{"operation":"document","citation":"PI-25-0013","title":"FlexSteel USA — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2025-12-09","effective_on":null,"summary":"PI-25-0013 response to FlexSteel USA concerning 192.3, 195.2.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-25-0013.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-25-0013.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-25-0013","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2026-05/FlexSteel-PI-25-0013-12-09-2025-Parts192.3-195.2-Signed-Combined.pdf","body":"<<<PAGE 1>>>\n\nMay 28, 2026\nMr. Kirk Francis, PE\nSenior Vice President, Engineering\nFlexSteel USA, LLC\n1221 Transport Drive\nAmeriport Industrial Park\nBaytown, TX 77523\nRE: Request for Interpretation – Determination of Outside Diameter for Classification of\nSteel-Reinforced, Multilayer Pipe under 49 CFR Parts 192 and 195\nDear Mr. Francis:\nIn a letter dated December 9, 2025, FlexSteel USA, LLC (FlexSteel USA) asked the Pipeline and\nHazardous Materials Safety Administration (PHMSA), Office of Pipeline Safety (OPS) for a\nwritten interpretation on the applicability of the Federal safety standards in 49 CFR Parts 192\nand 195 to gathering pipelines constructed with FlexSteel. FlexSteel is a three-layer composite\npipe product manufactured by FlexSteel USA that consists of (1) an innermost high-density\npolyethylene (HDPE) layer, (2) a steel-reinforcing layer, and (3) an outermost HDPE layer.\nFlexSteel USA seeks confirmation from OPS that the second, steel-reinforcing layer should be\nused in determining the outside diameter (OD) of a gathering line constructed with FlexSteel\nunder Parts 192 and 195. FlexSteel contends that this result is consistent with the approach used\nin determining the OD of traditional steel and plastic pipe designs and the risk-based framework\nfor regulating gathering lines. For the reasons provided below, OPS agrees that the steel-\nreinforcing layer should be used in determining the OD of a gathering line constructed with\nFlexSteel.\nBackground\nPHMSA has prescribed Federal safety standards for gathering lines in Parts 192 and 195. The\napplicability of these safety standards to onshore gathering lines depends, in certain cases, on the\nOD of the pipe.1 For example, Part 192 uses an OD threshold of “greater than or equal to 8.625\n1 OD is the actual, measurable external width of a pipe. nominal diameter (or nominal pipe size - NPS/DN) is a\nnon-dimensional, standardized designation for sizing. For pipes up to 12 inches, the OD is typically larger than the\nNPS, while for pipes 14 inches and larger, the NPS corresponds directly to the actual OD.\nThe Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety provides written clarifications of the Regulations (49 CFR\nParts 190-199) in the form of interpretation letters. These letters reflect the agency's current application of the regulations to the specific facts\npresented by the person requesting the clarification. Interpretations are not generally applicable, do not create legally-enforceable rights or\nobligations, and are provided to help the specific requestor understand how to comply with the regulations.\n\n<<<PAGE 2>>>\n\nPage 2 of 8\ninches” in determining if an onshore gas gathering line is subject to the requirements for Type C\ngas gathering lines. Part 195 also uses a threshold of “219.1 mm (8 ⅝ in) or less nominal” OD in\ndetermining if a pipeline qualifies as a gathering line and a “nominal diameter” threshold range\nof between “6 5/8 inches (168 mm) to 8 5/8 inches (219.1 mm)” in determining if a gathering\nline in a rural area qualifies a regulated rural gathering line.\nPointing to these regulations, FlexSteel USA states that “PHMSA has not directly addressed how\nto measure the OD of composite pipe for purposes of making jurisdictional and regulatory\ndeterminations.” FlexSteel USA further notes that “[w]ith respect to steel pipe, PHMSA\ngenerally bases the diameter of the pipeline on pipe mill records and does not include any\ncoatings or additional layers that may protect the pipeline while it is in operation when\ndetermining the OD of the pipe.” FlexSteel USA contends that “the same approach can be\napplied in determining the OD of steel reinforced, multilayer pipe” such as FlexSteel.\nFlexSteel USA further contends that applying that approach to FlexSteel leads to the conclusion\nthat the steel-reinforcing layer should be used in determining the OD. FlexSteel states that the\nsteel-reinforcing layer “provid[es] the pressure containment capacity” for the innermost HDPE\nlayer, which “determin[es] the throughput capacity.” The outermost HDPE layer, on the other\nhand, “shields the steel from corrosion and abrasion, serving a function similar to coating,”\nwhich is not considered in determining the OD of steel pipe.