Session: 04-01-06 Flexible Pipes VI

Submission Number: 176276

Life Extension of Unbonded Flexible Risers and Flowlines in Subsea Applications – Experience From North Sea Assets 

A significant number of offshore assets in the North Sea are now operating at or beyond their original design life. Industry best practices for integrity management recommend conducting life extension assessments to support decisions on the continued operation of subsea pipeline systems beyond their intended service period.

Reliable life extension is becoming increasingly important as operators seek to manage ageing infrastructure in a cost-effective manner while maintaining regulatory compliance and protecting company reputation.

Assessing the life extension feasibility for flexible pipes presents unique challenges due to their complex construction, use of advanced materials, wide range of potential failure modes, and the limited availability of proven, practical inspection and monitoring techniques.

This paper presents key insights and lessons learned from life extension assessments carried out on approximately 500 dynamic and static flexible pipes across 10 offshore assets in the UK and Norwegian sectors of the North Sea over the past decade. These pipes were originally designed for 20-25 years of operation, with proposed life extensions ranging from 25 to 60 years.

The paper focuses on sharing typical findings and engineering learnings, specifically:

· A practical approach to the life extension assessment process.

· Common design gaps identified during the gap analysis phase – often resulting from changes in design codes and standards since the original pipe design.

· Typical uncertainties and vulnerabilities revealed during current condition evaluation and risk assessment phases – frequently driven by significant changes in operating conditions or limitations in inspection and maintenance programs.

- Examples where risk evaluation relies on the findings from post-retirement inspection and testing (dissection).

In addition, the paper discusses issues that cannot be resolved through follow-up analyses or inspections and addresses frequently asked questions related to the process of extending the service life of flexible pipes. The paper also includes a brief discussion on the potential uses of monitoring solutions for risk management during periods of extended operation.

Presenting Author: Damir Tadjiev DT Engineering Consulting on behalf of 4Subsea

Presenting Author Biography: Damir Tadjiev is a Chartered Engineer with over 15 years of experience in the integrity management of subsea pipeline systems. With an academic background in materials science and mechanical engineering, his expertise includes risk-based assessment and inspection planning, anomaly evaluation, corrosion analysis, integrity status evaluation as well as lifetime extension assessments for ageing pipelines.

Authors:

Damir Tadjiev DT Engineering Consulting on behalf of 4Subsea
Andreas Gjendal 4Subsea