## 2 Materials and Methods
### Experimental Work Data Input  
There were two phases during the experimental work. The initial phase embraced the preparation, setup, testing, and calibration of the entire probe for the CUI experiment based on the Official Guide for Laboratory Experiment of Corrosion under Insulation (ASTM G198-07) specification, while the second phase was the modified experiment which is suited to the main parameters from the historical field data analysis [14]. Three main items, the insulation, rings specimen, and the solution reservoir, were properly prepared. The Perlite insulation in the initial phase was prepared according to ASTM G189-07, while in the modified phase, calcium silicate insulation (2.5-inch outside diameter and 1.6-inch thickness) was placed around the testing section to provide the annular space to retain the test environment, as shown in Figure 2a. For the rings specimen, a piping material of carbon steel grade A106B, density 7.86 g/cm\({}^{3}\) with a 2-inch diameter, 0.2-inch thickness, and specimen area of 9.58 cm\({}^{3}\) was used for both phases. Each ring specimen was surface finished, ground to 600 grit, soaked into a chemical cleaning solution which contained 1000 mL hydrochloric acid (HCl sp. Gr. 1.19), 20 g antimony trioxide (Sb\({}_{2}\)O\({}_{3}\)) and 50 g stannous chloride (SnCl\({}_{2}\)), and placed in an ultrasonic cleaning machine, S30H Elmasonic. The cleaning process was set to 3 min per specimen and dried using a dryer to ensure no pits or particles occurred on the rings' surfaces and weighted as initial mass to the nearest 0.1 mg according to the ASTM Practice G1-03. The ring specimens acted as test electrodes in two separated electrochemical cells, by a dam (bigger Teflon ring of 3.0 inch outside diameter) as presented in Figure 2b,c. The Teflon spacers were machined from the same spacer material, polytetrafluoroethylene (PTFE) resins. During the experiment, the carbon steel rings separated by Teflon spacers were held by blind flange pipe sections on both ends, as in Figure 2d. The solution reservoir is the solution that represents an atmospheric condensate with impurities of acids and chlorides found in industries. The solution made contained 100 ppm NaCl dissolved in reagent water and 1 M of sulfuric acid, H\({}_{2}\)SO\({}_{4}\), with pH 6. The flow of this solution was controlled by a micro-metering pump with a maximum capacity of 30 mL/min and a maximum stroke frequency of 300 strokes per minute. The pumping flow rate was tested and stabilized until the dropped solution was 5 mL/min with 14 strokes per minute. For one accelerated CUI experiment (accelerating the corrosion process), the wet and dry condition was controlled with a duration of 20 h wet and 4 h dry for each cycle minimum for 72 h continuously. The benefit of the accelerated CUI experiment, especially to study the performance of the CUI rate regarding the time elapsed, can be found in [15]. In the completed CUI cell run, both electrochemical cells comprised three (3) rings specimens. The center ring was used as the working electrode (WE), while the other two rings were used as the reference electrode (RE) and auxiliary electrode (AE) connected to a potentiostat, as in Figure 3a,c. The ring specimens acted as test electrodes in two separate electrochemical cells and were monitored by a Gill AC-1493 Sequencer software package specifically for the linear polarization resistance (LPR) function. The LPR function was used because it responded fast and could detect the changes in the corrosion rate during the experiment in minutes. Figure 2: The initial phase of the experiment (**a**) Preparation of insulation material; (**b**) The corrosion under insulation (CUI) cell mock piping with blind flanges; (**c**) The ring specimens after surface finishing; (**d**) Preparation of the carbon steel ring specimens and a Teflon spacer. As the CUI cell experiment should simulate the real field condition, the internal piping condition was filled with the synthetic oil, immersion heater, and temperature controller, as in Figure 3c,d.