\nFinally, FlexSteel USA contends that “[b]asing the OD of the multilayer pipe on the steel layer is\n. . . consistent with PHMSA’s established risk-based criteria for regulating certain gas and liquid\nlines.” FlexSteel USA states that “PHMSA has routinely recognized that the regulation of\ngathering lines and rural lines is based on the risk associated with the line, which is determined\nprimarily on the throughput of line and its proximity to communities.” Because the inner HDPE\nlayer and steel-reinforcing layers determine the volume and capacity of a pipeline constructed\nwith FlexSteel, FlexSteel USA states that using the steel-reinforcing layer to determine the OD is\n“consistent with PHMSA’s established risk-based approach for regulating certain gas and liquid\nlines.”\nPHMSA received a comment in support of FlexSteel USA’s position from the Plastic Pipe\nInstitute. PHMSA received comments opposing FlexSteel USA’s position from the National\nAssociation of Pipeline Safety Representatives (NAPSR) and Mary S. Friend, Director, Gas\nPipeline Safety Division, West Virginia Public Service Commission.\nRelevant Regulations\nThe following regulations are relevant in responding to FlexSteel USA’s request for\ninterpretation:\n§ 192.3 - Definitions\n§ 192.8 - How are onshore gathering pipelines and regulated onshore gathering\npipelines determined?\nThe Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety provides written clarifications of the Regulations (49 CFR\nParts 190-199) in the form of interpretation letters. These letters reflect the agency's current application of the regulations to the specific facts\npresented by the person requesting the clarification. Interpretations are not generally applicable, do not create legally-enforceable rights or\nobligations, and are provided to help the specific requestor understand how to comply with the regulations.\n\n<<<PAGE 3>>>\n\nPage 3 of 8\n§ 195.2 - Definitions\n§ 195.12 - What is a regulated rural gathering line and what requirements apply?\nAnalysis and Response\nUpon review of the question provided by FlexSteel USA, additional information received from\nFlexSteel after submitting its request, the public comments, and the relevant requirements in\nParts 192 and 195, PHMSA’s analysis and responses are as follows:\nQuestion: For purposes of complying with the Federal safety standards for gathering lines in\nParts 192 and 195, should FlexSteel USA use the steel-reinforced layer in determining the OD of\nFlexSteel composite pipe?\nPHMSA Response: Yes. While not cited by FlexSteel USA or the public commenters, Part 192\ndefines “composite materials” as “materials used to make pipe or components manufactured with\na combination of either steel and/or plastic and with a reinforcing material to maintain its\ncircumferential or longitudinal strength.”2 PHMSA added this definition to Part 192 in the final\nrule that established the safety standards for Type C onshore gas gathering lines in 49 CFR §\n192.9(e), including the provision in 49 CFR § 192.9(h) authorizing the use of composite\nmaterials through a 90-day prior notice and no objection process.3\nThe key criteria for determining whether something qualifies as composite material under the\nPart 192 definition are (1) the use of a combination of steel and/or plastic and (2) a reinforcing\nmaterial to maintain its circumferential or longitudinal strength. According to the information\nprovided by FlexSteel USA, FlexSteel pipe consists of three layers of material: (1) an innermost\nHDPE layer, (2) a steel-reinforcing layer, and (3) an outermost HDPE layer. The first HDPE\nlayer determines the throughout (or volume) of gas that can be transported in the FlexSteel pipe;\nthe second steel-reinforcing layer provides pressure containment for the gas being transported in\nthe innermost HDPE layer of the FlexSteel pipe; and the third HDPE layer provides protection\nfor the innermost HDPE layer and the steel-reinforcing layer of the FlexSteel pipe from\ncorrosion or external forces.\nIn these circumstances, the first and second layers are the composite materials used to make\nFlexSteel pipe as defined in Part 192. These two layers are made with a combination of plastic\nand steel, and the second steel-layer is the “reinforcing material” used to “maintain its\ncircumferential or longitudinal strength.” The third layer, by contrast, is used to protect the first\ntwo layers from other threats and is akin to the use of a coating for cathodic protection or a\n2 49 CFR § 192.3.