MENDT2015_44.pdf

Corrosion Under Insulation
and
Fire Proofing Materials
V. P. Sastry
TCR Arabia Company Ltd.
www.tcr-arabia.com
sales@tcr-arabia.com
Tel: +966-13-8475784/85
Seventh Middle East NDT Conference & Exhibition 2015, Bahrain 13-16 Sept, , 2015

 External corrosion under insulation (CuI) or Corrosion under
Thermal Insulation (CuTI) of insulated piping, equipment and
structural components is experienced worldwide, mainly due
to the entry of water /oxygen.
 Noticed in both cold and hot insulated systems as well as in
fire proofed systems-Corrosion under Fire Proofing (CuFP).
 Can not be noticed as the process is behind the insulation /
fire proofing.
Introduction
Seventh Middle East NDT Conference & Exhibition 2015, Bahrain 13-16 Sept, 2015

Moisture into the insulation system may further
• Carry the air borne pollutants/corrosive substances’
• Water leaches out chlorides, other halides or sulphates leading
to corrosion.
• Punctures, slipped cladding, seal deterioration aid the easy
entry of water into the insulation.
• Render the insulation ineffective. For example,1 vol.-% of water
in the insulation material leads to an approximate 4% increase in
the thermal conductivity. A water concentration of 5 vol.-% of the
overall insulation material’s volume, increases the l value by 20%.
Introduction

• Design specifications-to define all the measures for good quality
water tight insulated/fire proofed systems.
• Installation craftsmanship, and maintenance-less attention paid by
the owner users in terms of supervision.
• Openings thru. Insulation cladding for many reasons like poor
workmanship, misuse, deterioration of sealing materials.
• Presence of moisture or water, oxygen, chloride ions and other salts,
chemical contamination like acids, acidic gases, alkalis, salts... in a
process plant situation, many such possibilities may arise.
• Warm temperatures. ..this depends up on location.
• Abuse of insulation of insulated system- walking on the insulated
lines, misuse of lifting tools and tackles during maintenance.
Influencing factors

Specific locations and / or systems…penetrations in the insulation and visually damaged
insulation areas.
• Environmental or surrounding areas include:
• Insulated Carbon steel and low alloy systems, operating temperatures between -
5°C and 150°C, frequent or continuous condensation and re-evaporation of atmospheric
moisture, systems normally operate above 150°C but are in Cyclic thermal/ intermittent
service or subjected to frequent outages.
• Susceptible temperature range for Stainless Steels is 65 to 204 deg.C.
• Carbon Steels /Alloy Steels show pitting/loss of thickness, Stainless Steels show pitting,
SCC in Chloride contamination.
• Areas exposed to mist over spray from cooling towers, steam vents, fire water spray
systems, deluge systems, areas subject to process spills, ingress of moisture, or acid
vapors.
• Protruding dead legs and attachments,
• Vibrating systems may loosen the insulation cladding joints,
• Steam tracing leaks beneath the insulation,
• Systems with deteriorated coating and/or wrappings,
• Cold service operating below the atmospheric dew point.
• Weather Proofing/Mastic Wraps
Some of these are covered in case studies.
Susceptible areas for CUI:

Some of the insulation components inherently cause problem unless
enough care is taken.
•Cladding- It protects the insulated pipe/equipment. Cladding joints form
the basis for the leaks into the insulation through any openings. The
cladding joint foil many a time creates gap due to wavy stiff end, without
closely touching the mating surfaces.
•Cladding joint sealing materials- some of the sealing materials lose the
sealing property over a period of time due to weathering/deterioration.
Asbestos felt sealing may not be adequate.
•Screws-the screwed points are also a potential source for water ingress
into the insulation. Some of these screws may seen missing in plant visual
audit round.
•Fiber/powder based insulations retain water. Insulation materials such as
mineral wool, glass wool and Ca silicate have some chloride and other salt
contamination. Water leaches out these soluble salts from insulation.
•Vapor retarder, Insulation bonding agents
Cold/hot thermal insulation and components:

