Cured-in-place Pipe Liner Research Articles

Mechanical study and equations for gravity flow pipe liners stretching across ring fractures or joints under shear action

Cured-in-place-pipe (CIPP) liners have been widely used in rehabilitation of gravity flow pipelines. However, the host pipe rehabilitated by the CIPP liner may be subject to shear force and shear displacement at the joint. In this study, a finite element model of a rigid host pipe with liner under shear action is established and used to study the resulting behaviour. Controlling factors such as the gap spanned by the liner between host pipes across the joint, diameter, the liner thickness, the elastic modulus of the liner, and the coefficient of friction between host pipe and liner are studied. The liner stress, displacement, and shear force are reported. Shear stiffness and stress equations are then fitted based on 286 data points. The results show that the maximum stress on the inner surface of the liner occurs at the shoulder and haunch, and the maximum stress on the outer surface occurs at the springline. The inner surface stresses at the crown and invert decrease with increases in liner-host pipe friction, but increase at the shoulder and haunch. Coefficient of Friction has almost no effect on the stresses that develop on the outside surface of the liner.

Study on the Bearing Capacity of the Polyethylene Pipe–Cured-In-Place Pipe Liner Composite Structure under External Pressure

Cured-in-place pipe (CIPP) technology is used to repair deformed municipal polyethylene (PE) pipes caused by design flaws, construction issues, or external loads. However, research on CIPP for PE pipes is limited, restricting its broader application. This research focuses on the mechanical response characteristics and failure modes of the composite PE pipe–CIPP liner structure under external loads. Using experimental setups involving comparative test groups with different diameters and wall thickness ratios (DR values, defined as the ratio of the pipe’s outer diameter to its wall thickness), this study evaluates the effects of the liner’s elastic modulus, the bonding effectiveness at the PE pipe–CIPP liner interface, and the initial ovality of the pipes on the load-bearing capacity. The experimental results reveal that CIPP liners substantially enhance the stiffness and load-bearing capacity of PE pipes, with improvements ranging from 200% to nearly 500% depending on the pipe’s DR value. A novel ring stiffness prediction model is also introduced and validated against the experimental data. This model provides a theoretical framework for understanding the complex interactions at the PE pipe–CIPP liner interface and aids in designing more resilient urban drainage systems.

Testing and analysis of CIPP liner under simulated groundwater pressure

Cured-in-place pipe (CIPP) is commonly used to rehabilitate deteriorated culverts and drainage structures. During installation, factors like corrosion, joint staggering, and insufficient inflation can create an annular gap between the liner and host pipe, potentially leading to buckling failure under external loads. Existing design methods lack experimental evaluation, leading to discrepancies between simulations and monitoring. To address this, an experimental study was conducted using a carefully designed test system to minimize boundary condition influences. Two tests were performed with host pipes of 600 mm and 1000 mm outer diameters. Simulating underground water pressure, elliptical deformation of the CIPP liner was observed until the host pipe’s wall was contacted, with localized arching in non-contact areas. The width of the annular gap (Δd) between the liner and host pipe determined whether hydrostatic buckling occurred before critical buckling. However, the critical buckling pressure could not be accurately predicted by existing buckling models. In response to this issue, an improved model is proposed based on pressure from elliptical deformation and buckling caused by local arching. The experimental results showed that the simulation error ranges from -0.5 % to +1.1 %. Our study provides valuable insights into enhancing CIPP liner buckling resistance and offers a more accurate model for predicting critical buckling pressure, contributing to safer and more reliable CIPP rehabilitation methods.

Stability assessment of CIPP liner under varied boundary conditions: A theoretical and simulation study

The buckling of liners carries significant implications, including hampered medium transmission, structural damage, and the risk of leaks, adversely affecting production, economy, and the environment. The interface performance between Cured-in-place-pipe (CIPP) liners and host pipes is pivotal for overall structural stability. However, this interface's influence has been underestimated in engineering practices and laboratory research. This study introduces two novel hydrostatic pressure buckling models, enhancing constrained arch and energy-based Glock models, while considering both free and bonded boundary conditions. Subsequently, a validated 3D finite element model of CIPP lined pipes is established from full-scale tests. Through comprehensive sensitivity analysis, the study investigates the influence of diameter-to-wall thickness ratio (DR) and annular gap on liner buckling under free boundary conditions. Additionally, it explores the effects of DR value and ovality ratio on buckling behavior under bonded conditions. Results reveal distinct buckling and post-buckling modes under different boundary conditions. The proposed theoretical analysis method accurately predicts critical buckling pressure within a 10 % error margin, validated through experiments and numerical simulations, offering practical guidance for assessing repaired pipe stability.