\n3 Pipeline Safety: Safety of Gas Gathering Pipelines: Extension of Reporting Requirements, Regulation of Large,\nHigh-Pressure Lines, and Other Related Amendments, 86 Fed. Reg. 63,296 (Nov. 15, 2021).\nThe Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety provides written clarifications of the Regulations (49 CFR\nParts 190-199) in the form of interpretation letters. These letters reflect the agency's current application of the regulations to the specific facts\npresented by the person requesting the clarification. Interpretations are not generally applicable, do not create legally-enforceable rights or\nobligations, and are provided to help the specific requestor understand how to comply with the regulations.\n\n<<<PAGE 4>>>\n\nPage 4 of 8\ncasing to protect a pipeline from external force damage.4 As the latter is not being used as “a\nreinforcing material to maintain . . . the circumferential or longitudinal strength” of the FlexSteel\npipe, the third layer is not an essential element of the composite material as that term is defined\nin Part 192. Therefore, the OD of a gathering line constructed with FlexSteel should be based on\nthe steel-reinforcing layer, not the outermost HDPE layer, under Part 192.\nThough there is no comparable definition for “composite material” in Part 195, the OD of a\nhazardous liquid gathering line constructed with FlexSteel should be similarly based on the steel-\nreinforcing layer. Part 195 only prescribes safety standards for pipelines constructed with steel\npipes and includes a special notification process for operators that want to transport hazardous\nliquid or carbon dioxide in pipelines constructed with materials other than steel.5 Nothing in Part\n195 suggests there should be a difference between gas and hazardous liquid pipelines when\ndetermining the OD of composite pipe material. Nor is there anything in Part 195 to suggest that\nthe third HDPE layer, which provides protection from corrosion or external force damage,\nshould be included in determining the OD of a gathering line constructed with FlexSteel.\nThe comments submitted by NAPSR and Ms. Friend do not justify a different result. NAPSR\nand Ms. Friend both acknowledge that the function of the outer HDPE layer of the FlexSteel pipe\n“is to resist mechanical damage and provide environmental protection” but contend that “[a]ll\nthree layers appear to be required to make the product function.” Noting that “[t]he steel layer\nhas continuous helical gaps that create an annular space and natural capture layer for the gas\nwhich permeates the HDPE liner,” NAPSR and Ms. Friend also contend that “[t]he outer HDPE\nlayer appears to function as a gas containing layer due to the gas permeation of the inner HDPE\nliner.” NAPSR and Ms. Friend believe that the outer HDPE layer should be included in\ndetermining the OD of a gathering line constructed with FlexSteel under Part 192 for these\nreasons.\nNAPSR and Ms. Friend do not account for the definition of “composite materials” in Part 192 in\ntheir comments. That definition makes clear that the innermost HDPE layer and steel-\nreinforcing layer of FlexSteel pipe are the relevant composite materials. The outermost HDPE\nlayer, which NAPSR and Ms. Friend both recognize is used “to resist mechanical damage and\nprovide environmental protection,” is not “a reinforcing material” used “to maintain” the\n“circumferential or longitudinal strength” of FlexSteel pipe. Indeed, the outermost HDPE layer\nwould not qualify as a composite material even if, as NAPSR and Ms. Friend contend, that layer\ncould be used to contain gas that enters the annulus in the event that the innermost HDPE layer\nand steel-reinforcing layer are breached. FlexSteel USA has not represented that the outermost\nHDPE layer is designed for that purpose, and PHMSA does not ordinarily include measures that\nare used to prevent or mitigate pipeline failures in determining the characteristics of the pipe\nitself.\n4 See 49 CFR § 192.323 (prescribing requirements for “[e]ach casing used on a transmission line or main under a\nrailroad or highway); PHMSA Interpretation Response #PI-75-036 (discussing requirements in Parts 192 and 195\nthat apply to casings). PHMSA notes that the thickness of the outer layer is not adjusted based on the internal\npressure rating of the FlexSteel pipe but is instead constant for all pressure ratings of the same size pipe.\n5 See PHMSA Statement of Policy for Transporting Hazardous Liquids or Carbon Dioxide in Non-Steel Pipelines\n(May 18, 2026), available at https://www.phmsa.dot.gov/news/phmsa-statement-policy-transporting-hazardous-\nliquids-or-carbon-dioxide-non-steel-pipelines.