{"operation":"document","citation":"PI-76-065","title":"American Society of Mechanical Engineers — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1976-09-30","effective_on":null,"summary":"PI-76-065 response to American Society of Mechanical Engineers concerning 192.121, 192.123.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-065.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-065.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-76-065","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1976/PI76065.pdf","body":"<<<PAGE 1>>>\n\nMr. Manuel Gutierrez\nSecretary, Gas Piping Standards Committee\nAmerican Society of Mechanical Engineers\nUnited Engineering Center\n345 East 47th Street\nNew York, Street 10017\nDear Mr. Gutierrez:\nYou letter of July 7, 1976, asks the status of the petitions to revise 49 CFR Part 192, Sections\n192.121 and 192.123, as proposed by Mr. M.R. Green, Managing Director, Research, Codes, and\nStandards of ASME, in his October 23, 1972, letter. This letter enclosed a proposal from the Gas\nPiping Standards committee for increasing the 100mF temperature restriction to permit operation\nunder certain conditions up to 140mF and adopting a single design factor of f=0.32 for use with\nthermoplastic pipe in natural gas piping systems.\nThe Committee's proposal did not provide back up material to support their proposal. It was\nfound that data available to the Office of Pipeline Safety Operations (OPSO) on the characteristics\nof plastics at temperatures above 100mF was limited and that there was no reliable data available\non the actual plastic pipe temperatures measured at a sufficient number of locations across the\nnation to predict the maximum temperatures that may be anticipated in a given geographic\nlocation. Thus, processing was delayed pending search for and review of any information that\nwas or became available. Also, as we advised you in our letter of September 20, 1974, the\nstaffing limitations of our Office were causing further delays in the processing of all proposals for\nrulemaking received from the public.\nSome data on the high temperature performance of certain plastics was obtained from work done\nfor the American Gas Association by Battelle Memorial Institute and other work by the Plastics\nPipe Institute on hot water applications. A contract study performed for OPSO on the \"Pipeline\nIndustry's Practices Using Plastic Pipe in Gas Pipeline Facilities and the Resulting Safety Factors\"\nlisted some other sources of data on thermoplastic materials at elevated temperatures. At about\nthis same time, the DuPont Company began a series of tests at representative locations across the\nlower 48 States of the temperature of plastic service risers installed in steel pipe casing and has\nmade all of their data from this study available to OPSO. Data gathered during three summers in\nthis study shows a maximum temperature of 128mF measured on a thermocouple installed at\nmidwall on polyethylene pipe inside a model of a typical plastic service riser using a protective\ncasing of steel pipe. These tests were conducted under severe climate conditions in the Arizona\nand California desert regions.\nIn our review of the available data on the elevated temperature characteristics of plastic materials,\nit was discovered that some researchers were finding what they called a \"critical temperature\" at\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n1\n\n<<<PAGE 2>>>\n\nwhich the physical characteristics were more severely affected than at lower temperatures. This\ncritical temperature seems to occur on some thermoplastic materials in the range of 125mF to\n130mF.\nBased upon the above information, it appears appropriate to consider a new maximum\ntemperature at some level below the requested 140mF. It is our intention to issue a notice of\nproposed rule making proposing that the temperature design bases of plastic pipe be revised in a\nmanner that will recognize the various plastic material properties at different operating\ntemperature ranges. This notice will also consider modification of the design factor for plastic\npipe as recommended in your October 23, 1972, petition.\nIt is anticipated that a notice or notices of proposed rule making on temperature design limitations\nand design factors for plastic pipe will be issued in the fall of 1976.\nThank you for your interest in our pipeline safety program.\nSincerely,\nCesar DeLeon\nActing Director\nOffice of Pipeline\nSafety Operations\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n2\n\n<<<PAGE 3>>>\n\nMr. Cesar DeLeon\nOffice of pipeline Safety Operations\nDepartment of Transportation\n2100 2nd Street, S.W.\nWashington, DC 20590\nDear Mr. DeLeon:\nBy letter of October 23, 1972, Mr. M.R. Green, ASME Managing Director, Research,\nCodes and Standards, sent a proposal from the Gas Piping Standards Committee to your Office.