•Design aspects
specification is the key to cover all the design aspects of Insulation
Materials, cladding, Heat-traced Systems, Protective Coatings and
sealing, Shutdown/Mothballing, Quality Control/Quality Assurance
and follow.
Some examples include:
•Avoid creating inspection ports.
•Select where possible insulation systems like Foam glass which
hold less water.
•Old specifications did not call for protective coatings on the
pipe/equipment/structural, before applying the insulation. Use
coatings to prevent corrosion due to the entry of moisture. CuTI
resistant coatings are required for both cold and hot insulation7.
Coatings for systems without insulation may not work for systems
with insulation
Prevention

Inspection
One of the important inspection requirements is to get the metal
loss due to CuTI. For this first initial thickness is required.
Baseline surveys are best carried out during the construction
phase, before applying coating and insulation. This helps in taking
corrective actions for components not meeting the specification
can be readily done.
CuTI is difficult to identify and hence where to start is important.
An account of susceptible areas can be used as a guide. Insulated
systems are to be reviewed to identify periodic inspection for
critical areas to take corrective actions. The review is based on the
process and mechanical data. Where possible, remove the
insulation on the critical areas for inspection.

Inspection
DP, Ultrasonic thickness measurements are commonly used,
where the insulation is removed. In addition, advanced NDT is
also required.
For CuTI inspection, Visual examination (for all cases of
without/local/full removal of insulation) helps in eliminating
misinterpretation with other NDT.
If inspection program is planned for multi plant complex, number
of insulated lines may be at least one lakh in addition to
thousands of equipment.
Removing insulation of all these lines even in small lengths, for
inspection, would be highly laborious, time taking and cost
intensive.

Inspection
Large lengths of insulation removal mean that there is a
maximum possibility of affecting the process. This restricts the
inspection rate.
Cryogenic insulation removal is not advisable during operation
due to ice formation.
Hence, techniques to predict the condition of metal beneath
the insulation are required without its removal.

It is important to inspect insulated pipe work, equipment and structural to identify
CuTI/CuFP sites. One can detect hot/cold spots with at least 10 deg. C temperature
differential across the thickness of the Component.
It is a remote condition monitoring technique which identifies the presence of
moisture through mapped surface temperatures. For some field applications, consider
influencing factors such as changes in surface Emissivity, the affects of sunlight heat and
other atmospheric effects.
Ideally, Thermography should be done before rainy season and repeat at the end
of the season and correlate.
Thermogram of carbon steel insulated line, showing wet patch
Advance NDT : Thermography

This technique is used in the plant inspection. Where the process
plants use nucleonic gauges, the radiography source radiation
interferes with the nucleonic gauge radiation and plants may trip.
This problem becomes acute when the plants are adjacent to each
other. Also it is a slow technique when many lines are to be done.
Taking profile at multiple different angles is useful to catch the area
of Interest.
Profile radiography to check the wall loss
Advance NDT : Profile Radiography

Lixi profiler, a portable battery operated unit as shown in (figure), uses Gd153
radioisotope source. When detector assembly is placed around pipe, small
amount of focused radiation beam penetrates the diameter of the pipe. The
amount of radiation received by detector (figure) is converted to an equivalent
steel thickness measurement by the instrumentation. Variation in density
(thickness) is plotted on a computer screen in real time image.
1. Computer module 2. Uniconnect module 3. Detector module 4.HUD 5. C-Arm
2. 6. Source holder 7. Battery brick
Advance NDT : Lixi Profile

Applications of Lixi Profiler include:
Pipe wall thinning, Corrosion under Insulation (CUI, Pipe
Blockages such as Bitumen, Ice, or any another foreign material
Wet Insulation Cluster of Internal and external pitting, Wall
thickness measurement on insulated or bare pipes w/ or w/o
product, Wall thickness measurement on very hot pipes while in-
service, Weld Identification on Insulated Piping Systems.
The profiler can be used on hot permit system.
Advance NDT : Lixi Profile

Typical plot for a corroded insulated pipe

• Guided Wave Inspection
Ultrasonic screening in-service inspection tool to detect general corrosion and wall loss
for 100-150 ft. on either side of the probe.
Ultrasonic wave guide for CuTI inspection.
(a) Instrumentation
(b) Probe mounting on a small length of pipe where insulation is removed.
It is effective for T< 120 deg.C.
Operator skill is needed.
May not detect defects in immediate vicinity of welds.
Reliability decreases with length.
Signal will terminate at a flange or at second elbow.

