A formal quantitative risk assessment (QRA) shall be carried out for pipelines connected to permanently manned offshore complexes, except for pipelines transporting category A fluids. The necessary riser protection and safety systems shall be derived from this assessment.
1. The risk depends firstly on the expected frequency of failure, due to internal and external corrosion, external loading (e.g. impacts, settlement differences, free spans), material or construction defects, and operational mishaps.
2. Secondly, it depends on the consequences of the failure, based on the nature of the fluid in terms of flammability, stability, toxicity and polluting effect, the location of the pipeline in terms of ignition sources, population densities and proximity to occupied buildings, and the prevailing climatic conditions.
3. The expected frequency of failure and the possible consequences may be time-dependent and should be analysed over the entire life of the pipeline.
4. Risks levels can be reduced by using lower design factors (e.g. higher wall thickness or stronger steel), rerouting, providing additional protection to the pipeline, application of facilities to minimise any released fluid volumes, and controlled methods of operation, maintenance and inspection.
5. NOTE: Pipelines with a wall thickness lower than 10 mm are susceptible to penetration, even by small mechanical excavators. External interference by third parties is a major cause of pipeline failures. Specific precautions against this type of hazard should be addressed; this is particularly relevant to onshore pipelines transporting category C and D fluids.