A selection framework for infrastructure condition monitoring ...

Expert Systems with Applications 40 (2013) 1947–1958

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A selection framework for infrastructure condition monitoring technologies in water and wastewater networks P. Davis a,⇑, E. Sullivan b, D. Marlow a, D. Marney a a b

CSIRO Land and Water, Graham Road, Highett, VIC 3190, Australia AECOM, Level 9, 8 Exhibition Street, Melbourne, VIC 3000, Australia

a r t i c l e

i n f o

Keywords: Intelligent Networks Condition monitoring Water/wastewater Pipe networks Asset management

a b s t r a c t The global water sector faces significant challenges to maintain secure and reliable service provision in the context of ageing infrastructure, urban growth, and with investment capacity constrained by user affordability. As part of an on-going effort to meet these challenges, research has been undertaken to facilitate the diffusion of technological innovations within the concept of ‘‘Intelligent Networks’’. This diffusion has been facilitated by the formation of a consortium of water utilities in Victoria, Australia. The consortium has engaged with Intelligent Network concepts due to a need to prolong network asset life where possible; defer or remove the need for asset augmentation, reduce the operational expenditure (by reducing asset failures and incident response times), and minimise the impact of asset failures on communities and the environment. The literature on innovation diffusion indicates that the uptake of new technologies is influenced by subjective perceptions. As such, key research challenges were to understand where technologies could be used to improve asset management, identify potential condition monitoring techniques, elicit best available knowledge with respect these technologies and provide advice on where their application was likely to reflect a rational economic decision. To ensure a targeted review, ‘‘failure pathway’’ diagrams were first constructed to identify and relate influences controlling asset deterioration and failure. Elements of failure pathways were used to identify parameters that, by effective monitoring, could provide an early indication of asset distress and the opportunity to intervene and avoid reactive maintenance costs. Alternatively, parameters were also identified that could inform the deferral of capital expenditure on asset replacement and augmentation. The failure pathway provided the basis for the identification of 19 candidate monitoring technologies which were subsequently reviewed. Each technology identified was assessed against capital and on-going maintenance costs and the perceived benefit of implementation. Benefits were expressed in terms of how the new information acquired would enhance the asset owner’s ability to defer asset augmentation/renewals and avoid reactive maintenance costs/externalities. The project provided a prioritised set of monitoring technologies that are currently progressing towards pilot trials in the field. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.

1. Introduction Urban communities rely on a complex network of buried assets to connect them to the water resources used as both supplies of water and sinks for treated wastewater. Traditionally, provision of this infrastructure has been dominated by a focus on water quality and supply (Erbe et al., 2002), though more recently water has being treated as a scarce resource that requires management of both supply and demand issues (Rauch, Seggelke, Brown, & Krebs, 2005). While important from a broader sustainability perspective, such developments are often taking place against a backdrop of underinvestment in infrastructure. For example, a recent study ⇑ Corresponding author. E-mail addresses: [email protected] (P. Davis), [email protected] (E. Sullivan).

by the American Water Works Association (AWWA, 2012), indicates that a significant portion of the buried water infrastructure in the USA is nearing the end of its useful life. Similarly, studies undertaken in the USA have highlighted that there is widespread deterioration of both water and wastewater infrastructure – the rating given by the American Society of Civil Engineers (ASCE., 2009) to both reflected a ‘‘poor’’ rating, and only one grade higher than ‘‘inadequate/failing’’. For many cities, this decay is coincident with pressures of further urban growth (Vlachos & Braga, 2001). In the USA, restoration and expansion of existing infrastructure to meet the needs of a growing population is estimated to cost more than US$1 Trillion over the next 25 years (AWWA, 2012). The level of investment required represents such a financial challenge that the long-term financial sustainability of some communities has been questioned (Allbee, 2005). To a greater or lesser extent, these challenges are being experienced across the world, especially with

0957-4174/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.eswa.2012.10.004

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P. Davis et al. / Expert Systems with Applications 40 (2013) 1947–1958

respect centralised systems built during the first half of the last century. In Australia, recent estimates (Marney & Sharma, 2012) indicate that AU$0.6 Billion/year is spent on programmed replacement of water and wastewater network pipelines. A further expenditure AU$0.19 Billion/year is attributed to unplanned maintenance in response to failures in these networks. Underinvestment in infrastructure eventually leads to increases in asset functional failures, especially under extreme operating conditions caused by weather events like storms, drought or severe winters (Marlow, Person, Whitten, Hatton MacDonald, & Burn, 2011). In general terms, widespread or frequent asset failures result in a decrease in the quality, quantity or reliability of services provided at various scales, and corresponding increases in social and commercial disruption and health and/or environmental impacts. Failures such as water main bursts or sewage spills can also impose significant costs on both the service provider and the broader community. For example, Gaewski and Blaha (2007) conducted a study in which direct and societal costs were estimated for 30 large diameter water main breaks in the USA. Costs ranged from US$6000 to US$8.5 million with a mean of US$1.7 million (Gaewski and Blaha, 2007). Similarly, Marlow et al. (2007) document the failure of a large diameter water transmission pipeline in a densely populated area in Australia, which led to extensive flooding, property damage and severe disruption to freeway traffic. While many smaller diameter water pipelines are located such that the consequences of individual failure are relatively benign, their failure cannot be ignored in aggregate. For example, Gaewski and Blaha (2007) estimate that the direct costs from failures of small diameter pipelines is US$1.5 billion, with a similar magnitude of societal costs. In light of these issues, asset management as it relates to water and wastewater infrastructure can be considered a significant societal challenge, and advances in decision making and infrastructure technologies are required to help communities meet their needs in an affordable and sustainable manner (Marlow, Beale, & Burn, 2010a). In practice, this is difficult to achieve because many of the network assets are hidden from view, while being subject to diverse and varied deterioration processes. Currently, condition assessment is a key technique used to provide information to support decision making for such infrastructure (Marlow & Burn, 2008), and significant research and development has been expended toward the production of non-invasive and non-destructive technologies (Lillie et al. 2004, Reed et al. 2004, Thomson, 2008, Liu et al., 2010). However, the high costs of service interruptions and excavation mean that condition assessment is usually conducted at discrete points along the length of a pipeline or across a network (Marlow, DeSilva, Beale, & Marney, 2010). An example is the use of electromagnetic based tools to measure the remaining wall thickness in metallic pipes (DeSilva, Moglia, Davis, & Burn, 2006; Liu et al., 2010). In practice, a relatively small number of pits are excavated along the length of a pipeline and the remaining uncorroded wall thickness is measured using a tool applied to the pipe outer surface in these discrete locations (DeSilva et al., 2006). Pipeline condition between inspection points is then inferred using, for example, probabilistic methods (Davis, Burn, Moglia, & Gould, 2007; Davis & Marlow, 2008; DeSilva et al., 2006; Moglia, Davis, & Burn 2008). While this approach makes the best use of limited data from discrete inspections, it can lead to unnecessarily early replacement of those mains for which condition is, in reality, relatively good between sampling points. Furthermore, while the expenditure can sometimes be justified for large diameter pipelines, technologies to cost-effectively monitor the condition of smaller diameter network assets are not yet widely available. As described herein, as an alternative to the current approach to condition assessment, it is proposed that, with the adoption of

