Subsea High Integrity Pressure Protection System Design per IEC 61508
MetadataVis full innførsel
High-integrity pressure protection system (HIPPS) is one of various implementation of safety instrumented system (SIS) utilized in oil and gas production and it is installed to perform its safety instrumented function (SIF) by protecting flowlines and risers from overpressure situations. HIPPS offers a lot of savings in equipment cost and IEC 61508 provides general requirements for its design and implementation. Hardware requirements for HIPPS design includes but not limited to hardware fault tolerance, safe failure fraction, testing and diagnostics, accounting for systematic errors and quantification of probability of failure on demand. The high-integrity requirements of HIPPS must be verified during design. Redundancy is built into HIPPS and this can result in CCF and high probability of spurious trips. This should be taken into account during design. To ascertain integrity requirements are met, the PFDavg can be assessed using FTA which shows logical trail of component failures leading up to the system failure. FTA and approximation formulas can also be used to quantifying the spurious trip rate associated with a given HIPPS configuration.The main objective of this thesis, the design of subsea HIPPS per IEC 61508, is to prove compliance to existing and known reliability requirements in the oil and gas industry. The reliability analysis was carried out by first identifying the role of the HIPPS in the event of an accident and selecting the subsystems that make up the HIPPS. Other relevant concept for implementation was also applied. The quantitative analysis was performed using the fault tree method on assuming static behaviour for HIPPS and CARA FaultTree was used. Spurious trip rate for this particular configuration was also calculatedIt was found that with 2oo4 sensor, a logic solver and final element configured as 1oo2 and the HIPPS assumed operating in low demand mode, SIL 3 requirement is met. Analysis identified improvement areas within the Logic solver. Failure from this key component must be avoided and its reliability can be improved through adequate redundant design, improved testing methods and interval and protection against common cause failures.