Jack Control System-Resting And Simulation Of Operation
P.M. Berrefjord · Offshore Technology Conference · 1988
1. Introduction. This paper deals with the testing of the control system for the Ekofisk Deck Elevation. This includes the tests as well as implementation of the test programmes. For those who are not acquainted with the elevation operation and the related control system, a description can be found in appendix A, and in the papers refered to in this paper's reference list. 2. Project characteristica and philosophies. The selected control system design and test philosophy was closely related to the project requirements. We shall therefore provide some background information on this, and how the results were implemented in the project through the company organization. 2.1 Project characteristica. The following project characteristica had to be taken into account during design and testing of the control system:A potential high risk had to be minimized.No start-up periode for the control system, i.e. the system had to work at first attempt.No standardized solutions available for the elevation. Of particular importance was the dynamical interaction between the control system (closed control loops, hydraulic supplies and jacks), the structural arrangement supporting the jacks and the platform structures. Wind and waves had to be considered.Weather conditions. The operation was to be carried out within a defined weather window, i.e. worst weather conditions. The North Sea weather conditions are very unstable, becomming significantly worse from early autumn towards the winter. This includes both the possibility of sudden storms building up, and the general possibility of having conditions within the weather window. A major safety criterion for the operation therefore was to reduce the time spent during elevation to a minimum. As the elevation was scheduled to take place in late summer, no major slack in the time schedule could be allowed.The elevation was to be carried out within very tight tolerance limits. Max. ±6 mm deviation leg-to-leg within a platform, and max ±10 cm between adjacent platforms. It should be noted that for some of the platforms with particularly stiff deck constructions, a deviation of e.g. 10 mm between adjacent legs would transfer several hundred tons from one leg to the other.The project was to be carried out within tight time schedules. Detail design of the control equipment started less than one year before elevation. Consequently, design and manufacturing was carried out as parallel activities, and the manufacturing was carried out by a large number of manufacturers.Offshore commissioning was carried out according to a tight time schedule. Final offshore function tests started 3-4 weeks prior to elevation. Control system commissioning would have to be carried out while construction work etc. was ongoing, by a lot of personnel organized in four shifts. Consequently, effective procedures were essential, and the equipment when received offshore had to work.