CHAPTER 2 LITERATURE REVIEW
2.4 FACTORS AFFECTING THE PERFORMACE OF A WATERMAIN
2.4.1 CONDITION ASSESSMENTS
Condition assessment data is needed for engineering, operations and maintenance, planning and financial decision making (Beuken et al., 2010). The water industry now has a good understanding of how condition assessments are conducted by utilities. Unfortunately, these
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assessments are not done consistently and the underground condition data is not well known to most utilities. Indicators such as “good” or “poor” are often used, rather than more definitive parametric descriptions such as remaining useful life. These aspects of condition assessments need further improvements in the future in order to be more useful.
Kleiner and Rajani (2002) state, “The statistical analysis of historical breakage patterns of water mains is a cost effective approach to discern their deterioration, where physical mechanisms that lead to their deterioration are often very complex and not well understood.
Furthermore, data required to model these physical mechanisms are rarely available and prohibitively costly to acquire. Several models exist in the literature, which use various statistical methods to analyse patterns of pipe breakage histories. However, predicting a breakage pattern in an individual pipe has proven to be quite a challenge and the validation of these models is generally done on the basis of aggregate breakage rate although the model purports to predict individual pipe behaviour. The structural deterioration of water mains and their subsequent failure are affected by many factors, both static (e.g., pipe material, pipe size, age (vintage), soil type) and dynamic (e.g., climate, cathodic protection, pressure zone changes).”
Sophisticated computer methods are available for analysis (AwwaRF, 2005), but in order to make effective decisions, more accurate information regarding the actual condition of the pipe at the point in time that the analysis is conducted is required. If unreliable data is used for analysis, the results of this analysis will sub-optimal. Kleiner et al., (2001) makes the point that many of these analyses are also only suitable to small networks due to the complexities and limitations of techniques and equipment.
Beuken et al. (2010) stated, “Condition assessment technology is used to quantify if actual main characteristics meet their requirements. If better information on the condition of mains is available, adequate decisions can be taken on postponing investments for replacement.
Inspection technologies can be used to obtain more knowledge on the condition of mains and could therefore play an important role in improved management of underground assets. Inline inspection technologies are available for metal and cement mains larger than 250 mm.
Application of business cases shows that, even if inspection technologies would exist for smaller diameters, the total cost of inspection is higher than the savings due to postponement”.
There are a variety of destructive and non-destructive methods that can be employed to assess the state of readiness of a pipeline and its ability to perform a given function. The component condition of a water main or the system as a whole can be assessed (AwwaRF, 2005). The component assessment can be divided into three distinct groups:
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o Ground penetrating radar o Electromagnetic tests o Sonic and acoustic tests
o Wall thickness, corrosion and fragility tests:
o Coupon testing o Acoustic emissions o Ultrasonic tests o Infrared thermography
o Remote Field Eddy Current tests o Magnetic flux leakage
o Physical inspections o Tubercles and deposition:
o CCTV inspection
System assessments can be performed to evaluate the performance of the network as a whole and are broken up into the following four areas:
o Water loss accounting (Water Audits)
o Hydraulic evaluation (Models, Flow tests, Real time monitoring of key indicators such as minimum night flow, average daily demands, critical point pressures). The critical point in a zone is that point where the dynamic pressure is lowest.
o Water quality evaluations o Controlled destructive evaluation
Torterotot (2009), observed that the condition of assets changes over time, both continuously and in response to specific events. The technical and economic performance is dependent on the assets themselves and also on how these assets are operated. There is a relationship between condition and time to failure and therefore an understanding of the failure mechanics and advanced data management systems to record and assess this data is required.
Designing and implementing a water main decision planning system is an on-going evolutionary process. It begins with an assessment of the distribution system condition. From this assessment a reactive planning system may be designed and implemented. This, in turn, can lead to the development of a predictive planning system (USEPA, 2007).
Thornton et al. (2008) advises that the Utility consider the benefits of rehabilitation as opposed to replacement. Benefits can be gained by opting for a cheaper rehabilitation solution (often
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with a lower technical lifetime) as opposed to an outright replacement but this analysis is beyond the scope of this study.
Improved budgetary planning can be a means of justifying additional funding for system improvements (USEPA, 2007). There is convincing evidence supporting the requirement for effective condition assessment but the cautions that there are a number of obstacles to the implementation of this assessment:
• Lack of records
• Inability to inspect pipes in service
• Lack of funding
• Lack of understanding
• Lack of support
To mitigate against this, it is advised to develop better condition assessment tools, provide support and educate key role players regarding its necessity (management, staff and customers) and also to secure adequate resources and staff for its implementation.
AwwaRF (2005) recommend that each Utility compile a faults database and that the following information is included:
• Fault location and other inventory data
• Pipe size and depth
• Corrosion indication
• Type of break / fault
• Repair method utilised
• Pictures
The fault data collected by Dutch water utility Evides BV and the local eThekwini water utility (EWS) have been included in the Appendix.
To facilitate implementation it is advised to create easy templates to follow, incentives for gathering data and accurate and improved tools and materials. UKWIR (2003b) recommend that a mature Utility use electronic methods to capture, store and analyse this fault data. Training and Quality Control are an essential part of this process to ensure that valid representative data is collected.
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