Section 8 Design loadings and environmental criteria

8.1.1 All modes of operation are to be investigated using realistic loading conditions, including buoyancy and gravity loadings together with relevant environment loadings due to the effects of wind, waves, currents, vibrations, ice, and where necessary, the effects of earthquake, sea bed supporting capabilities, temperature, fouling, etc.

8.1.2 The allowable modes of operation the maximum internal pressure, product temperature, flow rate and maximum environmental criteria are to be stated in the Operations Manual.

8.1.3 The environmental criteria generally assumed in designs is to be based on a return period of 100 years. In regions where environmental data is well established a return period of 50 years may be accepted by LR.

8.2.1 When using acceptable wave theories to determine local wave velocities for smooth cylindrical members, it is recommended that for risers the values of drag, lift and inertia coefficients C_D, C_L and C_M be taken to be 0.7, 0.9 and 2.0 respectively. These values should be modified to allow for proximity to the seabed, or platform members. For pipelines, the values for these coefficients are dependent upon the flow conditions and this should be taken into account.

8.3.1 Where a current acts simultaneously with waves the effect of the current is to be included. The current velocity is to be added vectorially to the wave particle velocity. The resultant velocity is to be used to compute the total force.

8.3.2 In the absence of more detailed information, the distribution of current velocity with depth may be assumed to vary according to the 1/7 power law.

8.4.1 Consideration is to be given to the possibility of vibration of structural members due to von Karman vortex shedding. (This is to apply to wind on exposed risers, and to wave and current on immersed risers and pipelines).

8.5.1 Pipelines intended for operation in ice are to be designed to minimize the effect of ice loadings. Proposals are to be submitted for consideration.

8.6.1 All weight loadings are to be taken into account and to include self weight of pipeline, fittings and weight coating. Also the deadweight of contents is to be included.

8.6.2 Buoyancy of pipelines including attached equipment and weight coating is to be taken into account.

8.6.3 Constraints and loads arising from supports and attachments should be taken into account for risers and pipelines. Also any scour or subsidence of sea bed should be assessed.

8.7.1 Static pressure, pressure surge transients and any peak `hammer-blow' effects are all to be considered, together with corresponding temperatures.

8.7.2 Dynamic inertial vibrations and flutter induced by any activation including vortex shedding are to be considered.

8.8.1 Loads imposed during installation, including those due to motion of the laying vessel, are to be assessed and taken into account. The curvature taken up during laying and loads imposed thereby on weight coating and possibility of buckling of pipe are to be assessed and arrangements made for laying procedures to avoid any damage or overstress.

8.8.2 Loads arising during trenching and back-fill operations are to be assessed and taken into account.