The loadings that may result from the installation phase are:
oelastic bends (for instance from horizontal directional drilling)
otowing forces focused on a pulling point (especially offshore pipelines)
opreheating conditions (especially 'hot' pipelines, e.g. district heating lines)
osequence of installation phases (e.g. making use of the non-linear soil behaviour)
ouneven bottom conditions (e.g. pipe laying over subset dunes, pre sweeping)
These loadings result from the structure itself and generally consist of deadweight loading:
odeadweight of the pipeline structure
ooverburden weight of the soil
oadditional weight loadings configured by means of point load patterns
The loadings that generally result from operational conditions are:
ointernal or external overpressure
ovariations in temperature
odeadweight of the conveyed medium
o3D consolidation settlements of the soil body from extra loadings
osoil shrinkage as a result of previous soil skeleton disturbance (construction subsidences)
osoil displacements due to underground mining activities (new or old)
osoil displacements due to earthquakes
osoil displacements due to bottom erosion at rivers and estuaries
otemporary loadings on top of the soil, e.g. as a result of traffic loads
owave and current loadings offshore
The loading condition on the pipeline structure is constituted by means of individual load factors unequal to zero on each loading component.
The loading condition as a whole may be given an overall load factor (the loading safety factor) and all other load factors of applicable loading components are then set to 1. In this way it is possible to work in a traditional way with actual loadings and admissible stresses, that are derived from the ultimate stress state of the pipe material by means of a material safety factor.
Or to work in a more advanced way in which the various loading components each have their own individual loading factor, together constituting an ultimate loading condition to the pipeline. The overall load factor in this case is equal to 1. In this way the resulting stresses and strains are compared directly to the ultimate bearing capacity of the pipe material or pipe geometry. The ultimate bearing capacity in general is defined as the yield stress or the breaking stress, but can as well be a limit strain or buckling behaviour. For instance collapse of the cross-section or a buckled state.
Because the pipeline behaviour is highly non-linear (soil non-linear behaviour, geometric non-linear behaviour, structural non-linear behaviour, material non-linear behaviour), it is not possible (as is common in the analysis of building structures) to superimpose analysis results from the individual loading components. As a result each loading combination has to be analysed (computed) individually.
PipelineLoadings, last changed: 9/14/2016