Ensuring Quality Control in Cured-in-Place (CIPP) Applications

Quality Control in Cured-in-Place (CIPP) Applications
D638 Tensile- UV-cured Fiberglass

Cured-in-Place (CIPP) has transformed the rehabilitation of underground pipelines through its innovative approach and cost-efficiencies. A high level of quality control is imperative to achieve a high standard of materials, structural performance and longevity of the rehabilitated pipelines in reference to industry standards such as ASTM F1216, ASTM F1743 and guidelines by NASSCO and the American Water Work Association.

As the manufacturer of E Squared Flexpipe™ coated felts for CIPP lateral and mainline applications, we would like to provide further insights on critical quality control criteria in the manufacturing of high-quality thermoplastic coated liners that are compatible with thermosetting resin systems.

High performance USA manufactured polyurethane (TPU) and polyolefin (TPO) resins are carefully selected to provide the required mechanical performance, chemical and abrasion resistance, hardness levels and thermal performance in the manufacturing of coated liners on a variety of fiber materials including non-woven and fiberglass in widths up to 116″. Coating thickness ranges between 5 and 25 mils on fiber materials, subject to liner application. 

Prior to production, the incoming resins are tested in the laboratory to evaluate properties such as melt flow/viscosity consistency, film quality and clarity to ensure a stable extrusion coating process.

During production, polymer coating thickness and weight density are monitored real-time using online gage measurement devices to ensureuniformity across the web and length of the liner. Manufacturing process with proper drying equipmentto eliminate excessive moisture content in TPU, precise extrusion die and extrusion processcontrols (temperature, pressure, torque and speed) is necessary to maintain a homogenous extrudate and effective saturation of molten polymer on fiber substrates for maximum coating adhesion. Maximum coating adhesion to the fiber substrate without pin holes is critical to prevent delamination and failure of TPU/TPO coating during the wet-out, inversion and/or liner installation process. Different extrusion techniques may be applied to different fiber substrates and coating polymer in order to achieve maximum coating adhesion and liner stability.

Quality Control in Cured-in-Place (CIPP) Applications
D2412 Parallel Plate Load
D2290 Split-Ring Tensile
D695 Compression

Image Courtesy of HTS Pipe Consultants, Inc.

The following table illustrates our in-process and final product inspection criteria which are carried out during/after manufacturing of coated liners (not limited to). Specimens/samples are taken across the web including the extreme edges on every roll of coated liner, unless specified. Destructive testing is also carried out to determine composite tensile strength and coating adhesion performance.

Inspection Criteria Inspection Criteria and Critical Control Points Description
Total composite thickness (coating on fiber material) Measurements across the web using a weighted micrometer (constant pressure) with a dial graduated to 0.001 inches (ASTM D5119). Microscopic evaluation of cross-section of composite is randomly performed to determine coating integrity and saturation on fiber materials. Compression level during extrusion is also monitored to ensure total composite thickness meets required thickness and maximum coating adhesion.
Total composite weight (coating on fiber material) Measurements across the web (ASTM D751) Includes testing of plain felt rolls before extrusion coating.
Finished width and length of liner Measured and recorded for everyroll on Customer’s Inspection Report.
Coating adhesion (heat weld) Destructive heat weld method (ASTM D413).
Coating adhesion (Styrene immersion +1hrs at room temp / 180F) Destructive testing where specimens are immersed in styrene +1 hour. TPU/TPO coating must remain intact on fiber materials.
Break strength and elongation (2in) Destructive testing to determine tensile load or force required to rupture materials (ASTM D461)
Dimensional stability Measures the change in dimensions (machine and cross machine directions) on exposure to static heat 100oC (ASTM D1204).
Hydrostatic resistance (Mullens) Measures the resistance to water penetration under pressure and provides pressure readings up to 1500 PSI (ASTM D751A). Test also validates integrity of TPU/TPO coating on fiber materials (no pin holes and light coating spots).
Coating gloss finish Measures the consistency of gloss at 60o angle (ASTM D523).
Coefficient of friction Measures the slip properties when sliding to itself or over another substance (ASTM D1894). Testing by manufacturing lot / polymer type.

E Squared also works closely with reputable resins suppliers in the USAto ensure E Squared TPU/TPO Flexpipe™ liners are compatible with thermosetting resin systems used in the industry. Application testing is performed to establish coating-resin compatibility and thermal resistance to withstand the initiation temperature and chemistry used in the curing of impregnated liners. It is also important that the initial CIPP structural requirements which includes flexural strength, flexural modulus and tensile modulus in reference to ASTM F1216 are met/exceeded for coated liners with impregnated resin system. Coating adhesion is tested using hot styrene at 180F and TPU/TPO coating must remain intact without defects, delamination and blistering.

In conclusion, the art of manufacturing high quality coated felt liners requires a detailedquality control and testing program, supported by high-precision die extrusion process. E Squared adopts a wholistic approach to quality control and assurance, which includes sustainable sourcing (USA-made materials and PFOA/PFAS free materials), evaluation of incoming raw materials, monitoring of critical control points in the extrusion process to assessing the final product performance. We also focus on staying up-to-date with industry needs and technology advancements for continuous growth and innovation and ability to better support our customers and industry partners.


