Estimation of Shutdown Schedule to Remove Fouling Layers of Heat Exchangers Using Risk-Based Inspection (RBI)

1. Introduction

In general, any processing plant consists of a large number of critical and non-critical equipment that run continuously to fulfil the operating requirement. These pieces of equipment undergo periodically or non-periodically planned maintenance on the short or long time during their life cycle, taking a risk factor into account to avoid any defect or failure that may cause disastrous consequences during the normal operation of the plant. Therefore, the critical pieces of equipment cannot be subject to inspection and maintenance activities unless the plant is under an entire shutdown to conduct the maintenance activities. Maintenance is a philosophy resulting from a variation of its implementation from a company to another due to several aspects such as an economic aspect, the geographical conditions, and process configuration. Sahoo [1] indicated that a shutdown philosophy is scheduled maintenance of the plant to minimize downtime to maximize the efficiency of a plant. For instance, many processing companies have used turnaround terminology rather than shutdown terminology to execute maintenance activities of critical equipment. Levitt [2] stated that “a shutdown is a melting pot in accelerated time, which means that people will be operating at or near their limits”.

A planned shutdown is one of the biggest activities of maintenance for any processing plant in terms of manpower, materials, time, and costs. Emiris [3] stated that shutdown is primarily proactive maintenance because all facilities of the plant are out of service to perform inspections, repairs, replacements, and modification periodically, thus rendering this maintenance of paramount importance to avoid any threat that can have a significant effect on the reliability and efficiency of the system. Plant shutdown normally depends on the maintenance activities related to the critical equipment pieces [4]. Heat exchangers are one of the critical equipment pieces and a vital indicator to estimate the interval and duration of the shutdown.

Many critical failures overlapped on each other in heat exchangers, which require more time to identify them using RBI. Six critical failures in heat exchangers are identified: clogged flow due to fouling layers, leakages, vibration due to misalignment, internal and external corrosion, and cracks of the shell due to exceeding design pressure and allowed temperatures. A fouling layer is considered as the common failure in the heat exchangers...