51JR EAST Technical Review-No.37-2017

Special edition paper

1. Introduction

Electric power lines that supply power to trains are called overhead lines, and their steel supports such as pipe struts and beams are called railway electrification infrastructure. Fig. 1 is an example of the infrastructure. Various materials are used for that infrastructure, including reinforced concrete, steel, and aluminum, but galvanized steel has been widely used since the pre-privatization Japanese National Railways era due to its strength and resistance to corrosion. Galvanized steel is steel material coated with zinc, and it has strength equivalent to that of steel while gaining high resistance to corrosion from zinc’s cathodic protection and coating effects with zinc oxide. However, zinc is lost over the long term and steel loses strength due to corrosion;1) thus, rebuilding and application of anti-corrosion paint are imperative.

Fig. 2 shows the relationship between the volume of galvanized steel beams at JR East and the year they were installed. The peak of construction was in the 1960s to 1980s, which includes Japan’s era of high economic growth, when more than 1,000 new beams were installed annually. Corrosion rate determined from past exposure tests showed that galvanized steel beams of JR East have a life expectancy of about 60 years,2) and this large volume of infrastructure will soon be reaching the end of its service life. However, only about 600 new beams a year can currently be installed due to cost and construction capacity, so it will be difficult to rebuild all of the infrastructure at one time. In this study, we investigated the actual state of zinc and steel corrosion and developed anti-corrosion paint where the labor of application can be reduced with the aim of extending the service life of galvanized steel railway electrification infrastructure.

Research for Prolonged Life of Galvanized Steel Railway Electrification Infrastructure

* Technical center, Research and Development Center of JR East Group

Galvanized steel is usually used for railway electrification infrastructure. However, it requires rebuilding in the future because of corrosion by rain, sea wind, etc. Because there is much old galvanized steel railway electrification infrastructure at JR East, it is impossible to rebuild all of it at suitable timing. Therefore, we investigated corrosion using exposed test pieces to obtain detailed corrosion rate and developed a new single coat system.

Abstract

Takeshi Kurokawa*Masahiko Honda*

•Keywords: Galvanized steel, Corrosion survey, Single coat, Painting

0

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20162006199619861976196619561946

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Railway electrificationinfrastructure (beam)

Railway electrificationinfrastructure (pole)

Fig. 1 Railway Electrification Infrastructure Fig. 2 Volume of Existing Galvanized Steel Beams by Year Installed

52 JR EAST Technical Review-No.37-2017

Special edition paper

2. Zinc and Steel Corrosion Rate Investigation

Corrosion rate, the basis for life expectancy set up to now, was determined by exposure tests in typical places of environments such as urban areas and industrial belts. However, JR East’s railway electrification infrastructure is set up along railway lines, so we can surmise that corrosion rate differs by location. In order to identify the actual state of corrosion rate, we temporarily set up three zinc and three steel test pieces per power pole at 486 locations along JR East electrified lines and investigated corrosion rate from mass change before and after exposure.3) Fig. 3 shows an exposure test in progress. The interval between test pieces was set to approx. 15 km in ordinary sections taking into account Automated Meteorological Data Acquisition System (AMeDAS) observation intervals and approx. 5 km in sections with salt damage where corrosion progresses faster. Exposure times were set to 1, 2, or 3 years, with corrosion rate calculated as decrease in amount of thickness per 365 days of exposure. Fig. 4 shows zinc and steel corrosion rates and “sections where salt damage should be taken into consideration” from JR East electrification infrastructure (contact line) design and construction standards. Corrosion rate is found from test pieces with exposure time of 1 year where corrosion product protection effect is small, and the same applies with the following diagrams. Corrosion rates were compiled in corrosivity categories of ISO 9223 (2012) for ease of understanding. Table 1 shows the relation between corrosion rate and the atmospheric corrosivity categories in ISO 9223 (2012).

Overall, we obtained results that correspond to those of past findings where corrosion rate is faster in coastal areas and slower in inland areas, but localized variance was seen in corrosivity categories. Fig. 5 shows corrosion rate at the Keiyo, Uchibo, and Sotobo lines on the Boso Peninsula and estimated number of years it takes until galvanization loss. This estimated number of years it takes until galvanization loss was calculated from the minimum thickness of 76 μm in zinc galvanized coating standard HDZ55 and corrosion rate of zinc. Service life of infrastructure is related to corrosion of steel as well; but looking at estimated number of years it takes until galvanization loss tendencies for simplification reasons, we found that there was much variance with 30 to 65 years for the Keiyo Line, 26 to 84 years for the Uchibo Line, and 14 to 62 years for the Sotobo Line. At a location of increased corrosion rate at around the 70 km mark on the Sotobo Line (A in Fig. 5), track was laid in steep topography facing the ocean where Japan Meteorological Agency annual average coastal wave analysis charts show that wind blows from the ocean to the land. For this reason, corrosion is assumed to be particularly accelerated. Taking this into account, we assume that infrastructure can be used past its life expectancy of 60 years if taking into consideration individual location. On the other hand, at places where estimated number of years to galvanization loss is shorter than life expectancy, it is believed that the results of this investigation should be taken into consideration and plans promoted for rebuilding or coating.

