1、105 Decker Court, Suite 825, Irving, TX 75062 P:469-499-1044F: 469-499-1063 www.plasticpipe.org INVESTIGATION OF MAXIMUM TEMPERATURES ATTAINED BY PLASTIC FUEL GAS PIPE INSIDE SERVICE RISERS TR-30 2010 Foreword INVESTIGATION OF MAXIMUM TEMPERATURES ATTAINED BY PLASTIC FUEL GAS PIPE INSIDE SERVICE RIS
2、ERS This report was developed and published with the technical help and financial support of the members of the PPI (Plastics Pipe Institute). The members have shown their interest in quality products by assisting independent standards-making and user organizations in the development of standards, a
3、nd also by developing reports on an industry-wide basis to help engineers, code officials, specifying groups, and users. The purpose of this technical report is to provide essential information on a particular aspect of thermoplastic piping to engineers, users, contractors, code officials and other
4、interested parties. 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 any warranty, expressed or implied, including WARRANTIES OF MERCHANTABILIT
5、Y 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 manufacturer. The information in this report is offered for consideration by i
6、ndustry 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 comments and suggestions from users of the report. Please send suggestions of im
7、provements to the address below. Information on other publications can be obtained by contacting PPI directly or visiting the web site. This report was reviewed and republished with editorial corrections in December, 2010. The Plastics Pipe Institute (469) 499-1044 http:/www.plasticpipe.org This Tec
8、hnical Report, TR-30, was first issued in May 1978 and was revised in September 1980, in October 1988, in December 2006, and December 2010. INVESTIGATION OF MAXIMUM TEMPERATURES ATTAINED BY PLASTIC FUEL GAS PIPE INSIDE SERVICE RISERS 1.0 INTRODUCTION 1. 1 The maximum allowable temperatures for plast
9、ic piping systems used for fuel gas distribution are defined by Part 192, Transportation of Natural Gas and Other Gas by Pipeline: Minimum Safety Standards, Subchapter l), Pipeline Safety, of Title 49, Transportation, of the U. S. Code of Federal Regulations. By an act of Congress, the U. S. Departm
10、ent of Transportation regulates pipeline safety. 1.2 Section 375, Service Lines: Plastic, of Part 192 of the U. S. Pipeline Safety Regulations allows the use of properly designed metal-sleeved plastic riser pipe. A point that must be considered in proper design is the maximum temperature that can de
11、velop in the above-ground portion of the metal riser and its effect on the strength properties of the plastics gas carrier pipe. Section 121, Design of Plastic Pipe, of Part 192 limits the allowable operating temperature of a thermoplastic pipe to the highest value for which the pipes long-term hydr
12、ostatic strength has been established, except that it may not exceed 140F. 1.3 There has been some concern that the portion of a plastic riser pipe that is brought up out of the ground inside a protective metal sleeve for connection to a gas meter located outdoors may experience considerably higher
13、temperatures than buried pipe, possibly even above the 140F limit. Since metal-sleeved risers may be exposed to direct sunlight, they could become heated to higher than ambient temperatures. This report presents test data showing the maximum temperatures that may be obtained by thermoplastics pipe i
14、nstalled inside a metal protective sleeve and the conditions under which the maximum temperatures occur. The report includes: 1.3.1 A description of the test equipment, the environment, and the results obtained when evaluating for the effects of: a. wall contact; b. venting; c. shading; d. various i
15、nsulating materials; e. geographical location. 1.3.2 A correlation of actual and estimated service riser temperatures across the U.S.A. 1.3.3 An evaluation of the influence of temperature cycling on the hydrostatic strength of polyethylene pipe. 1.3.4 A description of a plastic-pipe/metal-sleeve ris
16、er assembly design that minimizes temperatures in the plastic pipe. 1.3.5 A list of plastic pipe materials that can be operated safely at the temperatures encountered in a properly-designed service riser. 2.0 CONCLUSIONS 2.1 The results of this study, in which a separation of at least 1/6 inch was m
17、aintained between plastic and metal, point to the following conclusions regarding proper design and installation of thermoplastic pipe gas service risers: 2.1.1 The plastic pipe must not touch the wall of the metal sleeve. Provisions must be included to assure that an annular space of at least 1/6-i