appropriate technologies, existing urban water networks can be transformed to ‘‘intelligent’’ networks with the inherent ability to monitor infrastructure condition and deterioration with far greater spatial coverage than is currently possible, without incurring the significant costs associated with excavations and service interruption. Combined with robust analysis of frequent spatially distributed sensor data and diagnostics, existing asset management practices could then be augmented to support the optimisation of capital and operational expenditure by prolonging asset life, deferring or removing the need for capacity augmentation, reducing asset failures and incident response times and thereby reducing any associated social disruption (e.g. interruptions to service and traffic disruption) and environment impacts (e.g. receiving water quality and odour). This ‘intelligent network’ (IN) concept represent a significant innovation within the water sector and there are thus various challenges to overcome with respect its uptake. Rogers (1995) refers to innovation uptake in terms of a ‘diffusion’ process, whereby the innovation is communicated through channels over time among the members of a social system. In the case of IN concepts, the relevant social system is the asset management community, consisting of practitioners, associated researchers, consultants and technology vendors. Critically, innovation diffusion is influenced by both the characteristics of the innovation itself and subjective perceptions, which are in turn influence by other factors such as geographical settings, societal culture and political conditions (Rogers, 1995; Wejnert, 2002). To facilitate diffusion of the IN concept, it is thus important to clearly identify its benefits with respect to a particular challenge as experienced in a specific context, while giving appropriate consideration to the underpinning technologies and communication of this information through the relevant social system. With these observations in mind, the uptake of IN concepts must involve close engagement with sector professionals, as well as investigations into the adoption and application of the associated technologies. The need for such an approach was recognised by a consortium of utilities in Victoria, Australia, who formed a practitioner’s network that provides a driver behind investigations into the IN concept and associated technologies, as well as the communication channels to (potentially) facilitate its diffusion. Given such network had been formed, the key challenge was to provide suitable guidance on the appropriateness of available technologies. To this end, this paper presents a selection framework that has been developed to ensure emerging technologies are best matched to industry needs. As described below, the selection framework consists of three stages: (1) Matching potential technologies to network assets and failure modes. (2) Prioritising technologies based on perceived value. (3) Development of an economic business case for technology pilot trials. Given the nature of innovation diffusion, a qualitative research approach was taken based on close interactions with utility practitioners within a specific geographical region. These practitioners constitute a relevant social system within which to discuss and communicate the IN innovation. Interactions involved meetings and workshops, as well as peer review of research outputs. The goal of the study was to identify a set of technologies that could be developed further through pilot trials conducted by the consortium. The development of the framework was thus undertaken to ensure, as far as was practicable, that these pilot studies were successful, thereby avoiding the potential to ‘lock-out’ the IN innovation due to early technological failures.

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that contribute to deterioration and asset failure. As an example, Fig. 1 shows the pathway diagram that was constructed to capture the process of deterioration and failure in gravity sewers. The deterioration process illustrated in Fig. 1 is interpreted as developing from right to left. The top section of the diagram indicates that, should sulphides be generated in sewage below the sewage fill-line, their subsequent conversion to sulphuric acid in the sewer air space can lead to internal corrosion in certain pipe materials (Mori, Nonaka, Tazaki, Hikosaka, & Noda 1992). Internal corrosion may also be exacerbated by lower pH environments in the sewer created from toxic discharge into the sewer network (O’Halloran et al. 1992). Should this internal corrosion proceed, the resulting loss of structural strength can lead to collapse pipe fracture, collapse and a resulting sewage spill (Davies, Clarke, Whiter, & Cunningham 2001). As shown in the middle section of Fig. 1, pipe fracture/collapse can also be attributed to a loss of soil support around the outside of a gravity sewer. Such a change in external loading conditions originates from joint leaks and sewage exfiltration, which in turn are attributed to soil movement and/or tree root penetration (Tran, Ng, Perera, Burn, & Davis 2006). The applicability of different aspects of the deterioration processes to different pipeline materials is also indicated in Fig. 1. Similarly, Fig. 2 shows the developed failure pathway diagram for leaks and bursts in water pipelines. Generally, this reflects

