## 2 Literature Review
The findings show the effect that different maintenance costs have on the economic benefits of an opportunistic maintenance strategy. [PERSON] et al. [26] established an efficient strategy in view of accessibility for offshore wind turbines to decrease maintenance costs. A failure rate based on minimal data has been estimated using the Weibull distribution with a three-parameter process approach. The opportunistic maintenance plan was implemented to minimize maintenance costs by optimizing the preventive maintenance age and an acceptable maintenance age. [PERSON] et al. [27] used the analytical hierarchy method and the other planning approaches for implementing maintenance plans based on analysis of the failure rate of the system and maintenance costs, respectively. [PERSON] et al. [28] also suggested a delay-time model to prevent system failure during the preventive maintenance cycle when the machines were damaged. [PERSON] et al. [29] proposed a strategy based on preventive maintenance for the manufacturing plant. The authors measured the criticality of the machines in the line and then categorized the machines. [PERSON] and [PERSON] [30] presented several practical solutions for enhancing reliability in the systems of arm loading. The purpose of this study is to prevent oil shipment delay. The previous study gives an insight about the normal behavior of similar equipment under the effect of aging. In other words, it shows the effect of wear out of such equipment. Additionally, it gives the impact of the changing operating conditions that might be experienced throughout the lifecycle of the unloading system. [PERSON] et al. [31] simulated the tank truck loading operations in a fuel distribution terminal to generate a theoretical simulation of the tank truck loading operation, which helps in improving the efficiency and effectiveness of the tank truck loading systems. Probability theories have been used to simulate tanks queuing for different fuel types aiming to improve the queuing policy. A simulation of varying fuel flow rates and number of fuel loading arms has been tested to come up with the new queuing policy. The results show that the simulation of the new optimum queuing policy has a more efficient use of resources than the previous policy, which was based on first-come-first-served. [PERSON] and [PERSON] [32] dealt with a maintenance-based reliability approach for a machine-scheduling problem. The authors proposed a nonlinear mixed-integer model to simultaneously increase efficiency, and reduce maintenance, delay, and interrupting costs. [PERSON] et al. [33] introduced an optimization model based on a reliability-based maintenance approach for the preventive design of corrosion, addressing the environmental effects and costs of the life cycle. The findings of their study showed a reduction in environmental impacts and life cycle costs using the proposed model. Based on the above literature review, it is clear that no study has assessed and evaluated the reliability of truck unloading systems. Even though international standards cover the minimum requirements for these systems, the design improvement and the maintenance scheduling to maintain uninterrupted operation needs to have a clear assessment of the effect of each component to the overall system reliability. Consequently, the aim of this study is to fill the gap of the previous works. In addition, this paper presents an operation strategy of the truck unloading system, the failure modes of the components within the system, and a bottom-up approach to the reliability of the system. It assesses the truck unloading system reliability during the operating lifecycle to the end of its useful life, investigates the effect of the preventive maintenance on the truck unloading system reliability, and identifies the major contributors to the system reliability for design improvement purposes.