Techniques Used in Research for the Prevention of Top-of-the-line Corrosion Figure 1: Schematic of Internal Pipeline Corrosion Issues
Condensed droplets/ film on top of line
Top-of-the-line corrosion Otherwise, batch treatment of inhibitors32,33,38 via pigging1,39,40 can
reach the top of the line. This is a complex and costly process that can only be carried out periodically and the inhibition effect needs to persist between treatments.1,41,42
A final approach that has been Vapour (gas) phase
explored is the use of continuously injected volatile corrosion inhibitors, which are intended to equilibrate between the liquid phase at the bottom of the line and the condensed water phase at the top of
General (uniform) corrosion
Underdeposit corrosion
Hydrocarbon (oil) phase Aqueous (water) phase
Solid debris deposit
The vapour (gas) phase will include hydrocarbons, H2O(g) and probably some CO2(g), CH3COOH(g) and H2S(g). In addition to condensed droplets at the top of the line, there may also be a condensed film, possibly flowing, on the sides of the pipe wall.
Figure 2: A Test Loop System Operated at the Institute for Energy Technology in Norway for Top-of-the-line Corrosion Studies
Ion exchanger Iron generator
Owing to the potential environmental and financial consequences associated with pipeline failure, strategies to avoid failure resulting from top-of-the-line Corrosion are necessary.
Mixing module To test sections Ejector Flow meter From test sections Venturi cone
Laboratory Approaches to the Study of Top-of-the-line Corrosion
Heating Cooling
TLC is one of the most complex forms of corrosion for which to reproduce the requisite conditions in a laboratory experiment and it is even more difficult to make meaningful measurements. The complex inter-related heat flow and mass flow processes arising due to transport
Low pressure tank Tank I © NACE International 2007. Source: Anderson et al., 2007.21 High pressure tank Tank II
Figure 3: Flow Loop System Operated at Ohio University for Top-of-the-line Corrosion Studies
A necessary condition for top-of-the-line corrosion to occur is condensation of water at the top of the line. The rate of condensation has been modelled for well insulated and less well insulated pipelines.
of gas that is cooled, resulting in condensation of some components of the gas, even before considering the chemical equilibria and kinetics involved in the corrosion reactions at the steel surface make it extremely challenging to reliably simulate field conditions.
© NACE International 2009. Source: Singer et al., 2009.22 Flow-through Systems (Flow Loops) Inhibition in Existing Infrastructure
Chemical inhibitor formulations are widely used to protect mild steel pipelines from internal corrosion.29–35
Continuous injection of inhibitor
can effectively guard against bottom-of-the-line corrosion.30,31,36 Continuous injection of inhibitor is not expected to be able to treat the top of the line (under stratified flow conditions). A creative solution to this has been proposed using ‘spreading inhibitors’,37 information is available on the application of this approach in the field.
but little 72
Owing to the numerous dynamic processes involved, TLC is a very difficult phenomenon to reproduce in the laboratory. Any simulation involving a flow of humidified hot gas entering a cooled section of pipe to generate condensation necessarily requires large and rather complex apparatus. Laboratory approaches to simulating TLC conditions therefore usually involve approximations or compromises.
Using a ‘pipe’ to achieve TLC requires a massive throughput of fluid (gas and maybe liquid). Even a recirculating ‘flow loop’ represents a
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 1
Volatile corrosion inhibitors have been suggested to operate via increasing the pH and/or promoting the formation of protective corrosion product scales.1,20,21,25,26,44,46
the line.43–45
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