Stress corrosion cracking

Last updated April 23, 2024

Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It can lead to unexpected and sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when exposed to a small number of chemical environments. The chemical environment that causes SCC for a given alloy is often one which is only mildly corrosive to the metal. Hence, metal parts with severe SCC can appear bright and shiny, while being filled with microscopic cracks. This factor makes it common for SCC to go undetected prior to failure. SCC often progresses rapidly, and is more common among alloys than pure metals. The specific environment is of crucial importance, and only very small concentrations of certain highly active chemicals are needed to produce catastrophic cracking, often leading to devastating and unexpected failure.^[1]

The stresses can be the result of the crevice loads due to stress concentration, or can be caused by the type of assembly or residual stresses from fabrication (e.g. cold working); the residual stresses can be relieved by annealing or other surface treatments. Unexpected and premature failure of chemical process equipment, for example, due to stress corrosion cracking constitutes a serious hazard in terms of safety of personnel, operating facilities and the environment. By weakening the reliability of these types of equipment, such failures also adversely affect productivity and profitability.

Mechanisms

Stress corrosion cracking mainly affects metals and metallic alloys. A comparable effect also known as environmental stress cracking also affects other materials such as polymers, ceramics and glass.

Metals

Lower pH and lower applied redox potential facilitate the evolution and the enrichment of hydrogen during the process of SCC, thus increasing the SCC intensity.^[2]

Alloy	K_Ic MN/m^3/2	SCC environment	K_Iscc MN/m^3/2
13Cr steel	60	3% NaCl	12
18Cr-8Ni	200	42% MgCl₂	10
Cu-30Zn	200	NH₄OH (pH 7)	1
Al-3Mg-7Zn	25	Aqueous halides	5
Ti-6Al-1V	60	0.6 M KCl	20

Certain austenitic stainless steels and aluminium alloys crack in the presence of chlorides. This limits the usefulness of austenitic stainless steel for containing water with higher than a few parts per million content of chlorides at temperatures above 50 °C (122 °F);
mild steel cracks in the presence of alkali (e.g. boiler cracking and caustic stress corrosion cracking) and nitrates;
copper alloys crack in ammoniacal solutions (season cracking);
high-tensile steels have been known to crack in an unexpectedly brittle manner in a whole variety of aqueous environments, especially when chlorides are present.

With the possible exception of the latter, which is a special example of hydrogen cracking, all the others display the phenomenon of subcritical crack growth, i.e. small surface flaws propagate (usually smoothly) under conditions where fracture mechanics predicts that failure should not occur. That is, in the presence of a corrodent, cracks develop and propagate well below critical stress intensity factor ( $K_{\mathrm {Ic} }$ ). The subcritical value of the stress intensity, designated as $K_{\mathrm {Iscc} }$ , may be less than 1% of $K_{\mathrm {Ic} }$ .

Polymers

A similar process (environmental stress cracking) occurs in polymers, when products are exposed to specific solvents or aggressive chemicals such as acids and alkalis. As with metals, attack is confined to specific polymers and particular chemicals. Thus polycarbonate is sensitive to attack by alkalis, but not by acids. On the other hand, polyesters are readily degraded by acids, and SCC is a likely failure mechanism. Polymers are susceptible to environmental stress cracking where attacking agents do not necessarily degrade the materials chemically. Nylon is sensitive to degradation by acids, a process known as hydrolysis, and nylon mouldings will crack when attacked by strong acids.

For example, the fracture surface of a fuel connector showed the progressive growth of the crack from acid attack (Ch) to the final cusp (C) of polymer. In this case the failure was caused by hydrolysis of the polymer by contact with sulfuric acid leaking from a car battery. The degradation reaction is the reverse of the synthesis reaction of the polymer:

Cracks can be formed in many different elastomers by ozone attack, another form of SCC in polymers. Tiny traces of the gas in the air will attack double bonds in rubber chains, with natural rubber, styrene-butadiene rubber, and nitrile butadiene rubber being most sensitive to degradation. Ozone cracks form in products under tension, but the critical strain is very small. The cracks are always oriented at right angles to the strain axis, so will form around the circumference in a rubber tube bent over. Such cracks are dangerous when they occur in fuel pipes because the cracks will grow from the outside exposed surfaces into the bore of the pipe, so fuel leakage and fire may follow. Ozone cracking can be prevented by adding anti-ozonants to the rubber before vulcanization. Ozone cracks were commonly seen in automobile tire sidewalls, but are now seen rarely thanks to the use of these additives. On the other hand, the problem does recur in unprotected products such as rubber tubing and seals.

