API 653 Welding Inspection 2 — Questions and Answers
Question 1: According to API 653, which welding process is most commonly specified for repair welding on aboveground storage tanks?
- Oxyfuel welding (OFW)
- Shielded metal arc welding (SMAW) (Correct answer)
- Electron beam welding (EBW)
- Friction stir welding (FSW)
Correct answer: Shielded metal arc welding (SMAW)
SMAW is the most commonly specified process for tank repair welding due to its versatility and wide applicability per API 653 requirements.
Question 2: When performing weld repairs on a tank shell that contains residual product, what is the MOST critical safety precaution before welding?
- Apply a rust-inhibiting primer to the weld area
- Gas-free the tank and confirm LEL is below 1% (Correct answer)
- Pre-heat the shell to 250°F minimum
- Install sacrificial anodes near the repair area
Correct answer: Gas-free the tank and confirm LEL is below 1%
Gas-freeing the tank and verifying the lower explosive limit (LEL) is below 1% is the most critical step to prevent explosion before any hot work.
Question 3: What does 'weld reinforcement' refer to in the context of tank shell welds?
- Additional backing bars placed behind the weld
- Weld metal deposited above the base metal surface plane (Correct answer)
- Post-weld heat treatment applied to strengthen the joint
- A second weld pass overlapping the first
Correct answer: Weld metal deposited above the base metal surface plane
Weld reinforcement is the weld metal that extends above the plane of the base metal surfaces on a groove weld.
Question 4: Per API 653, what is the minimum preheat temperature required for welding P-1 carbon steel material greater than 1 inch thick?
- 50°F (10°C)
- 150°F (65°C) (Correct answer)
- 200°F (93°C)
- 300°F (149°C)
Correct answer: 150°F (65°C)
API 653 referencing ASME Section IX and D1.1 requires a minimum preheat of 150°F for P-1 carbon steel over 1 inch thick to prevent hydrogen cracking.
Question 5: A butt weld joining two shell plates of different thicknesses requires tapering when the thickness difference exceeds what value per API 650?
- 1/16 inch (Correct answer)
- 3/16 inch
- 1/4 inch
- 3/8 inch
Correct answer: 1/16 inch
When adjoining plates differ in thickness by more than 1/16 inch, the thicker plate must be tapered at a 4:1 slope to provide a smooth transition.
Question 6: Which NDE method is best suited for detecting subsurface planar defects (such as lack of fusion) in a tank shell weld?
- Magnetic particle testing (MT)
- Liquid penetrant testing (PT)
- Radiographic testing (RT) (Correct answer)
- Visual testing (VT)
Correct answer: Radiographic testing (RT)
Radiographic testing (RT) is the best method for detecting subsurface planar defects such as lack of fusion and incomplete penetration inside welds.
Question 7: When a weld repair procedure requires PWHT and the tank cannot be furnace-heated, what alternative does API 653 permit?
- Skip PWHT if material is below 0.5 inch thick
- Perform local PWHT using resistance or induction heating (Correct answer)
- Substitute increased preheat temperature for PWHT
- Apply a stress-relief coating after welding
Correct answer: Perform local PWHT using resistance or induction heating
API 653 permits local PWHT using resistance or induction heating when furnace PWHT is not practical, provided thermal gradients are controlled.
API 653 Welding Inspection 2
According to API 653, which welding process is most commonly specified for repair welding on aboveground storage tanks?