2. Matching potential technologies to network assets and failure modes For any monitoring technology to be effective and provide benefit, it must be able to report on specific indicators relevant to the performance of that asset. In collaboration with industry partners, failure modes were thus prioritised as those incurring the highest consequence to asset owners. Although the overall study considered a range of different asset types, this paper illustrates the approach developed by focusing on buried water mains and sewer pipelines. In these cases, the identified set of high priority failure modes were: Gravity sewers – Blockage, sewage spill Water mains – Leakage, burst Based on these prioritised asset types and failure events, ‘‘failure pathway’’ diagrams were constructed that identified and related the influences controlling asset deterioration and failure in each case. The individual elements in each diagram indicate parameters (or distress indicators) that signal deterioration towards failure and can therefore provide useful information if monitored. The development of failure pathways relies on a detailed understanding of the physical processes and interactions

Gravity Sewers –Spill

M (ALL) Aggressive chemicals discharged into sewer

Materials key AC = asbestos cement CI(CL) = cast iron (cement lined) DI(CL) = ductile iron (cement lined) GRP = glass reinforced plastic MS(CL) = mild steel (cement lined) PE = polyethylene PVC = polyvinyl chloride RC = reinforced concrete

(AC, GRP, RC) Internal Corrosion

(AC, GRP, RC) Sulphuric acid generation

(AC, GRP, RC) Turbulent flow in sewer

(AC, GRP, RC) Sulphide generation in sewer

(AC, GRP, RC) Corrosion of pipe wall / Loss of strength

J

J, M

B, C

D

S

External Corrosion

(ALL) Soil environment change

(ALL) Climate Variables (temperature, rainfall)

F, G

EVENT SEWAGE SPILL

C, F, G

(ALL) Soil movement

External coating breach

(ALL) Pipe Fracture/ Collapse and/or Blockage

F, G

C, F, S (ALL apart from PE) Loss of soil support/ voiding

F, G, O, S

(ALL apart from PE) Sewage exfiltration

(ALL) Pipe deformation

F, G, O

F

F

(ALL) Pipe Blockage

(All apart from PE) Joint leak

(ALL) Formation of Root Mass

A, C (ALL) Accumulation of Fats

Fig. 1. Gravity sewer failure pathway: sewage spill.

(ALL apart from PE) Tree root penetration

(ALL) Discharge of Fatty Waste

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Fig. 2. Water main failure pathway: burst and leak.

internal/external corrosion combined with external loading conditions from changes in the surrounding soil environment (Sadiq, Rajani, & Kleiner 2004). For metallic pipelines, the pathway to internal corrosion is via cement leaching from internal linings (where present) followed by corrosion of the host metallic pipe (Yamini & Lence, 2010). External corrosion pathways in metallic pipelines are realised through the breakdown of external coatings (Song, Kirk, Graydon, & Cormack 2003) and (if present) the possible consumption of cathodic protection anodes (Rajani & Kleiner, 2003). For non-metallic pipelines, leaks and bursts are attributed to the action of mechanical loads from surrounding soils and excessive surge/cyclic pressures (Davis et al. 2007). As noted above, by identifying influences on relevant failure modes, elements in the failure pathway diagrams reveal parameters that could be monitored to indicate asset distress. The failure pathway diagrams therefore provided a rational basis for identifying candidate monitoring technologies. Table 1 summarises a set of candidate monitoring technologies that were identified as part of this study. In each case, supplementary information is given to identify asset types, failure modes and an indication of the elements of the relevant failure pathway that can be monitored. A unique identifier is also provided for subsequent cross-referencing to failure pathway diagrams. For completeness, Table 1 shows technologies related to both IN concepts and condition monitoring more generally and reference is made to other asset classes to which the technologies apply. The techniques are shown in the failure pathway diagrams in Figs. 1 and 2 above (technology IDs from Table 1 are indicated by the black boxes allocated to each element in the failure pathway diagram). Generally, monitoring technologies that appear toward the right hand side of the diagrams provide the facility for early detection of the onset of deterioration. With accompanying failure

prediction models (Kleiner & Rajani, 2001; Rajani & Kleiner, 2001), these technologies could provide sufficiently early indication of future failure to allow pre-emptive intervention, avoiding reactive maintenance consequences. An example is the use of technology ‘D’ in Fig. 1, which can be used for real-time monitoring of dissolved sulphide in sewers. As indicated by Sutherland-Stacey et al. (2008), high sulphide levels may be a pre-cursor to low-pH sulphuric acid environments, leading to internal corrosion of concrete gravity sewers. The early detection of high sulphide levels, allows sufficient time to chemically treat sewage and reduce the degree to which internal corrosion occurs, potentially helping to balance operational costs of sewage dosing against the extension of asset life. Alternatively, those technologies towards the left hand side of the failure pathway diagrams provide alerts of the occurrence of failure events themselves. For example, technology ‘R’ in Fig. 2 is permanent digital noise logging for leak and burst detection in water mains. It is possible that automated alerts from these devices may allow maintenance teams to reduce response times and associated operational costs in reacting to these events.

