Hydrocarbon Processing - October 2022 - 38

Plant Safety and Environment
por retarders are commonly used alongside
insulation materials to help impede
moisture infiltration. While effective
when executed correctly, vapor barriers
can be difficult to properly install and are
vulnerable to incidental damage and perforation,
especially if applied on top of a
permeable insulation.
Pipe coatings are another solution
that can be used to help prevent moisture
from encountering a metal pipe. These
coatings may be applied along the surface
of the pipe underneath the insulation to
provide an extra line of defense against
any moisture that makes its way into
the system.
FIG. 2. The proprietary systema
combines cellular glass insulation with a low-viscosity sealant
and utilizes the impermeability of the insulation to establish a vapor barrier that moisture cannot
pass through.
The operating temperature of piping
or equipment can also influence the rate
of corrosion. In general, the rate of corrosion
will increase with the process temperature,
as electrochemical reactions
typically occur faster at higher temperatures.
Pipes are considered at risk for corrosion
at temperatures where liquid water
can contact the metal surface, which
can be roughly viewed as -4°C-149°C.
Above these temperatures, moisture that
penetrates the insulation system tends to
evaporate before reaching the surface of
the pipe. However, even these pipes can
be at risk for CUI during temperature
cycling periods or during any shutdown
and restart procedures when moisture
that has been forced away from the pipe
is allowed to settle and rest against it.
Pipes operating at below ambient
temperatures also face risk of moisture
intrusion due to different mechanisms.
In these systems, vapor drive from ambient
air can force water vapor towards
cold pipes, which then condenses into
liquid moisture. If permeable insulations
are used and existing vapor barriers become
compromised, water can quickly
build up along the cold pipe surface in
the form of condensation, creating an environment
for CUI to take place. Below
roughly -4°C, a pipe may be considered
out of this range, as liquid moisture will
freeze into solid ice. However, like hot
systems, these pipes can become at risk
for corrosion if they experience frequent
temperature cycling or system shutdowns
as part of routine maintenance
38 OCTOBER 2022 | HydrocarbonProcessing.com
activities, where ice can thaw and once
again act as an electrolyte to the system.
Signs of a problem. A Houston, Texasbased
engineering consultant who formerly
served as CUI track chair for NACE
has seen a variety of corrosion situations in
a career spanning more than four decades.
According to the engineer, an early sign of
moisture ingress for cold and cryogenic
insulation is excessive condensation on
the system jacketing's surface. Excessive
condensation is the first fail test. Surface
condensation caused by a reduced surface
temperature is indicative of increased heat
transfer due to wet insulation. Eventually,
an ice ball will form on the metal jacketing,
leading to total insulation failure. The
potential presence of moisture within the
system can also be a concern because it
may indicate that CUI is potentially developing
hidden from plain view.
System strategies for
mitigating
CUI. Early attention to warning signs is essential
to address the problem and reduce
further damage. Three primary strategies
for mitigating CUI are keeping water out
of the insulation, changing the chemistry
of any moisture that enters the system
and providing a dedicated way out for any
moisture that does get into a system.
Thoughtful selection and proper installation
of an insulation system can
help mitigate the development of corrosion
under insulation and the problems
it presents. Because moisture poses a
damage risk to an insulated system, vaInsulation
use in mitigating CUI. As
noted earlier, mitigating CUI requires a
system approach that goes beyond insulation
to consider the right pipe material,
and appropriate and properly designed
claddings, coatings and non-permeable
insulation. Establishing a regular inspection
and maintenance program is also
essential. Beyond the insulating material,
the insulation system includes adhesives
and sealants, external coatings or claddings,
and accessories.
Beyond ensuring a material will not
absorb or retain moisture, specifying
engineers should consider an insulation
material's performance and dimensional
stability in the needed temperature range.
The material should also lack any chemistry
that could increase acidity and the
shedding of chloride ions (FIG. 2).
A material like closed-cell cellular glass
insulation can address each performance
aspect. Impermeable to water vapor and
liquids, cellular glass insulation does not
wick, retain or absorb moisture, including
hydrocarbon-based liquids. The insulating
material is dimensionally stable across
a wide temperature range and will not
warp or compress. Its glass composition
provides an inert chemistry that is also
low on leachable chlorides, much like a
beaker used in a laboratory. The insulation
can also be used with a range of materials
and multiple types of accessories in a larger
system. This type of insulating material
has been incorporated into sealed systems
designed to keep moisture from entering
the insulation or reaching the pipe.
Detailing a sealed system. An example
of a system designed to keep water
outa
combines cellular glass insulation

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