Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. This model is applied to the speci c case of high density polyethylene hdpe exposed to a chlorinated environment at a constant stress load. Numerical modeling of stress corrosion cracking of polymers. Stress corrosion cracking the international institute of. A unified chemomechanical model is developed to predict the stress corrosion cracking scc of a viscoplastic polymer. A deterministic modeling of slow stress corrosion sc crack growth process is. Plastic may take up to 1,000 years to completely biodegrade.
Stakeholder communications stress corrosion fact sheet. The mechanisms of environmental stress cracking proposed in the literature will be. Since variance of any of these factors can change the environmental stress crack resistance of the container, the test results are representative only of a given test performed under defined conditions in the laboratory. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Stress corrosion cracking scc in engineering thermoplastics is commonly observed in the form of a microcrack colony within a surface layer of degraded polymer exposed to a combined action of. Investigations on environmental stress cracking resistance of. Scc in pipelines is a type of environmentally assisted cracking. Request pdf stress corrosion cracking in plastic pipes. Another form of stress corrosion cracking is attributable to the effect of crackpromoting media such as wetting agents. Chemical permeationdesorption in new and chlorineaged polyethylene pipes, 2010. Environmental stress corrosion cracking resistance of high.
An illustration of the simplest tests will help define esc better. Additionally it is fda compliant, chemical and corrosion resistant and has no moisture absorption. The duct and grout then form a double corrosionprotection system for the. The polymer chains eventually creep toward the pull and deform. A unified chemomechanical model is developed to simulate stress corrosion cracking scc of high density polyethylene hdpe in a chlorinated environment. Todays approach to stress corrosion cracking in polyethylene coatings of steel pipes for standard applications in water and gas distribution systems merely considers the coating types featuring the low peeling resistance of the early editions of din 30670, i. For high density polyethylene xray scattering data indicate that the. In the case of solvent attack, the best solution is to actually increase the density of the polyethylene so that the penetration of solvent is slowed.
Stress cracking in hdpe protection ducts in segmental bridges32. The capped bottles are then placed in an oven at 60c and a stress is generated by the increased internal pressure. This is because stress from different sources increases during the summertime. Stress corrosion school of materials science and engineering. Nearneutralph scc is less temperaturedependent than highph scc. Stress corrosion cracking will usually cause the material to fail in a brittle manner, which can have grave consequences as there is usually little or no warning before the failure occurs. Stress corrosion cracking scc in engineering thermoplastics is commonly. All pe types are not resistant to strong oxidising materials e. It has been estimated that 15% of all failures of plastic materials in.
Environmental stress cracking resistance of polyethylene. Environmental stress crack resistance of polyethylene introduction to environmental stress cracking and escr over the past decade, highdensity polyethylene hdpe materials have improved significantly and now meet more stringent performance standards. Stress corrosion cracking scc in engineering thermoplastics is commonly observed in the form of a microcrack colony within a surface layer of degraded polymer exposed to a combined action of mechanical stresses and chemically aggressive environment. Hdpe and ldpe cover both ends of the application spectrum, from those requiring excellent impact resistance and durability to those requiring flexibility and tensity. Hdpe resin properties table hdpe plastic injection molding. In this technique, the bottles are filled with a stress cracking solution which fills 10 vol. A study of the stress corrosion crack initiation stage in. Environmental stress cracking esc is not the result of the continual battle that the plastics industry has in convincing environmentalists and politicians that plastics can be the solution to environmental problems and not the cause. Mdpe exhibited excellent scg and stress crack resistance, and dominated pe pipe manufacture for 30 years until the development of bimodal hdpe pe100. Numerical modeling of stress corrosion cracking in polymers. Cytec industries, the effects of chlorinated water on polyethylene pipes, plastics today, march 2011. Environmental stress cracking esc in plastics means the failure at about room temperature. Esc may be defined as the acceleration of stress cracking by contact with a liquid or vapor without chemical degradation of the plastic. Introduction to environmental stress cracking and escr over the past decade, highdensity polyethylene hdpe materials have improved significantly and now meet more stringent performance standards.
