A non-toxic corrosion inhibitor based on organic
compounds was developed to replace a heavy metal toxic inhibitor in MEA plants.
The tasks involved in the development program are presented in this hot topics
series.
A search for non-toxic organic chemicals with
potential inhibitive properties was performed first followed by the preliminary
screening tests. The best three chemicals were then tested in stirred autoclave
at several concentrations.
Slow strain rate runs were also performed to test the
susceptibility of welded as well as non-welded carbon steel specimens to stress
corrosion cracking. The single best performing chemical was then tested under
turbulent and laminar flow conditions in a flow loop. High alloys materials
typically found in amine plants were also tested in an autoclave setting to
determine if they were compatible with the inhibitor. The single best performing
inhibitor was then finally tested in a refinery gas plant for 18 months.
This article provides an introduction to inhibition
in Amine plants and the overall scope of this data development effort.
Subsequent articles will describe the data obtained and relevant analytical
trends.
Amine plants, using MEA as a sweetening agent, always
exhibit some degree of corrosion. The latter is minimized by keeping the amine
clean, holding acid gas loading within specifications, operating the still at
the lowest temperature possible and maintaining a regular testing
program.
Compounds based on inorganic, toxic materials such as
arsenic are still used as corrosion inhibitors in many amine plants around the
world. However, most manufacturers, especially in the USA, are not producing
these chemicals anymore. Due to non-availability of these toxic materials and
other environmental and safety problems in their disposal/storage, alternative
non-toxic and organic chemicals are needed to solve the corrosion problem.
These articles present the methodology used to
develop a non-toxic corrosion inhibitor for replacement of a heavy metal toxic
inhibitor in a MEA plant used for CO2 removal. The tasks involved in this
program included:
1. The search for candidate compounds.
2. The screening tests on all candidate inhibitors to select the best
performing inhibitor compatible and their optimum concentration .
3. The autoclave tests to verify corrosion behavior of the best
inhibitor and to test Stainless steel and Monel materials.
4. The slow strain rate tests for evaluation of SCC of steel base
metal and welded specimens with and without inhibitor.
5. The dynamic flow loop tests to simulate field flow conditions.
6. The field test.
The process for the search for candidate corrosion
inhibitors compounds involved extensive literature, patent, and computer
database searches of commercially available chemical agents with potential
viability for use as corrosion inhibitor formulations. The search was based on
several requirements including solubility, temperature stability, cloud point in
amine solvents. Additional requirements were that none of these compounds were
based on inorganic, toxic materials such as arsenic. Thirty six (36) corrosion
inhibitors based primarily on organic constituents compatible with MEA and
meeting all the requirement specified above were selected.