## 1 Introduction  
Corrosion is a natural phenomenon associated with metals that leads to material destruction. Corrosion is an engineering problem, as well as an economic problem as the financial losses associated with corrosion, is enormous. The cost of corrosion worldwide in 2017 [1] was shown to be approximately 3.4% of the global GDP ($2.5 trillion). The same published study showed the cost of corrosion in the US to be 3.1% of GDP ($276 billion). In India, the cost of corrosion was estimated as 2.4% of the GDP in 2011-12 [2]. Pipeline accidents, due to corrosion, are frequent in the oil and gas industries. A study conducted by Saudi Aramco in 2013 concluded that the cost of corrosion for their operations was around $900 million per year [3]. Corrosion is not completely avoidable, so the industry needs to find ways to monitor, control, mitigate, and reduce corrosion. Implementing a proper corrosion management approach in the industry requires an in-depth understanding of corrosion mechanisms and implementing reliable methods to assess the corrosion rate [4]. Corrosion assisted by flow causes severe damages to oil and gas pipelines, heat exchanger systems in process industries. Maintenance and replacement of these corroded components are very expensive. The corrosion rates depend upon many factors, such as dissolved oxygen concentration, temperature, total dissolved salts, pH, fluid dynamics, and presence of scale on internal surfaces [5]. [PERSON] [6], in his studies summarizes that the corrosion assisted by flow varies according to the material under investigation and with the exposure conditions. He also states that flow generally increases the corrosion rates, but in some special cases, the effect can be the opposite. Rotating disk electrode method and impingement jet systems are two conventional methods used to measure the corrosion rates in a flow system. In the work of [PERSON] et al. [7], a correlation between mass transfer and flow is developed using the rotating cylinder method to evaluate the corrosion of High Strength Low Alloy (HSLA) steel in 3.5% NaCl solution. However, it is not always possible to reproduce the exact flow patterns occurring in the pipeline system in the rotating cylinder device. A flow loop system provides a more realistic environment to evaluate the actual corrosion rates in a pipeline system [8]. The corrosion rate of steel in a flow loop system can be estimated using weight loss methods, electrochemical methods, and other methods, such as corrosion characterization, and acoustic emission measurements. [PERSON] et al. [9] investigated the corrosion rate at a pipe elbow using the electric resistance method to study the effect of the thermal flow field on corrosion rates. The corrosion rates were measured at a temperature range of 50-150 \({}^{\circ}\)C and flow velocities of 0-6 m/s, and the corrosion rate was found to have a nonlinear relationship with velocity [9]. Temperature and fluid velocity were the only two parameters that varied. Weight loss methods give an average corrosion rate over a period of time, but the measuring process takes a long time. The great difficulty with the weight loss method is the ability to hold all process parameters constant for a long period of time to see the effect of one parameter on the corrosion rate. For a pipeline, there are so many parameters that can affect its corrosion rate, each of which tends to have an exponential effect on the corrosion rate that most methods give poor and irreproducible results. Electrochemical techniques are ideal for the study of corrosion in pipelines--particularly the linear polarization resistance (LPR) method, since the measurement is rapid (less than 5 min), does not affect the sample, and can be automated to perform continuous measurement of corrosion rate. For this method to work, the material should be polarized typically on the order of \(\pm\)10 mV compared to the Open Circuit potential, when there is no net current is flowing.