3. Prioritising technologies based on perceived value The failure pathway diagrams provide a means of identifying condition monitoring technologies relevant to network assets and failure modes. The second stage of the selection framework is to prioritise technologies based on an assessment of perceived value to water utilities and wider stakeholders. A Multi Criteria Assessment (MCA) was thus conducted to identify the subset of monitoring technologies that merit further evaluation through pilot trials. Criteria used to rank the technologies were determined


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Table 1 Monitoring technologies identified during the global literature and practice review. Tech ID

Technology

Asset type (s)

Relevant failure event (s)

Primary distress indicator and pathway

A

Gravity sewer

Blockage

Pipe blockage; Local constriction to flow

Gravity sewer

Sewage spill

Decreased flow velocities; Siltation; Sulphide generation

Gravity sewer

Blockage; sewage spill

Pipe blockage; Local constriction to flow

Gravity sewer

Sewage spill

Sulphide generation; Internal corrosion, Collapse

Water; Sewer rising mains Gravity sewer; sewer rising mains; water Gravity sewer; sewer rising mains; water Sewer rising mains; water Sewer rising mains; water Gravity sewer

Burst main; Sewage spill Sewage mains Sewage main Sewage main Sewage main Sewage

spill; leak, burst

Spalling of cement mortar lining; Internal corrosion; Presence of occluded air in sewer rising mains Soil movement; pipe deformation; joint leak; surge pressure/ cyclic pressure Soil environment change; soil movement

spill; leak, burst

Soil environment change; external corrosion

spill; leak, burst

Soil environment change; external corrosion

spill; blockage

Sulphuric acid generation; internal corrosion

Water

Leak; burst main

Leak, burst main; surge pressure/cyclic pressure

Sewer rising mains; water Gravity sewers; drainage

Sewage spill; burst main

Surge pressure/cyclic pressure

M

Acoustic instrumentation to monitor head loss/roughness/blockage Flow velocity monitoring to detect sedimentation Flow monitoring to detect blockage in gravity sewers Real-time monitoring of dissolved Sulphide in sewers Pressure transients to detect internal deterioration Optical fibre monitoring for structural condition Soil temperature/moisture/pressure sensing to infer structural condition In-situ linear polarisation resistance to monitor soil corrosivity Surface-based resistivity to monitor soil corrosivity Continuous monitoring of H2S gas in sewer networks Statistical inference monitoring of existing network data Pump performance and condition monitoring In pipe sewage chemistry monitoring

Cross connections between drainage and sewer; unauthorised connections; surface water ingress at unsealed manholes

N

Cathodic protection monitoring

O

Infra-red thermography

P Q

Real-time hydraulic modelling Real-time water quality monitoring systems

Water Water; drainage

R

Acoustic noise loggers for leakage monitoring Ground penetrating radar

Water

Infiltration/Inflow; stormwater quality incident Sewage spill; leak; burst main Sewage spill; leak; burst main Leak, burst main Leak, burst main; drainage water quality incident Leak, burst main

Gravity sewers,

Sewage spill, infiltration

B C D E F G H I J K L

S

Sewer rising mains; water Gravity sewer; water

through facilitated workshop discussions with industry practitioners. The outcome of these discussions indicated that from the water industry perspective, technology assessment criteria must be based on financial, environmental and social parameters. Importantly, they also needed to align with regulatory requirements for expenditure. In general terms, this requires investment plans of each water business to be prudent and efficient, where prudence refers to the management of risk (to service levels) and efficiency refers to the on-going cost of managing assets. Through this process, the qualitative assessment criteria shown in Table 2 were adopted. Complex procedures have been used previously to elicit expert opinion for asset management applications (Marlow, Beale, & Mashford, 2012), but in this case a simple scoring scheme was considered sufficient because the aim was to assess the consortium’s perceptions of the various technologies given their particular business interests. In particular, the use of failure pathway diagrams allowed techniques to be ranked against the criteria reflecting the extent of failure pathway and ability for early detection. For example, technologies that provide information on the locations and timing of failure events themselves after they have occurred (i.e. the left hand side of the failure pathway diagrams in Figs. 1 and 2) were ranked highly against the environmental impact and social benefit criteria. It was reasoned that, since these techniques provide direct information on failure events, they also allow asset owners to respond quickly and reduce the consequences associated with asset failure once it has occurred. In contrast, those techniques that provide early detection of parameters that signal the onset of deterioration (i.e. the right hand side of failure pathway

spill; leak, burst

Cathodic protection failure; external corrosion Loss of support/voiding; exfiltration; leak; burst main Leak; burst main Source water chemistry change; leaching of cement mortar lining; sewage spill entering drainage network Leak, burst main, joint leak, perforation pitting, ductile rupture, fracture/blown section, Loss of soil support/voiding

diagrams in Figs. 1 and 2) are scored highly against the early detection criterion. The outcome of the MCA assessment is shown in Table 3. As shown, the following monitoring technologies were prioritised: (1) Permanent digital noise logging for automated leak and burst detection (Tech ID ‘R’). (2) Flow monitoring to infer blockages in gravity sewers (Tech ID ‘C’). (3) Surface-based resistivity to monitor corrosivity (Tech ID ‘I’). (4) Optical fibre monitoring for structural condition (Tech ID ‘F’). (5) Soil temperature/moisture/pressure sensing to infer structural condition (Tech ID ‘G’). (6) Pressure transient monitoring to detect internal deterioration (Tech ID ‘E’). A detailed description of prioritised technologies is contained elsewhere (Davis & Sullivan, 2012), but brief summaries are provided below. 3.1. Permanent digital noise logging for automated leak and burst detection (Tech ID ‘R’) This technology is intended to automate the detection of small leaks and burst events in water pipeline networks. Vibration sensors are attached to the outside surface of a below-ground pipe via magnetic contact (for metallic mains) or adhesive for non-metallics. The noise signal emitted from a leakage event in the vicinity of the vibration sensor is detected as a noise level change above

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Table 2 Multi-criteria assessment: ranking criteria and weightings (1 = Lowest; 2 = Low; 3 = Medium; 4 = High; 5 = Highest). Criteria

Description

Weighting

Potential to save operational expenditure response costs Potential to save preventative maintenance costs Potential to save capital through renewals or augmentation deferral Potential to improve levels of service at the same cost Relative cost to procure and install technology Relative cost to operate and maintain technology Relative asset coverage (length) covered by technology Extent of failure pathway addressed by technology Ability for early detection prior to failure event Potential to reduce environmental impacts

