API 653 Code Requirements 3 — Questions and Answers
Question 1: According to API 653, what is the maximum interval between internal inspections for a tank in normal service when the corrosion rate is unknown?
- 5 years
- 10 years (Correct answer)
- 15 years
- 20 years
Correct answer: 10 years
When the corrosion rate is unknown, API 653 limits the internal inspection interval to a maximum of 10 years.
Question 2: Per API 653, what is the maximum interval for external inspections of aboveground storage tanks?
- 1 year
- 3 years
- 5 years (Correct answer)
- 10 years
Correct answer: 5 years
API 653 requires external inspections at intervals not exceeding 5 years for tanks in normal service.
Question 3: Which of the following qualifications must an API 653 tank inspector possess according to the standard?
- A current API 653 certification or equivalent documented experience (Correct answer)
- A Professional Engineer (PE) license in the relevant state
- Completion of an AWS certified welding inspector course
- At least 10 years of field welding experience
Correct answer: A current API 653 certification or equivalent documented experience
API 653 requires that inspectors hold a current API 653 certification or meet the standard's equivalent experience and education requirements.
Question 4: When API 653 requires ultrasonic thickness (UT) measurements on a tank shell, what is the minimum number of readings required at each course?
- One reading per course is sufficient
- Readings must be taken at defined grid patterns per the standard (Correct answer)
- Exactly four readings per course are always required
- UT readings are only required at weld locations
Correct answer: Readings must be taken at defined grid patterns per the standard
API 653 specifies that UT measurements must follow defined patterns or grids to adequately characterize the corrosion profile of each shell course.
Question 5: Under API 653, what condition requires immediate removal from service or repair before continued operation?
- Any shell thickness below the nominal thickness
- Shell thickness below the calculated minimum allowable shell thickness (MAST) (Correct answer)
- Corrosion rate exceeding 0.010 inches per year
- Any visible surface rust on the shell exterior
Correct answer: Shell thickness below the calculated minimum allowable shell thickness (MAST)
When measured shell thickness falls below the minimum allowable shell thickness (MAST), the tank must be removed from service or repaired before continued operation.
Question 6: According to API 653, what is the required hydrostatic test fill rate to avoid overstressing the foundation?
- Fill at maximum pump capacity
- At a controlled rate not to exceed the rate specified in API 650 (Correct answer)
- Never faster than 2 feet per hour regardless of tank size
- The standard does not specify a fill rate limit
Correct answer: At a controlled rate not to exceed the rate specified in API 650
API 653 requires hydrostatic test fill rates to comply with API 650 provisions to prevent foundation overstress.
Question 7: Which type of tank bottom flaw is categorized as a Type 1 flaw under API 653 bottom evaluation criteria?
- Pinhole perforations through the bottom plate
- General corrosion affecting a large area of the bottom
- Pitting corrosion on the product side of the bottom (Correct answer)
- Cracks in bottom-to-shell junction welds
Correct answer: Pitting corrosion on the product side of the bottom
Type 1 flaws in API 653 refer to pitting or localized corrosion on the product (top) side of the tank bottom.
API 653 Code Requirements 3
According to API 653, what is the maximum interval between internal inspections for a tank in normal service when the corrosion rate is unknown?