A portion of Enbridge Pipelines 30 inch crude oil/NGL pipeline runs from Bay City, Michigan to Sarnia, Ontario. A geometry tool found a topside dent indication and GPS data indicated that the dent was located in the Saginaw River which is considered Coast-guard navigable. This pipe segment is located within a defined high consequence area making Pipeline and Hazardous Materials Safety Administration (PHMSA) timing applicable. On top of the normal problems associated with digging in a river, the riverbed soil was known to contain dioxin contamination related to its industrial history.This paper provides an overview of the practical problems encountered in completing this dig. Governmental construction permitting proved to be the most difficult aspect of the work. Contaminated soils caused Enbridge to hire a specialized water handling company. Significant engineering challenges included design and installation of a 100 × 50 foot coffer dam with 70 foot long sheets. The coffer dam design required a flood plain erosion study. After many months of permitting process, all required permits were obtained and construction was started.The construction included three major elements, water handling, coffer dam installation and excavation of the suspected defect. After 2 months of work to uncover the suspected dent, it was located and analyzed. The dent did not meet Enbridge repair criteria, but mechanical reinforcement was installed as a precaution. Final steps included backfilling and coffer dam removal. From start to finish the construction portion of the dig took about 5 months to complete.
展开▼
