It holds that when a hard part fails, the soft parts have to be replaced as well (see Section 2.3). Therefore, the costs are the same as scenario 1 plus the price of the failed hard parts. Costs are the same as scenario 1, plus 0,3 SC, which is the average price of a hard part in a regulator or monitor, based on data of Gasunies Purchasing department. Therefore, costs are 1,3 SC (regulator or monitor) and 0,93 SC (aid and pilot pressure regulator).
Opportunistic and preventive replacements
Scenario ‘OM’
Costs are 0,5 SC for regulators and monitors, based on costs of material and an estimated extra repair time of a number of hours (confidential information), in comparison with the scenario that no OM is performed.
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Scenario ‘PM’
Costs are 0,86 SC for regulators and monitors, based on the costs of a scenario 1 replacement minus the costs of transport of components in scenario 1. Transport costs of components to the technicians in the particular region can be done opportunistically, when the replacement is planned on forehand. Extra costs and a summary of costs per scenario
Extra costs due to first visit/summary of costs per scenario
As explained in Section 2.2, there are costs possible next to the described costs in this appendix, due to the required visiting the GDS when a failure occurs during operation. These costs only occur when the failure occurs during operation. Based on expert opinions, the duration of these visits is
estimated. The visits are nearly always done by two technicians. The costs per visit can be estimated to be equal to the resulting wage costs plus the transport costs. Because these costs only occur during operation, these costs can be multiplied by the ratio of failures detected during operation, as are given in Section 2.7. Using these ratios and the same costs for wages and transport as in the rest of this Appendix is done, the expected costs of visits per replacement can be calculated. Results are given in Table 24. In this table, the prices of all other scenarios are summarized as well.
Replacement scenario Replacement costs (SC) per replacement Avg. costs (SC) of visit after regulator failure Avg. costs (SC) of visit after monitor failure
Avg. costs (SC) of visit after aid & pilot pressure regulator failure Scenario 1 r&m 1,00 0,10 0,11 0,00 OM r&m 0,50 0,00 0,00 0,00 PM r&m 0,86 0,00 0,00 0,00 Scenario 5 r&m 1,30 0,10 0,11 0,00 Scenario 2 r&m 12,33 0,10 0,11 0,00 Scenario 3 r&m 23,80 0,10 0,11 0,00 Scenario 4 r&m 14,67 0,00 0,00 0,00 Scenario 1 a&p 0,61 0,00 0,00 0,09 Scenario 5 a&p 0,91 0,00 0,00 0,09 Scenario 2 a&p 4,20 0,00 0,00 0,09
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Appendix H: Data analyses performed to estimate the failure rate of gas pressure control components
This appendix explains the method of data analysing that is used to perform the analyses towards the failure rates of the three types of gas pressure control components. The two types of SAP data analyses are already explained in Section 2.5. Tis appendix gives potential drawbacks of these methods. Then is explained why and how a number of small adjustments is done on the detected failure rates. Finally is given which method is used to find the failure distributions and parameters that are presented in Section 2.5.
Drawbacks of the used research method in the first and second analysis
There are a number of drawbacks of the described methods of estimating the failure rates of the soft parts of the gas pressure control components of Gasunie. Certain factors influence the reliability of the orders and announcements in SAP. These are:
Technicians sometimes do not provide (easy to understand) explanations of their
observations and maintenance activities. These explanations are hard to understand as an outsider;
A large part of the component failures is caused by other problems. However, discovering these causes takes a long research time, because the explanations of the causes are often in other announcements by technicians;
The texts in the announcements were analyzed to estimate which part exactly failed. This analysis is subject to human errors and misunderstandings;
Because the last preventive replacements of soft parts at the GDSs are performed between 1991 and 1997 (differs per GDS), the number of analyzed pressure control components older than 19 years old is low. Nineteen years is the difference between 2016, the last year in the SAP analyses, and 1997. This probably reduced the detected failures at ages of 19 years and older;
SAP is introduced in 1999. The orders and announcements before 1999 are unknown. They are in the previous database Rayondis, but it would take too much time to collect these data. The given drawbacks resulted in a number of adjustments to the detected data. These adjustments are described in the following paragraph.
Analyses and adjustments of the results of the first and second analysis for regulators
For the analysis of failure rates, the last factor in the list of drawbacks of last paragraph, is most important. The result of the last factor is that there is no information about failures until 1999. Because the last preventive replacements of soft parts of gas pressure control components were between 1991 and 1997 (differs per GDS), there is very little information about failures in the first seven years of the lifetime of the soft parts. Therefore, a report of 1996 [7] is used to determine the failure rates for the first seven years. This report gives the number of failures per year on regulators, monitors and aid and pilot pressure regulators during the years 1988/1994.
The results of the first analysis, the second analysis and the information of the first seven years of regulators, were merged into Figure 6 in Section 2.5. In Section 2.5 is explained how the data in [7] is used to determine the failure rates of the first 7 years of regulators.
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Analyses of monitors and aid and pilot pressure regulators
The analyses of failure rates of soft parts of monitors and aid and pilot pressure regulators are done in a similar way as the analyses of the regulator soft parts. The information from [7] is used to determine the failure rates for the first seven years. This information is merged with the data from the first and second analysis to determine the failure rates.
Estimation of parameters
The estimations of parameters are performed in a Engineered Software Inc. (1999). This CD contains a software program developed specially to determine failure rate distributions and corresponding parameters of input data such as failure data.
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Appendix I: Code changes at standard model in order to perform sensitivity analyses