CXC5C4C3C2C1

Corrosivity category (zinc)

ISO9223(2012)

CXC5C4C3C2C1

ISO9223(2012)

Heavy salt damage

Salt damageOrdinary

Design/construction standard (sections where salt damage should be taken into consideration)

Corrosivity category (steel)

(Shown with line map and corrosivity categories added to Geospatial Information Authority of Japan online blank map)

100 km 100 km 100 km

■▲●

Category Unit Zinc Carbon steel Corrosivity C1

μm/Year

r≦0.1 r≦1.3 Very lowC2 0.1＜r≦0.7 1.3＜r≦25 LowC3 0.7＜r≦2.1 25＜r≦50 MediumC4 2.1＜r≦4.2 50＜r≦80 HighC5 4.2＜r≦8.4 80＜r≦200 Very highCX 8.4＜r≦25 200＜r≦700 Extreme

r: Corrosion rate

Table 1 Corrosion Categories of ISO 9223: 2012 and Corrosion Rate

Fig. 4 Corrosion Rate of Zinc and Steel from One Year of Exposure (shown with corrosivity categories in ISO 9223: 2012)

Steel test specimen

Zinc test specimen

Fig. 3 Zinc and Steel Test Specimen Exposure

53JR EAST Technical Review-No.37-2017

Special edition paper

3. Development of Single Coat Anti-corrosion Paint and Evaluation by Accelerated Degradation Tests

Coating with anti-corrosion paint is effective for extending the life of galvanized steel railway electrification infrastructure. However, coating of railway electrification infrastructure takes many days due to that being done in the short time when power is off and the need to apply a primer and top coat. Also, there is a high risk of processes being delayed by cancelation of work due to weather and train delays. We therefore developed a single coat anti-corrosion paint (without additional primer or topcoat) for heavy-duty anti-corrosion uses jointly with Japan Carboline Co., Ltd. in order to reduce the number of work days needed. Fig. 6 shows comparison of coating processes.

With the new paint, we aimed to gain equivalent or greater anti-corrosion and weather-resistance properties as the current two-coat system: Carbomastic 15 II (anti-corrosion paint) and Carbothane 133 HB (weather resistant paint) (hereinafter, the “current paint”) employed to coat galvanized steel railway electrification infrastructure.

In development, we made two types of prototype paint: silicone modified epoxy resin paint with an emphasis on weather resistance (developed paint 1) and epoxy polyol resin paint with an emphasis on anti-corrosion (developed paint 2). Those paints were applied to galvanized steel test samples where corrosion and pre-coating cleaning (surface treatment) were performed. And those samples were then evaluated by putting them through accelerated degradation tests. In accelerated degradation tests, we perform ultra-accelerated weather-resistance tests for 560 hours where approx. 10 years worth of ultraviolet energy is applied. Then, we put the tests samples through 800 hours of combined cycle of Cycle A in Annex C of JIS K 5600-7-9 in order to promote salt damage corrosion. For weather resistance, we evaluated the rate of decrease in coating thickness; and for corrosion resistance, we evaluated degree of coating blistering, rust, cracking by JIS K 5600-8 and adhesion by JIS K 5600-5-7.

Decrease in coating thickness after 560 hours of ultra-accelerated weather-resistance tests was 15.20 μm with the current paint, 11.29 μm with developed paint 1, and 15.60 μm with developed paint 2. From this, we discovered that developed paint 1 has better weather resistance than the current paint. Developed paint 2 was slightly poorer than the current paint, but that difference was just 0.3% the specified thickness of 125μm, and it is projected to be of a level equivalent to that of the current paint. Life expectation for coating is inversely proportional to amount of decrease, and developed paint 1 is projected to have better service life than the current paint and developed paint 2 an equivalent level of service life.

Table 2 shows the results of combined cycle tests. In those, evaluation of the test sample out of the three where corrosion damage was most advanced was extracted for each condition. Developed paint 1 has about an equivalent level of anti-corrosion performance as the current paint, regardless of the test sample base. Developed paint 2 has about an equivalent level of anti-corrosion performance as the current paint with test samples of rust steel plate (without surface treatment), but with test samples of conditions closest to those of infrastructure that is coated at JR East— rust steel plate (non-woven fabric abrasive preparation) and rust steel plate (wire brush preparation)—it exhibited superior anti-corrosion performance.

