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. Because parts made with vistamaxx enhanced hdpe are tougher than those made with pure hdpe, they are less likely to fail through environmental stress cracking. In fact, the designs for polyvinyl chloride pvc and high density polyethylene hdpe pipes are based on stressregression or stressrupture curves that are plots of the time to failure under various levels of constant stress. Oct 21, 2019 chloride stress corrosion cracking cscc is a type of intergranular corrosion. Sodium hypochlorite is available as solutions in varying strengths. Hdpe, like steel, is a semicrystalline material, with no crystals in the melted state. Following a number of failures caused by environmental stress cracking, the major tank design standard, the german merkblatt dvs 2205, omitted to list sodium hypochlorite within the. These reactions may reduce the physical properties of polyethylene. A uni ed chemomechanical model is developed to predict the stress corrosion cracking scc of a viscoplastic polymer. Coolpro is flexible and not prone to environmental stress cracking like other materials such as hdpe. Characterisation of aged hdpe pipes from drinking water distribution. The stress cracking is more severe with detergent, bleach, motor oil and some industrial chemical packaging. Esc may be defined as the acceleration of stress cracking by contact with a liquid or vapor without chemical degradation of the plastic.
Following a number of failures caused by environmental stress cracking, the major tank design standard, the german merkblatt dvs 2205, omitted to list sodium hypochlorite within the standard as a suitable application for polypropylene and hdpe. Mdpe exhibited excellent scg and stress crack resistance, and dominated pe pipe manufacture for 30 years until the development of bimodal hdpe pe100. It can be detrimental to austenitic stainless steels, one of the main reasons these steels are not considered a cureall for corrosion problems. Experimental study of stress cracking in high density. 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. Cytec industries, the effects of chlorinated water on polyethylene pipes, plastics today, march 2011. Sodium hypochlorite and its effects on polyethylene. Environmental stress crack resistance service temperatures up to 60c 140f is highly resistant to a wide variety of rather reactive cracking of escr is carried out on molded specimens 18 in. Chloride stress corrosion involves selective attack of a metal along its grain boundaries. Historically geomembrane resins have a lot in common with the piping industry. A number of myths have arisen as to the causes and remedies for stresscracking.
Environmental stress cracking, also referred to as esc, is a mechanism by which an organic chemical. With hdpe, it was observed that slow cooling or annealing of the. With the expanding application of plastic pipes and the use of chlorinated water, the physical properties of polyethylene pipe are under severe degradation stress. Carson municipal solid waste and residuals management branch waste minimization, destruction and disposal research division cincinnati. A recent report on a study of the expected lifetime of highdensity polyethylene hdpe pipes containing chlorinated potable waters adds a new, and perhaps primary, parameter to the conventional parameters of stresscracking resistance scr, oxidative induction time oit, and carbonyl index ci for the determination of remaining lifetime of hdpe piping. Some performance evaluation tests that once took only days to run now take months with todays. Fracture of highdensity polyethylene used for bleach bottles. A fracture mechanics approach was adopted to evaluate the environmental stress cracking resistance escr of two hdpe commercial grades used for bleach containers.
Technical note stress crack resistance for geomembrane products the stress crack resistance scr of polyethylene pe geomembranes has been the subject of study since the introduction of the materials over 20 years ago. The basic modes of interaction which cause simultaneous presence of three factors causes stresscracking. A commonly observed mechanism of initial attack on the immediate inner wall surface with additional penetration due to oxidant diffusion and free radical. Hdpe pipes are well suited for potable water applications in sizes ranging from 12 through over 54 diameter for a wide range of operating conditions. Environmental stress crack resistance of polyethylene ten rectangularshaped specimens are cut from a molded plaque prepared with standard methods.
Environmental stress cracking esc is a common cause of plastic product failure. Sc is a brittle failure that occurs at a stress level lower than the shortterm. Crazing can be induced at moderate to high stress levels by low molecular weight hydrocarbons. Concentrated solutions for disinfection purposes may contain 10% to 18% available chlorine while domestic and laundry bleaches typically contain 3% to 6% available chlorine. Environmental stress cracking resistance of polyethylene. The stress intensity factor range values aki for ct specimens 48 were. Alloy c276 has excellent resistance to pitting, stresscorrosion cracking and to oxidizing atmospheres. The effects of chlorinated water on polyethylene pipes. Degradation of an hdpe geomembrane without hals in chlorinated.
