API 653 Cathodic Protection Systems 2

Question 1

What is stray current corrosion in the context of cathodic protection systems for storage tanks?

Accepted Answer

Corrosion caused by electrical currents from external sources flowing through the tank structure

Answer

Corrosion caused by excessive CP current on the protected structure

Answer

Corrosion due to improper anode placement

Answer

Corrosion resulting from alternating current fluctuations in the rectifier

Question 2

What test is performed to evaluate whether a cathodic protection system is providing adequate protection at a tank bottom?

Accepted Answer

Pipe-to-soil potential survey

Answer

Hydrostatic pressure test

Answer

Ultrasonic thickness measurement

Answer

Radiographic inspection

Question 3

What is the purpose of a 'close-interval potential survey' (CIPS) for an aboveground storage tank bottom?

Accepted Answer

To obtain detailed potential readings at small spacing intervals around the tank perimeter to identify CP shielding or deficiencies

Answer

To measure the thickness of the tank shell at close intervals

Answer

To inspect the close proximity welds on the tank bottom

Answer

To test the dielectric isolation of the CP system at close range

Question 4

Which of the following would indicate OVERPROTECTION by a cathodic protection system on a coated steel tank bottom?

Accepted Answer

Potentials more negative than -1200 mV vs. CSE

Answer

Potentials more positive than -850 mV vs. CSE

Answer

Uniform potential distribution around the tank

Answer

Anode current output within design specifications

Question 5

Why is electrical isolation (isolation joints/flanges) important in a cathodic protection system for a storage tank?

Accepted Answer

To prevent CP current from being drained by connected pipelines or structures not intended to be protected

Answer

To prevent thermal expansion stresses from damaging the CP anode

Answer

To ensure the tank foundation is grounded properly for safety

Answer

To measure the CP system current output accurately

Question 6

According to NACE/API recommendations, how often should cathodic protection system performance be evaluated for an aboveground storage tank?

Accepted Answer

At least annually, with rectifier inspections more frequently

Answer

Every 10 years during scheduled tank inspection

Answer

Only when visible corrosion is detected on the tank bottom

Answer

Every 5 years during major turnaround inspections

Question 7

What type of interference test is performed to assess the impact of one CP system on an adjacent structure?

Accepted Answer

Electrical interference (stray current) survey

Answer

Hydrostatic interference test

Answer

Acoustic emission interference test

Answer

Magnetic flux interference test