DEWATERING

Process of dewatering is to remove the test water from the pipeline prior to drying. After the hydrotest the best dewatering methods leaves a film of water clinging to the inside pipe wall, so therefore, it is necessary to remove this water to eliminate the formations of hydrates and the possibility of the onset of internal corrosion causing carbon dioxide and hydrogen sulphide or to meet the moisture specifications for the delivered product. The pipeline is usually dewatered using a multi -pig train propelled with air. For pipelines that have been filled with seawater, or other non-potable water, the line may also be swabbed with fresh water to remove salt deposits and other contaminants. Several slugs of fresh water be run between pigs at the front of the dewatering train, followed by additional pigs in the dewatering train to ensure maximum bulk water removal.