How often does Crude Oil Washing (COW) occur in cargo tanks?

Crude Oil Washing (COW) is a process used primarily in oil tankers to clean cargo tanks and maximize the recovery of oil residues. This method involves utilizing the crude oil itself as a washing medium to remove residues from the interior surfaces of the tanks.

The correct answer indicates that COW occurs in one-quarter of the cargo tanks. This is based on operational practices designed to effectively manage the cleaning of the tanks while ensuring safety and efficiency. By washing one-quarter of the tanks during a single operation, the process ensures that tank cleaning is thorough and that the remaining tanks can continue to maintain their structural integrity and operational capabilities.

This periodic approach to COW also helps balance the risks associated with potential tank overloading and helps manage the operational parameters involved in ship loading and discharging. In contrast, washing every tank or every cargo load would not be practical, as it could lead to inefficiencies and potential hazards. Thus, performing COW systematically, focusing on a specific fraction of the tanks, helps optimize the overall cleaning and loading process.