LR specialists have issued GTT an Approval in Principle (AiP) for a membrane cargo containment system (CCS) for bunker ships to allow an increase in vapour pressure of up to 2barg.

The AiP follows a joint research and innovation programme between GTT and LR investigating cargo containment behaviour, looking at strength aspects in various applications, sizes and at different pressures. The close collaboration between Lloyd’s Register and GTT experts, through workshops using experimental and analytical results and data on internal pressures occurring in LNG tanks, studied the maximum compressive strength of the containment system on LNG carriers. 

Using a 4,000 cbm LNG bunker as a reference case, with two Mark III Flex membrane tanks and structural analysis – while considering navigation and operating conditions – in October 2015 LR issued AiP for a GTT Membrane system with an increase in vapour pressure up to 2barg for use in bunker ships.

Higher vapour pressures in CCS are relevant for gas-fuelled ships and small-scale LNGs – especially for LNG bunkering, to help manage boil-off gas. Strengthening the hull offers additional safety within the tank to withstand the boil-off gas generated.

The project required a clear engineering understanding of the membrane technology as well as the fundamental principles of applicable rules and regulations in order that the required safety and reliability levels are maintained, when implementation of membrane containment systems goes beyond atmospheric pressure applications.

Dariusz Boryszewski, Senior Specialist, Ship Structures, LR said: “The potential use of such applications in the gas as fuel and small-scale LNG market are many. This Approval in Principle opens the route to progress further with GTT towards project specific applications. This study carried out by our specialists and GTT’s was an effective marriage of our organisations’ capabilities. Getting to Approval in Principle with the novel idea of pressurised membrane tanks is a real achievement. Our review identified areas that can be engineered to help ensure the ship’s structure effectively supports the CCS.”

David Colson, Commercial Vice-President of GTT commented: “Thanks to our extensive knowledge and experience, GTT, together with Lloyd's Register, has been able to demonstrate the feasibility of operating membrane tanks at higher pressures. This is a significant step in increasing the use of membrane tanks in the LNG as fuel chain for fuel tanks and bunker vessels.”

This latest approval issued follows the Lloyd’s Register General Approval issued to GTT on 1 October 2015 for their Mark V cargo containment system, which you can read more about at