Environmental stress cracking an overview sciencedirect. Stress corrosion cracking of polyethylene practical. Proteus copolymer high impact resistant thermoplastic with excellent resistance to cracking at low temperatures. Experimental study of stress cracking in high density. With good mechanical properties, corrosion resistance, ease of manufacturing, and. Plastic failure through environmental stress cracking. Another feature of stress corrosion cracking is the planar nature of the fracture surface. It is important to note that solvents can also affect polyethylene, but in an entirely different manner than environmental stress cracking agents. Obviously, if bundles of fibers lie parallel to the plane of cracking, then fracture may deviate along the fibermatrix interface. Stress corrosion is a form of galvanic corrosion, where stressed areas of the material are anodic to the unstressed areas of the material. Plastic pipes have been used in pressure piping applications for many years. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact. The stress cracking is more severe with detergent, bleach, motor oil and some industrial chemical packaging.
Stress corrosion cracking scc in polymer composites. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. Both materials are easily machined, fabricated and thermoformed. Environmental stress cracking esc is a common cause of plastic product failure. Environmental stress cracking esc in plastics means the failure at about room. Mar 09, 2020 its weakness is that its resistance to aging and environmental stress cracking is not as good as that of ldpe. Plastic breaks down at varying rates depending upon environmental factors. Can be susceptible to environmental stress cracking if internal stresses are not minimized by proper design and use of lowest mfr material at a particular density level.
Aug 01, 2008 get a handle on stresscracking in hdpe bottles one of the first applications for blow molded hdpe bottles was the replacement of glass for bleach packaging. With force and time, crazing or stress cracking occurs. Esc of polymers is analogous to the stress corrosion problem in metals. Stress corrosion cracking in plastic pipes researchgate. This type of failure is known as stress corrosion cracking, often abbreviated to scc. In embrittled polyethylene pipe or coating material, crack initiation occurs in sites subject to additional external stresses such as point loads or point supports 2, 3. How to prevent stress cracking what is stress cracking.
According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused by tensile stresses less than its shortterm mechanical. This chemomechanical model is comprised of three components, each capturing a. Environmental stress cracking the the chemical agent does. Esc is the consequence of a combination of mechanical stress and exposure to an aggressive chemical. In contrast, environmentalstresscracking agents do not appreciably diffuse into polyethylene, and stiffness is unaffected. A materials resistance against this type of failure is called environmental stress cracking resistance escr. Experimental study of stress cracking in high density polyethylene. Stress corrosion cracking in plastic pipes springerlink. The chemical simply accelerates the stress cracking. Sunlight helps break down plastic faster than if it is buried. Modeling stress corrosion cracking in plastic pipes, asce pipelines 2008. Environmental stress cracking esc is considered a leading. Definition of environmental stress cracking esc environmental stress cracking esc in plastics means the failure at about room temperature due to continuously acting external andor internal stresses in the presence of surface active substances known as stress cracking agents such as alcohols, soaps, dyes, agents containing moisture.
Basic understanding of stress cracking in hdpe products. Jansen stork technimet new berlin, wisconsin e nvironmental stress cracking esc is a phenomenon in which a plastic resin is degraded by a chemical agent while under stress, and it is the leading cause of plastic component failure. Polypropylene is available in several grades and under the following names. Stress corrosion cracking in pipelines begins when small cracks develop on the external surface of buried pipelines. Numerical modeling of stress corrosion cracking of. What causes stress corrosion cracking in pipelines. Stress corrosion cracking scc in engineering thermoplastics is commonly observed in the form of. One such performance criteria is environmental stress crack resistance escr. Commonly used plastic pipe materials include polyethylene. Environment stress cracking of hdpe products is quite common due to its semi crystalline nature which gets attacked due to chemicals present in the environment. Especially, its performance will be lowered under the effect of thermal oxidation, so when made into plastic coils, highdensity polyethylene is often added with antioxidants and uv absorbers to improve the weakness. Soluble in hydrocarbons at temperatures greater than 140 f however, resistance to these materials is greater than that of ldpe resin.
