The Program

Ple4Win is a Computer Aided Design tool for the pipeline design engineer, who has to design and evaluate the strength and stability of buried or partly buried transport pipelines, that have to meet the safety requirements as they are specified in Pipelines Codes and Regulations.
The pipeline may be a high or low-pressure transmission pipeline, onland or offshore.

Geometry

Ple4Win is based on a 3D geometric model, in which the pipeline is schematised by means of a string of straight pipe, (elastically) curved bend, support, joint and T-connection elements.
Branches and loops are allowed and as a result stations may be analysed as well.

Pipe

Pipe diameter, pipe wallthickness with manufacturing tolerance and corrosion allowance, and the isotropic or anisotropic properties of the pipeline materials may vary along the pipeline axis.
At the locations of the bends (toroids) the reduction of the bending stiffness of the cross section, as a result of ovalisation, is taken into account. The counteracting effect of the internal pressure on this stiffness reduction is considered as well.

Soil

Support and loading of the pipeline result from the surrounding soil. The soil model is based on the mechanical properties of the soil, which depend on the deformation direction (upward, sideward and downward) of the pipe relative to the soil and counteracted by the friction reaction of the soil.
Based on soil failure mechanics in the four principal directions a 3-D soil model is built in such a way that in the model the soil reaction is defined in any direction of the pipeline displacement. The deformation behaviour of the soil is considered to be non-linear elastic or elasto-plastic and primarily based on a bi-linear curve. Over the first part of the curve the deformation behaviour of the soil is considered to be linear elastic (constant ratio between soil reaction and pipe displacement), whereas over the second part the soil behaviour is considered to be ideal plastic (constant soil reaction independent of the pipe displacement). Other, smooth, curves can be applied too. Even slacks (for instance in a jacket tube) are possible.
At the pipe bottom, variable soil support angles and at the sides horizontal soil support may be applied.

Boundary conditions

At the end points of the pipeline structure to be taken into account, a free end or rigid support or a connected half-infinite long pipeline can be specified. Along the pipeline axis external linear elastic supports can be specified. For instance a “table” support with friction properties.

Loadings

The loadings that may be placed on the pipeline structural model result from:

Installation conditions
  • elastic bends
  • towing forces focused on the pulling point
  • preheating conditions
  • sequence of installation phases

Operational conditions
  • internal or external overpressure
  • variations in temperature
  • deadweight of the pipeline structure

Environmental conditions
  • 3-D deformations of the surrounding soil as a result of consolidation settlements from extra loading and soil subsidence as result of disturbance of the soil structure or earthquakes
  • overburden soil weight
  • temporary loadings on top of the soil, e.g. as a result of traffic loads
  • wave and current loadings at sea
  • wind, snow and ice loads

Additional loadings may be modelled by means of point load patterns.

Analysis methods

Allowable stress method
  • linear elastic (an)isotropic pipe material
  • soil non-linear behaviour
  • geometric linear or non-linear behaviour
  • all loads without design factor
  • sequential loading allowed
  • evaluation on basis of allowable stress level (based on safety factor), allowable deformation and overall buckling

Limit stress method
  • linear elastic (an)isotropic pipe material
  • soil non-linear behaviour
  • geometric linear or non-linear behaviour
  • loads with specific design factors
  • sequential loading allowed
  • limited once-only yielding implicitly allowed by application of stress correction factors
  • evaluation on basis of ultimate (yield) stress, alternating yielding and overall buckling

Limit strain method
  • elasto-plastic isotropic pipe material
  • several stress-strain relations
  • geometric linear or non-linear behaviour
  • soil non-linear behaviour
  • loads with specific design factors
  • sequential loading not allowed (for the time being)
  • evaluation on basis of ultimate strain, alternating yielding and local buckling

Reported results of analysis

Longitudinal (beam) behaviour
  • pipe displacements
  • internal forces
  • soil and external support reactions
  • stiffness reduction and stress intensification factors for bends and T-connections
  • axial and rotational displacements in joint elements
  • free spans both above and below ground level

Cross-section behaviour
  • all cross-sectional loadings
  • cross-sectional deformations
  • longitudinal and circumferential stresses and strains
  • hoop stress
  • equivalent stress and strain according to Von Mises
  • principal stress and strain according to Mohr
  • shear stress and strain according to Tresca
  • uni-axial stresses and strains