ABSTRACT

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 paper. 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. The corrosion rates data, analytical results and physical inspection of the field equipment showed that the non-toxic corrosion inhibitor was very effective in reducing corrosion. Based on the results of the laboratory and field testing program, it was decided to replace the previous toxic corrosion inhibitor by the newly developed non-toxic corrosion inhibitor.

INTRODUCTION

Amine plants, using MEA as a sweetening agent, always exhibit some degree of corrosion. The latter is minimized by keeping the amine clew 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. This paper presents the methodology used to develop a non- toxic corrosion inhibitor for replacement of a heavy metal toxic inhibitor in a MEA plant used for C02 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.

SEARCH FOR CANDIDATE COMPOUNDS

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 volubility, 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.

SCREENING TESTS

The initial screening tests consisted of exposing two duplicate carbon steel specimens in 4 oz. jars filled with C02 saturated 20% MEA solution and 1000 ppm inhibitor at a temper

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