Durability Assessment of
Various Kinds of Construction
Materials by Means ofLong-term Exposure Tests-Durability Assessment by Means of Exposure Tests
at Okinotorishima and Suruga Bay-

A-01

B-07

B-14

B-01

B-08

C-01

B-02

B-09

C-02

D-06

B-03

B-10

C-03

D-07

B-04

B-11

D-01

D-08

B-05

B-12

D-02

D-09

B-06

B-13

D-03

D-10

The Japan Iron and Steel Federation

D-04

D-05

Research Group on Corrosion Protection and Durability of Offshore Steel Structures
Committee on Overseas Market Promotion
The Japan Iron and Steel Federation
3-2-10, Nihonbashi Kayabacho, Chuo-ku, Tokyo 103-0025
Phone: 81-3-3669-4815 Fax: 81-3-3667-0245
URL: https//www.jisf.or.jp
Mail address: sunpou@jisf.or.jp(cover)Photos of the appearance (surface) at the recovery stage of 28 typesof specimens after 24 years of exposure at the Marine Engineering Research
Facility in Suruga Bay. For the type of specimens, refer to Part 1: Table 1 on
page 3, and for details of photos, refer to Part 3: 4. Photos of Appearance ofSpecimens on page 58.

© 2021 The Japan Iron and Steel Federation(Printed in Japan July 2021)

Foreword
Steel structures and steel products accomplish a great role in the development of public
infrastructure. As with concrete, steel products are used as structural materials for not only
general on-land structures but also for port/harbor facilities and offshore structures, andaccordingly they are inevitable in developing and improving contemporary infrastructure
facilities.
Meanwhile, most of offshore and port/harbor steel structures are exposed to severely corrosive environments. In spite of this, it is possible to ensure the safety of these steel structures with proper countermeasures and maintenance, using suitable corrosion-protection
methods that can prevent the deterioration of functions and maintain these structures in asound condition over the long term.
The common corrosion-protection measures for steel structures constructed in an offshore environment are the cathodic protection method applied in submerged and sea bottom
zones and the coating/lining method applied in atmospheric, splash and tidal zones. As ameans of verifying the application effect and durability of these corrosion-protection methods, what is accepted as the most reliable approach is to conduct an exposure test for thesemethods in an actual offshore environment and to observe the exposure test results over thelong term.
At the Japan Iron and Steel Federation (JISF), the Research Group on Corrosion Protection and Durability of Offshore Steel Structures of the Kozai Club (currently the JISF) and
the Public Works Research Institute of the Ministry of Construction (currently the Ministryof Land, Infrastructure, Transport and Tourism) jointly conducted long-term exposure tests
from 1982 for various kinds of construction materials at Okinotorishima and the Suruga
Bay Marine Engineering Research Facility, two test sites with different corrosion environments. The major aim was to assess the durability of these materials subjected to offshore
environments.
Okinotorishima, at the southernmost tip of Japan, is located in the Pacific Ocean around
1,700 km south of Tokyo and around 1,800 km east-northeast of Manila. It is a coral island
located in a tropical zone, where the temperature, humidity and sunshine radiation are high.
Further, not only tidal currents and waves are high there, but the island is constantly subjected to seawater splashing. Accordingly, the corrosive environment at Okinotorishima is
far stricter than that in sea areas around Japan’s main islands.
In parallel with the exposure tests at Okinotorishima, JISF conducted offshore atmospheric exposure tests for these materials at the Marine Engineering Research Facility at
Suruga Bay in Shizuoka Prefecture in order to assess the long-term durability of various
kinds of construction materials applied in Japan’s peripheral sea areas.
In this report, exposure test results are compared that were obtained from two exposure
test sites with different corrosive environments. At the same time, these test results areorganized so that this brochure can serve as informative data pertaining to the durability ofvarious kinds of steel products and corrosion-protection coated/sprayed/lined/painted construction materials to be applied in tropical and other severe offshore environments.

Research Group on Corrosion Protection and Durability of
Offshore Steel Structures
Committee on Overseas Market Promotion
The Japan Iron and Steel FederationⅰIntroduction
This brochure of long-term exposure tests for various kinds of construction materials is
composed of the following three parts:-Part 1
Durability Assessment of Various Kinds of Construction Materials by Means of Long-term
Exposure Tests at Suruga Bay and Okinotorishima–Joint Research by Public Works Research Institute and the Japan Iron and Steel Federation• Outline of series of three tests• Comparison of two long-term exposure tests between Suruga Bay and Okinotorishima• Exposure tests particularly at splash to tidal zones at the Marine Engineering Research
Facility in Suruga Bay-Part 2Comprehensive Report of Exposure Tests at Okinotorishima to Assess the Durability of
Various Kinds of Construction Materials–Secular Change over 19 Years of Exposure• Secular change of long-term exposure test results at Okinotorishima (results in 3rd, 5th,
10th and 19th year of exposure)-Part 3
Survey/Analytical Report of Exposure Tests at the Suruga Bay Exposure Rack Employing
Identical Specimens Used for Exposure Tests at Okinotorishima–Results after 24 Years of
Exposure• Detail surveys and analysis of long-term exposure test results at Suruga Bay (results after
24 years of exposure)ⅱ

Contents
Part 1
Durability Assessment of Various Kinds of Construction Materials by Meansof Long-term Exposure Tests at Suruga Bay and Okinotorishima-Joint Research by Public Works Research Institute and The Japan Iron andSteel Federation1. Outline of Exposure Tests and Test Facilities
1.1 Purpose of Series of Three Tests ..........................................................................2
1.2 Exposure Test Environments .................................................................................3
2. Comparison of Atmospheric Exposure Tests between Suruga Bay (Marine Engineering Research Facility) and Okinotorishima
2.1 Exposure Test Specimens .....................................................................................3
2.2 Exposure Test Methods .........................................................................................4
2.3 Survey Items .........................................................................................................4
2.4 Survey Results for Exposed Specimens
2.4.1 Ordinary Carbon Steel .................................................................................42.4.2 Stainless Steel .............................................................................................4
2.4.3 Nonferrous Metal .........................................................................................5
2.4.4 Metallic-coated/sprayed Plates ....................................................................5
2.4.5 Organic-lined and Heavy-duty Painted Plates .............................................6
2.5 Two Reports of Survey and Analytical Results ......................................................7
3. Exposure Tests at Splash and Submerged Zones at Marine Engineering
Research Facility in Suruga Bay
3.1 Outline of Exposure Tests .....................................................................................7
3.2 Survey Results for Exposed Specimens
3.2.1 General Painted Specimens ........................................................................8
3.2.2 Highly Corrosion-resistant Metallic Material-lined Specimens .....................8
3.2.3 Organic-lined Specimens .............................................................................9
4. Conclusion
4.1 Comparison of Atmospheric Exposure Tests between Okinotorishima
and Suruga Bay (Marine Engineering Research Facility) ...................................10
4.2 Exposure Tests in Splash to Submerged Zones at Marine Engineering
Research Facility in Suruga Bay .........................................................................10
4.3 Conclusions on Exposure Tests in Three Environments Mentioned in 4.1
and 4.2 ................................................................................................................10ⅲ

Part 2Comprehensive Report of Exposure Tests at Okinotorishima to Assess the
Durability of Various Kinds of Construction Materials-Secular Change over 19 Years of Exposure1. Purpose .....................................................................................................................14
2. Exposure Test Environments .....................................................................................14
3. Exposure Test Methods .............................................................................................15
4. Details of Test Specimens .........................................................................................15
5. Survey Items and Items Subjected to Surveys ..........................................................18
6. Assessment of Exposure Test Results
6.1 Observation Results for Appearances .................................................................20
6.1.1 Ordinary Carbon Steel ...............................................................................22
6.1.2 Stainless Steel ...........................................................................................22
6.1.3 Nonferrous Metal .......................................................................................24
6.1.4 Metallic-coated/sprayed, Organic-lined and Heavy-duty Painted
Plates .........................................................................................................24
6.2 Calculation Results for Corrosion Amount, Mass Loss and Corrosion Rate .......26
6.2.1 Ordinary Carbon Steel ...............................................................................26
6.2.2 Stainless Steel ...........................................................................................28
6.2.3 Nonferrous Metal .......................................................................................28
6.2.4 Metallic-coated/sprayed Plates ..................................................................28
6.3 Measurement Results for Plate Thickness ..........................................................28
6.3.1 Ordinary Carbon Steel ...............................................................................28
6.3.2 Stainless Steel ...........................................................................................28
6.3.3 Nonferrous Metal .......................................................................................28
6.3.4 Metallic-coated/sprayed Plates ..................................................................28
6.3.5 Ordinary Carbon Steel, Stainless Steel, Nonferrous Metal andMetallic-coated/sprayed Plates ..................................................................28
6.4 Measurement Results for Pitting Corrosion and Crevice Corrosion ....................30
6.4.1 Ordinary Carbon Steel ...............................................................................34
6.4.2 Stainless Steel ...........................................................................................34
6.4.3 Nonferrous Metal .......................................................................................34
6.5 Measurement Results for Film Thickness ...........................................................35
6.5.1 Metallic-coated/sprayed Plates ..................................................................37
6.5.2 Organic-lined Plates ...................................................................................37
6.5.3 Heavy-duty Painted Plates .........................................................................37
6.6 Measurement Results for Adhesive Strength ......................................................38
6.6.1 Metallic-coated/sprayed Plates ..................................................................41
6.6.2 Organic-lined Plates ...................................................................................41
6.6.3 Heavy-duty Painted Plates .........................................................................41
6.7 Detection Results for Pinholes ............................................................................426.7.1 Metallic-coated/sprayed Plates ..................................................................43
6.7.2 Organic-lined Plates ...................................................................................43
6.7.3 Heavy-duty Painted Plates .........................................................................43
6.8 Measurement Results for Insulation Resistance .................................................43
6.8.1 Organic-lined Plates ..................................................................................43
6.8.2 Heavy-duty Painted Plates .........................................................................44
6.9 Measurement Results for Impedance .................................................................44
6.9.1 Organic-lined Plates ...................................................................................45
6.9.2 Heavy-duty Painted Plates .........................................................................45
6.10 Measurement Results for Color Difference and Glossiness .............................45
6.10.1 Measurement Results for Color Difference .............................................48
6.10.2 Measurement Results for Glossiness ......................................................48
6.11 Measurement Results for Film Hardness ..........................................................48
6.11.1 Organic-lined Plates .................................................................................48
6.11.2 Heavy-duty Painted Plates .......................................................................48
6.12 Observation of Metallic-coated/sprayed Sections (SEM Analysis) ....................49
6.13 Measurement of Cl Concentration (EPMA Analysis) .........................................50
7. Conclusion .................................................................................................................52ⅳ

Part 3
Survey/Analytical Report of Exposure Tests at the Suruga Bay Exposure Rack
Employing Identical Specimens Used for Exposure Tests at Okinotorishima-Results after 24 Years of Exposure1. Purpose .....................................................................................................................54
2. Details of Test Specimens .........................................................................................54
3. Survey Items and Items Subjected to Surveys ..........................................................58
4. Photos of Appearance of Specimens.........................................................................58
5. Assessment of Exposure Test Results
5.1 Observation Results for Appearance
5.1.1 Ordinary Carbon Steel ...............................................................................60
5.1.2 Austenitic-type Stainless Steel ...................................................................60
5.1.3 Duplex-type Stainless Steel .......................................................................60
5.1.4 Ferritic-type Stainless Steel .......................................................................60
5.1.5 Titanium......................................................................................................60
5.1.6 Copper........................................................................................................60
5.1.7 Aluminum Alloy ...........................................................................................60
5.1.8 Aluminized Stainless Steel Plate ................................................................60
5.1.9 Hot-dip Galvanized Plate ...........................................................................61
5.1.10 Zinc-Aluminum Alloy-sprayed Plate .........................................................61
5.1.11 Aluminum-sprayed Plate ..........................................................................61
5.1.12 Polyethylene-lined Plate ..........................................................................61
5.1.13 Polyurethane-lined Plate ..........................................................................61
5.1.14 Ultra-high Build Epoxy Resin-lined Plate .................................................61
5.1.15 Epoxy Resin/Polyurethane Resin-painted Plate ......................................61
5.1.16 Epoxy/Fluororesin-painted Plate ..............................................................61
5.1.17 Epoxy Resin/Acrylic Silicon Resin-painted Plate .....................................61
5.2 Calculation Results for Weight, Corrosion Amount and Corrosion Rate .............62
5.3 Measurement Results for Plate Thickness ..........................................................63
5.4 Measurement Results for Pitting Corrosion and Crevice Corrosion ....................64
5.5 Measurement Results for Film Thickness ...........................................................65
5.6 Measurement Results for Adhesive Strength ......................................................66
5.7 Detection Results for Pinholes ............................................................................67
5.8 Measurement Results for Insulation Resistance .................................................67
5.9 Measurement Results for Impedance .................................................................67
5.10 Measurement Results for Color Difference and Glossiness .............................69
5.11 Measurement Results for Film Hardness ..........................................................69
5.12 Observation of Metallic-coated/sprayed Sections (SEM Analysis) ....................70
5.13 Measurement of Cl Concentration (EPMA Analysis) .........................................71
6. Examination Results
6.1 Metallic Materials
6.1.1 Ordinary Carbon Steel ...............................................................................74
6.1.2 Stainless Steel ...........................................................................................75
6.1.3 Nonferrous Metal .......................................................................................75
6.2 Coated/Sprayed/Lined/Painted Plates
6.2.1 Metallic-coated/sprayed Plates ..................................................................76
6.2.2 Organic-lined Plates ..................................................................................76
6.2.3 Heavy-duty Painted Plates .........................................................................77
7. Conclusion .................................................................................................................77ⅴ

Part 1

Durability Assessment of Various Kinds of Construction
Materials by Means of Long-term Exposure Tests at
Suruga Bay and Okinotorishima-Joint Research by Public Works Research Institute and The
Japan Iron and Steel Federation■ Outline of Exposure Tests and Test Facilities■ Comparison of Atmospheric Exposure Tests between Suruga Bay (Marine
Engineering Research Facility) and Okinotorishima■ Exposure Tests at Splash and Submerged Zones at Marine Engineering
Research Facility in Suruga Bay■ Conclusion11. Outline of Exposure Tests and Test
Facilities
1.1 Purpose of Series of Three Tests
In order to develop a corrosion-protection technology targeting offshore steel structures and to assess its long-term
durability, the Public Works Research Institute of the thenMinistry of Construction (currently Ministry of Land, Infrastructure, Transport and Tourism) and the Research Groupon Corrosion Protection and Durability of Offshore Steel
Structures of the then Kozai Club (currently the Japan Iron
and Steel Federation) jointly conducted the long-term exposure tests for various kinds of construction materials from1982 at the Marine Engineering Research Facility in Suruga
Bay and at the test site in Okinotorishima, where the corrosion environments differ from each other. The specific aim
was to assess the long-term durability of these materials. It
is considered that the long-term exposure test data obtained
from these practical environments can serve as a very
useful data that directly connects to the durability of corrosion-protection technologies.

Okinotorishima is located in the southernmost tip ofJapan, where both temperature and humidity are high andthe marine environment is severe, and thus the conditions
for how to appropriately assess weather resistance and corrosion resistance are far stricter than those at the peripheral
sea areas of the main islands of Japan. Because it was considered that valuable data unavailable from the artificially-accelerated exposure tests was able to be obtained byconducting exposure tests under such severe environments
as at Okinotorishima, an offshore atmospheric exposure test
was promoted there over the long span of 19.5 years.
The Marine Engineering Research Facility at Suruga
Bay is engaged in the observation of natural conditions andfunctions as an offshore observation facility to grasp actual
natural conditions. It is a facility for use for not only comprehensive research on offshore technologies but for theobservation of offshore natural conditions. Fig. 1 and Photo
1 show an outline of the Marine Engineering Research
Facility. At the facility, a 24-year offshore exposure test was
conducted to promote comparison study of the exposure
test results obtained from Okinotorishima, and further a30-year exposure test was conducted at the splash to tidal
zones, the strictest corrosion environment.

Fig. 1 Outline of Marine Engineering Research Facility at Suruga Bay
Anemoscope/anemometer
Main
light

Observation
tower

CoatedspecimenObservationbuilding

Ultrasonic wave
height meter

Recorder, power source
Auxiliarylight(No. 1 deck)

Photo1 Marine Engineering Research
Facility at Suruga Bay
Long-term protective coating/painting

Corrosion-protection
specimen

Concrete
specimen(No. 2 deck)(splash and tidal zones)(No. 3 deck)

Flow direction/
velocity meter

Cathodic
protection
specimen

Cathodic protection specimen (large size)

Sea bottom
surface2

Corrosion-protection lining

Cathodic protection
Corrosion-protection method

2. Comparison of Atmospheric Exposure Tests between Suruga Bay(Marine Engineering Research Facility) and Okinotorishima

1.2 Exposure Test Environments
Okinotorishima is an island located in Japan’s tropical zone
at 20° 25’ north latitude and 136° 5’ east longitude. The
periphery of the island is surrounded by coral reefs and theisland measures 4.5 km from east to south and 1.7 km from
north to south. Its average temperature is 27.2°C, the average seawater temperature 28°C and the average humidity
73% (JAMSTEC data for 2001). Its natural environment
features high temperatures/humidity and sunlight radiation.
Further the tidal current is fast and the wave height is high,and the island is also constantly subjected to seawatersplashing. Thus, the conditions for how to appropriately
assess weather resistance and corrosion resistance is far
more severe than those of the peripheral sea areas of themain islands of Japan.
The Marine Engineering Research Facility at Suruga
Bay is located at 34° 47’ north latitude and 138° 19’ east
longitude and 250 m offshore from the Suruga coast of
Suruga Bay. Its average temperature is 16.6°C, the average
seawater temperature 21°C and the average humidity 67%(Japan Meteorological Agency data for 2001).
ISO 9223 defines wetting time as “times when the relative humidity is 80% or more and the temperature is higher
than 0°C.” When the annual wetting time is calculated fromthe annual average temperature and annual average relative
humidity, it reaches 4,476 hours at Okinotorishima and1,392 hours at Suruga Bay, and the annual cumulative sunlight radiation at Okinotorishima is about 1.3 times that at
Suruga Bay.

2.1 Exposure Test Specimens
In order to compare atmospheric exposure test results
between Suruga Bay (Marine Engineering Research Facility) and Okinotorishima, it was decided to expose the test
specimens prepared using identical construction materials
at both testing sites. Plate-shaped specimens (210×30~75
mm in dimension and 1.2~9 mm in thickness) were used
for the test, and a total of 28 types of specimens were
exposed:• Kind A: Ordinary carbon steel, 1 type (specimen type
No.: A-01)• Kind B: Various kinds of stainless steel, 14 types(B1~B14)• Kind C: Nonferrous metal (pure titanium, copper, aluminum alloy), each 1 grade (C-01~C-03)• Kind D: Coated/sprayed/lined/painted plates (metallic
coating/spraying, organic lining, heavy-duty painting), 10
types (D-01~D-10)
Table 1 shows details of specimens subjected to the
exposure test.

Table 1 Test Specimens Used for Long-term Exposure Tests
Specimen No.

Group
Ordinary carbon steel

Kind
Ordinary carbon steel

Type
Ordinary carbon steel

Austenitic type
Stainless steel

Duplex typeFerritic type
Nonferrous metal

Titanium
CopperAluminum alloy
Metallic coating/spraying

Coated/sprayed/lined/
painted plates

Organic lining

Heavy-duty painting

Titanium
CopperAluminum alloy
Aluminized stainless steel plateHot-dip galvanized plate
Zinc-aluminum alloy-sprayed plate
Aluminum-sprayed plate
Polyethylene-lined plate
Polyurethane-lined plate
Ultra-high build epoxy resin-lined plate(Epoxy resin/polyurethane resin)-painted plate(Epoxy resin/fluororesin)-painted plate(Epoxy resin/acrylic silicon resin)-painted plate32.2 Exposure Test Methods
At Okinotorishima, the specimens were nearly horizontally
exposed at the exposure rack with an angle of 5° oriented to
face south with a height of 15 m from sea level. At Suruga
Bay, the specimens were fixed using 2 bolts/nuts on the
exposure rack at an inclination of 30° oriented to face southwith a height of 13 m from sea level. The exposure environment at both testing sites corresponded to the offshore
atmospheric zone. The exposure test was conducted over
19.5 years at Okinotorishima and 24 years at Suruga Bay.
Then, the exposed specimens were recovered to conduct
surveys.

2.3 Survey Items
Table 2 shows the survey items for the respective specimens. The appearance was observed for all specimens.
Then, noting the mass loss and maximum pitting corros i o n depth, testing was conducted for non-coatTable 2 Main Survey Items at Exposure Tests

ed/sprayed/lined/painted materials, and for coated/sprayed/lined/painted materials, the film thickness, adhesive strength, and insulation resistance were measured andthe cross section was observed.

2.4 Survey Results for Exposed Specimens
2.4.1 Ordinary Carbon Steel
When the surface property of the ordinary carbon steel after
the exposure tests was observed, while a lot of pitting corrosion was found for the specimen at Okinotorishima,nearly no pitting corrosion was found for that at Suruga
Bay. Further, when calculating the corrosion rate using themass loss after exposure, while the rate at Suruga Bay was
0.015 mm/y, the rate at Okinotorishima was 0.18 mm/y,
which showed that the corrosion rate at Okinotorishima was
about 12 times that at Suruga Bay. When compared with thestandard corrosion rate of steel products at H.W.L. or
higher, 0.3 mm/y, described in the “Technical Standards
and Commentaries for Port and Harbor Facilities inJapan,” the test results at both testingsites showed lower corrosion rates
than the standard rate.

Ordinary Stainless Nonferrous Coated/sprayed/lined/painted plates(D)carbon steel steel
metal Metallic coating/ Organic Heavy-duty
spraying
liningpainting

Survey item
Appearance observation
Mass loss
Local corrosion depthFilm thickness
Adhesive strength
Insulation resistance (volume resistivity)
Observation of film cross section (SEM)

Maximum pitting corrosion depth (μm)

Fig. 2 Relationship between Maximum Pitting Corrosion Depth atGeneral Section of Stainless Steel and PREN
Okinotorishima: Austenitic type
Okinotorishima: Duplex type
Okinotorishima: Ferritic type
Suruga Bay: Austenitic type
Suruga Bay: Duplex type
Suruga Bay: Ferritic type

(PREN)

Maximum local corrosion depth atinsulation washer-specimen gap (μm)

Fig. 3 Relationship between Maximum Local Corrosion Depth at
Insulation Washer-Specimen Gap of Stainless Steel and PREN

4

Okinotorishima: Austenitic type
Okinotorishima: Duplex type
Okinotorishima: Ferritic type
Suruga Bay: Austenitic type
Suruga Bay: Duplex type
Suruga Bay: Ferritic type

(PREN)

2.4.2 Stainless SteelAs for the stainless steel exposed at
Suruga Bay, while no notable massloss was found for any of the specimens, slight pitting corrosion occurredand crevice corrosion occurred at theinsulation washer-specimen gap in thespecimens e x c l u d i n g S U S 3 1 2 L(B-07). As for the stainless steel
exposed at Okinotorishima, slight pitting corrosion and crevice corrosion
occurred in every specimen, whichshowed a trend of corrosion depths
higher than those at Suruga Bay.
The maximum pitting corrosion
depth at the general section of all
specimens (maximum value of respective specimens) was organized using
the pitting resistance equivalent
number (PREN: Cr+3Mo+16N; Cr,
Mo and N: mass %), as shown in Fig.
2, and it was learned from theseresults that there was a correlation
between the maximum pitting corrosion depth and the PREN. Further,crevice corrosion occurred at the insulation washer-specimen gap, and it
was confirmed that there was a correlation between the maximum crevice corrosion depth at the insulation
washer-specimen gap and the PREN
(refer to Fig. 3).
In the test results after 24 years of
exposure at Suruga Bay, when the
PREN was 30 or more, both the maximum local corrosion depth at theinsulation washer-specimen gap andthe pitting corrosion depth at the general section reached
100 μm or less. Meanwhile, in the exposure test results at
Okinotorishima, when the PREN was 30 or more, themaximum pitting corrosion depth at the general section
reached 100 μm or less as with Suruga Bay, but when the
PREN was 40 or more, the maximum local corrosion depth
at the insulation washer-specimen gap showed 100 μm or
less.
While the difference of maximum pitting corrosion depth
at the general section between Suruga Bay and Okinotorishima was slight, the maximum local corrosion depth at
the insulation washer-specimen gap was clearly higher at
Okinotorishima. The reason for this seemed to be attributable to a higher average temperature by 11°C and a longer
wetting time at Okinotorishima than at Suruga Bay.