Non-destructive testing of pipes with CIPP liner filling

Non-destructive testing of cured-in-place pipe (CIPP) is an important procedure for verifying the integrity and quality of newly installed or renovated pipes using CIPP technology. This technology is often used to repair or build pipelines, especially sewer and sewer systems. Testing ensures that the liner liner (CIPP) has been successfully installed and that the pipe will perform its function reliably without the need for further repairs. Next, we will present some possibilities of using non-destructive testing methods. After the CIPP is installed, a camera is inserted into the pipe to allow visual inspection of the liner fill. This can identify any defects, tears or other problems in the CIPP material. Compressed air or water testing is used to verify that the mattress pad can withstand pressure. The pipe is filled with air or water under a certain pressure and then monitored for leaks or deformations. Acoustic methods are used to detect cracks or leaks in pipes. Special sensors can pick up sound signals emitted by leaking liquids. The magnetic resonance method uses magnetic resonance to examine the condition of the lining fill and pipe walls. It provides detailed information about the material and the quality of the installation. Ultrasonic probes can be used to inspect CIPP for cracks, faults or variations in material thickness. X-rays or gamma rays can be used to obtain detailed images of the inside of the pipe and the lining fill. The choice of appropriate methods depends on the specific situation and project requirements. Non-destructive testing is essential to ensure the safety and functionality of CIPP lined pipelines and reduces the need for additional repairs and maintenance.

A novel test procedure for evaluating the performance of composite cured-in-place-pipe liners in water pressure pipe rehabilitation

The cured-in-place pipe (CIPP) is a pipe rehabilitation technique that is becoming increasingly popular due to its cost advantages, reduced environmental impact, and decreased time requirements compared to traditional pipe replacement. However, some CIPP rehabilitation projects have revealed deficiencies in predicted liner performance. This paper proposes and validates the Inner Balloon Pressure Test, a new test procedure for the quality control of CIPP rehabilitation liners. The test is intended to replicate the working stress conditions of an installed CIPP liner, and is proposed as an alternative to the curved specimen bending test recommended by the current CIPP standard and which has been shown to overestimate the ultimate stresses of cured CIPP liner specimens by more than 200%. Consequently, in a liner of DN 385 and 6 mm of thickness, a burst pressure of 138.2 bar was predicted through the bending test, whereas 62.8 bar was deducted from tensile tests. The experimental evidence provided in this study can significantly impact the design of CIPP pressure pipe liners. Inadequate sizing of the structural reinforcement can compromise the liner functionality and the rehabilitation of the pipeline. Therefore, this study provides a novel test that reduces uncertainties related to the strength analysis of CIPP liners. Furthermore, it contributes to optimizing and advancing existing design and quality control techniques.

Study on the impact of ovality defect on structural stability of CIPP liner of drainage pipeline

Cured-in-Place Pipe (CIPP) is a trenchless pipeline rehabilitation technology commonly used for repairing underground municipal pipes. It effectively, safely, and environmentally friendly resolves drainage pipe leakage and dripping issues by curing a new resin-impregnated liner inside the original pipe. However, in practical applications, ovality defects may occur in CIPP liners due to insufficient inflation, deformation of the original pipe, joint misalignment, and other problems. These defects have the potential to reduce the structural bearing capacity of the liners. To investigate the buckling mechanism of oval liner structures under external water pressure, two sets of OD 600 mm CIPP liner buckling tests were conducted. The critical buckling stress state and buckling mode characteristics exhibited similarities across liners with different initial ovalities. With an increase in the ovality defect of the liners from 0% to 5%, the critical buckling pressure decreased by 10.62%, while the maximum radial deformation displacement decreased by 62%. Existing models have shown an inability to accurately predict the buckling pressure of oval liners with an initial annular gap. Consequently, this study proposes an improved analytical solution for calculating the critical buckling pressure of liners with ovality imperfections under the influence of an annular gap, which aligns well with the experimental data. The conclusions drawn from this study provide substantial data support for ensuring the accuracy and safety of CIPP liner rehabilitation design.