The premature failure of polyethylene pipes in contact with high chlorine and chlorine dioxide, used as residual disinfectants in drinking water distribution, remains an area of concern for water companies. Geomembrane and polyethylene pipe both share requirements for chemical resistance, durability, and resistance against stress cracking. Below illustrates the formation of the disinfectanting free chlorine hocl and ocl from chlorine gas. Chlorine 10% in water hdpe and ldpe at 20c shows little or no damage after 30 days. For specific cases in which the effect of an environment on polyethylene has not been documented, testing is required to identify any possible environmentalstresscracking effect. Certain water treatment plant chemicals, including chlorine and ferric chloride, can cause stress corrosion, which can lead to cpvc and pvc pipe failures. Numerical modeling of stress corrosion cracking in polymers. Experimental study of stress cracking in high density polyethylene pipes a thesis submitted to the faculty of drexel university by jingyu zhang. Hdpe sheets stressrelieved s r these sheets have gone through an additional annealing process to reduce stress. To this end, creep tests were carried out at various stress levels on.
Aug 01, 2007 since the introduction of the first 2liter, onepiece pet bottle by continental can co. Hdpe pipes, nol ring creep test, ageing effects, fracture mechanism, crack. The mechanisms of environmental stress cracking proposed in the literature will. Chlorine liquid n n n n chlorinated water 10 ppm 82 60 60. Its resistance to stress cracking greatly exceeds that of ordinary tubing found at local hardware stores. Influence of hot chlorinated water and stabilizer package.
High stress crack resistance borsafe pe100 for the. In this study the environmental stress cracking resistance escr of various low density polyethylene ldpe and linear low density polyethylene lldpe materials are evaluated. New thoughts on hdpe pipe durability in chlorinecontaining. Stress cracking sc is recognized as one of the major concerns for high density polyethylene hdpe pipes. It is important to note that solvents can also affect polyethylene, but in an entirely different manner than environmental stress cracking agents. Another related mechanism is environmental stress cracking esc. 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. This paper outlines the development of a chlorine stress cracking test, the results of testing from.
Stress cracking is caused by a combination of tensile stress, a stress cracking chemical and the inherent susceptibility of a thermoplastic like polypropylene to stress cracking. A new index test method, the notched constant tensile load nctl test, for evaluating highdensity polyethylene hdpe geomembranes regarding stress cracking resistance is presented in this paper. Effect of chlorinated water on the antioxidant depletion of hdpe geomembrane without hals. Chemical permeationdesorption in new and chlorine aged polyethylene pipes, 2010. This chemomechanical model is comprised of three components, each capturing a. In many pipe systems, potable water is disinfected by chlorine to. Polymer solutions news team april 12, 2016 18 in the world of polymer science, a single, seemingly small change in a polymers molecular structure can have a huge impact on how a material behaves in the real world and on the products you make from that material. Although esc is often described as a chemical attack, it is a very complex combination of plasticizing, migration, low level stress and mechanical failure initiated by exposure to specific classes of liquids, primarily surfactants soaps.
Highdensity polyethylene hdpe can be blowmolded and used for the production of bottles for aggressive products. The current geomembrane resins known as hdpe are variations on pipe grade resins used for large diameter polyethylene pipe. These products can interact both chemically and physically with the polymer constituting these containers, leading to a decrease in the performance of the material and undermining the structural integrity of the component. Products such as acetone and xylene may cause stress cracking even at very low stress levels and should therefore be avoided. The main purpose was to correlate micro molecular structure, such as molecular weight mw, molecular weight distribution mwd, short chain branches scb and crystallinity to the escr of these materials. A controlled notch is cut horizontally across each specimen, which serves as a crack initiation point. Geosynthetic research institute drexel university philadelphia, pa 19104 cooperative agreement no. Chloride stress corrosion cracking clscc is a type of stress corrosion cracking scc and is one of the most well known forms of scc in the refining and chemical processing industries. Environmental stress cracking esc is one of the most common causes of unexpected brittle failure of thermoplastic especially amorphous polymers known at present. Pdf fracture of highdensity polyethylene used for bleach bottles. It is well known from the pipe and cable insulation industries that pe can stress crack over long periods of time. Moldedin stress can be another contributor to stresscracking.
Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. Chloride stress corrosion cracking inspectioneering. Polypropylene chemical compatibility chart from ism. Chemical resistance guide everything inside the fence. Jan 08, 2020 theyre particularly vulnerable to a class of chemicals called hydrocarbons which includes substances like benzene, as well as chlorinecontaining chemicals, oils including animal fats, and strong oxidants. In this paper we deal only with one aspect of pvc gas mains, the stress cracking phenomenon. Chemical resistance of thermoplastics piping materials. Environmental stress cracking an overview sciencedirect. This model is applied to the speci c case of high density polyethylene hdpe exposed to a chlorinated environment at a constant stress load. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Over time, the chemicals used by the water treatment plant can cause the plastic to crack, leading to water leaks. Reports of hdpe water pipe failures have linked the failures to oxidative degradation. When exposed to this last type of chemical, fpp liners may develop oxidative damage, including stress cracking along folds and wrinkles. Heatgard tm hdpe has excellent chlorine resistance, chemical resistance is fully stabilized against uv light exposure, and has excellent stress cracking resistance.
Research indicates that chlorine dioxide is the most aggressive disinfectant followed by chlorine and then chloramines. Ectfe surpasses pvdf in resistance to strong bases and is the best material for handling sodium hypochlorite even at high temperatures. 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. Pdf the effects of chlorinated water on polyethylene pipes. Hdpe highdensity polyethylene sheets offer excellent impact resistance, light weight, low moisture absorption, and high tensile strength. Hdpe stands up to harsh chemicals and high pressure, making it a great choice for chemical feed pump discharge. A fracture mechanics approach was adopted to evaluate the environmental stress cracking resistance escr of two hdpe commercial grades. Environmental stress cracking an overview sciencedirect topics. It occurs in austenitic stainless steel under tensile stress in the presence of oxygen, chloride ions and high temperature. Enhancing the environmental stress crack resistance of hdpe.
Comparison of different pond liner materials which is best. The amount of crystalline content in the container depends on the rate of cooling. Following a number of failures caused by environmental stress cracking, the most widely used and detailed tank design standard, the german merkblatt dvs 2205, omitted to list sodium hypochlorite within the standard as a suitable application for tanks in polypropylene and hdpe. 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. Jul 29, 2010 a recent report on a study of the expected lifetime of highdensity polyethylene hdpe pipes containing chlorinated potable waters adds a new, and perhaps primary, parameter to the conventional parameters of stress cracking resistance scr, oxidative induction time oit, and carbonyl index ci for the determination of remaining lifetime of hdpe piping. What is temperature it is more important than concentration of chloride and anything higher than room temperature higher is worse. With this highquality tubing youll see longer life less maintenance and less downtime. Chemicals that do not normally affect the properties of an unstressed thermoplastic may cause completely different behavior such as stress cracking when under thermal or mechanical stress such as constant internal pressure or frequent thermal or mechanical stress cycles. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. An illustration of the simplest tests will help define esc better. Superior chlorine resistance is imperative in the highly oxidative environments of water and wastewater treatment facilities. Even at fairly low concentrations and temperatures, ammonia and many amines are capable of rapid dehydrochlorination of cpvc. A guide to chemical resistance of polycarbonate sheet. Investigations on environmental stress cracking resistance of.
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 cracking in hdpe protection ducts in segmental. When considering a polyethylene product for use in secondary containment applications, it is. The specimens are bent and inserted into a c shaped bracket, creating a stress in the specimen. Specifying hdpe for the storage of sodium hypochlorite is not a good idea. Stress cracking behavior of hope geomembranes and its prevention. Since the introduction of the first 2liter, onepiece pet bottle by continental can co. Comparison of different pond liner materials which is. Some reduction in tensile strength and an increase in. Infrared reflection spectra of hdpe after 3 weeks in 60c water with and. Effect of stabilization on creep crack growth in highdensity polyethylene. The depletion of antioxidants and decrease in stress crack resistance.
