AWS AWS Distortion Control & Residual Stress 4 — Questions and Answers
Question 1: Which welding sequence technique involves completing each weld layer in short, alternating segments to minimize cumulative distortion?
- Backstep welding (Correct answer)
- Block sequence welding
- Cascade welding
- Progressive welding
Correct answer: Backstep welding
Backstep welding deposits short weld segments in a direction opposite to the overall progression, balancing heat input and reducing cumulative distortion.
Question 2: When welding a T-joint fillet weld, what is the primary cause of angular distortion?
- Uneven shrinkage across the weld cross-section due to temperature gradients (Correct answer)
- Excessive preheat causing base metal expansion
- Improper electrode angle causing arc blow
- High travel speed reducing heat input
Correct answer: Uneven shrinkage across the weld cross-section due to temperature gradients
Angular distortion in T-joints results from non-uniform transverse shrinkage across the weld cross-section as the top cools faster than the root.
Question 3: A welder notices that a long steel beam is bowing upward after welding along its bottom flange. Which corrective measure is most appropriate BEFORE welding?
- Pre-camber the beam opposite to the expected distortion direction (Correct answer)
- Increase interpass temperature to soften the steel
- Use a higher heat input to fully penetrate the joint
- Apply post-weld quenching with water
Correct answer: Pre-camber the beam opposite to the expected distortion direction
Pre-cambering positions the workpiece opposite to anticipated distortion so that after welding, the part returns to the desired geometry.
Question 4: Which type of residual stress is tensile in the weld metal and heat-affected zone after a weld cools?
- Longitudinal residual stress (Correct answer)
- Compressive residual stress
- Shear residual stress
- Torsional residual stress
Correct answer: Longitudinal residual stress
Longitudinal residual stresses in the weld and HAZ are typically tensile because the weld metal contracts along its length but is restrained by the surrounding base metal.
Question 5: What is the purpose of using strong-backs (strongbacks) during welding?
- To mechanically restrain joint members and limit distortion (Correct answer)
- To preheat the base metal before welding
- To support the electrode holder during overhead welding
- To protect the weld pool from atmospheric contamination
Correct answer: To mechanically restrain joint members and limit distortion
Strong-backs are rigid fixtures tack-welded or clamped to the workpiece to physically restrain movement and control distortion during and after welding.
Question 6: In a multi-pass groove weld, how does increasing the number of passes with lower heat input per pass affect distortion compared to fewer passes with higher heat input?
- Lower heat input per pass generally reduces distortion but may increase it if too many passes cause cumulative shrinkage (Correct answer)
- More passes always increase distortion regardless of heat input
- Fewer high-heat passes always minimize distortion
- Number of passes has no effect on distortion if total heat input is equal
Correct answer: Lower heat input per pass generally reduces distortion but may increase it if too many passes cause cumulative shrinkage
Lower heat input per pass reduces the thermal gradient each cycle, but cumulative shrinkage from many passes must be managed with proper sequencing to avoid distortion buildup.
Question 7: Which AWS-recognized method uses localized rapid cooling immediately after welding to reduce distortion in thin sheet metal?
- Quench and temper cooling
- Thermal stress relief annealing
- Chill bar technique (Correct answer)
- Peening while hot
Correct answer: Chill bar technique
Chill bars (copper or aluminum backing bars) are placed adjacent to the weld to rapidly conduct heat away, limiting distortion in thin materials.
AWS AWS Distortion Control & Residual Stress 4
Which welding sequence technique involves completing each weld layer in short, alternating segments to minimize cumulative distortion?