Water Journal : Water Journal May 2012
pipeline cleaning & maintenance refereed paper technical features 70 MAY 2012 water be recommended. If the scan (Figure 4) indicates potential corrosion sites, follow-up Ultrasonic Thickness (UT) testing could be performed. If the steel thickness indicates no concern for steel thickness reduction, no additional work is necessary. When the pipe has a cement-mortar coating, mortar is removed before UT testing. Samples of mortar are obtained, both for the joint mortar, if available, as well as for factory-applied mortar coating. Analysis of the mortar samples includes pH, chlorides and sulphates. Structural Assessment To provide the highest level of accuracy as to the remaining service life of a pipe, a section of pipe must be removed and sent to a structural laboratory for testing, which also requires that a detailed fieldwork plan to remove, repair and test the pipe needs to be prepared and approved prior to starting any work. If pipe removal is not possible or feasible, then a limited analysis of the thickness measurements from the previous fieldwork will have to suffice for the remaining service life estimate. Based on the results of the BEM, UT and acoustic testing to provide thickness results, a structural assessment is performed to determine a critical wall thickness and time to failure. There are several failure analysis models available and many utilities have developed their own tools. Concluding Remarks When condition assessment of a water transmission main is needed, implementing a cost-effective program means that not all methods need to be applied to all segments of the pipe; rather, the most appropriate inspection technology is applied when and where needed. More data does not necessarily mean better information. Data needs to be collected at locations with the greatest potential for damage to properly assess the appropriate solutions. Screening methods are useful to determine where more expensive or destructive methods are absolutely necessary. One method is not appropriate for all conditions or pipe materials. There are other potential methods available on the market in addition to those described here, but not all necessarily provide the same level of accuracy. If planned and executed appropriately, the inspection should yield valuable information to provide an expected remaining service life of the pipe. the Author Alison L. Ratliff (email: firstname.lastname@example.org) is a Principal Engineer with GHD's Sydney Water Group. She has over 26 years of project management and delivery experience, including supervision of project teams and contractors, budget management, schedule control, and development of studies, reports and design contract documents. Her specialty has been on water and wastewater condition assessment and rehabilitation projects in Australia, the US, the State of Kuwait, and Lima, Peru. Her recent focus is on water pipeline condition assessments using state-of-the-art technologies and practices to provide design and maintenance recommendations to extend the service life of these assets.
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