Paper No.
7246
FUSION BONDED EPOXY COATINGS (FBE) AND DISBONDMENT
M. Zamanzadeh, Ph.D., FASM, FNACE
NACE Certified Corrosion, Coatings, Materials Selection,
Design, Cathodic Protection Specialist
E-mail: [email protected]
Huiping Xu, PhD
Exova-Pittsburgh Corrosion Assessment Group.
100 Business Center Drive
Pittsburgh, PA 15234
ABSTRACT
Fusion Bonded Epoxy (FBE) coating has been used for corrosion protection of underground pipe lines
since the 1960’s. FBE provides protection of pipeline under cathodic protection even though there may
be dis-bondment or blistering. FBE does not shield cathodic protection current under normal conditions,
a characteristic which likewise distinguishes FBE coating from all other coating. In this paper failure
analysis methodology will be applied to the principal mechanisms by which FBE coatings fail during long
term service; with specific application to case studies involving blistering. The case studies apply
standard failure analysis techniques to determine the primary causes and modes of failures. Solution in
blistered areas, pH and presence of cations and chlorides on the surface and in the coating will provide
evidence for surface contamination/dis-bondment mechanism. If AC interference or shielding is present,
localized corrosion attack in blistered areas can be detected prior to deep penetration in to wall thickness
by effective corrosion monitoring. This can be achieved by on-time monitoring of soil corrosivity and
AC/DC interference by test coupons.
Keywords: Corrosion Protection, Pipeline, Coating, Fusion Bonded Epoxy Coatings (FBE), Blistering,
Coating Failure Mechanism, Cathodic Protection, AC Interference, DC stray Current Corrosion,
Shielding.
INTRODUCTION
There are over a million miles of distribution pipelines in the United States alone, carrying crude oil,
refinery products, natural gas, and other liquids. Consequently, keeping this infrastructure in service
through proper corrosion protection is a major priority.
METHODS FOR CORROSION PROTECTION
The key to preventing corrosion is to suppress or inhibit one of the components that make up the
corrosion process, e.g., either the anodic reaction, cathodic reaction, or the conduction of ions and
electrons by barrier coatings.
©2016 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, 15835 Park Ten Place, 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.
1
Coatings
One of the oldest measures of corrosion protection is to coat the substrate with a polymeric material. An
organic coating can protect a metal substrate by two mechanisms: serving as a barrier for the reactants:
water, oxygen, and various ions and serving as a reservoir for corrosion inhibitors that may assist the
surface in resisting corrosion attack.
There are a number of different types of coatings that have been used specifically to provide corrosion
protection for buried or submerged metal structures including coal-tar based coatings, polyolefins, shrink
sleeves, wax-based coatings, asphalt, urethanes and blends, epoxy phenolics, polyureas, esters, and
fusion based epoxy coatings (FBEs). These coatings are used for corrosion control and do not have to
"look good". The coatings are applied much thicker than above ground coatings and must be able to
withstand an underground environment. In order for a coating to operate safely for the intended life of
the component it is important to choose the right coating for the environment, not to exceed the operating
requirements for the coating, and ensure proper installation and handling of the coated structure. When
the application is underground, soil stress is the most critical factor. Coatings with little or no elongation
but good adhesion to the steel pipe are less susceptible to soil stress. Use temperature is also a critical
criterion. The maximum and minimum temperatures must be considered compared to the use
temperature and the glass transition temperature of the coating in question. Simply put, coatings that
perform at very high temperatures (thermosets) will probably not function well at very low
temperatures. Coatings that perform well at very cold conditions (rubbers) will not function well at very
high temperatures. At temperatures greater than 65° C, rubber adhesives can flow, causing a lack of
corrosion protection because water can penetrate into the voids and spaces of the flowing adhesive.