Numerical Study on Mechanical Properties of Corroded Concrete Pipes before and after Cured-in-Place-Pipe Rehabilitation

Cured-In-Place-Pipe (CIPP) rehabilitation technology is widely utilized in pipeline rehabilitation projects and has exhibited favorable results. Nevertheless, the mechanical characteristics of pipelines after CIPP rehabilitation and the effectiveness of CIPP rehabilitation in repairing these mechanical characteristics remain unknown. To address these issues, a three-dimensional numerical model of a corroded concrete pipe before and after CIPP rehabilitation was established in the present study. To authenticate the accuracy of the numerical model, the numerical simulation data were compared with the full-scale test data from prior research, and the comparison outcomes show that the numerical model formulated in this study is reasonable and reliable. To appraise the repair effectiveness of CIPP rehabilitation, the mechanical properties of a corroded pipe, a CIPP-repaired pipe, and a normal pipe under traffic load were computed and compared, and the comparison outcomes demonstrate that the stress in the pipe bell, stress in the pipe spigot, vertical displacement of the pipe crown, and vertical displacement of the pipe invert were reduced by 39.8%, 16.7%, 24.7%, and 24.4%, respectively, after CIPP rehabilitation. Moreover, a series of three-dimensional numerical models were constructed to scrutinize the impacts of factors such as corrosion degree, corrosion angle, and traffic load on the mechanical properties of corroded pipelines before and after CIPP rehabilitation. The findings indicate that the stress on the pipe escalates with increasing corrosion degrees and diminishes with increasing corrosion angles; there are no noteworthy differences between the vertical displacement of the pipe and the von Mises stress of the CIPP liner for diverse corrosion degrees and corrosion angles; the amplification of the traffic load will augment the stress and displacement of the pipe and increase the rotation of the pipe, resulting in a significant upsurge in the stress of the CIPP liner at pipe joints. When the traffic load magnitude rises from 0.7 MPa to 1 MPa, the stress and displacement of the pipe and the von Mises stress of the CIPP liner were increased by 18.9%, 42.3%, and 42.1%, respectively.

Health Risks Assessment from Cured-in-Place Pipe Lining Fugitive Styrene Emissions in Laterals

The aim of this study was to improve the understanding of styrene emissions in sewer laterals, resulting from the installation and steam curing of a resin impregnated cured-in-place-pipe (CIPP) liner, within a sanitary sewer. The study included development and performance assessment of a controlled field test program that measures and records styrene emissions before, during, and after steam-curing a CIPP liner. Measured styrene emissions are then compared with those of published studies and regulatory exposure guidelines to assess the potential risk exposure. The field study measurements confirmed that high styrene concentrations can exist in sewer laterals during the steam-curing of the CIPP liner. They also confirm that water, in proper functioning P-traps, will prevent high styrene emissions from exiting the lateral and into buildings. Fugitive emission modeling shows that the risk of exceeding the acute exposure guideline limits is very low, even when high styrene concentrations exist in a lateral with a dry P-trap, and the styrene odor threshold is exceeded within the building, that is, when the building occupants smell styrene.

Experiment and evaluation model of liner design for renewal of deteriorated reinforced concrete pipes utilizing cured-in-place-pipe technology

Cured-In-Place-Pipe (CIPP) is an emerging trenchless rehabilitation technology for repairing urban drainage pipes growing significantly in China. However, overestimated external loads due to a completely deteriorated-pipe assumption may increase conservatism in the CIPP liner structure design. In this study, ring stiffness test machine was employed to quantify the bearing characteristics of pipe-liner system. The concrete and reinforced concrete pipes with an inner diameter of 200 mm, which deteriorated to several states, were renewed with CIPP. Digital Image Correlation (DIC) was employed to reveal the contact characteristics between the host pipe and CIPP liner under external loads and the mechanism of loads transferred from the pipe to the liner. An evaluation model for load-bearing performance of reinforced pipe was established. Parametric studies were carried out including lateral load distribution angle, concentrated load dispersed angle, and lateral interactions. Furthermore, a case study was conducted in conjunction with the indirect design method for buried pipes, and then the improved model was compared with experiment results. An average value of 20 % reduction in CIPP liner thickness was achieved by employing the modified model than the ASTM standard. This study can serve as a database for engineers designing CIPP rehabilitation projects for concrete pipes whose structure has not been completely damaged.

Investigation of mechanical properties of corroded concrete pipes after cured-in-place-pipe (CIPP) rehabilitation under multi-field coupling

The pipeline is mainly subjected to soil load, fluid load and traffic load, the mechanical properties of corroded concrete pipes after cured-in-place-pipe (CIPP) rehabilitation under multi-field coupling have not been revealed. In this paper, a 3D numerical model of buried concrete pipes after CIPP rehabilitation under the coupled effects of the soil load, traffic load and fluid load were established based on the results of the full-scale test. The influence of cover depth, traffic load and fluid load on the maximum principal stress of the pipeline, vertical displacement of the pipeline, the von Mises stress of the CIPP liner and the circumferential bending moment of pipe-liner composite structure were analyzed. Results showed that the cover depth and traffic load have a greater influence on the crown, invert, and springline of the pipe and has a lesser influence on the shoulder and haunch of the pipe; The stress and the circumferential bending moment of the pipeline is mainly caused by the soil load, the vertical displacement of the pipeline and the von Mises stress of CIPP liner is mainly caused by the traffic load, and the fluid load has little effect on the pipe-liner composite structure.

