Chapter 5 - Survey Methods & Evaluation Techniques

Question 1

list 3 things that can determined by taking a potential measurement of a pipeline that is not under cathodic protection

Answer 1

• general idea of corrosion progress
• location of hot spots
• areas subject to stray current

Question 2

what is a potential reading “to close electrode”?

Answer 2

reference electrode placed directly over the top pf the line while measuring the potential

Question 3

which over-the-line potential survey method is considered easiest?

Answer 3

direct contact over-the-line survey

Question 4

which line current method is most accurate because it can be calibrated?

Answer 4

four-wire test points

Question 5

Describe 2 problems that can be avoided if resistance readings are taken on line current test leads before reading the actual voltage.

Answer 5

• changes in pipe size or wall thickness can result in the actual span resistance being substantially different than the calculated resistance
• the presence of an unknown mechanical pipe coupling could introduce enough resistance to make results erroneous

Question 6

give 2 reasons for soil resistivity surveys

Answer 6

• determine corrosivity of soil

- helpful in CP installation site selection

Question 7

describe what would happen if the line of soil pins for a soil resistivity test are placed parallel to a bare underground pipeline.

Answer 7

current can travel the path of the pipeline instead of the intended path, making the measured resistance inaccurate.

Question 8

At what depth should soil resistivity normally be tested?

Answer 8

depth equal to that of the pipeline being evaluated

Question 9

how can the resistivity of soil layers de determined?

Answer 9

by using Barnes method

Question 10

which constituents in the soil normally accelerate corrosion

Answer 10

chlorides, sulfates and acidity(pH)

Question 11

describe the differences in accuracy between a current requirement test on a bare pipeline compared to a current requirement test on a coated pipeline due to polarization.

Answer 11

• bare pipeline takes a long amount of time to completely polarize (possibly week), so test data is generally extrapolated instead of measured
• coated pipelines polarize very rapidly, so conditions generally stabilize within the first few minutes of the test current being applied.

Question 12

list 2 reasons to perform a coating resistance test on a pipeline.

Answer 12

• initial profile serves as a reference for subsequent tests

- comparisons could be made between initial and subsequent tests to determine how various factors affect the coating.

Question 13

if a bellhole examination reveals the presence of a layer of black iron sulfide coating the pipeline surfaces at coating defects, what is the likely cause?

Answer 13

anaerobic bacteria

Question 14

describe the remedy for the problem of bellhole with black iron sulfide coating the pipeline surface with coating defects.

Answer 14

increased the polarized potential criteria to -0.950V CSE.