What is a Reforming

Reforming is a trenchless rehabilitation process used to restore the original shape of deformed or collapsed drainage pipes, most commonly pitch fibre pipework. It involves physically reshaping or reconfiguring a distorted pipeline — typically one that has become oval, squashed, or partially collapsed — so that it regains a circular profile and can support the installation of a structural liner.

In drainage systems that include ageing or damaged pitch fibre pipes, reforming is often an essential preparatory step before cured-in-place pipe (CIPP) lining or other forms of no-dig pipe rehabilitation. Without restoring the correct geometry, lining may fail to bond or cure properly, resulting in leaks, blockages, or premature system failure.

Understanding Pitch Fibre Pipe Deformation

Pitch fibre pipes were widely used in the mid-20th century, particularly between the 1950s and 1970s, due to their light weight, ease of installation, and low manufacturing cost. These pipes were made by impregnating cellulose fibres with bitumen, forming a rigid but lightweight pipe.

However, the material is inherently vulnerable to deformation under certain conditions:

  • Moisture ingress: The cellulose absorbs water over time, leading to swelling and softening.

  • Chemical exposure: Some household and industrial chemicals degrade the bitumen matrix.

  • External ground pressure: Subsurface loads can compress the pipe into an oval or squashed shape.

  • Thermal fluctuations: Expansion and contraction cycles can contribute to structural fatigue.

As a result, pitch fibre pipes often become misshapen over time. In severe cases, they may partially collapse, restricting flow and making structural rehabilitation difficult without reforming.

The Purpose of Reforming

The main purpose of reforming is to reshape deformed pitch fibre pipes into a condition that allows for effective relining. Relining products — such as CIPP or other cured or thermoplastic liners — are designed to be installed within round host pipes. If the host pipe is significantly oval or squashed, the liner may wrinkle, fold, or fail to bond properly with the pipe wall.

Reforming restores a near-circular cross-section, providing a uniform host surface for the liner to bond with. This improves the structural performance of the final rehabilitated pipe, reduces the risk of liner failure, and helps maintain the original flow capacity.

The Reforming Process in Practice

Reforming is carried out using specialist equipment that is inserted into the existing pipework via a manhole or access chamber. The process can vary depending on the severity of deformation, the pipe diameter, and the available access, but generally follows these steps:

  1. CCTV survey and assessment: A camera inspection identifies the location and extent of pipe deformation.

  2. Pipe cleaning: High-pressure water jetting or mechanical cleaning removes debris, roots, and silt, exposing the true condition of the pipe.

  3. Insertion of reforming tool: A mechanical expander, reforming pig, or hydraulic former is introduced into the pipe run.

  4. Reforming operation: The tool is gradually pulled or pushed through the pipe, forcing the walls outward to reshape the pipe to a near-circular cross-section.

  5. Verification survey: Another CCTV inspection confirms the pipe has been sufficiently reformed and is ready for lining.

  6. Preparation for lining: Depending on the technique used, the reformed pipe may be stabilised with temporary support or immediately lined using a structural liner.

In some cases, hot water or steam may be used to soften the pitch fibre pipe during the reforming process. This helps reduce the risk of fracture and allows for more effective reshaping. However, this must be carefully controlled to avoid further degrading the material.

Equipment Used for Reforming

The type of equipment used depends on the pipe diameter, length, and condition. Common reforming tools include:

  • Mechanical pigs: Solid rubber or metal-bodied devices pulled through the pipe to push the walls outward.

  • Hydraulic expanders: Inflatable bladders that apply uniform radial pressure to the internal walls.

  • Rotating brushes or cutters: Used to remove internal scale or softened material before reshaping.

  • Specialist reforming rigs: In larger or severely deformed pipes, specialist contractors may use powered systems that combine mechanical pressure with rotation or vibration.

Tool selection must consider both the pipe’s vulnerability and the need to avoid causing additional damage.

Reforming vs Re-rounding

Although the terms are sometimes used interchangeably, there is a distinction between reforming and re-rounding.

  • Re-rounding refers specifically to restoring the circular profile of a pipe that has become oval.

  • Reforming has a broader scope. It includes reshaping pipes that are squashed, partially collapsed, or have more complex distortions, not just ovality.

In many practical contexts, reforming is considered a more comprehensive technique and may be required where re-rounding alone is insufficient.

When Is Reforming Necessary?

Not all deformed pipes require reforming. In some cases, liners can be installed directly if deformation is minimal. However, reforming becomes essential when:

  • The pipe has lost more than 10 to 15 percent of its internal diameter due to deformation

  • The ovality of the pipe exceeds manufacturer recommendations for liner compatibility

  • Internal CCTV shows crushing, flattening, or visible folds in the pipe wall

  • Pipe deformation causes hydraulic restriction or flow turbulence

  • There is evidence of softening or blistering, but the pipe still holds structural shape when reformed

Contractors often use deformation gauges or ovality sensors in combination with video footage to determine the need for reforming.

Risks and Limitations

While reforming is an effective way to restore shape and enable lining, there are limitations and risks associated with the process:

  • Risk of delamination: Pitch fibre pipes can delaminate under pressure, especially if the material has softened due to moisture or chemical exposure.

  • Pipe rupture: Excessive or uneven force may cause the pipe to crack, leading to complete failure.

  • Reversion risk: Unless lined promptly after reforming, the pipe may return to its deformed shape over time.

  • Limited use on fully collapsed pipes: Reforming cannot be used if the pipe has structurally failed or is completely flattened.

To reduce these risks, the process must be carried out by trained operatives using appropriate techniques and within the parameters defined by the pipe condition.

Reforming and Lining: A Combined Strategy

Reforming is rarely a standalone solution. Its true value lies in enabling the successful application of a structural lining system. Once the pipe has been reformed, it can be lined using:

  • Cured-in-place pipe (CIPP) lining

  • Slip-lining or fold-and-form liners

  • Spray-applied polymer coatings (in select cases)

These systems bond to the internal surface of the reformed pipe and create a new structural pipe within the host. Once cured, the new pipe restores hydraulic performance and provides long-term structural integrity, often with a design life exceeding 50 years.

Regulatory Considerations and Best Practice

In the UK, reforming and lining works must be carried out in accordance with water industry and WRc standards. Best practice includes:

  • Performing pre- and post-reforming CCTV surveys

  • Documenting all deformation measurements and structural assessments

  • Using WRc-approved liners and resin systems for CIPP installations

  • Following manufacturer recommendations for time between reforming and lining

  • Ensuring that health and safety risks — such as confined space entry — are properly managed

Some local authorities and water companies require evidence that reforming has been carried out to standard before approving liner installations.

Conclusion

Reforming is a critical trenchless rehabilitation method for restoring the shape of deformed or squashed pitch fibre pipework. It enables effective relining and prevents long-term drainage failure. While not suitable for every scenario, reforming offers a valuable solution in cases where excavation is impractical or the pipe still retains enough structural integrity for reshaping. When performed correctly and followed by structural lining, it extends the life of existing drainage infrastructure and helps maintain system performance with minimal disruption.