As for the copper (C-02) and aluminum alloy (C-03),
while mass loss was not observed, pitting corrosion at thegeneral section and crevice corrosion at the insulation
washer-specimen gap were observed. As for the copper,
while the maximum pitting corrosion depth was higher at
Okinotorishima, the maximum crevice corrosion depth at
the insulation washer-specimen gap was higher at Suruga
Bay. On the other hand, aluminum alloy showed test results
opposite from the above test results. As for the copper andaluminum alloy, no clear effect of the difference in test sites
on corrosion resistance was observed.

2.4.3 Nonferrous Metal
As for the pure titanium (C-01), mass loss, pitting corrosion
at the general section and crevice corrosion at the insulation
washer-specimen gap were not observed at either Suruga
Bay or Okinotorishima.

2.4.4 Metallic-coated/sprayed Plates
As shown in Fig. 4, as for the aluminized stainless steel
plate (D-01), while the formation of corrosion products wasobserved at both testing sites, the aluminum coating layer
remained, and thus it is assumed that the aluminized stainless steel plate had sound corrosion-protection performance.
As for the hot-dip galvanized plate (D-02), as shown in Fig.
5, the galvanized layer nearly completely disappeared after
19.5 years of exposure at Okinotorishima, but the galva-

Fig. 4 SEM Images at Cross Sections of Aluminized
Stainless Steel Plates

Fig. 6 SEM Images at Cross Sections ofZinc-Aluminum Alloy-sprayed Plates

Okinotorishima(after 19 years of exposure)

Suruga Bay(after 24 years of exposure)

Okinotorishima(after 19 years of exposure)

Corrosion productSpraying

× 100

× 100

Coating
Stainlesssteel

Suruga Bay(after 24 years of exposure)

Steel
plate

Corrosion
product

Stainlesssteel

Corrosion
product

× 100

Corrosion
product

Suruga Bay(after 24 years of exposure)

Average coating
loss rate=4 μm/y

Average coating
loss rate=2 μm/y

Coating(incl.
corrosion
product)× 1000Okinotorishima(after 19 years of exposure)

Coating
Steel
plate

Coating film thickness atcross section: 57 μm(Total film thickness:
79 μm; Initial value: 81 μm)

Suruga Bay(after 24 years of exposure)
Spraying
Steel
plate

Spraying
Steel
plate

Steel
plate
Coating film thickness atcross section: 97 μm(Total film thickness:
153 μm; Initial value: 88 μm)

Spraying film thickness atcross section: 242 μm(Total film thickness:
290 μm; initial value: 168 μm)

Fig. 7 SEM Images at Cross Sections of
Aluminum-sprayed Plates

× 100

Okinotorishima(after 19 years of exposure)

Spraying film thickness atcross section: 161 μm(Total film thickness:
179 μm; initial value: 173 μm)

Coating film thickness atcross section: 40 μm(Total film thickness:
57 μm)

Fig. 5 SEM Images at Cross Sections of Hot-dip
Galvanized Plates

Steel
plate

× 1000Coating film thickness atcross section: 27 μm(Total film thickness:
36 μm)

Spraying

× 1000× 1000Coating

Spraying film thickness
at cross section: 290 μm(Total film thickness:
320 μm; Initial value: 299 μm)

Spraying film thickness atcross section: 194 μm(Total film thickness:
256 μm; Initial value: 220 μm)

5primer coating, the annual average film thickness loss
rate of lined/coated/painted plates is shown in Fig. 8.
Fig. 9 shows the surface appearance of heavy-duty painted plate. In the figure, the surface where top coating wascompletely lost can be seen for respective heavy-duty-painted plates at both testing sites.
Fig. 10 shows the results of the measurement of insulation resistance (volume resistivity). A high insulation
resistance of 1010 Ω・cm or higher was observed at bothtesting sites, but the insulation resistance of every specimen at Suruga Bay was higher than that at Okinotorishima, and as a result, it is supposed that the deteriorationof the lined/coated/painted film was more severe at
Okinotorishima.

2.4.5 Organic-lined and Heavy-duty Painted Plates
At both testing sites, the polyethylene-lined plate (D-05)
showed considerable peeling of the lined polyethylene
from the plate edge due to the possibly inferior quality ofedge sealing materials, and thus the plate was excluded
from assessment. In other organic-lined/heavy-duty
painted plates (D-06~D-10), the lined/coated/painted
layer remained on all plates, and thus it is assumed thatthey had sound corrosion-protection performance.
Fig. 8 shows the annual film thickness loss obtainedby dividing the lined/coated/painted layer loss that was
found from the difference between the initial film thickness and the film thickness after exposure by the numberof years of exposure. In the polyurethane-lined plate inwhich the loss was highest, the loss at Okinotorishima
was larger by about 50% than that at Suruga Bay, whichcoincided with the ratio of sunshine radiation between
both testing sites. The loss in other lined/coated/painted
plates was larger at Okinotorishima, but the loss in theepoxy resin/acrylic silicon resin-painted plate was larger
at Suruga Bay.
As for the heavy-duty painted plate, while it is considered that the annual film thickness loss rate differs
respectively in top coating, intermediate coating or

Fig. 9 Surface Appearances of Heavy-duty
Painted Plates

Okinotorishima(after 19 yearsof exposure)
Suruga Bay(after 24 yearsof exposure)6

1.5 times
No clear trend is observed

Epoxy resin/acrylic Epoxy/fluororesin
top coating
silicon resin top(D-09)
coating (D-10)

Okinotorishima(after 19 years of exposure)

Suruga Bay(after 24 years of exposure)○Top coating (white):
Disappearance○Top coating (white):
Disappearance by a half

○Top coating (white):
Disappearance○Top coating (white):
Disappearance○Top coating (white):
Disappearance by a half

○Top coating (white):
Disappearance

Fig. 10 Insulation Resistance (Volume Resistivity) of
Organic-lined and Heavy-duty Painted Plates
after Exposure Tests
Initial value
Okinotorishima (after 19 years of exposure)
Suruga Bay (after 24 years of exposure)
Volume resistivity rate (Ω・cm)

Annual film thickness loss (μm/y)

Fig. 8 Loss of Film Thickness of Organic-lined andHeavy-duty Painted Plates(Lower table: Total loss at each exposure site)

Epoxy resin/
polyurethane resin
top coating (D-08)

nized layer remained even after 24 years of exposure at
Suruga Bay. Fig. 6 shows an SEM image of the cross section of zinc-aluminum alloy-sprayed plate (D-03), and Fig.
7 that of aluminum-sprayed plate (D-04). As for both of thezinc-aluminum alloy-sprayed plate and the aluminum-sprayed plate, while the formation of corrosion products was observed, the sprayed layer remained, and thus itis assumed that these plates had sound corrosion-protection
performance. Meanwhile, regarding the zinc-aluminumalloy-sprayed plate, because corrosion products occurred at
the exposed specimen at Suruga Bay, the sprayed film
thickness increased over that at Okinotorishima. Regarding
the aluminum-sprayed plate, while the film thickness
increased due to corrosion products at Suruga Bay andOkinotorishima, no difference of the increase in film thicknesses between both testing sites was found.

Polyurethane Ultra-high Epoxy resin/
Epoxy resin/
Epoxy/
liningbuild epoxy polyurethane fluororesin acrylic silicon(D-06)
resin lining resin painting painting resin painting(D-10)(D-07)(D-09)(D-08)
Polyurethane
lining(D-06)

Ultra-highbuild epoxy
resin lining(D-07)

Epoxy resin/
polyurethane
resin painting(D-08)

Epoxy/
fluororesin
painting(D-09)

Epoxy resin/
acrylic siliconresin painting(D-10)

2.5 Two Reports of Survey and Analytical
Results
Exposure tests conducted at Okinotorishima and Suruga
Bay were further subjected to detailed surveys and analysis,
the results of which are reported in Part 2 (Okinotorishima)
and Part 3 (Suruga Bay).

3. Exposure Tests at Splash and Submerged Zones at Marine Engineering Research Facility in Suruga Bay
3.1 Outline of Exposure Tests
The major aim of the exposure test was to expose the metallic materials and painted/lined materials to the corrosive
environment covering from an atmospheric zone to a submerged zone, mainly the most severe corrosive environment from a splash zone to a tidal zone, and to confirm thecorrosion resistance and durability of these materials. The
initial plan for the exposure test called for 10 years of exposure testing starting from 1984. Then, the test results thus
obtained were subjected to interim summarization andexamination to continue the test, and as a result the exposure test was promoted as a research project spanning up to
30 years at maximum. In order to confirm the secularchange of testing materials, appearance and detail surveys
were periodically and repeatedly conducted.

The exposure test was composed of the following threeresearch themes, and diverse kinds of tests were conducted
targeting the corrosion-protection specifications in accordance with these three themes.
• Theme 1: Examination of corrosion rate of corrosion protection-free structures and deterioration mechanism ofpainted materials• Theme 2: Establishment of low-cost corrosion-protection
technologies with longer service life by means of lining
with highly corrosion-resistant metallic materials• Theme 3: Confirmation of adequacy of new lining materials in practical application
In the following, the exposure test results for the test
specimens shown in Table 3 are introduced:
Fig. 11 shows the typical shape of specimens, and Photo
2 the installation conditions for the specimens. Taking into
account that the test specimens are installed on the siteextending from the splash and tidal zones to the submergedzone and that the specimens are installed directly on the test
site, steel tube measuring 165 mm in diameter and 3,500
mm in length and angle steel measuring 140 mm×140
mm×3,800 mm in length were settled on as the standard
specimen. The steel tube with a surface lined with target
metallic materials was settled on as the standard metal-lined
specimen.
In the surveys, appearance observation was applied to all
specimens; the measurement of plate thickness and pitting
corrosion was applied to corrosion protection-free and metallic material-lined specimens; and the measurement offilm thickness, adhesive strength, AC resistance and film
pinhole was applied to lined specimens.

Table 3 Corrosion-protection Specifications, Shapes and Exposure Period of Respective Specimens Applied for
Examining Three Research Themes
Research theme
1

Corrosion-protection specifications (film thickness)

Shape

Exposure period

Angle

20 yearsTube

20 years

General painting

Primer: Inorganic zinc (25 μm)
Intermediate and top coating: Tar epoxy (300 μm×2 layers)

Stainless steel lining

Ferritic type: Lining thickness 3 mm

Titanium lining

Pure titanium: Lining thickness 2 mm

Tube

30 years

Cupronickel lining

9-1 cupronickel: Lining thickness 3 mm

Tube

30 years

Organic lining

Primer: Organic zinc (20 μm)
Intermediate and top coating: Epoxy resin (1,250 μm×2 layers)Tube

20 years

Urethane elastomer lining (2,500 μm)

Tube

23 yearsAustenitic type: Lining thickness 3 mm2

3Duplex type: Material tube with wall thickness of 12 mm

Fig. 11 Typical Shape of Specimens

Splash/offshore atmospheric zone

Specimen

Tidal zone

Submerged zone
Photo 2 Condition of Installation of Specimens73.2 Survey Results for Exposed Specimens
3.2.1 General Painted Specimens
Fig. 12 shows the appearance survey results for generalpainted specimens after 5 years and 20 years of exposure.
After 5 years of exposure, corrosion was found in the submerged section of the specimen, and when the exposureterm surpassed 15 years, the corroded area rapidly
increased in the section covering from tidal to submergedzones. Fig. 13 shows the secular change of AC resistance ingeneral painted specimens. High AC resistance values weremaintained in the splash zone even after 20 years of exposure, but when the exposure term surpassed 15 years, theresistance abruptly lowered in the site covering from tidal
to submerged zones. Further, when the exposure term surFig. 12 Survey Results for Appearances of General
Painted Specimens

Splash zone

passed 15 years, the film thickness abruptly decreased.
Meanwhile, because the adhesive strength was measured by
selecting a sound section, its abrupt deterioration was notobserved even after 20 years of exposure.
3.2.2 Highly Corrosion-resistant Metallic Material-lined
Specimens• Stainless Steel-lined Specimens

The main corrosion of stainless steel was local corrosion
centering on the crevice corrosion that occurred beneath thelarge marine organism-adhered section in the tidal to submerged zones. The local corrosion in the splash zone waspitting corrosion, and the level of pitting corrosion in thesplash zone was considerably slighter than that in the tidal-submerged zones. Fig. 14 shows the relationship between
the stainless steel composition and the maximum corrosion
depth in the tidal-submerged zones where corrosion developed. As the pitting resistance equivalent number (PREN:
Cr+3Mo+16N; Cr, Mo and N: mass %) became larger, themaximum corrosion depth tended to become smaller, andwhen the PREN surpassed 38, pitting corrosion did notoccur in highly corrosion-resistant stainless steel.
Fig. 14 Relationship between Maximum Corrosion
Depth of Stainless Steel-lined Specimen and
PREN (Tidal Zone to Submerged Zone)

Maximum corrosion depth (mm)3

Tidal zone
Rust
sectionSubmerged zone

2.5

Specimen after
20 years of exposure

1.0E+101.0E+09
AC resistance (Ω・cm2)

38

1.5
1

Occurrence of
local corrosion

0.5

10

20

30

△

40

Cr+3Mo+16N（mass%）(PREN)

50• Titanium-lined Specimens

Fig. 13 Secular Changes of AC Resistance of General
Painted Specimens

As for the titanium-lined specimen, a titanium piece waspartially weld-joined to a specimen in order to artificiallycause crevice corrosion. Photo 3 shows the condition of thetitanium-lined specimen after 30 years of exposure. Corrosion was not observed beneath the organism-adhered section, and crevice corrosion was also not observed even at

1.0E+08
1.0E+07

Splash zone
Tidal zone

1.0E+06
1.0E+05

Submerged zone
Measurement : 1,000 Hz
0

5

10

15

Exposure period (y)8Outline mark: 9.5 years of exposure
Painted mark: 19.5 years of exposure

20Specimen after
5 years of exposure□ ■ Ferritic type
○ ● Austenitic type
△ ▲ Duplex type20

Photo 3 Titanium-lined Specimen after 30 Years of Exposure(Top: Submerged Zone; Botttom: Splash Zone)

the section where the crevice was artificially produced,
which thus showed that favorable corrosion resistance wasmaintained during exposure. Meanwhile, discoloration of
the specimen exposed to the splash zone to a red-browncolor was attributed to rust stains.

• Cupronickel-lined Specimens

Nearly no corrosion occurred in the cupronickel-lined specimen in the splash zone, but in the tidal-submerged zones
the thickness decreased slightly. Fig. 15 shows the distribution of thicknesses of cupronickel-lined specimen. The
thickness decreased by 0.2~0.3 mm in the tidal-submergedzones (corrosion rate: 0.01 mm/y), but local corrosion was
not observed, which thus showed the high corrosion resistance of cupronickel.

Fig. 15 Thickness Distribution of Cupronickel-lined
Specimens after 30 Years of Exposure

3.2.3 Organic-lined Specimens• Ultra-high Build Epoxy Resin-lined Specimens

Photo 4 shows the appearance of the ultra-high build epoxy
resin-lined specimen after 20 years of exposure. While corrosion of the exposed steel product was partly found in thesection like bruising, deterioration such as film thickness
loss and cracking was not observed, and thus the specimen
maintained a sound condition. Fig. 16 shows the secularchange of AC resistance in the splash zone. A high resistance of 108 Ω・cm2 was maintained over the long term. It
was also confirmed from the section-wise measurement
results for the specimen raised from the testing site that nodifference in deteriorated conditions between tidal and submerged zones was observed. Also, no considerable loss offilm thickness due to the lapse of exposure years wasobserved. To these ends, it was found that corrosion-protection performance was maintained for ultra-high build epoxy
resin-lined specimens.
Fig. 16 Secular Changes of AC Resistance of
Ultra-high Build Epoxy Resin-lined Specimens
1.0E+10

AC resistance (Ω・cm2)

Thickness of lined cupronickel (mm)Initial thickness

Splash
zone

Tidal
zone

1.0E+08
1.0E+07
1.0E+06
1.0E+05

Submergedzone

Splash zone

1.0E+09

0

5

10

15

20

25

Exposure period (y)(Upper-end
section)Position(mm)

Splash zone

① Pinhole of lining film

(Lower-end
section)①②③② Pinhole of lining film

Tidal zone

③ Pinhole of lining film

Submerged zone④

④ Peeling of lining film (about 10×25 mm)

Photo 4 Appearance of Ultra-high Build Epoxy Resin-lined Specimen after 20 Years of Exposure9Splash zone

Tidal zone

Submerged zone

Photo 5 Appearance of Urethane Elastomer-lined Specimen after 23 Years of Exposure• Urethane Elastomer-lined Specimens

Photo 5 shows the appearance of the urethane elastomer-lined specimen after 23 years of exposure. While ruststains were observed, cracking and peeling were notobserved, and thus sound condition was maintained. Fig. 17
shows the secular change of AC resistance in the splash
zone. It was seen from the figure that a high resistance of
108 Ω・cm2 or more was maintained over the long term. Further, it was confirmed from the section-wise measurement
results for the specimen raised from the testing site that
there was no difference in deterioration conditions between
the tidal and submerged zones. Also, no considerable lossof film thickness due to the lapse of exposure years wasobserved. To these ends, it was found that corrosion-protection performance was maintained for urethane elastomer-lined specimens.

AC resistance (Ω・cm2)

Fig. 17 Secular Changes of AC Resistance of Urethane
Elastomer-lined Specimens

Measurement section: Splash zone

0

5

10

15

20

25

Exposure period (y)4. Conclusion
4.1 Comparison of Atmospheric Exposure
Tests between Okinotorishima and
Suruga Bay (Marine Engineering Research Facility)• Remarkable differences in test results between both testing sites were seen in the following items:-Average corrosion rate (mass loss) of ordinary carbon
steel-Loss in hot-dipped galvanized mass
-Maximum corrosion depth at the insulation washer-specimen gap of stainless steel-Insulation resistance (volume resistivity) of organic-lined
steel products• While slight pitting corrosion and crevice corrosion
10

occurred in stainless steel at both testing sites, as the
PREN (Cr+3Mo+16N) increased, the maximum local
corrosion depth became smaller, and the materials with a
PREN of 40 or more showed high corrosion resistance.
• As for organic-lined specimen, corrosion resistance wasnearly maintained at both testing sites, but as forheavy-duty painted specimen, the annual film thickness
loss at Okinotorishima was larger than that at Suruga Bay,and thus it is considered necessary to shorten the repainting cycle.

4.2 Exposure Tests in Splash to Submerged
Zones at Marine Engineering Research
Facility in Suruga Bay• As for the general painted specimens, the corroded area

increased in the tidal-submerged zones after 5th year of
exposure. Further, when the exposure term surpassed 15
years, film thickness and AC resistance abruptly
decreased.
• As for the stainless steel-lined specimen, as the PREN
(Cr+3Mo+16N) increased, the maximum local corrosion
depth became smaller, and as for the specimen with a
PREN of 38 or more, no local corrosion occurred.
• As for the titanium- and cupronickel-lined specimens,
local corrosion did not occur even after 30 years of exposure, and high corrosion resistance was demonstrated.
• As for the ultra-high build epoxy resin-lined and urethane
elastomer-lined specimens, while they were exposed for
20 years and 23 years, they maintained sound conditions.

4.3 Conclusions on Exposure Tests in Three
Environments Mentioned in 4.1 and 4.2• As for stainless steel lining in the three exposure test

environments-atmospheric exposure testing at Okinotorishima, atmospheric exposure testing at Suruga Bay(Marine Engineering Research Facility) and exposure
testing in the splash to tidal zones at the Marine Engineering Research Facility at Suruga Bay, as the PREN
(Cr+3Mo+16N) increased, the maximum local corrosion
depth became smaller, and in stainless steel materials
with a PREN of 40 or more, high corrosion resistancewas demonstrated.
• As for titanium lining in any of the atmospheric exposure
testing at Okinotorishima, atmospheric exposure testingat Suruga Bay (Marine Engineering Research Facility)and exposure testing in the splash to tidal zones at the
Marine Engineering Research Facility at Suruga Bay, no
local corrosion occurred, and high corrosion resistancewas demonstrated.

References
1) Document of Public Works Research Institute (No.
4214): Durability tests for construction materials at
Okinotorishima (2012)
2) Joint Research Report of Public Works Research Instituteand the Japan Iron and Steel Federation (No. 347): Joint
research report on the improvement of durability of offshore structures-Research on corrosion-protection technologies for offshore steel structures in splash and tidal
zones, First working group (2003)
3) Joint Research Report of Public Works Research Instituteand the Japan Iron and Steel Federation (No. 347): Joint
research report on the improvement of durability of offshore structures-Research on corrosion-protection technologies for offshore steel structures in splash and tidal
zones, First working group-Research attainments in
30-year exposure tests (2016)
4) Document of the Japan Iron and Steel Federation: Analytical report on comparison surveys of test specimens
between exposure racks at Suruga Bay and Okinotorishima (2017)5) Research Group of the Japan Iron and Steel Federation
and Public Works Research Institute: Proceedings of“Materials and Environment” Conference, C-313 (2014)
6) Research Group of the Japan Iron and Steel Federation
and Public Works Research Institute: Proceedings of“Materials and Environment” Conference, B-304 (2018)11

Part 2

Comprehensive Report of Exposure Tests at Okinotorishima to Assess the Durability of Various Kinds of Construction Materials-Secular Change over 19 Years of Exposure■ Purpose■ Exposure Test Environments■ Exposure Test Methods■ Details of Test Specimens■ Survey Items and Items Subjected to Surveys■ Assessment of Exposure Test Results■ Conclusion

13

1. Purpose• Grasping the corrosion behavior of seawater-resistant

The exposure test to assess the durability of various kindsof construction materials started in July 1990 setting Okinotorishima as the test site under the guidance of the Public
Works Research Institute of the Ministry of Construction(current the Ministry of Land, Infrastructure, Transport andTourism). Okinotorishima is a coral island located at thesouthernmost tip of Japan, where not only temperature andhumidity are high but the marine environment is also very
severe. Thus, it is considered that valuable data unavailable
from artificially accelerated exposure tests can be obtained
from exposure tests at Okinotorishima.
The main aims of the exposure test are as in the following:• Grasping the effect of the marine environment at Okinotorishima on the corrosion of steel products by setting thecorrosion behavior of ordinary carbon steel (SS400
equivalents) as the parameter of assessing durability

stainless steel• Grasping the corrosion behavior of nonferrous metals(titanium, copper and aluminum alloy)• Confirmation of corrosion resistance of various kinds ofcoated/sprayed/lined/painted steel products (metallic
coating/spraying, organic lining, heavy-duty painting)
Table 1 shows the period and survey plan of the exposure test at Okinotorishima. As initially planned, detail surveys were conducted for the specimens in the 3rd year of
exposure and 5th year of exposure, and an appearance survey was conducted for the specimens in the 10th year of
exposure. In the 19th-year survey, all specimens that wereleft due to the closure of the exposure site in 2009 wererecovered, for which detail surveys were conducted.

2. Exposure Test Environments
Table 2 shows examples of the marine meteorological data

Table 1 Test Period and Survey
Year
Test period (y)89SurveyYear

Test period (y)SurveyNotes:○: Survey 1 (Recovery of 1 specimen/type, detailed survey of 1 specimen)△: Survey 2 (Recovery of 2 specimens/type, only appearance observation)◎: Survey 3 (Recovery of 5 specimens/type, detailed survey of 3 specimens)

Table 2 Oceanographic and Meteorological Data at Okinotorishima (July 15, 1990)
Time

Transmission Maximum Maximum Average
wave
wave
wave
time
heightperiod(hour/minute/ height
(m)
(s)
(m)
second)Averagewave
period
(s)

1/3
1/3
Wind
Wind
significant significant Tide level Hourly
precipitation direction velocity
wave height wave period (m)
(m)
(mm)
(m)
(s)

Tempe
rature
(ºC)

Solar
Water
Humidity temperature Atmosphere radiation
(%)
(mb)
(MJ)
(ºC)

Data No.: 1
No. of abnormality occurrence: 10
Data No.: 2
No. of abnormality occurrence: 8

Data No.: 3
No. of abnormality occurrence: 4
Data No.: 4
No. of abnormality occurrence: 3

Daily minimum value
Daily maximum value
Daily average value
Daily total value
Missing number

6 MHz zone

Data No.: 1
No. of abnormality occurrence: 5
Data No.: 2
No. of abnormality occurrence: 6148 MHz zone

Data No.: 3
No. of abnormality occurrence: 1
Data No.: 4
No. of abnormality occurrence: 1

12 MHz zone

16 MHz zone

Watch
item

at Okinotorishima. The annual average temperature is
27.2°C, the annual average seawater temperature 28°C andthe annual average humidity 73%, which show the temperature and humidity conditions higher than those at Japan’s
main islands. In addition, both sunlight radiation and waves
are high, and thus Okinotorishima seems to be exposed to avery severe corrosive environment.
The specimens were set on an exposure test rack
installed on a working platform and at a height ofabout 15 m above sea level, which falls under the offshore atmospheric zone in terms of corrosive environment classification. However, it is forecast that thefrequency of being splashed with tidal waves is notalways high for the rack due to its configuration. Further, the exposure rack was prepared on an observato-

ry base and the rack was installed on both sides of thewharf, and thus the specimen was to be exposed to the
corrosive environment of the submerged zone tothe-splash zone.

