48 MATERIALS PERFORMANCE August 2009

Case histories

Premature Coating

Disbonding on Ships and

Offshore Structures

Chung-Seo Park, ho-II Lee, Seong-Mo Son, Mong-kyu Chung,

and kI-Soo kIM, Hyundai Heavy Industries Co., Ltd., Ulsan, Korea

Epoxy/urethane coating systems are widely used for ships

and offshore structures because of their excellent

resistance to ultraviolet radiation and protection against

corrosion. Recently, some of these coating systems used in

Korea experienced premature failure. Tis work

investigated the root cause of the failures using pH tests

and Fourier transform infrared spectroscopy.

Delamination is the loss of inter-

facial adhesion between coating

layers and is a common type of

coating failure. In general, these

coating failures occur most often where

repair or maintenance coatings are being

applied over existing coatings that have

been in service for some period of time.1

There are, however, many causes for

intercoat delamination, such as incom-

patibility of adjacent coatings, improper

mixing of base resin with hardener, ap-

plication of the subsequent coating on the

fully cured coating surface, and surfaces

contaminated with amine blush and

moisture.

In the ship and offshore structure in-

dustries, the following three elements are

very desirable: 1) reduce dry times before

subsequent coating and seawater expo-

sure, 2) increase the maximum recoating

interval, and 3) maintain good adhesion.

In particular, to have better work-

ability and productivity regardless of the

season, coatings should have a short cur-

ing time. Consequently, amine-cured

epoxy coatings have been selected to

meet the fast curing requirement. Re-

cently, however, premature coating

failures occurred on Korean vessels and

structures. Epoxy/epoxy coating systems

or epoxy/urethane coating systems ex-

perienced intercoat adhesion failure

(Figure 1), especially during the winter

and spring seasons. Failures led to an

overall delay in the coating program and

subsequent delay in the construction

schedule.

In this study, the analyses of the root

cause of the intercoat delamination fail-

ure for epoxy/epoxy and epoxy/ure-

thane coating systems were carried out

using pH indicator paper and Fourier

transformed infrared (FTIR) spectros-

copy. We now use improved epoxy paints

for marine/offshore structures.

August 2009 MATERIALS PERFORMANCE 49

C O A T I N G S & L I N I N G S

Analytical Test Methods for Intercoat Delamination

Amine Blush Check Using

pH Indicator Paper

Amine curing agents mixed in the

epoxy coatings react with moisture and

atmospheric carbon dioxide (CO2) to form

amine salts such as ammonium bicarbon-

ate (NH4HCO

3) and/or ammonium

carbamate (NH4NH

2CO

2). Generally, pH

of the amine salt is of a high alkalinity (pH

>9), because it contains the ammonium

ion (NH4+).2-3 Therefore, there is a strong

correlation between pH of the delami-

nated coating film and the amine blush.

The presence of the amine blush can be

confirmed by comparing the color of the

saturated pH paper to the standard color

chart provided in the container.

FTIR Spectra Analysis

FTIR can measure the frequencies in

which the sample absorbs the radiation

and the intensities of the absorptions, to

allow identification of the sample’s chem-

ical makeup. Because chemical functional

groups are known to absorb infrared ra-

diation at specific frequencies, FTIR is the

typical chemical analysis technique used

in the laboratory for coating failures. At-

tenuated total reflection (ATR) FTIR

spectroscopy is also widely employed for

Premature adhesion failures in the shipyard and offshore structure.

Delamination of epoxy (EA)/urethane coating system.

