Safe Gas Containment
The objective of the designers of the Coselle™ was to create a containment system that maximizes safety and storage capacity while minimizing complexity, especially in valves and manifold piping. As a result, today’s Coselle™ is a very large pressure vessel consisting of small diameter pipe connected by way of a simple manifold and control system.
Extensive safety studies have been completed, supervised by the classification societies Det Norske Veritas (DNV) and the American Bureau of Shipping (ABS). These include: HAZIDs, HAZOPs, over-pressurization of the cargo hold, rapid dispersion of gas, and crew escape and evacuation. The results of this extensive work have been incorporated into the design and operational plans of the ships.
A safety study by DNV summarizes the inherent safety of the Coselle™ system.
The following is an extract from their study:
“The Coselle concept has several attractive features relative to other CNG concepts, including:
- The long small diameter containment system provides choke in case of rupture, reducing required capacity of emergency venting systems;
- Thin walled pipe means that sufficient material toughness is more readily obtained. If rupture occurs, the fragments have small mass posing little threat to adjacent pipe or hull structure;
- … the capacity of a Coselle is significantly larger (~order of magnitude) than containment sections of other bottle concepts. Reducing the number of containers simplifies piping layout, manifolds, valves etc.”
To ensure safety, the Coselle™ System employs a redundant inert gas containment system. Both the Coselle™ and surrounding cargo space are filled with an inert gas - nitrogen. In the highly unlikely event that a Coselle™ were to leak, the natural gas would safely enter a fully inert and benign environment. This arrangement eliminates any possibility of mixing natural gas and air within the Coselle™ structure, thus preventing a flammable mixture from occurring.
The Coselle™ is engineered to be the one of the world’s safest containment vessels.
Independent analysis by both DNV and ABS has concluded that even under the most severe failure modes, the resulting natural gas release can be safely vented to the atmosphere with no damage to adjacent Coselles™ or to the ship structure.
The American Bureau of Shipping (ABS), one of the preeminent ship classification systems in the world, has approved Sea NG’s Coselle™ ship design.
During its investigations, ABS examined and approved:
- Gas depressurization arrangements
- Piping and electrical systems
- Gas dispersion
- Radiant heat levels
- Fire protection
- Stability
- Vessel arrangements
- Hazardous areas
- Containment systems
- Fire protection
The specific hazard identification and hazard operability studies completed to date are:
- DNV Phase I, II and III Safety studies
- DNV – Initial HAZOP
- DNV Conclusion: Coselle Vessel “as safe as existing gas carriers.”
- ABS – Final HAZOP and HAZID (2005 – 2006)
To ensure a focus on safe operations, Sea NG collaborates closely with customers and other key stakeholders to implement a comprehensive risk management system that embraces all aspects of project operations.
