Environmental loads comprising wave and current forces act upon a pipeline resting on the seabed. In order to maintain integrity, the pipeline must resist lateral excursion. This can be achieved by designing the pipeline so that it has a sufficiently high submerged weight to resist these forces, or by shielding the pipe from the environment by trenching or burying. Additional weight is normally achieved by adding material in the form of a concrete coating or by increasing the wall thickness of the pipe.
The Pipeline Stability (2) (STB2) module evaluates the stability of a pipeline using the veritec recommended code of practice RP E305. This was intended to supersede earlier stability guidelines by using a modified 3D Morrison equation including wake effects downstream of the pipe. By using an interpolation methodology for the data presented in RP E305, the STB2 module has the ability to:
The accuracy of the results are dependent upon the suitability of the current and wave loads applied to the pipeline. Wave induced velocities are calculated in accordance with RP E305 which can be made physically realistic by use of a calibration factor. Wave states are characterised by energy density functions specified by wave height, spectral wave period and the Jonswap peakedness parameter. Current velocities from either an explicit value i.e the 1/7th power law, or a logarithmic relationship can also be specified.
The method used by the STB2 module to calculate the pipe-seabed interaction is as specified in RP E305 for sand soil and for clay. This involves determining the generalised weight parameter by interpolating between data-figures presented in the code.
The STB2 module is supplied with comprehensive theory, user and validation manuals describing worked examples in detail.