CWI Weld Discontinuities and Defects 5 — Questions and Answers
Question 1: What is 'reheat cracking' and in which type of steel is it most commonly encountered?
- Cracking during initial weld pass in plain carbon steel
- HAZ cracking that occurs during post-weld heat treatment (PWHT) in low-alloy Cr-Mo steels (Correct answer)
- Root cracking due to hydrogen in stainless steel
- Centerline cracking in aluminum welds during solidification
Correct answer: HAZ cracking that occurs during post-weld heat treatment (PWHT) in low-alloy Cr-Mo steels
Reheat cracking occurs in the coarse-grained HAZ of low-alloy Cr-Mo steels during PWHT or elevated temperature service when creep relaxation cannot occur without intergranular fracture.
Question 2: A weld inspector measures a fillet weld and finds the convexity exceeds the code limit. Which repair action is typically required?
- Additional weld passes to increase reinforcement
- Grinding to reduce the convexity to within acceptable limits (Correct answer)
- Preheating the weld area and re-welding the entire joint
- Applying post-weld heat treatment
Correct answer: Grinding to reduce the convexity to within acceptable limits
Excessive convexity is corrected by mechanically grinding the weld face to reduce the profile to within code-specified limits.
Question 3: Which discontinuity is described as 'wagon tracks' on a radiograph and what does it represent?
- Two parallel lines of porosity indicating root undercut on both sides
- A pair of parallel dark lines indicating incomplete fusion at the root of a double-V groove weld (Correct answer)
- Parallel slag lines from multiple weld passes
- Two cracks running parallel to the weld axis
Correct answer: A pair of parallel dark lines indicating incomplete fusion at the root of a double-V groove weld
Wagon tracks on a radiograph appear as two parallel dark lines representing incomplete fusion along both faces of the root pass in a double-V or CJP groove weld.
Question 4: When a weld shows evidence of 'crater cracks,' what is the primary corrective preventive measure during welding?
- Increasing interpass temperature
- Backstepping the weld and properly filling the crater before breaking the arc (Correct answer)
- Using a lower electrode classification
- Increasing travel speed at the end of each pass
Correct answer: Backstepping the weld and properly filling the crater before breaking the arc
Crater cracks are prevented by pausing at the end of each weld pass to properly fill the crater to a flat or slightly convex profile before extinguishing the arc.
Question 5: Linear porosity aligned along the weld axis MOST likely indicates:
- Excessive current for the electrode size
- Gas entrapment from a contamination source localized along the joint (Correct answer)
- Incorrect travel angle causing spatter
- Incorrect interpass temperature
Correct answer: Gas entrapment from a contamination source localized along the joint
Linear porosity aligned along the weld axis typically indicates a consistent contamination source along the joint, such as oil, moisture, or rust on the joint faces.
Question 6: A CWI is evaluating a weld using AWS D1.1. A surface crack is discovered. Under structural welding code provisions, surface cracks in groove welds are generally:
- Acceptable if shorter than 1/4 inch
- Acceptable only in non-primary members
- Not permitted regardless of length (Correct answer)
- Acceptable if the weld passes ultrasonic testing
Correct answer: Not permitted regardless of length
AWS D1.1 structural welding code prohibits cracks of any length in groove welds; cracks are a rejectable defect with no acceptance limit based on size.
Question 7: What is the purpose of the 'weld map' that a CWI maintains during construction of a pressure vessel?
- To record the arc voltage and travel speed for each weld
- To trace each weld to its welder, WPS, filler metal heat number, and inspection results (Correct answer)
- To calculate the total heat input for the vessel
- To document preheat temperatures only
Correct answer: To trace each weld to its welder, WPS, filler metal heat number, and inspection results
A weld map provides full traceability of each weld to its qualified welder, applicable WPS, filler metal heat number, NDE results, and PWHT records for quality assurance.
CWI Weld Discontinuities and Defects 5
What is 'reheat cracking' and in which type of steel is it most commonly encountered?