenance, good protection over an extended period of
time, and good application properties, which result in
excellent one coat systems. All of which mean storage tanks
and vessels will continue to be operated safely and
efficiently while meeting the challenges posed by the
modern oil and gas industry.
T&T
Figure 4.
Downtime of tanks is a major issue.
Figure 5.
Tank testing.
