Brian J. Mergelas

Financial Benefits from Seven Years of Water Loss Control Utilizing theSahara® System at Thames Water in the United Kingdom

Thames Water Utilities Limited is the largest water and wastewater services company in the United Kingdom. It serves 13 million customers in London and across the Thames Valley, from Kent and Essex in the east to the edges of Gloucestershire in the west. The utility business treats and supplies an average of approximately 2,700 million liters (713 million US gallons) of water per day. In London as a whole, over a third of mains are more than 150 years old. Over half are more than 100 years old. Thames Water initiated trunk main leakage reduction programs concentrating on unaccounted for water losses in its transmission mains before the distribution network. A range of new and traditional leak detection methods was compared. Parameters included cost of operation, sensitivity of detection and accuracy of location. Thames concluded that the Sahara® Leak Location system was the most accurate and cost effective way of detecting and locating trunk main leaks. Consequently, Sahara was used exclusively for subsequent phases. To date, over 960 surveys have been completed and over 960 leaks have been located with Thames Water reporting that, recently, the average leak repaired is approximately 0.15Ml/day (25 US gallons/day) arising mainly from deteriorated lead run joints on cast iron mains and corrosion through the wall of steel mains. In excavating at the identified locations, Thames Water quoted a near 100% accuracy record. This paper discusses the financial benefits to Thames Water from the annual volume of leaks identified within their water transmission system in the eight years from 1998 to 2005, including the cumulative leakage found as well as the approximate leak volume per distance inspected each year.

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.

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.

Anomalous Models of Defect Interactions in Electromagnetic Testing

Stress corrosion cracking (SCC) is a major concern in oil and gas transmission lines. Small external, axially aligned cracks are difficult to detect and size using present boreside inspection techniques. Remote field eddy current (RFEC) testing is an inspection technique for tubes currently in use for the inspection from well casings to small diameter heat exchange tubes. An advantage of this technique over conventional eddy current testing is its ability to detect both external and internal defects in ferromagnetic materials with approximately equal sensitivity. Because of RFEC’s proven sensitivity to external defects and the fact that eddy currents are induced in the circumferential direction, there is currently great interest in the technique for the inspection of pipelines.