For a coating to be effective, it should have the following properties (1,2):
1. High dielectric strength to insulate the buried metal structure from the soil
2. Excellent bond strength to insure continuous and permanent contact with the metal structure
3. Low water absorption in order to maintain the dielectric strength and physical properties of the
coating and prevent interfacial contamination
4. Good physical strength to avoid damage to the coating during shipping, installation and soil stress.
5. The coating should not act as a shield for cathodic protection.
Fusion bonded epoxy coatings (FBE) have been used for underground pipelines since the 1960's. It has
good track record for underground piping applications. It is also used to coat rebar used in bridge, road,
and building construction to help prevent corrosion when embedded in concrete. It is a heat-activated,
chemically cured coating system that is applied to preheated pipe. The typical formulation for FBE's
consists of the epoxy resin, curing agent, catalyst, accelerator, reinforcing pigment, and control agents
which regulate flow and stability. FBE’s are usually used in conjunction with cathodic protection. In most
cases dis-bonded areas under FBE coating is protected by cathodic protection. A fail-safe coating
system.
Cathodic Protection
Cathodic protection is a method for reducing corrosion by minimizing the potential difference between
the anode and cathode. In this method, a current is applied from an outside source to the structure to be
protected, such as a pipeline. When enough current is applied, the whole structure, (pipeline) will exhibit
one potential and the anodic sites on a pipe will cease to exist. For underground applications, there are
two types of cathodic protection systems: galvanic and impressed current. A galvanic cathodic
protection system utilizes the corrosive potential differences between different metals. Without cathodic
protection, one area of the structure will exist at a more negative potential than another, resulting in
©2016 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, 15835 Park Ten Place, 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.
2
corrosion. If an object with more negative potential is placed adjacent to the pipeline to be protected with
a metallic connection installed between the object and the structure, the object will become the anode
site and the entire pipeline becomes the cathode. Technically, the object is sacrificed to protect the
pipeline. Galvanic anodes are usually made of magnesium or zinc because these metals have higher
potentials than steel pipes.
The second form of cathodic protection is impressed current cathodic protection. The impressed current
system uses an external power source, usually a rectifier that changes input alternating current (AC) to
drive the current to the proper direct current (DC) power level. The rectifier can be adjusted so that the
proper output is maintained throughout the pipeline’s lifecycle. Impressed current anodes are usually
made of high-silicon cast iron or graphite.
Stray Current Corrosion
Stray current from external sources can result in accelerated corrosion of brand new fusion bonded epoxy
coated pipe in a rather short time. Stray current corrosion is due to currents following through paths other
than the intended circuit. The extent of damage, corrosion rate and loss in thickness can be estimated
by Faraday’s law, soil resistivity and time in service and is directly proportional to the magnitude of stray
current. This type of corrosion is localized in coated pipes and takes place at discharge points (pinholes
and mechanically damaged areas). Figure 1 shows localized corrosion due to stray current in rather short
service time (six months). Stray current corrosion can be prevented by eliminating the source, shielding
and cathodic protection.
AC Interference
Typically, FBE coated pipelines are located near electric transmission lines and run parallel to high
voltage transmission lines (HVTL). AC interference can take place by conduction or an induction
mechanism causing corrosion in the blistered areas of the FBE coating. The presence of AC interference
can cause serious pitting corrosion even on pipes under cathodic protection. This is even the case if the
-0.850 V CSE criterion is met. Uncertainties exist as to the reason for this. We believe the corrosion
attack in blistered areas and the formation of magnetite corrosion products inside the pit can be detected
from electrochemical data prior to initiation of pits penetrating the pipeline wall thickness, provided we
monitor AC interference data, on time CP data, and ER corrosion rate monitoring. This enables corrosion
attack to be detected prior to deep penetration into the pipeline wall thickness.
Figure 1-Stray current corrosion of a new FBE coated pipe
©2016 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, 15835 Park Ten Place, 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.
3
Coating Failure Mechanisms
Blisters are local defects that form because of the pressure exerted by an accumulation of water or
aqueous solution at the coating-substrate interface in conjunction with loss of adhesion and distention of
the coating. At these local regions, corrosion of the substrate may occur. But the loss of coating
adhesion is actually connected with the development of a cathodic area under the coating adjacent to
the defect. Oxygen also permeates the coating while ionic materials are leached from the substrate or
from the coating and these all concentrate to make an electrochemical corrosion cell beneath the
blister. Therefore blisters are an early sign of corrosion but are often neglected. Conversely, the
elimination, reduction, or delay in blister formation will delay the onset of corrosion of the steel
substrate. However, even with correctly applied cathodic protection, shielding can render CP locally
ineffective and corrosion can still occur. There is no consensus on the number of different forms and
the actual mechanisms for blister formation but the most likely possibilities are identified below. In
general, the mechanism of blistering is attributed to osmotic attack or the presence of defects in the
coating interfacial region, in combination with the influence of moisture (1,2). The following sequence of
events leading to blistering is general to most types:
1. The film absorbs water from solution, possibly containing dissolved salts.
2. Once sufficient chloride ions pass through to the underlying metal, primary corrosion is initiated
at sites along the interface, particularly at existing defective areas or areas of substrate
contamination.
