Effects of recycled hdpe and nanoclay on stress cracking of. Proteus copolymer high impact resistant thermoplastic with excellent resistance to cracking at low temperatures. 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. It has been estimated that 15% of all failures of plastic materials in. Investigations on environmental stress cracking resistance of. Significantly, in the absence of the chemical the plastic would undergo stress cracking in air, also known as creep rupture, given sufficient time. An illustration of the simplest tests will help define esc better. 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. Stress cracking in hdpe protection ducts in segmental bridges 32. 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.
Environmental stress cracking an overview sciencedirect topics. 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. Pvc was tested by several methods, including monotonic creep method,73. Obviously, if bundles of fibers lie parallel to the plane of cracking, then fracture may deviate along the fibermatrix interface. Stakeholder communications stress corrosion fact sheet. The action of either a tensile stress or a corrosive liquid alone would not be. 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. Experimental study of stress cracking in high density polyethylene pipes a thesis submitted to the faculty of drexel university by jingyu zhang. A probabilistic modeling of scc initiation is briefly discussed. Some performance evaluation tests that once took only days to run now take months with todays. A study of the stress corrosion crack initiation stage in alphabrass a dissertation submitted to the graduate faculty of the louisiana state university and. Additionally it is fda compliant, chemical and corrosion resistant and has no moisture absorption. 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. Jul 17, 2017 in other words, the crack sides have experienced metal loss from corrosion.
Environmental stress crack resistance of polyethylene. Both materials are easily machined, fabricated and thermoformed. Environmental stress cracking is involved with some 25% of plastic part failures. 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. Soluble in hydrocarbons at temperatures greater than 140 f however, resistance to these materials is greater than that of ldpe resin. Premature cracking can be caused by topload stress, internal pressure, moldedin stress, and tail swing. Stress cracking in hdpe protection ducts in segmental bridges32.
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. This is because stress from different sources increases during the summertime. 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. The chemical simply accelerates the stress cracking. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. 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. Stress corrosion school of materials science and engineering.
Therefore, a numerical approach is needed to investigate this issue. Esc of polymers is analogous to the stress corrosion problem in metals. This model is applied to the speci c case of high density polyethylene hdpe exposed to a chlorinated environment at a constant stress load. The nature of polyethylene pipe failure plasticstoday.
A materials resistance against this type of failure is called environmental stress cracking resistance escr. The duct and grout then form a double corrosionprotection system for the. Polypropylene is available in several grades and under the following names. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Stress corrosion cracking the international institute of. Stress corrosion cracking in plastic pipes springerlink. Plastic failure through environmental stress cracking.
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. Numerical modeling of stress corrosion cracking of polymers. The mechanisms of environmental stress cracking proposed in the literature will be. The copolymer is more pliable than the homopolymer. 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. It is important to note that solvents can also affect polyethylene, but in an entirely different manner than environmental stress cracking agents.
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. A uni ed chemomechanical model is developed to predict the stress corrosion cracking scc of a viscoplastic polymer. Stress corrosion cracking of polyethylene practical. According to astm d883, stress cracking is defined as an external or internal crack in a plastic caused. Because of this, environmental stress cracking and creep rupture are parallel failure mechanisms. 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. In this technique, the bottles are filled with a stress cracking solution which fills 10 vol. Another feature of stress corrosion cracking is the planar nature of the fracture surface.
All pe types are resistant to acids, alkaline solutions, salts and salt solutions, alcohols, oils, fats, waxes and many solvents. This chemomechanical model is comprised of three components, each capturing a. 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. 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. The polymer chains eventually creep toward the pull and deform. With hdpe, it was observed that slow cooling or annealing of the.
Refer to other fact sheets for specific discussion of issues related to corrosion in general, external corrosion, internal corrosion, and selective seam corrosion. Plastic breaks down at varying rates depending upon environmental factors. Numerical modeling of stress corrosion cracking of. Surfactant chemicals and other wetting agents are known to cause. Mar 09, 2020 its weakness is that its resistance to aging and environmental stress cracking is not as good as that of ldpe.
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. This model is applied to the specific case of high density polyethylene hdpe exposed to a chlorinated environment at a constant stress load. Stress corrosion is a form of galvanic corrosion, where stressed areas of the material are anodic to the unstressed areas of the material. In high wear environments, hdpe and ldpe resist stress cracking, moisture and chemicals for enhanced part integrity.