Ceramics

This effect is significantly less common in ceramics which are typically more resilient to chemical attack. Although phase changes are common in ceramics under stress these usually result in toughening rather than failure (see Zirconium dioxide). Recent studies have shown that the same driving force for this toughening mechanism can also enhance oxidation of reduced cerium oxide, resulting in slow crack growth and spontaneous failure of dense ceramic bodies.^[3]

Glass

Subcritical crack propagation in glasses falls into three regions. In region I, the velocity of crack propagation increases with ambient humidity due to stress-enhanced chemical reaction between the glass and water. In region II, crack propagation velocity is diffusion controlled and dependent on the rate at which chemical reactants can be transported to the tip of the crack. In region III, crack propagation is independent of its environment, having reached a critical stress intensity. Chemicals other than water, like ammonia, can induce subcritical crack propagation in silica glass, but they must have an electron donor site and a proton donor site.^[4]

Prevention

The compressive residual stresses imparted by laser peening are precisely controlled both in location and intensity and can be applied to mitigate sharp transitions into tensile regions. Laser peening imparts deep compressive residual stresses on the order of 10 to 20 times deeper than conventional shot peening, making them significantly more beneficial at preventing SCC.^[5] Laser peening is widely used in the aerospace and power generation industries in gas fired turbine engines.^[6]
Material Selection: Choosing the right material for a specific environment can help prevent SCC. Materials with higher resistance to corrosion and stress corrosion cracking should be used in corrosive environments. For example, using stainless steel instead of carbon steel in a marine environment can reduce the likelihood of SCC.^[7]
Protective Coatings: Applying a protective coating or barrier can help prevent corrosive substances from coming into contact with the metal surface, thus reducing the likelihood of SCC. For example, using an epoxy coating on the interior surface of a pipeline can reduce the likelihood of SCC.^[7]
Cathodic Protection: Cathodic protection is a technique used to protect metals from corrosion by applying a small electrical current to the metal surface. This technique can also help prevent SCC by reducing the corrosion potential of the metal.^[7]
Environmental Controls: Controlling the environment around the metal can help prevent SCC. For example, reducing the temperature or acidity of the environment can help prevent SCC.^[7]
Inspection and Maintenance: Regular inspections and maintenance can help detect SCC before it causes a failure. This includes visual inspections, non-destructive testing, and monitoring of environmental factors.^[7]

Notable failures

A 32-inch diameter gas transmission pipeline, north of Natchitoches, Louisiana, belonging to the Tennessee Gas Pipeline exploded and burned from SCC on March 4, 1965, killing 17 people. At least 9 others were injured, and 7 homes 450 feet from the rupture were destroyed.^[8]^[9]
SCC caused the catastrophic collapse of the Silver Bridge in December 1967, when an eyebar suspension bridge across the Ohio River at Point Pleasant, West Virginia, suddenly failed. The main chain joint failed and the entire structure fell into the river, killing 46 people who were traveling in vehicles across the bridge. Rust in the eyebar joint had caused a stress corrosion crack, which went critical as a result of high bridge loading and low temperature. The failure was exacerbated by a high level of residual stress in the eyebar. The disaster led to a nationwide reappraisal of bridges.^[10]
USS Hartford submarine periscope: In 2009, the periscope of the submarine USS Hartford failed due to SCC. The periscope is used to provide a view of the surface while the submarine is submerged. The failure occurred when the periscope was extended through the hull of the submarine, causing seawater to enter the periscope's seal. The seawater caused SCC to occur in the periscope's steel support structure, which led to the periscope falling back into the submarine. Fortunately, there were no injuries, but the submarine had to be taken out of service for repairs.^[11]
Trans-Alaska Pipeline: In 2001, a section of the Trans-Alaska Pipeline failed due to SCC. The pipeline is used to transport crude oil from the North Slope of Alaska to the Valdez Marine Terminal. The failure occurred when a 34-foot section of the pipeline ruptured, causing a spill of over 285,000 gallons of crude oil. The investigation into the failure found that SCC had occurred in the pipeline due to the presence of water and bacteria, which had created a corrosive environment.^[12]
Aloha Airlines Flight 243: In 1988, Aloha Airlines Flight 243 experienced a partial fuselage failure due to SCC. The Boeing 737-200 was flying from Hilo to Honolulu, Hawaii when a section of the fuselage ruptured, causing a decompression event. The investigation into the failure found that SCC had occurred in the aluminum skin of the fuselage due to the repeated pressurization and depressurization cycles of the aircraft. The incident led to changes in maintenance procedures and inspections for aircraft to prevent similar failures in the future.^[13]