Stress cracking is essentially a brittle cracking phenomenon that occurs at a constant stress lower than the short term yield strength or break strength of the material. Because the mechanisms of failure for solvent attack and environmental stress cracking are so different, the means of optimizing material parameters are different as well. Stress corrosion cracking of polyethylene practical. By environmental stress cracking, we understand a failure in which materials in. One of the first applications for blow molded hdpe bottles was the replacement of glass for bleach packaging. Hdpe and ldpe at 20c show some effect after 7 days. Stress cracking in upvc and high impact pipes in the. Such myths are either wholly wrong or correct just part of the time. The information contained within this chart is based upon data supplied by resin manufacturers and is intended to be a general guide. A new index test method, the notched constant tensile load nctl test, for evaluating highdensity polyethylene hdpe geomembranes regarding stresscracking resistance is presented in this paper. Stress cracking behavior of hdpe geomembranes and its prevention by robert m. They all work by generating free chlorine hocl and ocl. Hence, an important design factor for pe pipes became commonly known as environmental stress cracking resistance escr, which led to the development of mdpe. Environmental stress cracking in polyethylene takes place because of interlamellar failure, which in turn is caused by relaxation of tie molecules.
In order to qualify as a high stress crack resistant material suitable forcontainer alternative installation methods, such as directional drilling and pipe bursting, the material in pipe form is required to pass 8760 hours without failure, which. Who says hdpe isnt tough enough to handle chlorine. Basic understanding of stress cracking in hdpe products. Environmental stress crack resistance of polyethylene. Premature cracking can be caused by topload stress, internal pressure, moldedin stress, and tail swing. What is the maximum chloride in ppm that can be allowed in. Pdf failure analysis of lldpe based materials semantic. Pdf effect of chlorinated water on the antioxidant.
Experimental study of stress cracking in high density polyethylene. Pdf stress cracking resistance of hdpe geomembranes with. While thermoplastic pipe has good corrosion resistance, it unfortunately is not. A materials resistance against this type of failure is called environmental stress cracking resistance escr. This is because stress from different sources increases during the summertime. During the summer months, stresscracking of hdpe containers reaches its peak. Direct chemical attack frequently causes a severe reduction of mechanical physical properties such as tensile strength, ductility, and impact resistance, and susceptibility to cracking from applied stress stress cracking. It is important to note that solvents can also affect polyethylene, but in an entirely. Specifying hdpe for the storage of sodium hypochlorite is not.
Esc is the consequence of a combination of mechanical stress and exposure to an aggressive chemical. Modeling stress corrosion cracking in plastic pipes, asce pipelines 2008. 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. Other common plastic materials used for piping include polyvinyl chloride pvc, polypropylene pp. Also, it has excellent resistance to phosphoric acid at all temperatures below boiling and at concentrations lower than 65%. It does not have plasticizers, which can leach and.
Hmc pp resins have excellent resistance to environmental stresscracking. C276 also exhibits excellent resistance to corrosion. Chemical resistance data from immersion tests cannot be unconditionally applied to thermoplastic piping components subjected to continuous or frequent mechanical or thermal stresses. Compared to other synthetic geomembranes, this advantage leads to significant quality and cost benefits. Chemical resistance data from immersion tests cannot be unconditionally applied to thermoplastic. While crystallinity provides strength, it also can lead to. A fracture mechanics approach was adopted to evaluate the environmental stress cracking resistance escr of two hdpe commercial grades used for. High density polyethylene hdpe pipe is used in water and sewer pipe installations across the united states.
Chemical resistance chart for plastic storage tanks. Ectfe is not resistant to hot amines, sodium or potassium. Penetration of hbr possible chemical resistance precautionary note. Specifying hdpe for the storage of sodium hypochlorite is. 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. Hydrocarbon environments on high density polyethylene for oil and gas.
Chlorine dioxide resistant hdpe mechanism, analytical tools and solutions. The nature of polyethylene pipe failure plasticstoday. The addition of a surfaceactive chemical, an environmental effect, accelerates this type of failure, thus this mechanism is termed environmental stress cracking esc. Theyre particularly vulnerable to a class of chemicals called hydrocarbons which includes substances like benzene, as well as chlorinecontaining chemicals, oils including animal fats, and strong oxidants. The pipe system is typically joined by thermal fusion or welding through the use of buttwelding equipment or electrofusion saddles that are often used in trench to connect hdpe pipe segments. Degradation of an hdpe geomembrane without hals in. 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. Escr problems get more pronounced in the summer, because of several factors related to increased heat and humidity.
730 698 482 986 1290 820 429 558 626 721 635 1187 557 867 1006 1446 352 646 761 610 1640 288 3 1349 564 1142 1379 444 461 306 789 791 812 1321 1308 988 1429 1264 1199 998 156 844 809 113 1377