3. As corrosion proceeds at the anodic sites under the film, hydroxyl ions build up at cathodic sites.
4. The alkaline environment at the cathodic sites weakens or destroys the adhesion of the film while
producing osmotically active substances at the coating/metal interface.
5. The presence of these active substances at the interface causes osmotic (or endosmotic)
passage of water from the coating surface to the interface resulting in pressures that exceed the
interfacial strength of the film and eventually the fracture strength of the film causing further
delamination or coating rupture.
Four mechanisms are generally proposed to explain blister formation: volume expansion due to swelling,
gas inclusion or gas formation, electro-endosmotic blistering, and osmotic blistering. Some sources
consider phase separation during film formation resulting in the presence of a hydrophilic solvent a
separate mechanism, however it is really a subset of osmotic processes. Furthermore, this mechanism
is not applicable to FBE coatings since solvents are not involved in the application of the epoxy
resin. Interestingly, the first two mechanisms result in loss of adhesion of the coating (at least locally)
prior to the onset corrosion, while the later processes including cathodic delamination are the result of
corrosive action at the interface.
Surface Preparation and Application
Blister formation and FBE delamination can be controlled through appropriate application of the FBE
coating by (a.) being extremely careful in cleaning the substrate of all contaminants, and (b.)
implementing a quality control program to ensure there are no contaminants present on the substrate
prior to the coating application. The advantages to protecting the FBE coated pipe from such damage
include:
1. Extended coating and structure life yielding cost savings in replacement costs
2. Protection of the environment and cost savings from avoiding potential lawsuits
3. Improved public safety and avoidance of liability claims
©2016 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, 15835 Park Ten Place, 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.
4
4. Avoidance of costly litigation resulting from non-adherence to laws and regulations that
require appropriate protection of pipelines.
CASE STUDY
We were asked to perform a failure analysis investigation on a 12-inch diameter Fusion Bonded Epoxy
(FBE) coated steel pipe. The pipe carried natural gas for residential service and was under cathodic
protection while in service. We were asked to determine the cause of the blistering and any detrimental
effects to the pipe wall.
Laboratory Analysis and On-site Investigations
The laboratory analysis for this investigation included cross-section microscopy of the FBE coating in a
blistered and non-blistered area of the abandoned pipe; coating thickness measurements, chemical
analysis of liquid extracted from inside two blisters; chemical analysis of soil taken from near the
submitted pipe and SEM/EDS analysis of the underside of the coating from a blister and cross-sections
of two blisters.
Thickness Measurement of Sample Pipe from Site 1
The first work performed was the mapping and photography of five specified coated areas on pipe sample
cut from site 1. Each area was outlined with a dashed line and marked at 15 different spots with a single
black dot. The coating thickness was then measured at each of these 15 dots using a coating thickness
gage. Each dotted spot was also visually examined and categorized based on the condition of the
surrounding coating.
EDS Analysis
Three coating samples were selected for analysis by energy dispersive x-ray spectrometer (EDS). The
three samples were cleanly removed from the blistered areas of the coating during the on-site
investigation. The presence of chlorine, and sodium in all samples, is a strong indication of surface
contamination.
Backside Contamination Determination
The backside of delaminated coating samples identified as #2, #5a and #5b were selected for a
contamination analysis. The samples were evaluated at 30x magnification. The percent contamination
estimate was recorded at percentage of total area and presented in the following Table 1.
TABLE 1: Backside Contamination Estimation
Backside contamination
Sample
Blistered area %
Next to-blistered area %
#2
50
30
#5a
55
45
#5b
49
35
Cathodic Dis-bondment Test
Figure 2 shows typical delamination of FBE coating on underground pipes. Cathodic dis-bondment
testing was performed at -1.5 vs. Cu/CuSO4 for 48 hours on a coated sample cut from the pipe from site
1. 0.01 M NaOH was used as the electrolyte. In this test an artificial defect is introduced At the end of
the test, using a utility knife, the coating was chipped off until coating adhesion resisted the levering
action. The radius of the disbanded area from the holiday edge to the coating was measured to be 5.3
©2016 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, 15835 Park Ten Place, 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.