FIGURE 1

FIGURE 2

TAbLE 1

Physical properties of delaminated coating materials

Material Hardener Type

Mixing

Ratio (Vol) Pot Life (h) 5 °C 15 °C Remarks

EA Amine 4:1 3 (20 °C) —

8 (touch) 16 (through)

— —

Case I Case II

EB Amine 4:1 2 (23 °C) 3 (10 °C)

6 (touch) 20 (through)

— —

Case I

EC(a) Amide 1:1 6 (23°C) 7 (15 °C)

6 (touch) 38 (through)

3 (touch) 16 (through)

Case III

EC(b) Amide adduct 1:1 7 (23 °C) 7 (15 °C)

3 (touch) 25 (through)

1 (touch) 10 (through)

Case III

Drying Time (h)

analysis of a cured coating surface. It al-

lows minimum sample preparation with-

out grinding or pressing compared to

conventional FTIR analysis.4-5

In this study, ATR FTIR spectroscopy

was used to identify the absorbance peaks

of surface contaminants such as ammo-

nium carbonate, ammonium carbamate,

isocyanate group, etc.

Case Studies and Discussion

There are several types of coating

failures, notably intercoat adhesion fail-

ure, sagging, and longer drying time. In

particular, the coating delaminations oc-

cur most frequently in the winter and

spring seasons in Korea. Therefore, the

delay of coating projects and construction

50 MATERIALS PERFORMANCE August 2009

C O A T I N G S & L I N I N G S Premature Coating Disbonding on Ships and Offshore Structures

schedules was inevitable. Table 1 sum-

marizes the physical properties of de-

laminated coating materials employed in

the actual projects.

Case Study I—Coating Failures

by Amine Blush

Amine Blush Check by

pH Indicator Paper

It was well known that pH of the

amine salts such as ammonium bicarbon-

ate and/or ammonium carbamate is of

high alkalinity because of the presence of

the ammonium ion (NH4+). The presence

Coating failure and outdoor weather conditions.

FIGURE 4

Delamination of epoxy (EB)/epoxy (EB) coating system.

FIGURE 3

of amine blush can be easily detected by

the measurement of the pH value on the

epoxy coating surface.

Figures 2 and 3 show a coating de-

lamination and amine blush test results

for epoxy/epoxy and epoxy/urethane

coating systems. The pH values of both

coating systems were pH >9. The results

indicate a presence of ammonium carba-

mate or ammonium bicarbonate be-

tween the delaminated film surfaces.

They also confirm that these coating

failures were caused by an amine blush

reaction between the free amine with

moisture and CO2.

FTIR Spectra Analysis

To determine the cause of coating

delamination, the peeled epoxy film and

standard cured epoxy film were examined

using the attenuated reflectance (ATR

FTIR) technique. Both spectra appeared

to be of similar paint resin chemistry, and

were amine-based epoxy resin. We ob-

served in the spectrum of the failed film

an additional intense carbon-oxygen

absorption band at ~1,650 cm–1 and a

weak absorption band at ~1,716 cm–1,

which might indicate that it was bicar-

bonate or carbamate.

To identify the cause of coating de-

lamination, pH indicator paper and ATR

FTIR were used to determine the pH

level and identify the absorbance peak of

peeled film, respectively. As a result, we

concluded that the main cause of coating

failure was amine blush.

Case Study II—Isocyanate’s

Reactivity with Moisture

Amine Blush Check by

pH Indicator Paper

Figures 4(a) and (b) show coating de-

laminations and amine blush test results

for the failed epoxy/urethane coating

system. The pH appears to be neutral and

it indicates that there is no ammonium

carbamate and/or ammonium bicarbon-

ate between delaminated coating layers.

Therefore, it can be clarified that the

main reason of coating failure is not

amine blush.

The outdoor weather conditions (Fig-

ure 4[c]) show that the humidity was very

high and the outdoor temperature fluc-

tuation was very large during the urethane

painting. Also, the steel structure was near

wet ground. The urethane coating might

have been applied on a damp or icy sur-

face. The isocyanate might react with

water on the epoxy instead of reacting with

the polyol group to form urea. According

to the relative reactivity of isocyanates with

August 2009 MATERIALS PERFORMANCE 51

C O A T I N G S & L I N I N G S

active hydrogen compounds, the reaction

with water will lead to reduction in adhe-

sion strength at the interface of the epoxy

and urethane coating, and lead to inter-

coat adhesion failure.6

FTIR Spectra Analysis

Typically, the ratio of the reactive

groups of the polyol to isocyanate in a

liquid polyurethane is maintained at just

over 1.0 or slightly isocyanate-rich to

form the properly cured film.7 So the

proper urethane coating film has an ex-

cess of reactive isocyanate.