\nThis proposal recommended revisions to CFR 49, Part 192.121 and 192.123. The proposals\nincluded the establishment of four temperature bases of 73mF, 100mF, 120mF, and 140mF as a\nrefinement and extension of the existing single temperature basis of 100mF. There was additional\nmaterial on the development of a new single design factor instead of the four presently specified.\nRecently, I have received many questions from operators as to the status of this proposal.\nThese operators are especially concerned with the changes in the temperature bases due to a\ngrowing problem with the use of plastic service line risers. As the result of the 100mF\ntemperature basis presently specified, the operators are currently required to sleeve that portion of\nthe service line riser where it comes out of the ground and up to the meter set assembly. Usually,\nthis service line riser is made of steel and as a result, must be cathodically protected. This is\nusually accomplished through the mechanism of a galvanic anode. Since this galvanic anode\nconstitutes a form of a cathodic protection system, some agencies believe that it should be\nmonitored. This presents some very substantial problems. First, in many locations, the service\nline from the stop valve up through the meter set assembly is owned by the customer. Therefore,\nthere is a question of the company's obligation to monitor that galvanic anode. Secondly, there is\nthe problem of the sheer numbers of these installations and the practicality of checking each one.\nTherefore, we would like to know what your anticipated schedule is in terms of submitting this\nadvance Notice of Proposed Rulemaking.\nThank you very much.\nVery truly yours,\nManuel Gutierrez\nSecretary\nGas Piping Standards Committee\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n3\n\n<<<PAGE 4>>>\n\nMr. Paul J. Cory\nOffice of Pipeline Safety (TES-32)\nU.S. Department of Transportation\nWashington, D.C. 20590\nSubject: Proposed Revisions of DOT-OPS Federal Standards 192.121 and 192.123.\nDear Mr. Cory:\nPer your telephone request this afternoon, I have enclosed a copy of the following material for\nyour files:\nLetter, Joseph C. Caldwell to M.R. Green, November 20, 1972.\nLetter, M.R. Green to Joseph C. Caldwell, October 23, 1972.\nI trust this correspondence will complete your files on this subject.\nSincerely,\nHarvey Miller\nStandards Engineer\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n4\n\n<<<PAGE 5>>>\n\nMr. M. R. Green\nManaging Director\nResearch, Codes and Standards\nThe American Society of\nMechanical Engineers\n345 E. 47th Street\nNew York, New York 10017\nDear Mr. Green:\nThis will acknowledge receipt of your letter of October 23, 1972, which petitioned this Office to\nconsider the recommendations concerning limitations on plastic pipe operating temperatures and\ndesign factors for a Notice of Proposed Rule Making.\nThis matter is being studied for further action.\nSincerely,\nJoseph C. Caldwell\nDirector\nOffice of Pipeline Safety\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n5\n\n<<<PAGE 6>>>\n\nMr. Joseph C. Caldwell\nDirector\nOffice of Pipeline Safety\nDepartment of Transportation\n400 6th Street, S.W.\nWashington, D. C. 20590\nDear Mr. Caldwell:\nAt the August meeting of the ASME Gas Piping Standards Committee the attached proposal was\nunanimously approved for submission to your office. What this proposal represents is an updating\nand refinement of the basic design philosophy for plastic pipe. When the original plastic design\nconcept were developed for conclusion in the 1968 edition of the B31.8 Code there was little\noperating experience and little laboratory testing available. Therefore, certain assumptions and\njudgments had to be made which by necessity were grossly over-simplified and ultra-conservative.\nIn the years since the adoption of that first plastic pipe design system; thousands of miles of\nplastic pipe of various types have been designed, installed and operated successfully. Also,\nthousands of dollars of research have been conducted by A.G.A. at the Battelle Memorial\nInstitute, by the Plastic Pipe Institute, and by the various manufacturers. All of these data and\nexperience have been applied to a refinement of the plastic pipe design methods, with the result\nthat a significant improvement has been made in the precision of plastic pipe design. However, it\nshould be noted that this does not represent a wholesale increase in plastic pipe operating\npressures. It is merely the utilization of experience and testing data to refine the methodology.\nWe recommend the adoption of this proposal since it represents a substantial advance in plastic\npipe technology. Thank you very much.\nVery truly yours,\nM.R. Green\nManaging Director, Research, Codes and Standards\nEnclosure\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n6\n\n<<<PAGE 7>>>\n\nPROPOSED REVISIONS OF DOT - OPS FEDERAL\nSTANDARDS 192.121 AND 192.123\nSummary of Proposed Revisions\n1. 2.