The purpose of thesis: Research on the influence of climatic and environmental parameters to the formation, structure and properties of corrosion products formed on the WS surface in different climatic regions of Vietnam. Research on the mechanism of forming protective rust layer on WS and corrosion resistance of WS in tropical climate of Vietnam.
Trang 1MINISTRY OF EDUCATION
AND TRAINING
VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY
GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
…… ….***…………
HOANG LAM HONG
STUDY ON THE FORMATION AND CORROSION
PROTECTIVENESS OF RUST LAYER ON WEATHERING STEEL
IN TROPICAL ATMOSPHERE OF VIETNAM
Major: Metallography Code number: 9.44.01.29
ABSTRACT OF THESIS
Hanoi – 2019
Trang 2The Thesis finished at Graduate University of Science and
Supervisors: Assoc Prof Dr Le Thi Hong Lien
Dr Pham Thy San
Opponent 1: Assoc Prof Dr Nguyen Xuan Hoan
Opponent 2: Assoc Prof Dr Nguyen Van Tu
Opponent 3: Prof Dr Mai Thanh Tung
The Thesis will be defended at the doctoral council which organizes
by Graduate University of Science and Technology - Vietnam Academy of Science and Technology at … h…’ date ……… 2019
The Thesis can find out at:
- The Library of Graduate University of Science and Technology
- National Library of Vietnam
Trang 3THE LIST OF PUBLISHED PAPERS
1 Le Thi Hong Lien and Hoang Lam Hong, “Characteristics of corrosion product layer formed on weathering steel exposed to the tropical climate of Vietnam”, Material Science and Application, Vol 4, 7A, 2013, pp 6-16 , USA
2 Le Thi Hong Lien and Hoang Lam Hong, “Study on atmospheric corrosion of weathering steel in Vietnam”, Proceeding of JSCE Material and environments
2014
3 Hoang Lam Hong, Le Thi Hong Lien and Pham Thi San, “Atmospheric corrosion of weathering steel in marine environment of Viet Nam”, Tạp chí Khoa học và công nghệ, tập 53-1B (2015)
4 Thy San P., Hong Lien L.T., Lam Hong H., Trung Hieu N., Thanh Nga N.T.,
“Establish mathematical models to predict corrosion of carbon steel and weathering steel in atmosphere of Viet Nam”, Tạp chí Khoa học và công nghệ, tập 53-1B (2015)
5 Le Thi Hong Lien and Hoang Lam Hong, “Corrosion behavior of weathering steel in atmosphere of Vietnam”, Proceeding of JSCE Material and environments 2015
6 Le Thi Hong Lien, Hoang Lam Hong, Pham Thi San, “Corrosion behavior of weathering steel in tropical atmosphere of Vietnam”, International Journal of Engineering Research and Science (IJOER), Vol.2, Issue 11 (2016)
7 Le Thi Hong Lien, Hoang Lam Hong, Pham Thi San, Nguyen Trung Hieu and Nguyen Thi Thanh Nga, “Atmospheric corrosion of Carbon steel and Weathering steel – Relation of corrosion and environmental factors”, Proceeding of JSCE Material and environments 2016
Trang 5PREFACE
Weathering Steel (WS) is low alloy steel that has been using as un-painted steel in mild atmosphere due to forming protective layer of corrosion product (rust) on steel substrate, which can act as a protective barrier against the inward transportation of corrosive species Using the WS on steel structures reduces the
effectively applied WS to works of transportation, bridges, works of the century
WS has been used popular in temperate zones due to its corrosion resistance However, the WS types have just stated using in Vietnam The possibility to apply of the weathering steel in the humid tropical climate with heavy rain of our country has not been fully and systematically researched So, in order to build the scientific bases of applying WS to construction works, highway bridges, works of the century, in Vietnam, and provide the necessary information for selecting and using effectively WS (Corten B) in each climatic
