1、 1 Effects of Disinfection on Newly Constructed Polyethylene Water Mains TR-34 / 2001 B Plastics Pipe Institute www.plasticpipe.org 2 Foreword This report was developed and published with the technical help and financial support of the members of Plastics Pipe Institute, PPI. The members have shown
2、their interest in quality products by assisting independent standards-making and user organizations in the development of standards, and also by developing reports on an industry-wide basis to help engineers, code officials, specifying groups, and users. The intent of this technical report is to pro
3、vide information on the effects of chlorine disinfection on the durability of PE piping for water systems. The testing reported herein was conducted on service pipe sizes and on resins in the form of plaques in accordance with the various test methods employed. At the time the testing was conducted,
4、 high performance PE materials such as PE4710 were not available. In 2006, PPI established a new program to provide test information on high performance PE materials, and will update this report when the information is available. Tests on piping in this report were conducted on service sizes; howeve
5、r, larger PE pipes produced to AWWA C901 and AWWA C906 are subject to the identical water service design criteria and in-service operating stresses. Furthermore, chlorine resistance tests of other olefin materials such as PEX have demonstrated that tests of service sizes are representative of larger
6、 sizes. Therefore, the test results herein are expected to be representative of larger sizes. This report has been prepared by PPI as a service of the industry. The information in this report is offered in good faith and believed to be accurate at the time of its preparation, but is offered without
7、any warranty, expressed or implied, including WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Any reference to or testing of a particular proprietary product should not be construed as an endorsement by PPI, which does not endorse the proprietary products or processes of any manu
8、facturer. The information in this report is offered for consideration by industry members in fulfilling their own compliance responsibilities. PPI assumes no responsibility for compliance with applicable laws and regulations. PPI intends to revise this report from time to time, in response to commen
9、ts and suggestions from users of the report. Please send suggestions of improvements to the address below. Information on other publications can be obtained by contacting PPI directly or visiting the web site. The Plastics Pipe Institute http:/www.plasticpipe.org (Editorial Revisions, February 2007)
10、 3 Effects of Disinfection on Newly Constructed Polyethylene Water Mains Table of Contents 1. Introduction 4 2. Scope 4 3. Methods of Chlorination 4 4. Industry Practice 5 5. Test Results 5 5.1 Quick Burst 5 5.2 Sustained Hydrostatic Burst 7 5.3 Tensile and Elongation 9 5.4 Oxidative Induction Time
11、9 5.5 High Speed Tensile Impact 10 5.6 PENT Testing 11 6. Other Experience 12 7. Chlorine Dissipation Rate 13 8. Conclusions / Recommendations 13 9. References 13 4 1. Introduction Disinfecting of water mains has been a common industry practice for many years. The first AWWA standard covering this p
12、ractice was approved in September 1947 (as 7D.2-1948). In 1986, the designation of the standard was changed to AWWAC651; the latest revision is ANSI/ AWWA-C651-92. The standard describes methods of disinfecting newly constructed potable water mains; mains that have been removed from service for plan
13、ned repairs or for maintenance that exposes them to contamination; mains that have undergone emergency repairs due to physical failure; and mains that, under normal operation, continue to show the presence of coliform organisms. Because the chlorine disinfection process puts pipe in contact with a s
14、trong oxidizer, a task group was formed in June 1993, within the PPI Technical Committee to investigate possible effects of disinfection on the durability of PE piping in potable water service. While C651 covers all piping materials used in potable water service, this investigation was confined to p
15、olyethylene systems. Chlorine was the only disinfecting agent investigated; chloramines were not evaluated. All tests conducted were short term, run at ambient temperature conditions on pipe samples made from particular polyethylene pipe compounds. The report is not to be construed as an indicator o
16、f the long-term performance of polyethylene pipe in general, or in the specific users environment and operating conditions. 2. Scope At the first task group meeting, the following scope was adopted: To investigate and quantify, if possible, any effects on the durability of PE piping caused by disinf
17、ection per AWWA C651. Exposure times and concentration levels were chosen to be consistent with the requirements of the standard. Note that the disinfection practices outside the constraints used in this study (i.e., exposure time, etc.) may yield different results - e.g., if a contractor leaves a p
