Reliability modeling of subsea SISs partial testing subject to delayed restoration

Abstract

Subsea oil and gas production has always involved the challenging task of determining the overall reliability of safeguarding systems, such as safety instrumented systems (SISs). Partial testing and delayed restoration of SISs are the main issues in operation and maintenance activities. This paper proposes a novel reliability-modeling methodology for subsea SISs subject to partial testing and delayed restoration. The proposed methodology incorporates an increasing failure rate in conjunction with dangerous undetected failures for the final elements. Approximation formulas for evaluating the average probability of failure on demand are derived for SISs in the lowdemand operating mode. In addition, the effects of degradation are modeled by following Weibull rules in different subsequent partial testing intervals. In contrast to previous works, the present research accounts for delayed restoration after detecting failures and also considers the repair time for different scenarios. The proposed formulas are compared with the existing ones for partial verification. A case study on the shutdown valves of a subsea highintegrity pressure protection system is presented to illustrate the feasibility of the proposed methodology. It is also proven that the proposed approximation offers a robust opportunity for testing strategy optimization and performance improvement of SISs.

Reliability and availability modeling of Subsea Autonomous High Integrity Pressure Protection System with partial stroke test by Dynamic Bayesian

“…According to the literature, 10 the coverage of PST is 60% and the coverage of functional tests is 100%;…”

“…14 Advantages and disadvantages. As a supplement to functional testing, 10 PST is introduced in two different ways:…”

“…Repaired the faults detected by PST and functional tests, and the equipment was restored as new; 2. According to the literature, 10 the coverage of PST is 60% and the coverage of functional tests is 100%; 3. PST shall be conducted once a month and functional test shall be conducted once a year.…”

“…Frequent functional testing is impractical for offshore oil and gas exploration and production. 9,10 For HIPPS valves, FT can fully verify whether the valve can be closed as required. However, because of the strong stress FT may cause some damage to the valve.…”

Reliability and availability evaluation of subsea high integrity pressure protection system using stochastic Petri net

“…13 Innal et al 14 developed a general formulation of SIS using a multi-stage Markov model based on PST and different repair time effects. Wu et al 15 proposed a reliability evaluation method for SIS final components with time-varying failure rates, using the Petri net model for analysis, and the Weibull distribution was also used to analyze the degradation of the final components to develop an approximate evaluation formula for the average failure probability involving degradation. Jin et al proposed partial test and proof test simplified formulas for computation of the average on-demand failure probability.…”