Stress corrosion cracking in plastic pipes researchgate. A study of the stress corrosion crack initiation stage in. Numerical modeling of stress corrosion cracking in polymers. Mdpe exhibited excellent scg and stress crack resistance, and dominated pe pipe manufacture for 30 years until the development of bimodal hdpe pe100. A deterministic modeling of slow stress corrosion sc crack growth process is. All pe types are not resistant to strong oxidising materials e. Hdpe and ldpe cover both ends of the application spectrum, from those requiring excellent impact resistance and durability to those requiring flexibility and tensity. A unified chemomechanical model is developed to predict the stress corrosion cracking scc of a viscoplastic polymer.
During the summer months, stresscracking of hdpe containers reaches its peak. Plastic may take up to 1,000 years to completely biodegrade. 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. The capped bottles are then placed in an oven at 60c and a stress is generated by the increased internal pressure. Environmental stress corrosion cracking resistance of high. One such performance criteria is environmental stress crack resistance escr. Experimental study of stress cracking in high density. 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. 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. For high density polyethylene xray scattering data indicate that the. When force is applied to plastic, it travels along the polymer chains causing molecules to strain to remain in contact.
Another form of stress corrosion cracking is attributable to the effect of crackpromoting media such as wetting agents. What is stress corrosion cracking and why does it occur. Stress corrosion cracking scc in engineering thermoplastics is commonly observed in the form of. Chemical permeationdesorption in new and chlorineaged polyethylene pipes, 2010. Environmental stress cracking an overview sciencedirect. This type of failure is known as stress corrosion cracking, often abbreviated to scc. Environmental stress cracking esc is a common cause of plastic product failure. A unified chemomechanical model is developed to simulate stress corrosion cracking scc of high density polyethylene hdpe in a chlorinated environment. In the csm type of fiber reinforced polyester composites, stress corrosion cracking produces a characteristic planar fracture. Stress corrosion cracking scc in engineering thermoplastics is commonly.
Multiple cracks initiated along the interior edge of the part wall and coalesced to produce the fracture. Scc in pipelines is a type of environmentally assisted cracking. Environmental stress cracking the the chemical agent does. Stress corrosion cracking in pipelines begins when small cracks develop on the external surface of buried pipelines. What causes stress corrosion cracking in pipelines. 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. Cytec industries, the effects of chlorinated water on polyethylene pipes, plastics today, march 2011. Nearneutralph scc is less temperaturedependent than highph scc. Stress corrosion cracking scc in polymer composites. Hdpe resin properties table hdpe plastic injection molding. Esc is the consequence of a combination of mechanical stress and exposure to an aggressive chemical. 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. With force and time, crazing or stress cracking occurs. Highdensity polyethylene or hdpe is a commonly used petroleum thermoplastic and the most used of the three polyethylenes for a wide range of applications.
Modeling stress corrosion cracking in plastic pipes, asce pipelines 2008. Astm d2561 17 standard test method for environmental stress. 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. Sunlight helps break down plastic faster than if it is buried. Environmental stress cracking esc is considered a leading. How to prevent stress cracking what is stress cracking. Plastic pipes have been used in pressure piping applications for many years. With good mechanical properties, corrosion resistance, ease of manufacturing, and. 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. Request pdf stress corrosion cracking in plastic pipes.
Environmental stress cracking esc in plastics means the failure at about room temperature. Aromatics and halogenated hydrocarbons cause swelling. Esc may be defined as the acceleration of stress cracking by contact with a liquid or vapor without chemical degradation of the plastic. Experimental study of stress cracking in high density polyethylene.
Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. Environmental stress cracking esc in plastics means the failure at about room. The stress cracking is more severe with detergent, bleach, motor oil and some industrial chemical packaging. In contrast, environmentalstresscracking agents do not appreciably diffuse into polyethylene, and stiffness is unaffected. 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. Environmental stress cracking resistance of polyethylene. Commonly used plastic pipe materials include polyethylene.
1589 668 1432 901 637 779 943 177 1190 627 691 1450 1274 648 1479 1406 854 492 48 1363 420 702 1163 684 1459 1265 408 377 609 1226 464 1334 1035 1281 1422 13 591 223 384 124 1405 506 1116 228 769 26