Related Research Articles

Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe₂O₃·nH₂O) and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)₃), and is typically associated with the corrosion of refined iron.

Stainless steel, also known as inox, corrosion-resistant steel (CRES) and rustless steel, is an alloy of iron that is resistant to rusting and corrosion. It contains iron with chromium and other elements such as molybdenum, carbon, nickel and nitrogen depending on its specific use and cost. Stainless steel's resistance to corrosion results from the 10.5%, or more, chromium content which forms a passive film that can protect the material and self-heal in the presence of oxygen.

Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.

Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S²⁻ or a compound containing one or more S²⁻ ions. Solutions of sulfide salts are corrosive. Sulfide also refers to large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H₂S) and bisulfide (SH⁻) are the conjugate acids of sulfide.

<span class="mw-page-title-main">Hydrogen embrittlement</span> Reduction in ductility of a metal exposed to hydrogen

Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs most notably in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement.

Microbial corrosion, also called microbiologically influenced corrosion (MIC), microbially induced corrosion (MIC), or biocorrosion, is when microbes affect the electrochemical environment of the surface they are on. This usually involves building a biofilm, which can lead to either an increase in corrosion of the surface or, in a process called microbial corrosion inhibition, protect the surface from corrosion.

In materials science, environmental stress fracture or environment assisted fracture is the generic name given to premature failure under the influence of tensile stresses and harmful environments of materials such as metals and alloys, composites, plastics and ceramics.

Corrosion fatigue is fatigue in a corrosive environment. It is the mechanical degradation of a material under the joint action of corrosion and cyclic loading. Nearly all engineering structures experience some form of alternating stress, and are exposed to harmful environments during their service life. The environment plays a significant role in the fatigue of high-strength structural materials like steel, aluminum alloys and titanium alloys. Materials with high specific strength are being developed to meet the requirements of advancing technology. However, their usefulness depends to a large extent on the degree to which they resist corrosion fatigue.

Embrittlement is a significant decrease of ductility of a material, which makes the material brittle. Embrittlement is used to describe any phenomena where the environment compromises a stressed material's mechanical performance, such as temperature or environmental composition. This is oftentimes undesirable as brittle fracture occurs quicker and can much more easily propagate than ductile fracture, leading to complete failure of the equipment. Various materials have different mechanisms of embrittlement, therefore it can manifest in a variety of ways, from slow crack growth to a reduction of tensile ductility and toughness.

Crevice corrosion refers to corrosion occurring in occluded spaces such as interstices in which a stagnant solution is trapped and not renewed. These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles.

<span class="mw-page-title-main">Forensic materials engineering</span>

Forensic materials engineering, a branch of forensic engineering, focuses on the material evidence from crime or accident scenes, seeking defects in those materials which might explain why an accident occurred, or the source of a specific material to identify a criminal. Many analytical methods used for material identification may be used in investigations, the exact set being determined by the nature of the material in question, be it metal, glass, ceramic, polymer or composite. An important aspect is the analysis of trace evidence such as skid marks on exposed surfaces, where contact between dissimilar materials leaves material traces of one left on the other. Provided the traces can be analysed successfully, then an accident or crime can often be reconstructed. Another aim will be to determine the cause of a broken component using the technique of fractography.

