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53 NACE INTERNATIONAL: VOL. 56, NO. 5 MATERIALS PERFORMANCE MAY 2017 intrusive technique, which was developed based on the electrical resistance between two points. Based on Ohm's Law, given a constant electrical current, the EFM will measure the voltage between two points, which is directly proportional to the elec- trical resistance. The electrical resistance will vary depending on the resistivity of the metal and the volume of metal that will carry the electrical current. The measured electrical resistance will increase as the current carrying volume is reduced (i.e., as wall thickness is reduced due to corro- sion). 15 The configuration of the EFM sys- tem consists of 112 mild steel pins where the diameter for each pin is 6 mm (0.25 in) and the distance between each two pins is 25 mm (1 in). This article discusses the lab- orator y experimental program that was conducted to assess functionality and reli- ability of th e EFM t echniqu e for field applications. Experimental Procedures Three CS spools (internal diameter : 150 mm [6 in] and length: 300 mm [12 in]) were machined and welded with appropriate ports for gas in and out. Each spool con- tained a specific field simulated environ- ment representing a specific corrosive con- dition. An EFM system containing 112 pins was then installed between the 4 to 8 o'clock position of each spool. The system's pins covered the target location from the 4 to 8 o'clock positions. All test spools were connected in series with one inlet and out- let for the gas mixture for purging pur- poses. Figure 1 shows the experimental setup for the test spools. After that, the spools were carefully cleaned by using an acidic solution and dis- tilled water. Then, high total dissolved sol- ids (TDS) (field water with 24,000 TDS and pH = 3.5) solution was prepared and used for Conditions 1 and 2. Condition 3 was exposed to 10% hydrochloric acid (HCl) solution with pH = 1. Blended corrosive gas contained 0.1 mol% hydrogen sulfide (H 2 S), 0.39 mol% car- bon dioxide (CO 2 ), and was balanced with nitrogen (N 2 ). It was used in Spools 1 and 2 only. The blend gas was refreshed in Spools 1 FIGURE 1 Experimental setup. FIGURE 2 XRD analysis of an actual field sludge deposit collected from an oil pipeline. and 2 once per week for 15 min at 70 kPa (10 psi) pressure. After that they were kept under low pressure, ~40 kPa (6 psi) with no circulation f low. Spool 3 was exposed to acidic solution with 10% HCl. This spool was connected to a pump to circulate the acidic solution and no blend gas was introduced. The x-ray diffraction (XRD) analysis (Figure 2) indicated that the field deposit consisted mainly of calcite phase, which is ~85 wt%; and 8 wt% of pyrite (FeS 2 ) and 3 wt% of mackinawite (FeS). Some traces of palygorskite, quartz, and barite were observed in the XRD pattern.