Condition assessment is required to provide input into pipe lifetime models and is essential for critical mains when no failure history is available. Models currently being developed, such as the PARMS software suite focuses on providing optimised renewal strategies for buried assets, allowing limited condition monitoring to be utilised to predict the condition of critical networks. Although pipelines are designed for a particular lifespan under standard operating conditions, their deterioration never follows a set pattern. Environmental interactions (soil chemicals, ground movement) plus exposure to water quality variations and operating abnormalities ensure that pipeline deterioration is never uniform. Eventually, through a combination of internal and external stresses, the pipe fails. Sometimes this process is accelerated when defence measures such as protective coatings are damaged or not repaired properly. The challenge for condition monitoring is to provide information on the pipe and its environment to estimate, as accurately as possible, its time to failure or probability of failure.
Structural failure of pipelines is principally due to:
“¢ Deterioration of pipe wall strength
“¢ Changes in the external stresses
“¢ Effects of internal stresses (from water pressure, water hammer, etc.)
The techniques available for condition assessment fall into two categories – direct and indirect. The direct techniques are based on the physical properties of the pipe wall. Electromagnetic, ultrasonic, radiographic and acoustic techniques are examples of direct techniques, and were first developed for the oil and gas industry. Geochemical and geophysical techniques are considered indirect techniques as condition information is inferred through measurement of a surrogate property, such as the electrochemical properties of surrounding soil. While high-resolution direct techniques are potentially capable of identifying and dimensioning pits, indirect techniques can provide, at best, estimates of the average corrosion rate that a pipe has been subjected to over its lifetime.
Condition assessment techniques that can be applied to pipes in situ are the most attractive. While there are only a limited number that can be applied in situ, they have been developed primarily for the oil and gas industry and are designed to assess long lengths of pipes without sharp bends and T junctions. These tools are launched through special access ports and propelled through the pipeline by product pressure. Therefore, while some of these tools are unsuitable, others have been successfully adapted for water pipelines.
The team is working with research groups and industry to establish the data requirements needed by the water industry to aid in efficient asset management strategies and increase the lifetime of buried assets. This data definition is based on whole life costing strategies and includes information on asset lifetimes, customer preferences and externalities. The major science lies in establishing processes for determining much of this information and developing integrated systems for its use in advanced Asset Management systems. This data has been applied in the creation of the PARMS series of software, which has been developed to aid the planning, prioritisation and risk management of urban water infrastructure. This software has already identified major savings in the expenditure of water authorities on their infrastructure. This has enabled water authorities to establish more sophisticated management strategies to maximise the lifetime of their assets whilst minimising expenditure.
The PARMS software suite consists of 3 software tools, PARMS Planning, PARMS Priority and PARMS Risk.
PARMS Planning is a software package that allows whole life costing analysis of buried water reticulation assets for water authorities. The programme incorporates customer preference, the cost externalities and allows different management operational strategies to be analysed. This model has so far been sold to four Australian water authorities.
PARMS Priority is an extension of PARMS Planning focussing on providing optimised renewal strategies for buried assets.
PARMS Risk is the final stage of the PARMS suite and trades off probability and consequence of failure for critical assets. Since these assets have generated little or no historical failure data, the use of cost-effective condition assessment is essential to estimate failure probability.