API 653 Corrosion Assessment 2

Question 1

What type of corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte?

Accepted Answer

Galvanic corrosion

Answer

Galvanic corrosion occurs when dissimilar metals are electrically coupled in an electrolyte, causing the more active (anodic) metal to corrode preferentially.

Question 2

According to API 653, what is the minimum shell thickness (t_min) formula used for corrosion assessment of existing tanks?

Accepted Answer

t_min = 2.6D(H-1)G / SE

Answer

API 653 uses t_min = 2.6D(H-1)G / SE for existing tanks, which is a modified formula compared to the API 650 design formula.

Question 3

Which corrosion mechanism is characterized by localized attack beneath deposits, gaskets, or at crevices where oxygen is depleted?

Accepted Answer

Crevice corrosion

Answer

Crevice corrosion occurs in confined spaces where stagnant solution becomes depleted in oxygen, creating an aggressive local chemistry.

Question 4

When performing an internal inspection of a tank bottom, which measurement technique provides the most complete corrosion mapping?

Accepted Answer

Magnetic flux leakage (MFL) scanning

Answer

Magnetic flux leakage (MFL) scanning provides comprehensive coverage of the tank bottom and can detect both internal and external corrosion on floor plates.

Question 5

What does a high cathodic protection current demand typically indicate when assessing tank bottom corrosion?

Accepted Answer

There is significant coating disbondment or bare metal exposure

Answer

High cathodic protection current demand indicates that significant coating breakdown has occurred, exposing bare metal that requires protection.

(API 653) API 653 Aboveground Storage Tank Inspector Certification Practice Test

(API 653) API 653 Aboveground Storage Tank Inspector Certification Practice Test

API 653 Corrosion Assessment 2