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Report on flexible risers

The Petroleum Safety Authority Norway has commissioned a study to update our knowledge of unbonded flexible risers. Events in recent years associated with flexible risers on the Norwegian shelf demonstrate a need for updated knowledge in this area.

Events in recent years associated with flexible risers on the Norwegian shelf demonstrate a need for updated knowledge concerning unbonded flexible risers, with a focus on:

  • degradation mechanisms
  • failure modes
  • inspections
  • monitoring and integrity management.

The review concentrates on design, planning, operation, inspection and maintenance and how to secure adequate documentation and to utilise this information to operate flexible risers in the safest and most reliable way.

The work covered the following topics:

  • Overview of key features of the development of flexible risers
  • Overview of the most serious incidents
  • Relevant degradation mechanisms and failure modes
  • The present state of knowledge and potential future risks and uncertainties concerning degradation, ageing and life extension
  • Effects of degradation mechanisms on robustness
  • Future trends, developments and challenges
  • Integrity management (design and operation)
  • Inspection, maintenance and monitoring methodologies
  • Initiatives for improvements and knowledge sharing

The report is based on experiences from the Norwegian petroleum activities and international experiences.

The study has been undertaken by 4Subsea.  The Petroleum Safety Authority Norway has previously carried out the following work concerning flexible pipelines and risers:

Regulatory requirements
Section 11 of the Framework Regulations, concerning risk-reduction principles, and section 4 of the Management Regulations, concerning risk reduction, define a requirement to choose solutions and barriers (technical, operational and organisational) that offer the lowest possible risk.

Furthermore, section 5 of the Management Regulations include a requirement to establish barriers, both risk-reducing (i.e. preventive) and impact-reducing.

Section 23 of the Management Regulations, concerning continuous improvement, sets out a requirement to continuously improve health, safety and the environment, assess impacts and facilitate the application of experience from one's own and others' activities in the improvement work. In order to maintain an overview of incidents in the petroleum activities, section 29 of the Management Regulations, concerning notification and reporting of hazard and accident situations, and section 36, concerning the reporting of damage to load-bearing structures and pipeline systems, define a requirement to report incidents.

These requirements are important for the safe operation of flexible risers throughout their lives. Having clear rules and requirements for design, installation and operation – and sharing experience, learning from previous failures, and increasing the general level of knowledge in the industry – will make it possible to reduce the number of incidents associated with flexible risers.