5 And 6

Question 1

What are the 2 conditions that contribute to general corrosion?

Answer 1

1. Metal and water in the same environment

2. Chemical reaction between the metal and water to form an oxide.

Question 2

How is the rate of corrosion affected by Temperature?

Answer 2

Temperature rise from 20 F to 50 F doubles the corrosion rate.

Question 3

How is the rate of corrosion affected by water velocity?

Answer 3

High water velocity, 30-40 FPS will remove oxide film allowing for corrosion to increase.

Question 4

How is the rate of corrosion affected by oxygen?

Answer 4

There is a rapid reaction between oxygen and the layer of hydrogen absorbed on the oxide layer.

Question 5

How is the rate of corrosion affected by pH?

Answer 5

Anything outside of pH 4-10 range will cause an increase.

Question 6

How is the rate of corrosion affected by the condition and composition of the metal surface?

Answer 6

Deposits, scale or irregular surfaces create opportunities for local corrosion to initiate and proceed at a faster rate.

Question 7

How is the rate of corrosion affected by dissolved solids?

Answer 7

Dissolved solids make it easier for current flow, increasing corrosion.

Question 8

What are the 3 products formed from general corrosion of iron?

Answer 8

1. FeO
2. Fe2O3
3. Fe3O4

Question 9

What action is taken for initial fill of a system to limit general corrosion?

Answer 9

Pretreatment/pickling involves careful control of reactor coolant water chemistry and temperature during the pretreatment period to ensure the integrity of the protective film.

Question 10

What are the 4 methods used to chemically control general corrosion?

CCRP

Answer 10

1. Cathodic protection - external electric current to the iron so that it acts as a cathode and has no anodic areas.
2. Chemical addition to alter chemical reaction.
3. Removing corrodants to reduce the dissolved oxygen.
4. Passivators - metal that corrodes at a slow rate

Question 11

Galvanic Corrosion

Answer 11

Corrosion that results when 2 dissimilar Metals with different potentials are placed in electrical contact in an electrolyte.

Question 12

What are the two conditions that can cause galvanic corrosion?

Answer 12

???When two dissimilar Metals are joined together in s conducting medium.

Question 13

Two locations that are susceptible to galvanic corrosion?

Answer 13

1. Piping transitions between two dissimilar Metals.

2. Sacrificial anodes

Question 14

Four control measures used to minimize galvanic corrosion

Answer 14

1. Introducing a 3rd metal
2. Separating dissimilar Metals with non conducting material
3. Separating metals from conductive environment
4. Use of poorly conducting electrolytes. (Water)