C2012-0001674
Evaluation of FBE Coatings for High Temperature Pipeline Applications
Jose Martin Lizcano Contreras, MSc and
Miguel Mateus Barragan, MSc
ECOPETROL S.A
Km 7 Via to Piedecuesta
Piedecuesta, Santander
Colombia
Alban Jaimes Suárez, MSc
UT TIP Petrolabin Ltda
Km 7 Via to Piedecuesta,
Santander,
Colombia
Miguel Manrique Rojas, Eng
CIMA
Km 7 via to Piedecuesta,
Santander,
Colombia
ABSTRACT
In oilfields from Colombia, the surface operating temperatures of pipelines are around 120°C. Actually,
Canadian and ASTM standard tests set the conditions for Cathodic Disbonding Testing to maximum
temperature of 95 °C, while our scope for coating evaluation is between 95 to 150 °C. To select for
higher performance coatings systems, we have developed a testing protocol to be applied at the
factory, in the laboratory and in the field to assess the performance of coatings for operating conditions
between 95 to 150°C. The protocol involved the following tests: dry film thickness, porosity, mechanical,
abrasion resistance test, impact and elongation, adhesion, wet adhesion, immersion in chemical
solution, cathodic disbonding and electrochemical impedance.
The results in the laboratory can be correlated between the glass transition temperature and the
electrochemical response. To clarify damage level found in the coatings evaluated.
As a result of this work was found a reliable methodology for evaluating coatings at temperatures above
95°C. A good correlation was found in the results of electrochemical impedance tests and cathodic
disbondment evaluated to 150°C.
Key Words: electrochemical impedance, disbonding, epoxy, cathodic disbonding, permeation, pore of
resistance.
©2012 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International,
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INTRODUCTION
A research as need arises from the operation in oilfield, where fluids are produced with temperatures
above 120°C, the soil around the buried pipeline has a lower temperature, this condition in combination
with the high humidity generates a lot of steam at the interface pipeline / soil, affecting and degrading
the coating.
Currently, the standards to evaluate coatings have a limit in the testing temperature, 60°C for ASTM(1)
G42 and 95°C for CSA(2) Z245.20-101. In this paper, we present a methodology to evaluate the coating
performance; these tests involved mechanical evaluation of abrasion resistance, impact and elongation;
also immersion and electrochemical tests such as; adhesion, wet adhesion, immersion in chemical
solutions, cathodic disbonding and electrochemical impedance. With these investigations, we
developed a testing methodology to select coatings for high temperature, as much as 150°C.
BACKGROUND
According to our knowledge, in the open literature there are not any standard test methods for
evaluating epoxy coating performance above 95 °C. Kirkpatrick3, stated that test methods to predict the
long-term coating performance of fusion-bonded epoxy coatings at elevated temperatures need to be
developed. Papavinasam and Revie4 also stated that no industry standard exists to test coating
performance at high temperature. In Table 1 It is a summary of standard Cathodic Disbondment test
methods developed by different International Organizations.
Table 1
Summary of International Standards on Cathodic Disbondment Test 5
Voltage
Temperature
Standard
(Vs Cu/CuSO4)
(°C)
Duration
ASTM(1) G86
-1.45 to -1.55 V
25
30 days
ASTM(1) G197
-1.45 V
25
3 – 18 months
ASTM(1) G421
-1.5 V
60
30 days
ASTM(1) G808
-1.45 to -1.55 V
25
60 days
ASTM(1) G959
-3.20 V
25
90 days
CSA(2) Z45.21 (Sec
-1.50 V
20 – 95
28 days
10
12.3)
NACE RP039411
-1.50 V
66
28 days
Shukla12 et al, established that EIS is a good tool for coating deterioration research, specially on a
metal. EIS provides two very important pieces of information: (i) the absolute value of resistance and
change in capacitance of the organic film that relates to water uptake, and (ii) the value of charge
transfer resistance at the coating and metal interface. The deviation in capacitance and charge transfer
resistance is measured in terms of coating impedance. Development of pores in the coating or
disbonding of an electrolyte-saturated film at the onset of corrosion causes deviation from purely
capacitive behavior and results in a decreased charge transfer resistance.
Al – Borno et al13, developed a method to run cathodic disbonding test at high temperatures. They
design a cell for high temperatures; this cell test includes a cooling jacket which can be thermostatically
controlled easily allowing that higher test temperatures can be used without electrolyte evaporation up
to 180°C / 356°F .
(1)
(2)
American Society for Testing and Materials
Canadian Standards Association “Plant-applied external coatings for steel pipe, May 2010”
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EXPERIMENTAL PROCEDURE
Figure 1 shows a flow chart describing the proposed methodology. In addition to the traditional tests
such as; dry film thickness and porosity for quality control of the coating application, we propose the
use of mechanical, immersion, catholic disbonding and electrochemical impedance tests.