5
mm r (mm radius). This determination indicates a high FBE delamination rate on areas next to the
blisters. The delamination rate was estimated at 5.3 mm / 48 hours.
Cross Sectional Microscopic Characteristics
Figure 3 shows typical blistering and delamination of FBE coating due to surface contamination. Samples
from blistered and non-blistered areas of the abandoned pipe were prepared for cross-sectional optical
light microscopic (OLM) examination. Cross-section samples in blistered and non-blistered (good) areas
by sectioning transversely, mounting in epoxy resin and polishing. Table 2 presents a summary of the
cross sectional characteristics observed in Blister #1 (B-1), Blister #2 (B-2), Blister #3 (B-3) and both nonblistered areas (G-1 and G-2).
TABLE 2: Cross-sectional Characteristics
B-1
B-2
B-3
G-1
G-2
Irregular blasted steel profile, no abrasives in surface, some high temperature
iron oxide at surface, round bubbles in coating often near interface, no blister in
the sample.
Irregular blasted steel profile, no abrasives in surface, some high temperature
iron oxide at surface, round bubbles in paint, 1 ½ blisters in sample.
Irregular blasted steel profile, no abrasives in surface, some high temperature
iron oxide at surface, round bubbles in paint, 1 ½ blisters in sample.
Irregular blasted steel profile, no abrasives in surface, some high temperature
iron oxide at surface, round bubbles in paint often near interface.
Irregular blasted steel profile, no abrasives in surface, some high temperature
iron oxide at surface, round bubbles in paint often near interface, a few round
oxides in paint near interface.
Coating Thickness Measurements
Table 3 displays coating thickness values on the cross sectional samples B-1, B-2 and B-3 (blistered) as
well as G-1 and G-2 (good, not blistered). The average values in the blistered areas were not much
smaller than those in the non-blistered areas. This would suggest the coating had not degraded in the
blistered area. The thicknesses are measured in mils (0.001 inch).
TABLE 3: Cross-Section Coating Thicknesses (mils=2.5 thousandths of centimeter)
1
2
3
4
5
Average
B-1
8.78
8.42
9.83
9.34
9.90
9.25
B-2
10.33
9.06
12.37
9.94
8.49
10.04
B-3
11.28
11.17
10.54
11.74
11.88
9.73
G-1
11.10
10.54
11.74
11.88
9.73
11.00
G-2
11.21
11.81
11.28
10.75
11.84
11.38
Thickness measurements were also conducted on the submitted section of pipe in blistered (BL) and
non-blistered (NB) areas. The thicknesses in the blistered areas are somewhat lower than those in the
non-blistered areas, as shown in Table 4. Thicknesses below 12 mils are considered very low for
underground applications and corrosive moist soil. A minimum of 14-20 mils (35-50 thousandths of a
centimeter) is commonly specified.
©2016 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, 15835 Park Ten Place, 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.
6
TABLE 4: Pipe Coating Thicknesses (mils)*
BL
BL
NB
BL
NB
Area #1
Area #2 Area #3
Area #4 Area #5
1
10.50
13.00
13.30
11.20
13.60
2
9.20
10.80
12.60
12.30
11.60
3
9.40
10.90
12.30
11.60
13.30
4
11.90
11.60
12.50
9.90
13.20
5
13.20
11.70
12.60
9.00
13.60
6
10.50
9.60
12.40
9.50
13.30
7
11.50
10.30
11.60
8.30
13.40
8
13.40
10.50
11.50
10.50
12.10
9
10.10
11.50
9.20
10.00
11.00
10
10.40
13.00
10.30
10.70
10.70
11
11.20
14.10
10.90
9.80
11.90
12
12.00
14.00
11.80
9.10
11.00
13
10.80
12.50
11.50
8.90
10.90
14
15
10.50
9.50
11.60
13.50
10.30
9.40
9.40
9.60
15.10
13.50
*Note 1: Average thickness in the blistered areas is 10.94 mils and average thickness in the non-blistered
areas is 12.01 mils.
