Pipeline Condition Assessment. The Essential Engineering Step in the Asset Management Process Tom Sangster. Principal, Jason Consultants Group, Geneva, Switzerland Synopsis Condition assessment is a critical step in the asset management process. It is the point at which problems and challenges are understood and crystallise into definite plans, both operational and financial. This paper will describe the condition assessment process and its role within asset management. It will also describe the key elements in the condition assessment process and how they achieve the purpose of the assessment. This will include risk assessment, document and records review, physical inspection and finally distilling and interpreting all the data to make an assessment. This serves as a platform for all subsequent management decisions. The author will draw on examples of condition assessment projects in which he has been involved around the world. 1. Introduction Underground pipelines are among the most valuable, yet neglected, assets in the public arena. They provide essential services such as supply of energy and drinking water and collection of wastewater. But we install the cheapest we can, bury it and forget about it at least until something goes wrong. Then we are faced with having to fix the problem under emergency conditions, often considering only immediate needs and not the future operation of the pipeline in question. This infrastructure must be seen as an asset, and managed as such. Properly maintained the pipe networks are valuable assets that are critical to delivering services to customers, and in any business the means of connecting product or service to customers is a major link in the business value chain. Not to maintain this network is negligent bordering on criminal. 2. Asset Management Asset Management is the creation, acquisition, maintenance, operation, rehabilitation and disposal of assets to meet a required level of service in the most cost-effective manner for present and future customers. A structured approach to the management of infrastructure assets is essential in order to provide services cost-effectively over a long period and to demonstrate this to customers, investors and other stakeholders. An Asset Management philosophy focuses on the benefits of investment, as well as its costs, and takes a comprehensive view of the entire portfolio of infrastructure resources. Objective, fact-based tools and techniques are systematically applied to determine how best to deploy available resources in order to manage the inevitable trade-off between delivering agreed services sustainably at an acceptable level of risk and cost, increasing system demands, ageing infrastructure, and limited resources.
Asset Management also provides the capability to show how, when, and why resources should be committed. Water supply and wastewater companies and officials are being held ever more accountable by their customers who demand a consistently high return on the portfolio of public resources, which includes water supply, wastewater and stormwater infrastructure. The generic asset management process for water and wastewater assets is shown in the following Figure (from the US Water & Environment Research Foundation). 3. Condition Assessment 3.1 Role within Asset Management Assuming that the first two steps in this process have been done, the condition assessment becomes the basis for the subsequent assessment of options, cash requirements and long term funding plans which are themselves fundamental elements of an Asset Strategy. Condition Assessment should be a structured and logical process. The initial need is to understand causes of deterioration. Then to quantify deterioration in order to reach a sound understanding of the present condition. This leads to an assessment of remaining service life and, if necessary, of the intervention options to bring that service life to a desired level. The decisions on required service life, level of serviceability and acceptance of risk are management decisions by the owner or operator of the utility. 3.2 Condition Assessment Process It is important to understand that inspection is not the same as assessment, as many vendors of inspection technologies would have us believe. Inspection provides data that is an input into the assessment process. This assessment requires considerable
technical and engineering knowledge and expertise in order to achieve its objectives. It cannot be left to technology vendors who see merely one part of the picture from the perspective of their inspection work. Condition inspection is one element of condition assessment which is in turn one element of asset management. An assessment has four stages: 1. Initial identification of physical characteristics of a pipeline in terms of historical, environmental and operational data. From this data identify and prioritise assets or locations on the network for condition inspection. 2. Undertake risk assessment and determine what information is required from the inspection program. 3. Evaluate the possible methods of inspection for their appropriateness to provide the required type and level of information. Then undertake an inspection using the selected technologies. 4. Carry out a final condition assessment based on the information from the above stages, including the inspection, to provide an assessment of the likelihood and consequences of failure. Remember always that inspection provides data, not assessment, and needs to be interpreted. The assessment should include life expectancy curves and predictions of time to failure. Stage 1 The first step is to make a thorough review of all available information relating to the pipeline or network in question. This includes construction information, specifications, as-built drawings, soil and groundwater data, operating data such as pressure, surges, valve operation, air release valve operation, and maintenance and repair data including records of failures, repairs and rehabilitation undertaken, and results of any past inspections. This is mainly a desk study of drawings and documents. It may include also interviews with personnel with experience in the operation of the network; often their knowledge can give valuable insight into problems that have arisen. The result of this stage is a clear view of the available information, and a partial knowledge of the asset condition. Some prioritisation can take place. A further result is that the gaps in information and knowledge are clear. Stage 2 Risk assessment and inspection planning. Risk of failure is comprised of two elements: likelihood of failure and consequence of failure. The combination of the two drives decisions on intervention needed and the urgency of any such intervention. The Figure below illustrates this.