Ability of particular monitoring technique to provide early indication of failure events and the opportunity to intervene, reducing operational expenditure associated with the asset type Reflects the ability of particular monitoring techniques to allow the targeting of preventative maintenance spend to those assets that require it most Techniques that provide the asset owner with the ability to maximise the useful life of assets before programmed replacement are ranked highly against this criteria This ranking criterion provides an assessment of monitoring technique to improve levels of service

4

–

3

–

3

This ranking criterion is intended to reflect the extent of the network over which information can be gathered by the deployment of the monitoring technology Those technologies that provide information on a large number of parameters identified on failure pathway diagrams would score relatively highly against this criterion Those technologies that provide information on parameters that relate to the onset of the deterioration process identified on failure pathway diagrams would score relatively highly against this criterion This criterion reflects the ability of the monitoring technique to provide early indication on those failure events that will incur severe environmental impacts This criterion reflects the ability of the monitoring technique to provide early indication on those failure events that will incur severe social impacts

3

Potential to provide social benefit

some predetermined background noise level that corresponds to minimal leakage. The noise level alarm can be remotely sent to multiple mobile phones/e-mail addresses for widespread notification of the event. Detailed leak detection is then conducted to locate the position of the leak and effect repair. Preliminary field trials conducted in Victoria have indicate that permanent digital noise logging may also indicate noise associated with events that are pre-cursors to large scale bursts in water mains. It has been proposed that such pre-cursor noise may be attributed to smallscale cracking and leakage prior to pipeline bursts (City West Water & Australia, 2011). 3.2. Flow monitoring to infer blockages in sewer networks (Tech ID ‘C’) This technique involves the application of traditional level and flow velocity monitoring to specific sites in sewerage networks for prolonged duration. Traditional short-term flow and rainfall monitoring used for the calibration of hydraulic models provides a snap-shot of catchment conditions over a period of six to eight weeks. However, the installation of level and flow monitors over a longer period (in excess of 12 months) allows seasonal variations in base flows to be determined as well as wet weather responses for a large range of rainfall events. As demonstrated in a UK case study (Shepherd, Saul, & Hanson 2010), the interrogation of monitoring data over longer durations can also reveal data anomalies which are indicative of sediment accumulation, blockages, irregular inflows and other potential defects. For example, Shepherd et al. (2010) report the detection of blockages in a gravity sewer from observed increases in sewer level at manholes and corresponding reductions in flow velocities. 3.3. Surface-based resistivity to monitor soil corrosivity (Tech ID ‘I’) Rapid Transit Resistivity surveying is a surface-based technique that maps variations in soil electrical resistivity with depth. The technique is a variant on the resistivity surveys, but uses a mobile arrangement for the rapid surveying of the soil environment along extended pipe lengths. The technique consists of an underground dipole transmitter, receiver and a data logger. Rapid transit resistivity surveying methods use a capacitively-coupled resistivity metre that measures the electrical properties of rock and soil

4 3 2

3 3 2 2

without the requirement for galvanic electrodes that are used in traditional resistivity surveys. A simple coaxial cable array with transmitter and receiver sections is pulled along the ground either by a single person or attached to a small all-terrain vehicle. An AC current is coupled into the earth by the transmitter and measured at the receiver. This measured voltage is proportional to the resistivity of the earth between the dipoles. Apparent resistivity is calculated using the appropriate geometric factor for the capacitivelycoupled antenna array. Results are presented as colour contour map allowing areas of low resistivity soil environment to be identified. Comparison with the soil cover depth of the pipe gives a measure of the corrosivity of the soil, allowing areas of potentially high external surface corrosion rates for ferrous mains to be identified (Cull, Massie, & Jung, 2008).

3.4. Optical fibre monitoring for structural condition (Tech ID ‘F’) Fibre Optic Sensors (FOS) are used to measure real-time changes in physical properties such as displacement, strain, temperature, pressure, acoustic emission and vibration. Potential benefits lie in the ability to pinpoint condition along greater pipe lengths via a single FOS. While much of the reported use of FOS has been to detect strains in oil/gas pipelines (Inaudi, 2005), recent studies have also seen their application to strain measurement in water pipelines (Chaudry, Gheorghiu, & Hu 2007). Changes in chemical properties such as concentration and pH can also be measured using fibre optic sensors with tailored chemically-reactive coatings. As a result, these sensors are finding increased application in structural health monitoring. The fundamental principal relies on the coupling of an optical fibre to the structure under interrogation, launching light along the length of the fibre and then monitoring changes in the characteristics of this guided light as the structure is disturbed. Monitoring of circumferential and longitudinal strains can be used to determine changes in pipeline behaviour due to internal or external loading or wall thinning due to corrosion. Leakage is likely to be associated with acoustic emissions and changes in temperature and moisture content of surrounding soil. While FOS have the potential for spatially continuous sensing and monitoring of pipeline condition in new installations, a major challenge is the ability to retro-fit to existing assets, without

Table 3 Multi-criteria assessment outcomes: IWN technologies. Tech ID

Technology Description

Criteria Weighting and Description

OVERALL SCORE

4

4

3

2

3

3

3

3

3

2

2

Potential to save opex response costs

Potential to saw preventative maintenance costs

Potential to saw capital through renewals or augmentation deferral

Potential to improve levels of service at the same cost

Relative cost to procure and install technology

Relative cost to operate and maintain technology

Relative asset coverage (length) per monitoring device

Extent of failure pathway addressed per monitoring device

Potential to reduce disruption through early failure detection

Potential to reduce environmental impacts


OVERALL RANKING

TECHNOLOGY RANKING (1 =Worst, 5 = Best) A

C

D

E

F

G

H

I

J

3

3

3

3

4

3

3

2

3

2

3

94

16 of 19

3

3

3

3

4

4

4

1

3

2

2

95

15 of 19

3

3

3

3

3

4

5

3

3

4

4

109

2 of 19

4

4

4

3

2

3

2

2

5

2

3

102

10 of 19

4

4

4

3

2

3

4

3

4

2

3

108

3 of 19

4

4

4

3

2

2

4

4

4

2

3

108

3 of 19

4

4

4

3

3

4

1

4

4

2

3

108

3 of 19

4

4

4

3

2

3

1

3

4

2

3

99

12 of 19

4

4

4

3

3

3

3

3

4

2

3

108

3 of 19

4

4

4

3

2

3

2

2

4

2

3

99

12 of 19

1953

(continued on next page)


