Strategies for reliability in oil and gas
14 November 2011
A plant breakdown or accident in the oil and gas sector can have huge financial implications, which puts a strong emphasis on maximising safety, reliability and performance in every aspect of operation. These three crucial factors are not independent of each other – it is impossible to maximise plant safety and performance without addressing reliability.
Reliability is influenced by many factors, ranging from the inherent reliability of individual components to the overall complexity of a plant, its operating conditions and the effectiveness of its maintenance regime. It is, therefore, essential when specifying and acquiring new plant to adopt a proactive approach to ensuring reliability from the outset.
The first factor to consider is how the risk of failure can be designed out. A gravity fed water supply system, for example, will always be more reliable than one that depends on pumps, as gravity is unlikely to fail. Simplicity is the next key factor – the fewer components used in a system, the less likely it is to fail. Simplicity should, therefore, always be the aim in plant and equipment design.
Next, consideration should be given to reducing the likelihood of failure by selecting components with a known low failure rate, over-sizing the components, and ensuring that they are appropriately rated for the ambient conditions in which they will be used.
The underlying aim of enhancing reliability is to minimise the impact of failures on safety and productivity, so it is also pertinent to consider measures that are intended to deal with, rather than prevent failures. These include containment, so that the influence of the failure is limited, and reducing time to repair by, for example, adopting standard assemblies – such as withdrawable switchgear units – that can be replaced quickly and easily.
Duplication of equipment and building in redundancy also fall into this category as they offer a radical and, unfortunately, costly approach to minimising or even eliminating the effect of failures. These techniques are widely used in the oil and gas sector and they are often appropriate. Nevertheless, careful consideration should be given to the potential benefits before they are adopted.
The underlying issue is that duplication and redundancy significantly increase initial costs and the burden of maintenance. These factors may well be outweighed by the benefits, but this is not always true. A second consideration is that, in some cases, duplication and redundancy may not deliver the benefits that they appear to promise.
This is usually because common mode failures have either not been properly considered or are impossible to eliminate. A simple example is where the duplicate devices are installed in the same room and the temperature within the room rises to the point where their normal operation is disrupted. In such a case, the benefits of duplication would be minimal, as the duplicate devices would be susceptible to simultaneous failure.
Achieving optimum reliability is a complex task which requires the use of equipment that has been designed from the outset with reliability in mind, access to extensive engineering expertise, and an in-depth understanding of the applications for which the equipment will be used.
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