Pressurized force mains represent a relatively small percentage of the nation’s wastewater collection infrastructure, but are essential in many systems to move waste where gravity isn’t sufficient to sustain flow. Failure in a force main segment can cause major disruptions in service with costly operational and environmental consequences.
Historically, wastewater system operators have found it difficult to take a pro-active approach to force main maintenance because accessing buried pipes is difficult and costly and the use of conventional closed circuit television (CCTV) inspection equipment usually means the system must be shut down which requires a bypass system.
WERF — the Water Environment Research Foundation — has developed a study, Inspection Guidelines for Wastewater Force Mains that covers the latest methods and technologies for inspecting force mains and provides practical guidance for system operators in addressing this important task.
“A part of any asset management program is knowing the current state of your assets,” observes Walter Graf, WERF program director for asset management. “Condition assessment is one part of determining the remaining life of an asset and this report is the first effort to examine inspection methods particular to these pipes. Although representing a small percentage of buried wastewater infrastructure, force main failure can have greater consequences than those of gravity lines.”
Graf said information in the Inspection Guidelines for Wastewater Force Mains report supplements the extensive information in WERF’s web-based asset management knowledge base SIMPLE (Sustainable Infrastructure Management Program Learning Environment).
The force main report is available free of charge to WERF subscribers. It is available to the public in pdf format for $50.
The report was prepared for WERF by Jason Consultants. Principal investigator was James C. Thomson, C.Eng (chartered engineer). Authors are Thomson, Robert S. Morrison, P.E. and Tom Sangster, C. Eng., MBA.
Authors of the 370-page report note that it is well established from surveys, questionnaires and direct experience that very little or no assessment and inspection of force mains is being undertaken.
“The overriding reason for lack of inspection is operational: it is simply not practical to take a main out of service for inspection,” they write. “Current inspection of force mains is mainly limited to visual inspection, leak detection and a small amount of forensic testing where failures have occurred. [Another] factor is the relatively high cost of structural condition inspection. Currently, most utilities have to work on a reactive basis and accept that they will have to deal with failures when they occur. They have limited means of developing a proactive investigation and assessment policy as is now regularly done for gravity sewers.”
Techniques and methods used for condition assessment and inspection of pressure pipes have been areas of innovation and development in the last 20 years, the authors note. There now are many technologies that can be applied to the inspection of force mains.
“There is a clear need for practicing engineers now to have guidance on the effectiveness of the alternative methods and their appropriate, cost-effective use,” they conclude. “Utilities need to reduce the number of failures as they can lead to severe pollution and health risk as well as high remedial costs.”
The team identified the characteristics of the force main network, the pipe types and the modes of failure together with the indicators for inspection technology. This report provides information on the characteristics of the wastewater force main network and the most common defects encountered. It includes a comprehensive review of the current state-of-the-art inspection technology for pressure pipelines. The technologies and methods utilities used to inspect the force mains to identify and locate these defects are listed together with what are the perceived unmet inspection needs. The report reviews data management and processing and considers the application, effectiveness, and suitability of the technologies reviewed for use in force mains and includes a risk-based failure evaluation.
Innovative inspection technologies and methods for force main inspection are reviewed under five categories:
• External inspection of ferrous force mains;
• Internal inspection of ferrous force mains;
• Inspection of asbestos cement force mains;
• Inspection of pre-stressed concrete cylinder pipe force mains; and
• Inspection of plastic force mains.
The study includes 10 case studies of actual inspections undertaken on pressure mains using technologies reviewed in the report.
Benefits of the report include a detailed review of the characteristics of the wastewater force main network, information about experiences of wastewater utilities and the most common defects they encounter, a comprehensive review of currently available inspection technologies and their capability and feasibility in force main inspection, and guidelines for development and implementation of force main inspection within condition assessment and asset management programs.
The report proposes a structured approach to force main investigation driven by information need and cost-effectiveness within a condition assessment and asset management program. It provides guidelines for developing and implementing force main inspection programs.
Founded in 1989, WERF is a leading United States independent scientific research organization dedicated to wastewater and storm water issues. Over the past 20 years WERF has produced 300 research reports, valued at more $62 million.
To order a copy of the force main inspection report, call WERF at (571) 384-2100 or visit www.werf.org and click on “Search Research Publications & Tools”. Refer to: stock number 04CTS6URA.
SIMPLE (Sustainable Infrastructure Management Program Learning Environment) WERF’s web-based, asset management knowledge base contains more 16,000 pages of best practices and processes from around the world. SIMPLE offers users state-of-the-art strategies, tactics, decision support tools and resources.
The knowledge base is divided into two levels corresponding to the experience level of the user. The introductory level is available to the public free of charge; the advanced practitioner’s level is available to WERF and WaterRF subscribers only. Individual subscriptions also are available.