3. Exposure Test Methods
For the exposure method, a specimen exposure rack was
installed at the test site, on which various kinds of rectangular specimens were exposed to conduct the survey. The
exposure angle was set at 5° facing south.

4. Details of Test Specimens
Table 3 shows the kind and type of specimens subjected toTable 3 Kinds and Types of Exposure Test Specimens
SpecimenNo.

TypeSpecimen preparation company

Ordinary carbon steel (SS400)

Nippon Steel & Sumitomo Metal

Stainless steel (SUS304, 18Cr-8Ni)

Nippon Steel & Sumikin Stainless SteelStainless steel (SUS316L, 17Cr-12Ni-2.5Mo)

Nippon Steel & Sumitomo Metal

B-03

Stainless steel (SUS317L, 19Cr-13Ni-3.5Mo)

Nippon Steel & Sumikin Stainless Steel

B-04

Stainless steel (18Cr-13Ni-3Mo-0.15N)

JFE Steel

B-05

Stainless steel (20Cr-25Ni-5Mo-Ti)

Nippon Steel & Sumitomo Metal

B-06

Stainless steel (20Cr-17Ni-4.5Mo-N-L.C)

JFE Steel

Stainless steel (SUS312L, 20Cr-18Ni-6Mo-0.7Cu-0.2N)

Nippon Steel & Sumikin Stainless SteelStainless steel (SUS317J2, 25Cr-13Ni-0.9Mo-0.3N)

Nippon Steel & Sumikin Stainless Steel

B-09

Stainless steel (25Cr-22Ni-4.5Mo-0.2N)

JFE Steel

B-10

Stainless steel (22Cr-23Ni-5Mo-1.5Cu-0.2N)

Kobe SteelStainless steel (SUS329J4L, 25Cr-6Ni-3.5Mo-0.2N)

Nippon Steel & Sumitomo Metal

Stainless steel (SUS329J4L, 25Cr-7Ni-3.5Mo-0.5Cu-0.16N)

Kobe SteelStainless steel (SUS444, 19Cr-2Mo-Ti-Nb-Zr)

JFE Steel

Stainless steel (26Cr-4Mo)

JFE Steel

Titanium［JIS H4600 TP35H(KS50)］

Kobe Steel

Copper［C-1220］

Kobe Steel

A-01

Group
A

B-01
B-02

B-07
B-08

B

Kind

Ordinary
Ordinary
carbon steel carbon steel
Austenitic
type

Stainlesssteel

Duplex type

B-11
B-12

Ferritic type

B-13
B-14
C-01

Titanium

C-02

Nonferrous
Copper
metal

C

C-03

Aluminum alloy

Aluminum alloy［5083 (Al-4.5Mg)］

Kobe Steel

D-01

Metallic
coating/
spraying

Aluminized stainless steel plate

Nippon Steel & Sumikin Stainless Steel

Hot-dip galvanized plate

JFE SteelZinc-aluminum alloy-sprayed plate (Zn-13Al)

JFE Steel

Aluminum-sprayed plate

Nippon Steel & Sumitomo Metal

Polyethylene-lined plate

JFE Steel

Polyurethane-lined plate

JFE Steel

Ultra-high build epoxy resin-lined plate

Nippon Steel & Sumitomo Metal(Epoxy resin/polyurethane resin)-painted plate

Nippon Steel & Sumitomo Metal

D-09(Epoxy/fluororegin)-painted plate

Nippon Steel & Sumitomo Metal

D-10(Epoxy resin/acrylic silicon resin)-painted plate

Nippon Steel & Sumitomo Metal

D-02
D-03
D-04
D-05
D-06
D-07
D-08

D

Coated/sprayed/lined/
paintedplatesOrganic lining

Heavy-duty
painting

15

surveys, and Table 4 the dimensions of those specimens.
Tables 5.1~5.2 show the specifications for coating, spraying, lining and painting.
Table 4 Dimensions of Exposure Test Specimens
Specimen
No.

Type

Length (mm)Width (mm)Nominal*thickness (mm)Specific
gravity (g)A-01

Ordinary carbon steel (SS400)

210

75

30

7.87

B-01

Stainless steel (SUS304, 18Cr-8Ni)

〃

〃

9.0

7.93

B-02

Stainless steel (SUS316L, 17Cr-12Ni-2.5Mo)

〃

〃

4.0

7.98

B-03

Stainless steel (SUS317L, 19Cr-13Ni-3.5Mo)

〃

〃

9.0

7.98

B-04

Stainless steel (18Cr-13Ni-3Mo-0.15N)

〃

〃

9.0

7.97

B-05

Stainless steel (20Cr-25Ni-5Mo-Ti)

〃

〃

3.2

8.05

B-06

Stainless steel (20Cr-17Ni-4.5Mo-N-L.C)

〃

〃

1.5

8.03

B-07

Stainless steel (SUS312L, 20Cr-18Ni-6Mo-0.7Cu-0.2N)

〃

〃

9.0

8.03

B-08

Stainless steel (SUS317J2、25Cr-13Ni-0.9Mo-0.3N)

〃

〃

9.0

7.98

B-09

Stainless steel (25Cr-22Ni-4.5Mo-0.2N)

〃

〃

9.0

7.98

B-10

Stainless steel (22Cr-23Ni-5Mo-1.5Cu-0.2N)

〃

30

1.3

8.05

B-11

Stainless steel (SUS329J4L, 25Cr-6Ni-3.5Mo-0.2N)

〃

75

3.2

7.8

B-12

Stainless steel (SUS329J4L, 25Cr-7Ni-3.5Mo-0.5Cu-0.16N)

〃

52

3.0

7.8

B-13

Stainless steel (SUS444, 19Cr-2Mo-Ti-Nb-Zr)

〃

75

2.0

7.75

B-14

Stainless steel (26Cr-4Mo)

〃

〃

2.0

7.67

C-01

Titanium［JIS H4600 TP35H (KS50)］

〃

〃

5.0

4.54

C-02

Copper［C-1220］

〃

〃

6.0

8.96

C-03

Aluminum alloy［5083 (Al-4.5Mg)］

〃

〃

6.0

2.66

D-01

Aluminized stainless steel plate

〃

〃

1.2

D-02

Hot-dip galvanized plate

〃

〃

6.0

D-03

Zinc-aluminum alloy-sprayed plate (Zn-13Al)

〃

〃

6.0

D-04

Aluminum-sprayed plate

〃

〃

5.0

D-05

Polyethylene-lined plate

〃

〃

6.0

D-06

Polyurethane-lined plate

〃

〃

6.0

D-07

Ultra-high build epoxy resin-lined plate

〃

〃

9.0

D-08

(Epoxy resin/polyurethane resin)-painted plate

〃

〃

9.0

D-09

(Epoxy/fluororesin)-painted plate

〃

〃

9.0

D-10

(Epoxy resin/acrylic silicon resin)-painted plate

〃

〃

9.0

*The thickness of coated/sprayed/lined plates is expressed in terms of base plate thickness.

16

Table 5.1 Specifications for Coating, Spraying and Lining (1)Specimen No.

Type

Specifications for coating/spraying/lining

D-01

Aluminized stainlesssteel plate

1. Base metal: Ferritic-type stainless steel (19Cr-0.4Nb-0.4Cu)
2. Coating material: Hot-dip aluminum
3. Substrate treatment:―
4. Coating method: Immersion in molten aluminum
5. Film thickness: About 20 µm
6. Side surface/reverse side: Same as surface side

D-02

Hot-dip galvanized plate

1. Coating material: 100% Zn
2. Substrate treatment: H2SO4 pickling
3. Coating method: Immersion in molten zinc
Temperature 450℃; Time 5 min+3 min=8 min
4. Film thickness: About 85µm
5. Side surface/reverse side: Same as surface side

D-03

Zinc-aluminumalloy-sprayed plate

1. Spraying material: 87% Zn+13% Al (wire diameter φ3.1 mm)
2. Substrate treatment: ① Blasting: ISO 8501-1: 2007 Sa 2.5 or more
② Degreasing: Runner system
3. Spraying method: Gas wire thermal spraying
4. Film thickness: About 180 μm
5. Hole sealing: No sealing (water treatment by the use of ion exchange water)
6. Side surface/reverse side: Same as surface side

D-04

Aluminum-sprayed plate

1. Spraying material:100% Al (wire diameter φ3.1 mm)
2. Substrate treatment: Blasting
3. Spraying method: Gas wire thermal spraying
4. Film thickness: About 300 μm
5. Hole sealing: Epoxy resin paint (clear): 1 brush coating
6. Side surface/reverse side: Same as surface side

Table 5.2 Specifications for Coating, Spraying and Lining (2)Specimen No.

Type

Specifications for coating/spraying/lining

D-05

Polyethylene-lined plate

1. Lining material: ① Primer: Epoxy-type primer② Adhesive polyethylene③ High-density polyethylene (carbon black 2.5% contained)
2. Substrate treatment: Shot blasting
3. Lining method: Press pasting (pressure 2 kg/cm2)
4. Film thickness: About 1.5 mm
5. Side surface/reverse side: Tar epoxy coating (about 2 mm)

D-06

Polyurethane-lined plate

1. Lining material: ① Primer: Epoxy primer② Urethane elastomer
2. Substrate treatment: Shot blasting
3. Lining method: Hot air spray
4. Film thickness: About 3.5 mm
5. Side surface/reverse side: Tar-epoxy coating (about 2 mm)

D-07

Ultra-high build epoxy
resin-lined plate

D-08(Epoxy resin/polyurethane
resin)-painted plate

D-09(Epoxy/Fluororesin)-painted plate

D-10(Epoxy resin/acrylic
silicon resin)-painted plate

1. Lining material: ① Primer: Epoxy zinc-rich primer② Ultra-high build epoxy resin lining (1 layer)
2. Substrate treatment: Blasting
3. Lining method: Spray lining; Surface roller pressing 1.5 hours after coating
4. Film thickness: About 2.3 mm
5. Side surface/reverse side: Same as surface side
1. Painting material: ① Primer: Heavy-thick inorganic zinc-rich primer② Primer coating: Epoxy resin (mastic primer, 2 layers)③ Intermediate coating: Epoxy resin④ Top coating: Urethane resin
2. Substrate treatment: Blasting ISO 8501-1: 2007 Sa 2.5 or more
3. Painting method: Air spraying
4. Film thickness: About 500µm
5. Side surface: Tar epoxy painting (2 mm)
6. Reverse side: Same as surface side

1. Painting material: ① Primer: Heavy-thick inorganic zinc-rich primer② Primer coating: Epoxy resin (mastic primer, 2 layers)③ Intermediate coating: Epoxy resin④ Top coating: Fluororesin
2. Substrate treatment: Blasting ISO 8501-1: 2007 Sa 2.5 or more
3. Painting method: Air spraying
4. Film thickness: About 500µm
5. Side surface: Tar epoxy painting (2 mm)
6. Reverse side: Same as surface side

1. Painting material: ① Primer: Heavy-thick inorganic zinc-rich primer② Primer coating: Epoxy resin (mastic primer, 2 layers)③ Intermediate coating: Epoxy resin④ Top coating: Acrylic silicon resin
2. Substrate treatment: Blasting ISO 8501-1: 2007 Sa 2.5 or more
3. Painting method: Air spraying
4. Film thickness: About 500µm
5. Side surface: Tar-epoxy painting (about 2 mm)
6. Reverse side: Same as surface side17

5. Survey Items and Items Subjected
to Surveys
Tables 6.1~6.5 show the survey items/methods and items
subjected to surveys.
As for the specimens in the 19th year of exposure, 5specimens of respective types were recovered, and optional
three of the 5 specimens were subjected to durability
assessment. However, as for the polyethylene-lined plate(D-05), corrosion occurring from the edge and reverse sidedeveloped on the entire surface side of all 5 specimens tocause severe corrosion, for which an assessment was difficult to conduct, and thus the assessment was limited only tophotographing at the recovery stage. In addition, as for the
polyurethane-lined plate (D-06) and ultra-high build epoxy
resin-lined plate (D-07), severe corrosion from the edge
occurred each in two of the 5 specimens, and assessment
was conducted for the remaining 3 specimens.

Table 6.1 Survey Items/Methods and Items Subjected to Survey: Ordinary Carbon Steel (A-01)
Survey site

Survey item

Laboratory

Appearance photo

Survey method

Survey year
3rd year

5th year

○

○

○

○

○

○

○

○

○

○

○

○

○

○

○

○

○

○

Full view, before pickling
After pickling*

Appearance observation

Sketch (before pickling)Surface roughness

Surface roughness meter

Cl in rust

Chemical analysis of rustThickness loss

Micrometer

Pitting corrosion depth

Depth gauge

Weight loss

Precision balance*Pickling conditions: 20℃, 10% dilute hydrochloric acid+Hibiron ×Max. 30 min. (JISF method)○

10th year○

19th year
○
○

○

○

Table 6.2 Survey Items/Methods and Items Subjected to Survey: Stainless Steel (B-01〜B-14) and Nonferrous Metal (C-01〜C-03)
Survey site

Survey item

Laboratory

Appearance photo

Survey method

Survey year
3rd year

5th year

○

○

○

○

○

○

○

○

○

○

○

○

○

○

○

○

○

Full view, before and after water washing
After pickling*

Appearance observation

Sketch (after water washing)

Pitting corrosion depth

Optical microscope

Surface roughness

Surface roughness meter

Glossiness

Glossiness meter

Thickness loss

Micrometer

Weight loss

Precision balance○

10th year○

19th year
○
○

○

○
○

*Pickling condition (B-01~B-14, C-01): 90℃, 10% hydrogen citrate diammonium sol.×Max. 60 min*Pickling condition (C-03): 80℃, 20% chromic anhydride sol.×1 min*Pickling condition (C-02): 20℃, 15% dilute hydrochloric acid×3 min

Table 6.3 Survey Items/Methods and Items Subjected to Survey: Metallic-coated/sprayed Plates (D-01〜D-04)
Survey site
Laboratory

Survey item
Appearance photo
Appearance observation
PinholeFilm adhesive strength

Survey method

Survey year
3rd year

5th year

○

○

○

○

○

○

○

○

○

Full view, before and after water washing
After pickling*
Sketch (after water washing)Ferro-xylene test
Adhesion tester○

10th year○

19th year
○
○

○

○

Electromagnetic film thickness meter

○

○

○

Film cross-section
observation

Microscopic photographing

○

○

○

Film-under base steel
surface observation

Visual, photographing○○

Thickness loss

Micrometer

○

○

○

Weight loss

Precision balance

○

○

○

Film thickness loss

*Pickling condition (D-01, D-04): 90℃, 10% hydrogen citrate diammonium sol.×Max. 60 min*Pickling condition (D-02, D-03): 80℃, 20% chromic anhydride sol.×1 min

18○

Table 6.4 Survey Items/Methods and Items Subjected to Survey: Organic-lined Plates (D-05〜D-07)
Survey site

Laboratory

Survey item

Survey method

Appearance photo

Full view, before andafter water washingAppearance
observation*

Sketch (after water washing)

PinholePinhole tester

Film adhesivestrength

Adhesion tester,
peeling test

Film thickness loss

Electromagnetic film
thickness meterCl concentration

SEM analysis

Electric resistance

Guard ring method

Impedance

AC bridge method

Film-under base steel
surface observation

Visual, photographing

Survey year
3rd year

5th year

10th year

19th year

PencilFilm hardness**

BarcolDurometer

Weight loss

Precision balance

Glossiness

Glossiness meter

Color difference

Color difference meter*D-05: Only appearance observation**D-06: Measurement by the use of Durometer; D-07: Measurement of pencil hardness and Barcol hardness

Table 6.5 Survey Items/Methods and Items Subjected to Survey: Heavy-duty Painted Plates (D-08〜D-10)
Survey site

Laboratory

Survey item

Survey method

Appearance photo

Full view, before andafter water washingAppearance
observation

Sketch (after water washing)

PinholePinhole tester

Film adhesivestrength

Adhesion tester

Film thickness loss

Electromagnetic film
thickness meterCl concentration

EPMA analysis

Glossiness

Glossiness meter

Electric resistance

Guard ring method

Impedance

AC bridge method

Color difference

Color difference meter

Film-under base steel
surface observation

Visual, photographing

Film hardness
Weight loss

Survey year
3rd year

5th year

10th year

19th year

PencilBarcolPrecision balance196. Assessment of Exposure Test
Results
6.1 Observation Results for Appearance

kind and type of specimens based on the past threereports1)-3). The rearranged results are shown in Tables 7-8.
Specific appearance observation results by type of specimens are introduced below:

The observation results for appearance were rearranged by
Table 7 Observation Results for Appearance: Ordinary Carbon Steel, Austenitic/Duplex/Ferritic-type Stainless Steel
Kind
Ordinary
carbonsteel

Specimen Observation In 3rd and 5th years
No.
sectionof exposure
A-01

B-01

B-02

B-03

B-04

B-05
Austenitic-type
stainless
steel

B-06

B-07

B-08

B-09

B-10

B-11
Duplex-type
stainless
steel

B-12

B-13
Ferritic-type
stainless
steel

20

B-14

In 10th year of exposure

In 19th year of exposure

CenterSeveral-millimeterrough rust

Entire development of rustOccurrence of sizable unevenness,
peeling of layered rustAroundbolt hole—

Development of layered rust

Progress of corrosion,
sizable unevenness due to crevice corrosion

Center

Nearly no
development of rust

Entirely yellow
Development of island-state rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt hole—

Development of a lot of rust

Entire development of rust and corrosion pit

Center

Nearly no
development of rustLight brown on surface side,
light yellow on reverse side
Development of spotted rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt hole—

Development of rust on reverse side
Entire development of corrosion pit

Entire development of rust and corrosion pit

Center

Nearly no
development of rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt holeSurface side: Yellow (partly purple), development of spotted rustReverse side: Remaining of metallic glossiness,but development of island-state rust—

Entire development of rust and corrosion pit

Entire development of rust and corrosion pit

Center

Nearly no
development of rustSurface side: Yellow (partly purple)
Reverse side: Remaining of metallic glossiness,but development of island-state rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt hole—

Entire development of corrosion pit

Entire development of rust and corrosion pit

Center

Nearly no
development of rustSurface side: Dark brown, development of spotted rustReverse side: Light yellow, development of spotted rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt hole—

Entire development of corrosion pit
Development of dark brown rust on reverse side

Entire development of rust and corrosion pit

Center

Nearly no
development of rustSurface side: Dark brown (partly purple),development of spotted rustReverse side: Light yellow at edge, development of spotted rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt hole—

Entire development of rust and corrosion pit

Entire development of rust and corrosion pit

Center

Nearly no
development of rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt holeSurface side: Yellow (partly purple), development of spotted rustReverse side: Remaining of metallic glossiness,but development of spotted rust—Reverse side: Development of rust

Entire development of rust and corrosion pit

Center

Nearly no
development of rust

Entirely light yellow (light yellowish green,development of island-state rustAroundbolt holeSurface side: Yellow, development of spotted rustReverse side: Development of light brownspotted rust—

Entire development of corrosion pit

Entire development of rust and corrosion pit

Center

Nearly no
development of rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt holeSurface side: Yellow, development of spotted rustReverse side: Remaining of metallic glossiness,but development of spotted rust—

Entire development of corrosion pit
Development of purple rust on surface side

Center

Nearly no
development of rustAroundbolt holeSurface side: Light yellow,
development of purple spotted rustReverse side: Light yellow—

Entire development of corrosion pit

Entire development of rust and corrosion pit

Center

Nearly no
development of rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt holeSurface side: Dark brown, developmentof purple spotted rustReverse side: Development of spotted rust—

Entire development of rust and corrosion pit

Entire development of rust and corrosion pit

Center

Nearly no
development of rust

Entire development of rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt hole—

Entire development of corrosion pit

Entire development of rust and corrosion pit

Center

Nearly no
development of rust

Entire development of rust and pitting corrosion

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt hole—

Entire development of corrosion pit
Reverse side: Development of rust

Entire development of rust and corrosion pit

Center

Nearly no
development of rust

Entirely light yellow (light yellowish green),development of island-state rustAroundbolt holeSurface side: Light yellow, development of spotted rustReverse side: Remaining of metallic glossiness,but development of spotted rust—

Entire development of corrosion pit
Reverse side: Development of rust

Entire development of rust and corrosion pit

Entire development of rust and corrosion pit ,but less development of rust compared toother austenitic types
Entirely light yellow (light yellowish green),development of island-state rust

Table 8 Observation Results for Appearance: Titanium, Copper, Aluminum Alloy, Metallic-coated/sprayed,
Organic-lined and Heavy-duty Painted Plates
Kind
Titanium

CopperAluminumalloy

Specimen ObservationNo.
section
C-01

C-02

C-03

D-01

D-02
Metallic
coating/
spraying
D-03

D-04

D-05

Organic
lining

D-06

D-07

D-08

Heavyduty
painting

D-09

D-10

Center

In 3rd and 5th yearsof exposure

Only slight change to yellow or
purple, but no development ofrust, sound condition

Aroundbolt hole —CenterEntire formation ofbronze-black dense film
(verdigris, oxidized copper)

Aroundbolt hole —CenterFormation of spottedwhite-black rustAroundbolt hole —CenterAroundbolt hole
CenterDevelopment only of asmall amount of white rustAroundbolt hole —Center

In 19th year of exposure
Entirely gold (partly blue)

Surface side: Light yellow

No observation of notable discolorationand corrosion

Entirely verdigris color, development of floating rust(partly peeled)

Entirely verdigris color(particularly on reverse side)
Entire occurrence of pitting corrosion

Surface side: Black

Entire development of corrosion pit

Surface side: Light brown (rust stain), development of black rustReverse side: Covered entirely with white rust, partial
development of black rustCovered entirely with white rust

Entire development of white rust

Entire development of rust

Entire scatter of white rustSurface side: Development of black rust, observation of
Development of red rust on several red rustCovered entirely with white rusta site in 5th year of exposure Reverse side: Development of white rust (partly black rust)Covered entirely with white rustSurface side: Development of many white rustObservation of partial peeling of—Reverse side: Development of red rustaluminum coating
Surface side: Covered with white rust, development
Entire development
Covered entirely with white rust,of many red rustof white rust
exposure of many red rustReverse side: Covered with white rustAroundbolt hole —Center

In 10th year of exposure
Surface side: Purple (partly light yellow)
Reverse side: Gold
Partly: Confirmation of rust stain

Development only of a small amountof white rust Development of several
spotted red rust in 5th year of exposure

Aroundbolt hole —Reverse side: Development of many red rust—Surface side: Development of many white rustCovered entirely with white rust,
Edge: Development of red rustpartial observation of red rustReverse side: Development of island-state light white rustReverse side: Development of a lot of white rust to
partially form layered rustCovered entirely with white rust,partial observation of red rustCovered entirely with white rust, partial observationof rust stain (red rust)Covered entirely with white rust,partial observation of red rust—Covered entirely with white rust,partial observation of red rustCenterPeeling of lining from edge,
development of red rust frombase steel

No observation of lining film deterioration,
but peeling of lining film from steel product

Progress of corrosion from sealingmaterial-peeled section to lead to nearlyno remaining of steel productEndsealing—

Complete disappearance of end sealing material

Disappearance of end sealing material
similarly in 10th year of exposure

CenterDisappearance of glossiness, Disappearance of glossiness, occurrence ofbut nearly no change
ultraviolet ray-induced deteriorationEnd
sealing—

Observation of entire occurrence of chalking

Endsealing——

Remaining of end sealing material,no occurrence of corrosion in steel productCenterOnly discoloration to yellow,
and nearly no change

Surface side: Nearly no remaining of top coating film
Reverse side: Remaining of top coating film andglossiness as wellSurface side: Disappearance of
top/intermediate coating film
Reverse side: Remaining of painting filmEndsealing—

Development of red rust from peeled section

Remaining of end sealing material,no occurrence of corrosion in steel productCenterOnly discoloration to yellow,
and nearly no change

Entire chalking of top coating film
Partial peeling on surface side

Surface side: Disappearance of
top/intermediate coating film
Reverse side: Remaining of painting filmEndsealing——

Remaining of end sealing material,no occurrence of corrosion in steel productCenterEndsealing
Center

Progress of corrosion from lining film-peeled
section in 2 of 5 specimens

Disappearance of end sealing material in 2
of 5 specimens, but remaining of end
sealing material in 3 other specimens
Observation of discoloration and peeling
Disappearance of glossiness, Observation of discoloration and development of red of lining film in 2 of 5 specimens,
but nearly no change
rust at partial edge due to lining film crack
progress of corrosion from peeled section
Peeling of end sealing material in 2 of 5 specimens,
remaining of end sealing material in 3 other——specimens, but partial development of rustSurface side: Disappearance of top/intermediate coating film
Only discoloration to yellow, Entire chalking of top coating film
Reverse side: Observation of chalking,and nearly no change
Observation of top coating film peeling on surface side
but remaining of painting film

21

6.1.1 Ordinary Carbon Steel
Results in 3rd year and 5th year of exposure• Severe corrosion occurred, and rough rust in several millimeters developed in the 3rd year of exposure.
Results in 10th year of exposure• Rust developed on the entire surface side, and layered(lamellar) rust developed around the bolt hole.
• Layered rust developed on the entire reverse side.
• Layered rust (about 9~10 mm) developed at the side surface of the reverse surface to lead a condition in whichrust peeled off.
Results in 19th year of exposure• Severe corrosion occurred on both the entire and reverse
sides, and in particular the reverse side was dented due tolayered rust (about 7 mm). The area around the bolt hole
was further dented due to crevice corrosion.
• Considerably uneven rust developed, and layered rust
peeled off, which led to a rust appearance rating number*of 1.
*Note: Definition of rust appearance rating number: In theappearance rating numbers specified in the rust development assessment classification of JSSC Technical Report(No. 73), a rating number of 1 means that uneven rustdevelops and layered rust peels off or traces of the occurrence of layered rust remains.
6.1.2 Stainless Steel
Results in 3rd year and 5th year of exposure-Austenitic-type stainless steel• Needless to say, rust development was considerably lower
than that in ordinary carbon steel, and the rust development level was only a discoloration to yellow or the development of spotted rust at worst.
• Rust development was slow during the exposure period
from 3 years to 5 years.
• Differences in rust development among the steel types wasobserved, and rust development was less in types
B-05~B-09. In particular, types B-07 and B-09 showed
high corrosion resistance.
• It was types B-07 and B-09 that showed less crevice corrosion. Conversely, it was type B-01 that showed considerable rust development and crevice corrosion.
• It was considered from these observation results that rustdevelopment nearly coincided with the occurrence of
crevice corrosion, and if this coincidence is right, as thecontainment of Cr, Ni and Mo increases, corrosion resistance seems to become higher. However, it seemed thatthe specimen configuration, surface and other conditionsin addition to the chemical composition affect corrosion
resistance (for example, in spite of its thin plate thickness
and appropriate chemical composition, type B-10 showedcomparatively considerable rust development). As forcrevice corrosion as well, because insulation washer fastening conditions were not uniform for respective specimens, it cannot be said whether or not corrosion resistancewas correctly assessed, but it can be said that these observation results serve as a useful reference.
-Duplex-type stainless steel• Needless to say, rust development was considerably lower
than that in ordinary carbon steel, and the rust development level was only a discoloration to yellow or the development of spotted rust at worst.
22• Rust development was slow during the exposure period
from 3 years to 5 years.

