Added Values From CFD on Equipment Troubleshooting Diagnosis

Computational Fluid Dynamics (CFD) is branch of fluid mechanics that uses numerical analysis to simulate and solve fluid flow within products or systems operating under real-world conditions. It is a powerful tool that has numerous benefits in the oil and gas industry. Very often, CFD simulations are performed at design phase to ensure that equipment designed will achieve the desired performance. Similarly, CFD simulations can also be used to analyse existing equipment to ensure that it can adapt to new operating constraints and objectives. This paper focuses on the added values brought by CFD in diagnosing issues faced by a heat exchanger due to a change in its operating condition. A heat exchanger was reported to have perforated tubes, and a lab report showed that it was due to naphthenic acid corrosion (NAC) attack. Plant operators tried to resolve this by injecting a corrosion inhibitor (CI); however, the tube perforation still occurred. A CFD study was performed to understand and investigate the reason why tube perforation persisted even after CI introduction. The inlet and outlet areas of the heat exchanger were checked, as these areas corresponded to the tube perforation locations. CFD results showed presence of dead zones within the heat exchanger. A direct correlation was established between perforated tube locations and the dead zone locations where high acid Heavy Vacuum Gas Oil ( HVGO) had accumulated over time. Infinite contact time between the high acid HVGO and tube walls at these dead zones had subsequently rendered the CI ineffective. This led to direct NAC attack on the tube walls. Based on these findings, a countermeasure has been proposed and validated through CFD. The results show that dead zones are no longer present within the heat exchanger. Positive feedback from plant operators has been received, as no similar issue had been raised after three years since implementation. In second case study, the flow behavior within fire water system was replicated by means of CFD. Results show presence of deep vacuum within the overboard piping line during the operation of Pressure Control Valve (PCV). This led to huge force spike and pipe surge at the top pipe segment. Installation of vacuum breaker was recommended. Without being able to visualize the internal flow in the heat exchanger via CFD, it might have been difficult to anticipate the root cause behind this tube perforation. "X-ray vision" provided by CFD, gave engineers a better understanding of what had occurred, hence enabling us to pinpoint the exact root cause of the issue. This approach of troubleshooting and diagnosing equipment via CFD had not only provided significant cost cuts by minimizing physical assessments but had also delivered prompt responses and quick solutions to plant operators, ensuring fast turnaround.