A procedure is presented for the Quantitative Risk Assessment (QRA) of rigid riser systems attached to a Tension Leg Platform (TLP). It is shown how the results of the study may be integrated with the total platform QRA. The stages of the analysis are as follows:

  1. Safety Review

  2. Functional Block Diagrams

  3. Failure Modes and Effects Analysis

  4. Maintenance Effects Analysis

  5. Fault Tree Analysis

  6. Event Tree and Consequence Analysis

  7. Risk Assessment The risks assessed are those related to the safety of personnel, equipment damage and pollution of the environment.


Early in 1992, the Health & Safety Commission published a consultative document entitled "Draft Offshore Installations (Safety Case) Regulations 199 -", stating that QRA (or other means) should be used to assess the more severe risks identified for an installation. Initially, hazard identification will be by qualitative assessment combined with sound engineering judgement. With the recent introduction (Hutton, Jolliet, Snorre) and present development (Heidrun, Auger) of Tension Leg Platforms for deep-water installations, the need has arisen for the study of risk attached to a number of areas of new technology: one such area is that of rigid risers. This paper includes a methodology for the assessment of such risks and their incorporation into the platform-wide QRA. The approach, whilst geared to the particular case of the rigid risers, is also applicable to the risk analysis of any system. Rigid risers, held in tension in order to accommodate vertical motions of the TLP and mounted on flexible or tapered joints against horizontal and radial motions, may be used for drilling, production, oil export and gas export functions. The risks are considered from the points of view of safety of personnel, the environment and the installation.

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