* NOTE: Establish four temperature design bases of 73F, 100F, 120F and 140F as a\nrefinement and extension of the existing single temperature design basis of 100F.\nUse a single design factor of 0.32 instead of one of four (0.20 to 0.32) currently\nspecified. The design factor would be applied to the long-term hydrostatic\nstrength of the selected material at one of the temperature design bases outlined in\n(1) above.\nTo allow pipe producers sufficient time to develop the required test data at 100F\nto meet the proposed revision, a factor of 0.25 would be permitted to extend the\npresent 73F date to a design temperature basis of 100F until 1975 or two years\nfrom adoption; whichever is greater.\nReasons\n1. More efficient use of thermoplastic pipe will be accomplished by allowing the\ndesign engineer to equate material properties to design requirements over an extended\ntemperature range.\n2. The overall quality of thermoplastic piping will be improved because the proposed\ndesign concept will discriminate against pipe compounds which do not have satisfactory\nproperties for the anticipated operating conditions.\n3. Reliability and safety will be enhanced in the use of large size polyethylene pipe\nbecause of improved structural properties in underground service. Existing design\nrequirements may result in excessively heavy pipe walls in some applications, which causes\nthe pipe to behave more like a rigid structure than a flexible one. A flexible structure is\nmore capable of adjusting to soil movement or other secondary loads. Also, it becomes\nmore difficult to manufacture a product free from thermal stresses as the wall thickness is\nincreased.\nJustification for Revision #1\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n7\n\n<<<PAGE 8>>>\n\n1. There are applications for the use of plastic pipe where the temperatures exceed\n100F. Ground temperature at pipe depth in most of the United States would not exceed\n73F. In the southwest, however, ground temperatures could exceed 100F at service line\ndepth. Also, service lines brought above ground through protective sleeves could be\nsubject to temperatures about 100F in many areas of the country. The existing regulation\nprovides for a maximum of 100F in all systems. Existing requirements make no provision\nfor the use of thermoplastics at temperatures in excess of 100F where selected products\ncan provide safe service.\n2. Strengths of thermoplastics are generally reduced as their temperature increases.\nThe reduction in strength for thee plastics used for gas pipe is approximately 20% as the\ntemperature increases from 73F to 100F. At temperatures above 100F, some\nthermoplastic compounds are capable of providing satisfactory service, while others are\nnot. This is because the properties of all thermoplastic materials are temperature\ndependent, but not to the same degree (or better, perhaps, not of the same order of\nmagnitude). Test data show that specific commercial compounds having the same\nmaterial designation code (PVC 2110, PE 2306, etc) differ sufficiently among themselves\nat temperatures above 100F that it is impractical to use a single derating factor even for\nthe same given type of material. The difference between different plastic materials (i.e.,\npolyethylene vs. PVC) is even greater. To assure satisfactory performance, design\npressures for specified design temperature bases must be based on actual long term\nhydrostatic strength tests made on specific plastic compounds at a temperature equal to or\ngreater than the anticipated operating temperature. Extrapolation of data to a higher\ntemperature design basis is unsound. ASTM D-2837, \"Standard Method for Obtaining\nHydrostatic Design Basis for Therm-plastic Pipe Materials,\" warns against this practice.\nJustification for Revision #2\n1. From the standpoint of sound engineering design, it is appropriate that known\nvariables be accounted for directly, where feasible, and that the design factor be limited to\nvariables not otherwise determinable. If the design pressure is based on strength values\ndetermined at or above the anticipated operating temperature, as proposed, there is not\nneed to compensate for temperature in the design factor. On this basis, a design factor of\n0.32 provides a level of safety at least as great as the presently believers that the proposed\n0.32 design factor is still conservative but also believes its use is appropriate for all class\nlocations, for the following reasons:\na. Extensive field surveys by the A.G.A. Plastic Pipe Committee over the past several\nyears have not revealed a single incident attributable to stresses developed from\nallowable internal pressures. The potential problems associated with the stored\nenergy contained in highly compressed gas in steel pipe are controlled by the\ndesign factors for the various class locations. Control for plastic piping is provided\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n8\n\n<<<PAGE 9>>>\n\nb. c. d. e. by minimum pipe wall requirements and the limitation on the design pressure for\ndistribution systems of 100 psi contained in 192.123(a). With this kind of control,\nthe additional limitation provided by different design factors for the four class\nlocations is not needed.