Best Pipe Lining Options For High-Flow Sewers

High-flow sewer lines are the arteries of your collection system. When they start to fail, you’re not just dealing with a nuisance, you’re dealing with major risk: backups, overflows, regulatory violations, and expensive emergency work.

Choosing the best pipe lining for high-flow sewers isn’t as simple as picking a product off a shelf. You have to keep capacity, structural integrity, access constraints, and long-term operating costs in balance. Get it wrong, and you can lose valuable hydraulic capacity or end up with a lining system that can’t stand up to high velocities, aggressive chemistry, or extreme peak flows.

In this guide, you’ll walk through the key challenges of high-flow sewers, the main trenchless lining options, and how to build a decision framework that leads you to the right solution for your specific system. Along the way, you’ll see where technologies like CIPP, sliplining, spiral wound liners, GRP panels, and spray-applied linings tend to shine, and where they don’t.

NuFlow is a leading trenchless pipe repair and rehabilitation company serving residential, commercial, and municipal properties. If you’re already seeing warning signs or planning a major renewal program, you can get help with plumbing and sewer problems and request a free consultation through our dedicated plumbing problems page.

Understanding The Challenges Of High-Flow Sewer Lines

High-flow sewers, trunk mains, interceptors, large combined sewers, and industrial lines, operate under very different conditions than small laterals or local collectors. Before you choose a lining system, you need a clear picture of the forces acting on these pipes.

Hydraulic Performance Requirements

In high-flow sewers, hydraulic behavior dominates your decision-making:

• High velocities and shear stresses: Peak velocities often exceed 6–10 ft/s and can go higher during storm events or industrial discharges. Any lining must resist scour and maintain a smooth surface under constant abrasion.
• Capacity-sensitive assets: These mains usually run near capacity at peak events. Even a modest diameter reduction from a liner or carrier pipe can trigger upstream surcharging or downstream bottlenecks.
• Backwater and surcharge behavior: In combined systems, storm-driven peaks can fill pipes to the crown or beyond. Linings must perform both in open-channel and surcharged/pressure-like conditions.

The “best” lining for a high-flow sewer is usually the one that preserves hydraulic capacity while still delivering the required structural and durability performance.

Structural And Operational Demands

High-flow lines are typically:

• Deep and difficult to access – subjecting pipes to higher soil loads, consolidation, and, in some cases, traffic or building loads.
• Subject to ground movement – settlements, expansive clays, or seismic effects can all cause deflection or joint separation over time.
• Critical to system operation – failure can affect thousands of customers or entire districts.

This means your lining system has to:

• Provide either fully structural or semi-structural capacity depending on the host pipe’s condition.
• Tolerate cyclic loading, including pressure spikes in force mains and repeated peak flows in combined or industrial sewers.
• Offer high reliability at manholes, junctions, and transitions, which are frequent weak points.

Regulatory, Access, And Constructability Constraints

Even if a lining system looks perfect on paper, it still has to be buildable:

• Bypass pumping and flow control: Diverting large flows is expensive and risky. You may be forced to install liners under partial flow, at night, or within very tight shutdown windows.
• Traffic, business, and community impacts: Trunk sewers often run beneath major roads, commercial districts, or sensitive sites. Excavation for access shafts or shafts for sliplining and GRP panels may be heavily constrained.
• Permitting and environmental limits: Work adjacent to waterways, wetlands, or protected areas may restrict working hours, equipment types, and discharge options.

You’ll want to look not just at the engineering specs of the lining system, but at whether it can actually be installed within your regulatory, access, and constructability limits.

If you manage municipal or utility systems and need to weigh these constraints at scale, NuFlow’s municipalities & utilities resources can help you explore trenchless programs that reduce risk without blowing your capital budget.

Key Criteria For Selecting Pipe Lining In High-Flow Systems

Once you understand the challenges, you can narrow down lining options based on a handful of technical criteria. These become the backbone of your selection process.

Hydraulic Capacity And Flow Efficiency

For high-flow sewers, hydraulic capacity is usually the first gate:

• Roughness (Manning’s n): Many modern lining materials, epoxy, PVC, HDPE, GRP, have significantly smoother surfaces than old clay, brick, or concrete. This can partially offset a reduction in diameter.
• Effective internal diameter: Every millimeter of thickness counts. A thick carrier pipe used in sliplining will reduce diameter more than a thin CIPP or spray-applied liner. On long runs, this can translate into notable capacity losses.
• Localized losses: Bends, manholes, transitions, and protruding service reinstatements can all add minor losses. Your choice of technology affects how cleanly these features can be restored.

