API 653 Welding Inspection 4 — Questions and Answers
Question 1: What is 'lamellar tearing' and under what conditions is it most likely to occur in tank construction?
- Cracking along the weld centerline due to hot cracking
- Subsurface cracking in base metal parallel to the plate surface under through-thickness stress (Correct answer)
- Surface cracking caused by hydrogen embrittlement in the HAZ
- Cracking due to excessive weld reinforcement grinding
Correct answer: Subsurface cracking in base metal parallel to the plate surface under through-thickness stress
Lamellar tearing occurs in the base metal beneath welds when through-thickness stresses act on inclusion-rich steel with low ductility in the Z-direction.
Question 2: When API 653 requires radiography of a repaired weld, what percentage of the completed weld length must be radiographed as a minimum for spot examination?
- 5%
- 10% (Correct answer)
- 25%
- 50%
Correct answer: 10%
Spot radiography per API 650/653 requires a minimum of 10% of each welder's completed weld length to be examined radiographically.
Question 3: Which of the following best describes 'underbead cracking' in a welded joint?
- Cracking on the surface of the weld crown
- Hydrogen-induced cracking in the heat-affected zone below the weld (Correct answer)
- Incomplete fusion at the root of the weld joint
- Thermal fatigue cracking in the weld toe area
Correct answer: Hydrogen-induced cracking in the heat-affected zone below the weld
Underbead cracking is hydrogen-induced cracking that occurs in the HAZ just below the weld deposit, typically in high-carbon or alloy steels.
Question 4: An inspector notices that a vertical weld on a tank shell exhibits consistent undercut along both toes of the weld. What is the most likely root cause?
- Insufficient preheat temperature before welding
- Excessive welding current or travel speed (Correct answer)
- Incorrect shielding gas mixture
- Inadequate post-weld heat treatment
Correct answer: Excessive welding current or travel speed
Undercut is most commonly caused by excessive welding current or travel speed, which melts the base metal at the weld toes faster than it can be filled.
Question 5: When reviewing a weld map for a major shell repair, what information is MOST critical for the inspector to verify?
- The color-coding scheme used on the drawing
- That each weld is identified, the procedure and welder assigned, and NDE requirements noted (Correct answer)
- The signature of the project engineer approving the design
- The cost estimate for each weld repair item
Correct answer: That each weld is identified, the procedure and welder assigned, and NDE requirements noted
A weld map must identify each weld joint with its applicable WPS, assigned qualified welder, and required NDE to ensure all work is traceable and meets specifications.
Question 6: What is the significance of the 'essential variable' concept in ASME Section IX welding qualification?
- Variables that must be recorded but do not require requalification if changed
- Variables whose change requires requalification of the weld procedure (Correct answer)
- Variables that only apply to pressure vessel welding, not storage tanks
- Variables that determine the color code on the weld map
Correct answer: Variables whose change requires requalification of the weld procedure
Essential variables are welding parameters whose change beyond specified limits significantly affects weld mechanical properties, requiring a new procedure qualification.
Question 7: A weld repair on a tank shell in hydrogen service requires special consideration for which weld discontinuity?
- Surface porosity
- Lack of fill on the weld crown
- Hydrogen-induced cracking (HIC) in the HAZ (Correct answer)
- Excess weld reinforcement
Correct answer: Hydrogen-induced cracking (HIC) in the HAZ
Hydrogen service tanks require special attention to hydrogen-induced cracking in the HAZ, which necessitates low-hydrogen electrodes, preheat, and often PWHT.
API 653 Welding Inspection 4
What is 'lamellar tearing' and under what conditions is it most likely to occur in tank construction?