Forensic polymer engineering is the study of failure in polymeric products. The topic includes the fracture of plastic products, or any other reason why such a product fails in service, or fails to meet its specification. The subject focuses on the material evidence from crime or accident scenes, seeking defects in those materials that might explain why an accident occurred, or the source of a specific material to identify a criminal. Many analytical methods used for polymer identification may be used in investigations, the exact set being determined by the nature of the polymer in question, be it thermoset, thermoplastic, elastomeric or composite in nature.

Cracks can be formed in many different elastomers by ozone attack, and the characteristic form of attack of vulnerable rubbers is known as ozone cracking. The problem was formerly very common, especially in tires, but is now rarely seen in those products owing to preventive measures.

<span class="mw-page-title-main">Environmental stress cracking</span> Brittle failure of thermoplastic polymers

Environmental Stress Cracking (ESC) is one of the most common causes of unexpected brittle failure of thermoplastic polymers known at present. According to ASTM D883, stress cracking is defined as "an external or internal crack in a plastic caused by tensile stresses less than its short-term mechanical strength". This type of cracking typically involves brittle cracking, with little or no ductile drawing of the material from its adjacent failure surfaces. Environmental stress cracking may account for around 15-30% of all plastic component failures in service. This behavior is especially prevalent in glassy, amorphous thermoplastics. Amorphous polymers exhibit ESC because of their loose structure which makes it easier for the fluid to permeate into the polymer. Amorphous polymers are more prone to ESC at temperature higher than their glass transition temperature (T_g) due to the increased free volume. When T_g is approached, more fluid can permeate into the polymer chains.

Corrosion engineering is an engineering specialty that applies scientific, technical, engineering skills, and knowledge of natural laws and physical resources to design and implement materials, structures, devices, systems, and procedures to manage corrosion. From a holistic perspective, corrosion is the phenomenon of metals returning to the state they are found in nature. The driving force that causes metals to corrode is a consequence of their temporary existence in metallic form. To produce metals starting from naturally occurring minerals and ores, it is necessary to provide a certain amount of energy, e.g. Iron ore in a blast furnace. It is therefore thermodynamically inevitable that these metals when exposed to various environments would revert to their state found in nature. Corrosion and corrosion engineering thus involves a study of chemical kinetics, thermodynamics, electrochemistry and materials science.

Metallurgical failure analysis is the process to determine the mechanism that has caused a metal component to fail. It can identify the cause of failure, providing insight into the root cause and potential solutions to prevent similar failures in the future, as well as culpability, which is important in legal cases. Resolving the source of metallurgical failures can be of financial interest to companies. The annual cost of corrosion in the United States was estimated by NACE International in 2012 to be $450 billion a year, a 67% increase compared to estimates for 2001. These failures can be analyzed to determine their root cause, which if corrected, would save reduce the cost of failures to companies.

Static fatigue describes how prolonged and constant cyclic stress weakens a material until it breaks apart, which is called failure. Static fatigue is sometimes called "delayed fracture". The damage occurs at a lower stress level than the stress level needed to create a normal tensile fracture. Static fatigue can involve plastic deformation or crack growth. For example, repeated stress can create small cracks that grow and eventually break apart plastic, glass, or ceramic materials. The material reaches failure faster by increasing cyclic stress. Static fatigue varies with material type and environmental factors, such as moisture presence and temperature.

