API 510 Code Requirements 5 — Questions and Answers
Question 1: API 510 defines 'remaining life' of a pressure vessel as:
- The number of years since the vessel was last hydrotested
- The estimated time before corrosion reduces wall thickness to the minimum required thickness (Correct answer)
- The difference between the design life and current age
- The time remaining before the next scheduled inspection is due
Correct answer: The estimated time before corrosion reduces wall thickness to the minimum required thickness
Remaining life is the calculated time until corrosion will reduce the actual wall thickness to the minimum required thickness (Tmin) at the current or projected corrosion rate.
Question 2: Under API 510, when calculating the long-term corrosion rate, which inspection data points are used?
- Only the two most recent thickness measurements
- The initial thickness reading and the most recent reading, divided by the time between them (Correct answer)
- An average of all recorded thickness readings over the vessel's life
- The most recent reading compared to the minimum required thickness
Correct answer: The initial thickness reading and the most recent reading, divided by the time between them
The long-term corrosion rate uses the initial (or earliest reliable) thickness and the most recent thickness, divided by the elapsed time between them.
Question 3: API 510 permits the use of 'on-stream' (external) inspection in lieu of internal inspection. Which NDE method is most commonly used for this purpose?
- Magnetic particle testing (MT)
- Ultrasonic thickness measurement (UT) (Correct answer)
- Eddy current testing (ET)
- Radiographic testing (RT) with gamma rays
Correct answer: Ultrasonic thickness measurement (UT)
Ultrasonic thickness measurement is the primary NDE method used for on-stream inspection to measure remaining wall thickness without entering the vessel.
Question 4: According to API 510, what additional requirement applies when a vessel is rerated to a higher MAWP?
- A new nameplate must always be stamped before the higher MAWP is used
- Engineering calculations confirming adequacy and documentation in inspection records (Correct answer)
- Approval from the original vessel manufacturer only
- A pneumatic pressure test at 1.5 times the new MAWP
Correct answer: Engineering calculations confirming adequacy and documentation in inspection records
Rerating to higher MAWP requires engineering calculations showing the vessel is adequate at the new conditions and documentation of the rerating in the vessel's inspection records.
Question 5: Under API 510, what is required before a pressure vessel that has been out of service and opened can be returned to service?
- Only an external visual inspection by the operator
- An inspection by the authorized inspector to verify fitness for service (Correct answer)
- A full hydrostatic test regardless of the reason for shutdown
- A written authorization from the original equipment manufacturer
Correct answer: An inspection by the authorized inspector to verify fitness for service
Before returning a vessel to service after being opened, the authorized inspector must verify that all inspection, repair, and alteration activities are complete and the vessel is fit for service.
Question 6: API 510 exempts certain small, low-pressure vessels from some of its requirements. Which parameter combination typically qualifies a vessel for these exemptions?
- Vessels with a volume less than 5 cubic feet and MAWP below 250 psig
- Vessels with a volume less than 5 cubic feet or MAWP below 15 psig, per ASME Section VIII exclusions (Correct answer)
- Vessels operating at less than 100°F regardless of pressure
- Vessels fabricated from carbon steel with a wall thickness less than 0.25 inches
Correct answer: Vessels with a volume less than 5 cubic feet or MAWP below 15 psig, per ASME Section VIII exclusions
API 510 follows ASME Section VIII scope exclusions, which exempt very small-volume vessels (under 5 ft³) or very low pressure (under 15 psig) from full code requirements.
Question 7: When API 510 requires documentation of a vessel's inspection history, which document is considered the primary record?
- The original ASME Manufacturer's Data Report (Form U-1)
- The vessel inspection record maintained by the owner/operator and authorized inspector (Correct answer)
- The jurisdiction permit issued at the time of installation
- The welder qualification records from the original fabricator
Correct answer: The vessel inspection record maintained by the owner/operator and authorized inspector
The inspection record maintained by the owner/operator and the authorized inspector is the primary ongoing document tracking the vessel's condition, measurements, and inspection history.
API 510 Code Requirements 5
API 510 defines 'remaining life' of a pressure vessel as: