1、Chemical hydrocarbon-based fluids such as gasoline, motor oil, diesel fuel and kerosene; and detergents, bleaches and other cleaningsolutions are often stored, shipped and sold in high density polyethylene packaging.Sometimes polyethylene is even used for rehabilitating concrete pipe to extend its l
2、ife in a corrosive environment. And protective coatings are often times used to prolong the life of concrete and steel pipe, but always with added cost.Traditional drainage pipe materials such as concrete, steel and aluminum have varying levelsof resistance to chemicals. Acidic chemicals and saline
3、conditions, from road salts or seawater can often cause deterioration in these materials.Most corrugated polyethylene pipe systems include some type of gasket, usually made of a natural rubber or ethylene propylene (EPDM) compound. In terms of the success of the overall installation, gaskets are a c
4、ritical link in the drainage system. As such, the effects of caustic solutions and chemicals on the gasket material have alsobeen thoroughly investigated and tested. Detailed information on gasket chemical resistance can be obtained by contacting individual CPPA manufacturing members.Potentially agg
5、ressive chemicals commonly found in storm sewers include road salts, fuels, and motor oils. In some parts of the country, acidic runoff from mines creates very severe conditions. Contaminated soils, such as those with high levels of certainhydrocarbons, can also factor into the overall picture of ch
6、emical impact.A sampling of chemicals that have been tested for compatibility with polyethylene pipe of various materials is shown in Table 1. Resistance to Chemically Aggressive Environments5Table 1 Chemical Resistance of Polyethylene Pipe to Selected Substances*Polyethylene PipeChemical or Substan
7、ce (73F/23C)Alcohol, ethyl RAntifreeze agents, vehicle RBleaching solution, 12.5% active chlorine RBleaching solution, 5.5% active chlorine RBrake fluid RDiesel fuel RDiesel fuel/oil REthane RFertilizer salts, aqueous RFuel oil RGasoline R to CHydraulic fluid/oil RHydrogen peroxide, aqueous 10% - 90
8、% RJet fuels RMethanol, pure RMotor oil RNitric acid, 0% - 30% RNitric acid, 30% - 50% R to CPetroleum, sour, refined RSea water RSewage, residential RSoap solutions, aqueous RSulfuric acid, 70% - 90% RTwo-stroke engine oil RR = Plastic pipe is generally resistant (Specimen swells 3% or has weight l
9、oss of 0.5% and elongation at break is not significantly changed)C = Plastic pipe has limited resistance only and may be suitable for some conditions(Specimen swells 3% - 8% at weight and loss of 0.5% - 5% and/or elongation at break decreased by 50%)*A more complete listing of polyethylenes chemical
10、 resistance can be obtained by contacting the CPPA.67Chemicals and abrasion are the most common durability concerns for drainage pipes,especially when the effluent flows at high velocities. But in test after test, results show that it takes longer to abrade through polyethylene than concrete.Abrasiv
11、es, such as stones or debris, can result in a mechanical wearing away of the pipe. The extent of the problem depends on the type of abrasive, frequency that the material is inthe pipe, velocity of the flow, and the type of pipe material. The effect of abrasives may beseen in the pipe invert where ex
12、posure is most severe. Over time, abrasives can result in aloss of pipe strength or reduction in hydraulic quality as they gradually remove wall material.Abrasion Resistance Testing Pipe materials vary in their resistance to abrasives. Laboratory tests have been conducted toobtain wear rates of mate
13、rials under controlled conditions. One of the most widely recognizedprojects1was conducted in 1990 under the direction of Dr. Lester Gabriel at California StateUniversity. This project evaluated the wear rates of 12“ and 24“ (300 and 600 mm) concretepipe and smooth interior corrugated polyethylene p
14、ipe, among other materials, under laboratory conditions. Sections of pipe were charged with an abrasive slurry consisting of crushed quartz aggregateand water. The pipe ends were then capped. The pipe was attached to a rocker apparatus androtated such that the average velocity of the slurry was abou
