API 653 Welding Inspection 5 — Questions and Answers
Question 1: Per API 653, when is a hydrostatic test required after completing a weld repair on a tank shell?
- After every weld repair regardless of scope
- When a major repair is made to the shell or when required by the authorized inspector (Correct answer)
- Only when the tank has previously failed a leak test
- Whenever more than three weld repairs are made in a single inspection interval
Correct answer: When a major repair is made to the shell or when required by the authorized inspector
API 653 requires a hydrostatic test after major repairs to the shell or bottom, or when deemed necessary by the authorized inspector based on repair scope and risk.
Question 2: What is the allowable maximum undercut depth in a shell vertical seam weld per API 650 acceptance criteria?
- 1/64 inch (0.4 mm)
- 1/32 inch (0.8 mm) (Correct answer)
- 1/16 inch (1.6 mm)
- 3/32 inch (2.4 mm)
Correct answer: 1/32 inch (0.8 mm)
API 650 limits undercut depth to 1/32 inch (0.8 mm) maximum in shell vertical seam welds to prevent stress concentration and fatigue cracking.
Question 3: Which document formally authorizes a welder to perform production welding on an API 653 repair project?
- The welder's union card or trade certification
- A welder performance qualification record (WPQ/WPQR) per ASME Section IX (Correct answer)
- The project manager's written approval
- An API 653 inspector certification
Correct answer: A welder performance qualification record (WPQ/WPQR) per ASME Section IX
A Welder Performance Qualification Record (WPQ) documents that a welder has demonstrated the skill to produce acceptable welds under the applicable code.
Question 4: During visual inspection of a completed tank floor weld, an inspector finds a 2-inch length of weld that was skipped. What action is required?
- Accept the gap if it is not in a high-stress area
- Document it as an observation for the next inspection
- Require the gap to be filled by welding to complete the continuous weld (Correct answer)
- Apply a corrosion-inhibiting patch over the unwelded area
Correct answer: Require the gap to be filled by welding to complete the continuous weld
Skipped or incomplete weld segments compromise joint integrity and must be completed by adding weld metal to fill the gap to the full specified length.
Question 5: What is 'stress corrosion cracking' (SCC) in the context of welded tank components, and which zone is typically most susceptible?
- Uniform corrosion of the weld face; most severe in the weld cap
- Cracking caused by combined tensile stress and corrosive environment; most common in the HAZ (Correct answer)
- Erosion of the weld root due to fluid velocity; worst in inlet nozzles
- Galvanic attack between weld metal and base metal; limited to the fusion line
Correct answer: Cracking caused by combined tensile stress and corrosive environment; most common in the HAZ
SCC requires simultaneous tensile residual stress and a corrosive environment; the HAZ with its high residual stresses is most susceptible in tank welds.
Question 6: When a welded repair to a tank nozzle requires removal of an existing weld, which method is PREFERRED by API 653 to avoid damaging the base metal?
- Air carbon arc gouging followed by grinding to clean metal (Correct answer)
- Grinding only using angle grinders
- Flame cutting with an oxyfuel torch
- Chipping hammers for mechanical removal
Correct answer: Air carbon arc gouging followed by grinding to clean metal
Air carbon arc gouging followed by grinding to bright metal is the preferred removal method per API 653 as it efficiently removes weld metal while grinding ensures no carbon contamination remains.
Question 7: Per API 653, what is the minimum overlap required when installing a lap-welded patch plate on a tank shell?
- 1 inch (25 mm)
- 2 inches (51 mm) (Correct answer)
- 3 inches (76 mm)
- 4 inches (102 mm)
Correct answer: 2 inches (51 mm)
API 653 requires a minimum overlap of 2 inches (51 mm) for lap-welded patch plates on tank shells to ensure adequate fillet weld length and structural integrity.
API 653 Welding Inspection 5
Per API 653, when is a hydrostatic test required after completing a weld repair on a tank shell?