API Inspection and Maintenance 2 — Questions and Answers
Question 1: According to API 653, what is the minimum acceptable shell thickness for an atmospheric storage tank in service?
- The original mill tolerance thickness
- The calculated minimum thickness based on operating conditions (Correct answer)
- Half the original nominal thickness
- The thickness specified in the original design
Correct answer: The calculated minimum thickness based on operating conditions
API 653 requires that the minimum acceptable shell thickness be the greater of the calculated minimum thickness based on operating conditions or 0.05 inches.
Question 2: During an external inspection of a pressure vessel per API 510, which condition would most likely require immediate shutdown?
- Minor surface rust on the vessel exterior
- Bulging or distortion of the vessel wall (Correct answer)
- Insulation showing minor moisture damage
- Paint discoloration from heat exposure
Correct answer: Bulging or distortion of the vessel wall
Bulging or distortion of a pressure vessel wall indicates plastic deformation and potential imminent failure, requiring immediate shutdown.
Question 3: What does the term 'remaining life' mean in the context of API inspection standards?
- Time until the next scheduled turnaround
- Estimated time before equipment reaches its minimum allowable thickness (Correct answer)
- Operating hours remaining before equipment warranty expires
- Time until statutory inspection is required
Correct answer: Estimated time before equipment reaches its minimum allowable thickness
Remaining life is the estimated time before corrosion reduces the equipment thickness to its minimum allowable value, calculated using corrosion rate data.
Question 4: Under API 570, which piping class typically requires the most frequent thickness measurements?
- Class 3 — low-hazard utility piping
- Class 2 — moderate-consequence piping
- Class 1 — high-consequence piping carrying flammables or toxics (Correct answer)
- All classes require identical inspection frequency
Correct answer: Class 1 — high-consequence piping carrying flammables or toxics
Class 1 piping, which handles highly flammable, toxic, or high-pressure services, requires the most frequent inspections due to the highest consequence of failure.
Question 5: What is the primary purpose of a fitness-for-service (FFS) assessment per API 579?
- To determine if equipment can continue operating safely with existing flaws (Correct answer)
- To establish the original design parameters for new equipment
- To certify that equipment meets API manufacturing standards
- To schedule routine preventive maintenance intervals
Correct answer: To determine if equipment can continue operating safely with existing flaws
An FFS assessment evaluates whether equipment containing flaws or damage can continue to operate safely at its current or reduced operating conditions.
Question 6: When calculating the half-life inspection interval under API 510, the interval should not exceed:
- 5 years for internal inspection and 10 years for external inspection
- Half the remaining equipment life or 10 years for internal inspection, whichever is less (Correct answer)
- The time until the next scheduled turnaround regardless of corrosion rate
- 20% of the calculated remaining life
Correct answer: Half the remaining equipment life or 10 years for internal inspection, whichever is less
API 510 limits the inspection interval to the lesser of half the calculated remaining life or 10 years for internal inspections to ensure adequate safety margins.
Question 7: Which API standard specifically governs inspection practices for atmospheric and low-pressure storage tanks?
- API 510
- API 570
- API 653 (Correct answer)
- API 580
Correct answer: API 653
API 653 covers inspection, repair, alteration, and reconstruction of steel aboveground storage tanks built to API 650 or similar standards.
API Inspection and Maintenance 2
According to API 653, what is the minimum acceptable shell thickness for an atmospheric storage tank in service?