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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

By-Decade Inventory


The inventory opens in a new window and contains four tabs with information about miles of pipeline by decade of installation. The first three tabs contain reports for gas distribution, gas transmission, and hazardous liquid pipelines.

The first report on these tabs shows how the number of miles installed in each decade has changed since 2005. One bar chart shows the decades before 1970 and a separate chart shows decades after 1970. The first report also includes a table of the data. In the second report, you can select a single decade and see the trend line since 2005. For gas distribution, you can choose to see data for mains or services. For hazardous liquid, you can select one or more commodities.

Nationally, THIS REPORT shows the reduction in pre-1970 pipelines since 2005 for gas distribution, gas transmission, and hazardous liquid.

All inventory reports for gas distribution, gas transmission, and hazardous liquid can be limited to a single state by using the state prompt at the top.

The fourth tab in the inventory includes two reports ranking states by miles of pre-1970 pipelines. The first report is for gas pipelines and the second report is for hazardous liquid. The reports can be sorted by any of the columns.

Miles by Decade of Installation Inventory Reports

Pipeline Practices over the Decades

From the early 1900's through today gas transmission, hazardous liquid and gas distribution pipelines have all benefited through each decade from improvements in pipe manufacturing, construction, and operational and maintenance (O&M) practices.

  • Pipe Manufacturing Process included improvements in steel metallurgy, seam welding techniques, seam non-destructive testing, pipe rolling practices, and quality control through pressure testing and inspection before the pipe leaves the mill.

    Lap welded, hammer welded, low frequency electric resistance (LF-ERW) and flash welded (FW) pipe were all used starting in the early 1900's. Pipes manufactured during the post-World War II construction boom that lasted well into the 1960's were vulnerable to seam quality issues. Since the late 1960's and early 1970's, these seam types are no longer manufactured or installed by pipeline operators. They have been replaced with high frequency (HF) ERW pipe, submerged arc welded (SAW) or seamless pipe, which all have improved steel and seam properties.

    Current manufacturing processes include improved steel rolling practices, non-destructive seam inspection, and pressure testing of the pipe before it leaves the mill.

    Since the late 1960's, the use of plastic pipe in gas distribution pipelines has steadily increased. Some vintages installed between the 1960s and early 1980s have the potential for brittle-like cracking. The susceptibility is dependent on the resin, pipe processing, and service conditions.
  • Construction practice improvements have been in field girth welding and non-destructive testing (NDT), pipe coating, pipe bending, use of select backfill, in-place hydrostatic pressure testing and inspection.

    Construction practices beginning in the early 1900's included the use of wrinkle bends, threaded collars, oxy-acetylene welding, backing rings for welding, and non-coated pipe. Beginning in the 1930's and 1940's improved girth welds using shielded metal arc welding (SMAW), pipe bending practices, usage of pipe coating, and girth weld non-destructive inspection were beginning to be used by most pipeline operators. The need for pipeline non-destructive testing (NDT) grew very rapidly with the increase of offshore gas and oil exploration in the 1970s.
  • O&M practice improvement have included usage of cathodic protection for external corrosion mitigation, programs for internal corrosion such as operational pigging and inhibitor injection programs, integrity management assessments, smart pigging, remediation of defects found, and right-of-way monitoring that includes one-call programs.

    O&M practices in the early 1900's through the early 1950's by some pipeline operators did not include designs for operational pigging, usage of cathodic protection, and sometimes pipe external coatings. Beginning in the 1950's usage of full opening valves for pigging, cathodic protection, and external pipe coatings were being used by most pipeline operators. The first smart pig was developed in the 1960s using Magnetic Flux Leakage (MFL) technology to inspect the bottom portion of the pipeline. Development of both pipeline pigs for electromagnetic and ultrasonic detection of wall thinning, and X-ray crawlers for weld inspection in long runs of pipe occurred during the 1970s. Pigs and crawlers were the only means of inspecting for erosion, corrosion (internal and external) and other types of defect in buried pipes. Operator Qualification (OQ) regulation was implemented in 1999 to require that maintenance personnel performing the work on the pipeline were qualified. A critical improvement to O&M practices was integrity management program requirements to assess the condition of pipelines and remediate defects that compromised pipeline safety. Learn more about integrity management assessment techniques:

Overall improvements in pipe manufacturing, construction, and O&M practices have been an integral part of the pipeline industry efforts to reduce risk and improve public safety from incidents beginning in the 1900' through today. The Gas Code (Part 192) was implemented in 1970 and the Hazardous Liquid Code (Part 195) was implemented in 1979. Their basis was in the technical standard ASME B31.8. Many states had already adopted ASME B31.8 prior to the federal gas codes. The implementation of these codes has been an integral part in further reducing risks and improving safety through consistent regulations and standards for all pipeline operators.

Pipelines constructed before adoption of federal safety rules in 1970 were allowed a grandfathering exemption for establishing maximum allowable operating pressure (MAOP). This allowed natural gas transmission lines installed before July 1, 1970 to be operated in some cases without having been: pressure tested in the field, higher MAOPs than allowed for new pipelines constructed after implementation of the regulations, and without material records. Hydrostatic pressure testing can identify latent manufacturing and construction defects.

Eliminating or limiting the grandfather clause could have a significant impact on industry because about 50% of onshore natural gas transmission lines were constructed before 1970.

PHMSA held public a workshop, The Integrity Verification Process, which included discussion of possible removal of parts of the grandfather clause, remediation of pipe with seam integrity issues, and material documentation.