December 2019 Vol. 74 No. 12
Rehab Technology
Lessons Learned on Pressure Pipe Rehabilitation Projects
By David Kozman, HammerHead Trenchless, Joanne Carroll, Subtegic Group, and Matthew Coleman, Toronto Water; NASSCO Pressure Pipe Committee
EDITOR’S NOTE: This is the final installment of a three-part series on pressure pipe presented by members of the National Association of Sewer Service Companies (NASSCO) Pressure Pipe Committee. There will be an in-depth program track on these topics and more at UCT, Jan. 28–30, 2020, in Fort Worth, Texas.
Pressure pipeline rehabilitation technologies have been utilized successfully for over 100 years, with hand-troweled cement mortar lining (CML) first applied in aged cast iron pipelines in the early 1900s to improve hydraulics and water quality. This was followed by spincast application of CML in the 1930s and the development of spray-applied polymer linings in the 1970s, providing some structural enhancements to the existing pipeline.
Sliplining introduced fully structural repair in the 1940s and 1950s. Close-fit technologies such as cured-in-place pipe (CIPP) brought fully structural repair through applications in non-pressure sewer applications in the 1970s, while launching CIPP in the pressure pipe market in the 1980s. Today, a vast array of pressure pipe renewal solutions are available, contributing to rapid market growth and acceptance worldwide. Industry successes, failures and challenges have put increased emphasis on standards development, particularly as it relates to design, installation, testing and ongoing maintenance.
Intuitively, many aspects of the approach to the trenchless renewal of gravity flow sewer pipelines have been reciprocated onto pressure pipe projects. The first industry standard for trenchless applications, ASTM F1216, initially released in 1989, focused on CIPP installed using the inversion method. This included a non-mandatory design appendix with several design checks for partially deteriorated (interactive) and fully deteriorated (fully structural) gravity flow and low-pressure sewer pipe and force main applications.
This design approach has been used extensively for a wide range of products and applications within the non-pressure and pressure pipe sectors. Although it has served these markets well, its premise is not applicable to many coatings and linings, as it fails to address critical pressure pipe design elements.
More specifically, ASTM F1216 was developed around isotropic (homogeneous) composites that are unbonded to the host pipe. However, many pressure pipe lining systems are anisotropic with variable properties in the hoop (circumferential) and axial (longitudinal) directions, and some rely on adhesion to the host pipe for inherent hoop strength or to maintain hydrostatic integrity.
Industry, standards evolve
As the pressure pipe lining industry has evolved, so has the need for more representative design guidelines and standards. Currently, structural classifications of pressure pipe linings, from Class I corrosion barriers to Class IV fully structural systems, are loosely defined in Appendix A of the Third Edition of AWWA M28 Water Main Rehabilitation with no design guidance provided, leaving designers to devise their own means of determining structural adequacy.
Through the efforts of the AWWA Pipeline Rehabilitation Committee, a white paper was developed with industry consensus to better define lining classifications as well as establish more specific design, qualification and verification testing and acceptance criteria. This committee report, “Structural Classifications of Pressure Pipe Linings, Suggested Protocol for Product Classification” is scheduled for publication in late 2019, and the bulk of its content will be incorporated as a stand-alone chapter in the upcoming Fourth Edition of AWWA M28 targeted for 2020 publication.
The primary keys to successful rehabilitation using pressure pipe lining systems include:
• Owner/operator properly defining the objectives of the project/performance requirements
• Proper assessment and selection of renewal technology to meet objectives of the project
• Qualification of both the lining product chosen and contractor to perform the installation
• Effective communication with all involved parties with the ability to work together and adjust to unforeseen circumstances
• Cleaning and preparation of the host pipe
• Implementation of quality controls throughout construction
• Verification of proper installation through established testing and inspection methods (see Figure 1)
• Acceptance criteria and reconciliation
The ability of pressure pipe lining systems to succeed is largely affected by its fit within, or adhesion to, the host pipe. Because of this, acceptance criteria has historically relied heavily on post-installation inspection to confirm fit and finish, as well as mechanical properties testing from representative samples collected at the jobsite.
Adhesion
The pressure pipe industry has also gravitated towards requiring adhesion to the host pipe to ensure a watertight finished product. Although in some cases reliable adhesion may be desired for Class II systems lacking hoop strength, or to maintain hydrostatic integrity at services and lining terminations, there are situations where adhesion is not desirable.
Applications – including those with broad temperature swings or longitudinal movement due to expansive soils, frost heave or settlement – are examples where lining adhesion may actually be detrimental and not accounted for in ASTM 1216 design criteria. Consideration must also be given to the host pipe material type, condition, joining system, configuration, alignment and in situ conditions; and their potential impact on a lining system during the lining inspection, installation and hydrostatic testing process. For instance, if a host pipe is structurally compromised or is not anticipated to be able to withstand design maximum allowable operating pressure (MAOP) or hydrostatic test pressures, catastrophic failure of the host pipe can occur during testing or while in normal operation. In turn, this can compromise the lining system, particularly a bonded one.
The need for a close fit lining system, or one with minimal to no gap or interstitial space between liner and host pipe, is well substantiated, particularly for systems designed for reliable adhesion to the host pipe. A bonded lining system that does not make close contact with the host pipe ID about the entire circumference will endure stress risers across unsupported areas and can lead to failure. This can be prevented through proper sizing and installation of the lining system.
A properly designed close fit system will be sized appropriately to form tightly against the host pipe with the installed geometry that reflects relevant short-term and long-term type (laboratory) testing utilized for the basis of design. Interruption of hoop integrity due to material oversizing to achieve a tight fit and its impact on pressure ratings of Class IV lining systems should be considered in design and is discussed in the AWWA white paper.
This further substantiates the need to capture representative field samples for third party mechanical properties testing to verify installed properties. As a baseline requirement, enough material should be obtained to perform tensile and flexural in the hoop and axial directions.
As with any lining system application, many situations cannot be easily replicated or tested on the jobsite in terms of cause and effect without utilizing destructive means. That is, an owner’s objective may be to achieve water tightness at services, withstand pipe movement or obtain a level of reliable adhesion to the host pipe, but may not have a way to confirm it in the field. In such cases, demonstration testing is recommended.
These tests are typically conducted by the lining system manufacturer, or as directed by the owner, to simulate installed conditions and determine an end result. Specifics identified during demonstration testing (e.g. surface preparation, bond strength, allowance for wrinkles or fins) that contribute to achieving positive results can then be required during actual installation and field testing to better ensure project success.
Attend UCT 2020 and the Pressure Pipe Track to hear more Lessons Learned with Pressure Pipe Lining Systems. •
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