Integrity and efficiency in LNG transfer operations with flexible hoses

The work presented contributes to the LNG supply chain by the development of a validated calculation model for corrugated flexible hoses or pipes developed for LNG Transfer. The model builds upon experience gained by TNO Technical Sciences (Fluid Dynamics) in a large number of flow tests carried out on hoses in a large range of diameters from 4 to 18-inch. LNG transfer rates are in general relatively high as the time involved should be limited from economical point of view. In large scale offshore LNG transfer, flow rates up to 5000 m3/h are applied and in future flow rates up to 10.000 m3/h are foreseen. Typical values mentioned for offshore operations in tandem transfer range from 50 to 150 meters hose length and hose diameter up to 20-inch. The pressure losses in LNG offshore transfer, but also in smaller scale applications, can be considerable. The pressure loss depends on flow rate, length of the hose, internal diameter and internal hose corrugation geometry. High pressure losses will impose additional requirements on LNG pumps and might result in cavitation at the downstream end of the hose as the average pressure drops below vapor pressure. Furthermore the impact of local boiling phenomena due to heat-ingress and cavitation, possibly effected by vortex shedding along the internal corrugations, is not known. Once the gaps in the data base are filled a validated prediction model is available, which can be used in guidelines and standards. So far the EN1474 (part 2: Design and testing of transfer hoses) does not specify a maximum allowable pressure loss and the prescription of the requirement for the test is limited: “Flow rate testing (ambient or cryogenic): demonstrate that the hose is capable of operating at its maximum flow rate and confirm the predicted head loss” The final goal of the project is to obtain a validated prediction model for the calculation of pressure losses in LNG transfer with flexible multi-composite and metal hoses based on input of parameters as operating conditions and hose geometry. Also input for guidelines and standards in LNG transfer with flexibles such as EN1474 will be generated, which can be used in for qualification of LNG equipment.