(Community Engineering Services, was retained to provide a review of pipe liner methods on the market and in applicable technical literature. The following is not an endorsement of any contractor or methodology by the author)
Prepared by Dan Robles, PE
Currently, there are three technologies (with multiple sub-variants) in use by commercial construction, municipalities, and government facilities for the purpose of repairing or remediating corrosion in potable water systems. These include Epoxy coating, Polyurethane coating, and Polyethylene Liners (PET).
For the millions of structures built during the post war years from 1950-1970’s, water pipes are quickly approaching their expected lives. Since access to the pipe is often restricted by walls, additions, or machinery a liner that is “cured in place” may offer an affordable and long term solution to water flow problems inside deteriorating pipes.
As a result, a pipe lining industry arose to offer what is called a seamless application that restores impermeability. The market offering is to eliminate leaks and future deterioration due to oxidation while also improving flow.
The pH of water, chemical composition, delivery pressure, water temperature, and material of the pipe are some of the factors that contribute to pipe deterioration. Low or changing water pressure or green residue at fixtures or drains of copper pipe systems can be some of the initial outward signs of deteriorated pipes. Pin hole leaks, bursts at junctions, and lead contamination from leaching pipe joints can all be treated from within the pipe. Epoxy materials injected through clean outs, drains, and shut off valve terminations, coat pipe walls with a seamless, durable material much like the lining of premium canned food containers.
The Epoxy Lining Process:
The process involves drying the pipes, sandblasting the inside walls with pressurized air and a mineral that removes corrosion and oxidation and prepares the walls to accept the lining, then applying the epoxy lining. The process has been used on galvanized or black iron, steel, copper, or plastic piping, as well as, coal tar impregnated cellulose fiber pipes. Generally, wherever it is possible to create a pipe within a pipe, epoxy relining has been employed.
The process is inspected by using visual inspection systems and fiber optic lighting to inspect pipes before and during the process to gauge the degree of deterioration, diameter of the pipe, and effectiveness of the installation. There does not appear to be any advertised pipe-strength analysis prior to the installation or adhesion testing after the installation. Some pipe wall thinning is expected during the sand blasting process.
The industry has largely consolidated to two primary vendors of epoxy pipe liner.
Epoxy Coating: The overwhelming majority of articles about epoxy coatings have been positive. However, many of these references have been from industry sources or select testimonials. Failures are known to have been experienced, but those references are not popularized as much. The use of epoxy is still fairly new (15-20 years) and the application is governed by very few technical codes and standards. Obviously, the plumbing industry would be biased in the opposing view but that view must be included with the pro-epoxy contingency. It is imperative to rely on sound engineering principles when considering an epoxy liner solution.
American Water Works Association standard for application of epoxy coating. There are very few standards that cover the application of epoxy coating. Ideally, there should be standards for product quality, purity, preparation, application, inspection, and serviceability. Instead, we seek to apply any existing standard where applicable. This recent 2011 document is part of our collection collection. This document cites best practices per the AWWS: AWWA Epoxy Standard 2011
US Military Application Standards. One segment of the epoxy coating industry touts the successful use of epoxy at military installations. As such, it is our expectation that military standards would cover the formulation and application of the system. This document specifies military requirements and procedures for the use of epoxy in facilities. Strong attention should be paid to the quality controls on the application process. Military Application Epoxy Standard
Overseas Investigation of Epoxy coating issues: It is difficult to find failures of epoxy coatings in domestica water supply. So far, the material appears to have an excellent field record. One reason may be that the plumbing industry, who generally would fix a problem, is not a prolific research publishing body. In addition, not all epoxy is equal in formulation nor applied according to a documented standard. This failure investigation that occurred outside the united states demonstrates failure modes that have been discovered. It should not be taken as an alarm of epoxy, rather, an outlook to field experiences especially addressing performance at pipe joints and the vicinity of valves: INVESTIGATION REPORT ON THE FAILURE OF MAKKAH-TAIF WATER TR
Legal Action; Canada: This link connects to a Canadian suit brought against the epoxy applicators by a plumbing company. Obviously biased but it is important to look at the claims of the suit so that our analysis and bidding process can reflect consideration of these complaints. The first claim cited is the failure of epoxy coaters to perform a comprehensive condition assessment – this claim has been addressed with the piping assessment performed by GSG Group and funded by the HOA community, Likewise, we should seek to address all other claims as we consider any epoxy solution.