15、t 3 fps (0.9 m/s). Aggregate andpH were monitored throughout the test and adjusted as necessary to keep them as close aspossible to their original conditions. The test was completed after a specified number of rota-tions. Then the effect of the slurry was determined by measuring the loss of wall thi
16、ckness. Interpreting the test results requires an understanding of the wall sections and what constitutes a “failure” for each product. According to ASTM C76, 12“ (300 mm) concrete pipe must have a minimum of 0.5“ (13 mm) of concrete cover over the circumferential steel reinforcement. The failure po
17、int for concrete is typically assumed to be when the reinforcement is exposed; at this point some of the structural integrity has been lost and the reinforcement is vulnerable to corrosion.Durability Under Abrasive Conditions8Smooth interior corrugated polyethylene pipe in 12“ (300 mm) diameter has
18、a minimum liner thickness of 0.035“ (0.9 mm), although manufacturers typically use much heavier liners.The failure point of this product is assumed to be when the liner wears away. At this point, the strength of the pipe, supplied by the corrugated outer wall, remains intact.Table 2 presents the max
19、imum amount of wear that occurred during the test and the “expendable” wall thickness (e.g., the thickness of the wall that can abrade before reachingfailure). The remaining wall thickness is presented as a percentage of the expendable wallthickness, and is an indication of the amount of service lif
20、e remaining.Table 2 Abrasion Test Results Under Neutral Conditions (pH 7.0)Initial Max. Loss Expendable RemainingWall of Wall Wall WallThickness Thickness Thickness Thicknessin. (mm) in. (mm) in. (mm) % Visual Results12“ (300 mm) .110 0.021 0.035 40 Liner showed Smooth (2.8) (0.53) (0.89) some evide
21、nce Interior of wear; liner Polyethylene perforationPipe did not occur.12“ (300 mm) 2.15 0.79 0.5 0 Steel reinforce-Concrete Pipe (54.6) (20) (13) ment would havebeen exposed.*It was the intent of the project to test Class III reinforced concrete pipe. It was not realized until the tests had been co
22、mpletedthat the pipe was not reinforced. This booklet discusses the results of the project as if reinforcement was present, because itis commonly used in construction applications. 9Abrasion Test Results on 12“ (300 mm) Concrete and Smooth Interior Polyethylene Pipe Under Neutral Conditions (pH 7.0)
23、The test results show that polyethylene pipe had significantly more service life remaining after the test, as evidenced by the amount of wall thickness that was still present. Wall thickness alone, without regard to wear rate, is sometimes used to estimate service life.This test proved that evaluati
24、ng just the wall thickness can be deceiving. The heavier wall ofthe concrete pipe failed at some point prior to completion of the test, whereas 40% of the relatively thin liner on the corrugated polyethylene pipe remained intact even after theexperiment was completed. The wear rate of the material c
25、an - and in this case does - take precedence over the wall thickness. Combined Abrasion and Chemical Corrosion TestingAnother phase of the research described above was to conduct the same test but with a moderately acidic effluent. The objective was to determine what might be expected from thecombin
26、ed effects of a chemically aggressive environment and abrasives. The setup of the pipeand abrasives was the same as before, although the effluent pH was maintained at 4.0. Table 3shows the results of this trial. Table 3Abrasion Test Results Under Moderately Acidic Conditions (pH 4.0)10Initial Max. L
27、oss Expendable RemainingWall of Wall Wall WallThickness Thickness Thickness Thicknessin. (mm) in. (mm) in. (mm) % Visual Results12“ (300 mm) 0.110 0.024 0.035 31 Liner showed Smooth (2.8) (0.61) (0.89) some evidence Interior of wear; liner Polyethylene perforationPipe did not occur.12“ (300 mm) 2.15
28、 1.20 0.5 0 Loss of wallConcrete Pipe (54.6) (30.5) (13) thickness wasmuch higherthan in neutral conditions. Significant amounts of reinforcement would have beenexposed.11Abrasion Test Results on 12“ (300 mm) Concrete and Smooth Interior Polyethylene Pipe UnderModerately Acidic Conditions (pH 4.0)Mo
29、derately acidic conditions, similar to what could easily be expected in a dilute minedrainage application or perhaps in concentrated acid rain areas, caused dramatically different results for the pipe. The wear rate nearly doubled for concrete pipe compared to the neutral environment, whereas it inc
