Unique Spillstop— Advanced Oil Spill Avoidance System

An American underpressure system called Spillstop is an advanced spill avoidance system for oil tankers.

It employs slight, continuous, and pre-existing underpressure in a medium of inert gas of the ullage space of a ship's tank. Spillstop responds immediately in the event of an accidental hull rupture, according to MH Systems, Inc., which offers the system. From this baseline underpressure, timely reaction of the system is crucial.

Other underpressure systems on the market perform quite the opposite from Spillstop. No underpressure initially exists. These systems only begin to create underpressure with pumps after a rupture of the tanker's hull.

In the Spillstop system, the maximum underpressure is never allowed to exceed the structural capability of any tanker. Older tanker structures are thoroughly inspected, tested and analyzed prior to system installation. A comprehensive analysis by Dr. A. Mansour, professor of naval architecture and ocean engineering at the University of Cal lifornia, Berkley, and a noted expert in the field of structural analysis, has shown that, "effects of negative pressure on tanker structure" are insignificant.

According to California-based MH Systems, the Spillstop system maintains the IMO Inert Gas requirement as all times, even at the time of rupture. The Inert Gas system is a mandatory requirement for all tankers in excess of 20,000 tons in order to prevent accidental combustion and explosion.

The Spillstop system maintains the inert gas mixture under negative pressure. A general misconception is that an inert gas mixture cannot be effectively maintained under negative pressure. Not only can the mixture be maintained inert, claims MH Systems, but its effectivity is insensitive to variations in pressures. It is irrelevant to prevention of combustion or explosion whether the inert gas mixture is at a positive pressure or a negative pressure. Spillstop continuously compensates for ingress of oxygen due to leakage by introducing additional inert gas—the procedure that is currently followed in the positive pressure system for maintaining a specified inert gas mixture ratio.

Spillstop is computer controlled and totally automated with minimal need for human intervention.

The system can be considered both a wholly new physical formulation and a new high tech implementation of the existing inert gas systems that are already in place in oil tankers.

MH Systems reports that Spillstop eliminates potential boiloff of the volatile cargo by maintaining the underpressure value less than the cargo's vapor pressure.

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Maritime Reporter Magazine, page 20,  Nov 1991

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