What is a CIPP (Cured-In-Place Pipe)

CIPP, or cured in place pipe, is one of the most widely used trenchless rehabilitation techniques for restoring damaged, ageing or structurally compromised drainage and pipe systems without excavation. The method involves installing a resin impregnated liner inside the existing pipe and curing it to form a new, durable and watertight pipe within the old one. This technique has revolutionised pipeline rehabilitation across the wastewater, stormwater and potable water sectors by eliminating the need for disruptive digging, traffic closures and extensive reinstatement work.

CIPP is valued for its versatility, longevity and minimal environmental impact. It is suitable for pipes of varying diameters, shapes and materials, including clay, concrete, cast iron, pitch fibre and certain plastics. Once cured, the liner provides a seamless, joint free structural solution capable of withstanding loads and pressures similar to a newly installed pipe.

This article examines the CIPP process in depth, outlining its principles, materials, installation methods, applications, advantages, limitations and role in modern drainage engineering.

The principle behind CIPP technology

The core concept of CIPP is simple yet highly effective. A flexible tube, typically made from polyester, fibreglass or felt, is saturated with a thermosetting resin. This liner is inserted into the host pipe using inversion or pull in techniques. Once in place, heat, steam or ultraviolet light activates the resin, causing it to harden. The cured liner adheres to the internal wall of the existing pipe and becomes a strong, smooth and continuous pipe structure.

The key benefit is that the host pipe does not need to be excavated or removed. As long as the pipe retains enough structural integrity to accommodate the liner and withstand installation pressures, CIPP can restore full serviceability with minimal disruption.

Materials used in cured in place pipe systems

CIPP systems rely on three essential materials: the liner, the resin and the curing mechanism. The liner material varies depending on pipe size, load requirements and chemical resistance needs. Polyester felt liners are common in domestic and small diameter applications. For larger or more demanding environments, fibreglass reinforced liners offer superior strength and reduced wall thickness.

Resins used include polyester, vinyl ester and epoxy formulations. Each resin type has distinct characteristics. Polyester is cost effective and suitable for many wastewater applications. Vinyl ester provides improved chemical resistance, making it ideal for industrial environments. Epoxy offers exceptional adhesion and low shrinkage, resulting in high quality structural performance.

The curing mechanism depends on the chosen resin system. Hot water or steam curing is widely used for polyester and vinyl ester systems, while UV curing is increasingly popular due to its speed, precision and reduced environmental impact.

The CIPP installation process

Although CIPP is a trenchless method, it follows a detailed and controlled installation sequence to ensure structural reliability and long term performance. The process generally consists of cleaning, inspection, liner installation, curing and final testing.

A typical workflow includes the following stages:

• Preliminary cleaning and preparation of the host pipe using mechanical or high pressure water jetting to remove debris, sediment and obstructions

• CCTV inspection to identify defects, confirm suitability and determine liner specification

• Impregnation of the liner with resin under controlled conditions to ensure even saturation

• Installation of the liner using inversion or pull through methods, depending on site access and pipe geometry

Once the liner is positioned correctly, curing begins. For hot water or steam systems, pressurised water or steam circulates inside the liner, raising the temperature to initiate polymerisation. UV systems use an array of ultraviolet lamps pulled through the liner to cure the resin precisely and rapidly.

After curing, the ends of the liner are trimmed, laterals are reopened using robotic cutters and a final CCTV inspection confirms installation quality.

Hydraulic and structural performance of CIPP liners

A well installed CIPP liner provides both hydraulic and structural benefits. The smooth internal surface reduces friction and improves flow capacity, often exceeding that of the original pipe. Joint free construction eliminates infiltration and exfiltration pathways, reducing groundwater ingress and preventing wastewater leakage into surrounding soils.

Structurally, CIPP acts as either a fully structural pipe or a partially structural liner depending on design. Fully structural CIPP can support external loads without relying on the host pipe, while partially structural liners reinforce the existing pipe but rely on it for shape and load distribution. Engineering calculations follow recognised standards to ensure the liner meets performance requirements based on soil loads, groundwater pressure and pipe condition.

