4.3 WPS Essential Variables, Base Metal Ranges & Qualified Positions (Table 6.6)
Key Takeaways
- A WPS Essential Variable is any parameter change beyond codified limits that alters the mechanical properties of the weldment and legally mandates PQR requalification.
- A PQR coupon welded on plate with thickness T >= 1 in. (25 mm) qualifies the WPS for all production thicknesses from 1/8 in. (3 mm) to Unlimited.
- Heat input increases greater than 10% require WPS requalification whenever welding quenched and tempered steels (Group IV) or when CVN impact toughness is specified.
- Qualifying a CJP groove weld in the 1G (flat) position qualifies only the flat position, whereas qualifying in 1G, 2G, 3G, and 4G positions (or 6G pipe) qualifies the WPS for all positions.
- A change in vertical welding progression between vertical-up and vertical-down is a non-negotiable essential variable requiring complete procedure requalification.
WPS Essential Variables Framework (Table 6.6)
An Essential Variable is a welding parameter, material property, or joint characteristic which, if modified beyond the specific tolerances established in AWS D1.1 Table 6.6, could adversely affect the mechanical properties, soundness, or metallographic structure of the welded joint. Any change exceeding an essential variable tolerance immediately invalidates the WPS and mandates requalification through a new PQR.
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| WPS ESSENTIAL VARIABLE REQUALIFICATION TRIGGERS |
+-----------------------------------------------------------------------------------------+
| |
| +------------------------+ +------------------------+ +---------------------------+ |
| | PROCESS & METALS | | ELECTRICAL & HEAT | | POSITION & GEOMETRY | |
| +------------------------+ +------------------------+ +---------------------------+ |
| | * Change in process | | * Heat input > +10% | | * Change in position | |
| | * Change in Base Group | | (for Q&T or CVN) | | * Progression: Up vs Down | |
| | * Change in F-Number | | * Current: > +/- 10-15%| | * Omission of backing | |
| | * Change in Gas Ratio | | * Voltage: > +/- 7-10% | | * Change in Groove Type | |
| | (> 5% Ar/CO2 shift) | | * Travel Speed: > 15% | | * Root opening decrease | |
| +------------------------+ +------------------------+ +---------------------------+ |
| |
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Master Summary of Table 6.6 Essential Variable Changes
| Variable Category | Essential Variable Change Requiring WPS Requalification | Applicable Processes |
|---|---|---|
| Welding Process | Any change from one welding process to another, or combination of processes. | All Processes |
| Base Metal | 1. Change from one Base Metal Group (Table 5.6) to another.<br/>2. Welding an unlisted steel not qualified on the PQR.<br/>3. Change in base metal thickness (T) outside Table 6.2 limits. | All Processes |
| Filler Metal | 1. Increase in filler metal strength classification (e.g., E7018 to E8018).<br/>2. Change in AWS electrode classification F-number or A-number.<br/>3. Change in electrode nominal diameter by more than permitted. | SMAW, GMAW, FCAW, SAW |
| Shielding Gas | 1. Change in nominal shielding gas composition (> 5% variation in major component).<br/>2. Decrease in gas flow rate > 25% or increase > 50%.<br/>3. Change from single gas to mixture or vice versa. | GMAW, FCAW-G, GTAW |
| Electrical Variables | 1. Change in current type (AC vs. DC) or polarity (DCEP vs. DCEN).<br/>2. Amperage change outside ±10% to ±15%.<br/>3. Voltage change outside ±7% to ±10%.<br/>4. Travel speed change outside ±15%. | All Processes |
| Position & Progression | 1. Addition of welding positions not qualified by Table 6.1.<br/>2. Change in vertical progression from vertical-up to vertical-down or vice versa. | All Processes |
Electrical Variables & Heat Input Control (Clause 6.8, Table 6.6 & Table 6.8)
Heat Input Calculation Formula
Heat input represents the quantity of electrical energy delivered to the weldment per unit length of weld seam. It directly controls cooling rates, microstructural phase transformations, HAZ grain size, and mechanical toughness.
