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Amal Al-Borno, Ph.D.
Charter Coating Service (2000) Ltd.
Calgary, AB
Canada
Development of High
Temperature Cathodic
Disbondment Test Methods
Presentation Outline
● Project Background and Summary
● Technical Background
● Technical Objectives
● Design of Prototype Pressure Apparatus
● Test Results from Pressure Apparatus
● Design of Low Pressure Apparatus
● Further Test Results
● Conclusions
Project Background
● Increasing temperatures in oil industry means more testing needed at elevated temperatures.
● Many pipelines are now operating at service temperatures above 100oC/212oF.
● Cathodic disbondment (CD) tests evaluate protective coatings used on cathodically protected systems.
● Many current CD test methods are not for use at high temperatures (above 80oC/176oF)
Project Summary ● Both end users and coating suppliers expressed
interest in CD testing above 100oC/212oF.
● Current test methodologies are limited since test solutions must be below boiling point.
● This project includes design, building, testing and validation of a CD test apparatus for
> 100oC/212oF.
● Subsequent work includes the design, build and testing of a cooling jacketed test cell that allows for high temperature CD tests at ambient pressure.
Technical Background
● A combination of a protective coating and
cathodic protection (CP) is used to
suppress corrosion.
● Coating defects (holidays) can occur due
to poor application or damage.
● While protecting the steel, CP can be
detrimental to coatings by producing an
aggressive, caustic environment at
holidays.
Cathodic Protection – How
does it work?
- COM
Pipe
Reference
Electrode
Pipe Test
Lead
Digital Volt
Meter
SOIL
+ -
Ground Bed
Anode
DC Power
Supply
Current
+
VOLT
-0.850 V
Technical Objectives
● To design, build and test a high-temperature
and high-pressure (HT-HP) CD test
apparatus for > 100oC/212oF.
● To investigate possible alternative reference
electrodes.
● To develop a new test procedure by
modification of currently used CD standard
test methods.
Technical Objectives
● To investigate effect of increased pressure on
the adjusted potential and the disbondment of
different coating.
● To compare results from the HT-HP apparatus
and tests conducted at ambient pressure.
● To examine coating performance at
temperatures above 100oC/212oF.
● To examine the influence of Oxygen content.
● To develop a test cell that would allow for
testing up to at least 150°C/302°F.
Design of HT-HP Prototype
Operating Condition Maximum
Temperature (0C) 150
Pressure (MPa) 1.4
Liquid Phase Salt Water
Primary Gas Phase Air and Steam
Potential Gaseous
Reactants
Hydrogen and Chlorine
Operating Conditions for the HT-HP Prototype
Design of HT-HP Prototype
Body and Head Material 316L Stainless Steel
Internal Diameter (mm) 178
Wall Thickness (mm) 25.4
Height (cm) 25
Shell Bolt Grade 1
Shell Bolt Ultimate
Tensile Strength (MPa)
248
Number of Shell Bolts 8
Construction Materials and Dimensions
Schematic of HT-HP Cell
0.635 cm NPT Port
1.27 cm NPT Port
1.905 cm NPT Port
Thermocouple
Reference electrode
Electrochemical
Bulkhead
Electrochemical
Bulkhead
316L SS Head
Luggin Probe
Pressure
316L SS Body
17.78 cm
25 cm
Schematic of Electrochemical
Monitoring Equipment on HT-HP Cell
+ –
+
+
–
–
Sample
Pt. Electrode Luggin Probe
Ag / AgCl Reference Electrode.
DC Power Supply
Voltmeter (V-Ag / AgCl )
Voltmeter (V-Cu/CuSO4)
Cu/CuSO4 reference electrode
Thermometer
TOC
Brine
Displacer
Heat Source
Thermometer
Needle valve
Coolant
Luggin Probe Reservoir
Test Cell (pressurized)
HT-HP Apparatus
Note that different set
ups are required for
pressurizing, adding
electrolyte, and taking
electrical readings
● Two reference
electrodes were
examined:
● Internally a Ag/AgCl
electrode was used
● Externally a Luggin
probe assembly was
used with a
Cu/CuSO4 (CSE)
Reference electrodes and Luggin
Probe
Luggin
Capillary
Cu/CuSO4
Reference
electrode
Working
electrode
Reference electrode selection
Testing showed the internal Ag/AgCl electrode to be instable,
probably related to effects of pressure and temperature in
the test cell and so the external CSE in the Luggin probe was
selected for all future tests
Comparative Tests for Study
● To evaluate the HT-HP test procedure it was
compared with two standard CD tests that can
be run at high temperature with suitable
modifications:
● ASTM G42: sample in electrolyte bath; usually
the bath is heated but for this study the pipe
sample was heated internally.
● ASTM G95: sample heated on a sand bath to
achieve the appropriate sample temperature.
