6.1 Welding Procedure Specification (WPS)
Key Takeaways
- A WPS is the written "recipe" for making a weld — ensures consistency, quality, and documentation
- Essential variables affect mechanical properties — changing them requires a new PQR (re-qualification)
- Non-essential variables can be changed without re-qualification (but WPS must be revised)
- AWS D1.1 prequalified WPS: exempt from PQR testing when ALL prequalification conditions are met
- Only four processes are prequalified under D1.1: SMAW, GMAW, FCAW, SAW
- CWIs must be able to read and interpret a WPS — not create one
6.1 Welding Procedure Specification (WPS)
A Welding Procedure Specification (WPS) is a written document providing the required welding variables for a specific application to ensure repeatability by properly trained welders. It is essentially the "recipe" for making a weld.
Purpose of the WPS
The WPS serves three critical functions:
- Ensures consistency — every welder follows the same procedure for the same joint
- Ensures quality — variables are set to produce sound welds meeting code requirements
- Provides documentation — creates a traceable record of how each weld was made
WPS Contents (Typical Variables)
| Category | Examples |
|---|---|
| Joint design | Joint type, groove angle, root opening, root face, backing |
| Base metal | ASTM specification, P-number, thickness range |
| Filler metal | AWS classification, F-number, A-number, diameter |
| Position | Welding position (1G, 2G, etc.) and progression (up/down for vertical) |
| Electrical | Current type (AC/DC), polarity, amperage range, voltage range |
| Preheat/interpass | Minimum preheat temperature, maximum interpass temperature |
| Shielding | Gas type, flow rate, flux type |
| Technique | Stringer or weave, number of passes, single or multi-pass |
| PWHT | Temperature, hold time, heating/cooling rates |
Essential vs. Non-Essential Variables
| Variable Type | Definition | Consequence of Change |
|---|---|---|
| Essential | Variables that affect the mechanical properties of the weld | Changing beyond the qualified range requires a new PQR (re-qualification) |
| Supplementary essential | Variables affecting impact (notch toughness) properties | Requires re-qualification only when impact testing is required |
| Non-essential | Variables that do not significantly affect mechanical properties | Can be changed without re-qualification (but WPS must be revised) |
Examples of Essential Variables:
- Welding process (e.g., changing from SMAW to GMAW)
- Base metal type (P-number)
- Filler metal classification (F-number, A-number)
- Thickness range
- Preheat (decrease below qualified minimum)
- PWHT (adding or deleting)
- Current type (changing AC to DC)
- Position (adding vertical or overhead if not qualified)
Examples of Non-Essential Variables:
- Joint design (minor changes in groove angle, root opening)
- Travel speed
- Electrode diameter (within qualified range)
- Cleaning method
- Number of passes (more or fewer)
Prequalified vs. Qualified WPS (AWS D1.1)
AWS D1.1 provides a unique concept: prequalified WPS
| Type | Description | PQR Required? |
|---|---|---|
| Prequalified WPS | Uses prequalified joint details, processes, and base/filler metals from D1.1 Clause 5 | No — exempt from testing |
| Qualified WPS | Any WPS that does not meet all prequalification requirements | Yes — must be supported by a PQR |
Prequalified conditions (all must be met):
- Process: SMAW, GMAW, FCAW, SAW (only four)
- Base metal: listed in D1.1 Table 5.3
- Filler metal: matched per D1.1 Table 5.4
- Joint design: per D1.1 prequalified joint details (Figures 5.1, 5.2)
- Preheat/interpass: per D1.1 Table 5.8
- All other prequalification requirements met
For the Exam: CWIs must be able to read and interpret a WPS — not create one. Know the difference between essential and non-essential variables, and know that changing an essential variable beyond the qualified range requires a new PQR. Also know the concept of prequalified WPS under AWS D1.1.
What happens when an essential variable in a WPS is changed beyond the qualified range?
Under AWS D1.1, a prequalified WPS does NOT require a PQR when: