A several mile long, 72-in diameter urban water transmission main was completed and placed into service late in the fall of 2000.
Within two months, the pipeline failed twice at joints between pipeline sections and the municipal water department elected to take it out of service. After several months of deliberations among the designer, constructor and pipe supplier, agreement could not be reached whether these were isolated incidents - or indicators of a systemic defect. In August 2001, CTLGroup was commissioned to evaluate the root cause, extent and consequences of the failures, and develop a repair strategy for returning the pipeline to a serviceable condition. The investigation and repair were to be completed by May 2002 - the beginning of the area's high water use season.
The pipeline evaluation/rehabilitation team stretched its capacity to rapidly conduct a comprehensive investigation with support from the pipeline contractor. Sections of pipeline were exhumed for inspection and materials and structural testing, adopting a statistically defined sampling protocol. Pipe joint design was evaluated and repair concepts studied and validated in load tests of coupons extracted from exhumed sections.
Probability studies led to the conclusion that the frequency of defects was inordinately high and that the as-built pipeline could not be relied upon. By mid-November 2001 a pipeline structural repair plan was proposed - encompassing 500 full-circumference weld repairs over the pipeline's alignment. Working to meet the city's schedule, work was performed by the multiple construction crews within the confined space of the pipeline interior. The rehabilitated transmission main was successfully pressure & leak tested by the first week of May 2002, and continues to function without leakage or incident to this day.