Samples were prepared in the pipeline coating manufacturing plant in Cartagena, Colombia.
Start
Mechanical Tests
EIS, Immersion and CD Tests
Abrasion Resistance
Impact Resistance
Flexibility Test
Adhesion
Wet Adhesion
Immersion tests in Chemical Solutions
Cathodic Disbonding at 130, 150°C
Electrochemical Impedance at 130, 150°C
Figure 1: Methodology to evaluate and select coatings for high temperature.
Each of the tests is described below:
Abrasion Resistance: This test was conducted at two conditions. a) As received, after application and
curing of the coating, b) Aging samples for 28 days at 150°C, subsequently cooled to room temperature
to perform the testing in accordance with ASTM(1) D406015 standard and CS – 17 wheels were used.
Impact Resistance: The impact test was in accordance with ASTM(1) D279416 standard. This test was
conducted at two conditions. a) Aging samples for 28 days at 150°C, subsequently cooled to room
temperature to perform the testing, b) Aging samples for 2 days at 150°C, subsequently, to perform the
testing at 150°C.
Flexibility of Coatings: Following CSA(2) Z245.20-102 standard, section 12.1, the samples were bent
until failure.
Adhesion: The testing was in accordance with ASTM D4541 standard. This test was conducted at two
conditions. a) Aging samples for 28 days at 150°C, subsequently cooled to room temperature to
perform the testing, b) Aging samples for 2 days at 150°C, subsequently, to perform the testing at
150°C.
It should be noted that for this test, the maximum pulling stress is limited by the tester equipment, for
FBE coating is common to support the load without pulling out, in case of degradation if it is possible
take it as criterion of pass / fail.
Wet Adhesion: The samples were exposed in water at 150°C for 28 days.
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The test was in accordance with CSA(2) Z245.20-103 general standard specifications, section 12.14.
Immersion tests in chemical solutions: Aging samples in an oven for 28 days at 150°C, subsequently,
the samples were exposed to two different pH fluids (pH 3 and pH 7) during 400 hours at 95°C.
The values of pH were chosen in function of the pH of the soil which the operating conditions are above
95ºC. Normally, the pH of the soil in the oilfields is around of 4 – 6.8.
Both solutions have 10% NaCl. It should not be changes in color, corrosion products, blistering,
softening or delamination.
Cathodic Disbondment: Test temperatures of 130 and 150°C on steel surface with applied voltage of 1.5 Volts Vs SCE.
Electrochemical Impedance: Test temperatures of 130°C and 150ºC on steel surface.
Coating samples were applied in the factory and the aging was done in an oven, which remained
constant at 150ºC. The objective of the aging was to accelerate the degradation process in the coating
system.
To conduct electrochemical impedance and cathodic disbonding test, we designed a glass cell with
external water cooling. Figures 2 and 3 detail the assembly and cell used.
Figure 2: Assembly to run Cathodic Disbonding and Electrochemical Impedance test under
conditions of 130 and 150ºC.
Figure 3 shows cell design, the cell has a volume of 220mL with a solution of 3% NaCl.
To achieve the desired temperature of 150°C for cathodic disbondment, we used two heating means,
shot metal and sand. For shot metal, the temperature in shot metal bed was of 205°C, the steel
temperature was 150 ± 5°C, with the cooling system, the electrolyte temperature was maintained
around 60 ° C, enabling the possibility to run electrochemical tests. For sand, the temperature in sand
bed was of 260°C, the steel temperature was 150 ± 5°C, with the cooling system, the electrolyte
temperature was maintained around 60 ° C, enabling the possibility to run electrochemical tests.
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Figure 3: Design of Glass Cell for electrochemical tests.
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RESULTS AND DISCUSSION
Characterization Tests
Table 2 shows the characterization tests results. The systems A and B have the highest Tg among all
of the samples.
Test / System
Gel Time
Density
Cathodic Disbondment
Calorimeter
Table 2
Characterization Tests
Unit
A
Seconds
9
g/cc
1.53
mm
2.37
Tg.1 (°C)
56.3
Tg.2 (°C)
133.5
119
H (J/g)
B
9
1.37
1.83
56.4
154
158
C
14
1.42
3.16
60.7
97.7
67.6
D
15
1.59
3.05
61.2
104.6
48.3
Abrasion Resistance
Table 3 shows the abrasion test results. System D did not present significant changes between without
and with aging, it is noteworthy that after aging in oven at 150°C, all test systems showed a color
change due to thermal degradation and generated an increasing in coating hardness.