ASTM F1216-22 Standard Practice for Rehabilitation of Existing Pipelines and Conduits by the Inversion and Curing of a Resin-Impregnated Tube

ASTM F1743-22 Standard Practice for Rehabilitation of Existing Pipelines and Conduits by Pulled-in-Place Installation of Cured-in-Place Thermosetting Resin Pipe (CIPP)

ASTM D5813-04 Standard Specification for Cured-In-Place Thermosetting Resin Sewer Piping Systems


The Importance of CIPP and it’s Benefits

CIPP (Cured In Place Pipe) technology, also known as trenchless technology or in-situ pipe repair, enables the restoration of damaged sewer systems without the requirement for excavation or trench digging. This process involves deploying CIPP tubes using water, steam, or air pressure to line the existing pipes.

In our forthcoming four-part series, we will delve into various aspects of utilizing CIPP technology, with a focus on the following topics:

  • The Importance of CIPP and its Benefits.
  • Welding Techniques for CIPP and Implementation.
  • Ensuring Quality Control in CIPP Applications.
  • The Difference in Main Line CIPP and Laterals

The deteriorating state of wastewater systems in North America and Europe, along with the growing volume of wastewater worldwide, have resulted in the rise of pipes bursting and the overflow of wastewater outside of the pipe. The majority of pipes are buried underground, which may result in expensive repairs requiring excavating roadways and leading to major traffic delays for many days.

The concept of lining existing pipelines with a flexible material impregnated with resin was first explored in the 1950s. Early experiments focused on using fiberglass-reinforced materials as liners. The primary motivation was to find a less disruptive and more cost-effective method for rehabilitating aging sewer and water pipelines.

In the 21st century, CIPP technology continued to advance with improvements in liner materials, resin formulations, and installation techniques. It also found applications in rehabilitation projects for larger-diameter pipelines, stormwater systems, and other critical infrastructure. The technology’s versatility and ability to extend the life of pipelines made it a valuable asset for addressing the challenges of aging infrastructure.

Today, approximately 50% of all damaged pipes are being repaired using CIPP technology. In the U.S., trenchless technology continues an upward growth trend. It has captured nearly half of the $3.4 billion market for sewer line rehabilitation and about an eighth (12.9%) of the $1.5 billion spent on repairing potable water pipes, according to the 15th Annual Municipal Infrastructure Survey conducted by Underground Construction (Oildom Publishing Co., Houston, Texas).

Importance of CIPP and it's Benefits

Trenchless pipe relining is a popular technique for repairing damaged or clogged sewer lines, water lines where the pipes are pre-fabricated at the manufacturing facility and are pre cut and welded to form the tube, the liner goes through the wet-out process, where the line is saturated with a polyester, vinyl ester, or epoxy resin. The line is then transported using a refrigerated truck to the job site and is deployed at the job site utilizing steam, hot water or UV to form the shape of the damaged pipe, making it both more economical and effective.

The core principle behind CIPP involves inserting a flexible liner, often composed of materials like polyester, fiberglass, or felt, into the damaged or compromised pipe. Once in position, the liner is impregnated with a thermosetting resin that, upon curing, hardens to create a new, structurally sound pipe within the existing one. 

  1. CIPP typically consists of a resin-impregnated felt or fiber sleeve. With the resin in an uncured state, it forms a flexible, conformable tube that can be inserted into a damaged pipe. Some sleeves are manufactured inside out and are inverted as they are pushed into the existing pipe via air or water pressure.


Cross Section of a damaged pipe (before), and after rehabilitation using CIPP (After) 1

The CIPP technology was developed as a solution to the challenges posed by traditional pipeline repair and replacement methods, which often involve disruptive and costly excavation. CIPP offers several benefits, including:

1. Cost Savings: CIPP eliminates or significantly reduces the need for extensive digging, resulting in reduced labor and equipment costs associated with excavation.

2. Minimal Disruption: The non-disruptive nature of CIPP means that road closures, traffic disturbances, and disruptions to daily activities are minimized, making it ideal for urban areas.

3. Environmental Considerations: CIPP reduces the environmental impact by minimizing soil disturbance, energy consumption, and emissions from construction equipment. It also extends the lifespan of existing infrastructure, reducing the need for new material production.

4. Versatility: CIPP can be used on various types of pipes, including those made of clay, concrete, cast iron, PVC, and more. This versatility makes it suitable for a wide range of pipeline rehabilitation projects.

5. Structural Reinforcement: The cured resin inside the liner not only seals leaks and prevents infiltration but also reinforces the structural integrity of the pipeline.

6. Speed of Implementation: CIPP projects are often completed faster than traditional methods due to reduced preparation and construction time, minimizing service interruptions.

E Squared has been working closely with all the major CIPP pipe manufacturers, along with the TPU vendors, felt and non-woven manufacturers across the world, and the leading manufacturers of welding and sewing machines, to ensure that we have the right solution for your application. Our Research and Development facility at Hillside, New Jersey, is working on new development projects, including high-pile knits, TPO coatings and hybrid fleece. E Squared’s dedication in the CIPP industry can be seen with the opening of our new manufacturing facility in Bluefield, VA which is dedicated to manufacturing coated felts for CIPP applications.