Qualification and reliability in subsea electrical applications

Determination of life in subsea electrical systems continues to be a difficult challenge. The performance of materials in the subsea environment has many influences and determining the long-term effects of seawater under multiple stress conditions can be a daunting task. Historically, many of these factors have been captured in standards that provide a starting point for design margins and qualifications. These specifications undergo continuous improvement with the intent to show higher safety margins and increased performance based on ever changing industry requirements. As a larger knowledge base is accumulated around the effects of long-term pressure and voltage on materials, choices that are more educated can be made in the qualification regimes of new and existing products. Statistics provides one of the most useful tools for this effort, enabling a quantifiable rating to be given to a product's operational and reliability performance. This has the potential to definitively establish safety margins by providing realistic estimates of life based on probability. As an example, ODI has employed the use of statistical analysis capabilities to evaluate electrical breakdown values during accelerated qualification testing to determine a voltage rating for its product. This is a requirement that goes beyond the standard specification, but provides valuable insight to the performance of the product. This paper will highlight how experience and knowledge is used to provide a statistical basis for the understanding of information gained from accelerated life and qualification testing. It will explore some of the methods and expectations related to these analyses and show that statistical analysis can be used effectively to provide an increased understanding of the long-term effects of multiple stress conditions on a component/system, particularly as it relates to subsea electrical applications.