Session: 01-01-03 Offshore Platforms-3

Submission Number: 185520

System Based Calibration and Validation of Assessment Levels in ISO 19901-9, Second Edition (Fixed Offshore Structures) – Part 2 of 2 

ISO 19901-9 (second edition), Structural Integrity Management (SIM) Standard for Fixed Offshore Structures (hereinafter STANDARD), is anticipated to be published in late 2027. It has been developed as a global over-arching Standard with the main intention to:

·     create a holistic Assessment Framework (based on semi-probabilistic, reliability and risk-informed level-based approaches) with provisions for analytical methods that will ensure consistent safety levels representing the structural reliability implicit in the ISO 19900 series of Standards, and

·     define acceptance criteria for all Assessment levels that can be used to demonstrate fitness-for-service (FFS) of all fixed offshore structures globally.

The oil and gas industry sees need for a holistic assessment framework that can assist in performing robust fitness-for-service assessments to ensure safe and continuous production on offshore facilities. While the STANDARD has a bounty of diverse content relating to structural integrity management, an important feature is the inclusion of a structured assessment framework that satisfies the two above stated objectives. The framework includes level-based assessment approaches, each of which comprise of one or more analysis methods. Listing them in a hierarchical ladder, they are defined as Level 1 (Linear methods); Level 2 (Nonlinear methods); Level 3 (Structural Reliability Analysis methods); and Level 4 (Risk informed method).

The FFS pathway requires that the assessment to demonstrate structural compliance starts at Level 1 and if the outcome is unfavourable, the assessment may either proceed to a higher level or implement risk management measures, including, but not limited to, structural repairs or changing the platform consequence category. The key feature of this pathway is that when one moves up from a low assessment level to a higher level, there is a transition from less complex, yet conservative approach, to a more technically arduous (demanding higher engineering competency and experience), but less conservative (and more structure specific) approach. This can only be achieved when the assessment methods and their acceptance criteria are calibrated across all approaches in the framework.

Consistency in acceptance criteria across the assessment levels  is achieved through a structural reliability model that captures the environmental characteristics of different regions, as well as the load variability in random sea states. On the strength side the reliability model captures the ultimate strength of offshore platforms, accounting for the uncertainty in component and system strength, accumulated over many years of testing.

The authors constitute the core team responsible for developing the technical requirements for the STANDARD’s Assessment clauses. Through this paper, their aim is to present an overview of the assessment methods along with their acceptance criteria, and illustrate how the reliability model provides a means of establishing consistent levels of safety across:

(i)              regions with different environmental characteristics,

(ii)            installations with different consequence categories, and

(iii)           each of the hierarchical levels of assessment, whereby demonstrating the calibration between the assessment methods.

After introducing the methods, they are later presented in the order of Levels 3, 2 and 1, because Structural Reliability (Level 3) forms the basis of calibration of lower assessment levels. In addition, important validation points are highlighted which link back to the rich experience base with API RP 2A and ISO 19902.

The Assessment framework can also be implemented for life extension or repurposing projects. Thereby it is expected to become a valuable resource that will immensely benefit the offshore oil and gas industries including lower carbon energy sectors for Late Life Asset Management.

The exhaustive content of this technical work is split into two papers. This paper should be read in conjunction with OMAE2026-180926 Part 1 of 2, which showcases the Assessment Framework included in the STANDARD along with details of Level 3 (Structural Reliability Analysis method). The details of the Levels 1 and 2, along with their calibration and validation across all Assessment methods are covered in this Part 2 of the paper. The conclusion and all references called out in both papers are also located in this paper.

Presenting Author: Prof. Mike Efthymiou The University of Western Australia

Presenting Author Biography: After obtaining PhD in Civil & Structural Engineering, University of Manchester, UK, Mike worked with Shell for over 30 years in a wide range of roles, including research & development, execution of major oil & gas projects and as Engineering Manager for offshore facilities in Europe, Middle East & Africa. Mike played a pioneering role in the development of FLNG technology in Shell including the first implementation of this technology in Prelude FLNG operating offshore Australia and holds several Patents in these technologies. Mike is recognized internationally for his pioneering contributions to the offshore Oil & Gas industry, notably in structural reliability, safety and fatigue and for the impact of these contributions in shaping ISO Standards for offshore Oil & Gas facilities.

After retiring from Shell in 2013 Mike was appointed Professor of Offshore Structures at University of Western Australia which evolved into Adjunct Professor after 2022. In 2014 Mike was appointed to the Board of Directors of Cyprus Hydrocarbons Company, a role that he still holds.

Authors:

Prof. Mike Efthymiou The University of Western Australia
Partha Dev Rosenxt UK Ltd
Dr. Ramsay Fraser Kent plc.
Frank Puskar FJP Consulting