Stress corrosion cracking scc in polyolefin pipes usually starts as a microcrack colony within a degraded layer adjacent to the pipe surface exposed to combine action of mechanical stress and. A uni ed chemomechanical model is developed to predict the stress corrosion cracking scc of a viscoplastic polymer. Surfactant chemicals and other wetting agents are known to cause. In high wear environments, hdpe and ldpe resist stress cracking, moisture and chemicals for enhanced part integrity. Environmental stress cracking is involved with some 25% of plastic part failures. A probabilistic modeling of scc initiation is briefly discussed. Jan 18, 2011 hence, an important design factor for pe pipes became commonly known as environmental stress cracking resistance escr, which led to the development of mdpe. Some performance evaluation tests that once took only days to run now take months with todays. Refer to other fact sheets for specific discussion of issues related to corrosion in general, external corrosion, internal corrosion, and selective seam corrosion. If you look at this plastic under a microscope, you would see that it has a linear structure with few branches lending to its optimal strengthdensity ratio. Plastic pipes have been investigated as an economical and corrosionresistant alternative to steel pipe, but this material only works in moderate temperature and pressure environments. Stress cracking in hdpe protection ducts in segmental bridges 32.
A study of the stress corrosion crack initiation stage in alphabrass a dissertation submitted to the graduate faculty of the louisiana state university and. This model is applied to the specific case of high density polyethylene hdpe exposed to a chlorinated environment at a constant stress load. The copolymer is more pliable than the homopolymer. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused. The nature of polyethylene pipe failure plasticstoday. Environmental stress cracking can take place through continuous crack growth or via a stepwise progressive mechanism of cracking and arrest, depending on the molecular structure of the plastic, the composition of the chemical agent, the level of stress, and other environmental conditions. Pvc was tested by several methods, including monotonic creep method,73. Experimental study of stress cracking in high density polyethylene pipes a thesis submitted to the faculty of drexel university by jingyu zhang. Jul 17, 2017 in other words, the crack sides have experienced metal loss from corrosion.
Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. What is stress corrosion cracking and why does it occur. Multiple cracks initiated along the interior edge of the part wall and coalesced to produce the fracture. Highdensity polyethylene or hdpe is a commonly used petroleum thermoplastic and the most used of the three polyethylenes for a wide range of applications. May 03, 2016 carbon steel is the most common pipe material used in the hydrocarbon processing industry, but the materials susceptibility to corrosion is well known. The escr of polyethylene, one of the most widely used plastic materials, is of particular concern in the plastics industry and is the subject of this investigation. Grace hsuan, jy zhang and wk wong department of civil, architectural and environmental engineering, drexel university, philadelphia, usa abstract the 100year stress crack resistance scr of corrugated hdpe pipes was evaluated using a 600 mm diameter pipe.
During the summer months, stresscracking of hdpe containers reaches its peak. Astm d2561 17 standard test method for environmental stress. Therefore, a numerical approach is needed to investigate this issue. All pe types are resistant to acids, alkaline solutions, salts and salt solutions, alcohols, oils, fats, waxes and many solvents. Plastic waste in the oceans breaks down at a much faster rate, but leaves behind a number of pollutants that cause problems for marine life. Significantly, in the absence of the chemical the plastic would undergo stress cracking in air, also known as creep rupture, given sufficient time. For specific cases in which the effect of an environment on polyethylene has not been documented, testing is required to identify any possible environmental stress cracking effect. Premature cracking can be caused by topload stress, internal pressure, moldedin stress, and tail swing. Effects of recycled hdpe and nanoclay on stress cracking of.
Environmental stress cracking an overview sciencedirect topics. Aromatics and halogenated hydrocarbons cause swelling. Environmental stress crack resistance of polyethylene. In the csm type of fiber reinforced polyester composites, stress corrosion cracking produces a characteristic planar fracture. The action of either a tensile stress or a corrosive liquid alone would not be. With hdpe, it was observed that slow cooling or annealing of the.