18、ipe full of concentrated disinfectant for 6 months. 3. Methods of Chlorination Three methods of chlorination are explained in AWWA-C651: tablet, continuous feed, and slug. The tablet method is intended to give an average chlorine dose of approximately 25 mg/L, and precautions shall be taken to ensur
19、e that air pockets are eliminated and the water shall remain in the pipe for at least 24 hours. If the water temperature is less than 41F (5C), the water shall remain in the pipe for at least 48 hours ; the continuous feed to give a 24 hour residual of not less than 10 mg/ L; and the slug method to
20、give a 3 hour exposure of not less than 50 mg/L free chlorine. Residual free chlorine In the slug method, shall be measured as it moves through the main. If at any time it drops below 50 mg/ L, the flow shall be stopped, chlorination equipment shall be relocated at the head 5 of the slug, and, as fl
21、ow is resumed, chlorine shall be applied to restore the free chlorine in the slug to not less than 100 mg/ L. 4. Industry Practice To compare actual industry practice with AWWA C651 recommendations, a task group member conducted an informal survey of numerous City Water Departments. The survey was g
22、eographically broad and included utilities in Seattle (WA), Fresno (CA), Chicago (IL), Minneapolis (MN), San Antonio (TX), Savannah (GA) and Augusta (ME). It was learned that chlorine was by far the disinfectant of choice. All three methods described in C651 (tablet, continuous feed, and slug) are u
23、sed, with the tablet method being the most popular because it requires no additional equipment. For the tablet method, AWWA C-651 recommends the use of an average chlorine content of 25 mg/L for at least 24 hours. The utilities surveyed stated that concentrations ranging from 25-150 mg/L were used f
24、or durations from 24 to 72 hours. Preferably, disinfection should be carried out overnight, however, not on a day before the weekend or holidays In the continuous feed method, the chlorine may be added as dissolved calcium hypochlorite, sodium hypochlorite, liquid chlorine or dissolved chlorine gas.
25、 Several opinions were given that dissolved chlorine gas offered the “best” disinfection; however, environmental concerns and regulations have made this option less desirable. The water utilities that were interviewed use concentrations ranging from 25-60 mg/ L for durations of 24-72 hours. The slug
26、 method is generally used in conjunction with the tablet method. After the tablet method is completed and flushed, a heavily concentrated slug of chlorine is added to the main and slowly forced through the system. The concentration of the slug is monitored and more chlorine is added if the free chlo
27、rine residual drops below 50 mg/ L. Several of the utilities use this method at concentrations of 300-500 mg/L. Disposal and treatment of the heavily chlorinated water can become a problem with this procedure. 5. Test Results To evaluate the effects of chlorine exposure on PE water pipe during typic
28、al disinfection, physical properties of selected PE pipe samples were studied. Properties of pipe specimens exposed to chlorine were compared to properties of the same specimens that were not exposed. The test methods and the results of these tests are presented herein. 5.1 Quick Burst Test Objectiv
29、e: To determine if the chlorine exposure had a detrimental effect on the burst strength of the pipe. Testing was conducted on pipe specimens filled 6 with a 185-ppm chlorine water solution and conditioned for 72 hours at room temperature. Control specimens were also tested. The controls were not fil
30、led with tap water until tested. Test Method: Quick burst testing was then conducted in accordance with ASTM D-1599, Standard Test Method for Short-Time Hydraulic Failure Pressure of Plastic Pipe, Tubing, and Fittings. Several specimens were prepared from each sample. The specimens were 18” in lengt
31、h and sealed at each end with Swagelok fittings. For each sample, half the specimens were filled with water containing chlorine at 185 ppm, the other half were not filled until testing. The specimens exposed to chlorine were then placed on a sealed manifold for 72 hours. The control specimens were c
32、onditioned in the same room as the chlorine specimens for the same time period. Description of Test Samples: 1: ” SIDR 11.5 PE2306, ASTM D2239 2: ” SIDR 11.5 PE3408, AWWA C901 3: ” SDR 9 PE3406, ASTM D2737 4: ” SDR 9 PE3408, ASTM D2737 5: : SDR 9 PE 3408, ASTM D2737 Test Results and Data: Burst Pres
33、sures, psi Sample Without Chlorine With Chlorine 545 530 1 510 530 610 600 600 590 2 620 610 800 960 800 810 3 810 830 1040 1030 990 960 4 960 990 850 830 5 840 850 7 Failures for samples 2, 3, 4 and the chlorine specimens of sample 5 were in a ductile mode with ballooning prior to rupture. Failures