In this case of coating failure, the ATR

FTIR technique was performed on the

peeled urethane film and the cured stan-

dard urethane film. Two similar spectra

were obtained. In general, urethane coat-

ing film has the absorption bands at

1,730, 1,690 (a weak shoulder), and 1,530

cm–1, and the band of the isocyanate

group is near 2,270 cm–1.8 The two spec-

tra were for urethane coating films. The

good film has an intense isocyanate ab-

sorption band at around 2,270 cm–1,

while the failed film doesn’t have any

peak in the same band. In the case of the

failed film, it can be determined that the

isocyanate reacted with moisture on the

epoxy-coated film to form the incom-

pletely cured urethane film. As a result,

insufficient intercoat adhesion was

formed between the urethane coating and

the epoxy coating because some isocya-

nate reacted with water instead of the

polyol.9

Case Study III—Amine Blush-

Resistant Epoxy Coating System

To reduce the amine blush, carbamate

formation should be minimized by proper

formulation with a small free amine such

as the primary amine because the pri-

mary amine reacts with moisture and

CO2 to form amine blush. A method to

minimize carbamate is to prereact pri-

mary amines with epoxy resin.10 So, in

this study, the amine blush resistance

coating of the amide-cured epoxy coating

system was improved and applied by ad-

ducting a part of epoxy binder and am-

ide-hardener in advance.

The FTIR spectra of 1,640 cm–1 and

3,200 cm–1 generally indicate the carbon-

oxygen absorption band, which can be

assigned as the amide peak of epoxy

hardener. By adducting a portion of ep-

oxy binder and hardener in advance, the

absorption bands at the same peak be-

come weak. This phenomenon means

that the amine blush can be reduced by

adducting the epoxy resin and the amine

or amide curing agent in advance.

Figure 5 shows the results of adhesion

and amine blush resistance for epoxy/

urethane coating systems before and after

adduction of epoxy coating. Based on

adhesion test results after water immer-

sion for three days, the adhesion of the

adducted epoxy was superior to one of

nonadducted epoxy. The pH test results

indicated that the adducted epoxy coat-

ing surface appeared to be neutral, while

the nonadducted epoxy coating surface

revealed it to be alkali.

Based on these results, it was deter-

mined that all amine-and amide-cured

epoxy paint can produce amine blush at

the weather conditions of low tempera-

ture and high humidity. The amine blush

can be minimized by adducting the

amine or amide curing agents and the

proper coating material should be se-

lected.

Conclusions Based on the investigation of three

case studies on the failed epoxy/epoxy

and epoxy/urethane coating systems, the

following conclusions can be made:

• In the case of the adhesion failure

between epoxy and epoxy or ure-

thane coatings, the pH indicator

Evaluation of results (a) before improvement [EC(a)] and (b) after improvement

[EC(b)].

FIGURE 5

52 MATERIALS PERFORMANCE August 2009

paper test and ATR FTIR spectros-

copy can be used to analyze the

main cause of coating failures.

• Not only amine-cured epoxy paint

but also amide-cured epoxy paint can

produce amine blush at the weather

conditions of low temperature and

high humidity. The amine blush can

be minimized by adducting the

amine or amide curing agents.

• Application of the urethane coating

system on the epoxy coating surface

requires more strict control of mois-

ture condensation to prevent inter-

coat disbonding.

References 1 C.G. Munger, Corrosion Prevention by

Protective Coatings, L.D. Vincent, ed. (Houston, TX: NACE International, 1999), p. 363.

2 B.L. Burton, “Amine-Blush Problem? No Sweat!,” Procedures of Epoxy Resin Formulators’ meeting of The Society of the Plastics Industry (200l), p. 1.