H = (60 × E × I) / (1000 × S)
Where:
- H = Heat input in kilojoules per inch (kJ/in.) [or kJ/mm if divided by S in mm/min]
- E = Arc voltage (Volts)
- I = Welding current (Amperes)
- S = Travel speed of the arc (inches per minute [ipm] or mm/min)
- 60 = Conversion constant (seconds per minute)
- 1000 = Conversion constant (Joules to kiloJoules)
The > 10% Heat Input Rule for Toughness & Q&T Steels
AWS D1.1 Table 6.8 (supplementary essential variables for CVN applications) makes an increase of greater than 10% in heat input over the value recorded on the PQR an essential variable requiring procedure requalification, and Clause 7.7 separately caps heat input on quenched and tempered steels. This applies whenever:
- The procedure is applied to Group IV quenched and tempered steels (e.g., ASTM A514, A517, ASTM A709 Grades 100/100W).
- Charpy V-Notch (CVN) impact toughness is specified in contract documents for any base metal.
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| WORKED HEAT INPUT EVALUATION EXAMPLE |
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| |
| PQR Recorded Parameters (ASTM A514 Plate): |
| * Current (I) = 220 A |
| * Voltage (E) = 26 V |
| * Travel Speed (S) = 12.0 ipm |
| * PQR Heat Input: H_pqr = (60 * 26 * 220) / (1000 * 12.0) = 28.60 kJ/in. |
| * Maximum Allowable Heat Input (+10% Limit): 28.60 * 1.10 = 31.46 kJ/in. |
| |
| PROPOSED PRODUCTION WPS SETTINGS: |
| * Proposed Current = 250 A, Voltage = 28 V, Travel Speed = 11.0 ipm |
| * Calculated WPS Heat Input: H_wps = (60 * 28 * 250) / (1000 * 11.0) = 38.18 kJ/in. |
| * Evaluation: 38.18 kJ/in. > 31.46 kJ/in. (+33.5% increase) |
| * RESULT: REJECTED. Mandates complete procedure requalification via a new PQR. |
| |
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Position Qualification Rules & Qualified Thickness Ranges (Tables 6.1 & 6.2)
Position Qualification Matrix for Plate Groove Welds
In WPS qualification, testing in a specific position qualifies the procedure for specific production welding positions according to Table 6.1:
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| WPS POSITION QUALIFICATION RULES (TABLE 6.1) |
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| |
| PQR TEST POSITION QUALIFIED PRODUCTION POSITIONS |
| ============================================================================= |
| 1G (Flat Position) ---> Flat (1G) Groove & Flat (1F) Fillet only |
| 2G (Horizontal Position) ---> Flat (1G) & Horizontal (2G) Groove; 1F & 2F Fillet|
| 3G (Vertical Position) ---> Flat (1G) & Vertical (3G) Groove; 1F, 2F, 3F Fillet|
| 4G (Overhead Position) ---> Flat (1G) & Overhead (4G) Groove; 1F, 2F, 4F Fillet|
| |
| ALL-POSITION QUALIFICATION: |
| * Requires testing coupons in 1G, 2G, 3G, and 4G positions (or 2G + 3G + 4G), OR |
| * Qualifying on a 6G pipe test assembly per Table 10.8. |
| |
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Qualified Thickness Ranges for CJP Plate Coupons (Table 6.2)
AWS D1.1 Table 6.2 establishes the qualified base metal thickness range (T) based on the nominal thickness of the PQR test plate:
| PQR Test Plate Thickness (T) | Minimum Qualified Thickness | Maximum Qualified Thickness |
|---|---|---|
| 1/8 in. ≤ T < 3/8 in. (3–10 mm) | 1/8 in. (3 mm) | 2T |
| 3/8 in. ≤ T < 1 in. (10–25 mm) | 1/8 in. (3 mm) | 2T |
| T ≥ 1 in. (25 mm) | 1/8 in. (3 mm) | UNLIMITED (T = ∞) |
[!IMPORTANT] A test coupon welded on plate 1 in. (25 mm) thick or greater qualifies the WPS for all structural thicknesses from 1/8 in. (3 mm) to Unlimited. This is why the 1 in. plate test coupon is the industry standard for commercial procedure qualification programs.
A structural steel contractor qualifies a CJP groove weld procedure using a 1-inch (25 mm) thick plate test coupon per AWS D1.1 Table 6.2. What is the qualified base metal thickness range for production welding supported by this PQR?
A PQR for welding ASTM A514 quenched and tempered steel records an arc voltage of 24 V, current of 200 A, and travel speed of 10 inches per minute (heat input = 28.8 kJ/in.). What is the maximum allowable heat input that can be specified on the production WPS without requiring requalification per AWS D1.1 Table 6.6?
A fabricator successfully qualifies a CJP groove weld WPS on plate in the 3G (vertical) position only. Under AWS D1.1 Table 6.1, which production groove and fillet welding positions are qualified by this PQR?