ASTM G42
Mg anode
Heater Unit
Sample (cathode)
Test electrolyte
Iron filings used in sample
for heating
ASTM G95
Sample (cathode)
Sand bath – heats sample to set temperature
Pt anodes
Comparative Tests
● Identical samples, same sample temperatures
● 80°C, 120°C and 150°C sample temperatures
● Two novolac coatings rated for immersion
conditions up to 150°C / 302°F
● -1.5 V (versus CSA)
● 6 days
● 3% NaCl electrolyte
● Electrolyte temperature and other factors vary
Results
6 Day Cathodic Disbondment Results
for the Three Test Procedures
25
10 10
45 5
34 4
0
5
10
15
20
25
30
Tests at 80ºC Tests at 120ºC Tests at 150ºC
Dis
bo
nd
me
nt (
mm
)
HT/HP Test ASTM G42 ASTM G95
Results
Water Temperature for the Three Test
Methods
72
109
128
5357
67
54
70
83
0
20
40
60
80
100
120
140
Tests at 80ºC Tests at 120ºC Tests at 150ºC
Te
mp
era
ture
(ºC
)
HT/HP Prototype
ASTM G42
ASTM G95
24.61
6.28
4.44.95
3.984.98
22.81
5.69
0
5
10
15
20
25
30
Prototype 700 kPa Air-1.5V
Prototype Atm.-1.5V
Prototype 700 kPa-N2-1.5V
G95 Atm.-1.5V G95 Atm.-2.0V G95 Atm.-2.5V
Dis
bo
nd
men
t R
ad
ius (
mm
)Results (80°C)
CD Disbondment Results Under Various
Pressure, Gas and Potential Conditions
HT-HP
700kPa
Air -1.5V
HT-HP
Atmos.
Air -1.5V
HT-HP
700kPa
N2 -1.5V
G95
Atmos.
-1.5V
G95
Atmos.
-2.0V
G95
Atmos.
-2.5V
Results Theoretical Dissolved Oxygen Levels
35.4
28.8
24.2
5.3 4.94.1
5.23.8
2.6
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80ºC 120ºC 150ºC
Dis
so
lved
Oxyg
en
(p
pm
)
Test Temperature (Celsius)
HT/HP Test ASTM G42 ASTM G95
72ºC
109ºC
54ºC 53ºC 57ºC 70ºC
128ºC
67ºC 82ºC
Results
6 Day Cathodic Disbondment Results
for the Three Test Procedures
25
10 10
45 5
34 4
0
5
10
15
20
25
30
Tests at 80ºC Tests at 120ºC Tests at 150ºC
Dis
bo
nd
me
nt (
mm
) HT/HP Test ASTM G42 ASTM G95
Results 30 Day Cathodic Disbondment Results
for the Three Methods at 120°C
18.19
4.93
8.49
9.83
3.594.64
0
2
4
6
8
10
12
14
16
18
20
HT-HP Procedure ASTM G95 Modified ASTM G42 Modified
Dis
bo
nd
me
nt(
mm
)
Liquid Epoxy 1 Liquid Epoxy 2
Design of High Temperature Low
Pressure Test Apparatus
Concerns from use of the high pressure test apparatus :
● Multiple tests require multiple test set ups
● HT/HP results significantly accelerated and severe
● Electrolyte temperature is not representative of fluids
in normal service since:
●> 100°C would result in boiling and so a dry pipe
●fluids around a pipeline are cooled by the
environment
● Test pressure is not reproducing actual field conditions
● Test apparatus is complicated and expensive
Coolant in
Coolant out
Pt anode
Cooling
jacket
Cathodic
connection Sample
Heated
sand bath
High Temperature Low Pressure
CD Test Apparatus
Low Pressure CD Test –
Oxygen Level Effect
4.1 4.1
3
0
1
2
3
4
Oxygen: 2.0-3.5 mg/L Bubbling Air: Oxygen: 2.0-3.5 mg/L
Bubbling Oygen: Oxygen: 5.0-6.5 mg/L
Dis
bo
nd
men
t, m
m
High Temperature Low Pressure CD Test
Apparatus for Undersea Simulation
Electrolyte
temperature
Sample
temperature
Silicone
oil in
Silicone
oil out
Thermo-
statically
controlled
cooler
Insulation on test vessel
and tubing to maintain
Silicone temperature
Heated Sand Bath
CD Results: 3-Layer PP Coating,
28 days, 108°C, -1.5 V
PP, No pre-treatment PP, With pre-treatment
The thick top PP layer and some of a middle red adhesive layer were
removed using a powered steel brush and the base blue FBE coating was
rated for disbondment. The average of duplicate samples was 4.3 and 3.2
mm for the two different substrate pre-treatment methods.
Conclusions – HT/HP Apparatus
● Successful design, construction and
commission of HT-HP Apparatus
● Safe and reliable method
● Luggin Probe and CSE found to be best for
measuring and controling the potential
● Accelerated disbondment observed and more
severe than other CD test set ups; especially
when air is used for pressurization
● Severity related to higher electrolyte temp. and
dissolved oxygen concentration
● Better simulation of actual service conditions
● Control of both sample and electrolyte
temperatures
● Reaction of sample (blistering etc.) is always
visible
● Relatively low cost apparatus/equipment
● Can be used to very high temperatures (we
have worked to 180°C / 356°F )
● Potential for subsea environment simulation
Conclusions - Low Pressure CD Test
Apparatus
Thank You
● Questions?