30、reased about 15% for the smooth interior corrugated polyethylene pipe. The time at which the failure point was reached becomes even more obvious under this testcondition. Reinforcement on the concrete pipe would have been exposed, thereby failing thepipe, long before it had in the chemically neutral
31、 environment. By contrast, the polyethylenepipe did not experience significantly more wear in a chemically aggressive environment, and over 30% of the liner thickness, or service life, remained at the completion of this test. As in the previous trial, the larger diameter pipe wore at a noticeably lo
32、wer rate than thesmaller diameter material. 12Laboratory tests, like the one described previously, are usually conducted under a set of rigorous conditions designed to produce results in a reasonable length of time. Test conditions may somewhat resemble field conditions in the selection of abrasives
33、 and pH conditions, but deviate in the quantity of abrasives and the constancy of their application.Thus, laboratory tests are very important for providing information on relative wear rates and relative product lives, but will likely provide misleading results if extrapolated directlyinto actual se
34、rvice life values. Actual polyethylene pipe installations have demonstrated superior durability. In 1981, theOhio Department of Transportation installed a corrugated polyethylene pipe in a culvert application near an abandoned strip mine in southeast Ohio. Acidic (pH 2.5-4.0) and abrasive effluent h
35、ad limited the lives of previously used pipe materials to two to five years, at which time either the invert wore through or the pipe collapsed. The polyethylenepipe replaced a polymer-coated steel pipe which had reached the end of its service life. In 1990, a report2was published summarizing nine y
36、ears of periodic inspections. The pipe remained nearly unaffected by the abrasive and acidic conditions. A high bedload was noted during the inspection made in 1985; rocks, coal and sand had been piled on the bank in an area 35 long by 15 wide by 1 deep (10.5 m x 4.5 m x 0.3 m) on the downstream end
37、 of the pipe providing an indication of the type and velocity of the abrasives.An update3was published in 1996; after 14 years of service, or nearly three times that of any other material used in that application, the pipe was in excellent condition and ready for many more years of dependable servic
38、e. Durability and Service Life13SummaryNonpressure polyethylene pipe used in drainage applications has nearly 30 years of successful applications in the United States. A tremendous amount of information has been obtained from its application and from laboratory investigations which indicate a 50 yea
39、r minimum service life for typical storm drainage applications. Polyethylene has demonstrated very high resistance to environmentally aggressive applications where other materials performance falls short. Tests conducted at California State University to determine the effects of abrasives in neutral
40、 and acidic environments showed the service life of polyethylene to far exceed that of concrete.Additional tests are in progress that will support these long term performance behaviors. CPPA will report on those tests as the results become available. 14References1. Gabriel, Lester. “Abrasion Resista
41、nce of Polyethylene and Other Pipes.” California State University, Sacramento, California. 1990.2. Goddard, James. “Nine Year Performance Review of a 24-inch Diameter Culvert in Ohio.” Sargand, Shad; Mitchell, Gayle; and Hurd, John; eds. Structural Performance of FlexiblePipes. Proceedings of the Fi
42、rst National Conference on Flexible Pipes; October 21-23, 1990; Columbus, Ohio. Rotterdam, Netherlands: A.A. Balkema. 1990.3. Goddard, James. “Performance Review of a Corrugated Polyethylene Cross Drain.” Public Works Magazine. January 1996, p. 47.Your Information Resource CPPA1825 Connecticut Ave., NWSuite 680Washington, DC 20009800-510-2772Fax: 202-462-9779http:/cppa-info.org 1997 Corrugated Polyethylene Pipe AssociationPrinted on recycled paper with soybean ink.CORRUGATEDPOLYETHYLENEPIPEASS O CIATIONAC P PA division of the Plastics Pipe Institute, Inc.TM
