Question

You were identified as the scientist of the group and were

tasked to protect a stainless-steel water vessel in which 50000 gallons of water are stored. The water has some corrosive constituents such as chlorides and dissolved oxygen. Describe, in detail, how you were to accomplish such task (name any components along with their functions plus any chemical reactions if any)

Answer 1

Chlorine (strong oxidant) dissolved in water will give Cl^- ion which is very electronegative and reactive too and hence reacts with steel and starts the rusting of steel. Chlorine in water reacts each other and forms very corrosive HClO (hypochlorous acid) and hydrochloric acid (HCl).

Cl₂ + H₂O HCl +HClO

For 316 type steel, it is suggested that to use 15-20 ppm(mg/lt) free chlorine for a maximum of 24hour followed by chlorine free water flush. Maximum residual chlorine level in water for 304 type steel is 2ppm and 5ppm for 316 type steel which is the normal and increase in chlorine level from these values for both steel may cause corrosion of steel.

Chlorine will react with dissolved oxygen and forms ClO₂ which act as a sanitizer in contact with stainless steel and less harm the steel.

Cl₂ +2O₂ 2ClO₂

Prevention of the corrosion:

1. By regular cleaning

2. Protective coating

3. Use of marine paint when metal is in contact with water

4. Use a galvanization process

5. Selection of steel: Appropriate grade of stainless steel should be used and also keep in mind that carbon steel is not connected with stainless steel because it may cause rust formation. Stainless steel and carbon steel are different because of different chromium content.