• Differences in rust development among the types wasobserved, and rust development was less in type B-11.

• It was type B-11 that showed less crevice corrosion.
• It was considered from these observation results that rustdevelopment nearly coincided with the occurrence of
crevice corrosion, and if this coincidence is right, as thecontainment of Cr, Ni and Mo increases, corrosion resistance seems to become higher. However, it seemed thatthe specimen configuration, surface and other conditionsin addition to the chemical composition affect corrosion
resistance. As for crevice corrosion as well, because insulation washer fastening conditions were not uniform forrespective specimens, it cannot be said whether or not corrosion resistance was correctly assessed, but it can be said
that these observation results serve as a useful reference.
-Ferritic-type stainless steel• Needless to say, rust development was considerably lower
than that in ordinary carbon steel, and the rust development level was only a discoloration to yellow or the development of spotted rust at worst.
• Rust development was slow during the exposure period
from 3 years to 5 years.
• Differences in rust development among the types wasobserved, and rust development was less in type B-14.
• Conversely, it was type B-13 that showed considerable rustdevelopment and crevice corrosion.
• It was considered from these observation results that rustdevelopment nearly coincided with the occurrence of
crevice corrosion, and if this coincidence is right, as thecontainment of Cr, Ni and Mo increases, corrosion resistance seems to become higher. However, it seemed thatthe specimen configuration, surface and other conditionsin addition to the chemical composition affect corrosion
resistance. As for crevice corrosion as well, because insulation washer fastening conditions were not uniform forrespective specimens, it cannot be said whether or not corrosion resistance was correctly assessed, but it can be said
that these observation results serve as a useful reference.
Results in 10th year of exposure-Austenitic-type stainless steel♦ B-01 (SUS304, 18Cr-8Ni)• Both the entire surface and reverse sides were yellow, andit was observed that island-state rust developed there. It
was further observed that rust developed extensively at theedge and around the bolt hole.
♦ B-02 (SUS316L, 17Cr-12Ni-2.5Mo)• The entire surface side was light brown, and it wasobserved that rust (spotted) developed at the center. It was
further observed that corrosion pit grew around the bolt
hole.
• The entire reverse side was light yellow, and it wasobserved that rust (spotted) developed there. It was further
observed that rust developed and corrosion pit grewaround the bolt hole.
♦ B-03 (SUS317L, 19Cr-13Ni-3.5Mo)• The entire surface side was yellow (partly purple), and rust(spotted) developed there.
• It was observed that, while metallic glossiness partly
remained on the reverse side, island-state rust developed
at the center.

• It was observed that rust developed and corrosion pit grewaround the bolt hole on both the surface and reverse sides.
♦ B-04 (18Cr-13Ni-3Mo-0.15N)• The surface side was yellow (partly purple). It was further
observed that corrosion pit grew around the bolt hole.
• It was observed that, while metallic glossiness remainedon the entire reverse side, island-state rust was scattered at
the center. It was further observed that a lot of corrosion
pits grew around the bolt hole.
♦ B-05 (20Cr-25Ni-5Mo-Ti)• The entire surface side was dark brown, and it wasobserved that rust (spotted) partly developed there. It was
further observed that corrosion pit grew around the bolt
hole.
• The entire reverse side was light yellow. It was observedthat rust (spotted) partly developed there. Further darkbrown rust developed around the bolt hole.
♦ B-06 (20Cr-17Ni-4.5Mo-N-L. C)• Rust (spotted) developed in some places. The entire surface side was dark brown, but the peripheral section where
rust developed was purple. It was observed that rust developed, and corrosion pit grew around the bolt hole.
• The edge on the reverse side was light yellow. It wasobserved that several rust (spotted) developed there.
♦ B-07 (SUS312L, 20Cr-18Ni-6Mo-0.7Cu-0.2N)• The entire surface side was yellow (close to gold), and rust(spotted) was scattered. The peripheral section where rustdeveloped was purple.
• It was observed that, while metallic glossiness remainedon the entire reverse side, rust (spotted) was scattered
there. It was further observed that rust developed aroundthe bolt hole.
♦ B-08 (SUS317J2, 25Cr-13Ni-0.9Mo-0.3N)• The entire surface side was yellow, and rust (spotted)
developed in some places.
• Rust (spotted, light brown) developed on the entire reverse
side.
• It was observed that a lot of corrosion pits grew around thebolt hole on the surface and reverse sides.
♦ B-09 (25Cr-22Ni-4.5Mo-0.2N)• The entire surface side was yellow (close to gold), and it
was observed that a little rust (spotted) developed there. It
was further observed that rust (spotted, purple) developed
and corrosion pits grew around the bolt hole.
• It was observed that, while metallic glossiness remainedon the entire reverse side, rust (spotted) was scattered. It
was further observed that corrosion pit grew around thebolt hole.
♦ B-10 (22Cr-23Ni-5Mo-1.5Cu-0.2N)• The entire surface side was light yellow (close to gold). It
was observed that spotted rust (purple) extensively developed.
• The entire reverse side was light yellow.
• It was observed that corrosion pit grew on the surface andreverse sides.
-Duplex-type stainless steel♦ B-11 (SUS329J4L, 25Cr-6Ni-3.5Mo-0.2N)• The entire surface side was dark brown. Rust (spotted)
was scattered on the entire surface side. Further a lot ofrust developed around the bolt hole and some corrosion
pits grew.
• Spotted rust developed on the entire reverse side. It was

further observed that corrosion pit grew around the bolthole.
♦ B-12 (SUS329J4L, 25Cr-7Ni-3.5Mo-0.5Cu-0.16N)• Rust developed on the entire surface side. It was observedthat corrosion pit grew around the bolt hole.
• It was observed that rust developed on the entire reverse
side. It was further observed that corrosion pit grewaround the bolt hole.
-Ferritic-type stainless steel♦ B-13 (SUS444, 19Cr-2Mo-Ti-Nb-Zr)• Rust developed and pitting corrosion occurred on theentire surface side. It was further observed that corrosion
pit grew around the bolt hole.
• Rust (island-state) developed and pitting corrosion
occurred on the entire reverse side. Layered rust developed around the bolt hole and it was observed that a lot of
corrosion pits grew.
♦ B-14 (26Cr-4Mo)• The entire surface side was light yellow, and rust (spotted)
developed in the center. It was further observed that corrosion pit grew around the bolt hole.
• It was observed that, while metallic glossiness remainedon the entire reverse side, rust (spotted) developed in thecenter. It was further observed that rust developed, andthat corrosion pit grew around the bolt hole.
Results in 19th year of exposure-Austenitic-type stainless steel• It was observed that the entire surface and reverse sides
were light yellow (yellowish green), and that island-staterust developed. Further crevice corrosion occurred andcorrosion pit grew around the bolt hole. However, thedevelopment of crevice corrosion was comparatively lessfor type B-09 (25Cr-22Ni-4.5Mo-0.2N).
• In terms of ranking in the rust development rate or rating
number (RN)*, type B-01 (SUS304, 18Cr-8Ni) indicateda high corrosion development rate of about RN1, andtypes B-07 (20Cr-18Ni-6Mo-0.7Cu-0.2N) and B-09
(25Cr-22Ni-4.5Mo-0.2N) indicated a comparatively low
corrosion development rate of about RN3. For other types,
the rate was forecast to be about RN2, an intermediate rate
between B-01 and B-07 to B-09.
*Note: In the Japanese Industrial Standards (JIS 0595), therust development rate is classified into 10 levels or 10
rating numbers (RN0~9), where RN0 indicates the fulldevelopment of rust, and RN9 indicates almost no development of rust.
-Duplex-type stainless steel• The entire surface and reverse sides were light yellow (yellowish green), and it was observed that island-state rustdeveloped. Further crevice corrosion and corrosion pit
grew around the bolt hole.
• In terms of RN, type B-12 (SUS329J4L, 25Cr-7Ni-3.5Mo-0.5Cu-0.16N) indicated a high corrosion development
rate of about RN1, and the rate of type B-11 (SUS329J4L,
25Cr-6Ni-3.5Mo-0.2N) was forecast to be about RN2.
-Ferritic-type stainless steel• The entire surface and reverse sides were light yellow (yellow-green), and it was observed that island-state rustdeveloped. Further, crevice corrosion occurred and corrosion pit grew around the bolt hole.
• In terms of RN, type B-13 (SUS444, 19Cr-2Mo-Ti-Nb-Zr)
indicated a high corrosion development rate of about
23

RN1, and the rate of type B-14 (26Cr-4Mo) was forecast
to be about RN3, a comparatively low rate.
6.1.3 Nonferrous Metal
Results in 3rd year and 5th year of exposure-Titanium• Even after a lapse of 5 years of exposure, it showed only
discoloration to slightly yellow or purple, and further not
only rust did not develop but crevice corrosion did notoccur. Titanium was thus assessed as a very high-performance material.
-Copper• A dense bronze-black film (verdigris, oxidized copper)
was formed on the entire surface and reverse sides. It is
commonly said that this film protects the copper from corrosion.
-Aluminum alloy• Spotted white-black rust developed.
Results in 10th year of exposure-Titanium• The entire surface side was purple. It was observed that
there were sections dotted with yellow color. It was further
observed that rust stains developed partly in the surface
side. The section around the bolt hole was light yellow(close to gold).
• The entire reverse side was gold. It was observed that ruststain partly developed.
-Copper• The entire surface side was bronze. Floating rust developed at the edge and in the center, and part of the rust
peeled off. The section around the bolt hole was black.
• The entire reverse side was bronze, as with the surface
side. A lot of floating rust developed in the center, and it
was further observed these rust peeled off.
-Aluminum alloy• The entire surface side was light brown (rust stain developed), and it was further observed that spotted black rustdeveloped. It was also observed that white rust developedaround the bolt hole.
• The reverse side was covered entirely with white rust,
where black rust also developed. It was observed thatwhite rust developed around the bolt hole.
Results in 19th year of exposure-Titanium• The entire surface and reverse sides were gold (partlyblue) and after pickling caused partial discoloration due tooxidized film. It was observed that notable discoloration
was not caused around the bolt hole, and that crevice corrosion did not occur.
-Copper• Both the surface and reverse sides (particularly the reverseside) were covered entirely with bronze. After pickling,
the bronze was removed, but discoloration was caused dueto oxidized film. Pitting corrosion occurred extensively
and corrosion pit grew around the bolt hole.
-Aluminum alloy• Both the entire surface and reverse sides were covered
entirely with white rust. Crevice corrosion occurred
around the bolt hole.
6.1.4 Metallic-coated/sprayed, Organic-lined andHeavy-duty Painted Plates
24

Results in 3rd year and 5th year of exposure-Metallic-coated/sprayed plates• Spotted white rust developed in the aluminized stainlesssteel plate (D-01), and in the 3rd year of exposure whiterust developed entirely in the hot-dip galvanized plate(D-02).
• In the 5th year of exposure, spotted rust (red rust) developed at a certain section of D-01. The development ofwhite rust was less in the zinc-aluminum alloy-sprayed
plate (D-03) and aluminum-sprayed plate (D-04), but inthe 5th year of exposure, a little spotted red rust developedin D-04. In the zinc-aluminum alloy-sprayed plate, thesacrificial corrosion-protection performance of zinc mainly works, which led to the development mainly of whiterust (zinc-induced rust), but in the aluminum-sprayed
plate, there are cases in which the sacrificial corrosion-protection performance becomes difficult to work
due to the oxidized film on the aluminum surface, andthus it is considered that the base steel corroded and as aresult the red rust developed.
-Organic-lined plates• As for the polyethylene-lined plate (D-05), in the 3rd yearof exposure lined film peeled off from the edge and redrust intensely developed from the base metal, and after alapse of 5 years of exposure peeling off and red rust development greatly progressed.
• As for the ultra-high build epoxy resin-lined plate (D-07),in the 3rd year of exposure, only metallic glossiness was
lost, but no change was found.
-Heavy-duty painted plates• As for the epoxy resin/polyurethane resin-painted plate(D-08), epoxy/fluororesin-painted plate (D-09) and epoxy
resin/acrylic silicon resin-painted plate (D-10), even after
5 years of exposure, only discoloration to yellow occurred,
but no degradation was observed.
Results in 10th year of exposure-Metallic-coated/sprayed plates♦ Aluminized stainless steel plate• Black rust developed on the entire surface side, and it wasobserved that a little red rust (spotted) developed there.
Further, a lot of white rust developed around the bolt hole.
• White rust (partly black rust) developed on the entire
reverse side. Further, red rust (spotted) developed in thecenter and around the bolt hole.
♦ Hot-dip galvanized plate• The surface side was covered entirely with while rust,
where a lot of red rust (spotted) also developed.
• The reverse side was covered entirely with white rust. It
was observed that a lot of red rust (spotted) developedaround the bolt hole.
♦ Zinc-aluminum alloy-sprayed plate• A lot of white rust (spotted) developed on the entire surface side. It was observed that red rust (spotted) developedon the edge.
• Island-state thin white rust developed at the center ofreverse side. Further a lot of white rust developed aroundthe bolt hole and on the edge, part of which formed layered rust.
♦ Aluminum-sprayed plate• The surface side was covered entirely with white rust. It
was further observed that a few rust stains (red-rust color)developed.

• The reverse side was covered entirely with white rust. It

was further observed that rust stains (red rust color) developed at a certain section.
-Organic-lined plates♦ Polyethylene-lined plate• As for the surface side, it was observed that polyethylene
lining did not cause deterioration, but the lining peeled offfrom the base steel plate. Edge sealing material (tar epoxyfilm) fully disappeared.
• As for the reverse side, sealing material (tar epoxy film)
disappeared, and it was observed that base steel plate
caused corrosion. Most of the base steel plate did not
remain due to corrosion.
♦ Polyurethane-lined plate• Glossiness on the surface side disappeared, where ultraviolet ray-induced deterioration occurred.
• It was observed that chalking occurred entirely in the sealing material (tar epoxy film) on the reverse side.
♦ Ultra-high build epoxy resin-lined plate• It was observed that discoloration occurred on the entire
surface side. It was further observed that red rust due tolined film cracking developed partially on the edge.
• It was observed that discoloration occurred on the entire
reverse side. It was further observed that rust stain developed on the edge.
-Heavy-duty painted plates♦ Epoxy resin/polyurethane resin-painted plate• Chalking occurred in the top coating film (urethane film)of the surfaced side. It was observed that top coating film
partly peeled off.
• Chalking occurred in the top coating film (urethane film)of the reverse side.
♦ Epoxy/fluororesin-painted plate• Top coating film (fluororesin) on the surface side nearly
did not remain, and intermediate and primer coating films
were exposed. Red rust developed from the edge sealingmaterial-peeled section.
• Only part of the sealing material peeled off on the reverse
side, and not only top coating film (fluororesin) but glossiness remained.
♦ Epoxy resin/acrylic silicon resin-painted plate• Chalking occurred in the top coating film (acrylic siliconfilm) of the surfaced side. It was observed that part of thefilm peeled off. Intermediate and primer coating films
were exposed.
• The top coating film (acrylic silicon film) on the reverse
side remained, but chalking occurred there.
Results in 19th year of exposure-Metallic-coated/sprayed plates♦ Aluminized stainless steel plate• The surface and reverse sides were covered entirely withwhite rust, and in particular white rust developed considerably around the bolt hole. It was further observed that thealuminized coating peeled off partly around the bolt hole.
♦ Hot-dip galvanized plate• The surface and reverse sides were covered entirely withwhite rust, and a lot of red rust (spotted) was exposed.
• In terms of “coating deterioration assessment standards,”
the hot-dip galvanized plate was rated as V (the level inwhich coating film is consumed and deterioration reaches
the base metal). After pickling, the white rust disappeared
and further hot-dip coating itself considerably disap-

peared, and as a result rust developed into steel products.
♦ Zinc-aluminum alloy-sprayed plate• The surface and reverse sides were covered entirely withwhite rust, and in particular white rust developed considerably around the bolt hole. It was observed that red rust(spotted) partially developed.
• In terms of “spraying deterioration assessment standards,”
the zinc-aluminum alloy-sprayed plate was rated as II (thelevel in which white rust develops and red rust is observed
to develop on the edge). After pickling, white rust disappeared.
♦ Aluminum-sprayed plate• The surface and reverse sides were covered entirely withwhite rust, and in particular white rust developed considerably around the bolt hole. It was observed that red rust(spotted) partially developed.
• In terms of “spraying deterioration assessment standards,”
the aluminum-sprayed plate was rated as II (the level inwhich white rust develops and red rust is observed todevelop on the edge).
-Organic-lined plates♦ Polyethylene-lined plate• As for all 5 specimens recovered, the sealing material (tarepoxy) peeled off, and it was forecast that the corrosion ofsteel products progressed intensively from this peeled-off
section, and as a result most of the steel product did not
remain.
• It was confirmed that sealing material peeled off in the 5thyear of exposure, and the polyethylene-lined plate was incondition in which most steel product did not remain in
the 19th year of exposure as well as in the 10th year of
exposure.
♦ Polyurethane-lined plate• As for two of the 5 specimens recovered, corrosion intensively progressed from the tar-epoxy sealing material-peeled section as with the above-mentioned polyethylene-lined plate, and as a result most of steel product did
not remain.
• As for remaining 3 specimens, the sealing material
remained, and, while lining film glossiness was lowered,corrosion of steel product did not occur.
♦ Ultra-high build epoxy resin-lined plate• As for two of the 5 specimens recovered, the ultra-highbuild epoxy sealing material partly peeled off, and corrosion of steel product progressed considerably.
• As for remaining 3 specimens, while the sealing material
remained, rust developed partly on the edge.
• The hue of the coating film caused discoloration from grey
to white. This condition was the same as that in the 10thyear of exposure.
-Heavy-duty painted plates♦ Epoxy resin/polyurethane resin-painted plate• The tar-epoxy sealing material at the edge remained, andcorrosion of steel product did not occur. The hue of thepainting film of the top coating (urethane resin paint:
white) and intermediate coating (epoxy resin paint: white)on the surface side, excluding the section around the bolthole, nearly disappeared and the primer coating was
exposed. (In the 10th year of exposure, the intermediatecoating on the surface side mostly remained.)• While it was observed that chalking occurred on thereverse side, the painting film remained.
25♦ Epoxy/fluororesin-painted plate• The tar-epoxy sealing material at the edge remained, andcorrosion of steel product did not occur. The hue of thepainting film of the top coating (fluororesin paint: white)
and intermediate coating (epoxy resin paint: white) on thesurface side, excluding the section around the bolt hole,nearly disappeared and the primer coating was exposed.
(In the 10th year of exposure, the intermediate coating on
the surface side disappeared only at the edge.)• The painting film on the reverse side remained.
♦ Epoxy resin/acrylic silicon resin-painted plate• The tar-epoxy sealing material at the edge remained, andcorrosion of steel product did not occur.
• The hue of the painting film of the top coating (acrylic
silicon paint: white) and intermediate coating (epoxy
resin paint: white) on the surface side, excluding the section around the bolt hole, considerably disappeared andthe primer coating was exposed by about 50%. The painting film on the reverse side remained. (In the 10th year of
exposure, intermediate coating on the surface side disappeared only at the edge.)

6.2 Calculation Results for Corrosion
Amount, Mass Loss and Corrosion Rate
As for respective specimens subjected to pickling, the following items were calculated: initial weight, weight after
pickling, corrosion amount of total surface area, mass loss
Fig. 1.1 Secular Changes of Mass loss:
Ordinary Carbon Steeland corrosion rate. Table 9 and Figs. 1.1~1.2 show the calculation results.
The mass loss means the corrosion amount on one sideof the specimen. In the context of distinguishing the plate
thickness loss that covers both the surface and reverse sides
from the mass loss, it was decided to properly use the massloss or the plate thickness loss.
The data shown in Table 9 and Figs. 1.1~1.2 wereobtained by rearranging the calculation results for corrosion
amount, mass loss and corrosion rate based on the pastreports1),3).
6.2.1 Ordinary Carbon Steel
Results in 3rd year and 5th year of exposure• The annual corrosion rate was 0.097 mm/y (3rdyear)~0.087 mm/y (5th year), which meant a total massloss of about 0.435 mm (one side) after 5 years of exposure. This mass loss coincided nearly with that found in
two reports of the results of atmospheric exposure tests atcoastal areas (Handbook on Corrosion-protection Technologies or Data on Corrosion Protection of Steel Products of the Japan Iron and Steel Federation).
Results in 19th year of exposure• The corrosion rate in the 5th year of exposure was 0.087
mm/y and that up to the 19th year of exposure was 0.182
mm/y, which meant that in terms of calculation, the corrosion rate in the 5th year of exposure increased to about
twice that in the 19th year of exposure.
Fig. 1.2 Secular Changes of Mass loss:
Copper, Aluminized Stainless Steel Plate,
Hot-dip Galvanized Plate and
Zn-Al Alloy-sprayed Plate
Copper (C-02)

Ordinary carbon steel (A-01)

Aluminized stainless steel plate (D-01)
Hot-dip galvanized plate (D-02)

Mass loss (mm)

Mass loss (mm)Zn-Al alloy-sprayed plate (D-03)

Exposure period (y)26Exposure period (y)Table 9 Calculation Results for Corrosion Amount, Mass Loss and Corrosion Rate
In 3rd year of exposure

Kind

Specimen
No

Corrosionamount(g/cm2)Mass loss(mm)

Corrosion
rate(mm/y)-

In 5th year of exposure

Corrosionamount(g/cm2)Mass loss(mm)

Corrosion
rate(mm/y)

-

-

-

-

-

In 19th year of exposure

Corrosionamount(g/cm2)Mass loss(mm)

Corrosion
rate(mm/y)

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Ordinary
carbon steel

Austenitic-type
stainless steel

Duplex-type
stainless steel

Ferritic-type
stainless steel

Titanium
CopperAluminum alloy

Metallic-coated/
sprayed plates*Figures in parenthesis: The value was extremely small, and thus the reference values were shown.