corrosion protectiveness of rust layer on weathering steel in tropical atmosphere of Vietnam”
The purpose of thesis:
formation, structure and properties of corrosion products formed on the
WS surface in different climatic regions of Vietnam
The research object: Corten B steel
Methods for research:
the Vietnam climate, WS was exposed to three different climate zones: (1) Northern (Hanoi) with four seasons, the temperature in the year fluctuates sharply, high humidity, long time of wetness and cold winter; (2) The humid marine atmosphere at Dong Hoi with seasonal temperature changes and high content of airborne sea salt; (3) Dry marine atmosphere at Phan Rang with low rainfall and high temperature in the year The impacts of climatic and environmental parameters on atmospheric corrosion of WS were studied using the samples exposed at 15 difference climatic zones in Vietnam: Son La, Yen Bai, Tam Dao, Cua Ong, Con Vanh, Hanoi, Dong Hoi, Quang Ngai, Pleiku, Phan Rang, Bien Hoa, Ho Chi Minh City, Can Tho, Rach Gia and Ca Mau
Trang 6 The corrosion rate is determined by mass lost method The parameters of the environment are collected and determined simultaneously in the same
optical microscopy) are used to study the morphology, structure, chemical composition and phase composition of the rust formed on WS
impedance spectroscopy EIS) were applied to study the corrosion protectiveness able of rust that formed on WS
Vietnamese tropical climate was implemented systematically The effect of atmospheric conditions on corrosion dynamics and the formation of protective rust layer on WS is discussed Some critical values of using unpainted WS in Vietnamese climate are initially mentioned in the thesis
application of WS in Vietnam, and provide the necessary information for effective selection and us of WS types in each climatic zone
database of WS in humid tropics, especially in Asia
The composition of thesis: the thesis including 113 pages, 17 tables and 94
figures was separated to 4 chapter:
Chapter 1: The overview of atmospheric corrosion of WS
Chapter 2: Experience and methods of research
Chapter 4: The formation and protectiveness of corrosion product formed
Conclusion
List of published papers and references
Chapter 1 THE OVERVIEW OF ATMOSPHERIC CORROSION OF WS
humidity, rainfall and atmospheric pollutions) and alloying elements to WS corrosion resistance
Trang 7 The mechanisms of forming and growing corrosion protectiveness rust layer
on WS were discussed
un-coated WS in some atmosphere in the world were shown
Chapter 2 EXPERIMENTAL AND METHODS OF RESEARCH 2.1 Material
Tab 2.1 The chemical composition of materials, mass %
2.2 Methods of research
2.2.1 Exposed test
The samples were exposed to atmosphere following ISO 8565 standard [118] The corrosion product (rust) was removed according to the standard ISO
into two kinds: long term period (1, 3, 6, 12, 24 and 36 months) and short term period (1, 3, 5, 7 and 14 days) The 12-month exposure were repeated three
2.2.2 Study on structure and characteristic of the corrosion product by physical methods
investigated by Scaning Electron Microscope - SEM
Raman spectroscopy
Trang 8 The cross-section structure of CP was investigated using Optical Microscope.
