A CWI is reviewing the essential variables on a Welding Procedure Specification (WPS) for a Shielded Metal Arc Welding (SMAW) process. Which of the following changes would NOT typically require requalification of the WPS according to most welding codes?
- AA decrease in the specified preheat temperature by more than 100°F (55°C).
- BA change in electrode classification from E7018 to E6010.
- CA change in the base metal P-number from P-1 to P-3.
- DA change from stringer bead to weave bead technique.
Show answer & explanationAnswer & explanation
Correct answer: D. A change from stringer bead to weave bead technique.
In most welding codes (e.g., AWS D1.1, ASME Section IX), a change in technique from stringer bead to weave bead is typically considered a non-essential variable. This means it can be changed without requiring requalification of the WPS. The other options (change in P-number, significant decrease in preheat, change in electrode classification) are generally considered essential or supplementary essential variables that would require requalification.
Why the other options are wrong
- A. A significant decrease in preheat temperature (often more than 100°F or 50°F, depending on code/material) is a supplementary essential variable that impacts hydrogen diffusion and cracking susceptibility, requiring WPS requalification.
- B. Changing electrode classification to one with different operating characteristics (like E7018 low-hydrogen to E6010 cellulosic) is an essential variable, impacting mechanical properties and requiring WPS requalification.
- C. Changing P-numbers, especially across different groups, is an essential variable that typically requires WPS requalification due to different metallurgical properties.
WPS Essential Variables
Essential variables in a WPS are parameters that, if changed beyond specified limits, are considered to affect the mechanical properties of the weld and therefore require requalification of the WPS.
- Changes require WPS requalification.
- Examples: base metal P-number, filler metal F-number, preheat (significant changes).
- Non-essential variables do not require requalification.
- Supplementary essential variables apply to impact-tested materials.
Memory trick: Essential changes 'E'nsure 'E'valuation, non-essential 'N'ever 'N'eed 'N'ew tests.