Session: 02-11-01 Reliability Based Maintenance

Submission Number: 175610

Optimizing OPEX Using a Comprehensive Risk-Based Inspection Approach for Fixed Offshore Structures 

The oil & gas sector is facing major challenges in an era of energy transition, like dealing with increasing cost pressures whilst managing aging offshore facilities in depleting oil & gas reservoirs, thus encouraging operators to innovate and search for opportunities to reduce OPEX. This is why it is quite timely that the upcoming second edition of ISO 19901-9: Structural integrity management (SIM) Standard for fixed offshore structures (hereinafter STANDARD) will introduce powerful SIM toolkits to manage asset integrity efficiently.

The STANDARD (whose Project Leader is the first author of this paper) is scheduled for publication in late 2027 and will then become the over-arching global SIM standard. An important feature of the STANDARD is the introduction of a Risk-based Inspection (RBI) approach, which addresses an industry need for a holistic RBI framework that can be implemented consistently across all offshore facilities worldwide, akin to API 580 for mechanical equipment and pipelines. Presently, lack of RBI provisions for offshore structures in mainstream international standards creates uncertainties amongst engineers and discourages its global adoption. This motivated the STANDARD’s Project team, comprising of top international technical experts, to develop a practical RBI approach. This will encourage operators to implement optimized subsea inspection plans for their offshore facilities, based on the underlying principles of the RBI methodology.

One first such variation of the RBI approach, which will be included in the STANDARD, has been implemented by Eni Energy Netherlands who appointed Rosenxt Group for a pilot project (hereinafter PROJECT) on their offshore facilities in the North Sea, Dutch sector. In the PROJECT, the general principles of the RBI methodology have been successfully implemented to optimize subsea inspections on an operating Wellhead Jacket and a Production Platform’s Substructure.

There are three RBI methods used in the PROJECT, defined in the STANDARD as Qualitative, Semi-Quantitative and Quantitative methods. This paper focuses on Qualitative and Semi-Quantitative methods only. Fully Quantitative method, being numerically intensive, is required only when Semi-Quantitative methods cannot adequately address exceptional situations e.g., Wave-in-deck conditions and was thereby not included in the PROJECT scope.

The Qualitative method uses a set of weighted rules to categorize offshore structures within a fleet of assets based on their risk rating, which determines the inspection frequency and inspection type (pro-active or reactive). This brings a first cost optimization to the inspection effort and allows an Operator to focus on their most sensitive assets.

Semi-quantitative methods are meant to optimize the inspection plan at the component level of structures and are of two types – Simplified and Advanced method.

·       Simplified method is suitable for structures with broadly acceptable or tolerable risk rating and makes use of available assessment and inspection data (and does not require additional analyses).

·       Advanced method incrementally then overlays the contribution of individual structural components (joints and members) to the overall structural system strength, in addition to the criteria of Simplified method. This results in more focused inspection strategies that can be directed towards the critical components of a structure.

The RBI methodology enables OPEX investment on risk-based decisions rather than prescriptive rules (that are frequently based on design fatigue lives). The novelty in this RBI approach (besides achieving cost-optimizations) lies in uniquely identifying non-redundant critical links in a structure that potentially go undetected using traditional inspection approaches.

A high-level summary of results from the PROJECT has been presented in the paper that demonstrates significant savings achieved in subsea inspection scope, through reduced inspection frequencies, effective inspection techniques and optimized structural components identified for risk management measures. Another key takeaway highlighted is that implementing the presented comprehensive RBI approach also enhances asset safety. The paper will be referenced in the STANDARD, with the intention of familiarizing and encouraging operators around the world to adopt similar RBI methodologies on their offshore facilities. This will drive consistency of approach towards implementing Risk-based inspections on global facilities in the energy sector.

Presenting Author: Partha Dev Rosenxt UK Limited

Presenting Author Biography: Partha Dev has 36 years of offshore structural integrity management experience in the energy sector. He heads the Offshore Engineering Structures discipline of Rosenxt Group, Aberdeen UK and delivers holistic structural integrity management solutions for offshore facilities worldwide. In the past, Partha has led on major capital projects of the North-west shelf of Australia on Gorgon, Wheatstone, and North Rankin Redevelopment Projects in technical authority roles with several oil & gas operators including Chevron, Woodside Energy and Engie. Partha represents the International Organization for Standardization (ISO TC67 SC7) as the Project Leader of ISO 19901-9, 2nd edition (Structural Integrity Management of Fixed Offshore Structures).

Authors:

Partha Dev Rosenxt UK Limited
Hermann Meurou Eni Energy Netherlands BV
Hannah Scurr Rosenxt Group