Safety integrity level requirements in deepwater drilling — Where safety meets reliability

Safety in deep-water drilling is the top concern for companies that drill wells, oil companies, and original equipment manufacturers. Safety standards have evolved in this area pushing companies to design safer and more robust systems with which to do this complex work. The Norwegian government issued standards that require companies drilling in their waters to adhere to Safety Integrity Level (SIL) standards developed by the IEC. The true technical challenge when developing a SIL system for the drilling industry is in collecting consistent component reliability data. This data challenge occurs in most industries because each company that collects reliability data does so using their own methodology. These various methods often result in data sets that are either far more conservative than necessary or may actually discount certain failures that should be included. To design a safety system that is robust, the design team should use a method that is robust to variations in the failure rate data. Calculation of the probability of failure on demand includes the failure rate data, diagnostic coverage, test interval, and common cause failure analysis. By designing the appropriate proof tests, a safety system can be designed so that variations in the failure rate data will be less important because any fault in the equipment will be detected before the equipment is demanded in use.