PEC is a noncontact type inspection technique for carbon steel
objects, such as pipes and vessels.
It can measure % variations in steel thickness through any non-
conductive and non-magnetic material between sensor and steel
surface such as air, insulation material, concrete, plastics,
coatings, paint, sea water, marine growth deposits, oil etc.
Electrical current flows through the transmitter coils of probe and
generate a primary magnetic field. This field is unaffected by the
presence of any non-conducting and non-magnetic material and
penetrates undisturbed and magnetizes the top layer of the steel
beneath the transmitter coils.
Advance NDT : Pulsed Eddy Current (PEC)

1. Magnetization of the Steel
2. Induced eddy currents Generate secondary magnetic field in the receiver coil
3. Diffusion of eddy currents. Onset of fast decay occurs when far surface is reached.

The current in the transmitter coil is switched off, collapsing the primary magnetic field.
The changing magnetic field induces electrical ‘eddy’ currents in the surface of the steel.
These eddy currents generate a secondary magnetic field and induces an electrical voltage,
which in the receiver coils.
The magnitude of this voltage as a function of the time is referred to as the ‘PEC signal’.
The PEC signal contains information about the thickness of the steel, as described below. A
specimen has a near and a far surface. Initially the eddy currents are confined to the near
surface (closest to the PEC probe) but, as time elapses, they travel (or ‘diffuse’) outwards
towards the far surface (figure 9). As long as the eddy currents experience free expansion
in the wall, their strength decreases relatively slowly.

However, upon reaching the far surface, their strength decreases rapidly.
The moment in time where the eddy currents first reach the far surface is
indicated by a sharp decrease in PEC signal, known as ‘transition point’
(figure 9). The time of the transition point is therefore a measure of wall
thickness. For example, the earlier the transition point, the sooner the
eddy currents reach the far surface and the thinner the wall must be. In
practice, each time a PEC measurement is done; voltage across the
receiver coils of the PEC probe is amplified, sampled and digitized by the
PEC instrument. This gives a digital record of the PEC signal over 3000
sample moments in time. The digitized signals are stored in a connected
computer. Dedicated software is used to analyze the shape of all PEC
signals and thereby determine wall thickness.

Circumferential position at 90 degrees
Top side end Vertical Position A B C D
Distance between
two points is
0.1m
21 97.2 98.1 97.3 97
20 99.4 91.8 94.9 94.1
19 95.9 93.7 98.9 99.1
18 97.9 96.7 94.1 98.7
17 94.6 94.9 96.3 96
16 98.1 97.9 91.7 96.9
15 97.6 95.3 93.1 94.8
14 95.8 99.6 95.9 97.4
13 89.4 97.4 96.2 93.9
12 98.8 94.8 100 100.8
Distance between
two points is
0.5m
11 98.1 97.9 93.9 95.8
10 93.1 93.8 97.6 96.5
9 99.2 96.2 90.8 97.1
8 98.1 95.6 92.8 93.3
7 99.6 100.8 101.8 97.3
6 88.5 90.8 92.7 89.4
5 94.0 93.5 91.4 88.3
4 91.5 90.3 93.8 89.1
3 94.8 90.3 93.4 88.9
2 95.6 98.1 92.3 97.9
1 95.4 97.6 94.2 98.0
Ground side end
Remaining wall thickness of one leg of Horton sphere
Colour code: 85-90%; 90-110%

Examples of reasons for CuTI experienced, measures
taken.
Inadequate design aspects
Normally Stiffening rings, platform support rings and
Insulated support rings are not provided with drain holes
for possible collection of rain water on to the rings.
Hence corrosion is often vulnerable.
Connected to the process columns operating temperature
between 60 to 100 deg.C due to accumulation of Water
in the mineral wool insulation support ring.
As a corrective action, holes are drilled; apply suitable
paint to resist under insulation corrosion applied.
Update the specification.
Column ring without holes
causing corrosion due to
accumulation of water in
rainy season.
Case Studies

Fire proof insulation:
In the process column, bottom piping leaked exactly where the pipes crossing the fire
proofed skirt, due to long contact with water beneath the fire proofing. Specification is
updated to do CuTI paint before fire proofing.
Leakage of column bottom pipes in contact with column skirt fire proofing

12 O’clock clad joints
To protect water entry, the clad joints shall be at 6 O’clock
position
The clad joints shown with Arrow in 1 O’clock/12 O’clock poisons.
These should have been at 6 O’clock position to avoid direct water entry through
the joint gaps.
Update the specification.