27

6.2.3 Nonferrous Metal
Results in 3rd year and 5th year of exposure• The corrosion amount and crevice corrosion (fromappearance observation results) of titanium (C-1) were
small.
• The corrosion amount of copper (C-02) was far higher
than that of stainless steel.
• The weight of aluminum alloy (C-03) increased from its
initial weight.
Results in 19th year of exposure• Copper showed a comparatively high corrosion level, andcorrosion of titanium and aluminum alloy did not progress in terms of corrosion amount.
6.2.4 Metallic-coated/sprayed Plates
Results in 3rd year and 5th year of exposure• The corrosion amount (g/m2) of hot-dip galvanized plate(D-02) was far larger than that of other plates. Further, thecorrosion amount of zinc-aluminum alloy-sprayed plate(D-03) was also large.
• The corrosion amount of aluminized stainless steel plate(D-01) was comparatively small. The aluminum-sprayed
plate (D-04) showed no change in the corrosion amount.
Results in 19th year of exposure• As with the results in the 3rd year and the 5th year of
exposure, the corrosion amount of hot-dip galvanizedplate (D-02) was far larger than that of other plates. Furt h e r, t h e c o r r o s i o n a m o u n t o f z i n c - a l u m i n u malloy-sprayed plate (D-03) was also large.
• Aluminized stainless steel plate (D-01) and aluminum-sprayed plate (D-04) showed no change in corrosion
amount.

6.3 Measurement Results for Plate
Thickness
The plate thickness loss was found from both the initial
thickness and the thickness after pickling. The measurement of plate thickness loss was conducted at the position
identical to that used to measure the initial thickness (positions with identical distance) employing a both-side spherical micrometer. Table 10 and Fig. 2 show the measurement
results.
The data shown in Table 10 and Fig. 2 were obtained byrearranging the measurement results for plate thickness
based on the past reports1),3).
6.3.1 Ordinary Carbon Steel
Results in 3rd year and 5th year of exposure• The plate thickness loss (surface and reverse sides) was
28

about 0.53 mm in the 5th year of exposure.
6.3.2 Stainless Steel
Results in 3rd year and 5th year of exposure• The plate thickness loss was 0.02~0.03 mm or less. These
values were larger than the mass loss (Table 9). Differences between them were within the margin of error in
instruments and the deviation in measurement results, andit can be said from the appearance that full-surface corrosion did not occur.
6.3.3 Nonferrous Metal
Results in 3rd year and 5th year of exposure• The plate thickness loss was large in the copper (C-02) andthe aluminum alloy (C-03). It was observed that the plate
thickness loss was nearly zero in the titanium (C-01).
6.3.4 Metallic-coated/sprayed Plates
Results in 3rd Year and 5th year of exposure• There were no significant differences in plate thickness
loss between 3rd year and 5th year of exposure.
6.3.5 Ordinary Carbon Steel, Stainless Steel, Nonferrous
Metal and Metallic-coated/sprayed Plates
Results in 19th year of exposure• Because measurement was not conducted on the identicalsection in which the initial thickness was measured, negative values were observed, and thus the relative comparison between thickness loss and weight loss was difficult
to conduct.
Fig. 2 Secular Changes of Plate Thickness Loss:
Ordinary Carbon Steel
Ordinary carbon steel (A-01)

Thickness loss (mm)6.2.2 Stainless Steel
Results in 3rd year and 5th year of exposure• The corrosion amount (g/m2) was extremely small for
respective types of stainless steel, and even for the typethat showed high corrosion, its corrosion amount was
1/100 or lower that of ordinary carbon steel.
Results in 19th year of exposure• Because the corrosion was in the form of local corrosion,
it was observed that nearly all specimens did not show
the weight change due to corrosion.

Exposure period (y)Table 10 Measurement Results for Plate Thickness
Kind

In 3rd year of exposure
In 5th year of exposure
In 19th year of exposure
Speci3rd-year
5th-year
19th-yearmen
Initial average
Thickness loss Initial average
Thickness loss Initial average
Thickness loss
averageaverageaverageNo.
thickness(mm)(mm)
thickness(mm)(mm)
thickness(mm)(mm)
thickness(mm)thickness(mm)thickness(mm)Ordinary
carbonsteel

Austenitictype
stainlesssteel

Duplextype
stainlesssteel

Ferritictype
stainlesssteel

Titanium
CopperAluminumalloy

Metalliccoated/
sprayedplates

-

-

-

-

-

-

-

-

-

-

-

-

29

6.4 Measurement Results for Pitting
Corrosion and Crevice Corrosion
The measurement results for pitting corrosion and crevice
corrosion were rearranged by kind and type of specimen
based on the past reports1),3).

Table 11 Measurement Results for Pitting Corrosion
In 3rd year of exposure

Kind

Specimen No.

As for the respective specimens after pickling, excluding
kind D coated/sprayed/lined/painted specimens, pitting corrosion on the surface side and crevice corrosion around thebolt hole were measured using a depth gauge for ordinary
carbon steel and an optical microscope for other kinds. Five
pitting corrosion depths (maximum and four following
depths) on the general section, excluding around the bolthole, were measured, and three depths (maximum and two

In 5th year of exposure

In 19th year of exposure

Average pitting Maximum pitting Average pitting Maximum pitting Average pitting Maximum pitting
corrosion depth corrosion depth corrosion depth corrosion depth corrosion depth corrosion depth
(μm)
(μm)
(μm)
(μm)
(μm)
(μm)

Ordinary
carbon steel

69

Austenitic-type
stainless steel

66

Duplex-type
stainless steel

Ferritic-type
stainless steel

Titanium66

CopperAluminum
alloy

30

69

95

following values) each at the right and left sides at the insulation washer-specimen gap were measured (five depths forordinary carbon steel regardless of left and right sides).
Tables 11~12 and Figs. 3.1~3.5 show the measurement
results and other related data.
The average pitting corrosion depth shown in Table 11
was found by averaging 5 depths (maximum and four following depths) and further by averaging the depth of 3

specimens of an identical specimen type. The maximum
pitting corrosion depth in Table 11 was found by averaging
the maximum pitting corrosion depth of 3 specimens of an
identical specimen type.

Table 12 Composition of Stainless Steel and Measurement Results for Maximum Pitting Corrosion Depth
in 19th Year of Exposure
Kind

SpeciApproximatemencomposition
No.

Approximate composition
N

Test
piece
No.

Ni

Maximum pitting
corrosion depth (μm)

GeneralsectionInsulation washerspecimen gap

75

55

5
95

Austenitictype
stainless
steel

54

77
49
57

94

5
79

Duplextype
stainlesssteel

Ferritic-type
stainless
steel

7

54
55

4

31

Fig. 3.1 Secular Changes of Average Pitting Corrosion
Depth: Ordinary Carbon Steel

Fig. 3.2 Secular Changes of Average Pitting Corrosion
Depth: Austenitic-type Stainless Steel

Average pitting corrosion depth (µm)

Average pitting corrosion depth (µm)

Ordinary carbon steel (A-01)

Austenitic-type
stainless steel(B-01~B-10)

Exposure period (y)Fig. 3.3 Secular Changes of Average Pitting Corrosion
Depth: Duplex-type and Ferritic-type Stainless Steel

Exposure period (y)Fig. 3.4 Secular Changes of Average Pitting Corrosion
Depth: Nonferrous Metal
Nonferrous
metal

Duplex-type stainless steel(B-11~B-12)

Average pitting corrosion depth (µm)

Average pitting corrosion depth (µm)

Copper (C-02)
Aluminum alloy (C-03)

Ferritic-type stainless steel(B-13~B-14)

Exposure period (y)32Titanium (C-01)

Exposure period (y)Fig. 3.5 Relationship between Maximum Pitting Corrosion
Depth and Composition of Stainless Steel

Maximum pitting corrosion depth (µm)

General section
Austenitic type
Duplex typeFerritic type

Maximum pitting corrosion depth (µm)

Insulation washer-specimen gap
Austenitic type
Duplex type

Maximum pitting corrosion depth (µm)

Ferritic type

Austenitic type
Duplex typeFerritic type*
*PI (Cr+3Mo+0.5Ni)
Quotation of the “data on the effect of de-passivation pH andcomposition on crevice corrosion occurrence” from the paper (H.
Koayama et al), Tetsu-to-Hagane 63 (1977)

33

6.4.1 Ordinary Carbon Steel
Results in 3rd year and 5th year of exposure• Wide mouthed pitting corrosion was observed. The average pitting corrosion depth was 204~280 μm, and the
maximum pitting corrosion depth was 280~310 μm. It
was seen from these values that the surface side caused
corrosion close to full surface corrosion.
Results in 19th year of exposure• It was observed in the 19th year of exposure that about
1-mm deep pitting corrosion occurred at the general section and about 4-mm deep crevice corrosion occurred at
the insulation washer-specimen gap.
6.4.2 Stainless Steel
Results in 3rd year and 5th year of exposure• The pitting corrosion occurring on the surface side,
excluding the crevice corrosion at the insulation washer-specimen gap, was observed using a microscope.
While the pitting corrosion depth differed by type of
specimen, the average pitting corrosion depth in the 5thyear of exposure reached 13~142 μm and the maximum
pitting corrosion depth reached 15~185 μm. However, as
far as observation was made with the naked eye, the surface side of stainless steel saw basically no occurrence ofpitting corrosion and was fine. It was types B-11~B-14
that saw the occurrence of pitting corrosion with the
naked eye, and among these types, it was type B-13 thatsurely caused pitting corrosion. As for other types, it wasdifficult to find differences among pitting corrosion,
flaws, rolled surfaces (satin finish) and other surface conditions.
Results in 19th year of exposure• When comparing the maximum pitting corrosion depth at
the general section of various types of stainless steel, it
was observed that comparatively deep pitting corrosion
occurred in type B-02 (SUS316L, 17Cr-12Ni-2.5Mo) andtype B-13 (SUS444, 19Cr-2Mo-Ti-Nb-Zr). A trend was
also observed in which the maximum corrosion depth at
the insulation washer-specimen gap was generally higher
than that at the general section.
6.4.3 Nonferrous Metal
Results in 3rd year and 5th year of exposure• Small pitting corrosion occurred in the copper (C-02) andaluminum alloy (C-03). As for the titanium (C-01),
because its surface has a satin finish, it was not clear
whether or not pitting corrosion occurred, and accordingly longer-term exposure is required in order to confirm
the occurrence of pitting corrosion.
Results in 19th year of exposure• It was observed that pitting corrosion did not occur in thetitanium. In the copper and aluminum alloy, it wasobserved that pitting corrosion identical to that in thestainless steel occurred.

34

6.5 Measurement Results for Film
Thickness
As for the coated/sprayed/lined/painted plates (kind D), themeasurement of film thickness was conducted at a position
identical to that used to measure the initial film thickness,and the thicknesses thus obtained using an electromagnetic
film thickness meter were compared to the initial film
thickness. As for the metallic-coated/sprayed plates, thefilm thickness after pickling was measured. Table 13 andFigs. 4.1~4.2 show the measurement results.
The data shown in Table 13 and Figs. 4.1~4.2 wereobtained by rearranging the measurement results for film
thickness based on the past reports1),3).
The coating/spraying/lining/painting film thickness loss
used in the table and figure followed that used in the past
three reports, and indicates the loss (reduction) of film
thickness. The positive values in the table mean that thefilm thickness was lost or reduced.

Table 13 Measurement Results for Film Thickness

Kind

SpecimenSide
No.

In 3rd year of exposure

In 5th year of exposure

3rd-yearaveragefilm
thickness(μm)

5th-yearaveragefilm
thickness(μm)

Initial film
thickness(μm)

Surface-

Reverse--Filmthickness
loss (μm)

Initial film
thickness
(μm)

-

-

-

-

-

95

55

Surface
Metalliccoated/
sprayedplates

ReverseIn 19th year of exposureFilmthickness
loss (μm)

Initial film
thickness
(μm)

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Surface
ReverseSurface
Reverse

6
-

-

-

-

-

-

Surface
ReverseOrganiclined plates

19th-year
averagefilm
thickness
(μm)

Film
thickness
loss (μm)

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Surface
ReverseSurface
ReverseSurface
ReverseHeavy-duty
paintedplates

Surface
ReverseSurface
Reverse35

Fig. 4.1 Secular Changes of Film Thickness Loss:
Metallic-coated/sprayed Plates

Fig. 4.2 Secular Changes of Film Thickness Loss:
Organic-lined and Heavy-duty Painted Plates

Exposure period (y)Hot-dip galvanized plate (D-02)
Zn-Al alloy-coated plate (D-03)
Aluminum-sprayed plate (D-04)

36

Organic lining and heavy-duty painting

Film thickness loss (µm)

Film thickness loss (µm)

Metallic coating/spraying

Exposure period (y)Polyethylene-lined plate (D-05)
Polyurethane-lined plate (D-06)
Ultra-high build epoxy resin-lined plate (D-07)
Epoxy resin/polyurethane resin-painted plate (D-08)
Epoxy/fluororesin-painted plate (D-09)
Epoxy resin/acrylic silicon resin-painted plate (D-10)

6.5.1 Metallic-coated/sprayed Plates
Results in 3rd year and 5th year of exposure• It was the hot-dip galvanized plate (D-02) and aluminum-sprayed plate (D-04) that showed film thickness loss
each of 40 μm and 6 μm, and the loss in the 5th year of
exposure was 40 μm for D-02 and 6 μm for D-04. The
aluminized stainless steel plate (D-01) showed no change
in film thickness loss in the 3rd year and 5th year of exposure. On the other hand, the zinc-aluminum alloy-sprayed
plate (D-03) showed an increase of about 20~40 μm.
Results in 19th year of exposure• As for the aluminized stainless steel plate (D-01), it wasconsidered that, while the thickness in the 19th year of
exposure could not be compared to the initial thickness, asound aluminized layer remained. As for the hot-dip galvanized plate (D-02), the galvanizing layer did not remain
and the rust layer of steel product was measured, and thus
it was impossible to compare the initial value to the value
in the 19th year of exposure. As for the zinc-aluminumalloy-sprayed plate (D-03) and aluminum-sprayed plate(D-04), both plates showed a film thickness similar to theinitial thickness or an increase in thickness, which wasconsidered to be attributable to that corrosion products atthe spraying layer were not completely removed in pickling.
6.5.2 Organic-lined Plates
Results in 3rd year and 5th year of exposure• As for the polyurethane-lined plate (D-06) and ultra-highbuild epoxy resin-lined plate (D-07), the film thickness
loss was large. In particular, the polyurethane-lined plateshowed a large loss of 700~850 μm. As for the polyethylene-lined plate (D-05), the measurement result showed
an increase of thickness, but in the re-measurement madeafterward, it was shown that D-05 showed nearly nochange.

Results in 19th year of exposure• Of the organic-lined plates, the polyurethane-lined plate(D-06) showed a large film thickness loss when comparedto the initial thickness, which was considered to be attributable to the occurrence of chalking due to ultraviolet
ray-induced deterioration of the film. However, theultra-high build epoxy resin-lined plate (D-07) showed asmall loss. It was observed that there was no difference inthe ultraviolet ray-induced deterioration of the film
between the surface and reverse sides.
6.5.3 Heavy-duty Painted Plates
Results in 3rd year and 5th year of exposure• The epoxy resin/polyurethane resin-painted plate (D-08),
epoxy/fluororesin-painted plate (D-09) and epoxy
resin/acrylic silicon resin-painted plate (D-10) showed afilm thickness loss of 30~70 μm.
Results in 19th year of exposure• As for all heavy-duty painted plates, it was observed thatthe top coating and intermediate coating disappeared,
which was considered to be attributable to chalking due tothe ultraviolet ray-induced deterioration of the film. As forthese plates, it was observed that there was a difference infilm thickness loss between surface and reverse sides,
which coincided with the fact that the top coating andintermediate coating were observed to remain on thereverse side by means of appearance observation.

37

6.6 Measurement Results for Adhesive
Strength
Measurement by the use of adhesion tester (metallic coated/sprayed D-01~D-04, lined/coated D-06~D-10):
A “Dolly” adhered to the film surface was pulled by the useof adhesion tester to find the adhesive strength from the
maximum fracture load.

Peeling test (lined D-05):
The film edge forcibly peeled by the use of tension tester
was picked to find the average adhesive strength at thestage when the film is pulled and peeled.
Tables 14~15 and Figs. 5.1~5.4 show the measurement
results.
The data shown in Tables 14~15 and Figs. 5.1~5.4 wereobtained by rearranging the measurement results for adhesive strength based on the past reports1),3).

Table 14 Test Results for Peeling Strength (Adhesive Strength)
Kind

Metalliccoated/
sprayedplatesSpecimen
No.

Initial level
Peeling
strength(kgf/cm²)

In 3rd year of exposure

Peeledsection (%)

−

−

−

−

−

70 or more

Peeling
strength(kgf/cm²)

Peeledsection (%)

Peeling
strength(kgf/cm²)

Peeledsection (%)

Adhesion
peeling5Adhesion
peeling9Adhesion
peeling
Cohesion
fracture

Adhesion
peeling

70 or more

Adhesion
peeling

Adhesion
peeling
Cohesion
fracture

Adhesion
peeling
Cohesion
fracture

Adhesion
peeling
Cohesion
fracture

Adhesion
peeling

Adhesion
peeling

Adhesion
peeling

Adhesion
peeling

Adhesion
peeling

Cohesionof primer
coating

70 or more

No peeling70 or more−

70 or more

No peeling70 or moreNo
description

Cohesion
fracture

Heavy-duty
paintedplate

9

Cohesion
fracture

Cohesion
fracture

Adhesion
peeling
Cohesion
fracture

Steelinterface
Adhesion
peeling
Cohesion of
top coating
Cohesion ofprimer coating

Cohesion of
top coating

Adhesion
peeling 95

Adhesion
peeling

Cohesion of
top coating

Cohesion ofprimercoating

Adhesion
peeling

Adhesion
peeling

Cohesion of
top coating

Cohesion of
top coating

Cohesion ofprimer coating

Cohesion ofprimer coating

Adhesion
peeling
Cohesion ofprimercoating
Adhesion
peeling

Adhesion
peeling

Adhesion
peeling

Adhesion peeling: Film peeling from adhered surface; Cohesion fracture: Cohesion fracture within film

38

In 19th year of exposure

Peeledsection (%)−

No
description

Organiclined plates

Peeling
strength(kgf/cm²)

In 5th year of exposure

Cohesion of
top coating
Cohesion ofprimer coating

Table 15 Test Results for Peeling Strength (Adhesive Strength)
Kind

SpecimenNo.

Organic-lined
plates

D-05

Initial level

In 5th year of exposure

In 3rd year of exposure

Peeling strength(kgf/10 mm)

Peeling strength(kgf/10 mm)

PeeledsectionPeeling strength(kgf/10 mm)

Peeledsection18

18.3

Cohesion
fracture

18.5

Cohesion
fracture

Fig. 5.1 Secular Changes of Adhesive Strength:
Metallic-coated/sprayed Plates

Fig. 5.2 Secular Changes of Adhesive Strength:
Organic-lined Plates
Organic lining

Adhesive strength (kgf/cm2)

Adhesive strength (kgf/cm2)

Metallic coating/spraying

Exposure period (y)Aluminized stainless steel plate (D-01)
Hot-dip galvanized plate (D-02)
Zn-Al alloy-coated plate (D-03)
Aluminum-sprayed plate (D-04)

Exposure period (y)Polyurethane-lined plate (D-06)
Ultra-high build epoxy resin-lined plate (D-07)

39

Fig. 5.3 Secular Change of Adhesive Strength:
Heavy-duty Painted Plates

Fig. 5.4 Secular Changes of Adhesive Strength:
Organic-lined Plates (Peeling Test)

Heavy-duty painting

Peeling test

Peeling strength (kgf/10mm)

Adhesive strength (kgf/cm2)

Exposure period (y)Epoxy resin/polyurethane resin-painted plate (D-08)
Epoxy/fluororesin-painted plate (D-09)
Epoxy resin/acrylic silicon resin-painted plate (D-10)

40

Organic lining

Exposure period (y)Polyethylene-lined plate (D-05)

6.6.1 Metallic-coated/sprayed Plates
Results in 3rd year and 5th year of exposure• As for the aluminized stainless steel plate (D-01) andhot-dip galvanized plate (D-02), the metallic coating film
peeled off from the adhesive-applied adhered surface (referred to as “adhered surface”). In D-01, because of theprobable lack of adhesive strength between the adheredsurface and the aluminized surface, the peeling strength
was low, at 3~5 kg/cm2.
• As for the zinc-aluminum alloy-sprayed plate (D-03) andaluminum-sprayed plate (D-04), the spraying film peeled
off from the adhered surface at a high level of peelingstrength over the limit of the measurement instrument (70kg/cm2). This high peeling strength was assumed to be
attributable to the fact that the adhesive penetrated into
the porous sprayed film and as a result the apparent peeling strength increased.
Results in 19th year of exposure• As for the aluminized stainless steel plate (D-01),zinc-aluminum alloy-sprayed plate (D-03) and aluminum-sprayed plate (D-04), because the coating/spraying
film fractured at the interface between the adhered surface and the coating/spraying layer, it was impossible tocorrectly measure the adhesive strength between the coating/spraying film and the steel surface. As for the hot-dip
galvanized plate (D-02), while partial cohesion fracturingof the film was observed, the coating layer nearly disappeared, and thus it was impossible to correctly measure
the adhesive strength between the coating film and thesteel surface.

6.6.3 Heavy-duty Painted Plates
Results in 3rd year and 5th year of exposure• As for the epoxy resin/polyurethane resin-painted plate(D-08), the peeling strength after 3~5 years of exposure
was 38~39 kg/cm2, and the initial strength was 43 kg/cm2,
thereby showing almost no difference. The fracture typewas of mixed peeling of peeling from the adhered surface+cohesion fracture.
• As for epoxy/fluororesin-painted plate (D-09), the initialpeeling strength was 55 kg/cm2, and the strength in the
3rd and 5th year of exposure was 41~67 kg/cm2, and as aresult it could be judged that there was almost no difference between them. The fracture type was of mixed peeling of peeling from the adhered surface+cohesion fracture.
• As for epoxy resin/acrylic silicon resin-painted plate(D-10), the peeling strength in the 3rd and 5th year of
exposure was 32~62 kg/cm2, which showed nearly no difference from the initial value of 55 kg/cm2. The fracture
type was of interface peeling between the adhered surface
and the film.
Results in 19th year of exposure• As for three types of heavy-duty painted plates, because
the fracture occurred mostly at the interface between theadhered surface and the film, it was impossible to correctly measure the peeling strength between the coating film
and the steel surface. It was considered from the peelingstrength thus observed that the adhesive strength between
the coating film and the steel surface did not lower.

6.6.2 Organic-lined Plates
Results in 3rd year and 5th year of exposure• As for the polyurethane-lined plate (D-06), there wasnearly no change between the initial adhesive strength(66 kg/cm2) and that after 5 years of exposure. The lining
film peeled off from the adhered surface.
• As for the ultra-high build epoxy resin-lined plate (D-07),
the adhesive strength lowered from the initial value (70kg/cm 2 or more) to about half (28~38 kg/cm2 ) due toexposure. The peeling type was of the steel interface peeling or mixed peeling of peeling from the adhered surface+cohesion fracture within the film (cohesion fracture).
• Only the polyethylene-lined plate (D-05) was subjected tothe peeling test. There was absolutely no change between
the initial value (18 kg/cm2) and the value after 5 years of
exposure.
Results in 19th year of exposure• As for the polyurethane-lined plate (D-06), because thelining film fractured at the interface between the adheredsurface and the polyurethane layer, it was impossible tocorrectly measure the adhesion strength between the lining film and the steel surface. As for the ultra-high build
epoxy resin-lined plate (D-07), it was observed that theadhesive strength lowered from the initial value. This
lowering was caused by the cohesion fracture of thelower layer, and it was further considered that the lowering was caused by the deterioration of lining material
itself.

41

6.7 Detection Results for Pinholes
Ferro-xylene test (metallic coated/sprayed D-01~D-04):
The filter paper to which ferro-xylene solution was soaked
was adhered tightly to the test surface, which was left for 7
minutes. Then the paper was fully washed and dried, and it
was detected from the spots transcribed to the paper whether or not pinholes occurred.
Inspection by means of pinhole tester (lined/coatedD-05~D-10):

An electric current is flown to the base steel set as a positive electrode, and the metal brush set as a negative electrode is placed on the lining/coating film; then in the casewhen conduction is confirmed, a pinhole is judged to occur.
Whether or not the pinhole occurred was detected by theuse of this method.
Tables 16~17 show the inspection results.
The data shown in Tables 16~17 were obtained by rearranging the detection results for pinholes based on the pastreports1),3).

Table 16 Ferro-xylene Test Results for Pinholes
In 3rd year of exposure

Kind

Specimen No.

Metallic-coated/
sprayed plates

In 5th year of exposure

Surface side

Reverse side

Surface side

Reverse side

No pinhole

No pinhole

No pinhole

No pinhole

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

Table 17 Detection Results for Pinholes
Kind

Organic-lined
platesSpecimen
No.