\nThe Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety provides written clarifications of the Regulations (49 CFR\nParts 190-199) in the form of interpretation letters. These letters reflect the agency's current application of the regulations to the specific facts\npresented by the person requesting the clarification. Interpretations are not generally applicable, do not create legally-enforceable rights or\nobligations, and are provided to help the specific requestor understand how to comply with the regulations.\n\n<<<PAGE 5>>>\n\nPage 5 of 8\nIn summary, OPS agrees with FlexSteel USA that the steel-reinforcing layer should be used in\ndetermining the OD of a gathering line constructed with FlexSteel under Parts 192 and 195.\nIf we can be of further assistance, please contact Joe Berry (720) 601-3577.\nSincerely,\nCAMERON H Digitally signed by CAMERON\nH SATTERTHWAITE\nSATTERTHWAITE Date: 2026.05.28 17:21:10\n-\nCameron H. Satterthwaite\nActing Director, Office of Standards\nand Rulemaking\nThe Pipeline and Hazardous Materials Safety Administration, Office of Pipeline Safety provides written clarifications of the Regulations (49 CFR\nParts 190-199) in the form of interpretation letters. These letters reflect the agency's current application of the regulations to the specific facts\npresented by the person requesting the clarification. Interpretations are not generally applicable, do not create legally-enforceable rights or\nobligations, and are provided to help the specific requestor understand how to comply with the regulations.\n\n<<<PAGE 6>>>\n\nFlexSteel USA, LLC 1221\nTransport Drive\nAmeriport Industrial Park\nBaytown, TX 77523, USA\nOFFICE 281.918.3400\nwww.flexsteelpipe.com\nDec. 9, 2025\nMr. John Gale\nDirector of Standards and Rulemaking\nOffice of Pipeline Safety\nPipeline and Hazardous Materials Safety Administration\nU.S. Department of Transportation\n1200 New Jersey Avenue SE\nWashington, DC 20690\nRE: Request for Interpretation – Determination of Outside Diameter for Classification of\nSteel-Reinforced, Multilayer Pipe under 49 C.F.R. Parts 192 and 195\nMr. Gale:\nFlexSteel USA, LLC requests PHMSA’s interpretation on how to classify steel reinforced,\nmultilayer pipe systems—such as FlexSteel—used in onshore gas and liquid gathering pipelines\nunder 49 C.F.R. Parts 192 and 195. Specifically, the company seeks clarification on the correct\nmethod for calculating outside diameter (OD) for these composite pipelines to ensure accurate\njurisdictional and regulatory determinations under the pipeline safety regulations. Consistent with\nPHMSA’s standards for steel and traditional plastic pipe, FlexSteel is requesting confirmation that\nthe OD of steel reinforced, multilayer pipe is based on the diameter of the steel layer, excluding\nouter HDPE layers.\nBackground\nUnder 49 C.F.R. § 192.8, an onshore gas gathering pipeline is considered Type C if it is in a Class\n1 location and:\n• The OD of the pipe is greater than or equal 8.625 inches, and\n• For metallic pipe, the maximum allowable operating pressure (MAOP) produces hoop\nstress of more than 20% SMYS, or\n• For metallic pipe, if the stress level is unknown and the MAOP is more than 125 psig; or\n• For non-metallic pipe, the MAOP is more than 125 psig.\nType R gas gathering lines are those located within Class 1 or Class 2 locations that do not meet\nthe criteria of any other gas gathering pipeline designation.\nUnder 49 C.F.R. § 195.2, a liquid gathering line is defined as a “pipeline 219.1 mm (8 ⅝ in) or\nless nominal outside diameter that transports petroleum from a production facility.” Section 195.11\ndefines a regulated rural liquid gathering line as one that meets a number of requirements,\nincluding that it “[h]as a nominal diameter from 6 ⅝ inches (168 mm) to 8 ⅝ inches (219.1 mm).”\n2\n\n<<<PAGE 7>>>\n\nFlexSteel USA, LLC 1221\nTransport Drive\nAmeriport Industrial Park\nBaytown, TX 77523, USA\nOFFICE 281.918.3400\nwww.flexsteelpipe.com\nOutside Diameter Determination\nPHMSA has not directly addressed how to measure the OD of composite pipe for purposes of\nmaking jurisdictional or regulatory determinations. With respect to steel pipe, PHMSA generally\nbases the diameter of the pipeline on pipe mill records and does not include any coatings or\nadditional layers that may protect the pipeline while it is in operation when determining the OD of\nthe pipe. This same approach can be applied in determining the OD of steel reinforced, multilayer\npipe.