Cargo tank stripping
The final stage in bulk liquid pumping from a tank or pipeline. To achieve this, it is often necessary to list the ship to avoid suction loss. A large stern trim assists in draining, particularly if product is trapped in the centreline bulkhead corrugations.
Chemical cargoes, which create threat to the marine environment, must be discharged until there is virtually no residue left on board. Modern chemical tankers are designed from the outset with efficient stripping in mind; cargo tanks are smooth-walled, bulkheads are either corrugated or provided with stiffening located in the adjacent spaces. The clearance between the impeller of a submerged pump and the bottom of suction well can be as small as 20 mm. The cargo left in each pump and its piping can be stripped to shore by blowing air or nitrogen through the system. In this arrangement, residue quantities in the region of 50 litres per tank are achievable.