For a cast-iron natural gas main, initial replacement options for Peoples Gas in Chicago seemed straightforward—plastic or steel pipes. However, logistical, operational and system constraints led the utility to explore an alternative solution: trenchless pipe-lining technology. This case study highlights the decision process and outcomes.
Project: Replacement of 24-inch cast-iron medium-pressure gas main
Location: Chicago
Client: Peoples Gas, Chicago
Date: Spring–Summer 2023
The 2,000-foot section of cast-iron pipeline, installed in 1909, was one of three critical natural gas feeds supplying downtown Chicago. The section of pipeline had undergone more than 43 repairs since 2000. In addition to complications under the ground, the pipeline’s location presented multiple challenges for repair and restoration:
It is in a dense urban area.
The Chicago River is just north and west of the site.
The pipeline crossed under ramps leading to Interstate 90/94, a major highway with heavy truck and passenger traffic.
An elementary school is located within the project footprint.
There are multiple railroad crossings to the east.
The engineering team at Peoples Gas began by considering traditional replacement methods. However, the team explored alternative options based on operational and system constraints in the immediate and surrounding areas.
While plastic is a common choice for medium-pressure natural gas lines, the largest available diameter for plastic piping is 18 inches—significantly smaller than the existing 24-inch cast-iron pipe. The design analysis revealed that downsizing this feeder main to an 18-inch plastic pipe would not provide adequate gas supply to customers in the immediate and surrounding areas.
The decision to use lining for the 24-inch cast-iron natural gas main in Chicago highlights the growing role of trenchless technologies in the natural gas industry.
Steel was the next option considered. Installing a 24-inch steel pipe would require extensive excavation in the heavily trafficked area, particularly around the interstate ramp. Steel installation takes longer and comes with a higher price tag than plastic, further complicating its viability. The operational realities and cost concerns associated with steel made it a less attractive option for this project.
With plastic and steel posing challenges—along with a limited number of existing services coming off the existing 24-inch CIMP, a relatively straight pipe run with minimal bends and the largerdiameter main having an increased wall thickness—the engineering team turned to a trenchless technology. Lining was fairly new to Peoples Gas, having been used in only a few low-pressure segments. However, it has been successfully used in parts of the United States, Europe and Japan for more than 30 years.
Peoples Gas reviewed research from the Pipeline and Hazardous Materials Safety Administration and Cornell University,1 which demonstrated that lining effectively seals pipes and eliminates methane emissions. However, pipe relining does not address the structural integrity of at-risk pipe. The liner is not intended to be a stand-alone pipe; it relies on the structural strength of the host pipe. This requires the operator to maintain the structural integrity of the host pipe to ensure the liner does not become freestanding.2, 3 Continuing to perform leak surveys of the cast iron and the liner is still required.
The utility ultimately chose lining technology, specifically a cured-in-place lining, or CIPL, as the best solution for this project. Specific advantages of lining for this project include:
Flow capacity: Lining allowed the utility to maintain the required gas flow through the existing 24-inch main.
Cost savings: The total cost of lining was estimated to be 30% lower than a full replacement with steel.
Minimal excavation: Lining required only four access pits, compared to the extensive trenching needed for steel.
Reduced traffic disruption: By minimizing excavation, the project avoided major disruptions to traffic, particularly near the interstate ramp.
Faster completion: Lining shortened the overall project timeline, reducing restoration time by four weeks and reducing excavation by two weeks.
Because multiple contractors are involved in the construction process of a lining project, communication, planning and coordination are critical to its success.
After selecting contractors through a bidding process, preconstruction planning began. Collaboration with excavation and lining contractors was critical during the design phase. Key challenges addressed included traffic-flow management, installing a linestopper and removing a drip pot.
Implementation of the CIPL involved several key steps:
Pipe access and excavation: Strategic excavation of access pits to minimize surface disruption.
Precleaning and CCTV inspection: Cleaning the pipeline and inspecting it with closed-circuit television to assess initial conditions.
Surface preparation and liner application: Applying the liner using an inversion method with a drum, followed by curing and pressure monitoring.
Post-lining inspection and testing: Conducting CCTV inspections and pressure tests to ensure the liner was properly installed.
Service reinstatement: Reconnecting the gas services and completing final tie-ins.
The project was completed on schedule, with the contractors working in close coordination. Regular meetings helped keep the process on track and ensured smooth transitions between different phases of the project.
One year after the lining completion, the results have been positive. “We haven’t had to go back in for repairs,” said Peoples Gas senior engineer Ernie Crafton, adding that the project “helped us decrease methane emissions, which was a major goal.”
Post-lining inspections showed that all leaks had been eliminated. In addition, the natural gas flow to downtown Chicago was maintained, and the cost savings were substantial. Lining reduced the overall project budget by 30%, shortened the timeline and minimized the disruption to traffic in the area.
By including lining in their consideration set and the alignment of system needs, project location and existing services, Peoples Gas was able to preserve a critical natural gas feed while minimizing cost, project time and public disruption.
As utilities continue to face the challenge of maintaining infrastructure, trenchless technologies offer cost-effective solutions for extending the life of existing pipelines.
NYSEARCH/Northeast Gas Association completed a two-year cured-in-place lining research and development project in 2015 with support from National Grid, PECO Energy, Public Service Electric and Gas, Con Edison and the Pipeline and Hazardous Materials Safety Administration. www.progressivepipe.com/test-data
ASTM International standard specification for cured-in-place pipe lining system for rehabilitation of metallic gas pipe, ASTM F2207-06 (2019). F2207 Standard Specification for Cured-in-Place Pipe Lining System for Rehabilitation of Metallic Gas Pipe (astm.org)
CIPP Workshop Sponsored by NYSEARCH/Northeast Gas Association. PHMSA Technical and Research Perspectives for Cured-in-Place Liners (Aug. 20, 2015). PHMSA PowerPoint Template (squarespace.com)
Progressive Pipeline Management specializes in trenchless technologies that inspect and renew underground infrastructure pipelines of all types and sizes.