Hydrocarbon Risers in Caissons and I/J Tubes – Inspection issues and recommendations
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:
- A lack of knowledge and use of recognised Industry good practice;
- Failure to implement suitable and sufficient performance measures within the platform verification scheme;
- Poor communication and coordination between pipeline operator and the platform duty holder.
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.
Key Items Causing Concern
- The integrity management arrangements for hydrocarbon risers within caisson, I/J tubes can be missed or "fall through the gap" at the pipeline and topsides interface. This can result in maintenance being overlooked.
- Riser in caisson and I/J tube annulus management and inspection are often not adequately considered.
- Limited evidence of regular monitoring/review of industry good practice and adoption of emerging new and improved maintenance and inspection techniques.
- Alarms associated with riser in caisson or I/J tube annulus pressure and gas detection are not always effectively integrated into the platform's alarm response strategy.
- Project handover to operations personnel following new build risers in caissons or I/J tubes can fail to effectively address or implement suitable integrity management arrangements for the new equipment.
Good Practice Guidance
The following relevant good practice guidance is available:
- Energy Institute Publication: Guidelines for the Management of Integrity of Subsea Facilities, April 2009 (Energy Institute Ref: ISBN 978 0 85293 537)
- Det Norske Veritas: DNV-RP-F116 Integrity Management of Submarine Pipeline Systems, October 2009.
- Det Norske Veritas: DNV-RP-F206 Riser Integrity Management, April 2008.
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; eg 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:
- Establishing a suitable and sufficient Integrity Management strategy, including details of planned maintenance, inspection, testing and condition monitoring arrangements and based on:
- A review and assessment of the design intent of the installed riser in caisson or I/J tube to better understand how the principal design considerations may impact on future integrity management considerations;
- Evaluation of the principal threats and failure modes
- Assessment of risk attributed to each failure mode
- Adoption of a suitable range of complimentary inspection, monitoring, maintenance and testing techniques. In consideration to continuing advances in technology and improvements in inspection techniques it is important that pipeline operators regularly review their integrity management arrangements to ensure they reflect Industry good practice.
- Providing systems which detect any degradation at an early stage;
- Formally documenting arrangements and associated key decisions.
- Undertaking regular reviews of the integrity management arrangements throughout the whole lifecycle of the equipment, taking cognisance of technological developments and improvements in integrity management techniques, equipment and practise;
HSE Intervention Priorities
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