Functional Safety Analysis of a Subsea Compressor Protection System

With the fast growing demand of resources from the society, comes a much greater need for a more reliable and safer industries. Accidents in the past which caused loss of lives, damage to properties and destruction to the environment have impacted us more than we can imagine. Because of this, safety standards and recommended practices have been developed by different technical organizations to guide the industry practitioners to design, validate, operate and maintain the systems in a more reliable and safer way. Risk analysis has always been practiced in the process industry and has proven to help identify, assess, quantify and mitigate the hazards that are brought by these systems. In order to mitigate these hazards, different protection layers are utilized, such as safety instrumented system, which is conceptualized through its safety instrumented function. To design, maintain and assess these functions, functional safety analysis is being carried out. This master's thesis conducts an in-depth functional safety analysis of a subsea compressor anti-surge protection system presented in a case study. First, an introduction to the topic is discussed, followed by presenting the main objective which is 'to conduct a functional safety analysis using the procedure in the standard in a subsea application', then followed by elaborating how the study is approached, and finally, discussing the limitations of the paper. After the preliminary introduction, the paper enumerates the different industry standards related to functional safety, such as IEC 61508 and IEC 61511. Important risk and reliability theories used all throughout the study, such as SIF (safety instrumented function) and SIS (safety instrumented system), are also introduced. It is the followed by a thorough literature review of the two main topics which are functional safety and anti-surge system. Lastly, different mathematical and risk analysis methods that is vital in achieving a successful functional safety analysis are elaborated. The introduction and presentation of all the important concepts is then followed by an in-depth functional analysis. The analysis begins by introducing the case study, the conditions and the main problem to be solved. It is then followed by the steps reflected in IEC 61508 and IEC 61511 until SRS (safety requirements specifications) is produced. The results from the analysis finds that the safety functions in the case study are reliable. It also suggests strategies in order to achieve the desired safety functions, solutions to the problem and ways improve the reliability of the system in the study. After results and discussion, the paper then concludes that the functional safety analysis procedures presented in the standard is applicable for subsea safety functions. It also verifies the practicality of integrating mathematical methods along with risk analysis method to find and confirm safety integrity of a safety instrumented function. The paper recommends that more studies should be conducted to formulate a specific functional safety analysis for subsea SIFs and that subsea specifications should be more established in the future.