Optimization of Design, Safety and Cost of Pressure Protection Systems
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The purpose and application of the High Integrity Pressure Protection System (HIPPS) has been explored, both in general and in the specific case for Kristin. As the HIPPS was a fairly novel off- shore technology in 2005, the examination of how the system was introduced on Kristin, which challenges to overcome and how it is currently operated established some early considerations and ideas for the later parts of the thesis. This was in particular installation considerations and points of emphasis for the design approach. Also during the introductory parts were the presentation of the potential for the HIPPS as a tool for cost saving, and the relevancy that brings to the present situation.While thinking of the introduction of a HIPPS as a measure towards cost efficiency is not unfamiliar, the thesis additionally brings up how to implement this measure in the most efficient way possible, with a proposed guideline in figure 8.1. This guideline builds on four main steps - Design screening, SIL requirement, SIL verifiaction and LCC analysis - and aims to streamline the integration of reliability- and cost-optimization within the design process.The particular considerations when installing a HIPPS were primarily examined through two methods, and were highly influencial for the later stages of the report. The first method was through discussions and small presentations from Statoil employees, where they explained what kind of operational and natural obstacles they needed to overcome in order to conduct safe drilling operations on Kristin. A notable takeaway from these were the relative importance of limiting downtime caused by HIPPSs, as the main cause for profit loss. Relative is here meant in comparison with other cost-reducing factors. The second was through studying internal Sta- toil documents, where operational experiences were examined. These resulted in the under- standing of why vigilant testing is so important, as there are no real demands to analyze on the employed HIPPSs to date.Four design alternatives were concluded upon as examples for the proposed process, and were analyzed in order to find the most efficient alternative. The special considerations surrounding each specific design were also examined and discussed.The factors that were deemed the most important in the design and operation of HIPPSs were: Safety Integrity Level (SIL) requirements including internal frequency demands for overpressure scenarios and the already existing Protective layers (PLs); Maintenance and operational factors, which are essential to the performance of these low demand systems, and were examined in order to make a comparison between designs with different emphasis on and basis for maintenance; Cost factors, which were central throughout the thesis, and are important fac- tors for the current use and future development of HIPPSs; Eligibility for tie-ins and extensions were chosen as a factor at an early stage of the process, but did not prove to be hugely influential, partly due to the already existing tie-in opportunity on the subsea templates; Reputational risk is more of a qualitative term, but with huge potential consequences which are important to keep in mind.After examining which factors that were the most important for the four design alternatives, and understanding which inputs were needed in order to do an analysis and comparison be- tween them, the relevant data were identified and presented. Some of it were gathered at Statoil, while some were gathered from external sources or through estimates.The literature study was initially focused on Life Cycle Cost (LCC), and how this could and should be employed towards this particular system. The study expanded through the process, to include accident cost challenges and SIL requirements. The change in the literature study was partly due to the change of direction the thesis took during the process, which are discussed in chapter 8.2.The proposed design approach is in some ways a natural product of the sequence of the objectives. That starts with understanding how and why HIPPSs are employed, and the changes it can make. The design approach follows the objectives throughout the merging of the different approaches for LCC analysis from the literature study, and ends up in a design approach that can be followed as it currently exist. It also has a lot of potential for growth, adjustment, and specification.The final conclusions from chapter 7 are both quantitative in terms of a specific design alter- native recommendation, and qualitative through a methodical guideline and important design factors.