Pipeline On-Bottom Stability Assessment

Method notes for engineering and data workflows.

The challenge

Organise the inputs, calculations and reporting into a repeatable workflow with checks.

Solution Approach

Methodology

DNV-RP-F109 Generalized Stability Method (absolute stability) applied systematically using digitalmodel's on_bottom_stability module. The method evaluates pipeline stability by comparing hydrodynamic loads from wave and current action against the soil resistance, accounting for pipe weight, buoyancy, and seabed friction.

Technical Implementation

Parameter Definition

Input parameters were organized into three categories: pipe properties (outer diameter, wall thickness, concrete coating thickness and density), environmental parameters (significant wave height Hs, peak period Tp, current velocity, water depth at each KP station), and soil properties (friction coefficients per DNV-RP-F109 Table 3-2 for clay, sand, and mixed soil zones).

Automated Sweep

Each KP station along the route was evaluated against the load cases. The automated sweep systematically combined environmental conditions with local seabed properties to produce a complete stability map of the pipeline route.

Result Classification

Results were classified by utilisation ratio: green (ratio < 0.8, stable with margin), yellow (ratio 0.8–1.0, marginally stable), and red (ratio > 1.0, unstable, remediation required). This classification enabled rapid identification of problem spans without reviewing individual calculation sheets.

Technical References

Tools

• digitalmodel OBS module (Python): Core stability calculations per DNV-RP-F109
• aceengineer.com OBS Calculator: Interactive demo for single-point assessments

Related methods

• Multi-Code Wall Thickness Comparison
• OrcaFlex Riser Sensitivity Automation

Summary

Review the inputs, assumptions and calculation results for the stated scope.

Engineering workflows · Technical articles