B

Acoustic instrumentation to monitor head loss/roughness/ blockage Flow velocity monitoring to detect sedimentation Flow monitoring to detect blockage in gravity sewers Real-time monitoring of dissolved Sulphide in sewers Pressure transients to detect internal deterioration Optical fibre monitoring for structural condition Soil temperature/ moisture/ pressure sensing to infer structural condition In-situ linear polarisation resistance to monitor soil corrosivity Surface-based resistivity to monitor soil corrosivity Continuous monitoring of H2S gas in sewer

Tech ID

Technology Description

Criteria Weighting and Description

OVERALL SCORE

4

4

3

2

3

3

3

3

3

2

2

Potential to save opex response costs

Potential to saw preventative maintenance costs

Potential to saw capital through renewals or augmentation deferral

Potential to improve levels of service at the same cost

Relative cost to procure and install technology

Relative cost to operate and maintain technology

Relative asset coverage (length) per monitoring device

Extent of failure pathway addressed per monitoring device

Potential to reduce disruption through early failure detection

Potential to reduce environmental impacts


OVERALL RANKING

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Table 3 (continued)

TECHNOLOGY RANKING (1 =Worst, 5 = Best) K

M

N

O P

Q

R

S

3

3

3

3

3

3

5

3

3

4

4

106

8 of 19

3

3

3

3

4

4

1

1

3

2

2

86

19 of 19

4

4

4

3

3

3

2

2

4

2

3

102

10 of 19

4

4

4

3

4

4

3

1

4

2

3

108

3 of 19

4

4

4

3

1

2

2

2

3

2

3

90

3

3

3

3

3

3

5

3

3

4

4

106

8 of 19

3

3

3

3

3

3

2

2

3

2

3

88

18 of 19

3

4

3

3

4

3

3

3

4

4

4

110

1 of 19

4

4

4

3

2

3

1

3

4

2

3

99

12 of 19

17 of 19


L

networks Statistical inference monitoring of existing network data Pump performance and condition monitoring In pipe sewage chemistry monitoring Cathodic protection monitoring Infra-red thermography Real-time hydraulic modelling Real-time water quality monitoring Permanent digital noise logging Ground penetrating radar

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P. Davis et al. / Expert Systems with Applications 40 (2013) 1947–1958 Table 4 Cost/benefit parameters for economic business case development. Parameter

Description

Capital cost Operating cost Maintenance cost Benefit realisation cost

The purchase cost of the required number of monitoring technology units within the proposed pilot trial area Examples are estimates of installation cost, staff salary costs to operate units/analyse data The cost of items such as monitoring technology units, software license fees, battery replacement The cost associated with any potential benefits that may be realised by the monitoring technology. For example, the cost of pre-emptive replacement of water mains ahead of incurring reactive maintenance consequence costs for bursts. This is estimated from the number of pipelines that would incur reactive maintenance responses within the pilot trial area (per year) that can be pre-empted and the cost of planned replacement of those pipelines (Davis & Sullivan, 2012). For sewer-related technologies, reactive maintenance is captured as cleanup costs for the expected number of sewage spills and realisation costs from blockage planned blockage removal (Davis & Sullivan, 2012) Potential savings (i.e. from reduced leakage levels) associated with delaying capital expenditure associated with network augmentation. For water network related technologies, these benefits are calculated from the Long-Run Marginal Cost of water supply; the estimated volume of water attributed to leaks and bursts; and the response time reduction expected from technology uptake and improved leak and burst detection (Davis & Sullivan, 2012) Savings realised from removing the need for traditional condition assessment technologies (i.e. rolling leak detection programs). This is calculated from the unit cost ($/km) for an existing technology application and the proposed network length to be covered by the new technology in the pilot trial (km) Response cost savings associated with pre-empting and avoiding water main burst and sewage spills. For water related technologies, these benefits are estimated from the number of pipelines that would incur reactive maintenance costs within the pilot trial area (per year) and the average cost (per event) of reactive maintenance (Davis & Sullivan, 2012). For sewer-related technologies, these benefits are estimated form the expected number of sewage spills in the pilot trial area that can be pre-empted and the cleanup cost of each spill event Savings realised from reducing the number of environmental fines incurred by a water authority from sewage spills. For sewer-related technologies, the benefit is estimated from the number of expected sewage spills that can be pre-empted and the estimated dollar value of environmental fines per sewage spill. No environmental benefit was captured for water related technologies Savings realised from reducing the number of unplanned interruptions to water supply and associated customer rebates. For water related technologies, this benefit is estimated from the customer rebate (in $/customer) payable by a water utility for exceeding a regulated number of unplanned interruptions; the customer rebate (in $/per customer) payable by a water utility for exceeding a regulated duration of unplanned interruptions; an assumed reduction in the number of customers affected by unplanned interruptions after the uptake of technology

Benefits from water savings and deferred capital expenditure for augmentation

Benefits from technology replacement savings

Benefits from reduced maintenance response costs

Benefits related to environmental impacts

Benefits related to social impacts

Tech ID

Description

NPV (Aggregated over 25 years)

Return on investment (ROI)

R C F E G I

Permanent digital noise logging Flow monitoring to detect blockage in gravity sewers Optical fibre monitoring for structural condition Pressure transients to detect pipe wall deterioration Soil sensing to infer structural condition Surface-based resistivity to monitor soil corrosivity

$275, 610 +$51, 494 +$26, 513 $122, 702 $188, 584 +$173, 460

N/A (NPV < 0) < 1 Year 10 years N/A (NPV < 0) N/A (NPV < 0) 2 years

incurring the associated impracticalities of service interruption, surface disruptions in urbanised areas and high economic cost.

