WERF Releases Force Main Inspection Study

By Jeff Griffin, Senior Editor | April 2012, Vol. 67 No. 4
Walter Graf.

“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.

Inspection categories
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.