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Keiyo Line kilometrage

Zinc (left axis) Steel (right axis)

To Tokyo To Soga

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0 20 40 60 80 100Sotobo Line kilometrageTo Chiba To Awa-Kamogawa

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0 20 40 60 80 100 120Uchibo Line kilometrageTo Soga To Awa-Kamogawa

Keiyo Line

Uchibo Line

Awa-Kamogawa

ChibaSoga

Tokyo

A

39 years58 years

30 years38 years 37 years 44 years

65 years

26 years 29 years 63 years 84 years

Zinc (left axis) Steel (right axis)

Zinc (left axis) Steel (right axis)

(Shown with line map and place names added to Geospatial Information Authority of Japan online shaded-relief map)

Sotobo Line

62 years 58 years 50 years52 years

35 years 54

years 41 years

24 years31 years

14 years16 years

42 years 41 years

Fig. 5 Corrosion Rates on Keiyo, Uchibo, and Sotobo Lines

54 JR EAST Technical Review-No.37-2017

Special edition paper

Material costs of developed paint 1 are anticipated to be about 1.7 times that of the current paint and those of developed paint 2 are expected to be about 1.2 times. However, overall cost reductions are anticipated with the decreased labor costs accompanying reduction in number of days for work. Next, we plan to apply the two developed paints to JR East galvanized steel railway electrification infrastructure. Upon confirming workability, economy, and other factors, we plan to implement effective increase in infrastructure service life by expanding the areas where they are applied.

4. Conclusion

This paper introduced the issues faced by railway electrification infrastructure using galvanized steel. We further covered the actual state of corrosion rate of zinc and steel affecting life expectancy and the development and evaluation of single coat anti-corrosion paint, which improves on the issues of paint as a means to increase life expectancy.

Corrosion of galvanized steel railway electrification infrastructure is progressing constantly. But we intend to use the methods covered herein to improve life expectancy of infrastructure in areas where corrosion rate is slow and places where rebuilding will be difficult, such as at bridges and viaducts. Through this, we intend to harmonize rebuilding costs and achieve facility maintenance with high cost effectiveness.

Reference:1) Makoto Tanaka, Takafumi Enari, Hiroto Machida, “Extension of Service Life of Corroded Hot Dip Galvanized Steel and Weathering Steel”

[abstract in English], RTRI Report Vol. 15, No. 7 (2001): 35-40,2) Tadashi Yoshida, “Development of Beams for Sections Susceptible to Salt Damage”, JR EAST Technical Review No. 17 (2010): 37-40.3) Masahiko Honda, Masashi Shimbo, “Corrosive environment survey using steel and zinc test piece in eastern Japan”, Proceedings of the 22nd Jointed

Railway Technology Symposium ( J-Rail 2015) No. 15-63 (2015).

Before coating Day 1 (night) Day 2 (day) Day 2 (night) From Day 3 (day)

Current coating/double coat

Waiting to dry Top coat Completed

Developed paint/single coat

Cleaning + primer

Cleaning + single coat Completed

Fig. 6 Comparison of Coating Processes

Test piece base Type of paint

Test piece evaluation (compared with JIS K evaluation sample, smaller values are better)JISK5600-8-2 JISK5600-8-3 JISK5600-8-4 JISK5600-5-7

Blistering Rust Cracking Adhesion (pull off method)Size Density Class Size Fracture strength

Galvanization0 0 Ri 0 00 0 Ri 0 0

Current paint Developed paint 1Developed paint 2Current paint Developed paint 1Developed paint 2Current paint Developed paint 1Developed paint 2

Current paint Developed paint 1Developed paint 2Current paint Developed paint 1Developed paint 2

0 0 Ri 0 0

MPaMPaMPa

Zinc/steel alloy layer0 0 Ri 0 00 0 Ri 0 00 0 Ri 0 0

MPaMPaMPa

Rust steel(wire brush preparation)

2 2 Ri 1 02 2 Ri 1 00 0 Ri 0 0

MPaMPaMPa

Rust steel(non-woven fabric

abrasive preparation)

3 2 Ri 1 02 2 Ri 1 00 0 Ri 0 0

MPaMPaMPa

Rust steel(no preparation)

3 2 Ri 2 00 0 Ri 0 03 2 Ri 1 0

MPaMPaMPa

Table 2 Test Sample Evaluation After Ultra-accelerated Degradation Tests and Combined Cycle