GPT Corrosion Control & Cathodic Protection 2

Question 1

What is the purpose of an electrical isolation fitting (insulating union or flange) installed on a buried gas service line?

Accepted Answer

To electrically isolate the service line from the customer's piping and prevent CP current loss

Answer

To reduce gas flow velocity at the meter

Answer

To act as a pressure regulator at the service entrance

Answer

To provide a test point for leak detection

Question 2

Microbiologically influenced corrosion (MIC) on buried gas pipelines is primarily caused by:

Accepted Answer

Sulfate-reducing bacteria (SRB) producing hydrogen sulfide in anaerobic soils

Answer

Ultraviolet radiation degrading the pipe coating

Answer

High operating pressures causing stress corrosion

Answer

Electrostatic discharge from passing vehicles

Question 3

A rectifier output current on an impressed current CP system has dropped significantly with no change in the circuit resistance. This most likely indicates:

Accepted Answer

AC power supply to the rectifier has failed or the rectifier fuse has blown

Answer

The pipeline is now fully protected and requires less current

Answer

Pipe-to-soil resistivity has decreased due to rainfall

Answer

The sacrificial anodes need replacement

Question 4

Which pipe coating system is commonly applied at the mill and provides excellent protection against soil-side corrosion on steel gas mains?

Accepted Answer

Fusion-bonded epoxy (FBE)

Answer

Tar paper wrap

Answer

Asphalt enamel over kraft paper

Answer

Black iron oxide primer only

Question 5

When performing a close-interval potential survey (CIPS), readings are taken:

Accepted Answer

At intervals of approximately 1 to 5 feet along the pipeline route using a trailing reference electrode

Answer

At 1,000-foot intervals using a GPS-tagged test station

Answer

Only at valve and tee locations where current drain is highest

Answer

Annually at rectifier test points only

Question 6

Galvanic corrosion between two dissimilar metals connected in a buried environment is driven by:

Accepted Answer

A difference in electrochemical potential (voltage) between the two metals

Answer

Differences in pipe wall thickness

Answer

Differences in operating gas pressure

Answer

The relative depth of burial of each metal

Question 7

What is the primary reason cathodic protection test stations are installed along a buried gas pipeline?

Accepted Answer

To allow periodic measurement of pipe-to-soil potential without excavation

Answer

To provide emergency shut-off access below ground

Answer

To equalize pressure between pipeline segments

Answer

To anchor the pipe against thermal movement