Analysis of the structure of liners used for the modernisation of brick collectors

Abstract Brick sewers were designed as egg-shaped, pear-shaped, bell-shaped, vaulted, and even rectangular (sometimes with granite ceilings and floor slabs). In exceptional cases, circular sections were also made of brick. Efforts were made in order to ensure optimal flow conditions, and also that the cross-section was adapted to the shape of the rock mass pressure line. This is due to the fact that the most advantageous shapes for masonry collectors are shapes in which no tensile stresses will occur in any part of the cross-section under the influence of external loads. Nevertheless, sewage conduits degrade over time. The boundary conditions of their use also change, which affects the magnitude of mechanical and hydraulic loads. Further use of a sewer in such a case requires its renewal, and less frequently, modernization that results from the necessity to change its function. This is usually done by introducing a new conduit into the interior of the renovated or modernized sewer, which in literature is called a liner. The aim of the analysis was to determine the thickness of the liners that strengthen the structures of brick channels with an inverted egg cross-section and with dimensions of 1050 × 700 mm, which are intended for gravitational sewage systems. The analysis included the performance of variant static and strength calculations for the assumption that the conduit after its modernization will be replaced with a conduit operating in the pressure system, which is a very rare requirement. It was assumed that the best solution would be to use a CIPP (Cured In Place Pipe) liner.

Full-scale experimental investigation of the mechanical characteristics of corroded buried concrete pipes after cured-in-place-pipe rehabilitation

Cured-in-place pipe (CIPP), the most common approach employed in trenchless sewer rehabilitation technology, has been increasingly used in recent years. To examine the mechanical characteristics of corroded buried concrete pipes after semi-structural rehabilitation of CIPP, a series of full-scale tests was performed. The influence of traffic, surcharge, and fluid loads as well as cover depth on the mechanical properties of the pipe–liner composite structure was analyzed. The following results were obtained. (1) The longitudinal strain of the CIPP liner at the pipe joint is significantly greater than that at the pipe barrel. (2) The cover depth has a greater impact on the circumferential strain and a smaller impact on the longitudinal strain of the pipe-liner composite structure. (3) The above-ground concentrated loads such as surcharge and traffic loads, which will significantly increase the circumferential strain of the pipe-liner composite structure and sharply increase the longitudinal strain of the CIPP liner in shallow cover depth, greatly affect the circumferential and longitudinal strains of the pipe-liner composite structure. (4) The fluid load has little effect on the mechanical properties of the pipe-liner composite structure.

Mechanical sensitivity analysis of pipe-liner composite structure under multi-field coupling

Cured-in-place pipe (CIPP) has become one of the most widely used pipeline trenchless rehabilitation technologies because it has the advantages of needing no grouting, rapid curing, and short construction time. However, previous research has not yet revealed the mechanical sensitivity of pipe-liner composite structures. In this paper, a numerical model for a pipe-liner composite structure under multi-field coupling of the traffic load, earth pressure and water flow was first established based on an Abaqus, Fluent and mesh-based parallel code coupling interface (MpCCI). Then, the maximum principal stress of the pipeline, vertical displacement of the pipeline, von Mises stress of the CIPP liner and vertical displacement of the CIPP liner were selected as evaluation indicators, and the CIPP thickness, cover depth, traffic load, corrosion width, corrosion depth, and water quantity were selected as sensitive factors of the pipe-liner composite structure. Finally, the mechanical characteristics of the pipe-liner composite structure were analysed under condition of different sensitive factors; moreover, the sensitivity of the sensitive factors was ranked based on the sensitivity coefficient. The research results are consistent with previous research providing a theoretical basis for the optimal design of wall thicknesses for CIPPs.

Short- and Long-Term Structural Characterization of Cured-in-Place Pipe Liner with Reinforced Glass Fiber Material.