Blister Liquid Analysis
A hypodermic syringe was used to extract liquid from inside Blister #1 and Blister #2 during the on-site
investigation for subsequent laboratory analysis. The liquid samples were analyzed to reveal their
chemical analysis and determine if they were harmful to the carbon steel pipe. The results of the analyses
are displayed in Table 5
TABLE 5: Liquid Analysis
Analysis
pH
Calcium
Chloride
Magnesium
Nitrates
Nitrites
Phosphates (as P)
Sulfates
Sodium
Blister 1
11.7
30 ppm
<50 ppm
<10 ppm
614 ppm
<10 ppm
<100 ppm
1.62%
Blister 2
11.45
100 ppm
<50 ppm
<10 ppm
0.16%
40 ppm
<10 ppm
40 ppm
1.16%
©2016 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, 15835 Park Ten Place, 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.
7
The large amounts of nitrates and sodium are significant because they usually do not permeate through
the coating readily, which means they were present prior to the application of the coating. Water and
oxygen will permeate through the coating and combine with the sodium to create sodium hydroxide. We
also performed SEM/EDS on paint cross sections.
Soil Sample Analysis
A sample of soil was collected from an area near the submitted pipe for laboratory analysis. The soil was
analyzed to determine its chemical make-up. The results of the analysis are displayed in Table 6.
Table 6: Soil Analysis
Analysis
pH
Calcium
Chloride
Magnesium
Nitrates
Nitrites
Phosphates (as P)
Sulfates
Sodium
Sample
(10/30/02)
10.00
12.7%
4.2 mg/kg
2.19%
162 mg/kg
66 mg/kg
190 mg/kg
3204 mg/kg
980 mg/kg
Soil Resistivity Measurements
The resistivity of the soil around the pipe was measured on-site from areas at the bottom of the pipe, top
of the pipe and near a blister. The resistivity was lowest near the blister. The results are listed in Table
7.
TABLE 7: Soil Resistivity
Sample
Top
Bottom
Near Blister
Resistivity
(ohm-cm)
7400
6000
2000
Discussion
Coatings degrade and fail for a variety of reasons. These can be categorized as either environmental
(moisture/oxygen transmission through the film) or application effects (surface preparation, coating
thickness), which can be exacerbated by complimentary corrosion protection processes.
In order to prevent corrosion of underground structures, moisture must be prevented from reaching the
steel surface. The penetration of moisture through the coating to the substrate is a controlling factor in
the corrosion process. Propelling forces are osmotic and electroendosmotic pressures with transport
aided by thermally induced molecular movements and vibrations within the coating. But, all coatings will
also possess varied imperfections that will allow the environment to easily reach the metal surface. For
this reason, cathodic protection is used in conjunction with coatings to protect those exposed areas. But
©2016 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, 15835 Park Ten Place, 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.
8
cathodic protection can introduce other problems for the coating. Hydroxyl ions (OH-), which are caused
by cathodic reactions at the cathode, may cause blistering or cathodic delamination of the coating in the
presence of contaminants at the interface. This can result in the loss of adhesion between the metal and
coating and eventual exposure of the metal surface to the environment. Hydroxyl ions (OH-) are one of
the most aggressive chemical species and nearly all organic binders and oxides are capable of reacting
with them.
Coating Failure Mechanism-Blister Formation
FBE blisters are local defects that form because of the pressure exerted by an accumulation of water or
aqueous solution at the coating-substrate interface in conjunction with loss of adhesion and distention of
the coating.
In general, the mechanism of blistering is attributed to osmotic attack and/or the presence of
contamination in the coating interfacial region, in combination with the influence of moisture and cathodic
protection. The following sequence of events leading to blistering is general to most types:
1. The coating absorbs moisture. The presence of contaminant substances at the interface causes
osmotic (or endosmotic) passage of water from the coating surface to the interface.
2. As oxygen reduction takes place at the contaminant site under the film, hydroxyl ions build up in
the blister solution resulting in alkaline high pH environment in the blister.
3. The alkaline environment at the cathodic sites weakens or destroys the adhesion of the film while
producing osmotically active substances at the coating/metal interface. The presence of alkaline
in the environment results in extensive disbanding and delamination of the coating in the blistered
areas.