3.6. Pressure transient monitoring to detect internal deterioration (Tech ID ‘E’)

3.5. Soil temperature/moisture/pressure sensing to infer structural condition (Tech ID ‘G’)

This technology infers to the location of internal deterioration sites in pressurised pipelines from induced pressure transients, or small water hammer events. Induced transients propagate unimpeded through smooth uniform sections of pipe. However, as these waves arrive at changes in the cross-sectional properties of the pipeline (such as junctions, changes in diameter, changes in pipe material, or corroded or damaged sections of pipe), they are partially transmitted and reflected. In this manner, the properties of the system are encoded, or embedded, in the behaviour of the water hammer waves. A pipeline system under investigation is instrumented with numerous pressure transducers, a controlled water hammer event is induced within the system, and the pressure variation response of the water hammer wave is measured at the transducer locations. From the resulting measured pressure trace, signal processing techniques can be used to make inferences as to the properties of the pipeline system (Stephens, Lambert, Simpson, Nixon, & Vitkovsky, 2005). The wave speed of a section of pipeline is extremely sensitive to the combined effect of the loss of the cement mortar lining, corrosion of the metal wall and slight increase in the internal diameter of the pipeline. The wave speed is also sensitive to the reduction of wall thickness caused by external corrosion (that is, pipe wall thinning should give slower wave speed and a micro-reflection regardless of whether it is due to external or internal corrosion).

Recent research addressing the mechanisms of deterioration and failure in below-ground pipelines has highlighted potential benefits from the relatively low cost monitoring of changes in the surrounding soil environment. Rather than monitor the pipeline asset directly, this is a ‘surrogate’ technique in which changes to the pipe condition are inferred indirectly from monitoring changes in the surrounding soil environment. For example, monitoring soil movement and earth pressure may be used to infer changes in the structural condition of below-ground pipelines. Levels of support provided to below-ground pipelines and strains imparted from expansive soils may be detected by monitoring soil movement and earth pressure. Sensors to monitor changes in the surrounding soil environment are relatively inexpensive compared to direct methods of condition monitoring. However, the linkage between changes in surrounding soil environment and pipeline condition needs to be thoroughly understood for this kind of inference monitoring to provide benefit. Recent research conducted in Australia (Gallage, Chan, Gordon, & Kodikara, 2009; Gould, 2011) clearly demonstrates the link between soil shrinkage (from moisture depletion in expansive clay soils) and increased flexural stresses in below-ground pipelines.

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Table 5 Summary of prioritised IWN monitoring technologies for enhanced asset management. Technology description

Suggested pilot trial guidelines to maximise value (benefits less costs)

Permanent digital noise logging

Large diameter, relatively old metallic mains in critical locations. This will target high consequence mains and test the hypothesis that noise loggers can provide early detection ability to pre-empt high consequence bursts Water mains constructed of Medium Density Polyethylene (MDPE). This will verify the enhanced performance of noise loggers in leak detection for low stiffness, noise-attenuating materials where traditional leak detection is difficult Vitreous clay gravity sewers in areas of sandy soils and within close proximity to trees. These areas will exhibit relatively high likelihood of tree root blockages that might also be reflected in historical data Network locations where environmental impacts from sewer spills are perceived to be relatively high. This ensures that benefits from avoiding direct costs associated with fines and indirect environmental impacts are high New pipe installations in high consequence areas. This presents an opportunity to investigate the efficacy of

Flow monitoring to detect blockage in gravity sewers

Optical fibre monitoring for structural condition

external application of fibre optics on new mains without incurring the cost of exposing mains and re-instating For Mild Steel mains, areas where stray current corrosion is possible, the installation of fibre optics should be considered to detect leakage noise from localised corrosion in areas of coating breakdown and inadequate cathodic protection For Glass Reinforced Plastic mains (GRP), where bending stress from differential soil movement is thought to be possible. Fibre optics should be considered for new installations to monitor pipe wall strains from loss of support and bending Abandoned mains/mains in low consequence areas. This presents an opportunity to investigate the retro-fitting Pressure transients to detect internal deterioration

Soil temperature/moisture/pressure sensing to infer structural condition

Surface-based resistivity to monitor soil corrosivity

fibre optics internally to an existing below-ground main to detect leakage noise Large diameter, relatively old metallic mains in critical locations, where internal corrosion is suspected. This will target high consequence mains and confirm the hypothesis that pressure transients can locate areas of spalled cement mortar lining and internal corrosion of metallic pipe wall, and pre-empt high consequence bursts Although this technique has primarily been developed and trialled for water supply mains, it may also have the potential to detect the presence of air pockets in sewer rising mains. Asbestos Cement sewer rising mains in environmentally sensitive areas may represent an effective pilot trial that tests ability to pre-empt internal corrosion and bursts Smaller diameter mains, susceptible to bending loads. These include cast iron, asbestos cement. However, note that while these mains are vulnerable to soil movement, the corresponding consequences incurred on failure may be relatively small Areas of the network where expansive soils are known to exist and areas where associated social and environmental consequence are perceived to be severe. This will target areas where benefits are high and test the hypothesis that soil sensing can provide early warnings of future failures Large diameter, relatively old metallic mains in critical locations. This will target high consequence mains and test the hypothesis the technique can precisely locate areas where external corrosion is severe Long mains in areas of the network where localised saturated clay soils of low resistivity are thought to exist

