API 653 Welding & Metallurgy 2 — Questions and Answers
Question 1: Which weld discontinuity is most likely to cause a stress concentration leading to fatigue cracking in a storage tank shell?
- Porosity
- Undercut (Correct answer)
- Slag inclusion
- Overlap
Correct answer: Undercut
Undercut creates a sharp notch at the weld toe that acts as a stress concentrator, making it particularly detrimental under cyclic loading.
Question 2: According to API 653, what is the minimum preheat temperature required when welding on a tank shell plate with carbon equivalent (CE) greater than 0.43?
- 50°F (10°C)
- 150°F (65°C) (Correct answer)
- 200°F (93°C)
- 250°F (121°C)
Correct answer: 150°F (65°C)
API 653 references ASME Section IX and AWS D1.1 requirements, which generally specify 150°F (65°C) preheat for higher carbon equivalent steels to prevent hydrogen-induced cracking.
Question 3: What type of weld joint is typically used for attaching nozzle reinforcing pads to an API 653 tank shell?
- Full penetration butt weld
- Fillet weld on both sides (Correct answer)
- Single bevel groove weld
- Plug weld
Correct answer: Fillet weld on both sides
Reinforcing pads are typically attached with continuous fillet welds on both the inside and outside edges to ensure full sealing and structural attachment.
Question 4: In the context of API 653 tank repairs, what is 'hydrogen-induced cracking' (HIC) primarily associated with?
- High welding speeds causing rapid cooling
- Atomic hydrogen diffusing into steel during welding (Correct answer)
- Oxidation of the weld pool surface
- Excessive interpass temperature
Correct answer: Atomic hydrogen diffusing into steel during welding
HIC occurs when atomic hydrogen generated during welding diffuses into the steel and recombines at discontinuities, creating internal pressure that leads to cracking.
Question 5: Which nondestructive testing method is most effective for detecting planar defects (cracks) oriented parallel to the surface in a tank shell weld?
- Radiographic testing (RT)
- Magnetic particle testing (MT)
- Ultrasonic testing (UT) (Correct answer)
- Liquid penetrant testing (PT)
Correct answer: Ultrasonic testing (UT)
UT using angle beam transducers can detect planar defects parallel to the surface that RT may miss because radiation passes through them without significant attenuation.
Question 6: What is the purpose of post-weld heat treatment (PWHT) when applied to a repaired tank shell section?
- To increase the hardness of the weld
- To relieve residual stresses and temper the heat-affected zone (Correct answer)
- To improve corrosion resistance by oxidizing the surface
- To increase the carbon content of the weld metal
Correct answer: To relieve residual stresses and temper the heat-affected zone
PWHT reduces residual welding stresses and softens the hardened heat-affected zone, improving toughness and resistance to stress corrosion cracking.
Question 7: When performing an API 653 weld repair on a tank bottom plate, which welding position designation applies to welding on the flat bottom surface from inside the tank?
- 1G (flat) (Correct answer)
- 2G (horizontal)
- 3G (vertical)
- 4G (overhead)
Correct answer: 1G (flat)
Welding on a flat horizontal surface with the weld axis horizontal is the 1G (flat) position, which is the easiest and most common position for tank bottom work.
API 653 Welding & Metallurgy 2
Which weld discontinuity is most likely to cause a stress concentration leading to fatigue cracking in a storage tank shell?