SET OF SPECIFICATIONS OF THE FLOW LOOP EXPERIMENTAL TESTING (Corrosion)
1. 2. 3. 4. 5. 6. 7. 8.
Bibliographical study about existent flow loop testing systems. Defining the ranges of the operating conditions in the flow loop system. Sizing the tank and choosing its material. Sizing the pipelines and choose its material. Choosing the pumps. Choosing the valves. Sizing the injection systems (CO2, H2S, Corrosion inhibitors…). Choosing the corrosion monitoring technics. (Corrosion Coupons).
C.Gouta
1. Bibliographical study about existent flow loop testing systems: Within the petroleum industry, there are several flow loop-testing systems, those systems were designed to simulate the field conditions in a laboratory scale. Those systems are widely used I the petroleum companies laboratories. This paper expose two-flow loop testing systems designed to monitor the corrosion via several technics but we will focus only on the corrosion coupons.
1.1 Flow loop-testing system designed by Jepsen This system is design by Jepsen in the purpose of simulation the field conditions in a laboratory scale. This experimental system do assess the corrosion inhibitors efficiency by injecting them in the loop of a single or a multiphase liquid.
1.1.1 Description of the flow loop The experimental setup is shown in Figure 3 The system consists of a 1.2 m3 316 stainless steel tank, which serves as a storage and separation unit for the multiphase oil/water/gas mixture. The temperature in the system is maintained by two Chromalox 3.75 kw heaters present in the stainless steel tank. A 3.73 kw. Vertiflo centrifugal pump, pumps the oil and water mixture into a 7.6 cm ID PVC pipeline. The flowrate is controlled by valves and a bypass. The flowrate is measured by an orifice meter in the PVC section. The liquid is then forced under a gate into the 10 m long, 10.1 cm ID Plexiglas pipeline where it forms a fast moving liquid film. Carbon dioxide from compressed cylinders is allowed to first pass through an expansion tank before it enters the system. The carbon dioxide enters at H, downstream of the gate G. The carbon dioxide is also used to pressurize the system. The system pressure is monitored by gauge B. Oil, salt-water and carbon dioxide are used as the working fluids. By measuring the wetted perimeter of the pipe that is contacted with liquid and the film depth, the area of flow and the mean velocity of the liquid film is calculated. The liquid film velocity is used to calculate the Froude number as described earlier. Downstream of the gate G a stationary slug is generated. The hydraulic jump is maneuvered and kept stationary at the test section by controlling the gas flowrate into the pipeline at J1 and by the backpressure valve. A Cole-Palmer rotameter is used to measure the gas flowrate into the system. The liquid-gas mixture flows into the storage tank where the gas is released into the atmosphere while the oil-water mixture is recirculated.
Figure 1: Layout of the Experimental System
1.1.2 Description Testing Section The test section is illustrated in Figure 2. It consists of a 2 m long, 10.1 cm ID plexiglass pipe. At position A and B, flush mounted Electrical Resistance (E.R.) probes, manufactured by Rohrback Cosasco, are inserted to measure the corrosion rate at the top and the bottom respectively. At position B a coupon holder is inserted. The coupons are flush mounted and are used for weight-loss measurements and for Scanning Electron Microscopy (SEM) studies. The coupons are made of 1cm diameter, 0.4 cm thick 1018 carbon steel to simulate pipeline conditions. Four coupons are placed on a holder and, inserted flush with the pipe wall. At position E, a flush mounted TSI hot-film sensor is used to measure the wall shear stress and turbulent intensity of the flow at the wall of the pipe. Pressure tappings are located at points D and measure the pressure drop across and within the slug body using an U tube manometer. The manometer is filled with a Meriarn blue colored fluid of specific weight 1.75. Probe C consists of a 6 mm. diameter sampling probe which is used to withdraw fluid samples to measure the void fraction and oil-water fractions across the slug body. This tube is also used to test the pH as well as the concentration of oxygen, and iron ions present in the system.
Figure 2: Test Section
1.2 Top-of-line corrosion testing flow loop system 1.2.1 Top of line corrosion definition Top of the Line Corrosion occurs in the transportation of wet gas when significant heat exchange between the inside of the pipe and the outside environment is present causing the water vapor carried by the wet gas to condense on the interior wall of the pipe. Due to gravity forces, most of the condensed water drains to the bottom of the pipe and a thin film of condensed water forms on the sides and at the top of the internal pipe walls (see Figure 3).
Figure 3: Liquid condensation inside the pipe
1.2.1 Experimental procedure The Institute for Corrosion and Multiphase Technology at Ohio University, Athens Ohio, has build, with a support of the company TOTAL, an experimental flow loop especially designed for the study of the Top of the Line Corrosion. A schematic representation of the loop is presented in Figure 1. The flow loop, mainly made of stainless steel 316, can be divided in three main parts: the tank, the pump and the loop.
- The tank is used for the storage and the heating of the water. It is filled with dionized water and acetic acid is added to reach the specific concentration required in the tests. Two heaters immerged in the water warm the liquid. The mixing of water vapor and carbon dioxide occurs at the upper part of the tank.
- The pump moving the gas is a positive displacement progressive cavity pump. It is continuously lubricated with water from the tank. - The 4” diameter flow loop is 30 meters long and horizontally leveled.
The gas mixture of water vapor and carbon dioxide flows along the pipe and the condensation of water occurs as this mixture contacts the cooled section of the loop. The test section where the measurements are taken, is located 8 meters after the exit of the tank. The test section (Figure 2) is a 1.5 meters long pipe spool. Four probe ports are installed (two at the top, two at the bottom). The copper coils enrolled around the pipe act like a heat exchanger forming the condensation device. Sample of condensed liquid and pH measurements can be taken at the test section. The experimental procedure is as follow: the tank is first filled with 1 m3 of de-ionized water and carbon dioxide is injected in the loop at a specific pressure. The water is then heated up to the specific temperature by two electrical resistance heaters. The pump is started and the vapor-gas mixture flows in the loop. If de-oxygenation is needed, the system is flushed until the concentration of oxygen is low enough (150 ppb). When condensation is required, the test section is cooled using the condensation device and the condensation rate is set. When the steady state is reached, the corrosion probes are introduced in the test section and the experiments begin. A data acquisition device is used in order to continuously measure the inlet and outlet temperature of the gas and of the cooling liquid at the test section, the total pressure, the condensation rate and the cooling liquid.
Figure 4: Top of the line corrosion loop schematic
