API 510 Pressure Vessel Design & Inspection Codes 2 — Questions and Answers
Question 1: Under ASME Section VIII Division 1, what is the maximum allowable working pressure (MAWP) based on?
- The design pressure specified by the owner
- The weakest element of the completed vessel (Correct answer)
- The shell thickness alone
- The nozzle reinforcement calculations
Correct answer: The weakest element of the completed vessel
MAWP is determined by the weakest element of the completed vessel, considering all components including shells, heads, and nozzles.
Question 2: According to API 510, a corrosion allowance is used primarily to:
- Allow for fabrication tolerances during manufacturing
- Provide metal that can be consumed by corrosion between inspections (Correct answer)
- Increase the safety factor beyond code minimums
- Account for thermal expansion stresses
Correct answer: Provide metal that can be consumed by corrosion between inspections
Corrosion allowance is extra metal thickness provided to allow for corrosion that will occur during service between inspection intervals.
Question 3: When calculating the required shell thickness for a cylindrical vessel under internal pressure, which formula from ASME VIII Div. 1 is applied?
- t = PR / (SE - 0.4P) (Correct answer)
- t = PR / (2SE + 0.8P)
- t = PR / (SE + 0.6P)
- t = 2PR / (SE - P)
Correct answer: t = PR / (SE - 0.4P)
The formula t = PR / (SE - 0.4P) is the ASME VIII Div. 1 formula for longitudinal seam efficiency in cylindrical shells under internal pressure.
Question 4: What does the joint efficiency 'E' represent in ASME Section VIII pressure vessel design calculations?
- The ratio of actual weld strength to base metal strength
- A factor reflecting the quality and type of radiographic examination performed on the weld (Correct answer)
- The percentage of weld reinforcement removed by grinding
- The corrosion resistance factor of the weld metal
Correct answer: A factor reflecting the quality and type of radiographic examination performed on the weld
Joint efficiency E is a factor between 0 and 1 that reflects the radiographic examination category and weld joint type, accounting for potential weld discontinuities.
Question 5: A hemispherical head on a pressure vessel, compared to an ellipsoidal head, requires:
- Greater thickness due to higher stress concentration at the knuckle
- Less thickness because it has the most favorable shape for resisting pressure (Correct answer)
- The same thickness as a 2:1 ellipsoidal head
- Greater thickness because it has a larger surface area
Correct answer: Less thickness because it has the most favorable shape for resisting pressure
A hemispherical head has the most efficient shape for internal pressure and requires approximately half the thickness of a comparable cylindrical shell.
Question 6: According to API 510, what action is required when the remaining thickness of a pressure vessel falls below the minimum required thickness?
- The vessel may continue in service indefinitely with increased inspection frequency
- The vessel must be repaired, altered, rerated, or removed from service (Correct answer)
- The operating pressure must be doubled to compensate for metal loss
- The vessel must be immediately scrapped regardless of condition
Correct answer: The vessel must be repaired, altered, rerated, or removed from service
When remaining thickness is less than the minimum required, API 510 requires the vessel to be repaired, altered, rerated, or removed from service.
Question 7: In ASME VIII Division 1, the term 'design pressure' differs from 'operating pressure' in that design pressure:
- Is always equal to the operating pressure
- Is typically set at or above the highest expected operating pressure to account for transients (Correct answer)
- Is set 10% below operating pressure as a safety margin
- Refers only to the pressure at the bottom of the vessel
Correct answer: Is typically set at or above the highest expected operating pressure to account for transients
Design pressure is set at or above the most severe coincident pressure expected during normal operation, including transients, to ensure the vessel is rated above actual service conditions.
API 510 Pressure Vessel Design & Inspection Codes 2
Under ASME Section VIII Division 1, what is the maximum allowable working pressure (MAWP) based on?