SHEAR STRESS SIMULATION AND DESIGN MODIFICATION OF ROTATING CAGE AUTOCLAVE (RCA) IN CORROSION STUDY OF API 5L X60 AND 5CT L80 STEEL AT CO2 AND H2S ENVIRONMENT

• Main Author: Pratiwi, Irma
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/49033
• Institution: Institut Teknologi Bandung

Corrosion is a common problem in the oil and gas industry. Metal pipeline is the most vulnerable component that is attacked by corrosion. Besides transmitting crude oil, pipeline transmit corrosive substances as well such as brine, CO2, and even H2S. Fluid flow rate inside the pipe can cause thickness decreasing of the pipe as well due to shear stress. Simulations and experiments in the Laboratory were carried out in order to duplicate field condition. The rotating cage method is the widely used method for screening materials, crude oil, and corrosion inhibitors. This study aims to understand the hydrodynamic condition in the form of shear stress profile on the surface of rotating cage specimen in existing and modified design and to find out the effect of temperature, rotation speed, crude oil content, and inhibitor concentration on the corrosion rate of specimen. An ANSYS Fluent simulation is performed to picture shear stress profile on specimen surface. Rotating Cage Autoclave (RCA) testing was conducted to determine the rate and type of corrosion in CO2/H2S environment. This RCA testing was conducted in high H2S concentration where pCO2/pH2S ratio is 35. In Indonesia, RCA testing at high H2S concentration has never been done before. Viscosity measurement was carried out to obtain the brine viscosity at various temperatures. The research showed that in the existing design, the highest shear stress was 89.31 Pa at the leading edge of specimen at 715 rpm rotation, while in the modified design, the highest shear stress was 10.52 Pa at parallel position to the stirrer’s wing at 715 rpm rotation. An increase of temperature up to 80oC increases corrosion rate of X60 steel specimen, whereas in L80 steel, an increase in temperature from 80oC to 120oC decreases corrosion rate. The highest inhibition efficiency is 88.60% that is shown by the addition of 50 ppm inhibitor at 80oC.