Hydrocarbon Processing - September 2021 - 80

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laying activities and regular monitoring
post-insulation to minimize CUI on SS.
Pre-insulation laying activities include:
1. Hiring an insulation contractor of
good repute is an important step
to avoid CUI problems. Before
laying the insulation, ensuring a
selection of good-quality vapor
barrier mastic, glass cloth fabric,
foam sealer and SS jacketing is
vital for achieving a leakproof
arrangement and eliminating the
ingress of rainwater or moisture
into the insulation material.
2. Insulation material lots received
at the site are often dumped into
a corner without adequate storage
to prevent moisture ingress.
Such practices must be strictly
avoided. ASTM C390, the
standard practice for sampling
and acceptance of thermal
insulation lots, provides helpful
insight in this regard.
3. Insulation of equipment and
piping should be carried out
at the site after installation. If
the insulation is carried out at
a vendor shop for some reason,
it must be ensured that there is
no possibility of water/moisture
ingress during transportation.
A detailed procedure must be
prepared and approved by a
competent authority prior to
shipping. This is specifically
important when the insulated
equipment/piping is transported
through a sea route, as the sea
atmosphere is high in moisture
and salt laden, which can have
detrimental effects on insulation
material during transportation.
4. Some standards suggest the use
of aluminum over the metal
surface prior to laying insulation
to shed water; however, it should
be noted that aluminum is a
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80 SEPTEMBER 2021
potential fire hazard due to its
low melting point. The use of
aluminum should be avoided in
fire hazard zones.
5. Some specifications recommend
the application of paints prior to
laying insulation; however, the
effectiveness of this procedure
must be checked with the
insulation material specialist
for the intended use.
Regular
monitoring
post-insulation
activities include:
1. An insulated surface always looks
acceptable from the outside.
This may give a false impression,
as the surface below the insulation
could be encountering CUI,
which can go unnoticed for a
considerable period of time.
2. All the low points under
insulation in vertical equipment,
such as dish heads, bottoms of
horizontal vessels, individual
nozzle low points, nozzle
interfaces, piping low points,
areas near supports, etc., must
be regularly monitored for
corrosion. These low points
typically show signs of CUI, as
the moisture/water generally
drips down to these areas due
to gravity. A portion of the
insulation can be opened up
for inspection. In case of doubt,
the previously mentioned tests
can be repeated to ascertain
any signs of CUI.
3. Upon opening the affected area,
if any pitting is observed on the
surface, then loss of thickness
must be assessed for fitnessfor-service
(FFS) of pressure
equipment using standards such
as API 579-1/ASME FFS-1.
Based on the results of the
assessment, it should be decided
whether or not the equipment
should be put back in service.
4. A periodic inspection schedule
should be in place to check the
insulated surfaces for any sign
of CUI or leakage.
CUI on SS may not be eliminated
completely; however, it can be reduced to
a great extent using the approaches outlined
in this article.
SUTHAN RUPESH is a Consulting
Mechanical Engineer based in
Kerala, India. He has more than
17 yr of experience in the field of
static equipment. He has also
worked as a Lead/Senior Engineer
for EPC companies such as
Worley/Jacobs (Singapore), JGC Corp. (Saudi
Arabia), Engineers India Ltd., Larsen & Toubro and
Atkins (India). His research interests include shelland-tube
heat exchangers and corrosion studies.
Mr. Rupesh is also a Member of The Institution of
Engineers (India), and he holds a BEng degree
in mechanical engineering from Lukhdhirji
Engineering College in Morbi, India.
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