Metal-induced embrittlement (MIE) is the embrittlement caused by diffusion of metal, either solid or liquid, into the base material. Metal induced embrittlement occurs when metals are in contact with low-melting point metals while under tensile stress. The embrittler can be either solid (SMIE) or liquid. Under sufficient tensile stress, MIE failure occurs instantaneously at temperatures just above melting point. For temperatures below the melting temperature of the embrittler, solid-state diffusion is the main transport mechanism. This occurs in the following ways:

Corrosion inhibitors for the petroleum industry are substances used in the oil industry to protect equipment and pipelines against corrosion. Corrosion is a daily problem in the oil industry due to the presence in crude oil of water contaminated with salts, gases and other corrosive contaminants in the production process. Corrosion inhibitors can be classified according to their chemical composition as either organic inhibitors or inorganic inhibitors. They can also be classified by the way they act as anodic or cathodic inhibitors. Cathodic inhibitors act as catalysts to slow down corrosion, while anodic inhibitors protect metal surfaces by acting as physical barriers.

Corrosion inhibitors are substances used in the oil industry to protect equipment and pipes against corrosion. Corrosion is a common problem in the oil industry due to the presence of water, gases, and other corrosive contaminants in the production environment.

References

Notes

↑ "Chapter 32: Failure Analysis". Metals Handbook (Desk ed.). American Society for Metals.
↑ Gu, B.; Luo, J.; Mao, X. (January 1999). "Hydrogen-facilitated anodic dissolution-type stress corrosion cracking of pipeline steels in near-neutral pH solution". Corrosion. 55 (1): 96–106. doi:10.5006/1.3283971. ISSN 0010-9312. Archived from the original on 2023-02-21. Retrieved 2023-02-21.
↑ Munnings, C.; Badwal, S. P. S.; Fini, D. (20 February 2014). "Spontaneous stress-induced oxidation of Ce ions in Gd-doped ceria at room temperature". Ionics. 20 (8): 1117–1126. doi:10.1007/s11581-014-1079-2. S2CID 95469920.
↑ Wachtman, John B.; Cannon, W. Roger; Matthewson, M. John (11 September 2009). Mechanical Properties of Ceramics (2nd ed.). John Wiley and Sons. doi:10.1002/9780470451519. ISBN 9780471735816.
↑ "EPRI | Search Results: Compressor Dependability: Laser Shock Peening Surface Treatment". Archived from the original on 2022-12-06. Retrieved 2023-02-21.
↑ Crooker, Paul; Sims, William (2011-06-09). "Peening for mitigation of PWSCC in alloy 600" (PDF). nrc.gov. Archived (PDF) from the original on 2022-10-06. Retrieved 2022-06-01.
1 2 3 4 5 "Irradiation-Assisted Stress-Corrosion Cracking", Stress-Corrosion Cracking, ASM International, pp. 191–220, 2017-01-01, doi:10.31399/asm.tb.sccmpe2.t55090191, ISBN 978-1-62708-266-2, OSTI 7010172 , retrieved 2023-04-26
↑ Corrective Action Order Regarding the TGP 100 Pipeline (PDF) (Report). US Department of Transportation Pipeline and Hazardous Materials Safety Administration. Dec 3, 2010. Archived from the original (PDF) on 2016-12-26.
↑ "17 Killed As Gas Line Explodes". The Washington Observer. Mar 5, 1965. Archived from the original on 2021-11-02. Retrieved 2023-02-21.
↑ Lewis, Peter Rhys; Reynolds, Ken; Gagg, Colin (2003-09-29). Forensic Materials Engineering. CRC Press. doi:10.1201/9780203484531. ISBN 978-0-203-48453-1.
↑ Hsu, Jeremy (March 23, 2009). "USS Hartford Periscope Snaps, Falls Into Submarine". Live Science.{{cite web}}: Missing or empty |url= (help)^{[ failed verification ]}
↑ Busenberg, George J. (September 2011). "The Policy Dynamics of the Trans-Alaska Pipeline System". Review of Policy Research. 28 (5): 401–422. doi:10.1111/j.1541-1338.2011.00508.x. ISSN 1541-132X.
↑ Hong-bing, Du; Qing-qing, Zhang (June 2015). "Simulation of the effect of safety investment on flight safety level in the airlines". 2015 International Conference on Transportation Information and Safety (ICTIS). IEEE. pp. 780–786. doi:10.1109/ictis.2015.7232149. ISBN 978-1-4799-8694-1. S2CID 2908608.

