The loadings that may result from the installation phase are:
|o||elastic bends (for instance from horizontal directional drilling)|
|o||towing forces focused on a pulling point (especially offshore pipelines)|
|o||preheating conditions (especially 'hot' pipelines, e.g. district heating lines)|
|o||sequence of installation phases (e.g. making use of the non-linear soil behaviour)|
|o||uneven bottom conditions (e.g. pipe laying over subset dunes, pre sweeping)|
These loadings result from the structure itself and generally consist of deadweight loading:
|o||deadweight of the pipeline structure|
|o||overburden weight of the soil|
|o||additional weight loadings configured by means of point load patterns|
The loadings that generally result from operational conditions are:
|o||internal or external overpressure|
|o||variations in temperature|
|o||deadweight of the conveyed medium|
|o||3D consolidation settlements of the soil body from extra loadings|
|o||soil shrinkage as a result of previous soil skeleton disturbance (construction subsidences)|
|o||soil displacements due to underground mining activities (new or old)|
|o||soil displacements due to earthquakes|
|o||soil displacements due to bottom erosion at rivers and estuaries|
|o||temporary loadings on top of the soil, e.g. as a result of traffic loads|
|o||wave 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: 14/09/2016
The pipeline configuration
The pipeline model
Pipe/soil interaction model
External supports and end points
Main analysis methods