CWI Welding Process Fundamentals 5 — Questions and Answers
Question 1: Which of the following welding processes uses a non-consumable electrode?
- SMAW
- GMAW
- GTAW (Correct answer)
- FCAW
Correct answer: GTAW
GTAW (TIG welding) uses a non-consumable tungsten electrode to maintain the arc, with filler metal added separately if needed.
Question 2: What is the function of 'preheat' when welding high-carbon or alloy steels?
- To increase travel speed and productivity
- To slow the cooling rate, reducing the risk of hydrogen cracking and hard brittle microstructures in the HAZ (Correct answer)
- To eliminate the need for post-weld heat treatment
- To increase penetration by raising base metal temperature above melting point before welding
Correct answer: To slow the cooling rate, reducing the risk of hydrogen cracking and hard brittle microstructures in the HAZ
Preheat reduces the thermal gradient and slows cooling, allowing hydrogen to escape and preventing the formation of brittle martensite in the heat-affected zone.
Question 3: In friction stir welding (FSW), the joint is made by:
- Melting the base metal with a high-energy laser beam
- A rotating non-consumable tool that generates frictional heat and mechanically stirs the plasticized material (Correct answer)
- Pressing two heated workpieces together under high force without a tool
- Depositing filler wire into a friction-heated groove
Correct answer: A rotating non-consumable tool that generates frictional heat and mechanically stirs the plasticized material
FSW is a solid-state process where a rotating probe tool generates heat through friction and mechanically intermixes the plasticized (but not melted) material to form a weld.
Question 4: What does DCEN (Direct Current Electrode Negative) polarity mean for GTAW?
- Current flows from the base metal to the power source positive terminal
- The electrode is connected to the negative terminal; electrons flow from electrode to workpiece, concentrating heat in the base metal (Correct answer)
- The electrode alternates between positive and negative 60 times per second
- The tungsten is connected to the positive terminal for cleaning action
Correct answer: The electrode is connected to the negative terminal; electrons flow from electrode to workpiece, concentrating heat in the base metal
In DCEN (straight polarity), electrons leave the negative tungsten and strike the positive workpiece, directing about two-thirds of the heat into the base metal for deep penetration and minimal tungsten heating.
Question 5: A CWI finds incomplete fusion (lack of fusion) in a groove weld. Which root cause is MOST likely?
- Excessive amperage melting the base metal too deeply
- Improper electrode angle or insufficient heat causing the weld pool to fail to fuse to the sidewall or previous pass (Correct answer)
- Too slow a travel speed depositing excess metal
- Hydrogen contamination from wet consumables
Correct answer: Improper electrode angle or insufficient heat causing the weld pool to fail to fuse to the sidewall or previous pass
Lack of fusion results when the weld pool fails to fuse to the base metal or preceding weld pass, typically due to insufficient heat input, improper technique, or wrong electrode angle.
Question 6: What is the primary purpose of post-weld heat treatment (PWHT) on pressure vessels?
- To increase hardness and tensile strength of the weld metal
- To relieve residual stresses and temper hard HAZ microstructures, improving toughness and dimensional stability (Correct answer)
- To re-melt the weld surface to improve appearance
- To remove excess weld reinforcement before radiographic testing
Correct answer: To relieve residual stresses and temper hard HAZ microstructures, improving toughness and dimensional stability
PWHT reduces residual welding stresses, tempers brittle microstructures in the HAZ, and is required by codes such as ASME Section VIII for certain materials and thicknesses.
Question 7: In SMAW, what is the significance of the 'F' number classification for filler metals in AWS D1.1?
- It indicates the flux composition used in the electrode coating
- It groups electrodes with similar usability characteristics to qualify welders across grouped processes (Correct answer)
- It specifies the minimum tensile strength of the deposited weld metal
- It defines the position in which the electrode can be used
Correct answer: It groups electrodes with similar usability characteristics to qualify welders across grouped processes
F-numbers group filler metals by similar welding characteristics; a welder qualified with one electrode in an F-number group is generally qualified for other electrodes in the same group.
CWI Welding Process Fundamentals 5
Which of the following welding processes uses a non-consumable electrode?