2.2.3 Study on corrosion protective property by electrochemical methods
2.2.4 Chemical methods for atmospheric impurities analysis
Chapter 3 THE CHARACTERISTIC OF WS CORROSION IN THE
VIETNAMESE CLIMATE 3.1 The corrosion mass lost of WS
During the periods less than 6-12 months, the corrosion mass losses (ML) of
WS and CS are similar because the rust is porous and uncover entire of surface
Tab 3.1: The environmental parameter of the exposed test (annual value,
Time
of dryness h/y
Trang 9After 6 months (in marine sites) or 12 months (in urban sites), ML of WS
at the test sites in Hanoi and Dong Hoi where the climate is humid, - is greater than that in the dry climate of Phan Rang
The ML and CR of WS at the test sites show that the corrosion is most severe at Dong Hoi site, at Hanoi is lower and it is lowest at Phan Rang site
3.2 Kinetics of WS atmospheric corrosion
exposure time in urban of HN
exposure time in marine of DH
exposure time in marine of PR
Fig.3.6 The ML of CS by exposure
time at test sites
0 40 80 120 160
0 3 6 9 12 Exposed time, month
0 50 100 150 200 250
0 3 6 9 12 Exposed time, month
0 100 200 300
0 3 6 9 12 Exposed time, month
Trang 10The variation of ML depending exposure time was built from the experimental and fitted using Excel software, the results show that:
equation at Dong Hoi > at Phan Rang > at Ha Noi which shows that the time
to form protective CP at Dong Hoi is longer than that of two other sites
covered fully WS substrate, or the structure of CP was porous, t CP doesn’t
WS surface and the dense rust layer was formed at very close WS substrate,
kinetic equations of CS It shows that the ML of WS and CS are more and more diffirent over exposure time andthe corrosion protectiveness of WS in atmosphere of Vietnam is better than CS clearly
Tab.3.2 The kinetic equations of WS at test sites
Tab.3.3 The kinetic equations of CS at test sites (calculated from fig.3.6)
Trang 11using un-coated WS (the ML after 20 years is 120 μm [45]), it is possible to use bare WS in Hanoi and Phan Rang atmosphere
ML, g/m2
ML,
Increment
of ML, % (*)
ML, g/m2
ML,
Increment
of ML, % (*)
Hanoi, Dong Hoi, Quang Ngai, Pleiku, Phan Rang, Bien Hoa, Ho Chi Minh
corrosion of WS were studied on samples exposed every month in year at the
3.3.1 The effect of temperature
because air temperature accelerates corrosion reactions
Trang 12 T > 200C: The ML of WS decreases with the increasing of air temperature because TOW and solubility of oxygen as well as other gases into water thin film on WS surface are decreased when air temperature increases
3.3.2 The effect of wet-dry cycle
t is exposure time
wet.; When the drying time is longer, the evaporation of water only makes oxygen dissolved easily into water film and makes the concentration of
because the drying time is long enough in order to dry the WS surface
3.3.3 The effect of rainfall total
Fig.3.7 The effect of temperature to
the ML of WS
d/w < 0,5 0,5 < d/w < 1
d/w > 1
Trang 13
Fig.3.9 The relationship between ML and rainfall total
total either because the thickness of water film increases, or because rain water is kept in the porous rust layer which prolongs the time of wetness
on WS surface
rain and it makes corrosion reduced
3.3.4 The effect of airborne salinity (Cl - )
The airborne salinity accelerates the ML of WS in the atmospheric regions
3.3.5 The effect of SO 2 deposition rate
atmospheric increases, however this relationship is not apparent
3.3.6 The effect of season
3.3.6.1 Hanoi test site:
Hanoi has four seasons: high temperature and rainfall in the summer, low temperature and little sunshine in the winter, therefore, the environment shows the different effects to corrosion of WS depending the exposure duration in the
Fig.3.10 The relationship between
ML and airborne salinity
Trang 14year The monthly of ML shows that the TOW dominates atmospheric