When you compare systems, model both normal flow and peak/surcharged conditions with and without the liner. That’s where you’ll see the real hydraulic impact.

Structural Strength And Design Life

High-flow assets are typically “big-ticket” infrastructure with long planning horizons. You’re not looking for a band-aid: you’re looking for a 30–50+ year solution.

Key questions:

• Is the liner fully structural (able to stand alone if the host pipe fails) or semi-structural (relies on some residual strength in the host)?
• Does the design account for external loads (soil, traffic), internal pressure/surcharge, and vacuum conditions if applicable?
• What is the documented design life and warranty period, based on tested material performance and real-world track record?

At NuFlow, for example, our epoxy pipe lining systems are designed for 50+ years of service life and are backed by warranties, making them suitable for high-consequence applications where repeat rehabilitation isn’t an option.

Chemical, Abrasion, And Temperature Resistance

High-flow sewers experience:

• Sulfuric acid attack from hydrogen sulfide in sanitary and combined systems.
• Aggressive industrial discharges (solvents, oils, fats, high/low pH, salts).
• Thermal loads from hot effluents.
• Continuous abrasion from grit and suspended solids at high velocity.

Your lining material must be matched to the exposure class:

• Cementitious linings can be economical but may need added protection in severe H₂S or industrial environments.
• Epoxy, vinyl ester, or novolac resins in CIPP and spray-applied systems handle higher chemical and temperature loads.
• GRP and HDPE offer strong resistance but need careful resin and gasket selection.

Installation Constraints: Bypass Pumping, Traffic, And Wet-Weather Flows

Installation realities can make or break a project:

• Bypass feasibility: Can you realistically bypass the entire flow? If not, technologies that tolerate installation under live or partial flows (e.g., some CIPP, spiral wound systems) become more attractive.
• Working window: Nighttime-only work or very short shutdowns may rule out slower processes like large-diameter sliplining with major shaft construction.
• Site logistics: Long curing times, extensive staging areas, or heavy equipment may not fit your corridor.

NuFlow’s trenchless methods are designed for minimal disruption, often completing major repairs in 1–2 days without tearing up roads, landscaping, or structures, a major plus when high-flow sewers run through busy corridors.

Cost, Risk, And Asset Management Considerations

Finally, you have to make the numbers work over the entire lifecycle:

• Capital cost: Trenchless linings typically cost 30–50% less than full dig-and-replace, especially on deep or hard-to-access lines.
• Risk profile: Consider risks such as liner collapse during installation, incomplete curing, dimensional mismatches, or future operational constraints.
• System-level impacts: Will reduced capacity force parallel projects (e.g., upsizing elsewhere)? Does the technology allow staged work to spread costs and risk?

This is where a structured decision framework, backed by modeling and scenario analysis, becomes invaluable, which you’ll see later in this guide.

Overview Of Major Pipe Lining Technologies For High-Flow Sewers

Each trenchless lining technology has a distinct profile of strengths and trade-offs. Your job is to match these to your asset’s hydraulic, structural, and constructability needs.

Cured-In-Place Pipe (CIPP) Liners

CIPP is one of the most widely used rehabilitation methods for gravity sewers and, increasingly, some force mains.

How it works: A resin-saturated tube (felt or fiberglass) is inverted or pulled into the host pipe, then cured (steam, hot water, or UV) to form a tight-fitting, jointless liner.

Pros for high-flow sewers:

• Thin wall thickness for a given structural capacity, preserving diameter.
• Smooth internal surface with low roughness.
• Can negotiate bends and diameter changes better than rigid systems.
• Available in chemically resistant resin systems suitable for harsh environments.

Cons/limitations:

• Requires reliable flow control during installation and curing.
• Quality depends heavily on correct wet-out, curing regime, and QA/QC.
• Service reinstatement requires robotic cutting, which must be done carefully to avoid hydraulic protrusions.

Sliplining With HDPE Or Other Carrier Pipes

Sliplining involves inserting a new, smaller-diameter pipe into an existing host pipe and grouting the annular space.

