As energy companies move towards major decommissioning projects, there is a need to establish balanced and consistent criteria for establishing post-decommissioning inspection plans for subsea pipelines left in situ. One of the most effective strategies for addressing the post-decommissioning phase and managing any pipelines left in-situ is the implementation of a risk-based inspection plan.
The risk profile of a decommissioned pipeline differs significantly from when it was operational and risk based inspection plans are, therefore, crucial for several reasons. Firstly, they help identify the potential hazards that decommissioned pipelines may pose to other users of the sea. By performing survey trending exercises, companies can determine how the seabed is changing over time and assess the likelihood of buried pipelines becoming exposed, or for exposed pipeline to develop freespans. This information is vital for preventing accidents and ensuring the safety of maritime activities.
Secondly, the plans allow for a structured approach to assessing the risks associated with decommissioned pipelines. The development of a tailored risk matrix allows companies to evaluate the likelihood and consequences of potential hazards specific to the decommissioning project, ensuring that inspection intervals are correlated with risk levels, providing a clear framework for ongoing monitoring and maintenance. An expert inspection plan is also a key factor in aiding in a decommissioning project’s regulatory compliance, ensuring it abides by industry best practice.
Subsea engineering consultants Jee Ltd aided a client in the creation of a risk-based inspection plan for pipelines which had been left in-situ within a decommissioned field in the Southern North Sea. The pipelines included in the scope of work were all buried and had been subject to pre and post decommissioning surveys. The client was now required to agree a legacy inspection plan with OPRED for the pipelines in question and engaged Jee to support them with this.
Jee was asked to perform a survey trending exercise for the pipelines to identify the presence of any features that could present a hazard to other users of the sea, and to determine how the adjacent seabed was changing over time. The results of the trending exercise provided crucial information on the risk the pipelines posed, the likelihood of the buried pipelines becoming exposed in the future and the potential timeframes over which this could happen.
Jee was also asked to develop a risk-based assessment process that the client could use for risk assessing of any other pipelines that they decommissioned in-situ within the UKCS. To meet this objective, Jee developed a risk matrix tailored specifically for assessing pipelines decommissioned in-situ. The likelihood and consequence definitions in the matrix were made specific to decommissioned pipelines, and suggested inspection intervals were correlated against risk matrix positions. Jee presented the proposed risk matrix to OPRED and other stakeholders, along with the rationale that was used to build it and ultimately arrived at a position where OPRED approved the client to use the risk matrix going forward.
Jee then risk assessed the pipelines within the scope of work against the approved risk matrix and developed a proposed legacy inspection plan which was then submitted to OPRED for acceptance. The success of Jee’s project meant that the client now has a regulator approved framework for risk assessing all their UKCS pipelines which are decommissioned in-situ. The benefit this provides is consistency in legacy pipeline inspection planning.
In conclusion, risk-based inspection plans are essential for managing decommissioned subsea pipelines. They provide a systematic approach to identifying and mitigating potential hazards, ensuring the safety of maritime activities and the integrity of pipelines. The case study of Jee’s project demonstrates the Life after decommissioning- the importance of inspection plans for in-situ pipelines effectiveness of these plans and highlights their importance in achieving regulatory approval and maintaining consistency in legacy pipeline inspection planning.
For more information on Jee, visit www.jee.co.uk or call +44 (0)1732 371 371.
