Xiangjie Kong

Best Practices in the Condition Assessment of Water Transmission Mains

Large diameter water transmission mains represent a significant portion of the underground assets of any given water utility. Until recently, there have been few options available for ascertaining the actual condition of these assets. One notable exception has been Prestressed Concrete Cylinder Pipe (PCCP). Since the invention of RFTC technology, developed at Queens University in Kingston, Ontario, Canada in the early 1990s, more than 4,000km of PCCP has been assessed. This condition based asset management technique has become the standard for those utilities who want to establish a long term maintenance and management plan for their PCCP networks. With the introduction of the Sahara leak detection system, the industry now has a powerful tool to gather direct information about the condition of any transmission main — regardless of its material construction type. The Sahara system accurately pinpoints the location and size of leaks as small as 1 liter/hour. A utility can utilize this system to precisely locate leaks, reduce non-revenue water, identify leaks causing pipeline commissioning delays, and as a condition assessment / risk management / asset validation tool that provides information that forms the basis of future asset management strategies.

Practical Engineering Considerations for Developing a Free-Swimming Tool for RFEC/TC Inspection of PCCP Transmission Mains in a Live Operating Environment

Condition assessment of Prestressed Concrete Pressure Pipe (PCCP) has evolved over the past 10 years mainly due to the development of the Remote Field Eddy Current / Transformer Coupling (RFEC/TC) inspection technique. By conducting RFEC/TC inspections to determine the actual condition of their pipelines PCCP owners and operators can make informed decisions regarding strategic repairs and selective rehabilitation. However, RFEC/TC inspections can, in some circumstances, be a challenge to conduct. Various designs of manned tools and tethered systems have been successfully used in the field but they require dewatering and/or depressurizing which can be costly and prevent the inspection of pipelines that can not be taken out of the service. To overcome these challenges a free-swimming tool for RFEC/TC inspection of PCCP in a live operating environment is currently being developed. This paper describes practical engineering considerations for such a development.

RFEC/TC TECHNOLOGY ADVANCEMENT THROUGH GMRA EXPERIENCE

North Africas Great Man Made River Authority (GMRA) owns and operates the worlds largest single prestressed concrete cylinder pressure pipes (PCCP) project. This paper discusses the Remote Field Eddy Current/Transformer Coupling (RFEC/TC) technology GMRA has been using since April 2000 to inspect the system to detect and quantify prestressing wire breaks in its PCCP. The data obtained has allowed GMRA to advance its understanding of the capabilities and characteristics of the RFEC/TC pipeline evaluation system. Additionally, the adoption of a co-operative and systematic approach involving calibration studies, field inspection data review and theoretical studies has enabled PPIC to develop a prediction system that can compensate for a variety of features during practical analysis so that estimation of the number of wire breaks can be made more accurately.

RFEC/TC Inspection of PCCP with no Shorting Straps at the San Francisco Public Utilities Commission

In December 2004, the Pressure Pipe Inspection Company (PPIC) conducted a nondestructive evaluation of the Prestressed Concrete Cylinder Pipe (PCCP) portion of the Bay Division Pipeline No. 4 for the San Francisco Public Utilities Commission (SFPUC) using its patented Remote Field Eddy Current/Transformer Coupling (RFEC/TC) Technology. The RFEC/TC inspection was conducted over an overall distance of approximately 8.2 miles (13.12 km) and spanned a total of 2,167 inspected pipes. Several sections of the pipeline had a large number of reported wire breaks. After consulting Simpson Gumpertz & Heger Inc. (SGH) regarding the probability of pipe failure, SFPUC proceeded to conduct a simple verification of four pipe sections before making any decisions regarding repairs or replacement. The field verification exercise grew in magnitude as a series of successively more invasive tests failed to verify PPIC’s results. Two new test procedures; X-Ray and turn-to-turn resistance measurements were attempted with mixed results. After these tests were complete, SFPUC, on the advice of SGH proceeded to put the pipeline back into service with no repairs. The details surrounding the unusual and unexpected results of the SFPUC verification using accepted practices and two new technologies are of interest to owners and operators of PCCP pipelines as well as their consulting engineers since they threaten to undermine confidence in the RFEC/TC in general.

NDE Inspection of PCCP Using Remote Field Eddy Current/Transformer Coupling

As the age of our pipeline infrastructure increases, non-destructive evaluation becomes more and more important. A new electromagnetic technique called remote field eddy current/transformer coupling (RFEC/TC) has been developed to meet the NDE inspection needs of prestressed concrete cylinder pipe. The method has been used successfully to detect prestressing wire failures in PCCP. This paper explains the technology and presents recent test results and field applications. Case study describes the updated inspection experience with several pipeline owners, and demonstrates tile benefits of RFEC/TC inspection.

RECENT ADVANCES IN PIPE WALL ASSESSMENT TECHNOLOGY

Most of North Americas oldest water mains are constructed of ferrous material, in particular cast iron, ductile iron, and steel. As utilities rarely have funds to replace all of these pipelines at the end of their design life, utilities are forced to carefully target their replacement and rehabilitation budgets. Critical for this targeting of funds is the availability of accurate knowledge of the actual pipeline conditions, in particular assessing the condition of the pipe wall and its impact on the remaining useful life of the pipeline. With this clear and impending need, a variety of technologies are becoming available for pipe wall assessment. This paper details developments and advances over the past two years in several technologies for pipe wall assessment. The results provided by each technology are outlined, as well as how these results can be used to assess progression along the failure paths of various types of pipelines. The tools are grouped in a systematic way, illustrating how they fit into three fundamental philosophies towards condition assessment. Examples of their application are provided for tools advanced beyond the R&D phase. Abstract ID 112 1. FAILURE MODES OF METALLIC MAINS Pipes fail when some portion of the pipe is no longer strong enough to withstand the stress applied to it. This can happen when unexpected stress is placed on the pipe, or when the pipe loses enough strength to be overcome by the planned stress of normal operation. In most cases, it is a combination of the two: an unexpected stress, such as a water hammer, causes a failure at a point that has been weakened by one or more factors, such as cracking or corrosion. (Makar et al, 2001) Different types of pipe have various mechanisms of failure, and hence different failure rates. Cast iron pipes are by far the most prone to failure. Cast iron pipes corrode, are brittle, are prone to cracking, and generally employ bell and spigot joints that can lose their sealing integrity. Many older North American cities contain cast iron pipe installed in the 1800s, when methods of construction were not uniform and formal quality control (inspection) and pipeline standards did not exist. For example,

An Update on RFEC/TC Technology and Use

Non-destructive evaluation of the Prestressed Concrete Cylinder Pipelines (PCCP) enables the selective repair or replacement of distressed sections, and can alleviate the prohibitive cost of complete replacement. The RFEC/TC inspection technology is capable of detecting prestressing wire failures in PCCP and is currently being used to identify and assess distressed pipe sections. An update on the technology and its use is presented including field experiences from recent projects.