API 653 Pressure Testing 4 — Questions and Answers
Question 1: Under API 653, what is the maximum allowable test pressure for a pneumatic pressure test on a tank shell expressed relative to the design pressure?
- 1.1 times design pressure (Correct answer)
- 1.25 times design pressure
- 1.5 times design pressure
- Equal to the design pressure only
Correct answer: 1.1 times design pressure
API 653 limits pneumatic shell tests to 1.1 times the design pressure to reduce the stored energy risk associated with compressed gas.
Question 2: An inspector observes that the roof-to-shell junction is weeping during a hydrostatic fill. According to API 653, what is the correct course of action?
- Mark the location and continue filling to maximum test level
- Stop filling, de-water, repair the junction weld, and retest (Correct answer)
- Apply an external sealant clamp and complete the test
- Reduce fill level to 80% and hold for 24 hours
Correct answer: Stop filling, de-water, repair the junction weld, and retest
Any active leak discovered during a hydrostatic test requires stopping the test, removing the water to a safe level, repairing the defect, and performing a retest.
Question 3: For an API 653 inspection, what type of nozzle attachment weld repair on a shell course would trigger a requirement for a shell hydrostatic test or radiography?
- Replacement of a flanged nozzle with identical dimensions
- Any full penetration groove weld repair on a shell nozzle (Correct answer)
- Application of a reinforcement pad over an existing nozzle
- Cleaning and recoating of a shell nozzle exterior
Correct answer: Any full penetration groove weld repair on a shell nozzle
Full penetration groove weld repairs on shell nozzles are pressure-retaining welds that require post-repair hydrostatic testing or radiographic examination per API 653.
Question 4: According to API 653, which of the following is an acceptable leak test method for a reconstructed tank annular weld where water flooding of the foundation is a concern?
- Dye penetrant test only
- Vacuum box testing of the inside bottom edge weld (Correct answer)
- Radiographic testing of the annular plate
- Ultrasonic thickness testing of the annular ring
Correct answer: Vacuum box testing of the inside bottom edge weld
Vacuum box testing of the inside bottom edge (annular-to-shell) weld is an API 653 accepted alternative when water flooding of the ring foundation must be avoided.
Question 5: When calculating the maximum allowable fill height for an API 653 hydrostatic test, which factor primarily limits how high the tank may be filled?
- The yield strength of the roof plates
- The allowable stress in the lowest shell course (Correct answer)
- The capacity of the fill pump
- The anchor bolt design load
Correct answer: The allowable stress in the lowest shell course
Hydrostatic hoop stress is highest at the lowest shell course, and the allowable stress in that course determines the maximum safe fill height.
Question 6: API 653 states that settlement readings during a hydrostatic test should be taken at a minimum of how many equally spaced points around the tank circumference?
- 4 points
- 6 points
- 8 points (Correct answer)
- 10 points
Correct answer: 8 points
API 653 requires a minimum of 8 equally spaced settlement measurement points around the tank periphery during the hydrostatic test fill.
Question 7: Under API 653, who has the authority to approve a deviation from the standard hydrostatic test procedure for a specific reconstructed tank?
- The authorized inspector alone
- The tank owner without additional review
- The engineer of record in consultation with the owner/operator (Correct answer)
- The local building code official
Correct answer: The engineer of record in consultation with the owner/operator
API 653 places authority for approving deviations from the standard hydrostatic test procedure with the engineer of record, in coordination with the owner/operator.
API 653 Pressure Testing 4
Under API 653, what is the maximum allowable test pressure for a pneumatic pressure test on a tank shell expressed relative to the design pressure?