3 C.K. Park, et al., “Lessons Learned from Winter Season Application of Epoxy/Urethane Coating System for the Off-shore Structure,” CORROSION 2004 (Houston, TX: NACE, 2004).

4 S. Ekgasit, et al., “A Novel ATR FT-IR Microspectroscopy Technique for Sur-face Contamination Analysis Without Interference of the Substrate,” The Japan Society for Analytical Chemistry, Analytical Sciences 23, 7 (2007): p. 863.

5 G.T. Bayer, Failure Analysis of Paints and Coatings, Matco Associates, Inc., August 3, 2004.

6 D. Klempner, et al., Polymeric Foams and Foam Technology (Munich, Germany: Hanser Publishers, 2004).

7 “Curing Composition for Acrylic Polyol Coatings and Coating Produced,” U.S. Patent 5545824, August 13, 1996.

8 A. Luisa, et al., “Moisture Curing Kinetics of Isocyanate Ended Urethane Quasi-Prepolymers Monitored by IR Spectroscopy and DSC,” J. of Applied Polymer Sci. 107 (2008): pp. 700-709.

9 D. Klempner, et al., Polymeric Foams and Foam Technology, 2nd ed. (Munich, Germany: Hanser Publishers, 2004).

10 D.J. Weinmann, et al., “Amine-Func-tional Curatives for Low Temperature Cure Epoxy Coatings.”

This article is based on CORROSION

2009 paper no. 09015, presented in Atlanta,

Georgia.

C O A T I N G S & L I N I N G S Premature Coating Disbonding on Ships and Offshore Structures

ChuNG-SeO PArk is a senior researcher at the Protective Coatings and Corrosion research Dept., Industrial research Institute, at hyundai heavy Industries Co., Ltd., 1, Jeonha-Dong, ulsan, 682-792, korea, e-mail: jojoran@hhi.co.kr. he has 10 years of experience in the field of protective coatings and corrosion prevention. he has an M.S. degree in industrial chemical engineering from the Pukyung National university in korea; is a NACe-certified Coating Inspector, Levels 1 and 2; and is a member of the korean Corrosion Society and korean Industrial Chemical engineering Society.

hO-II Lee is a senior researcher at the Protective Coatings and Corrosion research Dept., Industrial research Institute, at hyundai heavy Industries Co., Ltd., e-mail: hilee@hhi.co.kr. he has 14 years of experience with protective coatings and corrosion prevention. he has an M.S. degree in metallurgical engineering from the Yonsei university in korea; is a NACe-certified Coating Inspector, Levels 1 and 2; and is a member of the korean Corrosion Society.

SeONG-MO SON is chief researcher at the Protective Coatings and Corrosion research Dept., Industrial research Institute, at hyundai heavy Industries Co., Ltd., e-mail: smchem91@hhi.co.kr. he has six years of experience in coatings formulation for paint manufacturers and four years of experience with protective coatings and corrosion prevention. he has an M.S. degree in chemistry from the Dong-a university in korea; is a NACe-certified Coating Inspector, Levels 1 and 2; and has published two papers in the Journal of Organo-metallic Chemistry.

MONG-kYu ChuNG is a senior researcher at the Protective Coatings and Corrosion research Dept., Industrial research Institute, at hyundai heavy Industries Co., Ltd., e-mail: bio@hhi.co.kr. he has 10 years of experience with protective coatings and corrosion prevention. he has an M.S. degree in environmental engineering from the Pusan National Fisheries university in korea; is a NACe-certified Coating Inspector, Levels 1 and 2; and is a member of the korean Corrosion Society.

kI-SOO kIM is manager of the Block Painting Dept. of the Shipbuilding Division at hyundai heavy Industries Co., Ltd. he has 26 years of experience in coatings design, inspection, and painting management. he has a B.S. degree from ulsan university in korea; is a NACe-certified Coating Inspector, Levels 1 and 2; and is certified to Frosio Level III.