Pros:

• Very robust structural performance: essentially a new pipe inside the old.
• Excellent chemical and abrasion resistance with materials like HDPE.
• Simple, proven joints (butt fusion, gasketed systems) for long runs.

Cons:

• Significant reduction in internal diameter, especially critical in high-flow sewers.
• Requires access pits/shafts and relatively straight alignment with limited bends.
• Can be disruptive in urban areas if large shafts are needed.

Spiral Wound Lining Systems

Spiral wound liners are formed in situ by winding a PVC or composite strip into the host pipe, sometimes with grouting of the annular space.

Strengths:

• Can be installed from existing access points in many cases, reducing excavation.
• Good for large diameters and even some non-circular shapes.
• Some systems allow installation under live flow with minimal bypass.

Considerations:

• Structural performance depends on system type and whether the annulus is grouted.
• Requires skilled installation and careful handling of joints to avoid leakage or deformation.

Segmental GRP Panels And Panel Liners

For very large trunk sewers and tunnels, segmental glass-reinforced plastic (GRP) panels or panels plus grout are a common solution.

Advantages:

• High strength and stiffness for large spans.
• Excellent corrosion resistance.
• Customizable geometry for non-circular sections.

Challenges:

• Requires significant access (shafts, adits) and internal working space.
• Installation is labor-intensive and sensitive to alignment and joint details.
• Often best suited to major capital projects rather than quick interventions.

Spray-Applied Cementitious And Polymeric Linings

Spray-applied linings use robotic or manual application of cementitious material, epoxy, or other polymers to create a bonded liner.

Pros:

• Very thin linings preserve hydraulic capacity.
• Excellent for targeted structural enhancement or corrosion protection.

Cons:

• Achieving uniform, verified thickness and bond can be challenging.
• Structural performance may be limited unless designed as a composite with the host pipe.

NuFlow has extensive experience with epoxy coating and lining systems for sewers and pressurized pipes, leveraging spray and pull-in-place techniques to provide long-lasting, corrosion-resistant linings with minimal disruption to surrounding properties.

CIPP For High-Flow Sewers: When It Works Best

CIPP is often the first technology you’ll evaluate for high-flow sewers because of its balance of structural capacity, hydraulic efficiency, and constructability.

Material Options: Felt, Fiberglass, And Resin Choices

Your CIPP design should start with the right material and resin pairing:

• Felt tubes: Common for standard gravity sewers, well-suited for moderate diameters and loads.
• Fiberglass-reinforced tubes: Offer higher modulus and strength at reduced wall thickness, ideal when you can’t afford much diameter loss.
• Resin options:
• Polyester and vinyl ester resins for typical sanitary environments.
• Epoxy or specialized vinyl esters for high chemical and temperature resistance or force mains.

NuFlow specializes in epoxy-based CIPP and coating systems, chosen for their strong bond, chemical resistance, and long design life in both gravity and pressure applications.

Hydraulic Impacts: Roughness, Diameter Loss, And Flow Capacity

With CIPP, you gain a smoother surface but lose a small amount of diameter. For high-flow sewers, you need to quantify this trade-off:

• Use realistic Manning’s n values for old vs. new surfaces. Older concrete or clay may have n ≈ 0.013–0.015: CIPP liners can be closer to 0.010–0.012.
• For large diameters, even a 0.5–1.0 inch wall can represent a relatively small percentage loss in area, especially with fiberglass CIPP.
• Hydraulic modeling will often show that a well-designed CIPP liner maintains or even slightly improves capacity compared to a rough, deteriorated host pipe.

Installation In Live Or Partially Bypassed Sewers

Flow control is the biggest hurdle with CIPP in high-flow lines:

• Full bypass: Ideal for quality control but expensive and complex for large interceptors.
• Partial flow with inversion: Some systems allow installation under low depth of flow, but curing and resin containment must be tightly managed.
• Segmented installations: Breaking long runs into manageable reaches can reduce risk and bypass requirements.

An experienced contractor will design the bypass or flow management plan around your system’s constraints. As trenchless technology leaders, NuFlow focuses heavily on planning and staging so liners are installed safely and efficiently, without unexpected surcharging or spills.