The first step is to understand the consequences of failure. If they are high, for example if the pipeline runs under a main road, past the entrance to a hospital and supplies a large population with no alternative supply route, then it is important to know the likelihood of failure. If the consequences are low then it is less important to know the likelihood, since it has little effect on decisions. So this step defines priorities for determining the likelihood of failure. Likelihood of failure is what the condition assessment process identifies. This may be likelihood of failure now or in the short term, or the likelihood in the longer term which defines remaining service life. The inspection planning is driven by this. The gaps in information identified in Stage 1 need to be filled where it is necessary to know likelihood of failure. So at the end of Stage 2 we have a clear idea of which areas of a pipeline or network to inspect, and what information we require from the inspection works. Stage 3 Inspection. There is a large range of inspection technologies available for underground pipes. Each is effective in different circumstances. Field inspection is expensive and can be disruptive so the method must be carefully chosen to obtain the required information as cost-effectively as possible. The amount of information required is also an important consideration. Internal inspection can give data for 100% of a pipe s length but this is very expensive. External inspection is less costly but gives data for only a small sample of the pipe s length. For example, CCTV cameras are widely used for internal inspection in pipelines. In gravity sewers a CCTV inspection gives most of the information required most of the time. We want to know whether pipes are broken, whether there is root intrusion, whether there is infiltration at joints or in the pipe wall itself, and the condition of lateral connections. All of this can be seen from a good CCTV survey. But in a pressure pipe we need to know wall thickness, corrosion levels, etc. and a CCTV survey cannot show this. So there is limited value in a CCTV survey of a water main or a sewer force main.
The inspection technologies for pressure pipes tend to be specific to one pipe material, or to a small group of materials. Ultrasonic and electromagnetic methods for determining wall thickness of ferrous pipes (steel, CI & DI) are useful only on those materials. Remote field methods that detect wire breaks in prestressed concrete pipes are similarly only applicable to that material. And there is as yet no proven nondestructive inspection technology for asbestos cement or plastic pipes. Generally we are looking for different things in different circumstances. The following Tables show these for different materials in pressure pipe networks. Form of Failure Causes of failure Indicators of failure Burst failure Burst failure External pitting and graphitization corrosion weakening wall often combined with induced strains Internal pitting and graphitization corrosion weakening wall often combined with induced strains Damaged protection - wall loss from external pitting, Graphitization (hard to detect) Leaks. External loads pressure variations Damaged lining wall loss from internal pitting, Graphitization (hard to detect) Leaks. External loads, pressure variations Burst failure 3rd party impact damage Construction activity Structural failure Structural failure Circumferential cracking- smaller diameters <12 Structural failure Longitudinal cracking- larger diameters >12 Leaks wall perforations and joints Movements from Thermal, Seismic, external loading. Thermal contraction, poor support leading to movement, internal pressure Internal pressures External loadings Thermal stresses Can lead to loss of soil support and bending failure Joint Leaks, poor bedding, pipe movements. Circumferential cracks, Frost regions, leaks, pipe movements Longitudinal cracks Frost regions, changed internal/external loads Leak noise and wet areas Ductile Iron Pipes
Form of Failure Burst failure Longitudinal cracks Causes of failure Pitting corrosion weakening wall. Thinning from general corrosion. Areas of pitting corrosion Indicators of failure Damage to coating/linings - Wall loss pitting. Leaks Graphitization Groups of pitting, wall loss Pipe Bursts Third party damage Construction activity Leaks wall perforations and joints Thinning of invert Can lead to loss of soil support and bending failure Abrasion Leak noise and wet areas Loss of wall thickness Cement Mortar Lined Steel Pipe Component Indicator Comment Mortar Coating Spalling Crack circumferential Crack longitudinal Coloration First indication of corrosion Indicator of longitudinal movement Indicator of low hoop resistance Indicator of corrosion Prestressed Wire Wire breaks Increasing number of breaks equates to lower factor of safety Concrete core Delamination Circumferential Longitudinal Crack density Sounding Indicator of poor bonding between concrete and wire or steel cylinder Indicator of longitudinal movement Indicator of wire breaks Greater the number the higher the stress Sounding can indicate laminated or hollow areas Pipe geometry Out of roundness Indicator of wire breaks Joint Change in alignment Cracks adjacent to joint Indicator of ground movement Not uncommon because of lack of crack reinforcement Prestressed Concrete Cylinder Pipe When the decision on the appropriate inspection approach (internal or external, rate of inspection, and information required from the inspection) the most suitable technology can be selected and the inspection undertaken. For sewers the inspection is almost always internal and uses CCTV. For pressure pipes either internal or external
