API 653 Tank Inspection, NDE & Testing 3

Question 1

API 653 defines the 'critical zone' of a tank floor as the area within what distance from the shell-to-floor weld?

Accepted Answer

12 inches

Answer

API 653 defines the critical zone as the area of the tank floor within 3 inches of the inside of the tank shell, where corrosion is most likely and structurally consequential.

Question 2

What is the primary purpose of performing acoustic emission (AE) testing on an in-service aboveground storage tank?

Accepted Answer

Detecting active corrosion, cracking, or leakage while the tank remains in service

Answer

Acoustic emission testing is used to screen in-service tanks for active defect growth (corrosion, cracking) or leaks without requiring the tank to be taken out of service.

Question 3

When applying the API 653 formula to calculate minimum acceptable shell thickness, which factor is NOT included in the standard calculation?

Accepted Answer

Wind load on the shell

Answer

The API 653 minimum shell thickness formula (modified API 650) accounts for hydrostatic head, allowable stress, and a corrosion allowance, but wind load is not part of the minimum thickness calculation for corrosion retirement.

Question 4

A tank inspector identifies pitting on the internal shell surface. Which measurement is most critical for determining whether the shell remains fit for service?

Accepted Answer

The remaining wall thickness at the deepest pit location

Answer

The remaining wall thickness at the deepest pit determines whether the shell still meets the minimum acceptable thickness per API 653, making it the critical measurement.

Question 5

Which of the following correctly describes the use of the 'point-of-tangency' method in API 653 shell inspection?

Accepted Answer

It identifies the exact line where the shell plate transitions from vertical to the knuckle radius

Answer

The point of tangency is the location where the shell plate transitions from the vertical cylinder to the curved knuckle radius, important for determining weld locations and inspection zones.

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

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

API 653 Tank Inspection, NDE & Testing 3