CC513 - 2008 Assignment #3

Corrosion Inhibition in Cleaning Acids

You will find the necessary information to solve the following problem in two Modules, i.e. Electrochemical Techniques and Corrosion Inhibitors.

In this problem, you are asked to decide on the appropriate inhibitor X concentration to reduce the corrosion of your cleaning acid equipment made of carbon steel by a factor of 20. You have requested your technical laboratory to carry out four linear polarization resistance (LPR) measurements. You were sent the following four plots:

• No inhibitor

• 15 ppm of inhibitor X

• 25 ppm of inhibitor X

• 50 ppm of inhibitor X

Use these curves to answer the following questions. In answering these questions you can assume that |b_a| and |b_c| are both equal to 0.1 V.

1. Evaluate the corrosion currents and corrosion rates (mm/y) of carbon steel in the acidic environment plus ...

   • 0 ppm inhibitor

   • 15 ppm inhibitor

   • 25 ppm inhibitor

   • 50 ppm inhibitor

2. Calculate the corrosion inhibition efficiency of:

   • 15 ppm inhibitor

   • 25 ppm inhibitor

   • 50 ppm inhibitor

3. Draw a curve of the corrosion rates as a function of inhibitor concentration. Hint: you should expect an exponential relation between the inhibitor concentration and corrosion rates (CR).

4. Deduce, from this plot the optimal inhibitor concentration to achieve your goal, i.e. extending the life of your equipment by a factor of 20.

OK, you still need help! Please follow these steps:

1. Go to the main index page

2. Look under the letter L

3. Click on the following link: Linear polarization resistance (LPR)

4. Or, alternatively you can search the the Web with Google for "linear polarization resistance" to discover that the Corrosion Doctors Web is the best source of information after all.