Interpretation Response #PI-19-0014
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Dr. Randy Knapp
Director of Engineering
Energy Piping Systems Division
Plastics Pipe Institute
105 Decker Court, Suite 825
Irving, TX 75062
Dear Dr. Knapp:
In your correspondence to the Pipeline and Hazardous Materials Safety Administration (PHMSA) dated October 16, 2019, you requested an interpretation of the pipeline safety regulations in 49 Code of Federal Regulations (CFR) Part 192. Specifically, you requested applicability of the § 192.121 requirements to Class 1 and Class 2 locations, by posing the following question:
Do the limitations for pressure and diameter in 49 CFR parts 192.121(b), (c), (c)(2)(i) and (c)(2)(iii) (i.e., limits of 125 psig and 12-inch diameter) apply to Polyethylene pipe installed in Class 1 or 2 locations?
A detailed response to this question requires understanding the regulatory history of these requirements. When 49 CFR Part 192 was first promulgated in 1970, the design pressure limit for plastic pipe used in distribution systems and Class 3 and 4 locations was set at 100 psig (689 kPa), which was the design pressure limit in ANSI B31.8 Standard, Gas Transmission Distribution and Piping Systems (35 FR 13257; August 19, 1970). In 2004, the design pressure was raised for polyethylene (PE) 2406 and PE 3408 thermoplastic pipe because of new developments in PE materials and better technology for detecting the rate of crack growth (69 FR 32886; June 14, 2004). The 2004 final rule was based on a petition for rulemaking submitted by the American Gas Association (AGA) in 1998 and amended in 1999. AGA specifically stated in its petition that this increase in the pressure limitation for thermoplastic pipe used in gas distribution systems was clearly supported by the proven performance of modern PE pipe and the successful operation of pipe at greater than 100 psig (689 kPa) under the authority of waivers granted by state pipeline regulators (65 FR 15290; March 22, 2000). Therefore, PHMSA intended for the allowance of a maximum design pressure of 125 psig (862 kPa) for thermoplastic pipe to apply to plastic pipe used in distribution systems and Class 3 and 4 locations.
In the recent plastic pipe final rule, PHMSA amended § 192.121 to allow for certain new and replaced PE pipe to operate with a design factor of 0.40 (previously 0.32), though it is limited to a minimum wall thickness of 0.090 inches (83 FR 58694; November 20, 2018). PHMSA noted during the rulemaking process that at 0.32, operators may still use the design formula in § 192.121 in accordance with the applicable standard. Additionally, PHMSA stated that it was not lowering the minimum wall thickness for 0.40 design factor pipe, as the more conservative wall thickness is necessary to mitigate sidewall fusion and tapping risks, among others, that exist at the higher design factor (Id.). The application of the 0.40 design factor for plastic pipe used in a specific class location must take into consideration the requirements of §§ 192.121(b) and (c). Furthermore, in the final rule, PHMSA merged the design limitations which were previously located in § 192.123 into § 192.121 (Id.).
Therefore, based on the rulemaking history of § 192.121 and previous § 192.123, PHMSA provides the following response to your question.
Section 192.121(b)(1) limits the design pressure for plastic pipe to not exceed a gauge pressure of 100 psig (689 kPa) for pipe used in distribution systems or transmission lines in Class 3 and 4 locations. However, the requirements of § 192.121(b)(2) through (b)(4) apply to all plastic pipe, including PE pipe in Class 1 and 2 locations.
For PE pipe produced after July 14, 2004, but before January 22, 2019, the exception in § 192.121(c)(1) to exceed the 100 psig limit for up to and including 12 inches in diameter, but limited to up to 125 psig, is only applicable to PE pipe subject to the requirements of § 192.121(b)(1) (i.e., plastic pipe and components, including PE pipe, installed in distribution systems or transmission lines in Class 3 or 4 locations). On the other hand, PE pipe produced prior to January 22, 2019, in Class 1 and 2 locations and not used in a distribution system does not have size and pressure limitations when using a design factor of 0.32 as specified in § 192.121(a). However, the maximums used in practice are limited by the design formula and the limitations within § 192.121(a), as well as limitations inherent to hydrostatic design basis, standard dimension ratio, and the practical limitations of PE pipe.
Likewise, PE pipe in Class 1 and 2 locations and not used in a distribution system and produced after January 22, 2019, does not have explicit limitations for design pressure and outer diameter when using a design factor of 0.32 as specified in § 192.121(a). However, the exception in § 192.121(c)(2) allowing the use of a 0.40 design factor for PE pipe produced after January 22, 2019, is applicable to all PE pipe, including PE pipe in Class 1 and 2 locations. Therefore, limitations on maximum design pressure and maximum outer diameter for plastic pipes with a design factor of 0.40 apply to all PHMSA regulated PE pipe produced after January 22, 2019, regardless of the PE pipe function or location.
If we can be of further assistance, please contact Tewabe Asebe at 202-366-5523.
John A. Gale
Director, Office of Standards
|§ 192.121||Design of plastic pipe|