Limitations And Common Failure Modes

CIPP is powerful but not bulletproof. You should be aware of typical pitfalls:

• Inadequate curing leading to soft spots or incomplete polymerization.
• Wrinkles or folds that disrupt flow and trap debris, especially in bends or diameter transitions.
• Poorly sealed terminations at manholes and structures, allowing infiltration or exfiltration.
• Chemical mismatch where the selected resin isn’t compatible with actual sewer chemistry or temperature.

These risks underscore the value of choosing a partner with a proven track record and robust QA/QC processes. If you’d like to see real-world results of CIPP and epoxy lining projects, you can explore NuFlow’s sewer and water case studies to understand how these systems perform over time.

Sliplining For Large-Diameter, High-Velocity Applications

For some very large or deeply buried high-flow sewers, sliplining with a new carrier pipe can be the most robust long-term solution.

Compatible Pipe Materials And Jointing Methods

Typical sliplining materials include:

• HDPE (high-density polyethylene) – highly flexible, excellent chemical and abrasion resistance, fusion-welded joints.
• PVC or PVCO – stiffer but smooth and corrosion-resistant.
• GRP carrier pipes – high strength and stiffness for large diameters.

Jointing methods vary:

• Butt-fusion welds (HDPE) create fully restrained, leak-tight joints ideal for long continuous pulls.
• Gasketed bell-and-spigot joints may be used for GRP and PVC, particularly when installation space limits continuous pulls.

Hydraulic Trade-Offs: Diameter Reduction Versus Improved Roughness

Sliplining almost always reduces internal diameter more than CIPP or spray linings. But, you still gain from a smoother pipe material.

To evaluate hydraulic impacts:

• Calculate the new cross-sectional area and compare it to existing.
• Apply realistic roughness coefficients for both the old pipe and the new carrier.
• Consider future flow growth, especially in combined or rapidly growing service areas.

For some systems, sliplining is acceptable because the trunk main was originally oversized or because system upgrades (additional storage or parallel relief sewers) are already planned.

Constructability: Access Shafts, Bends, And Service Reinstatements

Sliplining constructability comes down to geometry and access:

• You need entry and exit pits or shafts large enough to handle the carrier pipe sections.
• Sharp bends and significant alignment changes are difficult or impossible to negotiate.
• All service connections must be located and reconnected, which can be challenging in large, deep systems.

These requirements can heavily impact cost and feasibility in dense urban environments. In many such cases, owners pivot to CIPP, spiral wound, or spray-applied lining to avoid major excavation.

Risk, Cost, And Typical Use Cases

Sliplining is often preferred when:

• You want a near-new-pipe condition with excellent structural capacity.
• You’re dealing with very large trunk lines where other linings aren’t available or economic.
• You have good access corridors (e.g., easements, rights-of-way) for shafts and staging.

Risk-wise, sliplining is a mature, proven technology, but you still need to manage:

• Grouting the annular space to prevent buoyancy issues and void migration.
• Potential for carrier pipe damage during insertion.

In many capital planning programs, sliplining is one of several tools used selectively for the most demanding or accessible segments, while less invasive trenchless methods handle the rest.

Spiral Wound And GRP Panel Liners For Major Trunk Sewers

When you’re working with very large, non-circular, or otherwise complex high-flow sewers, spiral wound liners and GRP panels offer geometry flexibility that other systems struggle to match.

Hydraulic And Structural Performance Characteristics

Both spiral wound and GRP panel systems can be engineered for substantial structural capacity:

• Spiral wound liners can be designed as fully structural when combined with annular grouting and correct profile selection.
• GRP panels provide high stiffness and can handle large spans and loads.

Hydraulically, these systems:

• Offer smooth, low-roughness internal surfaces.
• Can be sized to optimize between maintaining capacity and providing adequate structural thickness.

But, you should carefully model partial filling, surcharge, and debris transport, as geometry changes and local irregularities at joints can affect flow patterns.

Suitability For Egg-Shaped And Non-Circular Sewers

Egg-shaped and horseshoe sewers were originally designed for self-cleansing at low flows and added capacity at high flows. Rehabilitating them with circular pipes can compromise that behavior.

Spiral wound and GRP panels allow you to:

• Closely match original shapes, preserving hydraulic characteristics.
• Address local defects while maintaining the designed flow regime.

This makes them particularly attractive for older brick or masonry trunk sewers in historic urban cores.

Installation Under Continuous Or Difficult Flow Conditions

One of the main selling points of some spiral wound systems is the ability to install under continuous or high base flows with limited bypassing.