34、 for samples 1 and the non-chlorine specimens of sample 5 were in the slit mode. Conclusion: The burst strength of Polyethylene (PE) pipe exposed to 185 mg/L chlorine for 72 h, showed no apparent difference from that filled with tap water. 5.2 Sustained Hydrostatic Burst To further evaluate the poss
35、ible effects of chlorine exposure on actual pipe samples, sustained pressure testing per ASTM-D1598, Standard Test Method for Time-to-Failure of Plastic Pipe Under Constant Internal Pressure, was conducted on samples of the PE3408 pipe. Testing was performed at 176F to accelerate any adverse effects
36、 on performance. Two different conditioning times were used: 72 hours and 240 hours. Further details of the test and results are listed below. Set 1 Conditioning: 72 hours 73+3F 321 mg/ L free chlorine at start of conditioning Control samples were not exposed to any chlorine during conditioning Test
37、ing: 176+3F Specimen Hoop Stress Conditioning Failure 1 600 psi Chlorine 916 hr (no failure) 2 600 psi Control 916 hr (no failure) 3 600 psi Chlorine 916 hr (no failure) 4 600 psi Control 916 hr (no failure) 5 600 psi Chlorine 916 hr (no failure) 6 600 psi Control 916 hr (no failure) 7 750 psi Chlor
38、ine 953 hr (no failure) 8 750 psi Control 953 hr (no failure) 9 750 psi Chlorine 953 hr (no failure) 10 750 psi Control 953 hr (no failure) 11 750 psi Chlorine 953 hr (no failure) 12 750 psi Control 953 hr (no failure) 8 Set 2 Conditioning: 240 hours 73+3F 305 mg/ L free chlorine at start of conditi
39、oning: 210 mg/L at 120 hrs, refilled; 309 mg/ L at refilled (120 hrs); 217 mg/ L at 240 hrs Control samples were not exposed to any chlorine during conditioning Testing: 176+3F Specimen Hoop Stress Conditioning Failure 1 600 psi Chlorine 420 hr (no failure) 2 600 psi Control 420 hr (no failure) 3 60
40、0 psi Chlorine 420 hr (no failure) 4 600 psi Control 420 hr (no failure) 5 600 psi Chlorine 420 hr (no failure) 6 600 psi Control 420 hr (no failure) 7 750 psi Chlorine 446 hr (no failure) 8 750 psi Control 446 hr (no failure) 9 750 psi Chlorine 446 hr (no failure) 10 750 psi Control 446 hr (no fail
41、ure) 11 750 psi Chlorine 446 hr (no failure) 12 750 psi Control 446 hr (no failure) Although somewhat limited, the results of sustained hydrostatic burst testing do not suggest any significant effect of chlorine exposure on long term performance. Unfortunately, testing could not be continued longer
42、because of the need for the test stations being used. Ideally, data at sufficient pressures and times to permit calculation of Hydrostatic Design Basis would provide a better estimate of long term performance. It should be noted that all of the specifications for polyethylene water pipe (ASTM D2239,
43、 D3035, D2447, etc.) contain a sustained pressure requirement. The high-density material used for this study would be required to pass a 176F sustained pressure test of 60 hours (minimum) at 725 psi or 150 hours (minimum) at 580 psi. It can be seen that all of the samples used in this study easily m
44、et these requirements. 9 5.3 Tensile and Elongation A standard PE 3408 resin was compression molded in accordance with Procedure C of ASTM Method D1928. The molded specimens were randomly divided into two groups. One group was placed in a glass vessel containing a 200-ppm chlorine water solution at
45、room temperature. Measurements of free chlorine were made every other day and sodium chlorite solution added to maintain the 200-ppm target. The second group of specimens was exposed to “tap water” with a measured chlorine content of approximately 1 ppm. Samples were then removed periodically from t
46、he vessel and tested for tensile strength at yield and elongation at break in accordance with ASTM D638. A grip separation rate of 2-in/ minute was used. It should be noted that, because of the large number of samples required, only two specimens were tested at each of the time periods noted. This u
47、ndoubtedly contributed to the scatter seen in the results. Based on the early test results, exposure times were extended well beyond the original intent in an attempt to detect any possible downward trend. Exposure testing was carried out to 1176 hours without any indications of adverse effects. Tes
48、t results are summarized below: Tensile Strength (Break) (Elongation Break) Hours Chlorine Water Chlorine Water 24 4210 805 48 4141 796 72 4180 748 168 4285 4262 760 762 336 4249 4484 731 779 504 4314 4902 730 756 672 4753 805 840 4125 4329 793 752 972 4107 721 1008 4272 3990 781 788 1176 4310 803 5
49、.4 Oxidative Induction Time Because the chlorine disinfection process puts polyethylene pipe in contact with a strong oxidizer, it was decided to monitor the effect on chlorine exposure on thermal stability. Oxidative Induction Time as measured by a differential scanning colorimeter (DSC) was used as an indication of thermal stability. The same compression molded samples (PE3408) and chlorine solution (200 ppm) used for tensile strength and elongation measurements in Section 5.4 were used in this 10 study. Again, exposure times were extended well beyond the original
