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

bond

men

t (m

m)

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

Tem

pera

ture

(ºC

)

HT/HP PrototypeASTM G42ASTM G95

24.61

6.28

4.4 4.953.98

4.98

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

bond

men

t Rad

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 4.9 4.15.23.8 2.6

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80ºC 120ºC 150ºC

Dis

solv

ed O

xyge

n (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

bond

men

t (m

m) HT/HP Test ASTM G42 ASTM G95

Results 30 Day Cathodic Disbondment Results

for the Three Methods at 120°C

18.19

4.93

8.499.83

3.594.64

0

2

4

6

8

10

12

14

16

18

20

HT-HP Procedure ASTM G95 Modified ASTM G42 Modified

Dis

bond

men

t(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

bond

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?