Between 2002 and 2007 there were a number of failures of hydrocarbon risers inside caissons and I/J tubes giving rise to potentially hazardous releases on offshore installations. Related inspection and investigation activities identified some deficiencies in the associated integrity management arrangements for this equipment with emerging issues as follows:
Regulation 13 of the Pipelines Safety Regulations 1996 (PSR) requires the pipeline operator to ensure that a pipeline is maintained in an efficient sate, in efficient working order and in good repair.
Regulation 17 of PSR and Regulation 8 of the Offshore Installations and Pipeline Works (Management & Administration) Regulations 1995 (MAR) require pipeline and platform operators to co-operate with each other.
Regulations 19 to 21 and Schedule 7 of the Offshore Installations (Safety Case) Regulations 2005 (OSCR) require the installation duty holder to put into effect and maintain a verification scheme. This should cover safety critical elements including all caissons containing hydrocarbon risers. It requires written schemes to be produced to ensure that these elements are suitable and remain in good repair and condition. There should be independent and competent assurance on ongoing suitability of caissons and risers.
The following relevant good practice guidance is available:
Due to the nature and structural configuration of caissons or I/J tubes, they are considered to be an integral part of any associated pipeline riser system. Also, such hydrocarbon containing riser systems are typically considered as safety critical on an offshore platform. Whilst caissons and I/J tubes are designed and installed to protect risers from hydrodynamic loading and environmentally induced corrosion, they also obstruct access to the outer wall of the riser within the annulus, which makes inspection more challenging. Internal inspection of the riser along with the requirement to manage the annulus contents will be important considerations in determining a suitable and sufficient integrity management strategy for such riser systems.
Clearly defining failure criteria will be an essential element to the risk assessment process and for triggering appropriate remedial actions to manage/control those risks. Failure is often associated with a loss of containment event. However, this clearly represents the ultimate or final stage of deterioration and prevents an opportunity to implement remedial actions or a maintenance response to help manage/control any deterioration in the condition or state of the riser; e.g. loss of wall thickness equal to the corrosion allowance could be one example of a failure criterion, which if detected would allows the integrity management system to react and implement suitable remedial measures thus preventing further deterioration leading to catastrophic failure.
To understand the integrity threats for a particular riser in caisson or I/J tube system it is pertinent to understand the detailed component layout and design intent as each caisson and I/J tube are likely to be slightly different from each other.
Pipeline Operators should implement integrity management good practice guidance or other alternative arrangements which provide an equivalent level of safety integrity. Such arrangements will normally be implemented during design but should be able to be retrospectively applied to existing equipment and should include:
Continue with proactive communications and engagement with pipeline operators and other relevant stakeholders to help improve the adoption and use of recognised industry good practice for the integrity management of hydrocarbon risers in caissons and I/J tubes. Target inspection of management arrangements/practice and related safety critical element Verification activities for hydrocarbon risers in caissons and I/J tubes to drive improvements in integrity management performance.
Updated issue date: 20 August 2010
HID Gas and Pipelines Unit