Processing plants consist of thousands pieces of equipment that operated continuously under harsh operating conditions resulting from overpressures and fluctuated temperatures. Some pieces of equipment usually subject to various maintenance strategies during the normal operation of plant. However, there are critical pieces of equipment that can't be inspected and maintained during the regular operation of plant unless plant facilities are totally shut downed in order to execute TAM event. In general, TAM activities of some oil and gas companies is based on recommended periods of the Original Equipment Manufacturers (OEMs). However, this suggestion is not the most optimum strategy in the long-term due to operating conditions and economic conditions that vary significantly from company to another [1]. Lawrence [2] reported that oil and gas plant facilities that operated continuously under overpressures and fluctuated temperatures must be shut downed operations to subject essential maintenance, modification and inspection work every few years to avoid any extreme consequences may impact production and production units. Therefore, TAM is one of major activities to oil and gas companies to avoid any a decrease in the availability of operating facilities and to lose in the profitability [3] due to a rise in the cost of the TAM event and a decline in the revenue which may be amounting to millions of dollars. Duffua and Daya [4] reported that TAM is a periodic maintenance during a certain period to perform inspections, repairs, replacements and modifications that can be executed only when the entire plant facilities are shutdown.  If plant shutdown interval between TAM cycle is too long. This will result a decrease in the production loss and a decrease in the inspection and maintenance cost. However, the expected risk will be high. Therefore, this work presents a framework to determine an optimal interval of TAM for processing plants based on the pressure drums to increase reliability and availability of plants.