Typical features include:

• Insertion through existing manholes.
• Robotics or winding machines that form the liner in place.
• On-the-fly adjustment to minor alignment variations.

GRP panel systems, by contrast, usually require more significant access and dry conditions to place panels and grout.

If your high-flow sewer simply can’t be fully bypassed, spiral wound liners are often worth a serious look.

Designing For Long-Term Durability In Aggressive Environments

For major trunk sewers, durability is non-negotiable:

• Select resins and gaskets resistant to sulfuric acid and industrial chemicals.
• Ensure annular grouts are compatible and durable, avoiding shrinkage or cracking that could compromise liner support.
• Account for differential movement between the liner and host (e.g., where shallow sections experience temperature swings or live loads).

NuFlow and our contractor network focus heavily on matching material systems to your real-world exposure environment. If you’re evaluating options for a large trunk main, it’s often worth engaging a specialist early for a free consultation on plumbing and sewer rehabilitation so you can avoid missteps that could shorten service life.

Special Considerations For Combined, Industrial, And Force Mains

Not all high-flow sewers are alike. Combined sewers, industrial lines, and force mains each require extra attention beyond the basics.

Combined Sewers With Extreme Peak Flows

Combined sewers see the widest range of operating conditions:

• Very low dry-weather flows.
• Extremely high, debris-laden storm flows.
• Frequent surcharge above the crown.

For these assets:

• Prioritize abrasion resistance and smooth surfaces to help move grit and trash.
• Ensure the liner can handle rapidly fluctuating hydraulic grades and occasional pressurized conditions.
• Model CSO (combined sewer overflow) behavior after lining to ensure you don’t inadvertently increase overflow frequency or duration.

CIPP, spiral wound, and GRP liners can all perform well in combined systems when properly designed and installed.

Industrial Sewers With High Chemical And Temperature Loads

Industrial sewers are unforgiving if you misjudge chemistry or temperature:

• Verify actual pH, temperature, chemical composition, and cleaning practices (e.g., CIP systems) over time.
• Use chemical-resistant resins and barrier layers where needed.
• Consider redundancy in protection, e.g., an epoxy liner over a structural CIPP or GRP base in extremely harsh situations.

In many industrial settings, spray-applied epoxy or specialty CIPP systems are preferred because they can be tailored with specific resins and fillers. NuFlow’s epoxy technologies, for example, are selected and tested for their resistance to the actual chemicals present, not just generic lab conditions.

Pressure And Force Mains: Surge, Fatigue, And Leakage Control

Force mains introduce a different set of stresses:

• Internal pressure and water hammer from pump starts/stops.
• Fatigue from repeated pressure cycling.
• High consequences of even small leaks.

For force mains, you should:

• Use lining systems rated for pressure service, not just gravity loads.
• Pay close attention to joint details, transitions, and connections to valves and appurtenances.
• Evaluate surge control measures in parallel with lining to protect both the host and the liner.

CIPP designed for pressure, sliplining with HDPE, and certain spray-applied epoxy linings can all be options here, but the design must be carried out by engineers experienced in pressure pipeline rehabilitation.

Developing A Decision Framework For Selecting The Best Lining System

With so many variables, the best way to choose a lining system for high-flow sewers is to use a structured decision framework rather than relying on product marketing alone.

Assessing Condition, Capacity, And Criticality Of The Asset

Start with a clear baseline:

• Condition: CCTV, laser profiling, sonar, and defect coding to quantify structural and infiltration issues.
• Capacity: Hydraulic modeling to understand current performance, bottlenecks, and future flow projections.
• Criticality: Consequences of failure, environmental impact, customer outages, repair complexity, and cost.

This triad helps you decide where you need fully structural solutions, where you can accept capacity loss, and where you might prioritize speed over longevity (or vice versa).

Comparing Lining Options With Hydraulic Modeling

Once you have candidate technologies, CIPP, sliplining, spiral wound, GRP panels, spray-applied linings, compare them directly:

• Build before-and-after models for each option, including diameter changes and new roughness coefficients.
• Simulate peak storm events, industrial discharge scenarios, and surcharged conditions.
• Check effects on upstream levels, downstream constraints, and overflow behavior.

This step often reveals that an initially attractive solution (e.g., sliplining) isn’t feasible without parallel capacity upgrades, or that a thin, structural liner can deliver both performance and cost savings.