inspection may be appropriate, but internal inspection is likely to require taking the pipe out of service which can be expensive and disruptive. At this stage there is a temptation to maximise the inspection undertaken in order to maximise the information obtained. This is poor engineering. Perfect information will never be obtainable at an acceptable cost, so there will inevitably remain gaps in the information. These have to be filled with engineering judgement and experience. The knowledge of an expert cannot readily be replaced by technology. Stage 4 This is the stage at which the full assessment can be made and the condition of the pipe or network fully understood. The inspection results together with the data reviewed and the expertise and experience of the engineer provide the basis for a complete condition assessment. This will define the current condition of the pipe and its capability to achieve required levels of serviceability. Moreover it will compare this with the original condition and may be sufficient to establish a rate of deterioration so that the future performance of the pipe or network can be predicted to some degree. Such predictions are of course only estimates, but they can be sufficiently accurate for planning of interventions and investments. 4. Use of Condition Assessment The result of the assessment is most commonly fed into an asset management process in order to determine the necessary and cost-effective interventions to achieve the predetermined desired service level and lifetime. So neither the inspection nor the assessment are isolated processes, they are both parts of an overall programme of asset management. This is true even when the asset management refers to a single main; it does not have to be a grand scheme covering a lot of assets. Before condition assessment is complete there is no rational basis for any decisions on asset management. There is merely a set of assets of unknown condition and therefore of unknown value in terms of their performance in service in the future. What the assessment provides is a clear view of the current and likely future performance of the infrastructure assets. This enables the higher level asset management to be undertaken with a rational platform of knowledge. 5. What Does This Have to do With Trenchless Technology? So far we have made no mention of trenchless technology, the theme of this conference. Some of the inspection technologies used are indeed trenchless in that they work inside the pipe and through existing openings such as manholes. But that is not what we generally understand by trenchless technology. Where existing assets are concerned we think of trenchless technology as renovation and rehabilitation. Condition assessment is the precursor of such interventions. Just as the inspection tools used have to be appropriate to the circumstances and materials, so the rehabilitation technologies have to be appropriate to solve the problems identified. Trenchless rehabilitation, done well, is a very cost-effective tool in asset management to maintain assets and serviceability levels. But the right method needs to be chosen
and for the right reasons. The result will be appropriate use of trenchless technologies and proof of their cost-effectiveness which will in turn stimulate the market for their use. Condition assessment supports those decisions on methods and reasons. An example of failing to do so is illustrative. An overseas utility was concerned about the performance of a large, steel cement-lined sewer pressure main. With minimal inspection or assessment they decided to line it with a technology that is designed for gravity sewers. This was done some 10 years ago and is now failing. Not only will another costly rehabilitation be necessary, but the presence of the first lining makes inspection and assessment at this stage much more difficult. The result has been significant expenditure without solving the problems. A proper assessment and identification of the problems and serviceability requirements would have led to a better rehabilitation decision and massive cost savings. 6. Conclusions Condition assessment is the key stage in the asset management process. It provides a rational platform for the whole asset management programme and does so in a logical and structured manner. It enables resources to be allocated efficiently and trenchless rehabilitation solutions to be employed cost-effectively. However there are barriers to effective condition assessment of underground infrastructure assets. There is a need for a lot of data, and this can be costly to obtain. A recent U.S. EPA forum on Condition Assessment of Ferrous Water Systems concluded that data collection and management has significant scope for improvement. It also concluded that predictive models need to be developed so that the value of the inspection and the data it produces are maximised. Good condition assessment leads to good and cost-effective asset management, including trenchless rehabilitation. It is in all our interests, system owners and operators, regulators, engineers, contractors and technology vendors, as well as the public at large who rely on the water and wastewater services, that this become the accepted way of managing underground infrastructure assets.