This paper describes the results of experimental work and simulations of pressure surges resulting from fast closing valves and activation of an emergency release coupling (ERC) in ship-to-ship LNG transfer. The first part presents the results of an ambient water flow test with a fast closing 4-inch full bore valve in combination with a 4-inch flexible multi-composite hose. High amplitude pressure surges up to 4 times the working pressure occur upstream of the valve. Pressure surge amplitudes strongly depend on valve closing time and flow rate. The propagation speed in the upstream hose is lowered considerably due to the hose flexibility. Furthermore the temporarily deformation of the hose results in loss of energy and acoustic damping of the pressure surge amplitudes.
The measurement results are compared to the results of modeling. Acoustic damping and propagation speed of sound show a non-linear behavior of the hose, due to a varying internal pressure, which is not captured in the present modeling techniques.
The second part of the paper describes the results of a full scale flow test on an 8-inch ERC (KLAW make) for LNG ship-to-ship transfer (Figure 1). The ERC in the test is located downstream of an 8-inch 15-meter long multi-composite flexible hose. The test is intended to investigate operational and mechanical integrity, spill rate and the impact of pressure transients and shock loads on the ERC including upstream hose and downstream piping.
Upon hydraulic activation the ERC separates in two parts, each provided with a fast closing butterfly valve. The complete operation takes about 0.2 s and the actual valve closure duration is about 0.02 s resulting in a negligible spill of less than 0.002 m3. Pressure transients from 34 to 100 bar, over 10 times the operating pressure, occur at the maximum flow rate of 1000 m3/hr, resulting in shock loads and high acceleration levels. The mechanical integrity remains intact even after four successive releases at the maximum flow rate of 1000 m3/hr. The results contribute to the certification of the ERC by Lloyds B.V.
Further development in modeling is necessary to obtain a validated model for the calculation of pressure surges due to emergency shutdown in a LNG transfer.