Pacific Northwest Pollution Prevention Resource Center issued the following Rapid Research Paper related to the use of epoxy coating in Potable Water systems. Epoxy-Lined_Pipes_risk
Madison Chemical industries, Ontario CA; This white paper is provided by a chemical manufacturer with an obvious bias toward several formulations of polyurethane for the coating of potable water pipes. While few companies actually use polyurethane, it is instructive to see the parameters upon which the epoxy is evaluated. of particular interest is the adherence to steel, the impact resistance, and toughness of the materials.
THESIS_Revised: This is a Masters Degree thesis that includes a comprehensive literature review of epoxy coatings. The first chapter consists of a references documenting known water quality impacts from epoxy liners. Both laboratory experiments and case studies are included in the review. The second chapter provides the experimental design, data and results, discussion, and possible improvements/future research for the AWWA RF-funded bench-scale epoxy studies.
Polyurethane Paper This paper was presented at the Middle East Corrosion Conference in 2001 by a manufacturer of Polyurethane As such, the objectivity of the paper should be noted. However, it does provide a clear distinction to epoxy as well as several significant case studies that can be used as precedent. My interest lies in the higher quality control and tactile inspection capability of the polyurethane application. My concern is the sensitivity of the formulation; i.e., if we want more flexibility, we sacrifice some adhesion and vice versa. Formulation would be important.
Note; Polyurea is an important sub variant of polyurethane and is a proven water proofing material. However, its application in pipe lining is too highly specialized for consideration in this application.
Polyurethane vs Epoxy:
Fortunately, there is some healthy competition between these Polyurethane and epoxy technologies. Unfortunately, unbiased research may be difficult to find. We may want to stray a little bit beyond the pipe liner application to find some answers that are important to us.
Polyurethane_epoxy comparison A complete evaluation program was designed to review the various types of lining systems that are presently available in North America for municipal pipeline internal coating application. These systems included 100% solids polyurethanes, ceramic epoxies, and polyethylenes used for the internal protection of potable water and wastewater mains. Key performance properties of the lining systems were reviewed and tested, together with handling and safety characteristics,. The behavior of the two 100% solids polyurethanes was excellent not only in all tests but in their handling and safety characteristics as well. Polyethylenes were good in many tests such as impact resistance and abrasion resistance, but performed poorly in the cathodic disbond test. Even though the ceramic epoxy showed relatively good chemical resistance and undercutting resistance, its poor adhesion, low impact resistance and brittleness raised concerns about its ability to provide long term corrosion protection in aggressive sewer applications.
PET (sometimes called PETE) stands for Polyethylene terephthalate and is very familiar material used in food packaging and plastic bottles. Polyethylene is a family of plastics with many uses and characteristics. Polyethylene products widely used in children’s playground equipment, plastic Kayaks, storage containers, etc. PET is also similar to PEX which is another technology under consideration in this analysis.
For comparison reference, PEX is highly “crosslinked” so that it has a memory – this means that if you stretch it within certain limits, then it will return to it’s original size allowing it to be formed tightly over valves and unions for plumbing applications. On the other hand PET is not highly “crosslinked” and has very little memory. As such, if PET is stretch within certain limits, it stays where stopped. This makes it good for sealing the internal diamer of pipe because the applicator can slip uniform rigid tube of a smaller diameter within the larger pipe and expanded with heat and pressure. This technique is widely used in commercial, municipal, and even medical applications.