The interaction of fluid transients with pipeline anomalies (2021)
Type of ContentTheses / Dissertations
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
A functional and secure water supply is essential for supporting social and economic development. However, although pipelines account for the majority of water infrastructure assets and require a significant amount of capital and operational expenditure, knowledge of network condition is generally poor. As networks age, the gap between asset renewal and depreciation is widening. The formation of long-term renewal plans is hampered by lack of access and of a consistent testing methodology. A pro-active and non-intrusive approach is required to enable effective prioritisation of repairs and renewal.
Fluid transients may be used as a tool for diagnosing anomalies which compromise the operation of water supply pipe networks. Controlled transients can be generated in pipe networks and the resulting pressure disturbances measured at receivers. Any anomalies in the system’s physical properties create wave reflections which may be interpreted to assess the type, location, and severity of the anomaly. While the method has promise, the effects of possible system features and faults must be well understood so that meaningful conclusions can be drawn from the transient signals.
This thesis explores the effects of two key anomaly types on the transient response: air pockets and deteriorated sections. The work includes experimental investigations using the University of Canterbury laboratory facilities and evaluation of numerical modelling approaches in the time and frequency domain. The primary aim is to identify key characteristics of the transient interaction with each fault type and identify modelling methods which are able to accurately reproduce these characteristics. The findings inform the further development of transient-based diagnostic techniques.
A comprehensive set of experimental data is collected to investigate the effect of air pockets on the transient response, spanning a range of pocket volumes, initial hydrostatic pressures, and air pocket configurations. A short duration pulse is used to obtain specific information regarding the transient transmission and reflection. Air pockets are characterised in the time domain by their reflectivity, which is calculated based on impedance theory. The lack of dependence on flow rate allows air to be differentiated from solid blockages. The presence of air is also observed to increase the transient damping rate. However, the most identifiable effects of air are observed in the frequency domain. The frequency-dependent reflectivity of in-line and off-line air pockets is due to the resonant properties of air, and is primarily determined by the pocket geometry. This frequency-dependent behaviour is unique to air among common pipeline faults, so is a potentially useful tool when developing diagnostic frameworks.
It is also important to investigate how the air-transient interaction may be incorporated into transient modelling approaches. The method of characteristics time domain model is combined with a variable wave speed consideration to more accurately describe the timing of the transient response due to an in-line air pocket. When modelling an off-line air pocket, inertia in the connecting water column should also be considered. A frequency response model based on plane wave theory is developed to improve upon previous modelling approaches which have treated the connecting water column as an incompressible unit.
The final section of this thesis assesses an accelerated corrosion methodology for testing a range of deterioration scenarios in the laboratory. A series of small-scale and large-scale mild steel pipe specimens are subjected to internal, external, or internal and external corrosion, and the transient wave speed is measured at regular intervals to track the reduction in wave speed with wall thickness loss. The findings show that reductions in the wave speed observed in the field are likely to correspond to either severe corrosion or erroneous pipe material records. The key consideration associated with the accelerated corrosion method is managing precipitate build-up, particularly on the internal surface of the pipe.
RightsAll Right Reserved
Showing items related by title, author, creator and subject.
Kashima, Ayaka (University of Canterbury, 2015)Fluid transients are potentially devastating phenomena in pipelines. However, some of their attributes can bring benefits to various areas of research. This thesis explores three different effective ways to use transients. ...
Tuck, Jeffrey (University of Canterbury, 2016)Reliable water supply is an integral component of any functioning society, improving quality of life through health and sanitation and promoting economic growth. Condition assessment of pipelines is central to the ...
Smith, B.W.; Chase, Geoff; Shaw, Geoff; Nokes, R.I. (University of Canterbury. Mechanical Engineering.University of Canterbury. Civil Engineering., 2006)A minimal closed-loop cardiovascular system (CVS) model has been developed that can simulate ventricular interaction due to both direct interaction through the septum and series interaction through the circulation system. ...