Voltage(KV)

In 3rd year of exposure
Reverse side

Surface side

Reverse side

Surface side

Reverse side

No pinhole

No pinhole

No pinhole

No pinhole

-

-

〃

〃

〃

〃

42

In 19th year of exposure

Surface side〃

Heavy-duty
painted plates

In 5th year of exposure

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

〃

No pinhole

No pinhole

〃

〃

〃
〃
〃
〃

〃
〃
〃
〃

Pinhole〃No pinhole

〃

〃

〃

〃
〃
〃

Pinhole
〃
〃

〃
〃
〃
〃
〃
〃

6.7.1 Metallic-coated/sprayed Plates
Results in 3rd year and 5th year of exposure• The pinhole was not detected even after 3~5 years of
exposure.
6.7.2 Organic-lined Plates
Results in 3rd year and 5th year of exposure• The pinhole was not detected even after 3~5 years of
exposure.
Results in 19th year of exposure• The pinhole was not detected even after 19 years of exposure.
6.7.3 Heavy-duty Painted Plates
Results in 3rd year and 5th Year of Exposure• The pinhole was not detected even after 3~5 years of
exposure.
Results in 19th year of exposure• As for the epoxy resin/polyurethane resin-painted plate(D-08) and epoxy resin/acrylic silicon resin-painted plate(D-10), the pinhole was detected on the surface side,which coincided with the disappearance of the top coating and intermediate coating and the exposure of theprimer coating on the surface side.

6.8 Measurement Results for Insulation
ResistanceA 4 cm×4 cm aluminum foil was prepared as an electrode,and the foil was adhered closely to the film by setting it as anegative electrode; then the base steel was set as a positiveelectrode, to which electric current was reciprocally applied
using an insulation resistance meter. The resistance occurring at that stage was measured. Table 18 shows the measurement results.
The data shown in Table 18 were obtained by rearranging the measurement results for insulation resistance basedon the past reports1),3).
6.8.1 Organic-lined Plates
Results in 3rd year and 5th year of exposure• As for three types of organic-lined plates (D-05~D-07),
the volume resistivity of the lining film was 1013 in the
3rd year of exposure and 1017 or more in the 5th year of
exposure, which showed favorable results. As for typeD-07 (initial volume resistivity: 1.05×1013 Ω • cm), it was
judged that no deterioration from the initial level due tothe exposure test was found.

Table 18 Measurement Results for Insulation Resistance (Volume Resistivity)
Kind

Initial level
In 3rd year of exposure
Specimen
Surface side Reverse side Surface side Reverse sideNo.

(Ω-cm)

In 5th year of exposure
Surface side

In 19th year of exposure

Reverse side Surface side

Reverse side

Organic-lined
platesHeavy-duty
paintedplates43

6.8.2 Heavy-duty Painted Plates
Results in 19th year of exposure• The insulation resistance (volume resistivity) loweredfrom the initial level. However, every specimen showed
108 Ω • cm or more, and no effect of lowering on the corrosion resistance was found. As for the epoxy resin/polyurethane resin-painted plate (D-08) and epoxy
resin/acrylic silicon resin-painted plate (D-10), no effectof the pinhole on the volume resistivity was found.

Fig. 6 Secular Changes of Impedance:
Organic-lined and Heavy-duty Painted Plates
Organic lining
Heavy-duty paintingtan

Results in 19th year of exposure• The insulation resistance (volume resistivity) loweredfrom the initial level. However, every specimen showed
108 Ω • cm or more, and no effect of lowering on the corrosion resistance was found. It was considered that thecorrosion-protective performance was sound.

6.9 Measurement Results for Impedance
As for the organic-lined and heavy-duty painted specimens(D-06~D-10), impedance was measured to find the conductivity loss coefficient (tan δ value). Table 19 and Fig. 6
show the measurement results.
The data shown in Table 19 and Fig. 6 were obtained byrearranging the measurement results for impedance basedon the past reports1),3).

Exposure period (y)Polyurethane-lined plate (D-06)
Ultra-high build epoxy resin-lined plate (D-07)
Epoxy resin/polyurethane resin-painted plate (D-08)
Epoxy/fluororesin-painted plate (D-09)
Epoxy resin/acrylic silicon resin-painted plate (D-10)

Table 19 Measurement Results for Impedance
Kind

Organic-lined
platesHeavy-duty
paintedplates44

Specimen
No.

Initial level
Surfaceside

Reverseside

In 3rd year of exposure

In 5th year of exposure(tan δ)In 19th year of exposure

Surfaceside

Surfaceside

Surfaceside

Reverseside

Reverseside

Reverseside

6.9.1 Organic-lined Plates
Results in 19th year of exposure• As for the polyurethane-lined plate (D-06), the initialvalue was not measured, and thus it was impossible to
make a comparison. As for the ultra-high build epoxy resin-lined plate (D-07), the tan δ value increased from theinitial value.
6.9.2 Heavy-duty Painted Plates
Results in 3rd year and 5th year of exposure• As for the heavy-duty painted plates (D-08~D-10), the tanδ value lowered slightly as the exposure years lapsed.
Results in 19th year of exposure• As for the epoxy resin/polyurethane resin-painted plate(D-08), epoxy/fluororesin-painted plate (D-09) and epoxy
resin/acrylic silicon resin-painted plate (D-10), the levelof tan δ<0.2 was maintained. In the comparison between
the surface and reverse sides, the surface side where thedisappearance of the film was large tended to show a highlevel of tan δ.

6.10 Measurement Results for Color
Difference and Glossiness
After slight water washing of specimens, the color difference and glossiness mainly at the center of the surface side
was measured using a color difference meter and a glossiness meter (60 degrees). Because the initial data wasunavailable, the color difference and glossiness were compared setting the level in the 3rd year of exposure as the initial level. Tables 20~21 and Figs. 7.1~7.4 show the measurement results.
The data shown in Tables 20~21 and Figs. 7.1~7.4 wereobtained by rearranging the measurement results for color
difference and glossiness based on the past reports1),3).

Table 20 Measurement Results for Color Difference
Kind

Specimen
No.
Side

L*

a*

b*

In 19th year of exposure

In 5th year of exposure

In 3rd year of exposure
L*

a*

b*

∆E*
(Note)

L*

a*

b*

∆E*
(Note)

Surface
ReverseHeavy-duty
paintedplates

Surface
ReverseSurface
ReverseNote: Calculated by setting the result in 3rd year of exposure as an initial value
ΔE＝√((L*-L*')^2 +(a*-a*')^2 +(b*-b*')^2)
L*, a*, b*: Value in 3rd year of exposure; L*', a*', b*': Value each in 5th year of exposure and in 19th year of exposure45

Table 21 Measurement Results for GlossinessIn 3rd year of exposure
Kind

Specimen
No.

Side

GlossinessIn 5th year of exposure

Glossiness

Surface
ReverseSurface
ReverseSurface
ReverseSurface
ReverseSurface
Austenitic- typestainless steel

ReverseSurface
ReverseSurface
ReverseSurface
ReverseSurface
ReverseSurface
ReverseSurface

Duplex-type
stainless steel

ReverseSurface
ReverseSurface

Ferritic-type
stainless steel

Titanium
CopperAluminum alloy

ReverseSurfaceOver

ReverseOver

Surface
ReverseSurface
ReverseSurface
ReverseSurface
ReverseHeavy-duty painted
plates

Surface
ReverseSurface
Reverse46

Glossinessretaining rate(% to 3rd-year
glossiness)

In 19th year of exposure

Glossiness

Glossinessretaining rate(% to 3rd-year
glossiness)

Fig. 7.1 Secular Changes of Color Difference ∆E*
Heavy-duty painting

Fig. 7.2 Secular Changes of Color Difference L*
Heavy-duty painting(surface side)(reverse side)(surface side)(reverse side)(surface side)(reverse side)(surface side)(reverse side)(surface side)(reverse side)(surface side)(reverse side)

Exposure period (y)Exposure period (y)Epoxy resin/polyurethane resin-painted plate (D-08)
Epoxy/fluororesin-painted plate (D-09)
Epoxy resin/acrylic silicon resin-painted plate (D-10)

Epoxy resin/polyurethane resin-painted plate (D-08)
Epoxy/fluororesin-painted plate (D-09)
Epoxy resin/acrylic silicon resin-painted plate (D-10)

Fig. 7.3 Secular Changes of Color Difference a*Fig. 7.4 Secular Changes of Color Difference b*

Heavy-duty painting

Heavy-duty painting(surface side)(surface side)(reverse side)(reverse side)(surface side)(surface side)(reverse side)(reverse side)(surface side)(surface side)(reverse side)(reverse side)

Exposure period (y)Epoxy resin/polyurethane resin-painted plate (D-08)
Epoxy/fluororesin-painted plate (D-09)
Epoxy resin/acrylic silicon resin-painted plate (D-10)

Exposure period (y)Epoxy resin/polyurethane resin-painted plate (D-08)
Epoxy/fluororesin-painted plate (D-09)
Epoxy resin/acrylic silicon resin-painted plate (D-10)

47

6.10.1 Measurement Results for Color Difference
Results in 3rd year and 5th year of exposure• When judging in terms of △E, notable changes after 3
years to 5 years of exposure were not observed inheavy-duty painted plates.
Results in 19th year of exposure• As for heavy-duty painted plates, while the change incolor difference on the reverse side was slight, the primer
coating on the surface side was exposed thereby causing
a notable change in color difference on the surface side.
6.10.2 Measurement Results for GlossinessResults in 3rd year and 5th year of exposure• As for the stainless steel, glossiness was naturally affectedby the surface finish. For example, because SUS316L(B-02), type 20Cr-25Ni-5Mo-Ti (B-05) and SUS329J4L(B-11) were of a satin finish, glossiness was low. Further,spotted rust developed unevenly, and thus a deviation inglossiness occurred. As a result, the glossiness retaining
rate after 3~5 years of exposure was diverse, but theglossiness retaining rate of 40~60% was observed in mostof the stainless steel specimens. As for the nonferrous
metal, glossiness was generally low due to the material
property and surface finish peculiar to nonferrous metal.
As for the heavy-duty painted plate, in contrast to thestainless steel, no deviation in glossiness was observed,
and the rate on the surface side was lower than that on thereverse side because of the probable effect of sunlight-induced deterioration (occurrence of chalking) on the rateof the surface side.
Results in 19th year of exposure• As for the heavy-duty painted plate, glossiness on both thesurface and reverse sides was low and the glossinessretaining rate also lowered, which meant a loss of glossiness. While the top coating and intermediate coating on
the surface side remained in the 3rd year of exposure,
those disappeared in the 19th year of exposure, and thus it
was impossible to make simple comparison of glossinessbetween them.

6.11 Measurement Results for Film
Hardness
As for the organic-lined and heavy-duty painted specimens,
the film hardness was measured. Table 22 shows the measurement results.
The data shown in Table 22 were obtained by rearranging the measurement results for film hardness based on thepast report3).
6.11.1 Organic-lined Plates
Results in 19th year of exposure• As for the polyurethane-lined plate (D-06), the shore hardness increased from the initial hardness. As for theultra-high build epoxy-resin-lined plate (D-07), while thepencil hardness showed no change, the Barcol hardness
lowered. It was forecast that the hardness lowered due tothe effect of water absorption on the film.
6.11.2 Heavy-duty Painted Plates
Results in 19th year of exposure• As for the epoxy resin/polyurethane resin-painted plate(D-08), epoxy/fluororesin-painted plate (D-09) and epoxy
resin/acrylic silicon resin-painted plate (D-10), it wasobserved that both the pencil hardness and the Barcol
hardness showed no remarkable changes from the initialhardness.

Table 22 Measurement Results for Film Hardness
Pencil hardness
Kind

Organic-lined
platesSpecimen
No.

Barcol hardness

Side

Initial hardness

Hardness in
19th yearof exposure

Initial hardness

Hardness in
19th yearof exposure

Surface

-

-

-

-

Reverse

-

-

-

-

Surface
Reverse

-

-

-

-

Surface
ReverseHeavy-duty
painted plates

-

-

-

Surface
Reverse---Surface
Reverse

48

-

-

-

Shore hardness
Initial hardness

Hardness in
19th yearof exposure

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

6.12 Observation of Metallic-coated/
sprayed Sections (SEM Analysis)
As for the metallic coated/sprayed plates, the coated/sprayed sections after pickling was observed. Photos
1~4 show the observation results in the 19th year of exposure.
The following observation results were obtained by rearranging the observation results based on the past report3).
Results in 3rd year and 5th year of exposure• As for the hot-dip galvanized plate (D-02), it wasobserved that corrosion form appeared. Further, minutecracks occurred. For other plates, no particularly notablechanges were observed.

Results in 19th year of exposure• As for the aluminized stainless steel plate (D-01), the alu-

minizing layer soundly remained. Accordingly, it wasconsidered that D-01 still possessed corrosion-protective
performance. As for the hot-dip galvanized plate (D-02),
the galvanizing layer disappeared, and cracks occurred in
the zinc-iron alloy layer, from which rust developed. As
for the zinc-aluminum alloy-sprayed plate (D-03) andaluminum-sprayed plate (D-04), a spraying layer of 100 μm or more still remained, and thus it was considered thatthese plates possessed corrosion-protective performance.
In the spraying layer, it was observed that the gap probably formed during spraying developed.

Aluminizing
Base steel

Photo 1 Observation of Metallic-coated/sprayed Sections: Aluminized Stainless Steel Plate (D-01)

Hot-dip
galvanizing
Base steel

Photo 2 Observation of Metallic-coated/sprayed Sections: Hot-dip Galvanized Plate (D-02)

Zn-Al alloy
spraying
Base steel

Photo 3 Observation of Metallic-coated/sprayed Sections: Zn-Al Alloy-sprayed Plate (D-03)

Aluminumspraying
Base steel

Photo 4 Observation of Metallic-coated/sprayed Sections: Aluminum-sprayed Plate (D-04)
Measurement instrument: Scanning electron microscope (SEM) S4300SE by Hitachi Ltd.

49

6.13 Measurement of Cl Concentration(EPMA Analysis)
As for the organic-lined and heavy-duty painted plates, Cl
concentration in the section of coating film was measured
by means of EPMA analysis. Figs. 8.1~8.5 and Photos 5~9
show the measurement results.
Results in 3rd year and 5th year of exposure• As for the polyethylene-lined plate (D-05) and polyurethane-lined plate (D-06), Cl concentration on the lining
film showed almost no change before and after exposure.
As for the ultra-high build epoxy resin-lined plate (D-07),

Cl concentration after 5 years of exposure was slightly
higher than that before exposure, but the deviation in themeasured results was large and also the cause was notclear. As for the epoxy resin/polyurethane resin-painted
plate (D-08) and epoxy/fluororesin-painted plate (D-09),
no difference of Cl concentration before and after exposure was observed. As for the epoxy resin/acrylic siliconresin-painted plate (D-10), when compared to the sample
before exposure, the Cl concentration tended to show ahigher level at probably both the top coating acrylic layer
and the epoxy layer under the acrylic layer after 5 yearsof exposure.

Cl concentration (%)

Fig. 8.1 Measurement of Cl Concentration: Polyurethane-lined Plate (D-06)

A

Base steel

Lining film

Photo 5 Cl Concentration:
Polyurethane-lined Plate (D-06)

A

Distance from steel surface (μm)

Project: 5-11-036_0027 D6-1
Dec. 04 15:12 2009
Stage scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.003e-008 A
Beam shape: Circular
Beam diameter (um): 20
Measurement time (ms): 500.00
Stage No.: 1
X: 15.6996 mm
Y: -19.5182 mm
Z: 10.9875 mm
Direction: Optional
Number: 3000
Gap: 1.06 um
Distance: 3.187 um
Cl WDS CH-1 PET
Ka primary ray
Peak: 151.4200 mm
Integration frequency: 1
Maximum value: 0.271
Minimum value: 0.000
Average: 0.052
A value, B value: 7.3780, 0.0000

Cl concentration (%)

Fig. 8.2 Measurement of Cl Concentration: Ultra-high Build Epoxy Resin-lined Plate (D-07)

A

Base steel

Lining film

Photo 6 Cl Concentration:
Ultra-high Build Epoxy Resin-lined Plate (D-07)

A

Distance from steel surface (μm)

Project: 5-11-036_0028 D7-1
Dec. 04 15:43 2009
Stage scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.011e-008 A
Beam shape: Circular
Beam diameter (um): 20
Measurement time (ms): 500.00
Stage No.: 1
X: -20.6514 mm
Y: -21.2427 mm
Z: 11.0640 mm
Direction: Optional
Number: 3000
Gap: 0.74 um
Distance: 2.222 um
Cl WDS CH-1 PET
Ka primary ray
Peak: 151.4200 mm
Integration frequency: 1
Maximum value: 0.487
Minimum value: 0.000
Average: 0.177
A value, B value: 7.3780, 0.0000

Note:Measurement instrument used for Figs. 8.1~8.5: X-ray electron probe micro analyzer (EPMA) JXA-8230 by JEOL Ltd.

50

Cl concentration (%)

Fig. 8.3 Measurement of Cl Concentration: Epoxy Resin/Polyurethane Resin-painted Plate (D-08)

A

Base steel

Project: 5-11-036_0029 D8-1
Dec. 04 16:15 2009
Stage scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.003e-008 A
Beam shape: Circular
Beam diameter (um): 20
Measurement time (ms): 500.00
Stage No.: 1
X: 24.6957 mm
Y: 17.8961 mm
Z: 11.0290 mm
Direction: Optional
Number: 3000
Gap: 83.4 um
Distance: 250.00 um

BCoating film

Photo 7 Cl Concentration:
Epoxy Resin/Polyurethane Resin-painted Plate (D-08)

A

Distance from steel surface (μm)

Cl WDS CH-1 PET
Ka primary ray
Peak: 151.4200 mm
Integration frequency: 1
Maximum value: 0.184
Minimum value: 0.005
Average: 0.054
A value, B value: 7.3780, 0.0000

B

Cl concentration (%)

Fig. 8.4 Measurement of Cl Concentration: Epoxy /Fluororesin-painted Plate (D-09)

A

Base steel

Project: 5-11-036_0026 D9-2
Dec. 04 14:42 2009
Stage scan
Acceleration voltage: 15.0 kV
Irradiation current: 4.959e-008 A
Beam shape: Circular
Beam diameter (um): 20
Measurement time (ms): 500.00
Stage No.: 1
X: -22.5325 mm
Y: 18.0229 mm
Z: 10.9680 mm
Direction: Optional
Number: 3000
Gap: 90.0 um
Distance: 270 um

B

Coating film

Photo 8 Cl Concentration:
Epoxy /Fluororesin-painted Plate (D-09)

A

Distance from steel surface (μm)

B

Cl WDS CH-1 PET
Ka primary ray
Peak: 151.4200 mm
Integration frequency: 1
Maximum value: 0.175
Minimum value: 0.000
Average: 0.053
A value, B value: 7.3780, 0.0000

Cl concentration (%)

Fig. 8.5 Measurement of Cl Concentration: Epoxy Resin/Acrylic Silicon Resin-painted Plate (D-10)

A

Base steel

Project: 5-11-036_0030 D10-3
Dec. 04 16:57 2009
Stage scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.007e-008 A
Beam shape: Circular
Beam diameter (um): 20
Measurement time (ms): 500.00
Stage No.: 1
X: 22.9817 mm
Y: -25.1553 mm
Z: 11.1320 mm
Direction: Optional
Number: 3000
Gap: 0.12 um
Distance: 364.30 um

BCoating film

Photo 9 Cl Concentration:
Epoxy Resin/Acrylic Silicon Resin-painted Plate (D-10)

A

Distance from steel surface (μm)

B

Cl WDS CH-1 PET
Ka primary ray
Peak: 151.4200 mm
Integration frequency: 1
Maximum value: 0.130
Minimum value: 0.000
Average: 0.044
A value, B value: 7.3780, 0.0000

Note:Measurement instrument used for Figs. 8.1~8.5: X-ray electron probe micro analyzer (EPMA) JXA-8230 by JEOL Ltd.

51

Results in 19th year of exposure• As for the polyurethane-lined plate (D-06), it wasobserved that there was an area where the Cl concentrated partly in the vicinity of the surface side. As for theultra-high build epoxy resin-lined plate (D-07), the Cl
concentrated entirely in the lining film, which was considered to be attributable to the containment of a certain
level of Cl in the lining film itself. As for the epoxy
resin/polyurethane resin-painted plate (D-08), epoxy/fluororesin-painted plate (D-09) and epoxy resin/acrylic silicon resin-painted plate (D-10), the Cl concentration was
detected in the thick inorganic zinc-rich primer coating
layer on the steel surface. However, no notable Cl concentration was detected in the intermediate coating layer,
and thus it could not be judged whether or not the Cl concentration was caused by external Cl factors. In all of thespecimens, no notable changes from the initial Cl concentration level were observed.

7. Conclusion
The long-term offshore atmospheric exposure test started
with Okinotorishima as the test site, and the data on exposure test results thus obtained was rearranged as the datathat show secular (time-history) changes in the exposure
test. Useful knowledge involved in the following test purposes was obtained:• Grasping the effect of the marine environment at Okinotorishima on the corrosion of steel products by setting thecorrosion behavior of ordinary carbon steel (SS400
equivalents) as the parameter of assessing durability• Grasping the corrosion behavior of seawater-resistant
stainless steel• Grasping the corrosion behavior of nonferrous metal (titanium, copper and aluminum alloy)• Confirmation of corrosion resistance of various kinds ofcoated/sprayed/lined/painted steel products (metallic
coating/spraying, organic lining, heavy-duty painting)
References
1) Kozai Club (currently the Japan Iron and Steel Federation): Report of Joint Research on Assessment of Durability of Materials for Civil Engineering Steel Structures(Report of Construction Material Durability Test at
Okinotorishima)-Metallic Types, Survey Results in 3rdYear and 5th Year of Exposure, March 2001
2) The Japan Iron and Steel Federation: Interim Report ofConstruction Material Durability Test at Okinotorishima
and Assessment of Exposure Test Specimens in 10th
Year of Exposure, March 2002
3) Technical Dept. of Nippon Steel Anti-Corrosion Co.,
Ltd.: Report of Completion of Survey and Analysis ofSpecimens Used for Exposure Tests at Okinotorishima toAssess Durability of Construction Materials, February2010 (delivered to the Japan Iron and Steel Federation)

52

Part 3

Survey/Analytical Report of Exposure Tests at the Suruga
Bay Exposure Rack Employing Identical Specimens Used
for Exposure Tests at Okinotorishima-Results after 24 Years of Exposure■ Purpose■ Details of Test Specimens■ Survey Items and Items Subjected to Surveys■ Photos of Appearance of Specimens■ Assessment of Exposure Test Results■ Examination Results■ Conclusion

53

1. Purpose

No. 1 Deck at Marine Engineering Research Facility

In order to make a comparative survey of the exposure tests
conducted at Okinotorishima, which started in July 1990,
the exposure tests at the Marine Engineering Research
Facility in Suruga Bay started in 1991, one year after thestart at Okinotorishima, using two specimens each in the
category of the kind and type of specimens similar to those
applied at Okinotorishima. The No. 1 exposure deck at the
Marine Engineering Research Facility was adopted for thetesting site.
Photo 1 shows the exposure test conditions, and Table 1
the test period and the survey plan.

2. Details of Test Specimens
Table 2 shows the kind and type of specimens subjected tothe survey, and Table 3 shows the dimensions of the specimens. Tables 4~5 show specifications for coating, spraying,lining and painting.
Note: The following revisions were made to Tables 2 and 3.
The composition of exposure test materials at Okinotorishima in the past report1) were revised as in the following
manner:• B-07: 22Cr-18Ni-6Mo-0.7Cu-0.2N→
20Cr-18Ni-6Mo-0.7Cu-0.2N (standardization after
exposure)• B-08: 25Cr-13Ni-0.7Mo-0.3N→
25Cr-13Ni-0.9Mo-0.3N (standardization after
exposure)

Photo 1 Exposure Testing Conditions at Marine Engineering
Research Facility in Suruga Bay

Table 1 Test Period and Survey
Year

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

0

1

2

3

4

5

6

7

8

9

Year

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Test period (y)

10

11

12

13

14

15

16

17

18

19

Year

2011

2012

2013

2014

2015

2016

Test period (y)

20

21

22

23

24

25

Test period (y)Recovery/survey

Recovery/survey

Recovery/survey
Notes:
1) △: Recovery of specimen (recovery of 1 specimen/type)〇: Detailed survey (each specimen)
2) One of two specimens is continually exposed.

54

Table 2 Kinds and Types of Exposure Test Specimens
Specimen Group
No.

