The problem
An international offshore operator manages an extensive system of subsea pipelines in the North Sea, transporting gas and associated liquids. Seventeen of these pipelines were approaching the end of their certified life by 2025 and required lifetime extension assessments and re-certification to continue operating beyond 2025.
Jee has decades of experience of Lifetime Extension Assessments, having performed numerous studies for operators around the world, and was the author of ISO 12747, the international standard for pipeline life extension assessment. Being the ideal partner, Jee was engaged for the preparation of the lifetime extension (LTE) assessments of these seventeen pipelines. A major 3rd party verification body was engaged for the independent review and verification of Jee’s LTE studies and the issue of Declaration of Lifetime Extension of the Pipeline certificates.
The pipeline systems include both rigid and flexible sections although the scope of this assessment was limited to rigid pipeline components only. The study required a systematic evaluation of historical design assumptions, operational changes, inspection and survey data, and time-dependent degradation mechanisms to determine remnant life and define future integrity requirements.
The solution
Jee structured the LTE assessment around a risk-based integrity framework, aligned with current offshore pipeline standards and industry best practice.
Data collation and review
A comprehensive data collation exercise was undertaken for each pipeline system, including a review of design documentation, material specifications, route information, and construction records. The operational history was assessed to understand pressure, temperature, and fluid composition over the life of the pipelines. Available inspection and integrity data were also reviewed, including in-line inspection results, cathodic protection survey data, coating condition information, and pressure test records, to establish the current condition of each asset and the history of operation.
Design and standards review
A review of the original design basis of each pipeline was carried out against current pipeline design and integrity standards to ensure that the pipeline complied with current design standards. The original designs of all seventeen pipelines were reviewed and confirmed compliant with current design standards.
Threat and risk assessment
A structured threat identification and risk assessment was undertaken, incorporating both the industry-wide experience of Jee’s integrity engineers and the asset specific experience of the client’s engineers. This identified the key risks, particularly in respect to time-dependent degradation mechanisms, that required detailed assessment to establish remnant life.
Consideration of key threats, included: – Internal corrosion – External corrosion and CP performance – Fatigue driven by pressure and temperature cycling – Mechanical and environmental loading
Detailed integrity assessments
Detailed integrity assessments were performed for each pipeline over the proposed extended operating period. Internal corrosion was assessed based on service conditions, fluid composition, corrosion modelling, available in-line inspection data, and pressure test results. External degradation was evaluated through review of coating condition and cathodic protection system effectiveness, with allowance made for continued deterioration and integration of survey and inspection data where available. Operational fatigue assessments considered both historical and forecast pressure and temperature cycles to evaluate fatigue damage accumulation during extended operation.
Outcomes
The LTE assessments delivered pipeline-specific outcomes, including:
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Confirmation of continued fitness-for-service
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Definition of allowable life extension durations
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Identification of necessary mitigation and remediation actions
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Specification of inspection, monitoring, and integrity management requirements for extended operation.
The study provided a robust and auditable technical basis for safe continued operation of offshore pipeline systems beyond their original design life, supporting informed asset management and regulatory assurance.
With these assessments, the client has obtained the required verification body certification to continue pipeline operations beyond 2025.
For more information, visit www.jee.co.uk/integrity-management
To contact our Head of Integrity Management, Graham Wilson, email graham.wilson@jee.co.uk, or call +44 (0)1732 371 371.
Jee Ltd
