scope:

Introduction

ABS has been requested by various designers to review their proposed design scenarios for the transportation of compressed natural gas (CNG) by sea. The proposed CNG carrier designs considered thus far are considered somewhat novel in that they differ from any one of the vessels that are currently transporting methane by sea, not only in that the methane will not be transported as a cryogenic liquid, LNG, but also in several key areas, including the following:

• Pressure and temperature of the cargo being carried

• Possible storage of cargo above the main deck

• Proposed method for loading and off-loading the cargo

• Proposed deviations from the IMO Gas Code factors of safety for hoop stress in independent Type B and C tanks.

This Guide provides requirements for design, construction and periodic surveys required for maintenance of classification that would be applicable to CNG carriers, where it is intended to obtain ABS class for the vessels. These requirements may also serve to satisfy Port State and Flag State Regulations as they develop. As these projects are still at the concept stage and various scenarios are being considered at this time, the objective will be to establish an overall philosophy or approach to provide a framework of reference material and cite precedence, where applicable, as to what methodologies followed by designers in similar projects have proven successful in the past.

While it is certainly not the intent of ABS to in any way prevent or stifle creative development of new ideas and concepts, ABS will point out where a proposal appears to go beyond the bounds of what has been accepted practice in the past. In such cases, ABS will provide the designer with a list of steps considered necessary to establish that such a proposal, in fact, does not compromise the level of safety well established in the published Rules of the American Bureau of Shipping and those of applicable national and international Regulatory bodies.