18、nch is maintained. 2.1.2 In all areas of the U.S. except the desert southwest, 120F is an appropriate temperature to use as the hydrostatic design basis for the plastic pipe. 2.1.3 In the desert areas of southwestern U.S., 140F should be used as the appropriate temperature for this purpose. 2.1.4 Th
19、ermoplastic pipe may be utilized safely and effectively in metal-sleeved risers when the above provisions are observed and when pipe selection and design are based upon appropriately established hydrostatic design ratings and the applicable design factors identified in DOT Document 192. Note If an i
20、nstallation has less than the 1/6-inch separation used in this study, check the plastic pipe temperature to insure that it does not exceed either the pipe material limitations or the applicable code requirements. 3.0 TEST ASSEMBLIES 3.1 The assemblies used for these tests consisted of 3-foot pipe le
21、ngths of 3/4-inch IPS polyethylene pipe installed in a 1-1/4-inch metal pipe. The two ends of the plastic pipe were stoppered and the ends of the metal pipe were capped. The plastic pipe was secured in the metal pipe by thumbscrews, so the annular space could be maintained at about 1/6 inch at all p
22、oints and the plastic did not touch the metal pipe. By adjusting the thumbscrews, the plastic pipe could be brought into contact with the metal pipe when desired. 3.2 The assembly included a thermocouple with the sensing element at the mid-wall of the plastic pipe. A continuous strip-chart recorder
23、measured the temperature. Figure 1 shows a cross section of the assembly, in which the thumbscrews are identified as spacers. Two of these complete test assemblies were used for tests that were carried out at various locations throughout the United States. Figure 2 is a photograph of a typical test
24、arrangement, showing both test assemblies and the recorder. 4.0 SUMMARY OF TEST RESULTS AND OBSERVATIONS 4.1 The effect of wall contact - In assemblies where the plastic pipe touches the metal pipe, temperatures in excess of 140F are possible. Examples of several measured temperatures are shown in T
25、able 1. Table 1 Effect of Wall Contact Location Plastic Pipe Touching Metal Wall Temp. F Plastic Pipe Controlled (Not Touching) Temp. F Ambient Air Temp. F Unshaded Wilmington, DE 143 110 94 Orange, TX 149 116 96 Phoenix, AZ 156 122 107 San Francisco, CA 144; 140 - 95 4.2 The effect of shading - A d
26、efinite temperature reduction of the plastic pipe was obtained by shading the assembly. With one assembly shaded, its temperature was approximately 10F lower than that of the unshaded assembly. Figure 3 is a photograph showing the arrangement in which one assembly is shaded and the other is exposed
27、to the sun. Figure 3. Arrangement of Test Assemblies and Recorder with One Test Assembly Shaded and One Unshaded 4.3 The effect of venting - The metal sleeve was vented to determine whether this would have an effect on the temperature of the enclosed plastic pipe. This experiment was carried out bec
28、ause a hypothesis had been advanced that holes in the metal casing would allow air circulation and thus reduce the temperature. To determine the effects of venting, the caps were removed from both ends of one assembly only and both assemblies were then exposed to exactly the same environment. The pl
29、astic pipe temperatures in the vented and unvented assemblies differed by no more than 2F, so the results indicate that there is no significant advantage to be obtained by venting. 4.4 The effects of insulating materials - Various types of insulation were placed between the plastic and metal pipes t
30、o study their possible effects. The materials evaluated were polystyrene foam, rubber, urethane foam, and asbestos. None of these insulators proved to be any more effective than air in the annular space. 4.5 The effects of geographic location - A series of tests were performed in several areas of th
31、e United States, representing significantly different climatic conditions. The basic test assemblies were used, with stoppered plastic pipes, capped metal casings, and a 1/6-inch insulating air space between the pipe and casing. Table 2 lists temperatures recorded at these sites during the summers o
32、f 1973 through 1975 and Table 3 lists the values obtained during the winter of 1975-76. From these data, it is obvious that the air temperature completely controls the plastic pipe minimum temperature under winter conditions. Table 2. Temperatures Attained by Plastic Pipe in Test Assemblies During S
33、ummer Seasons Test Location Test Dates Days Operated Maximum Pipe Temp. (F) Total Hours* Pipe Above 100F Total Hours* Pipe Above 120F Wilmington, DE July, 1973 10 115 3 0 Tulsa, OK August, 1973 3 120 4 0 Keene, NH July, 1973 6 112 2 0 Hialeah, Fl Sept., 1973 9 120 4.5 0 Orange, TX July,1974 4 118 5.