Kind

Type

Specimen preparationcompany

Ordinary
carbon steel

Ordinary carbon steel (SS400)

Nippon Steel &Sumitomo Metal

B-01

Stainless steel (SUS304, 18Cr-8Ni)

Nippon Steel & Sumikin
Stainless Steel

B-02

Stainless steel (SUS316L, 17Cr-12Ni-2.5Mo)

Nippon Steel &Sumitomo Metal

B-03

Stainless steel (SUS317L, 19Cr-13Ni-3.5Mo)

Nippon Steel & Sumikin
Stainless Steel

B-04

Stainless steel (18Cr-13Ni-3Mo-0.15N)

JFE Steel

Stainless steel (20Cr-25Ni-5Mo-Ti)

Nippon Steel &Sumitomo Metal

Stainless steel (20Cr-17Ni-4.5Mo-N-L.C)

JFE Steel

Stainless steel (SUS312L, 20Cr-18Ni-6Mo-0.7Cu-0.2N)

Nippon Steel & Sumikin
Stainless Steel

B-08

Stainless steel (SUS317J2, 25Cr-13Ni-0.9Mo-0.3N)

Nippon Steel & Sumikin
Stainless Steel

B-09

Stainless steel (25Cr-22Ni-4.5Mo-0.2N)

JFE Steel

B-10

Stainless steel (22Cr-23Ni-5Mo-1.5Cu-0.2N)

Kobe Steel

B-11

Stainless steel (SUS329J4L, 25Cr-6Ni-3.5Mo-0.2N)

Nippon Steel &Sumitomo Metal

Stainless steel (SUS329J4L, 25Cr-7Ni-3.5Mo-0.5Cu-0.16N)

Kobe SteelStainless steel (SUS444, 19Cr-2Mo-Ti-Nb-Zr)

JFE Steel

Stainless steel (26Cr-4Mo)

JFE Steel

Titanium

Titanium［JIS H4600 TP35H(KS50)］

Kobe Steel

CopperCopper［C-1220］

Kobe Steel

Aluminumalloy

Aluminum alloy［5083］

Kobe Steel

Aluminized stainless steel plate

Nippon Steel & Sumikin
Stainless Steel

Hot-dip galvanized plate

JFE SteelZinc-aluminum alloy-sprayed plate

JFE Steel

Aluminum-sprayed plate

Nippon Steel &Sumitomo Metal

Polyethylene-lined plate

JFE Steel

Polyurethane-lined plate

JFE Steel

D-07

Ultra-high build epoxy resin-lined plate

Nippon Steel &Sumitomo Metal

D-08(Epoxy resin/polyurethane resin)-painted plate

Nippon Steel &Sumitomo Metal(Epoxy/fluororegin)-painted plate

Nippon Steel &Sumitomo Metal(Epoxy resin/acrylic silicon resin)-painted plate

Nippon Steel &Sumitomo Metal

A-01

A Ordinary
carbon steel

B-05
B-06
B-07

Austenitictype
B Stainlesssteel

Duplex type

B-12
B-13
Ferritic type
B-14
C-01
C-02

C

Nonferrous
metal

C-03
D-01
D-02

Metallic
coating/
spraying

D-03
D-04
D-05
D-06

D-09
D-10

D

Coated/sprayed/lined/
paintedplatesOrganic lining

Heavy-duty
painting

55

Table 3 Dimensions of Test Specimens at Exposure Tests
Specimen
No.

Type

Width
(mm)

210

75

Nominalthickness*
(mm)

A-01

Ordinary carbon steel (SS400)

B-01

Stainless steel (SUS304, 18Cr-8Ni)

9.0

B-02

Stainless steel (SUS316L, 17Cr-12Ni-2.5Mo)

4.0

B-03

Stainless steel (SUS317L, 19Cr-13Ni-3.5Mo)

9.0

B-04

Stainless steel (18Cr-13Ni-3Mo-0.15N)

9.0

B-05

Stainless steel (20Cr-25Ni-5Mo-Ti)

3.2

B-06

Stainless steel (20Cr-17Ni-4.5Mo-N-L.C)

1.5

B-07

Stainless steel (SUS312L, 20Cr-18Ni-6Mo-0.7Cu-0.2N)

9.0

B-08

Stainless steel (SUS317J2、25Cr-13Ni-0.9Mo-0.3N)

9.0

B-09

Stainless steel (25Cr-22Ni-4.5Mo-0.2N)

9.0

B-10

Stainless steel (22Cr-23Ni-5Mo-1.5Cu-0.2N)

30

1.25

B-11

Stainless steel (SUS329J4L, 25Cr-6Ni-3.5Mo-0.2N)

75

3.2

B-12

Stainless steel (SUS329J4L, 25Cr-7Ni-3.5Mo-0.5Cu-0.16N)

52

3.0

B-13

Stainless steel (SUS444, 19Cr-2Mo-Ti-Nb-Zr)

75

2.0

B-14

Stainless steel (26Cr-4Mo)

2.0

C-01

Titanium［JIS H4600 TP35H (KS50)］

5.0

C-02

Copper［C-1220］

6.0

C-03

Aluminum alloy［5083］

6.0

D-01

Aluminized stainless steel plate

1.2

D-02

Hot-dip galvanized plate

6.0

D-03

Zinc-aluminum alloy-sprayed plate

6.0

D-04

Aluminum-sprayed plate

5.0

D-05

Polyethylene-lined plate

6.0

D-06

Polyurethane-lined plate

6.0

D-07

Ultra-high build epoxy resin-lined plate

9.0

D-08

(Epoxy resin/polyurethane resin)-painted plate

9.0

D-09

(Epoxy/fluororesin)-painted plate

9.0

D-10

(Epoxy resin/acrylic silicon resin)-painted plate

9.0*The thickness of coated/sprayed/lined plates is expressed in terms of base plate thickness.

56

Length(mm)

30

Table 4 Specifications for Coating, Spraying and Lining (1)Specimen No.

KindSpecifications for coating/spraying/lining

D-01

Aluminized stainlesssteel plate

1. Base metal: Ferritic-type stainless steel (19Cr-0.4Nb-0.4Cu)
2. Coating material: Hot-dip aluminum
3. Substrate treatment:––
4. Coating method: Immersion in molten aluminum
5. Film thickness: About 20 μm
6. Side surface/reverse side: Same as surface side

D-02

Hot-dip galvanizedplate

1. Coating material: 100% Zn
2. Substrate treatment: H₂SO₄ pickling
3. Coating method: Immersion in molten zinc Temperature 450℃; Time 5 min+3 min=8 min
4. Film thickness: About 85 μm
5. Side surface/reverse side: Same as surface side

D-03

Zinc-aluminumalloy-sprayed plate

1. Spraying material: 87% Zn+13% Al (wire diameter φ3.1 mm)
2. Substrate treatment: ① Blasting: SIS Sa 2.5 or more
② Degreasing: Runner system
3. Spraying method: Gas wire thermal spraying
4. Film thickness: About 180 μm
5. Hole sealing: No sealing (water treatment by the use of ion exchange water)
6. Side surface/reverse side: Same as surface side

D-04

Aluminum-sprayed plate

1. Spraying material:100% Al (wire diameter φ3.1 mm)
2. Substrate treatment: Blasting
3. Spraying method: Gas wire thermal spraying
4. Film thickness: About 300 μm
5. Hole sealing: Epoxy resin paint (clear): 1 brush coating
6. Side surface/reverse side: Same as surface side

Table 5 Specifications for Coating, Spraying and Lining (2)Specimen No.

KindSpecifications for coating/spraying/lining

D-05

Polyethylene-lined plate

1. Lining material: ① Primer: Epoxy-type primer② Adhesive polyethylene③ High-density polyethylene (carbon black 2.5% contained)
2. Substrate treatment: Shot blasting
3. Lining method: Press pasting (pressure 2 kg/cm2)
4. Film thickness: About 1.5 mm
5. Side surface/reverse side: Tar epoxy coating (about 2 mm)

D-06

Polyurethane-lined plate

1. Lining material: ① Primer: Epoxy primer② Urethane elastomer
2. Substrate treatment: Shot blasting
3. Lining method: Hot air spray
4. Film thickness: About 3.5 mm
5. Side surface/reverse side: Tar-epoxy coating (about 2 mm)

D-07

Ultra-high build epoxy
resin-lined plate

1. Lining material: ① Primer: Epoxy zinc-rich primer② Ultra-high build epoxy resin lining (1 layer)
2. Substrate treatment: Blasting
3. Lining method: Spray lining; Surface roller pressing 1.5 hours after lining
4. Film thickness: About 2.3 mm
5. Side surface/reverse side: Same as surface side

D-08

(Epoxy resin/
polyurethane resin)painted plate

1. Painting material: ① Primer: Heavy-thick inorganic zinc-rich primer② Primer coating: Epoxy resin (mastic primer, 2 layers)③ Intermediate coating: Epoxy resin④ Top coating: Urethane resin
2. Substrate treatment: Blasting SIS Sa 2.5
3. Painting method: Air spray painting
4. Film thickness: About 500 μm
5. Side surface: Tar epoxy painting (2 mm)
6. Reverse side: Same as surface side

D-09

(Epoxy/Fluororesin)painted plate

1. Painting material: ① Primer: Heavy-thick inorganic zinc-rich primer② Primer coating: Epoxy resin (mastic primer, 2 layers)③ Intermediate coating: Epoxy resin④ Top coating: Fluororesin
2. Substrate treatment: Blasting SIS Sa 2.5
3. Painting method: Air spraying painting
4. Film thickness: About 500 μm
5. Side surface: Zinc-rich primer
6. Reverse side: Same as surface side

D-10

(Epoxy resin/
acrylic silicon resin)painted plate

1. Painting material: ① Primer: Heavy-thick inorganic zinc-rich primer② Primer coating: Epoxy resin (mastic primer, 2 layers)③ Intermediate coating: Epoxy resin④ Top coating: Acrylic silicon resin
2. Substrate treatment: Blasting SIS Sa 2.5
3. Painting method: Air spraying painting
4. Film thickness: About 500 μm
5. Side surface: Tar-epoxy painting (about 2 mm)
6. Reverse side: Same as surface side57

3. Survey Items and Items Subjected
to Surveys
Tables 6~10 show the survey items/methods and items subTables to
6~10
show theitems/methods
andcategory
items subjectedsurveys.
Twosurvey
specimens
each in theofjectedtosurveys.
Twospecimens
each
in
the
categoryofrespective kinds and types of specimens were exposed, andrespective
kinds
and
types
of
specimens
were
exposed,andone of these two specimens was recovered and subjected to
one of these two specimens was recovered and subjected toassessment.
assessment.

4. Photos of Appearance of Specimens

In order to assess the durability of various types of speciIn order
to assessof various
specimens
subjected
to thethe durability
exposure test,
photostypes
wereof
taken
of
mens
subjected
totheexposure
test,
photos
were
taken
of
the appearance (surface) of the 28 specimens. These photos
the appearanceof the 28
specimens. These
photosareuploaded to(surface)
another sourceas Attachments,
and arenotareuploadedtoanothersourceas
Attachments,
and
are
not
published in this brochure.
publishedinthisbrochure.
https://www.jisf.or.jp/en/activity/sc-reports/index.html• Access:
https://www.jisf.or.jp/en/activity/sc-reports/index.html• Access:
The four
Attachments are as follows:Thefour
as follows:at the recovery stage
AttachmentAttachments
1: Photos ofare
appearance
Attachment
1:
Photosofappearance
at the recovery stage(Photos 1~30)(Photos
1~30)
Attachment 2: Photos and sketches of appearance after
Attachment
Photos31~59)
and sketches of appearance after
water
washing2:(Photos
water
washing(Photos
31~59)
Attachment 3: Photos of appearance after pickling (Photos
Attachment 3: Photos of appearance after pickling (Photos
60~78)
60~78)
Attachment
4: Supplementary photos (standard photos
Attachment
Supplementary
photos (standard photos
taken
to assess4:thelevel of rust development)
taken to assess the level of rust development)
Notes to Four Attachments
Notes
to Four
Attachments
1)
Photosof appearance
at the recovery stage
1) Photos of appearance at the recovery stage

As for the ordinary carbon steel (A-01), the photo showsAs forthe ordinary
steelof(A-01),
the asphotothespecimen
aftercarbon
removalrust, andfor showsotherthespecimenafter
removal
of
rust,
and
as
for washothertypes, the photos show the specimens before watertypes,
thephotosshow
thespecimens
beforewater
washing. The photos of both the surface and reverse sides
ing. The
photosof boththeofsurface
and reverse
sides
were
taken
for every
type
specimens
targeted
for
were
taken
for
every
type
of
specimens
targetedforassessment. The photos of both side surfaces were addiassessment.
Thephotosof
bothside
surfaces
wereadditionally taken for the ordinary carbon steel (A-01) andtionally taken for the
carbon steel (A-01) andpolyethylene-lined
steelordinary
plate (D-05).
polyethylene-lined
steel
plate
(D-05).
2) Photos and sketches of appearance after water washing2) Photos
and sketches
appearance
afterwerewater
washing
Some comments
onoftheappearance
additionallySome
comments
ontheappearance
wereadditionallydescribed for the respective appearance photos. Meandescribed
forthetheordinary
respective
appearance
photos.
while,
as forcarbonsteel (A-01),
theMeancomwhile,
as
for
the
ordinary
carbonsteel(A-01),
the comment on the appearance after exposure was described.
mentphotos
on the ofappearance
after exposure
was sides
described.
The
both the surface
and reverse
wereThe
photosofboththesurfaceandreversesides
were
taken for every type of specimens targeted for assesstaken
for
every
type
of
specimens
targetedforassessment. The photos of both side surfaces were additionallyment. for
Thethephotosof bothsidesteelsurfaceswere additionallytakenordinary
carbon(A-01).
taken
for
the
ordinary
carbonsteel(A-01).
3) Appearance photos after pickling3) Appearance
after
pickling
Pickling wasphotos
appliedto theordinary carbon steel, stainPickling
wasappliedtothecarbonsteel, stainless steel, nonferrous metal ordinary
and metallic
coated/sprayedlesssteel,
nonferrous
metal
and
metallic
coated/sprayed
plates (A-01~D04). The pickling condition is suppleplates (A-01~D04).
is supplemented
in Tables 6~8.The
Thepicklingphotos ofcondition
both the surface
andmentedinTables6~8.
Thephotosofboththesurfacereverse sides were taken for every type of specimens andtarreverseforsides
were taken
forphotos
every typeof specimens
targeted
assessment.
Theof bothside surfaces
geted
for
assessment.
Thephotosof
bothside
surfaceswere additionally taken for the ordinary carbon steel
were additionally taken for the ordinary carbon steel(A-01).
(A-01).
4) Supplementary
information4) Supplementary
information
The standard photos
used for assessing rust development
The
standard
photosused for assessing
rust developmentlevels are shown in Attachment
4.
levels are shown in Attachment 4.

Table 6 Survey Items/Methods and Items Subjected to Survey: Ordinary Carbon Steel (A-01)
Survey site

Survey item
Appearance photo

Laboratory

Survey method

Surveyed

Full view, before pickling
After pickling*

Appearance observation

Sketch (before pickling)

Pitting corrosion depth

Depth gauge

Thickness loss

Micrometer

Weight loss

Precision balance*Pickling conditions: 20℃, 10% dilute hydrochloric acid+Hibiron×Max. 30 min. (JISF method)

Table 7 Survey Items/Methods and Items Subjected to Survey: Stainless Steel (B-01〜B-14) and
Nonferrous Metal (C-01〜C-03)
Survey site

Survey item
Appearance photo

Laboratory

Survey method
Full view, before and after water washing
After pickling*

Appearance observation

Sketch (after water washing)

Pitting corrosion depth

Optical microscope

Thickness loss

Micrometer

Weight loss

Precision balance*Pickling condition (B-01~B-14, C-01): 90℃, 10% hydrogen citrate diammonium sol. Max. 60 min*Pickling condition (C-03): 80℃, 20% chromic anhydride sol.×1 min*Pickling condition (C-02): 20℃, 15% dilute hydrochloric acid×3 min

58

SurveyedTable 8 Survey Items/Methods and Items Subjected to Survey: Metallic-coated/sprayed Plates (D-01〜D-04)
Survey site

Survey item
Appearance photo

Laboratory

Survey method

Surveyed

Full view, before and after water washing
After pickling*

Appearance observation

Sketch (after water washing)Film adhesive strength

InstronFilm thickness loss

Electromagnetic film thickness meter

Film cross-section observation

Microscopic photographing

Thickness loss

Micrometer

Weight loss

Precision balance*Pickling condition (D-01, D-04): 90℃, 10% hydrogen chromate diammonium sol.×Max. 60 min*Pickling condition (D-02, D-03): 80℃, 20% chromic anhydride sol.×1 min

Table 9 Survey Items/Methods and Items Subjected to Survey: Organic-lined Plates (D-05〜D-07)
Survey site

Laboratory

Survey item

Survey method

Appearance photo

Full view, before and after water washingAppearance observation

Sketch (after water washing)

PinholePinhole tester

Film adhesive strength

InstronFilm thickness loss

Electromagnetic film thickness meterCl concentration

EPMA analysis

Electric resistance

Guard ring method

Impedance

AC bridge method

Film hardness

Pencil: D-7
Barcol: D-7
Shore D: D-5, D-6

Surveyed

Table 10 Survey Items/Methods and Items Subjected to Survey: Heavy-duty Painted Plates (D-08〜D-10)
Survey site

Laboratory

Survey item

Survey method

Appearance photo

Full view, before and after water washingAppearance observation

Sketch (after water washing)

PinholePinhole tester

Film adhesive strength

InstronFilm thickness loss

Electromagnetic film thickness meterCl concentration

EPMA analysis

Glossiness

Glossiness meter

Electric resistance

Guard ring method

Impedance

AC bridge method

Color difference

Color difference meter

Film hardness

Pencil: D-8, D-9, D-10
Barcol: D-8, D-9, D-10

Surveyed59

5. Assessment of Exposure Test
Results

Table 11 Rust Development Rates of Austenitic-type
Stainless Steel

5.1 Observation Results for Appearance

SpecimenNo.

Approximate composition

Rust developmentlevel (RN: Rating
Number*)Surface Reverse
side
side

The following assessment results after 24 years of exposure
were obtained from the photos of appearance at the specimen recovery stage shown in Attachment 1, photos ofappearance and sketches after water washing in Attachment
2, photos of appearance after pickling in Attachment 3 andstandard photos used for assessing rust development levels
in Attachment 4.
5.1.1 Ordinary Carbon SteelThe rust particle size was mostly 1~2 mm and uniform, andthe color tone was brown. As a result, it was judged by theappearance of the rust development condition that the steel
had favorable corrosion resistance, which led to an appearance rating grade* of 4.
*Note: In the Japan Bridge Association, the rust development condition for steel products is assessed by means of
the rust-development appearance rating grade from 1 (dangerous state) to 5 (favorable state).
5.1.2 Austenitic-type Stainless SteelAs for type B-01 (SUS304, 18Cr-8Ni), the rust development rate was highest among 10 austenitic types, and thesurface side indicated around RN* (rating number) 5, andthe reverse side around RN3. Remarkable pitting corrosion
occurred around the bolt hole. As for type B-02 (SUS316L,
17Cr-12Ni-2.5Mo), both the surface and reverse sides indicated around RN6.
As for other types, the rust development rate wasextremely low, or about RN9. (Table 11)
Note: *In the Japanese Industrial Standards (JIS 0595), therust development rate is classified into 10 levels or 10
rating numbers (RN0~9), where RN0 indicates the fulldevelopment of rusting, and RN9 indicates nearly no development of rusting.
5.1.3 Duplex-type Stainless SteelAs for type B-11 (SUS329J4L, 25Cr-6Ni-3.5Mo-0.2N), it
seemed to indicate around RN8.
As for type B-12 (SUS329J4L, 25Cr-7Ni-3.5Mo-0.5Cu-0.16N), it indicated around RN4, and the reverse side
was covered entirely with light yellow (yellowish green)rust. (Table 12)5.1.4 Ferritic-type Stainless SteelAs for type B-13 (SUS444, 19Cr-2Mo-Ti-Nb-Zr), the entire
reverse side was light brown (yellowish green), and it wasobserved that island-state rust developed. Crevice corrosion
occurred around the bolt hole. In terms of the rust development rating, it indicated around RN3.
As for type B-14 (26Cr-4Mo), it indicated around RN9,
and it was observed that the trend of rust development was
low. (Table 13)
5.1.5 Titanium
The entire surface side was gold, but after the removal of60*In the Japanese Industrial Standards (JIS 0595), the rustdevelopment rate is classified into 10 levels or 10 rating numbers(RN0~9), where RN0 indicates full development of rusting, and RN9
indicates nearly no development of rusting.

Table 12 Rust Development Rates of Duplex-type
Stainless SteelSpecimenNo.

Approximate composition

Rust developmentlevel (RN: Rating
Number)Surface Reverse
side
side

Table 13 Rust Development Rates of Ferritic-type
Stainless SteelSpecimenNo.

Approximate composition

Rust developmentlevel (RN: Rating
Number)Surface Reverse
side
side

rust, it showed a metallic color tone. The cause for discoloration seemed attributable to rust stains. It was observed thatcrevice corrosion did not occur.
5.1.6 Copper
The surface side was covered entirely with verdigris (lessverdigris on the reverse side). After pickling, while the verdigris was removed, discoloration was caused by the oxidized film.
5.1.7 Aluminum Alloy
Both the surface and reverse sides were covered entirely
with white rust. Thick white rust occurred around the bolthole, where crevice corrosion also occurred.
5.1.8 Aluminized Stainless Steel Plate
Both the surface and reverse sides were covered entirely
with white rust, and it was observed that blackish discoloration was caused on the reverse side.

5.1.9 Hot-dip Galvanized Plate
Both the surface and reverse sides were covered entirely
with white rust. But it was observed that red rust (spotted)
did not occur. In terms of the assessment standard for thedeterioration of galvanizing layer, the plate showed condition II (condition in which the deterioration of the galvanized layer has progressed and the iron-zinc alloy layer ispartly exposed).

ing was exposed. On the reverse side, while chalking wasobserved, the painting film remained.

5.1.10 Zinc-Aluminum Alloy-sprayed Plate
The color tone on the surface side changed to brown color,and it was observed that the plate was dotted with spottedwhite rust. The reverse side was covered entirely with whiterust.
5.1.11 Aluminum-sprayed Plate
Both the surface and reverse sides were covered entirely
with white rust, and minute unevenness occurred in thesprayed film.
5.1.12 Polyethylene-lined Plate
It was observed that the end sealing material (tar epoxy)partly peeled off and corrosion developed from the peeled
section. However, the steel product itself mostly remained.
5.1.13 Polyurethane-lined Plate
The sealing material remained, and while the glossiness of
the lined film disappeared, it was observed that red rust was
not exposed on the surface side.
5.1.14 Ultra-high Build Epoxy Resin-lined Plate
The sealing material partly peeled-off, and corrosion
occurred on the steel product. The hue of the lined filmchanged from grey to white.
5.1.15 Epoxy Resin/Polyurethane Resin-painted Plate
The end tar-epoxy sealing material remained, and it wasobserved that red and other rust were not exposed. As to thehue of the painted film on the surface side, excluding
around the bolt hole, the top coating (polyurethane resin
coat: white) and the intermediate coating (epoxy resin
paint: white) nearly halfway disappeared, and the primer
coating was exposed. On the reverse side, while chalking
was observed, the painting film remained.
5.1.16 Epoxy/Fluororesin-painted Plate
The end tar-epoxy sealing material remained, and it wasobserved that red and other rust were not exposed. As to thehue of the painted film on the surface side, excluding
around the bolt hole, the top coating (fluororesin paint:
white) and the intermediate coating (epoxy resin paint:
white) nearly disappeared, and the primer coating was
exposed. On the reverse side, while chalking was observed,
the painting film remained.
5.1.17 Epoxy Resin/Acrylic Silicon Resin-painted Plate
The end tar-epoxy sealing material remained, and it wasobserved that red and other rust were not exposed. As to thehue of the painted film on the surface side, excluding
around the bolt hole, the top coating (acrylic silicon resin
paint: white) and the intermediate coating (epoxy resin
paint: white) completely disappeared, and the primer coat61

5.2 Calculation Results for Weight,
Corrosion Amount and Corrosion
Rate
Respective specimens were subjected to pickling and theirweight before and after pickling was measured using a precision balance. Table 14 shows the measurement results.
Table 14 Measurement Results for Weight
Specimen
No.

Initial weight
B (g)After pickling
C (g)Weight loss
D=B-C (g)Surface area
E (cm²)

Corrosion amount
F=D/E (g/cm²)

Corrosionrate(mm/y)

Pickling condition(Hydrochloric acidpickling: JISF method)
12% dilute hydrochloric
acid sol.
20℃×Max. 33 min.

(Citric acid pickling)
10% hydrogen citrate
diammonium sol.
90℃×Max. 60 min.

(Citric acid pickling)
10% hydrogen citrate
diammonium sol.
90℃×Max. 60 min.
(Hydrochloric acid pickling)
15% dilute hydrochloric
acid sol.
20℃×3 min.
(Chromic acid pickling)
20% chromic acid sol.
80℃×1 min.