\nThe design factors for plastic pipe are applied to the minimum wall thicknesses\nspecified in ASTM D2513. The actual wall thickness of plastic pipe is normally\ngreater than the minimum because of the nature of the manufacturing process; i.e.,\nthe extruder must set his median wall thickness someplace above the minimum.\nThe result of 12 years of research on plastic pipe at Battelle Memorial Institute and\nadditional research at other laboratories show that the long-term hydrostatic\nstrength of plastic pipe obtained in tests with natural gas at 73.4F is essentially the\nsame as that obtained with water. A design factor of 0.50 is used for water.\nA gas design factor for polyethylene pipe slightly higher than 0.50 is used\nsuccessfully in Europe and Australia.\nFor a typical plastic pipe installation, the maximum seasonal diurnal temperature\nwould occur for only a few days or few hours per day for only part of the year.\nThe strength data used to calculate the hydrostatic design basis are obtained with\nthe walls of the plastic pipe maintained at the designated temperature continuously\nfor the entire test period. This provides an additional conservative design bias\nfrom the hoop stress standpoint.\nPlastic pipe, unlike more rigid piping materials, does not rely entirely on beam\nstrength to resist the effect of secondary loading but to some extent on flexibility\nand plasticity. The effect of soil movement or superimposed external forces on\nplastic pipe are less severe than those associated with more rigid pipe.\nParadoxically, the use of overly conservative design factors reduces safety by\nincreasing the external stresses that arise from secondary loading. Because of the\nexcessive wall thickness required, the pipe becomes more rigid and thus less able\nto compensate for soil movement and other sources of secondary loads.\nHistorical Background\nHistorically, the design factors given in Section 192.121(b) were developed in ASA B31.8\nin 1864 based on consideration of the following:\n1. With limited background and experience, it was decided to adopt a conservative\napproach and use a design strength for gas which was one-half the design strength then in\nuse for water. The design strength for water had been established as one-half the long\nterm hydrostatic strength of the pipe. The 0.50 design factor for water adopted in 1964\nf. DB\nWP51\\INTERPRT\\192\\121\\76-09-30\n9\n\n<<<PAGE 10>>>\n\nwas based on experience gained in the early use of plastic pipe. Its use eliminated the\nburst type failures which had previously occurred occasionally, and since 1964 has been\nshown to be an appropriate design factor for water. The basic design factor, then, for\nnatural gas was 0.25 of the long term hydrostatic, strength. There were two reasons for\nthe selection of a more conservative design factor for natural gas. The first was the fact\nthat long term test data obtained at 73.4F would be used to establish design pressures for\noperation at temperatures up to 100F. This aspect was based on test data which showed\nthat the appropriate amount of derating for this temperature difference is about 20%. The\nsecond was to compensate for the then little-known effects of natural gas on plastics. This\nallowance was quite conservative, being based primarily on the requirements of CAB\nwhich for all practical purposes is no longer being specified for gas service. Both PE and\nPVC are a great deal more chemically inert than CAB in natural gas services.\n2. Prior to the inclusion of plastic pipe provisions in the B31.8 Code, a gas design\nfactor of 0.40 was used in the equivalent to Class 2 and 3 locations. It provided\nsatisfactory performance. Based on satisfactory field experience for all materials, a design\nfactor higher than 0.25 was indicated.\n192.123 DESIGN LIMITATIONS FOR PLASTIC PIPE\n(a) (b) (c) (d) The design pressure may not exceed 100 psi for plastic pipe used in:\n(1) Distribution systems; or\n(2) Class 3 and 4 locations\nPlastic pipe may not be used where operating temperatures of the pipe will be:\n(1) below minus 20F; or\n(2) Above 140F for thermoplastic pipe or above 150F for reinforced\nthermosetting plastic pipe\nThe wall thickness for thermoplastic pipe may not be less than 0.062 inches.\nThe wall thickness for reinforced thermosetting plastic pipe may not be less than\nthose listed in the following table:\nNominal Size in Inches Minimum Wall Thickness in Inches\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n10\n\n<<<PAGE 11>>>\n\n2 0.060\n3 0.060\n4 0.070\n6\n0.100\nDB\nWP51\\INTERPRT\\192\\121\\76-09-30\n11","truncated":false,"body_characters":18780}