34、5 0 Phoenix, AZ August, 1974 4 124 8 3 San Ramon, CA July, 1975 3 100 0 0 Pico Rivera, CA August, 1975 4 112 4.5 0 Borrego Spring, CA August, 1975 4 125 6.5 2.5 *On hottest day Table 3. Temperatures Attained by Plastic Pipe in Test Assemblies During Winter Season Test Locations Test Dates Days Opera
35、ted Minimum Air Temp., F Minimum Pipe Temp., F Wilmington, DE December, 1975 3 15 15 Fitzwilliam, NH January, 1976 3 16 16 Soda Springs, ID February, 1976 7 2 2 5.0 ESTIMATED SERVICE RISER PIPE TEMPERATURES ACROSS THE U.S. 5.1 A correlation has been established between the ambient air temperature an
36、d the plastic pipe temperature in the simulated meter riser device, placed in stringent summertime environments. The value of this correlation is that it permits estimation of the number of hours the pipe will be above 120F or above 100F from a knowledge of the air temperature vs. time plot. Followi
37、ng are several such relationships: 5.1.1 When the air temperature is between 100F and 105 F for 7-1/2hours, the temperature of the plastic pipe will be above 120 F for 2-1/2hours. 5.1.2 When the air temperature is between 100F and 102F for 3 hours, the temperature of the plastic pipe will be above 1
38、20F for 1 hour. 5.1.3 If the air temperature is less than 100F, the plastic pipe temperature will not reach 120F. 5.1.4 If the air temperature is below 80F, the plastic pipe temperature will not reach 100F. 5.1.5 Air temperatures between 80F and 99F will probably cause the plastic pipe temperature t
39、o exceed 100F. The pipe temperature will likely be above 100F for about one-third of the daylight hours that the air temperature is between 80F and 99F. 5.2 A typical air temperature vs. plastic pipe temperature relationship is shown in Figure 4. A number of such relationships were used to arrive at
40、 the observations listed in 5.1 above. 5.3 The United States Weather Bureau issues specific climatic data from key U.S. cities on a monthly basis. Such data allowed use of the relationships described in the preceding section of this report to estimate how many hours per year the plastic pipe in the
41、metal casing would exceed 120F. The appended Table 4, consisting of five pages, shows data from the U.S. Summer Weather Record for 21 cities during the period from 1971 to 1974. For each of these cities, listed data include the highest temperature attained during the months of June through September
42、, the highest temperature during the year, and number of days during the year when the temperature exceeded 90F. The last column lists the estimated percentage of time during the year that the plastic pipe in a metal sleeve would have reached 120F or higher in an unshaded stringent environment. Note
43、 that, in most cases, this column shows 0%. Phoenix is the only notable exception, and here the 120F temperature is attained less than 2% of the time. 6.0 INFLUENCE OF TEMPERATURE CYCLING ON HYDROSTATIC DESIGN PROPERTIES OF POLYETHYLENE PIPE 6.1 In plastic pipe design, the practice is to employ the
44、highest temperature of the application as the basis for selecting the Recommended Hydrostatic Design Stress (RHDS). Such practice insures a conservative stance to follow when the environment of the application is not fully defined or the influences of variable temperatures on the pipe are not known.
45、 6.2 The temperature ranges experienced by the plastic pipe in a metal casing have been well established by the series of experiments described in this report. An evaluation of the effect on polyethylene pipe under temperature cycling conditions has shown that the pressure -bearing capability of the
46、 pipe is better when cycled than when held continuously at the highest temperature. In this temperature cycling evaluation, the Hydrostatic Design. Basis of the pipe was determined using the method defined in ASTM D-2837, “Obtaining Hydrostatic Design Basis for Thermoplastic Pipe Materials“. Water w
47、as used as the pressure-imposing fluid and its temperature was subjected to the following program: - Hold at 73F for three hours. - Raise to 140F in a one-hour period. - Hold at 140F for three hours. - Reduce to 73F in one hour. - Repeat. The regression curve of polyethylene pipes subjected to this
48、cycle for 10,000 hours demonstrated a Hydrostatic Design Basis of 800 psi. When the pipe was held continuously at 140F, the Hydrostatic Design Basis was 630 psi. So, evidently, temperature cycling of PE pipe with its induced stresses has less effect on the long-term strength of the pipe than continu
49、ous high temperature exposure. This characteristic offers a measure of safety to pipe used in a meter riser. 7.0 OPTIMUM DESIGN FOR THERMOPLASTIC GAS PIPE WITH METAL SLEEVE ASSEMBLY 7.1 For an optimum design, use spacers that maintain a uniform annular space between the plastic pipe and the metal sleeve so that the plastic does not touch the metal. Spacers may be rubber or flexible plastic, placed at intervals along the length of the assembly. Air is the most effective insulation and certainly the most economical. Products incorporating these desig
