PR-015-143601-Z01 Drying Time of Residual Hydrotest Water in Crevices and Dead Legs

The objective of this project was to evaluate the effectiveness of the dewatering process after hydrotesting and to examine the internal corrosion threat posed by residual water trapped in crevices and water pushed into a dead leg. A “time to dry” calculation for both cases was conducted based on pipeline operating conditions. Analysis of the evaporation of water trapped in crevices indicated that maintaining low pressures and high temperatures are the most effective measures for drying the trapped water. At the lowest pressure of 14.7 psi and at 100 °F, trapped water can be dried in days. At increased pressure or decreased temperature, a pipeline may become saturated with water vapor, completely stopping evaporation. Other factors such as crevice geometry, water content, and water type had insignificant effects on water drying from a crevice. The geometry considered for water drying in a dead leg included the entire dead leg, a section of the main line, and a section of the lateral line in a horizontal orientation. Analysis indicated that gas flow in the main pipe forced the accumulated liquid water from the dead leg to move upstream in the main and subsequently evacuate through the lateral and pipe exit. The process of purging 99% of the liquid water from the dead leg was rapid, usually within minutes into operation of the pipeline. However, the small droplets, streaks and globules of water that are left behind may take a longer time to evaporate or be purged. A sloped dead leg configuration may enable a standing pool of water to accumulate in the dead leg, which would take substantially longer to evaporate than small water droplets. Further study that ac-counts for different dead leg orientations is recommended to provide a more complete understanding of the internal corrosion risk in dead legs.