Tulsa Structural Condition Assessment Water Pipeline
Following a significant pipe rupture in December 2012, Tulsa Metropolitan Utility Authority (TMUA) performed a detailed structural assessment on a critical section of one of the city’s major drinking water pipelines in November 2013. This recent work builds upon the TMUA’s rapid response forensics investigation completed in January 2013.
To determine the baseline condition of this major transmission main – which is made of 48-inch (1200-mm) Prestressed Concrete Cylinder Pipe (PCCP) – the city dewatered the pipeline and performed a comprehensive internal inspection using visual and sounding techniques, and electromagnetic (EM) technology.
This specific pipeline was constructed in 1975 and had not experienced a failure before December 2012. The 2012 failure caused major commuter disruptions, evacuations and damage to a local church; in an article published in Tulsa World, City Engineering Director Paul Zachary said that this failure cost roughly $400,000 to rectify. The 2013 inspection will help prevent another failure on this transmission main by identifying pipe sections that have distress and could fail if left in operation.
In total, roughly two miles made up of 688 pipe sections were assessed in November using visual and sounding techniques and EM technology.
Visual and sounding inspections are a reliable method of detecting pipes in an advanced state of distress. The inspections require manned entry to the pipeline and dewatering; any pipes judged to be in a state of incipient failure will be reported to allow for immediate replacement or rehabilitation.
The failed 48-inch pipe section from December 2012.
Pure Technologies staff complete verification work on Tulsa’s PCCP water mains.
EM inspections of PCCP pipelines identify the quantity and location of broken wire wraps. The wire wraps in PCCP are the main structural component – as wraps begin to deteriorate and break, the pipe section becomes weaker and more likely to fail catastrophically.
The inspections showed that 81 of 688 pipe sections had broken wire wraps, indicating some level of distress. Based on a structural analysis, it was recommended that 32 of the distressed pipe sections be replaced immediately. In addition, the pipeline has 120 deteriorating joints that should be repaired in the near term. As a result, the City is moving forward with a rapid response construction project to address the pipeline’s deficiencies in early 2014.
Through the use of comprehensive condition assessment, TMUA has increased service reliability and taken major steps toward ensuring another failure does not occur.
By identifying specific areas of distress along this critical transmission main, TMUA has also avoided completing an expensive and time-consuming replacement project of the entire transmission main. This approach helps to preserve capital budget for other projects by avoiding unnecessary replacement of pipe sections in good condition.
The City of Tulsa supplies drinking water to more than 133,500 metered accounts in the City and more than 500,000 people in the metropolitan area. Tulsa’s two water treatment plants treat between 90 and 190 million gallons of drinking water a day. The TMUA is a public trust organization created by City charter. TMUA’s primary responsibilities are to manage, construct, and maintain Tulsa’s water works and sanitary sewer systems, and to fix rates for water and sewer services rendered within its boundaries.
Visual Inspections and Soundings have successfully been used to quickly identify pipes in the state of incipient failure. Issues other than wire breaks can also be identified through visual inspections, such as unusual cracking and poorly detailed or damaged joints.
Pure Technologies is helping utilities manage their buried infrastructure through its Assess & Address which can often be implemented for only a fraction of the capital replacement cost.