A contribution to reliability qualification of new technical equipment: – with focus on subsea production equipment

Abstract

This PhD thesis proposes new frameworks and methods which give new insights to qualification and reliability assessments of new subsea systems. The subsea oil and gas industry is an industry with strict requirements to the reliability of their equipment. The provision of new subsea technology with an acceptable level of reliability is a prerequisite to achieve high production availability, low maintenance costs and less consequences such as oil spills to the environment or other types of accidents.

Before a new technology or a new system is accepted for use, the equipment supplier must convince the operator that the reliability of the new technology/ system is sufficiently high. This may be accomplished through a technology qualification program (TQP).

The objective of this PhD project has been to develop systematic approaches that contribute to the reliability qualification of new subsea equipment and to the following-up of reliability in the operational phase.

The main contributions from this PhD project are:

• A technology qualification framework which is integrated with a product development model, and highlights the key features of commonly used TQP approaches.

• A method for reliability prediction of new subsea equipment based on comparison with similar topside equipment and using the available field data.

• An approach for how to consider and monitor human and organizational factors (HOFs) influencing common cause failures (CCFs) in the operational phase. Along with suggestion of supplementary questions to be added into the IEC 61508 approach for determining CCF factor.

• An approach for failure rate updating during various product’s life cycle.

• An approach for reliability prediction of offshore oil and gas equipment operating in arctic environment based on proportional hazard model and the levels of data availability.

• An approach for outlining the reliability improvement process for subsea equipment that can be integrated with the product development process of Murthy et al. [57]. The results of this thesis may academically be used by researchers with interest in the same research field and practically be used by producers, suppliers, end users, decision-makers and other organizations within the field of subsea equipment and oil and gas industry. The generic principles from the proposed frameworks, or methods with minor modifications can also be applied for other new equipments in other industry sector where high reliability is a requirement, such as military, aviation, and so on. Therefore, it is important to share the contributions and ideas for further work with others. The contributions have been presented in eight articles, where two have been published in international journals, one have been submitted for publication, and five have been presented at conferences and have been published in conference proceedings. Currently, there are several TQP approaches have been suggested, but only two of these approaches are mainly used in the Norwegian offshore oil and gas industry; one proposed by Det Norske Veritas (DNV) in their recommended practice DNV-RP-A203 and one based on NASA’s technology readiness levels (TRLs) approach. Combinations of the two approaches are also used. This PhD thesis presents and discusses the main TQP approaches highlights challenges related to methodological and procedural issues and provides a set of suggestions for improvement. Criteria are established to facilitate comparison and identification of strengths and weaknesses of the TQP approaches. These results, combined with a thorough literature review, have been used to develop a framework that is practical for qualifying new subsea systems. As part of the TQP, reliability analyses and predictions are performed in the early stages of product development process. Currently, no practical method is available that can be used to extrapolate the available reliability data from similar and known systems and come up to a failure rate prediction for new systems operating in a different environment. This PhD thesis suggests a practical approach on how to predict the failure rate of new subsea systems that has been adapted (i.e., “marinized”) from known topside systems. The reliability assessment should not finish when the equipment enters the operating phase, but should be followed-up during the operational and maintenance phases. Safety-instrumented systems (SISs) are important safety barriers in many technical systems in the subsea industry. CCFs represent a serious threat to the reliability of SISs. For quantitatively incorporating the effects of CCFs, the beta-factor model is often used. During the operational phase of SIS, the hardware architecture and the components will usually remain unchanged. Therefore, any changes in CCF might be as a result of factors including environmental exposure or human and organizational acts. This PhD thesis highlights the importance of HOFs in estimation of β for SISs during the operational phase.In addition this PhD thesis suggests a set of supplementary questions to the existing methods of beta estimation for SIS such as IEC 61508 approach, for more accurate determination of beta-factor. HOFs are difficult to predict, and susceptible to be changed during the operational phase. Without proper management, changing HOFs may cause the SIS reliability to drift out of its required value. This PhD thesis also proposes a framework to follow the HOFs effects and to manage them such that the reliability requirement can be maintained. Failure rate prediction provides a quantitative basis for decision-making regarding the adequacy of a design from the early phases in the life cycle. In reallife operation and maintenance, the operating and environmental conditions may change compared to what was assumed by the producer in the design and development phases. Changes in these conditions and unexpected disruptions may make the current predicted failure rate inaccurate and updating is required as a response to such disruptions and changes. This PhD thesis discusses the need for failure rate prediction in the various phases of a product’s life cycle and proposes a framework for updating the failure rate prediction to obtain a more realistic prediction. As the offshore oil and gas industry is currently considers moving into the arctic region. The harsh arctic environment will have an unavoidable influence on the reliability of the equipment operated in it. To understand this influence is of vital importance to ensure the reliability of the equipment and the production availability of the systems. Several types of data, such as data on design, production, usage intensity, and operating environment are required to assess and verify the reliability of the equipment. This PhD thesis proposes a framework for reliability assessment based on proportional hazards modeling and various types of data. It presents important arctic factors influencing the physical performance and discusses how these may influence the reliability of the equipment. Developing a product with high reliability cannot be achieved overnight and the subsea industry has to adopt a long-term improvement strategy and needs to learn from other industries that are exposed to similar strict reliability requirements, such as the nuclear, aviation, and space industries. This PhD thesis outlines how to integrate continuous reliability improvement into the various phases of the development of new subsea equipment, according to the product development model of Murthy et al. [57]. The areas for further research regarding this PhD project and proposed frameworks and method can be classified into three categories: (1) Development and improvement of proposed frameworks and method, (2) Practical implementation of them into existing industry practices, and (3) Handling of uncertainty.