Corrosion rate (mm/y) =Corrosion amount (g/cm²)
Specific gravity*³

÷24 (y)×10 (mm)*³ Calculated using specimen type A=7.86, type B=7.93, type C-01=4.51, type C-02=8.92, type C-03=2.66*Initial weight, surface area: Use of the data of identical specimen numbers described in the past report*

62

5.3 Measurement Results for Plate
Thickness
The plate thickness of the specimens subjected to pickling
was measured. Table 15 shows the measurement results.

Table 15 Measurement Results for Plate Thickness
Plate thickness (mm)Specimen
Measurement position
No.

Average

Initialaverage

Loss*Initial average: Average value of the data of identical specimen numbers described in the past report**Loss of plate thickness: Significant figures in three decimal places (however, the initial thickness was calculated in two decimal places.)63

5.4 Measurement Results for Pitting Corrosion and Crevice Corrosion
The pitting corrosion on the surface of respective specimens after pickling and their crevice corrosion around thebolt hole, excluding coated/sprayed/lined/painted plates(kind D), were measured-ordinary carbon steel specimens
by the use of a depth gauge and stainless steel/nonferrous
metal by the use of an optical microscope.

In the measurement of pitting corrosion, 5 corrosion
depths covering from the maximum value to the following
4 values in the general section of specimens were recorded,
and in the measurement of crevice corrosion, 3
left/right-side corrosion depths covering from the maximum
value to the following 2 values at the insulation washer-specimen gap were recorded (ordinary carbon steel specimen: 5 depths regardless of left and right sides).
Table 16 shows the measurement results.

Table 16 Measurement Results for Pitting Corrosion Depth and Maximum Crevice Corrosion Depth at Insulation
Washer-Specimen Gap(μm)
SpecimenNo.

Pitting corrosion depth at general section

Maximum crevice corrosion depth at insulation
Average washer-specimen gap
of 5
depths
Right
Right
Right
Left
Left
Left
1
2
3
1
2
3

Reference

Depth gaugemeasurement
Opticalmicroscopemeasurement*Underlined figures: Maximum pitting corrosion and crevice corrosion depth

645.5 Measurement Results for Film
Thickness
The film thickness of coated/sprayed/lined/painted plates(kind D) was measured. Regarding the metallic-coated/sprayed plates of these specimens, the film thickness
after pickling was measured. Table 17 shows the measurement results.

Table 17 Measurement Results for Film Thickness
Specimen No.

Measurement position(mm)
Average

InitialaverageChangeof film
thickness

Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Measurement instrument: SWT-8200 II (Sanko-made) (1 mm or lower)
A456CFTS (Elcometer-made) (1 mm or higher)
D-01: Initial value of coating film thickness―No data
D-06~D-10: Initial value at reverse side―No data65

5.6 Measurement Results for Adhesive
Strength
The adhesive strength of coated/sprayed/lined plates (kindD) was measured using an Instron tester. Table 18 shows
measurement results.

Table 18 Measurement Results for Adhesive Strength
Specimen
No.

Initial adhesivestrength(kg/cm²)

Adhesive strength (kg/cm²)
2nd

1st

3rd

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion fracture

Adhesion peeling
Cohesion of primer
coating

Adhesion peeling
Cohesion of primer
coating

Cohesion ofintermediate coatin
Cohesion of primer
coating

Cohesion ofintermediate coatin
Cohesion of primer
coating

Cohesion ofintermediate coatin
Cohesion of primer
coating

Cohesion ofintermediate coatin
Cohesion of primer
coating

Cohesion of top
coating
Cohesion of primer
coating

Cohesion of top
coating
Cohesion of primer
coating

Cohesion of top
coating
Cohesion ofintermediate coatin
Cohesion of primer
coating

Adhesion peeling
Cohesion ofintermediate coatin
Cohesion of primer
coating

Adhesion peeling

Adhesion peeling: Film peeling from adhered surface; Cohesion fracture: Cohesion fracture within film
Measurement instrument: Instron 3366 (Instron-made)66

70 or more

5.7 Detection Results for Pinholes
Organic-lined and heavy-duty painted plates were subjected
to pinhole detection. Table 19 shows the detection results.
Pinholes were not detected on the surface side of all ofthese plates. While pinholes were detected on the reverse

Occurrence/no occurrence of pinhole
Surface side

Reverse side

5.8 Measurement Results for Insulation Resistance
The insulation resistance of organic-lined and heavy-duty
painted plates was measured to find the volume resistivity.
Table 20 shows the measurement results. All plates showed
an insulation resistance of 1011 Ω・cm. However, the effectof insulation resistance lowering on corrosion resistance
was not found, and thus it is considered that these plates
have sound corrosion resistance.

Table 19 Detection Results for Pinholes
Specimen No.

surface of polyethylene-lined plate (D-05), the cause of pinhole detection was due to the deterioration of edge sealingmaterials.

Voltage

5.9 Measurement Results for Impedance
The impedance of organic-lined and heavy-duty painted
plates was measured to find the dielectric loss coefficient(tan δ value). Table 21 shows the measurement results.

×: Occurrence of pinhole○: No occurrence of pinhole
Measurement instrument: PINHOLEDETECTOR TRC-250B(Sanko-made)Table 20 Measurement Results for Insulation ResistanceSpecimen No.

Film
thickness(μm)

Measurement value (Ω)
1-minute value

2-minute value

Volume resistivity rate (Ω·cm)(1-minute value)(2-minute value)

Initial volume
resistivity rate(Ω·cm)

Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside
Surfaceside
Reverseside

Measurement instrument: SM-8220 (HIOKI-made)Electrode area: 4×4 cm² Measurement voltage: 100 V
Volume resistivity rate (Ω·cm)=[Insulation resistance (Ω)×Electrode area (cm²)]/Film thickness (μm)

67

Table 21 Measurement Results for ImpedanceSpecimen No.

Surfaceside

Reverseside

Surfaceside

Reverseside

Surfaceside

Reverseside

Surfaceside

Reverseside

Surfaceside

Reverseside

Surfaceside

Reverseside

68

Measurement instrument: D-55 Type (Mita Musen Kenkyusho-made) Electrode: 4×4 cm²
f: Frequency (Hz) D: Dielectric loss coefficient (tan δ) C: Electrostatic capacity (nF) G: Conductance (μS) R: Resistance (Ω)*tan δ=1/(2πfCR)

Initial value(tan δ)5.10 Measurement Results for Color
Difference and Glossiness
The color difference and glossiness of heavy-duty painted
plates were measured. Table 22 shows the measurement
results.
Table 22 Measurement Results for Color Difference and GlossinessColor difference

Specimen No.

Glossiness

Surface side
Reverse side
Surface side
Reverse side
Surface side
Reverse side
*Color difference: Average value obtained by measurement of 3 sections of specimen*Glossiness: Measurement of center section of specimen surface using glossiness meter (60°)
Color difference measurement instrument: CR-400 (Minolta-made)
Glossiness measurement instrument: IG-331 (HORIBA-made)5.11 Measurement Results for Film
Hardness
The film hardness of organic-lined and heavy-duty painted
plates was measured. Table 23 shows the measurement
results.
Table 23 Measurement Results for Lining/Painting Film Hardness
Pencil hardness
Specimen No.

24th year

Initialvalue

Barcol hardness
24th year

Initialvalue

Shore hardness
24th year

Initialvalue

Surface side
Reverse side
Surface side
Reverse side
Surface side
Reverse side
Surface side
Reverse side
Surface side
Reverse side
Surface side
Reverse side
Barcol hardness meter: GYZJ 943-1 (BARBER-COLMAN COMPNY-made)Shore hardness meter: Shore D MK-19-2 (Teclock-made)69

5.12 Observation of Metallic-coated/sprayed
Sections (SEM Analysis)
As for the metallic-coated/sprayed plates, the coated/sprayed section after pickling was observed. Photos 2~5
show the observation results.
As for the aluminized stainless steel plate (D-01), thealuminized layer remained soundly in place. It is consideredfrom observation results that the aluminized stainless steel

plate maintained corrosion resistance.
As for the hot-dip galvanized plate (D-02), deteriorationof galvanizing layer progressed and cracking occurred in
the zinc-iron alloy layer. However, it was confirmed that
corrosion did not yet reach the surface of steel product.
As for the zinc-aluminum alloy-sprayed plate (D-03)
and aluminum-sprayed plate (D-04), the sprayed layer of
100 μm or more remained, and thus it is considered thatthese plates maintained corrosion resistance.

Coating

Steel

Photo 2 Observation of Metallic-coated Sections: Aluminized Stainless Steel Plate (D-01)

Coating

Steel

Photo 3 Observation of Metallic-coated Sections: Hot-dip Galvanized Plate (D-02)

Spraying

Steel

Photo 4 Observation of Metallic-sprayed Sections: Zinc-Aluminum Alloy-sprayed Plate (D-03)

Spraying

Steel

Photo 5 Observation of Metallic-sprayed Sections: Aluminum-sprayed Plate (D-04)
Measurement instrument: Scanning electron microscope (SEM) S4300SE (Hitachi-made)70

5.13 Measurement of Cl Concentration(EPMA Analysis)
As for the organic-lined and heavy-duty painted plates,
chlorine (Cl) concentration on the lined/painted section wasmeasured by means of EPMA analysis. Figs. 1~6 andPhotos 6~11 show measurement results.
As for both of the polyethylene-lined plate (D-05) andpolyurethane-lined plate (D-06), it was seen that chlorine
did not penetrate into the lining and chlorine did not concentrate at the lining.

As for the ultra-high build epoxy resin-lined plate(D-07), it was seen that chlorine existed in entire lining, but
it is considered that the cause for this was derived from theepoxy resin proper.
As for both the epoxy resin/polyurethane resin-painted
plate (D-08) and epoxy/fluororesin-painted plate (D-09), it
was seen that a trace amount of chlorine uniformly existed in
the painting film. However, it could not be judged whether or
not the existence of chlorine was caused by external factors.
As for the epoxy resin/acrylic silicon resin-painted plate(D-10), it was seen that chlorine did not penetrate into the painting film and chlorine did not concentrate at the painting film.

Fig. 1 EPMA Analytical Results for Cl Concentration: Polyethylene-lined Plate (D-05)

D-05-109 16 09:56 2016
Stage: Scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.012e-008 A
Beam shape: SPOT
Beam diameter (um): 0
Measurement time (ms): 500.00
Number: 256
Gap: 7.24 um
Distance: 1.846 mm
Average: 0.036

Cl
concentration
(%)

Steel

Distance from base steel surface (mm)FilmPhoto 6 Polyethylene-lined
Plate (D-05)

Fig. 2 EPMA Analytical Results for Cl Concentration: Polyurethane-lined Plate (D-06)

D-06-109 16 10:09 2016
Stage: Scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.015e-008 A
Beam shape: SPOT
Beam diameter (um): 0
Measurement time (ms): 500.00
Number: 256
Gap: 13.68 um
Distance: 3.488 mm
Average: 0.084

Cl
concentration
(%)

Steel

Distance from base steel surface (mm)FilmPhoto 7 Polyurethane-lined
Plate (D-06)

71

Fig. 3 EPMA Analytical Results for Cl Concentration: Ultra-high Build Epoxy
Resin-lined Plate (D-07)
D-07-109 16 10:20 2016
Stage: Scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.012e-008 A
Beam shape: SPOT
Beam diameter (um): 0
Measurement time (ms): 500.00
Number: 256
Gap: 8.68 um
Distance: 2.213 mm
Average: 0.389

Cl
concentration
(%)

Steel

Distance from base steel surface (mm)FilmPhoto 8 Ultra-high Build
Epoxy Resin-lined
Plate (D-07)

Fig. 4 EPMA Analytical Results for Cl Concentration: Epoxy Resin/Polyurethane
Resin-painted Plate (D-08)
D-08-109 16 10:29 2016
Stage: Scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.011e-008 A
Beam shape: SPOT
Beam diameter (um): 0
Measurement time (ms): 500.00
Number: 256
Gap: 1.28 um
Distance: 326.40 mm
Average: 0.096

Cl
concentration
(%)

Steel

Distance from base steel surface (mm)

72

Film

Photo 9 Epoxy Resin/
Polyurethane Resinpainted Plate (D-08)

Fig. 5 EPMA Analytical Results for Cl Concentration: Epoxy/Fluororesin-painted
Plate (D-09)
D-09-109 20 10:30 2016
Stage: Scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.012e-008 A
Beam shape: SPOT
Beam diameter (um): 0
Measurement time (ms): 500.00
Number: 256
Gap: 1.30 um
Distance: 331.50 mm
Average: 0.088
Cl
concentration
(%)

Steel

Distance from base steel surface (mm)FilmPhoto 10 Epoxy/Fluororesinpainted Plate (D-09)

Fig. 6 EPMA Analytical Results for Cl Concentration: Epoxy Resin/Acrylic Silicon
Resin-painted Plate (D-10)
D-10-10
2 20 09:33 2017
Stage: Scan
Acceleration voltage: 15.0 kV
Irradiation current: 5.012e-008 A
Beam shape: SPOT
Beam diameter (um): 0
Measurement time (ms): 500.00
Number: 256
Gap: 1.02 um
Distance: 260.10 mm
Average: 0.094
Cl
concentration
(%)

Steel

Distance from base steel surface (mm)FilmPhoto 11 Epoxy Resin/Acrylic
Silicon Resin-painted
Plate (D-10)

73

6. Examination Results
6.1 Metallic Materials
As for the ordinary carbon steel, stainless steel and nonferrous metal, the measurement results for corrosion amount,plate thickness loss and maximum corrosion depth,
obtained from the 24-year exposure test at Suruga Bay,
were organized, the result of which is shown in Table 24.
The table also shows the pitting corrosion index (PREN) of
stainless steel. The following examination results weremade clear for these materials.

6.1.1 Ordinary Carbon SteelThe corrosion rate at Suruga Bay was 0.02 mm/y. When
compared to the corrosion rate of 0.18 mm/y at Okinotorishima and the average corrosion rate at general splash
zones (0.2~0.4 mm/y), the corrosion rate at Suruga Bay wasconsiderably low.

Table 24 Assessment Results for Corrosion Amount of Metallic Materials
Specimen
No.

Plate
Maximum Maximum
crevicethickness
pitting
corrosion
measurement corrosion
depth atdepth
atCorrosion Average plate
insulation
Corrosion
Weight amount rate
thickness loss generalwasher-specsection (ɥm) imen gap (ɥm)
loss (g) (g/cm²) (mm/y)
(mm)

Weigh
measurement

SpecimenGroup Kind
Ordinary
Ordinary
carbon steel carbon steel

Type

Composition

PREN

Austenitic type
Stainlesssteel(No corrosion) (No corrosion)

Duplextype
Ferritic
type
Titanium

Nonferrous Copper
metal Aluminumalloy(No corrosion) (No corrosion)*Data adjustment for B-07: While 22Cr was adopted in the past report*, in the current assessment 20Cr was adopted that seems correct.
*Data adjustment for B-08: While 0.7Mo was adopted in the past report*, in the current assessment 0.9Mo was adopted that seems correct.

74

6.1.3 Nonferrous Metal
In titanium, corrosion was not found. In copper, slight pitting corrosion and crevice corrosion occurred, and in aluminum alloy, pitting corrosion and crevice corrosion surpassing 100 μm occurred.

Suruga Bay

Crevice corrosion depth (μm)
Crevice corrosion depth (μm)

Suruga Bay

Austenitic type
Duplex typeFerritic type

Suruga Bay

Austenitic type
Duplex typeFerritic typeFig. 9 Relationship between Maximum Pitting
Corrosion Depth of Stainless Steel and Pitting
Corrosion Index (PREN) (General Section)
Suruga Bay

Austenitic type
Duplex typeFerritic type

Austenitic type
Duplex typeFerritic typeFig. 10 Relationship between Maximum Crevice
Corrosion Depth of Stainless Steel and Pitting
Corrosion Index (PREN) (Insulation WasherSpecimen Gap)
Crevice corrosion depth (μm)

Pitting corrosion depth (μm)

Fig. 7 Relationship between Maximum Pitting
Corrosion Depth of Stainless Steel and Pitting
Corrosion Index (PREN) (General Section)

Fig. 8 Relationship between Maximum Crevice
Corrosion Depth of Stainless Steel and Pitting
Corrosion Index (PREN) (Insulation WasherSpecimen Gap)

Pitting corrosion depth (μm)

6.1.2 Stainless SteelSlight pitting corrosion and crevice corrosion occurred inall stainless steel specimens. As shown in Fig. 7, the maximum pitting corrosion depth at the general section (maximum value of each specimen) was organized using the pitting corrosion index (PREN: Cr+3Mo+16N), and as aresult, it was known that the maximum pitting corrosion
depth of stainless steel can be organized using the PREN.
The crevice corrosion occurred at the insulation washer-specimen gap, and the crevice corrosion depth could beorganized using the PREN (Cr+3Mo+16N or
Cr+3Mo+0.5Ni), as shown in Fig. 8. In the survey of stainless steel specimens at Suruga Bay, when the PREN of
Cr+3Mo+16N (or Cr+3Mo+0.5Ni) was 30 or more, notonly the maximum pitting corrosion depth at the general
section but also the maximum crevice corrosion depth at
the insulation washer-specimen gap were 100 μm or lessafter 24 years of exposure. As a result, it can be said thatstainless steel with a PREN of 40 or more is particularlyhigh in corrosion resistance.
Further, the maximum pitting corrosion depth at the general section and the maximum crevice corrosion depth at
the insulation washer-specimen gap were organized using
the PREN (Cr+3Mo+10N) used in the “Research on Corrosion-protection Technologies for Steel Structures in Splash,
Tidal and Submerged Zones” of the Public Works ResearchInstitute, and as a result, it was known that these depths canbe organized even by the use of PREN (Cr+3Mo+10N) as
with the use of PREN (Cr+3Mo+16N) as used in the survey(refer to Figs. 9 and 10).

Suruga Bay

Austenitic type
Duplex typeFerritic type75

6.2 Coated/Sprayed/Lined/Painted Plates
The following results were understood from the survey ofmetallic material-coated/sprayed, organic-lined and heavy
duty painted specimens (see Table 25).
6.2.1 Metallic-coated/sprayed Plates
In every exposed specimen, it was observed that corrosion
loss did not reach the base metal beneath the coated andsprayed layers and deterioration in the adhesion of coatedand sprayed layers was not observed. In all of aluminizedstainless steel plate (D-01), hot-dip galvanized plate (D-02),zinc-aluminum alloy-sprayed plate (D-03) and aluminum-sprayed plate (D-04), while white rust occurred, thecoated or sprayed layer showed no corrosion loss but
remained, and as a result, it is considered that metallic-coated/sprayed plates maintained corrosion resistance.
While the loss of the galvanizing layer in coastal areas is
generally 2 μm/y, no change was observed in the film thickness of hot-dip galvanized plate (D-02), but the film thickness increased on the reverse side of zinc-aluminumalloy-sprayed plate (D-03). As for the sprayed film, it wasobserved that the thickness of the film of zinc-aluminumalloy-sprayed plate (D-03) increased by about 1.5 times,
and that of the aluminum film of aluminum-sprayed plate(D-04) increased by about 1.1 times. The increase of film
thickness is considered to be attributable to swelling of thesprayed film caused by rusting of the film. In metallic material coating/spraying, the film loss did not occur for morethan 20 years of exposure even at the offshore dry environment at Suruga Bay, and thus metallic material coating andspraying are assessed as a useful corrosion-protection
method.

6.2.2 Organic-lined Plates
As for the polyethylene-lined plate (D-05), it was observed
that, following the occurrence of cracking at the sealed section, lined materials peeled off from the sealing edge. Peeling occurred on about a half area of specimen surface, andwhile the lowering of insulation resistance and impedancefrom their initial level was observed at the section where
peeling was not caused, these values were kept to a sufficient level, and it is judged that high corrosion resistance
was maintained.
As for the polyurethane-lined plate (D-6), it is judgedthat polyurethane lining maintained high corrosion resistance due to such factors as maintaining of high-level insulation resistance and impedance, no observation of chlorine
penetration into the lined layer and maintaining of highadhesive strength of 4 MPa or more in spite of the loweringof the adhesive strength from its initial level. The loss offilm thickness due to ultraviolet ray-induced film deterioration was 636 μm, and the average film loss rate at 25 μm/y
was high, but because several-millimeter thick polyurethane was lined, it is assumed that the polyurethane-lined
plate will offer sufficient corrosion resistance even overcoming decades.
As for the ultra-high build epoxy resin-lined plate(D-07), cracking and peeling were observed in the thin film
section at the sealing material edge. Further, the film thickness loss due to ultraviolet ray-induced film deterioration
showed a low value of 108 μm, but the lowering of the surface layer hardness was observed. In spite of these adverse
conditions, it is assumed that corrosion resistance wasmaintained due to such factors as maintaining of high-levelinsulation resistance and impedance at the center of thespecimen and no observation of chlorine penetration into
lined layer.

Table 25 Survey Results for Metallic Coating/Spraying, Organic Lining and Heavy-duty Painting
Kind

Metallic coating/spraying

Organic lining

Heavy-duty painting

76

Specimen No.

Assessmentof corrosion
resistance

Survey results

D-01

Coated layer remained and corrosion resistance was assumed to maintain.

D-02

Coated layer remained and corrosion resistance was assumed to maintain.

D-03

Sprayed layer remained and corrosion resistance was assumed to maintain.

D-04

Sprayed layer remained and corrosion resistance was assumed to maintain.

D-05

Deterioration from sealing edge was observed, but remaining lined section was
sound.

D-06

Film thickness loss was observed, but corrosion resistance was favorable.

D-07

Film thickness loss was observed, but corrosion resistance was favorable.

D-08

Top-coating layer at surface side disappeared. Corrosion resistance atintermediate and primer coatings were sound.

D-09

Top-coating layer at surface side disappeared. Corrosion resistance atintermediate and primer coatings were sound.

D-10

Top-coating layer at surface side disappeared. Corrosion resistance atintermediate and primer coatings were sound.

Except for polyethylene lining for which corrosion resistance could not properly be assessed due to the deterioration of sealing edge, it is expected for organic linings to beable to maintain corrosion resistance over coming decades
in the exposure test.

• Organic-lined steel products: While deterioration at part6.2.3 Heavy-duty Painted Plates
In every heavy-duty painted specimen, loss of the top-coating layer at the surface side was observed.
As for the epoxy resin/polyurethane resin-painted plate(D-08), the top-coating layer completely disappeared at ahalf of the painted surface, and primer-coating layer was
exposed. However, it is considered that corrosion resistance
was still maintained in spite of the lowering of insulation
resistance, impedance and adhesive strength from their initial level.
As for the epoxy/fluororesin-painted plate (D-09), thetop-coating layer completely disappeared on entirely painted surfaces, and the primer-coating layer was exposed.
However, it is considered that corrosion resistance was still
maintained in spite of the lowering of insulation resistance,
impedance and adhesive strength from their initial levels.
As for the epoxy resin/acrylic silicon resin-painted plate(D-10), the top-coating layer completely disappeared on
entirely painted surfaces, and the primer-coating layer was
exposed. However, it is considered that corrosion resistance
was still maintained in spite of the lowering of insulation
resistance, impedance and adhesive strength from their initial level.
The loss rate of painting film was D-10 (12 μm/y)＞
D-09 (9 μm/y)＞D-08 (7 μm/y), which showed that the loss
rate of acrylic silicon painting film was high and that ofpolyurethane painting film was low. In the offshore area,
because the loss of the top coating due to ultraviolet ray-induced deterioration was high in the top coating for use formaintaining color tone, it is recommended to apply repainting at an earlier stage.

Reference
1) Report of Specimen Installation, Construction Material
Durability Tests at Okinotorishima: 1st-phase Research
Plan (Dec. 1990), the Kozai Club (currently The Japan
Iron and Steel Federation)of the sealed section and ultraviolet ray-induced loss ofthe organic resin layer were observed, it is considered that
corrosion resistance is still sound even after 24 years of
exposure.

7. Conclusion
Surveys were made of steel products, nonferrous metals
and various types of coated/sprayed/lined/painted steel materials exposed over 24 years at the No. 1 deck of the
Marine Engineering Research Facility at Suruga Bay. The
environment at Suruga Bay is categorized as a C4 corrosive
environment and is a typical offshore corrosive environment in Japan. The results of long-term exposure tests conducted for a wide-range of steel products are scarcely available, and accordingly the data obtained in this test over 24
years of exposure is valuable, among which are:• Ordinary carbon steel: The average corrosion rate was
0.02 mm/y.
• Stainless steel: In the PREN range of (Cr+3Mo+16N)≧
30 or (Cr+3Mo+0.5Ni)≧30, favorable corrosion resistance was obtained.
• Nonferrous metal: Corrosion was not observed in titanium, but pitting corrosion and crevice corrosion wereobserved in aluminum alloy and copper.
• Metallic-coated/sprayed steel products: The corrosion-protection layer or the metallic-coated/sprayed layer
remained, and thus it is considered that corrosion-protection performance is sound.
77The Japan Iron and Steel Federation