Pipeline Relining Methods for Potable Water Distribution and Trunk Mains: A Comprehensive Guide

Potable water pipelines, including distribution mains (smaller pipes delivering water to homes and businesses) and trunk mains (larger pipes transporting water across regions), face challenges like corrosion, leaks, and structural degradation over time. Replacing these pipelines is often costly and disruptive, especially in urban areas or sensitive environments. Relining offers a non-invasive alternative, reinforcing existing pipes while ensuring compliance with safety standards like NSF/ANSI 61, which certifies materials for potable water use.

Below, we dive into the most common pipeline relining methods for potable water systems, drawing from industry practices and recent advancements.

1. Cured-In-Place Pipe (CIPP) Lining

Cured-In-Place Pipe (CIPP) lining is one of the most widely used trenchless rehabilitation methods for potable water pipelines. A flexible, resin-saturated liner (typically made of felt or fiberglass) is inserted into the existing pipe, either by inversion (using air or water pressure) or by pulling it through. The liner is then cured using heat (hot water or steam) or ultraviolet (UV) light, forming a seamless, jointless pipe within the old pipe.

Key Features

• Materials: Epoxy or polyester resins certified for potable water (e.g., NSF/ANSI 61-compliant).

• Pipe Sizes: Suitable for a wide range of diameters, from small distribution mains (4 inches) to larger trunk mains (up to 96 inches or more).

• Applications: Effective for addressing leaks, corrosion, and structural weaknesses in cast iron, ductile iron, steel, and asbestos cement pipes.

• Curing Methods: Hot water, steam, or UV light, depending on the system and site conditions.

Benefits

• Non-Invasive: Minimal digging reduces surface disruption in urban or environmentally sensitive areas.

• Durability: The new pipe can last 50+ years, with improved flow characteristics due to its smooth interior.

• Versatility: Adapts to bends, curves, and varying pipe diameters.

• Cost-Effective: Typically 30-50% cheaper than full pipe replacement.

Limitations

• Requires thorough cleaning of the host pipe to remove scale, debris, or tuberculation before lining.

• Temporary water service interruptions during installation.

• Not ideal for pipes with severe structural damage or significant diameter reductions.

CIPP is widely used in municipal water systems, such as in cities rehabilitating aging cast iron distribution mains. For trunk mains, CIPP can handle high-pressure environments, making it suitable for large-diameter pipelines. An example of CIPP lining systems is the Rhino lining system

2. Spray-Applied Lining

Spray-applied lining involves spraying a thin layer of epoxy, polyurethane, or cement mortar onto the inner surface of the pipeline using a rotating spray head that is winched through the pipe. This creates a protective coating that seals leaks and prevents corrosion.

• Materials: NSF/ANSI 61-certified epoxy or polyurethane for potable water systems; cement mortar for larger trunk mains.

• Pipe Sizes: Best suited for smaller distribution mains (4-12 inches), though some systems can handle larger diameters.

• Applications: Ideal for addressing pinhole leaks, corrosion, and minor structural issues in steel, cast iron, or ductile iron pipes.

Benefits

• Speed: Quick application process, often completed in a single day for shorter pipe sections.

• Cost-Effective: Lower material and labor costs compared to other methods.

• Minimal Disruption: Requires only small access points for equipment.

Limitations

• Thin coating (1-2 mm) offers less structural reinforcement than CIPP or sliplining.

• Less effective for pipes with significant structural damage or large cracks.

• Requires precise application to ensure uniform coating thickness.

Spray-applied epoxy linings are commonly used in urban distribution systems where small-diameter pipes suffer from corrosion-induced leaks. For example, a city might use this method to extend the life of a 6-inch cast iron main without excavating busy streets.

Slipline installation by Interflow, using their Primus system.

3. Sliplining

Sliplining involves inserting a new, smaller-diameter pipe (typically high-density polyethylene, HDPE, or PVC) into the existing pipeline, with the annular space between the old and new pipes grouted to secure it. For potable water systems, the new pipe must meet NSF/ANSI 61 standards.

Key Features

• Materials: HDPE or PVC pipes, often NSF/ANSI 61-certified for potable water.

• Pipe Sizes: Suitable for both distribution mains and larger trunk mains (up to 60 inches or more).

• Applications: Used for pipes with moderate structural damage, leaks, or corrosion in materials like cast iron, steel, or asbestos cement.

Benefits

• Structural Strength: The new pipe provides full structural integrity, effectively replacing the old pipe.

• Longevity: HDPE and PVC pipes resist corrosion and can last 50-100 years.

• Versatility: Can be used in straight or slightly curved pipelines.

Limitations

• Diameter Reduction: The new pipe reduces the internal diameter, potentially impacting flow capacity, especially in smaller distribution mains.

• Access Requirements: Requires larger access pits compared to CIPP or spray lining.

• Grouting Challenges: Improper grouting can lead to voids or instability.

Sliplining is ideal for rehabilitating long, straight sections of trunk mains in rural or suburban areas, where flow reduction is less critical, and access pits can be excavated without major disruption. An example of a slip line is the Interflow Primus Line, a kevlar reinforced polyproylene liner which can quickly be installed in aging infrastructure.

4. Pipe Bursting/Splitting

Pipe bursting or splitting involves breaking the existing pipe while simultaneously pulling a new pipe (typically HDPE) into its place. A bursting head fractures the old pipe outward, and the new pipe fills the expanded space. This method is considered semi-trenchless, as it requires access pits.