Sources

ASM International, Metals Handbook (Desk Edition) Chapter 32 (Failure Analysis), American Society for Metals, (1997) pp 32–24 to 32-26
ASM Handbook Volume 11 "Failure Analysis and Prevention" (2002) "Stress-Corrosion Cracking" Revised by W.R. Warke, American Society of Metals. Pages 1738-1820
ASTM (5 November 2018). "ASTM G36-94 (2018) Standard practice for evaluating stress-corrosion-cracking resistance of metals and alloys in a boiling magnesium chloride solution". astm.org. Archived from the original on 3 December 2022. Retrieved 1 June 2022.
Wachtman, John B.; Cannon, W. Roger; Matthewson, M. John. "Chapter 8". Mechanical Properties of Ceramics.

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[:1-1] "Chapter 32: Failure Analysis". Metals Handbook (Desk ed.). American Society for Metals.

[2] Gu, B.; Luo, J.; Mao, X. (January 1999). "Hydrogen-facilitated anodic dissolution-type stress corrosion cracking of pipeline steels in near-neutral pH solution". Corrosion. 55 (1): 96–106. doi:10.5006/1.3283971. ISSN 0010-9312. Archived from the original on 2023-02-21. Retrieved 2023-02-21.

[3] Munnings, C.; Badwal, S. P. S.; Fini, D. (20 February 2014). "Spontaneous stress-induced oxidation of Ce ions in Gd-doped ceria at room temperature". Ionics. 20 (8): 1117–1126. doi:10.1007/s11581-014-1079-2. S2CID 95469920.

[4] Wachtman, John B.; Cannon, W. Roger; Matthewson, M. John (11 September 2009). Mechanical Properties of Ceramics (2nd ed.). John Wiley and Sons. doi:10.1002/9780470451519. ISBN 9780471735816.

[5] "EPRI | Search Results: Compressor Dependability: Laser Shock Peening Surface Treatment". Archived from the original on 2022-12-06. Retrieved 2023-02-21.

[Crooker_2011-6] Crooker, Paul; Sims, William (2011-06-09). "Peening for mitigation of PWSCC in alloy 600" (PDF). nrc.gov. Archived (PDF) from the original on 2022-10-06. Retrieved 2022-06-01.

[:0-7] 1 2 3 4 5 "Irradiation-Assisted Stress-Corrosion Cracking", Stress-Corrosion Cracking, ASM International, pp. 191–220, 2017-01-01, doi:10.31399/asm.tb.sccmpe2.t55090191, ISBN 978-1-62708-266-2, OSTI 7010172 , retrieved 2023-04-26

[8] Corrective Action Order Regarding the TGP 100 Pipeline (PDF) (Report). US Department of Transportation Pipeline and Hazardous Materials Safety Administration. Dec 3, 2010. Archived from the original (PDF) on 2016-12-26.

[9] "17 Killed As Gas Line Explodes". The Washington Observer. Mar 5, 1965. Archived from the original on 2021-11-02. Retrieved 2023-02-21.

[10] Lewis, Peter Rhys; Reynolds, Ken; Gagg, Colin (2003-09-29). Forensic Materials Engineering. CRC Press. doi:10.1201/9780203484531. ISBN 978-0-203-48453-1.

[11] Hsu, Jeremy (March 23, 2009). "USS Hartford Periscope Snaps, Falls Into Submarine". Live Science.{{cite web}}: Missing or empty |url= (help)^{[ failed verification ]}

[12] Busenberg, George J. (September 2011). "The Policy Dynamics of the Trans-Alaska Pipeline System". Review of Policy Research. 28 (5): 401–422. doi:10.1111/j.1541-1338.2011.00508.x. ISSN 1541-132X.

[13] Hong-bing, Du; Qing-qing, Zhang (June 2015). "Simulation of the effect of safety investment on flight safety level in the airlines". 2015 International Conference on Transportation Information and Safety (ICTIS). IEEE. pp. 780–786. doi:10.1109/ictis.2015.7232149. ISBN 978-1-4799-8694-1. S2CID 2908608.

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