Hydrocarbon Processing - July 2021 - 83

Maintenance and Reliability
2. Equipment submerged in wet
pits, where salty water could be
present and microbes are in
contact with stainless steel
3. Equipment enclosed in insulation,
where salty water from a marine
environment or rain water
containing some chlorides may
accumulate on stainless steel.
All these conditions may cause accumulation
of chlorides on the external surface.
Similarly, underground buried and
submerged equipment may encounter
microbial activity. Both equipment scenarios
can create an environment that is
conducive for pitting, crevice and microbial
corrosion, and even stress corrosion
at moderate temperatures.
To maintain corrosion resistance
stress
against external
crevice, pitting,
corrosion cracking and MIC, the severity
of corrosion should be assessed. One
option to mitigate against corrosion is to
select corrosion-resistant material to ensure
internal and external corrosion-resistant
conditions. The second option is to
implement an external coating on stainless
steel surfaces to avoid direct contact
of corrosive species with the equipment
external surface. The most economical
way to protect against external damage
is to apply a coating to exposed external
surfaces, which will avoid direct contact
of corrosive chlorides and microbes with
the stainless steel components.
It is important that the coating is applied
as per the manufacturer's coating
application guidelines to avoid coating
defects. Surface preparation and application
are key to ensuring the coating
integrity. For buried equipment, where
regular coating inspection is not possible,
the application of sacrificial or impressedcurrent
cathodic protection, along with
coating, can help improve design life and
equipment integrity. Cathodic protection
additionally protects equipment in case of
coating damage due to defect or physical
damage. Note: The selection of cathodic
protection type and design is a wide subject
and is not covered here.
Various international standards and
company specifications prescribe coatings
on stainless steel if corrosion conditions
exist. For example, coating systems
are used as specified in TABLE 1 and
TABLE 2 for austenitic and duplex stainless
steels, respectively.
Buried, submerged and insulated
stainless steel components can encounter
chloride and microbial corrosion attack.
Stainless steels in these scenarios require
external coating; otherwise, external
coating on stainless steel components is
not necessary.
RATNAKAR KADIKAR is Global
Manager, Materials for ITT Corp.
Industrial Process Group.
He provides metallurgical
and materials technology for
ITT Corp.'s business, as well as
technical support to ITT customers
and product specialists. He has more than 21 yr
of experience in corrosion monitoring, corrosion
evaluation, material selection, failure investigation,
heat treatment, micro-structural analysis and
training on metallurgical aspects. He has also
worked in corrosion loop risk-based inspection
study, integrity operating window, cathodic
protection, painting/coatings and residual life
assessment of static equipment. Mr. Ratnakar holds
BS and MS degrees in metallurgical engineering.
He is a qualified NACE International Senior Corrosion
Technologist and is API 571/API 653 certified.
LIVE WEBCAST
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Siemens
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Lee Nichols
Editor-in-Chief/Associate Publisher
Hydrocarbon Processing
Hydrocarbon Processing | JULY 2021 83

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Hydrocarbon Processing - July 2021

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