\nAlthough current OD standards were developed for traditional steel and plastic pipe designs, using\nthe steel layer as the basis for measuring multilayer pipe OD aligns with PHMSA’s established\napproach for these conventional pipelines. Steel-reinforced composite pipe utilizes a multilayer\ndesign, with the innermost HDPE layer determining the throughput capacity of the line and the\nsteel layers providing the pressure containment capacity. The outer HDPE layer shields the steel\nfrom corrosion and abrasion, serving a function similar to coating on steel pipe.\n1 The OD of this\ndesign, therefore, should be measured from the steel layer to remain consistent with PHMSA’s\nstandards as applied to steel and traditional plastic pipe, where the OD is based on the diameter\nof the line pipe excluding any coatings.\nBasing the OD of the multilayer pipe on the steel layer is also consistent with PHMSA’s\nestablished risk-based criteria for regulating certain gas and liquid lines. In Parts 192 and 195,\nPHMSA has routinely recognized that the regulation of gathering and rural lines is based on the\nrisk associated with the line, which is determined primarily on the throughput of line and its\nproximity to communities.2 The inner HDPE layer in the multilayer design determines the volume\ncarried by the pipeline and the steel layers provide pressure capacity, as confirmed by testing\nconducted by FlexSteel, while the outer HDPE layer simply adds corrosion and abrasion\nprotection. The steel layer is determinative of the capacity of the line and, therefore, should be\n1 PHMSA has recognized that the HDPE layer of this design functions similarly to a coating in its special\npermits and State waiver no objection letters. See, e.g., California State Waiver Issued to RockPoint Lodi\nGas Storage, LLC, Res. GSRB-2 (Jan. 30, 2025); PHMSA’s Special Permit Issued to National Fuel Gas\nSupply Corp., PHMSA-2021-0042 (2021) (requiring annulus space monitoring between the “inside liner and\nouter jacket HDPE materials” and noting that “[p]ositive pressure indicates the outer jacket material is intact\n(holiday free), demonstrating a ‘perfect coating’, thus external corrosion cannot occur. It indicates that the\nHDPE liner material is intact and containing bore gas pressure as intended”). See also State Waiver Issued\nto Cinco Natural Resources Corporation, Docket No. 09903 (Feb. 9 2010) (approved by PHMSA on Apr.\n21, 2010) (referring to the outer polyethylene layer as the “outer coating”).\n2 See, e.g., Safety of Gas Gathering Pipelines: Extension of Reporting Requirements, Regulation of Large,\nHigh-Pressure Lines, and Other Related Amendments, 86 Fed. Reg. 63266, at 63280, 63286 (“[T]he new\nregulatory requirements are tailored to the potential hazards the newly regulated gathering lines may pose.\n. . The risk-based application of each of these Type C requirements is based on the operational and\nfunctional characteristics of those lines and strikes an appropriate balance between the need to protect\npeople and the environment from the risks associated with large-diameter, high-pressure gathering lines\nand the need to exercise caution imposing regulatory burdens before more detailed information can be\ncollected.” (emphasis added); see also Protecting Unusually Sensitive Ares and Rural Onshore Hazardous\nLiquids, 73 Fed. Reg. 31634, at 31640 (Jun. 3, 2008) (“In this initial phase, PHMSA is implementing full\nregulation of the higher-risk, larger-diameter rural low-stress pipelines.”).\n3\n\n<<<PAGE 8>>>\n\nFlexSteel USA, LLC 1221\nTransport Drive\nAmeriport Industrial Park\nthe basis for the OD determination to be consistent with PHMSA’s established risk-based\nBaytown, TX 77523, USA\napproach for regulating certain gas and liquid lines.\nOFFICE 281.918.3400\nwww.flexsteelpipe.com\nInterpretation Request:\nFlexSteel USA respectfully requests PHMSA’s confirmation that, for purposes of onshore gas and\nliquid gathering classifications under 49 C.F.R. Parts 192 and 195, the outside diameter used in\njurisdictional and regulatory determinations for steel-reinforced multilayer pipe should be based\non the steel reinforcement layer, excluding the HDPE outer layer.\nThank you for your consideration of this request. Please let us know if you have any questions\nor if we can provide further information or clarifications to support our position.\nSincerely,\nKirk Francis, PE\nSenior Vice President, Engineering\nFlexSteel USA, LLC\nCC: Max Kieba, Director of Engineering, Office of Pipeline Safety\nCameron Satterthwaite, Deputy Director of Standards and Rulemaking, Office of Pipeline\nSafety\n4","truncated":false,"body_characters":22497}