Bottom-of-Line (BOL) corrosion inhibitor design and production has been a successful story and a mature technology in oil and gas industry. However, preventing Top-of-Line (TOL) corrosion with inhibitors is very challenging, and even more challenging when pursuing dual functional corrosion inhibitors that serve for both BOL and TOL at the same time. Designing a dual functional corrosion inhibitor for both BOL and TOL is a difficult and challenging task, with several hurdles to overcome in this endeavor. Some of the difficult issues are: calculate the treating weight between the top of line and bottom of line, how to make the combined products perform effectively for both top and bottom of lines, how to make the low and high volatile molecules for mitigating BOL and TOL corrosion to be compatible and homogenous in a single blend.
More than 60 active components were used to develop more than 30 formulated products. These products were screened using a TOL rig, RCE and RCA methods to pare down the products. These were then subjected to various physical properties such as flash point, viscosity requirements, emulsion and foaming tendencies as well as thermal stability issues. Finally, two products were selected that satisfied all desired chemical characteristics and performance.
One BOL and TOL combined product denoted as TB-3 was developed for treating both BOL and TOL applications. TB-3 is a water-soluble product that exhibited excellent thermal stability up to 110°C and demonstrated high efficacy in corrosion inhibition for both BOL and TOL applications under sweet or sour conditions with or without the presence of organic acids.
TOL corrosion is reported to occur in large diameter wet gas pipeline in stratified flow conditions due to low fluid velocities1 . With increasing distance from the inlet, the wet gas pipeline becomes cooler as it loses heat to the environment. Such cooling causes water, hydrocarbon, and other high vapor pressure species to condense on the pipe wall. The upper part of the pipe will constantly be supplied with freshly condensed water while the less corrosive water saturated with corrosion products will be drained along the pipe wall to the bottom of the line. The presence of acidic components in the gas phase, such as CO2 and H2S, promotes corrosivity in gas transportation and production pipelines. The condensation of water can occur at the top of the pipeline due to the temperature difference of the top and bottom sections of the flow line. This condensed water can be corrosive when the acid gases and low molecular weight organic acids become dissolved in it. The condensed water and CO2 undergo a hydration reaction to form carbonic acid (H2CO3, eq 1). The dissociation of carbonic acid leads to hydrogen and bicarbonate ions (eq 2). H2S will dissolve in condensed water to produce hydrogen and bisulfide ions (eq 4) and further dissociation would yield another hydrogen ion and a sulfide ion (eq 5) 2. These ionic species are in equilibria. Although normal oil field brine carries various ionic species such as bicarbonates to control pH, the condensed water does not carry salt. Therefore, without pH controlling salts, these soluble acid gases and volatile organic acids dissolved in condensed water can be corrosive with low pH, as shown in the following reactions:
