The PIPE computer program is a design tool for on-bottom submarine pipelines, which calculate the submerged pipe weight to meet specified design criteria.

The PIPE computer program is based on the use of non-dimensional parameters which allow scaling of the environmental load effects, the soil resistance and the pipeline response (lateral pipe displacement). The PIPE computer program was initially developed as a part of a comprehensive research program PIPESTAB, and has been further revised as a consequence of the development of new models for the hydrodynamic and soil-force description.

The design philosophy allows for limited movements of the pipeline during extreme environmental conditions.

The design process utilizing the program starts with a definition of a long-term wave environmental description. Three main options are possible. The first option is based on utilization of a scatter diagram of significant wave height, Hs, and the peak period, Tp. The second option is based on an analytical model for the long term distribution of Hs and Tp. The third option fits a Weibull distribution based on the definition of wave height and spectral peak wave period for two return periods. Wave directionality and shortcrestedness can be specified for all options.

The long term wave elevation data are transformed to water particle velocity data as significant amplitude and upcrossing period of water velocity at the seabed. These data then form the basis for the description of the long term hydrodynamic loading process, and are used by the program for the pipeline stability design according to the specified design criteria.

Two principally different design checks are made for the stability control of the pipeline:

1. The first design check is relevant for an as laid on-bottom section (not artificially trenched or buried). The on-bottom design control is based on a specified permissible pipeline displacement for a given design load condition (return period). The basis for the design process is in this case a generalized response database generated through series of pipeline response simulations with the computer program PONDUS.
2. The second design check makes an absolute static stability calculation of a pipeline trenched and/or buried in the soil, sand or clay. This design check is based on a static equilibrium between the hydrodynamic design loads and the soil capacity. Hydrodynamic forces are obtained from maximum conditions and soil resistance forces are based on updated models. This design control opens for the possibility to check the necessary artificial trenching or burial for absolute stability of a specific pipeline case.

Pipe program overview

Method description

The general procedure for stability calculation in the PIPE program can be summarized as follows:

•  Description of long term wave environment
•  Calculation of design significant velocity, Us, and period Tu
•  Extraction of results from response database (on-bottom stability)
•  Calculation of break-out force (static stability)