Cured-in-place pipe (CIPP), as a kind of trenchless sewer rehabilitation technology, is a method to repair sewer pipe using unsaturated polyester resin. This study develops a CIPP liner using hot water or steam curing as well as glass fiber, in contrast to traditional methods, which use nonwoven fabric. Composite material samples were fabricated by combining liner materials using various methods, and the structural characteristics of the liners were compared and analyzed through short- and long-term flexural strength tests. A long-term test was conducted for 10,000 h, and the results revealed 13.3 times higher flexural strength and 8 times higher flexural modulus than the American Society for Testing Materials minimum criteria for CIPP short-term properties. The maximum creep retention factor was 0.64, thereby reducing the design thickness of the CIPP by up to 54%. The structural characteristics also improved when glass fibers were mixed with traditional CIPP liner, making it possible to reduce the thickness by 30%. Glass fibers result in high structural strength when combined with unsaturated polyester resin. Structural strength increased, even when glass fibers were mixed with traditional CIPP liner. The main contribution of this research is the development of a high strength CIPP liner and improvement of the structural properties of CIPP lining without using the specially formulated resin or lining materials.

Performance of ductile iron push-on joints rehabilitated with CIPP liner under repetitive and seismic loadings

The cured in place pipe (CIPP) liner technology is to install flexible polymeric liners with thermosetting resin inside existing pipelines. Compared with traditional methods of pipeline retrofits, CIPP provides an economic and environmentally friendly alternative for pipeline rehabilitation. However, the lack of proper constitutive models of the push-on joints and the CIPP-liner reinforced joints remains a critical deficiency in current numerical simulations of buried segmental pipelines. This paper presents new constitutive models of ductile iron (DI) push-on joints, before and after reinforced with one type of the CIPP liners, commonly used in pipeline retrofits. The proposed models were calibrated from the full-scale quasi-static tests performed on water-pressurized DI pipelines with push-on joints. These new joint models, considering strength degradation and energy dissipation of the joint, well characterizes the longitudinal behavior of the push-on joint and the liner-strengthened joints under repetitive axial loading, which primarily represents the expansion and contraction effects of the joints due to thermal effects or seismic waves traveling along the buried pipelines. Moreover, this paper also provides a rational procedure for evaluating the seismic performance of buried pipeline with different push-on joints. The proposed numerical procedure could be generally applied to quantify the seismic performance of buried straight pipelines incorporating the proposed joint models under seismic wave propagation. Numerical results indicate that the CIPP liner can significantly improve the seismic performance of the push-on joints subjected earthquake induced transient ground deformations.

The Mechanical Properties of High Strength Reinforced Cured-in-Place Pipe (CIPP) Liner Composites for Urban Water Infrastructure Rehabilitation

Most urban areas in the world have water infrastructure systems, including the buried sewer and water pipelines, which are assessed as in need of extensive rehabilitation. Deterioration by many other factors affects structural integrity. Trenchless technologies such as Cured-in-Place Pipe (CIPP) are now applied in numerous projects while minimizing disturbance in an urban environment. The main purpose of this study is to develop a high strength CIPP material using various composite materials (e.g., glass fiber, carbon fiber, polyester felt, unsaturated polyester resin, and others). Composite samples were made of the materials and tested using three-point bend apparatus to find mechanical properties, which include the flexural modulus, strength, and deflection. A composite combination with glass fibers with thin felt layers shows the best results in mechanical properties. Flexural modulus is a key factor for CIPP liner thickness design. Glass fiber composite yields between four and nine times higher values than the minimum value specified in the American Society for Testing and Materials (ASTM) F1216. This study provides a fundamental baseline for high strength CIPP liners that are capable of using conventional curing technologies.

Evaluation of testing methods for tracking CIPP liners’ life-cycle performance

Despite the significant investments made in the use of cured-in-place pipe (CIPP) rehabilitation technologies, quality assurance (QA) and quality control (QC) practices can vary widely among munici...

Numerical analysis of the mechanical behaviors of pressurized underground pipelines rehabilitated by cured-in-place-pipe method

Due to the humid climate in Taiwan area, the underground pipes are prone to be damaged by corrosion, which could be more severe for the environment with high salinity near the coast. In addition, the situation could be worse where the underground pipeline planning was not enforced. For example, a water pipe or a sewage pipe may be too close to a pressurized pipe, which could be corroded if the water pipe or the sewage pipe leaked. In this study, the numerical simulation software ABAQUS was used to simulate underground pipelines damaged by corrosion. The stress and displacement behavior was analyzed for scenarios with different internal pressure and surface loading conditions. In addition, the performance of the cured-in-place-pipe (CIPP) method, a trenchless rehabilitation method was also numerically analyzed. The results suggest that it can reinforce the damaged pipe by reducing the stress concentration and reducing the differential displacement. However, the design of the CIPP liner could be further optimized in terms of its design thickness.

Change in Toughness Parameters of Sewer Pipes Rehabilitated with Two Types of Epoxy CIPP Liners

AbstractThe main objective of the investigation was to evaluate the influence of the installation of two kinds of epoxy cured-in-place pipe (CIPP) liners (adhesive and independent) on the change in...