Interpretation Response #PI-76-065
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Mr. Manuel Gutierrez
Secretary, Gas Piping Standards Committee
American Society of Mechanical Engineers
United Engineering Center
345 East 47th Street
New York, Street 10017
Dear Mr. Gutierrez:
You letter of July 7, 1976, asks the status of the petitions to revise 49 CFR Part 192, Sections 192.121 and 192.123, as proposed by Mr. M.R. Green, Managing Director, Research, Codes, and Standards of ASME, in his October 23, 1972, letter. This letter enclosed a proposal from the Gas Piping Standards committee for increasing the 100mF temperature restriction to permit operation under certain conditions up to 140mF and adopting a single design factor of f=0.32 for use with thermoplastic pipe in natural gas piping systems.
The Committee's proposal did not provide back up material to support their proposal. It was found that data available to the Office of Pipeline Safety Operations (OPSO) on the characteristics of plastics at temperatures above 100mF was limited and that there was no reliable data available on the actual plastic pipe temperatures measured at a sufficient number of locations across the nation to predict the maximum temperatures that may be anticipated in a given geographic location. Thus, processing was delayed pending search for and review of any information that was or became available. Also, as we advised you in our letter of September 20, 1974, the staffing limitations of our Office were causing further delays in the processing of all proposals for rulemaking received from the public.
Some data on the high temperature performance of certain plastics was obtained from work done for the American Gas Association by Battelle Memorial Institute and other work by the Plastics Pipe Institute on hot water applications. A contract study performed for OPSO on the "Pipeline Industry's Practices Using Plastic Pipe in Gas Pipeline Facilities and the Resulting Safety Factors" listed some other sources of data on thermoplastic materials at elevated temperatures. At about this same time, the DuPont Company began a series of tests at representative locations across the lower 48 States of the temperature of plastic service risers installed in steel pipe casing and has made all of their data from this study available to OPSO. Data gathered during three summers in this study shows a maximum temperature of 128mF measured on a thermocouple installed at midwall on polyethylene pipe inside a model of a typical plastic service riser using a protective casing of steel pipe. These tests were conducted under severe climate conditions in the Arizona and California desert regions.
In our review of the available data on the elevated temperature characteristics of plastic materials, it was discovered that some researchers were finding what they called a "critical temperature" at which the physical characteristics were more severely affected than at lower temperatures. This critical temperature seems to occur on some thermoplastic materials in the range of 125mF to 130mF.
Based upon the above information, it appears appropriate to consider a new maximum temperature at some level below the requested 140mF. It is our intention to issue a notice of proposed rule making proposing that the temperature design bases of plastic pipe be revised in a manner that will recognize the various plastic material properties at different operating temperature ranges. This notice will also consider modification of the design factor for plastic pipe as recommended in your October 23, 1972, petition.
It is anticipated that a notice or notices of proposed rule making on temperature design limitations and design factors for plastic pipe will be issued in the fall of 1976.
Thank you for your interest in our pipeline safety program.
Office of Pipeline
|Design limitations for plastic pipe