Key Features

• Materials: HDPE pipes, NSF/ANSI 61-certified for potable water applications.

• Pipe Sizes: Suitable for distribution mains (4-12 inches) and larger trunk mains.

• Applications: Used for severely damaged or undersized pipes that need full replacement, including cast iron, asbestos cement, or PVC.

Benefits

• No Diameter Reduction: The new pipe can match or even increase the original pipe’s diameter, maintaining or improving flow capacity.

• Complete Replacement: Replaces heavily damaged pipes without full excavation.

• Durability: HDPE pipes are corrosion-resistant and long-lasting.

Limitations

• Disruption: Requires excavation for access pits, which can be disruptive in urban settings.

• Cost: More expensive than CIPP or spray lining due to equipment and labor needs.

• Not Ideal for Bends: Best suited for straight pipe sections.

Pipe bursting is often used for replacing small-diameter distribution mains in residential areas where the existing pipe is too deteriorated for relining. It’s also effective for upsizing trunk mains to meet growing water demand.

5. Close-Fit Lining

Close-fit lining involves inserting a folded or compressed HDPE or PVC pipe into the existing pipeline, then expanding it to fit tightly against the host pipe’s inner wall. This minimizes diameter reduction compared to traditional sliplining.

Key Features

• Materials: NSF/ANSI 61-certified HDPE or PVC.

• Pipe Sizes: Suitable for distribution mains and some trunk mains (4-36 inches).

• Applications: Used for pipes with moderate corrosion or leaks but sufficient structural integrity.

Benefits

• Minimal Diameter Loss: The close-fit design preserves most of the original pipe’s flow capacity.

• Trenchless: Requires minimal excavation, similar to CIPP.

• Durability: Provides a corrosion-resistant, long-lasting solution.

Limitations

• Complex Installation: Requires specialized equipment to fold and expand the liner.

• Cost: Can be more expensive than CIPP or spray lining due to material and equipment costs.

• Pipe Condition: Not suitable for heavily damaged pipes.

Close-fit lining is ideal for distribution mains in urban areas where maintaining flow capacity is critical, and excavation is impractical. It’s less common for large trunk mains due to installation complexity.

6. Flexible Hose Lining

Flexible hose lining involves pulling a thin, flexible hose (often made of reinforced polymer or fabric) through the existing pipe. The hose is designed to withstand internal pressure and is certified for potable water use.

Key Features

• Materials: NSF/ANSI 61-certified polymer or fabric hoses.

• Pipe Sizes: Typically used for smaller distribution mains (4-12 inches).

• Applications: Best for pipes with minor leaks or corrosion but sufficient structural integrity.

Benefits

• Quick Installation: Faster than CIPP or sliplining for small pipe sections.

• Minimal Disruption: Requires small access points.

• Cost-Effective: Lower material costs compared to HDPE sliplining.

Limitations

• Limited Structural Support: Provides minimal reinforcement for severely damaged pipes.

• Diameter Reduction: Slightly reduces internal diameter, though less than traditional sliplining.

• Pressure Limitations: Not ideal for high-pressure trunk mains.

Flexible hose lining is used in small-scale projects, such as rehabilitating short sections of distribution mains in residential neighborhoods with minimal corrosion issues.

Considerations for Choosing a Relining Method

Selecting the right relining method depends on several factors:

• Pipe Condition: Severely damaged pipes may require pipe bursting or sliplining, while pipes with minor leaks suit spray lining or CIPP.

• Pipe Diameter and Material: Smaller distribution mains (4-12 inches) are compatible with most methods, while large trunk mains may require CIPP or sliplining for structural integrity.

• Flow Requirements: Close-fit lining or pipe bursting minimizes diameter reduction, critical for high-demand systems.

• Site Constraints: Urban areas favor fully trenchless methods like CIPP or spray lining to avoid excavation.

• Budget: Spray lining and flexible hose lining are generally cheaper, while pipe bursting and close-fit lining are more costly.

• Regulatory Compliance: All materials must meet NSF/ANSI 61 standards for potable water safety.

Recent advancements are enhancing pipeline relining for potable water systems:

• UV-Cured CIPP: Faster curing times and reduced environmental impact compared to traditional heat-cured systems.

• Robotic Joint Repairs: For targeted repairs in distribution mains, robotic systems can seal leaking joints internally, complementing relining methods.

• Smart Pipe Monitoring: Post-relining, some systems incorporate sensors to monitor pipe condition, helping utilities manage assets proactively.

• Sustainable Materials: New eco-friendly resins and liners are being developed to reduce the carbon footprint of relining projects.

Pipeline relining offers a versatile, cost-effective, and environmentally friendly solution for rehabilitating potable water distribution and trunk mains. Methods like CIPP, spray-applied lining, sliplining, pipe bursting, close-fit lining, and flexible hose lining each have unique strengths, making them suitable for different scenarios based on pipe condition, size, and project constraints. By choosing the right method, water utilities can extend the life of aging infrastructure, reduce leaks, and ensure safe, reliable water delivery for decades to come.

For more information on specific relining solutions or to explore NSF/ANSI 61-certified options, consult with trenchless technology providers or visit industry resources like US Pipelining or WaterWorld.