Deviation from design conditions
Different Normally No Flow (NNF) hydrocarbon carbon steel lines or dead legs of varied
diameters are hot mineral wool insulated expecting above ambient temperatures. But these
lines did not have any flow, experienced only ambient temperatures.
Pipe wall thinning as much as 50% in 15 years of time under insulation.
All such affected lines are replaced with new lines and CuTI resistant paint was applied
before insulation.
But these lines did not have any flow, experienced only ambient temperatures.
One such PSV upstream line was mineral wool insulated as per Line Designation Table (LDT),
but remained at ambient temperature.
Corroded insulated PSV upstream
line due to ambient temperature
Mineral wool insulated lines as per LDT but remained at
ambient T-used intermittently during plant shutdowns, for
commissioning/ decommissioning.
CuTI on intermittent
service line

Heat traced lines to maintain the liquid temperature and hence insulation was used.
Electrical heat traced lines, found corroded in-service.
These lines were audited/reassessed and found that the tracing is not required.
So the electrical tracing was disabled. So this 2”, Sch. 40 Carbon steel line carrying
fuel gas experienced ambient temperatures leading to corrosion under mineral
wool insulation .
Remedial action done included replacing the corroded length, removal of heat
tracing and application Paint to resist Corrosion under Insulation.
Insulation removed for inspection.
Electrical heat tracing is disabled.
Corrosion noticed under insulation.

Similarly Steam tracing line leaked and corroded the pipe under mineral wool
insulation as steam tracing is not activated on 6” Sch. 40 carbon steel lines for
benzene service.
CuTI on steam tracing inactivated line
Abuse of insulated lines as some personnel walk on them

Corroded cladding
Direct water entry is possible through the cladding damages.
Corroded insulation cladding. GI sheet performs poorly as a cladding material.

Cladding joints sealing material life.
Sealing material works for some time. After that, due to dry up cracks or fall off,
the joints are exposed. Well before monsoon, these joints are to be inspected
and rectified in the problem areas. Another problem noticed is that the cladding
ends should not have wavy pattern to have proper sealing. If found, they have to
be smoothened / straightened.
Clad joint sealant with proper sealing
Clad sealing. Mark 1 is the asbestos sealant and
Mark 2 shows the absence of sealing on top allowing
the possibility of any contamination / ingression.

Exposed insulation
Exposed insulation at the ends of the lines, supports etc. due to improper or
incomplete or no cladding
Incomplete installation of insulation. Incomplete provision of insulation.
Cladding cover is missing.

Influence of neighboring plants.
Insulated Stainless steel type 304 lines are vulnerable for cracking.
Make up water to De-aerator T 60 deg.C .
These lines are prone to failures as exposed to neighboring continuous plume from
cooling tower fan exhaust and steam leakages and contamination.
Corroded lines were replaced and provided with SS foil before insulation.
SCC on stainless steel line

Leakage of steam tracing leaks
External corrosion of a pipe and
flange joint / fasteners at the
break of mineral insulation due
to leaky steam tracing.
Maintenance
Insulation and cladding improperly done / not redone during maintenance
Improperly done cladding.
No sealing also for clad joints
Inadequacy in Insulation of Piping supports
CuTI Deposits in the Support Lugs

Corrosion of piping supports
Piping support corrosion is a frequently noticed problem under insulation.
They have to be inspected closely and take corrective actions. In case of new
plants, adequate focus has to be given in specification preparation to minimize the
problem.
In the field, they have to be maintained with a close watch.
Another example of corrosion under insulation of a 2"
carbon steel pipe near bottom welded support.
The support pipe covered under the piping insulation is also
found corroded and perforated.

a) Open inspection pocket b) Improperly fitted Inspection pocket
RECOMMENDATIONS:
• Insulation system is designed and done as per international
norms, codes and standards.
• Learn from others’ problems, conduct necessary audits and
take precautions by the owner users for the assets.

Insulation system is designed and done as per
international norms, codes and standards.
• Learn from others’ problems, conduct necessary
audits and take precautions by the owner users for the
assets.
Recommendations

The author thanks the organizers for accepting the paper for
presentation.
Acknowledgments

MENDT2015_44.pdf

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