2.2 Essential Variables for Procedure Qualification (Section 5.4)
Key Takeaways
- Section 5.4: a change to any Table 1 essential variable requires requalification of the WPS (or qualification of a new WPS); other changes need only a WPS revision.
- Table 1 is split into Category I (standard WPS) and Category II (when the company specifies hardness and/or toughness requirements) — Category II holds the tighter ranges, e.g., ±25% on wall thickness.
- Base material: a change to a higher nominal SMYS than qualified requires requalification; equal or lower nominal SMYS is covered (22nd edition rule — no more Groups a/b/c).
- Filler metal: below X65 nominal SMYS, a change of Table 2 group is essential; at X65 and above, a change of AWS classification is essential.
- Thermal variables: any decrease in minimum preheat, an interpass increase above 500°F (260°C) or more than 100°F (55°C) over the recorded maximum, and a heat-input change beyond ±20% of the qualified value each require requalification.
Last updated: August 2026
2.2 Essential Variables for Procedure Qualification (Section 5.4)
A qualified WPS is bounded by essential variables: parameters whose change beyond the qualified limits alters the mechanical properties or soundness of the weld. Section 5.4.1 states the rule simply — welding procedure specifications are limited by the applicable essential variables in Table 1, and a change to an essential variable necessitates requalification of the WPS or establishment and qualification of a new one. Changes to anything else may be made by revising the WPS, without a new test weld.
Table 1 divides every variable into two categories:
- Category I (Standard WPS): applies when the company does not specify hardness or toughness values.
- Category II (Hardness and/or Toughness): applies when the company does specify them — the ranges tighten considerably (for example, wall-thickness coverage collapses to ±25% of the qualified thickness).
Master Table of Essential Variables (Table 1, 5.4.2.1-5.4.2.14)
| Variable | Change Requiring Requalification | Rationale |
|---|---|---|
| Welding process (5.4.2.1) | Any change of process for any pass or pass grouping; any change between manual and semiautomatic application | Alters arc physics, thermal efficiency, dilution, and hydrogen risk |
| Base material (5.4.2.2) | Change to a base material with a higher nominal SMYS than qualified; thickness outside t→2t (t < 0.154 in.), 0.154 in.→2t (0.154 ≤ t ≤ 1.00 in.), or 0.5t→unlimited (t > 1.00 in.); Category II: ±25% of qualified thickness | Higher-strength steels carry higher hardenability and HAZ crack risk; thickness drives cooling rate |
| Joint design (5.4.2.3) | Fillet weld to groove weld (but not vice versa); a major change in joint type (square, single-V, single-U, double-V, J, etc. — a compound-bevel change within a major type is NOT major) | Changes root access, restraint, and heat dissipation |
| Backing material (5.4.2.4) | Deletion or change of backing material (root pass only; weld metal is not backing) | Backing controls root-side fusion and shape |
| Position (5.4.2.5) | Roll welding to fixed position — but not vice versa | Fixed position adds vertical/overhead pool-control demands |
| Filler metal (5.4.2.6) | Below X65 nominal SMYS: change of Table 2 group or deposition sequence of groups; at/above X65: change of AWS classification or deposition sequence; plus designator rules (e.g., a G-suffix filler: change of manufacturer or trade name) | Controls strength matching, toughness, and diffusible hydrogen |
| Shielding gas (5.4.2.7) | Change in AWS A5.32 classification; flow rate more than 20% below the qualified nominal; deletion/composition change of backing gas | Gas chemistry sets arc stability and metal-transfer mode |
| Electrical (5.4.2.8) | Change of current/polarity type (DCEN/DCEP/AC); change to or from a waveform-controlled process; heat input change beyond ±20% of qualified | Heat input drives cooling rate, HAZ microstructure, and toughness |
| Preheat (5.4.2.9) | Any decrease in minimum preheat below the qualified temperature; if no preheat was used in qualification, the WPS minimum may not exceed the lesser of 60°F (16°C) or the actual base-metal temperature recorded before qualification welding | Lower preheat accelerates cooling toward martensite and HACC |
| Interpass temperature (5.4.2.10) | Increase above 500°F (260°C), or more than 100°F (55°C) above the maximum recorded during qualification | Excess interpass temperature coarsens grains and degrades strength/toughness |
| Pass sequence (5.4.2.11) | With a temper-bead technique, a change in bead deposition sequence | Sequence is what performs the tempering |
| Cooling (5.4.2.12) | Addition/deletion of deliberate cooling; change to a faster cooling method; increase in maximum weld temperature before cooling | Changes the thermal cycle and resulting microstructure |
| Postheating (5.4.2.13) | Eliminating hydrogen-diffusion postheat; reducing postheat temperature more than 60°F (33°C); reducing time at temperature | Postheat is the hydrogen escape path |
| PWHT (5.4.2.14) | Addition or deletion of PWHT; any change in the PWHT procedure | Alters stress relief and final microstructure |
Heat input itself is calculated per 5.3.2.6 — for non-waveform-controlled processes:
with V = average arc voltage, A = average current, S = travel speed (in./min or mm/min). Waveform-controlled processes use instantaneous energy or power per 5.3.2.6 Equations (2) and (3).
Worked Field Scenarios
- Scenario A (direction change): A downhill SMAW crew asks to switch the root pass to uphill progression on a steep crossing. Requalification required — direction of welding is an essential variable under both Section 5 (procedure) and Section 6 (welder).
- Scenario B (lower strength substitution): A WPS qualified on X60 is proposed for an X52 section. No requalification — X52 nominal SMYS (52 ksi) is below the qualified 60 ksi. The 22nd edition covers equal-or-lower nominal SMYS.
- Scenario C (higher strength substitution): The same X60-qualified WPS is proposed for X70. Requalification required — a change to a higher nominal SMYS is an essential variable (Table 1, 5.4.2.2 a). Note how the 22nd edition answers this differently from 21st-edition group rules.
- Scenario D (heat input drift): Production monitoring shows heat input running 25% above the PQR value. Requalification required — Table 1 (5.4.2.8 c) allows only ±20%.
Test Your Knowledge
Under API 1104:2021 Section 5.4, which parameter change requires complete requalification of the WPS?
A
B
C
D
Test Your Knowledge
A contractor qualified a WPS on API 5L X60 and now wants to weld API 5L X70. What does API 1104:2021 Table 1 require?
A
B
C
D
Test Your Knowledge
Under Table 1 of API 1104:2021, a change from an E6010 electrode (Group 1) to an E7018 electrode (Group 4) on pipe below X65 nominal SMYS is what kind of variable?
A
B
C
D