Chemical Engineering January 2017 - 38

provement plans. This plan should consist
of the following three steps:
1. Consider the assessment of the outdoor
air and indoor environment with
regard to corrosion potential. ANSI/
ISA Standard 71.04-2013 (hereafter
ISA 71.04) can be used to provide
site-specific data on the types
and levels of gaseous contamination
in the amount of corrosion being
formed. Corrosion classification coupons
(CCCs, Figure 3) can be used
as a survey tool to establish baseline
data necessary to determine if and
what type of environmental controls
are needed.
2. Develop and specify a targeted contamination-control
strategy.
FIGURE
4. Atmospheric corrosion monitors
(ACMs) provide realtime data on the
performance of the corrosion-prevention
measures in a control room, including
chemical-filtration and air-quality systems
cerns regarding equipment corrosion in
research documents, technical papers
and site planning guides. These companies
also provided guidance in terms of
the environmental conditions necessary
to protect their computer equipment
(Figure 2) [3].
Manufacturers of industrial computer
equipment still specify the control of corrosive
gases in their site planning guides
or in the terms and conditions necessary
to maintain warranties and service
contracts. Even in environments previously
considered benign with regard to
electronics corrosion, serious problems
as a direct result of RoHS compliance
are being reported.
Contamination control process
With the changes to process measurement
and control equipment mandated
by the various RoHS directives, process,
facility and instrumentation engineers
should include environmental
contamination monitoring and control
as part of overall site planning, as well
as risk management, mitigation and imClass
G1
G2
Severity
level
Mild
TABLE
1. CLASSIFICATION OF REACTIVE ENVIRONMENTS
Silver
Copper
reactivity
<300 Å
Moderate <1,000 Å
Comments
reactivity
<200 Å
<1,000 Å
Corrosion is not a factor in determining equipment
reliability
Corrosion effects are measurable and corrosion may
be a factor. Electroless nickel immersion gold (ENIG)
and immersion silver (ImmAg) printed circuitboard
surface finish failures
G3
GX
38
Harsh
Severe
<2,000 Å
≥2,000 Å
<2,000 Å
≥2,000 Å
High probability that corrosive attack will occur.
Organic solderability preservative (OSP) and immersion
tin (ImSn) PCB surface finish failures
Only specially designed and packaged equipment
expected to survive
Corrosion
in an indoor environment is most
often caused by a short list of chemical
contaminants or a combination
of contaminants. The contaminants
present in a specific area are highly
dependent on the controls put in
place to mitigate them. These efforts
mainly involve the selection and application
of the appropriate chemical
filtration systems to clean both the
outdoor air being used for pressurization
and ventilation, as well as any
recirculation air.
3. Establish a realtime environmentalmonitoring
program based on the
severity
levels
established
in
71.04. Realtime atmospheric corrosion
monitors (ACMs, Figure 4) can
provide accurate and timely data on
the performance of the chemical filtration
systems as well as the room
air quality.
The absence of gaseous contamination
controls can be the result of a lack
of knowledge and education. Often, the
relationship between corrosion levels
and hardware failures is overlooked or
unknown. However, due to the continuing
efforts of automation and control
companies, this knowledge gap
is shrinking, and successful corrosion
monitoring and control programs are
being developed and implemented,
assuring reliable operation of process
measurement and control equipment.
Environmental assessments. A simple
quantitative method to determine the
airborne corrosivity in a control room
environment is by " reactivity monitoring "
as described in ISA Standard 71.042013:
Environmental Conditions for
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Chemical Engineering January 2017

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