Surge pressures are generated in any pipeline system where there is a sudden change in flow. This may be caused by either the opening or closing of a valve, the start up or shutdown, of a pump or a combination of the two. If the pressure surge in the pipeline results in stresses in excess of the strength of the pipe or its components, then there may be a rupture leading to an oil spillage which could have major economic and environmental implications. Offshore loading/unloading facilities (cargo transfer systems) incorporating onshore tankage and pipework together with loading/unloading arrangements (via fixed jetty or CALM system) are in use worldwide and, in view of the fact that such systems are often composed of system components having different pressure ratings, susceptibility to damage due to excessive surge is a major factor to be considered in the design. J P KENNY & PARTNERS LIMITED have carried out many comprehensive surge analyses of pipeline systems, including offshore loading/unloading facilities. This paper presents some key findings arising out of such projects with a view to highlighting the major design criteria and stating recommendations for safe and effective operations.
A major concern in the design of cargo transfer systems of the type used in tanker loading-unloading facilities, is the prevention of excessively high pressures during system operations. The highest pressures are often found to occur on closure of tanker valves during loading, and hence it is particularly important to predict these pressures at the design phase using appropriate modelling techniques to simulate the valve closure scenarios of interest (Ref. 1). Clearly, the implications of. excessive surge pressure in pipeline systems such as ship/shore cargo transfer facilities are very substantial, and the need to predict such pressures accurately is vital.
