Water and wastewater utilities are faced with an increasing problem associated with ensuring reliability of their large diameter pipelines, many of which exceed 100 years of service life. The American Society of Civil Engineers? (ASCE) 2011 Failure to Act report documents that in 2010, a funding gap of $54.8 billion exists between what is necessary to maintain our water infrastructure and what was actually invested. The lack of investment, particularly in large diameter pressurized pipe, is resulting in an increased frequency of major pipeline failures that are often aired on local news publicly displaying this problem and decreasing public trust in water and wastewater systems.
The days of managing pipelines through an approach of ?bury and forget? or ?run to failure? are gone. This was documented in the AWWA ?Buried No Longer? report. To have confidence in these pipelines, their condition should be periodically assessed to facilitate better pipeline management strategies. This need for better management of pressure pipe has driven the trenchless technology and engineering industry to develop a growingly diverse number of technologies and methodologies to provide data on the condition of large diameter pressure pipe. Armed with data from these inspection tools, utilities are now able to make informed decisions on how to effectively manage their pipelines. ?
Condition assessment of pressurized pipelines has only recently become a part of a utility?s options to manage these critical assets. As a result, many utilities have not established budgets for condition assessment programs or these budgets are often minimized. However, the implications of not performing or performing a poor quality assessment can lead a utility to large, unnecessary and sometimes catastrophic failures, the costs of which far exceed the cost of condition assessment.
Transmission Mains: Should They be Replaced or Managed?
A common and effective method of managing small diameter water distribution mains is to replace a small percentage each year, effectively allowing the entire distribution system to be replaced prior to end of its useful life.? For instance, if a utility replaces 1 percent of its distribution mains each year, the entire distribution system will be replaced in 100 years.
This capital replacement approach of management is not practical for large diameter water transmission systems or wastewater force mains. These mains often lack redundancy and are located in developed areas. The fiscal implications of replacing these pipelines can be daunting if not impossible, which leaves utilities with a major challenge: their transmission system is old and starting to fail, but replacement is not financially possible or practical. The good news is that, as the condition assessment industry matures, it is finding that transmission mains and force mains do not fail along their full length, but instead in isolated areas typically only one pipe section at a time. If localized areas are found to be problematic, isolated repairs can be implemented and the service life of a pipe can be safely extended often by decades. As a result, water utilities are turning to the ?Assess and Address? management technique to proactively manage their transmission and force main systems, rather than the traditional approach of capital replacement programs.
Financial Implications
In the past, many utilities have operated under a ?three strikes and you?re out? approach. Meaning, they have replaced entire pipelines if they failed multiple times expending significant capital costs for a pipeline that may have had many decades of remaining useful life. Many of these pipelines are prematurely discarded when they could have been reliably managed. Condition assessment data from hundreds of miles of concrete pressure pipe inspection and assessment show that less than 5 percent of the pipeline usually has any form of deterioration. Further, less than 1 percent require immediate repair. This means that more than 95 percent of the pipe is in ?like-new? condition and 99 percent of the pipeline can be safely retained without any repair. Taking advantage of these statistics allows utilities to implement an Assess and Address approach to save millions of dollars that would have been unnecessarily spent on replacing or sliplining a pipeline that is mostly in sound condition.? ?
The Washington Suburban Sanitary Commission (WSSC) is one such utility that has taken advantage of these statistics. WSSC was having multiple failures of the transmission system, including the failure of a 66-in. main that resulted in the helicopter evacuation of morning commuters from flooded cars. WSSC looked at the feasibility and cost of replacing their transmission system ? the traditional method of infrastructure renewal ? but found it to be cost prohibitive and logistically difficult as many of the pipelines are now situated in heavily developed communities.
Since 2008, WSSC has implemented an aggressive Assess and Address program relying on condition assessment, targeted repairs and active monitoring of their water transmission main system. By the time the Assess and Address program is fully implemented through WSSC?s approximately 150 miles of large diameter pipe, it is estimated that just over $50 million will be invested into the transmission system.? For less than 2 percent of the capital replacement cost, WSSC will have identified and repaired problematic locations of pipe and implemented a ?Smart Pipe? monitoring program that alerts WSSC to any pipes that are approaching failure.
Other utilities across North America are implementing similar programs.? Miami-Dade, City of Dallas, Baltimore City, Tarrant County, Region of Peel, Metropolitan Water District, Tucson Water, San Diego County Water Authority, and the City of San Diego are a few examples. Experience from these projects show that a utility can perform comprehensive condition assessment, isolated repairs and management for $46-per-ft, while typical replacement for the pipelines would have been $2,055-per-ft.
The Real Costs of Assessment
Funding condition assessment programs is not a simple task for budget strapped utilities. Since pressure pipe condition assessment programs have historically not been part of the budgeting process, utilities are attempting to squeeze a project or program into their existing budgets. This may lead utilities to minimize condition assessment budgets and provide inadequate funds to properly assess a pipeline. This is a mistake that can lead to costly expenses in the future. Condition assessment is only one part of a pipeline management program and if implemented correctly, can usually be the least costly part. Following the condition assessment project, a utility has to make some significant decisions on the future of a pipeline. Do they replace it completely or target specific repairs? What should be repaired? How should it be repaired? These rehabilitation decisions and their costs far outweigh the cost of a condition assessment program. If a proper assessment is not performed, rehabilitation costs cannot be properly focused and significant resources may be wasted.
Condition assessment of pressurized pipe is not a simple task and utilities should focus on quality, not cost. Pressure pipe deterioration may occur on the outside or inside of the pipe, so only performing an internal visual inspection is not adequate. Further, since problem locations are usually isolated to small areas, excavation and test pitting is usually not sufficient. Test pits typically expose less than 1 percent of the pipeline and will not provide a true assessment of the pipe. Test pits are an important part of condition assessment, but when performed on their own, can lead to a false sense of confidence in the pipeline. Conversely, if a deteriorated zone was excavated, an inappropriate lack of confidence can result.
Mike Higgins is a Vice President for Pure Technologies.???
