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South Africa Condition Assessment Large Diameter Pipe

The Usutu Water Scheme supplies raw water to a number of coal-fired power stations and towns in the Mpumalanga province of South Africa. The bulk water pipeline, completed in the late 1970s, consists of large diameter (DN1300 mm) pre-stressed concrete non-cylinder pipe (PCP) that links two mains for a total of 90 kilometers between the Rietspruit, Davel and Kriel Reservoirs.

Recognizing that the infrastructure might be reaching the end of its lifespan, the Department of Water and Sanitation (DWS) called on SSIS Pipeline Services, which represents Pure Technologies in South Africa, to conduct a comprehensive condition assessment of the pipelines.

Destructing the old to help evaluate the current pipe state

Due to a lack of records, DWS provided Pure with old removed pipes, as well as spare pipes that were destructively evaluated to determine the design specs and calibrate the electromagnetic signal to accurately detect wire breaks.

Every pipeline is unique, and if a utility has a strong understanding of the operational conditions of different areas in their system, an appropriate and defensible inspection plan can be developed, pipe by pipe. Pure came onboard bringing its inspection, risk assessment and engineering analysis services, along with its comprehensive suite of technologies to survey the pipeline for leaks, gas pockets and wire breaks.

Civil Engineering Cover June 2015

Pipediver Field crew operators insert the PipeDiver inspection tool into the pipeline.

Field crew operators insert the PipeDiver inspection tool

Pipediver Field crew operators insert the PipeDiver inspection tool into the pipeline.

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Project begins with leak detection surveys

For DWS, Pure and SSIS began with leak and air pocket detection surveys, employing Pure’s proprietary SmartBall™ technology. As the free-swimming SmartBall tool rolls through the pipeline, it collects acoustic data. The acoustic sensor identifies the sound of water leaving the pipeline, or the sound of trapped air at the top of the pipeline, which can reduce the water flow and increase strain on the pumps.

Easy to deploy, the SmartBall tool is an excellent screening tool for PCP inspection programs by identifying leaks and air pockets in the main. These areas provide a preliminary look at the condition of the pipeline.

As a follow-up to the SmartBall survey, SSIS employed its Sahara® platform, a tethered tool with attached audio-video surveys to gain a better understanding of the leak locations along the pipeline. A total of ten leaks were detected and accurately located using SmartBall and Sahara.

PipeDiver™ electromagnetic survey evaluates the pre-stressing wires

Because the Usutu pipelines could not be taken out of service, crews inserted Pure’s revolutionary PipeDiver™ tool, which features collapsible fins that allows it to pass through sharp bends, diameter reductions and butterfly valves as it is carried by the flow of water.

The free-swimming PipeDiver inspection platform uses electromagnetic (EM) sensors to evaluate the existing condition of the pre-stressing wires. EM inspections collect a magnetic signature for each pipe section to identify anomalies that indicate zones of wire break damage. The presence of wire breaks in concrete pressure pipe is often a sign of impending failure. This inspection method is the best available technology to determine the baseline condition of the PCP mains.

While the PipeDiver survey was performed, the critical pipeline remained in operation. The entire 90 kilometers of pipeline was inspected in three runs, and the inspections found the majority of pipes to be in good condition.

Investigation replaces uncertainty with peace-of-mind risk assessment

In addition to using to the monitoring technologies described above, Pure also conducted a variety of other risk assessment and engineering analysis services for the project.

This included field verification data to compile a calibrated hydraulic model to mime the steady state and transient behaviour of the pipelines. The results showed that DWS’s current operating procedures worked well to control the flow and prevent pressure surges.

Pure Technologies also completed a finite element analysis (FEA) to quantify the structural ramifications of the broken pre-stressing wires detected by electromagnetic inspection. This analysis was used in tandem with the electromagnetic inspection results in the risk assessment.

DWS sets a good example for managing its transmission main assets

The project highlights the value of embracing a proactive pipeline condition assessment programme using best practices, expertise, and cutting-edge technology.

The investigation confirmed the asset life can be extended, while managing DWS’s exposure to risk and sets a good example for other South African utilities to follow in developing a sustainable long-term strategy for managing their asset

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