4. Development of an economic business case for technology pilot trials The third stage in the selection framework is to develop an economic business case for pilot trials of the prioritised technologies. For each of the technology in the prioritised subset, the business case as developed by considering costs and benefits associated with technology uptake. As a first approximation, only those costs and benefits realised internally within a water utility were considered – indirect costs/benefits incurred by customers and the broader community were not considered directly. From a utility perspective, this reflects a desire to develop a prudent and efficient business case based on actual expenditure. However, it is recognised that costs born by others can also strongly influence asset management decisions. For example, the inclusion of any significant costs born by external stakeholders in the analysis of asset investments brings the time of any intervention forward (Marlow et al., 2011). Similarly, the value of technology uptake for IN concepts will be strongly influenced by the consideration of such costs. As such, the consideration of internal utility costs alone represents a ‘worse case’ justification from the perspective of the community. Table 4 lists the cost and benefit variables that were considered in the economic business case development. For each prioritised technology, the costs and benefits in Table 4 were estimated for a hypothetical network pilot trial length of 15 km of water or sewer pipelines. Estimated technology costs and technology service lives were obtained from technology providers in each case. Inputs to the calculation of benefits (i.e. reactive maintenance rates and response unit costs; planned replacement unit costs; sewage spill rates and clean up costs; blockage clearance costs) were obtained from a metropolitan

water utility. Where actual data was unavailable, estimated values were applied after discussion with practitioners. Based on guidance from the Australian Government Office of Best Practice Regulation, a discount rate of 7% was applied to all figures to capture the time value of money. Net Present Value (NPV) was then evaluated for each technology over a 25 year period. Full details of the business case development is contained elsewhere (Davis & Sullivan, 2012) and is summarised in Table 4. As shown, tech ID’s C (Flow monitoring to detect blockages in gravity sewers); F (Optical fibre monitoring for structural condition) and I (Surface-based resistivity to monitor soil corrosivity) all show positive NPV values, indicating that conducting pilot trials would be economically justifiable. While the remaining technologies exhibit negative NPV values (indicating pilot trials are not cost-effective), it should be noted that the results are highly sensitive to the assumed number of reactive maintenance responses that can be avoided and their corresponding cost. Relatively small increases in the rates of reactive maintenance events and associated costs can shift a previously negative NPV to a positive outcome. In practice, this suggests that no single technology represents a cost-effective investment for all water and wastewater networks. Rather, the decision to trial and uptake a condition monitoring technology is site specific and should be based on actual failure rates and costs incurred for particular assets and networks. In light of this sensitivity, pilot trial guidelines were also provided to maximise the value from each condition monitoring technology, as shown in Table 5. 5. Conclusions As part of an on-going effort to meet asset management challenges associated with ageing water and wastewater


infrastructure, research has been undertaken to facilitate the diffusion of an innovation referred to herein as the ‘Intelligent Network’ concept. This diffusion has been facilitated by the formation of a consortium of water utilities in Victoria Australia. This consortium engaged with IN concepts due to the need to address asset management challenges, including the desire to prolong asset life where possible, defer or remove the need for asset augmentation, reduce operational expenditure (by reducing asset failures and incident response times), and minimise the impact of asset failures on communities and the environment. More broadly, when considered in light of the backlog in investment described earlier, the implementation of IN concepts has important implications across the globe. In particular, IN concepts have the potential for allowing available budgets to be used effectively, facilitating the management of critical infrastructure and providing sustainable and affordable service to communities. The literature on innovation diffusion indicates that the uptake of new technologies is influenced by subjective perceptions. As such, it was important to ensure that practitioners were provided with ‘best available information’. The key research challenges were thus to understand where technologies could be used to improve asset management, identify potential condition monitoring techniques, elicit best available knowledge with respect these technologies and provide advice on where their application was likely to reflect a rational economic decision. The framework developed to achieve these ends ensures that emerging technologies can be matched to industry needs. In the first stage of the framework, ‘‘failure pathway’’ diagrams are developed that identify and relate factors that drive asset deterioration and failure mode of concern. This allows potential monitoring parameters to be identified that provide either an early indication of distress to optimise intervention. This in turn facilitates identification of appropriate monitoring technologies. In the second stage, the value of identified technologies is analysed using a Multi Criteria Assessment approach, designed to capture the context of the technology end users. The criteria used to rank the technologies were based on relevant financial, environmental and social parameters. Based on this assessment, a prioritised subset of technologies was identified with perceived high value to water utilities: - Permanent digital noise logging for automated leak and burst detection. - Flow monitoring to infer blockages in gravity sewers. - Surface-based resistivity to monitor corrosivity. - Optical fibre monitoring for structural condition. - Soil temperature/moisture/pressure sensing to infer structural condition. - Pressure transient monitoring to detect internal deterioration. In the final stage of the framework, a cost-benefit analysis was undertaken to develop an economic business case for conducting pilot trials. Outcomes indicated that pilot trials for three of the six technologies where justified (positive Net Present Value). While the remaining technologies were not justified in this study, it is noted that the decision to trial and uptake a condition monitoring technology is context specific. Based on the application of the framework, the consortium is currently progressing pilot trials of the prioritised technologies. These have the potential for maximising the useful service lives of assets, and to provide early warnings that allow utilities to pre-empt failure and avoid costly reactive maintenance and associated failure consequences. This has the potential to yield significant benefits from avoided costs. For example, a deferral of just 10% of the current estimated annual investment in such assets for Australia (Marney & Sharma, 2012) would correspond to a cost avoidance of AU$60 million/year. Given the context specific nature

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