
Slip Lining: What It Is and Why It Works
Maintaining underground infrastructure is one of the most complex and costly challenges municipalities face today. Aging pipelines — responsible for transporting wastewater, stormwater, and other critical resources — are often at risk of collapse, corrosion, or leakage. Traditional repair methods frequently require disruptive excavation, resulting in road closures, traffic delays, and high costs. This is where slip lining comes into play. As one of the most effective pipeline rehabilitation methods, slip lining offers municipalities a proven solution to extend the service life of pipelines without disrupting daily life above ground.
What is slip lining?
Slip lining is a trenchless technology used to rehabilitate existing pipelines by inserting a new, smaller-diameter pipe into the deteriorated host pipe. This process creates a “pipe within a pipe” system, successfully restoring structural integrity and preventing further leaks or failures.
The inserted pipe is chosen based on the specific demands of the pipeline, such as fluid type, flow rate, and environmental conditions. Once the new pipe is installed, the annular space — the gap between the host pipe and the new pipe — is typically grouted to ensure stability and prevent water infiltration.
Slip lining is often used in gravity sewer lines, storm drains, and pressure pipelines where structural deterioration or leaks have compromised the pipeline’s functionality.
How slip lining works
While the concept of slip lining seems straightforward, its implementation requires precision and technical expertise. Here’s a step-by-step breakdown:
- Assessment and preparation: Using closed-circuit television (CCTV) inspections, technicians assess the condition of the existing pipeline to verify it’s suitable for slip lining. The interior must be cleaned of obstructions, such as debris, roots, or hardened sediment.
- Pipe selection and sizing: Engineers select the new pipe material and diameter based on hydraulic requirements and the host pipe’s condition. Proper sizing helps minimize the loss of flow capacity.
- Insertion of the new pipe: The new pipe, which is frequently fused into longer continuous sections, is carefully pulled or pushed into the existing pipeline. In some cases, segmented pipes are inserted piece by piece and joined underground.
- Grouting the annular space: After the new pipe is in place, a structural grout is pumped into the annular space to provide stability, eliminate voids, and prevent groundwater intrusion.
- Sealing and reconnection: End seals are installed to prevent leaks at the entry and exit points, and lateral connections are re-established.
- Final inspection and testing: After installation, the rehabilitated pipeline undergoes pressure testing and final CCTV inspections to confirm proper alignment, sealing, and functionality.
Every stage of slip lining requires meticulous planning and execution to avoid alignment errors, voids in grouting, or damage to the new liner during insertion.
Why choose slip lining
Slip lining restores structural stability to aging pipelines, mitigating the risks of future collapses or failures. Modern pipe materials, such as high-density polyethylene (HDPE), are highly resistant to corrosion, chemical attack, and abrasion, ensuring an extended service life — generally 50 years or more.
One common misconception about slip lining is that reducing the internal diameter of the pipeline will result in lower flow rates. In reality, the smooth inner surface of materials like HDPE often compensates for the decreased diameter by improving flow efficiency and lessening friction losses.
Slip lining isn’t just for minor cracks or leaks. It can address severe structural damage, including pipeline deformation and corrosion.
Since slip lining requires only minimal excavation at entry and exit points, it reduces surface disruption compared to traditional “dig-and-replace” methods. This means fewer traffic delays, a diminished environmental impact, and less disruption to businesses and communities. The trenchless nature of slip lining also translates to lower costs associated with excavation, soil disposal, and site restoration.
When slip lining is the right choice
Slip lining can be applied across a variety of pipeline diameters and types, including sanitary sewers, storm drains, industrial pipelines, and even pressurized water mains. It’s equally effective for pipelines constructed from concrete, clay, metal, or plastic.
While slip lining is a versatile solution, it’s best used in the following scenarios:
- Structural damage without collapse: The host pipe must retain enough structural integrity to support the insertion process.
- Leakage and infiltration issues: Slip lining seals off cracks and prevents groundwater from entering or wastewater from escaping.
- Limited surface disruption is required: In urban or heavily trafficked areas, minimizing surface excavation is usually a top priority.
- Preventative rehabilitation: Slip lining is an excellent preventative measure for aging infrastructure before catastrophic failures occur.
Partnering with an experienced team
Slip lining is not a one-size-fits-all solution. Its success depends on precise execution, expert knowledge, and a deep understanding of the pipeline’s current condition and long-term operational needs. Qualified providers like Envirowaste Services Group (EWSG) can perform a thorough assessment to determine whether slip lining is the right choice for your project. They also have the equipment and expertise to adapt slip lining techniques to various pipe sizes.
By partnering with an experienced team like EWSG, you can ensure every step of the slip lining process — from assessment to final inspection — is handled with accuracy and care, so your infrastructure will remain resilient and efficient for years to come.