Chemical Engineering March 2014 - 39

Cover Story
Feature Report
Implementing a CorrosionUnder-Insulation
Program
CPI facilities need to put
in place a systematic
program for preventing
and mitigating corrosion
under insulation
Russ Davis
The Mistras Group, Inc.
C
orrosion to the external surface
of process piping and vessels
that is hidden under the
insulation is referred to as
corrosion under insulation (CUI).
Aging piping and equipment in
chemical plants and petroleum refineries
have made CUI detection
and assessment requirements increasingly
important. Because the
need to detect and assess CUI is
critical in chemical process industries
(CPI) facilities, inspection and
testing methodologies have been
pushed to improve. However, many
CPI facilities lack an insulationrepair
program. The best approach
to address the problem of CUI is to
develop and adopt a comprehensive
and facility-wide CUI program. This
article describes the components of
such a program and is designed to
help facility managers and engineers
identify strategies to implement
it.
Industry estimates indicate that
CUI costs the chemical and oil-andgas
industries in excess of $100 million
annually. This cost represents
only the estimated damage to the
equipment, and does not include
the losses that may be associated
with process downtime. Taking
equipment and piping out of service
when they are needed to make
product will raise the level of losses.
This estimate also does not include
Initiate CUI
Phase 1
evaluation, identify
suspect equipment
CUI Initial Descision Tree
Pre-inspection
Is
construction
material carbon
steel?
YES
Is
Operates
between 10
and 400°F?
NO
Cycling
in and out of
10 and 400°F
range?
YES
YES
Potential for
CUI exists
Cycling
in and out
of 120 and
400°F?
NO
No CUI expected
Implement
risk-based
inspection
program
YES
YES
Potential for
stress-corrosion
cracking exists
NO
operating
temperature
between 120 and
400°F?
NO
Is it
austenitic
stainless
steel?
NO
YES
Consult
with materials
engineer for CUI
susceptibility
IDMS download
of identified
equipment
susceptible to CUI
Perform risk
assessment
to prioritize
inspection plan
Perform field
walkdown, review
asset history,
cyclic service,
plant turnaround
schedule
Figure 1. The initial phase
of a comprehensive CUI program
involves a team assessment
of process vessels and
piping to determine which
pieces of equipment may be
susceptible to CUI
the risk posed by CUI for potential
exposure to hazardous chemicals, as
well as the potential fire and explosion
hazards, resulting from the loss
of containment of highly hazardous
chemicals. Sometimes, corrosionpreventive
painting programs are
cut when budgets are tight.
CUI primarily affects carbonsteel
and low-alloy steel vessels and
piping. Operating conditions noted
for making equipment susceptible
to CUI range from 10°F (-12°C)
to 400°F (205°C). Austenitic stainless
steels and duplex stainless
40 ChemiCal engineering www.Che.Com marCh 2014
steels are also susceptible to CUI,
especially in coastal geographic regions
where the normal atmosphere
contains chlorides and where the
equipment operates between 140°F
(60°C) and 400°F (205°C). Chlorideinduced
stress corrosion cracking
(SCC) has been found in austenitic
stainless steels due to the chloride
content of the normal environment.
Program components
It is essential that a programmatic
approach to reducing the risk of
operations includes a focus on CUI
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Chemical Engineering March 2014

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