A welding inspector is conducting a visual inspection of a Gas Metal Arc Welding (GMAW) root pass on a pipe. The welder used a spray transfer mode. Which of the following visual characteristics would indicate an issue with the transfer mode selection or parameters for a root pass?
- AA narrow, convex bead profile with good penetration.
- BExcessive spatter on the pipe surface adjacent to the weld.
- CA smooth, uniform bead appearance with good fusion.
- DEvidence of burn-through or excessive melt-through on the root.
Show answer & explanationAnswer & explanation
Correct answer: D. Evidence of burn-through or excessive melt-through on the root.
Spray transfer is characterized by high heat input and a continuously molten electrode transfer, which provides good penetration. However, for a root pass, especially on pipe, this high heat input often leads to burn-through or excessive melt-through if not precisely controlled, making it generally unsuitable for open-root passes. Short-circuit or pulsed-spray transfer modes are typically preferred for root passes to control heat input and prevent such issues.
Why the other options are wrong
- A. A narrow, convex bead with good penetration is generally a good characteristic, but 'excessive' melt-through (burn-through) indicates a problem for a root pass, even if penetration is good.
- B. While spatter can be an issue, it's more characteristic of globular transfer. Spray transfer is typically spatter-free. More importantly, burn-through is a direct consequence of spray transfer's high heat.
- C. This describes a desirable outcome for a weld bead, not an issue.
GMAW Spray Transfer Limitations (Root Pass)
Gas Metal Arc Welding (GMAW) spray transfer is characterized by high heat input, deep penetration, and high deposition rates. While excellent for fill and cap passes on thick materials, its high heat makes it generally unsuitable for open-root passes, as it can easily lead to burn-through, excessive melt-through, or an overly large and uncontrolled root bead, especially on pipe.
- High heat input transfer mode.
- Deep penetration.
- Continuous stream of molten droplets.
- Unsuitable for open-root passes.
- Prone to burn-through or excessive melt-through.
- Better for fill/cap passes or thicker sections.
Memory trick: For 'Root' passes, 'Spray' is 'Too Hot', leading to 'Holes'.