The samples A, B and C showed increases in the abrasion resistance in samples after aging.
System
A – single layer
B – single layer
C – dual layer
D – dual layer
Table 3
Abrasion Resistance Results
Wear Index Observations
Wear Index
(mg/cycle)
(mg/cycle)
31
Without aging
68
43
Without aging
74
55
Without aging
72
75
Without aging
76
Observations
With aging
With aging
With aging
With aging
Figure 4: Changes in Abrasion Resistance.
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Impact Resistance
Table 4 shows the results of impact test. System C did not present significant changes without and with
aging. The systems A, B and D showed a loss in the impact resistance. This indicates that there is a
negative relation between the properties of Abrasion and Impact resistance.
System
A – single layer
B – single layer
C – dual layer
D – dual layer
Table 4
Impact Resistance Results
Impact Failure
Observations
Impact
(J)
Failure (J)
7.5
Without aging
4.3
8.4
Without aging
6.8
5.4
Without aging
5.7
7.0
Without aging
5.2
Observations
With aging
With aging
With aging
With aging
Figure 5: Changes in Impact Resistance.
Flexibility Test
Table 5 shows flexibility test results. The results reported below were obtained deflecting samples until
failure.
E
= Elongation = 0.5d/R
(1)
°/PD = Grade / pipe diameter
% E = 50d/R.
d
= OD of the pipe.
R = Radius to the neutral axis of the circle to which the pipe can be bent to the maximum limit without
any coating damage.
Table 5
Flexibility Test Results without aging
thickness
System
º/PD
(FBE + metal)
mm
A – single layer
2.1
7.865
B – single layer
2.2
7.805
C – dual layer
3.3
8.03
D – dual layer
2.3
8.025
%E
1.89
1.91
2.88
1.97
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Adhesion Test
Table 6 shows adhesion test results. The system A showed an adhesion loss in samples with aging at
150°C for 28 days.
System
A – single layer
B – single layer
C – dual layer
D – dual layer
A – single layer
B – single layer
C – dual layer
D – dual layer
Table 6
Adhesion Test Results
Value
Percentage of
MPa (psi)
failures
60% Adhesive,
20.68 (3000)
40% Cohesive
failure
100% Adhesive
20.68 (3000)
Failure
100% Adhesive
15.86 (2300)
Failure
90% Adhesive
15.51 (2250)
Failure
>22.06 (3200)
Glue Failure
>22.06 (3200)
Glue Failure
>22.06 (3200)
Glue Failure
>22.06 (3200)
Glue Failure
Observations
Aging for 28 days
at 150°C and test
at room
temperature
Aging for 2 days at
150°C and
evaluated at 150°C
Wet Adhesion
Table 7 shows wet adhesion test results. The immersion time was 28 days at 150ºC.
The temperature of 150ºC was selected with the objective to simulate the real conditions and more
critical.
Table 7
Wet Adhesion Test Results
Rated agreed to
Coating System
CAN Z245.20-10
A – single layer
Rating 1
B – single layer
Rating 1
C – dual layer
Rating 1
D – dual layer
Rating 1
In mechanical tests performed for impact, abrasion and pull off, it was observed an aging effect,
because of the change in properties.
Immersion tests in chemical solutions
In the samples evaluated, from visual inspecting only color change was identify; no corrosion products
were observed, neither softening and blistering of coating, which means a good chemical resistance of
the samples.
Table 8 shows test results. The coating systems suffered damage by the effect of temperature,
however, when the samples were exposed to acidic and neutral fluids did not suffer any visual damage.
©2012 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International,
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Table 8
Immersion tests in chemical solutions pH 3 and pH 7
Coating System
failure type
A – single layer
Strong Color
Change
B – single layer
Strong Color
Change
C – dual layer
Strong Color
Change
D – dual layer
Strong Color
Change
Cathodic Disbonding
Table 9 shows the cathodic disbonding test results at 150°C during 14 days.
Table 10 shows the cathodic disbonding test results at 150°C during 14 days and 150 º C during 28
days.
Samples C and D did not show changes in the cathodic disbonding.
Table 9
Cathodic Disbonding results at 150ºC – 1.5V Vs SCE, 14 days.