4. The presence of these active substances at the interface causes osmotic (or endosmotic)
passage of water from the coating surface to the interface resulting in pressures that exceed the
interfacial strength of the film and eventually the fracture strength of the film causing further
delamination or coating rupture in delaminated areas.
Figure 2- Coating Delamination and surface corrosion products
©2016 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, 15835 Park Ten Place, 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.
9
One of the main factors in the blistering of the FBE coating was determined by the chemical analysis of
the liquid inside the blisters and of the back contamination observed on delaminated coatings. As oxygen
reduction takes place at the contaminant site under the film, hydroxyl ions build up in the blister solution.
The alkaline environment at the cathodic sites weakens or destroys the adhesion of the film while
producing osmotically active substances at the coating/metal interface. Sodium was not detected in the
coating cross section so it must have been present on the surface of the pipe before the coating was
applied. EDS analysis of the backside of the delaminated FBE coating samples indicated the presence
of sodium and chlorine. SEM/EDS analysis of the coating shows there is no sodium in the coating, which
confirms it was not permeating through the coating but rather already present on the pipe surface as a
contaminant.
Figure 3- FBE samples from blistered area of the pipeline.
The alkaline environment inside the blisters, the presence of negatively charged ions (nitrates) in the
blister liquid, and the presence of contaminants (such as sodium and chlorides) are all indications of
osmotic (or endosmotic) passage of water from the coating surface to the interface. This resulted in
pressures that exceeded the interfacial strength of the film. Eventually the fracture strength of the film
would be affected, which would cause further delamination of the coating.
Conclusion
Based on testing and analysis, it was determined that the root cause of blistering of the fusion bonded
epoxy (FBE) coated steel pipe was due to surface contamination of the pipe prior to or during the coating
application. This determination is based on the following items detailed in this report:
1. The presence of chlorine in Sample, nitrate ions in the blister solution and sodium in all three
samples, is a strong indication of surface contamination.
2. The presence of nitrates, sodium and chlorine (on the backside of the delaminated coating) in the
blisters confirms the proposed failure mechanism.
3. A delamination rate of 5.3 mm / 48 hours was measured in a 0.01 M NaOH solution. The CDT
test indicates a high FBE delamination rate on areas next to the blisters.
4. Sodium was not detected in the cross section analysis, therefore, it must have been present on
the surface of the pipe.
©2016 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, 15835 Park Ten Place, 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.
10
5. SEM/EDS analysis of the coating shows there is no sodium in the coating, which confirms it was
not permeating through the coating but rather already present on the pipe surface as a
contaminant.
6. The blister liquid analysis indicates the CONTAMINATION WAS present prior to the application
of the coating.
Recommendations
To ensure public safety and avoid liability claims, it is very important that the blister growth, FBE
delamination, adhesion loss and cathodic protection effectiveness on this pipe be monitored. Special
attention should be given to cathodic protection shielding in presence of river weights, rocks and metallic
objects and AC interference.
In our opinion the pipe should be recoated in areas were extensive delamination of the coating is
observed. This is to avoid localized corrosion of the pipe in the event there is lack of protection,
inadequate cathodic protection, AC interference or shielding effects.
Significant increase in current requirements for cathodic protection suggests extensive blistering and
delamination.
Oxygen reduction and resulting alkaline environment inside the blister weakens or destroys the adhesion
of the FBE film while producing osmotically active substances at the coating/metal interface. The
delamination process is, and will be, an accelerated and on-going process. It should be noted that all
three random sites that were selected for inspection exhibited blisters and adhesion loss of fusion bonded
epoxy coating. Therefore, consideration should be given to inspecting statistically representative sites to
determine how wide spread the contamination problem may be on the pipe.
In summary the pipe should be recoated in areas were general delamination of the coating is observed.
This is to avoid localized corrosion of the pipe in the event there is inadequate cathodic protection, or
shielding barriers to CP current is present.
REFERENCES
1-Alan Kehr, “Fusion Bonded Epoxy (FBE): A Foundation for Pipeline Corrosion Protection”, NACE
International-January 2003.
2-Henry Leidheiser Jr, Corrosion of Painted Metals-A Review, Corrosion, July 1982, Vol 38, No7, pp4374
©2016 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, 15835 Park Ten Place, 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.
11