I

API 651

REVIEW Section 4

1. Corrosion may be defined as the deterioration of a: Metal due to a reaction with its environment. 4.1.1

2. At the anode, the base metal _______ by releasing electrons and forming positive metal ions.

Corrodes. 4.1.1 (a)

3. The electrolyte for the external tank bottoms is usually:

Moist soil. 4.1.1 (d)

4. Individual corrosion cells are large and a distinct anode and cathode area can be identified in ____________ corrosion.

Pitting. 4.1.2

5. In _________ corrosion, the individual corrosion cells are larger and distinct anode and cathode areas can be identified.

Pitting. 4.1.2

6. Physical and chemical properties of the electrolyte may influence the location of cathodic areas on the metal surface. Areas of lower oxygen concentrations become anodic and areas with higher oxygen concentrations become cathodic. This can cause corrosion in areas, where? Clay or other debris contacts a steel tank bottom constructed on a sand cushion foundation. 4.1.4

7. Interference currents travel through the soil electrolyte and on structures for which they are not intended. These currents are known as:

Stray currents. 4.2.1

8. Direct stray currents are generated from grounded DC electric power systems such as:

Electric railroads, welding machines, and other cathodic protection systems. 4.2.1

9. Electric current takes the path of __________ resistance.

Least. 4.2.2

10. The two most significant factors in galvanic corrosion in the corrosion of a tank bottom when a stainless steel or a copper pipe is connected to a tank are the:

Relative areas of the cathode and anode and the relative position of the cathode and anode in the galvanic series. 4.2.211. Current, in galvanic corrosion, is considered to flow from the:

More active metal (anode) to the less active metal (cathode). 4.2.2

12. We learned earlier in section 4 that there are 2 major types of corrosion, general and pitting. To a lesser extent there is another problem that can be considered a manner of corrosion mechanisms. What is it?

Environmental cracking. 4.2.3

1