Balancing Performance, Risk, Budget, And Construction Impacts

Finally, layer in practical constraints:

• Performance: Does the liner meet or exceed your structural, hydraulic, and durability requirements?
• Risk: Installation risk, QA/QC complexity, and consequences if things go wrong.
• Budget: Not just capital cost, but lifecycle O&M and risk mitigation costs.
• Construction impact: Traffic disruption, business impacts, environmental sensitivities, and community tolerance.

This is where a partner with broad trenchless experience becomes invaluable. NuFlow has decades of experience rehabilitating sewer lines, drain pipes, and water systems without excavation, using CIPP lining, epoxy coating, and UV-cured solutions to balance cost and risk.

If you’re an engineer, facility manager, or municipal decision-maker looking to standardize on a set of trenchless solutions, you can review NuFlow’s project case studies for examples of how others have approached similar decisions.

Contractors interested in expanding their services with advanced trenchless technologies can explore NuFlow’s become a contractor program and learn how joining our global contractor network helps deliver consistent, high-quality lining solutions to demanding clients.

Conclusion

High-flow sewers are some of the most challenging assets you’ll ever rehabilitate. There’s no single “best” pipe lining for every situation, but there is a best-fit solution for your specific combination of flows, geometry, chemistry, access, and risk tolerance.

• CIPP often offers the best balance of hydraulic performance, structural strength, and constructability.
• Sliplining delivers near-new-pipe robustness where you can live with some capacity loss and have room for access shafts.
• Spiral wound and GRP panel systems shine in large, non-circular, or hard-to-bypass trunk sewers.
• Spray-applied linings are powerful tools for corrosion control and thin-section rehabilitation when structural demands are moderate or can be met with composite design.

The key is to treat lining selection as an engineering decision, backed by condition assessment, hydraulic modeling, and a clear view of long-term asset management goals.

NuFlow helps residential, commercial, and municipal clients navigate exactly these decisions, using trenchless technologies that typically cost 30–50% less than dig-and-replace, deliver 50+ year design lives, and keep disruption to a minimum.

If you’re weighing options for a high-flow sewer or other critical pipeline, you don’t have to figure it out alone. You can get help with plumbing and sewer problems today to request a no-obligation, free consultation, or browse our sewer and water case studies to see how similar projects have been successfully delivered.

With the right information and the right partner, you can rehabilitate your high-flow sewers confidently, safely, and cost-effectively, without digging up your city or your property.

Frequently Asked Questions About Pipe Lining for High-Flow Sewers

What is the best pipe lining for high-flow sewers?

There is no single best pipe lining for high-flow sewers. The right choice depends on hydraulic capacity, structural needs, chemistry, access, and budget. CIPP, sliplining, spiral wound liners, GRP panels, and spray-applied linings can all be “best” in different situations when evaluated through hydraulic modeling and lifecycle analysis.

How does CIPP perform in high-flow sewer applications?

CIPP performs well in high-flow sewers because it offers a thin wall for strong structural capacity, a smooth low-roughness surface, and the ability to handle bends and diameter changes. When properly designed and cured, it can maintain or even slightly improve flow capacity while delivering 30–50+ year design life.

How do I choose between CIPP, sliplining, and spiral wound liners for a trunk sewer?

Start with condition assessment, hydraulic modeling, and criticality ranking. CIPP is often favored for balancing strength and capacity with minimal excavation, sliplining for near-new-pipe robustness where some diameter loss is acceptable, and spiral wound liners for large or non-circular sewers and sites where full bypassing or major shafts are difficult.

What pipe lining is best for industrial sewers with aggressive chemicals and high temperatures?

For industrial sewers, the best pipe lining typically uses epoxy, vinyl ester, or novolac resins in CIPP or spray-applied systems, sometimes over GRP or structural bases. Selection should be based on verified pH, temperature, and chemical exposure data, ensuring the resin system is specifically rated for those conditions and cleaning practices.

Can pipe lining increase the capacity of a high-flow sewer?

Pipe lining usually reduces internal diameter slightly, but smoother materials can offset this. In some cases, especially with rough, deteriorated concrete or clay, a thin, smooth liner (like fiberglass-reinforced CIPP or spray-applied epoxy) can maintain or marginally improve effective capacity, provided hydraulic modeling confirms performance under peak and surcharged flows.