Abstract
Oil and Gas plants consist of a set of heat exchangers, which are used in recovering the waste heat from product streams to preheat the oil. The heat transfer coefficient of exchangers declines considerably during the operation period due to fouling. Fouling in heat exchangers is a complex phenomenon due to the acceleration of many layers of chemical substances across tubes of heat exchangers resulting from chemical reactions and surface roughness. In this paper, the fouling process was determined as a critical failure in the heat exchanger. Failure is an accelerated fouling layer across the heat exchanger tubes, which can be the reason for the clogging of tubes. Hence, a risk assessment was conducted using the Risk-Based Inspection (RBI) approach to estimate the probability of fouling in heat exchangers. The results showed that the RBI approach can be used successfully to predict the suitable time to shut down the plant and conduct the fouling cleaning process.
Highlights
Any processing plant consists of a large number of critical and non-critical equipment that run continuously to fulfil the operating requirement
Where ER is the estimated risk, PoF is the probability of fouling, and CoF is the cost due to the consequence of failure (more details of this cost can be found in Equation (4))
Risk-Based Inspection (RBI) application of fouling layers across tubes has become an applicable approach in oil and gas plants to avoid dangerous consequences resulting from plant shutdown to conduct maintenance activities
Summary
Any processing plant consists of a large number of critical and non-critical equipment that run continuously to fulfil the operating requirement. A cleaning of fouling is a dominating activity in the maintenance of heat exchangers to restore the efficiency of equipment and mitigate any threat that may occur during the normal operation of the plant. To remove deposits across tubes of heat exchangers, mechanical and chemical techniques (Routine Maintenance) can be applied during normal operation of equipment (Figure 1); it is necessary to shut down equipment to execute maintenance activities to avoid increased fouling layers, which may result in unexpected consequences on humans and infrastructure of a plant. The cleaning process of heat exchangers or any piece of equipment is very costly due to the shutdown period of the plants and the cost of cleaning materials and labor. Minimizing the cleaning cycle period based on the cleaning method or maximizing the operating time before the shutdown may reduce the total cost of routine maintenance. The optimization of cleaning schedule results showed a saving of 23% of maximum potential savings
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