ABSTRACT
All equipment breaks down from time to time, requiring materials, tradespeople to repair it, and causing some negative consequences, such as loss in production or transportation delays. To reduce the number of these breakdowns, planned maintenance actions are implemented. One of the familiar planned maintenance actions is inspection. The main purpose of an inspection is to determine the state of equipment based on the chosen indicators, such as bearing wear, gauge readings, and quality of a product. The classification proposed divides the known models into four main groups of inspection strategies: single-unit systems, multi-unit systems, hybrid inspection models, and models dedicated to solving other maintenance problems. In some systems, such as critical infrastructure where the safety issues are very important, reliability analysis carried out in relation to two-state technical objects usually is insufficient. The standby units are characteristic for many engineering systems. Spare components, or systems, that are not in continuous operation are the examples of this sort of unit.