Hanoi 3.3.6.2 Dong Hoi test site:
WS in Dong Hoi
Fig.3.15 The relationship between ML and airborne salinity in Dong Hoi
Trang 15Chapter 4 THE FORMATION AND PROTECTIVENESS OF
CORROSION PRODUCT FORMED ON WS IN CLIMATE OF
CS The durability of rust depends on the structure, properties as well as the process of forming the protective layer on the steel surface Thus, in Chapter 4, the mechanism of formation and development of corrosion products on WS was discussed in order to elucidate the protective possibility of rust formed on WS
in the atmosphere of Vietnam
4.1 The formation of corrosion product on WS substrate in early stage of exposure
In order to study the formation of CP on WS substrate, the samples were exposed at Hanoi, Dong Hoi and Phan Rang for the short periods: 1, 3, 7, and
14 days The variation of environmental parameters over time are shown on the fig.4.1 and 4.2
Fig.4.1 The variation of temperature and humidity at the test sites during short periods of exposure
Trang 16In atmospheric condition, the moisture and impurities from atmosphere adsorb to the steel substrate and the electrolytic solution film was formed which corrodes steel substrate as follows:
4.1.1 The morphology of corrosion product
Fig.4.3 The surface of samples after short exposed time
almost surface after 14 exposed day (fig.4.3)
Dong Hoi - Phan Rang In Phan Rang, the high temperature and long drying
Trang 17time delayed the corrosion process occurred, which formed the rust with small size and dense CP (fig.4.4)
water evaporation and formed the rust with smaller size in comparison with Hanoi
4.1.2 The formation the chemical compound of CP in the early exposed
stage
The anlysis results of micro Raman and X-ray were detected Goethite, Lepidocrocite, Maghemite in bulk of CP after short time exposure in Hanoi and Dong Hoi; Especially, the goethite α-FeOOH – most stable phase appeared after only one day- exposure at Dong Hoi and after three day-exposure at Hanoi test site
Fig.4.5 The Raman spectrum of WS samples after 1 and 3 day exposed in
Hanoi and Dong Hoi
increased, as a results, the drying time promoted the transformation of phases
Trang 18during the surface changes from wetting to drying stage In Hanoi, this variation of
VNU-HN-SIEMENS D5005 - Mau HN3d
11-0196 (D) - Copper Oxide Sulfate - CuSO4·CuO - d x by: 1.000 - WL: 1.54056 38-1479 (*) - Eskolaite, syn - Cr2O3 - d x by: 1.000 - WL: 1.54056 08-0098 (N) - Lepidocrocite - FeO(OH) - d x by: 1.000 - WL: 1.54056 29-0713 (I) - Goethite - FeO(OH) - d x by: 1.000 - WL: 1.54056 06-0696 (*) - Iron, syn - Fe - d x by: 1.000 - WL: 1.54056 File: Hong-Vien KHVL-HN3d.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 70.000 ° - Step: 0.030 ° - Step time: 1.0 s - Temp.: 25.0 ° C (Room) - Anode: Cu - Creation: 05/10/10 11:09:48
01-0132 (N) - Iron Chloride Hydrate - 2FeCl3·7H2O - d x by: 1.000 - WL: 1.54056
33-0645 (*) - Hydromolysite, syn [NR] - FeCl3·6H2O - d x by: 1.000 - WL: 1.54056
25-0269 (I) - Atacamite - Cu2Cl(OH)3 - d x by: 1.000 - WL: 1.54056
36-1330 (N) - Chromium Oxide - Cr3O8 - d x by: 1.000 - WL: 1.54056
25-1437 (I) - Guyanaite - Cr2O3·1.5H2O - d x by: 1.000 - WL: 1.54056
08-0098 (N) - Lepidocrocite - FeO(OH) - d x by: 1.000 - WL: 1.54056
29-0713 (I) - Goethite - FeO(OH) - d x by: 1.000 - WL: 1.54056
39-1346 (*) - Maghemite-C, syn - Fe2O3 - d x by: 1.000 - WL: 1.54056
06-0696 (*) - Iron, syn - Fe - d x by: 1.000 - WL: 1.54056
File: Hong-Vien KHVL-QB1d.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 70.000 ° - Step: 0.030 ° - Step time: 1.0 s - Temp.: 25.0 ° C (Room) - Anode: Cu - Creation: 05/10/10 11:13:46
comparison with Hanoi
Fig.4.7 The X-ray spectrum of WS sample after 1 day exposed in Dong Hoi
Fig.4.8 The transformation
in CP of WS [57,63,64,67,68,99-107]
Wet stage
Stage of change from
wet to dry in the surface
Lepidocrocite -FeOOH
Amorphous compounds FeO x (OH) 3-2x
Goethite α-FeOOH