Applications of CIPP across sectors

CIPP is used across a diverse range of sectors due to its adaptability and strong performance characteristics. It is commonly applied in municipal sewer networks, private drainage systems, industrial pipelines and stormwater culverts. The method is suitable for pipes with cracks, fractures, root intrusion, joint displacement, corrosion or deformation.

Industrial facilities use CIPP to rehabilitate chemically aggressive pipelines where excavation would disrupt operations. Housing developments and commercial sites rely on CIPP to repair drainage lines beneath buildings, roads or landscaped areas.

CIPP can also be used for vertical installations such as downpipes, as well as non circular pipes including egg shaped and rectangular profiles found in older sewer networks.

Planning and site considerations

A successful CIPP installation requires detailed planning tailored to site constraints. Access points for insertion and curing must be identified, often through manholes or excavation of small launch pits. Traffic management may be necessary where road access is required. Temporary bypass pumping is often used to divert flow away from the section being rehabilitated.

Key planning considerations include resin handling requirements, curing equipment positioning, weather impacts and coordination with stakeholders to minimise disruption. Safety planning is essential, particularly where steam curing or confined space entry is involved.

Advantages of CIPP

CIPP offers several major advantages over conventional excavation based pipe replacement. These benefits have contributed to its rapid growth in the water industry.

Key advantages include:

• Minimal excavation, reducing disruption to residents, businesses and transport networks

• Faster installation compared to open trench replacement, with many lines rehabilitated within a single day

• Long service life, often exceeding 50 years when properly designed and installed

• Improved structural integrity and elimination of joints, reducing risk of infiltration and exfiltration

CIPP also supports sustainability goals by reducing waste, lowering carbon emissions associated with excavation and preserving existing infrastructure wherever possible.

Limitations and challenges of CIPP

While highly effective, CIPP is not suitable for all situations. Severely collapsed pipes may not provide sufficient space or alignment for liner installation. Significant deformation can lead to wrinkling or incomplete curing. High groundwater pressure may require additional sealing measures.

Odour emissions during curing, especially from polyester resins, can be problematic in sensitive areas. UV curing reduces this issue but requires straight and clean access.

Other limitations include reliance on accurate CCTV surveys, dependence on specialist contractors and the need for precise temperature control during curing. Improper installation can lead to defects such as wrinkles, blisters or inadequate bonding to the host pipe.

Environmental and regulatory considerations

CIPP must comply with environmental regulations governing resin handling, emissions and water protection. Proper containment of resin mixtures is essential to prevent spills. Curing emissions must be controlled to avoid nuisance or health concerns. Discharge of water used for cooling or cleaning must be managed carefully, ensuring no contamination reaches surface water or groundwater.

Regulators increasingly expect evidence of liner performance, including calculations, testing and certification. Installations in potable water systems require specialised materials approved for contact with drinking water.

Post installation testing and quality assurance

After curing, CIPP installations undergo rigorous quality assessment. CCTV inspection verifies that the liner is smooth, continuous and free from defects. Mechanical and hydraulic testing may be performed to confirm structural performance. Samples of the liner may be taken for laboratory testing to ensure correct resin cure and mechanical strength.

Quality assurance documentation is usually provided to asset owners, including design calculations, resin batch information, curing logs and inspection reports.

The role of CIPP in modern drainage rehabilitation

As infrastructure ages and urban populations grow, the need for efficient and reliable rehabilitation methods continues to increase. CIPP provides a cost effective and low impact solution capable of restoring entire networks with minimal disruption. Its adaptability and proven longevity make it a cornerstone of modern trenchless technology.

Ongoing innovations in UV curing, liner materials, robotic reinstatement and digital monitoring continue to enhance performance and reduce installation times. As sustainability and resilience become central to water management planning, CIPP will remain an indispensable technique for renewing drainage assets while minimising environmental impact.

Cured in place pipe technology demonstrates how engineering ingenuity can extend the life of ageing infrastructure, reduce disruption and deliver long term value across the water industry.