Lab test methods to determine type of corrosion inhibitor 3

[rhackney]

Hello,

I'm relatively new to the oil and gas industry, and am in process of preparing for a job interview with a petrochemical company. During my first interview with them, they asked a question that I wasn't able to answer, so for the follow-up interview, I'm doing my best to try and come up with answers to their prior questions. I'm having a bit of trouble with one of the questions asked, however, which is summarized as follows;

>> What lab testing methods could you use to determine the type of corrosion inhibitor (broad classifications of corrosion inhibitors being anodic/cathodic/mixed, organic or inorganic, etc.)?

I've found a considerable amount of information about how to evaluate the performance of different types of corrosion inhibitors (CIs), but I'm unable to find any on characterization methods using lab testing procedures, or even where to start.

Any advice or guidance on where to start answering this question is highly appreciated, thank you in advance!

 

[SJones]

For the inhibition mechanism, generally, electrochemical testing can be deployed. Take a look at ASTM G170. For characterising the makeup of the chemical, it will be some form of chromatography or spectroscopy, such as high performance liquid chromatography (HPLC).

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[Dery Kurniawan]

Maybe, you can use Rotary Cage type for inhibitor effectiveness testing.

 

[rhackney]

thank you for the help!

 

[J Fletcher]

Years ago I worked in an R & D position where I worked on a team that studied carbon steel corrosion in oil filed environments. Some of the testing included working with corrosion inhibitors and measuring corrosion rates with electro chemistry techniques using a Gamry Instruments system and software as well as wet chemistry techniques to measure chemical and physical properties of water based inhibitors.
The electrochemistry techniques included producing polarization resistance curves in heated and stirred glass kettles. The light brine solution was deoxygenated with metered N2 flow and the test station had the capacity to provide CO2 and H2S to the test environment. The pH was monitored with a double junction pH probe and a pH controller. When the pH increased to a set point the controller triggered a pump that circulated test brine through an ion exchange resin that brought the pH down to a predetermined set point. Once a steady state corrosion rate was reached corrosion inhibitor was added and a new corrosion rate was produced.

This test technique evolved into measuring the natural inhibition of field condensate at different oil cuts and became a screening test to help pick starting parameters for testing. The Gamry Instruments probe was modified so that hastalloy material was used on reference and common electrode and the material of interest was used on the working electrode. A clear water white oil was used to develop this process. A brine concentration close to the produced water was used to obtain a base line corrosion rate. Field condensate that had already been deoxygenated by vacuum and N2 addition cycles was added to brine with a syringe. Once a new steady state corrosion rate was obtained more additions of condensate were added. Brine was subtracted to achieve higher oil cuts due to kettle volume limits. Also, the probe was lengthened so that the material would be in the water layer during higher oil cuts when test environment was not stirred.

A wet chemistry technique that measures how much water based corrosion inhibitor remains in water when introduced to an oil mixture is done in a wet chemistry laboratory with separation funnels and an analytical meter. Also, there is a foaming test where a solution of inhibitor and brine is agitated by gas flow and the head, if any, is measured. When the gas flow is stopped foam head loss is timed until there are no bubbles in solution.

Closed container constant volume testing with stirring and temperatures and pressures representing field conditions with and without corrosion inhibitors is a laboratory technique where corrosion inhibitors are tested. More than once I have seen corrosion inhibitors INCREASE corrosion rates compared to the exact same testing parameters that contained no corrosion inhibitors. It was a couple of hard weeks at work because the engineers have a corrosion prediction model and the actual corrosion rate was much higher than calculated. When the results were repeated with more testing it verified the testing technique and I earned some respect for my work and ability to follow directions.

This is a summary of test methods and not every detail of testing is provided. Hope this helps.