Maximum Radius
System
Photographic Register
(mm)
A – single layer
2.9
B – single layer
3.9
C – dual layer
3.8
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System
Maximum Radius
(mm)
D – dual layer
3.0
Photographic Register
Table 10
Comparison between two Cathodic Disbonding tests
CD
CD
(mm) at 150°C during (mm) at 150°C during
System
14 days
28 days
Voltage
CD(mm)
Voltage
CD (mm)
A – single layer
-1.5V
2.9
-1.5V
4.8
B – single layer
-1.5V
3.9
-1.5V
10.2
C – dual layer
-1.5V
3.8
-1.5V
3.3
D – dual layer
-1.5V
3.0
-1.5V
2.2
Electrochemical Impedance
Table 11 shows the electrochemical impedance test results, at 150°C, for 30 days. This test is
developed with the objective to evaluate the grade of water permeation in the coating.
The results show a reduction in the protective properties of samples evaluated, comparing the behavior
at 0 hours and 720 hours, except for sample A that shows a good behavior. The reduction percentage
of protection is calculated in terms of pore resistance, as follows:
% RP = (Pore Resistance at 30 days – 720 hours/ Pore Resistance at 0 day – 0 hours)*100
(2)
Table 11
Electrochemical Impedance Test Results at 150ºC, 10000Hz – 0.01Hz – 10mV rms Vs OCP.
Pore Resistance
Pore Resistance
%Reduction of
Protection
System
0 hrs ( )
720 hrs ( )
8
7
A – single layer
8.9x10
2.015x10
2.3
B – single layer
1.037x109
5.5x108
53
C – dual layer
1.16x109
5.3x108
45.7
D – dual layer
8.07x108
1.08x108
13.4
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CONCLUSIONS
A good correlation was found between electrochemical impedance tests and cathodic disbondment.
The evaluated FBE coating systems showed thermal degradation on mechanical properties.
At 150°C, the combined effect of voltage, time and temperature promotes a loss in the resistance to
cathodic disbondment.
A methodology was developed for coatings selection at temperatures above 95°C, which provides
reliable and comparable results, which allow selecting different FBE coating systems.
RECOMMENDATION
The authors want to establish that this investigation is an input for developing the experimental basis of
the new standards to evaluate FBE coating systems at high temperatures (>95°C).
REFERENCES
1.
ASTM G42 96(latest revision), “Standard Test Method for Cathodic Disbonding of Pipeline
Coatings Subjected to Elevated Temperatures” (West Conshohocken, PA: ASTM).
2.
CSA Z245.20-10, “Plant applied external coatings for steel pipe”.
3.
D. Kirkpatrick, F. Aguirre, and G. Jacob. “Review of Epoxy Polymer Thermal Aging Behavior
Relevant to Fusion Bonded Epoxy Coatings.” Proceedings of the CORROSION/2008
Conference, Paper 08037. Houston, Texas: NACE. 2008.
4.
S. Papavinasam and R.W. Revie. “Coating for Pipelines.” International Workshop on Advanced
Research & Development of Coatings for Corrosion Protection. Golden, Colorado: Colorado
State University. 2004.
5.
S. Papavinasam, S. Attard, and R.W. Revie. “Modified Cathodic Disbondment Testing of
External Polymeric Pipeline.” Proceedings of the CORROSION/2007 Conference, Paper 07021.
Houston, Texas: NACE. 2007.
6.
ASTM G8 - 96(latest revision), “Standard Test Methods for Cathodic Disbonding of Pipeline
Coatings” (West Conshohocken, PA: ASTM).
7.
ASTM G19-04(latest revision), “Standard Test Method for Disbonding Characteristics of Pipeline
Coatings by Direct Soil Burial” (West Conshohocken, PA: ASTM).
8.
ASTM G80(latest revision), “Standard Test Method for Specific Cathodic Disbonding of Pipeline
Coatings” (West Conshohocken, PA: ASTM).
9.
ASTM G95 – 07(latest revision), “Standard Test Method for Cathodic Disbondment Test of
Pipeline Coatings” (West Conshohocken, PA: ASTM).
10.
CSA Z245.21-10, “Plant applied external coatings for steel pipe”.
©2012 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International,
Publications Division, 1440 South Creek Drive, Houston, Texas 77084. The material presented and the views expressed in this paper are solely those of the
author(s) and are not necessarily endorsed by the Association.
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11.
NACE RP0394-2002(latest revision), “Standard Recommended Practice Application
Performance, and Quality Control of Plant Applied, Fusion Bonded Epoxy External Pipe
Coating”.
12.
P. Shukla, R. Pabalan and L. Yang. “On Development of Accelerated Testing Methods For
Evaluating Organic Coating Performance Above 100 °C”, Proceedings of the
CORROSION/2010 Conference, paper 10006. Houston, Texas, NACE. 2010.
13.
A. Al – Borno, M. Brown, S. Rao. “High Temperature Cathodic Disbondment Tests”,
Proceedings of the CORROSION/2010 Conference, paper 10008. Calgary, Alberta, NACE.
2010.
©2012 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International,
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