A hybrid WPS with a GTAW root pass and SMAW fill is one of the most common procedures in pipe shop work, food-grade fabrication, and any application where a high-cleanliness root is required but bulk fill is too slow to do entirely in GTAW.

Because GTAW isn't on the AWS D1.1 prequalified list, the entire procedure must be qualified by test. Here is what a clean hybrid WPS looks like.

Identification block

  • WPS number: WPS-25-029
  • Revision: 0
  • Date: 2026-05-08
  • Code: AWS D1.1/D1.1M:2025
  • Scope: Hybrid GTAW root + SMAW fill on ASTM A106 Gr. B pipe (or A36 plate), thickness 1/4 in to 1 in, in 5G / 6G positions
  • Status: Qualified by test per AWS D1.1 Clause 6 — see supporting PQR-25-008

Process declarations

Two processes, both fully specified:

GTAW root pass

  • Process: GTAW (Gas Tungsten Arc Welding), manual
  • Current: DC
  • Polarity: DCEN (Direct Current Electrode Negative, straight polarity)
  • Electrode: 2% thoriated (EWTh-2) or 2% ceriated (EWCe-2) tungsten, 1/16 in or 3/32 in diameter
  • Filler: A5.18 ER70S-2 or ER70S-6, 3/32 in diameter, hand-fed
  • Shielding gas: 100% Argon, 15–25 CFH [7–12 L/min]
  • Purge gas: 100% Argon, 5–10 CFH on the back side (for pipe)
  • Amperage range: 70–130 A (root pass on 1/4–1 in pipe)
  • Travel speed range: 4–8 ipm

SMAW fill passes

  • Process: SMAW, manual
  • Filler: A5.1 E7018-H8, 3/32 in or 1/8 in
  • Current: DC
  • Polarity: DCEP
  • Amperage range: 90–145 A (depends on diameter)
  • Travel speed range: 4–8 ipm

Base metal

  • Specification: A106 Gr. B (pipe) or ASTM A36 (plate, for groove work)
  • Group number: Group I per Table 6.9 (2025)
  • Thickness range: 1/4 in (6.4 mm) to 1 in (25 mm)
  • Diameter range (pipe): 2 in NPS to 12 in NPS

Joint detail

  • Joint type: Open root, V-groove, no backing
  • Root opening: 1/16 in to 1/8 in
  • Root face: 1/16 in to 1/8 in
  • Groove angle: 60° to 75°
  • Joint sketch: embedded as figure 1

Open-root joints are exactly why GTAW root passes exist — GTAW lays a controlled, fused root without backing.

Position

  • 5G: pipe horizontal, weld progression vertical-up (with restart positions documented)
  • 6G: pipe at 45°, all-position
  • Plate equivalents: 3G, 4G

Hybrid WPSs are usually documented for the 6G position because 6G qualifies all other positions per Clause 6.

Preheat and interpass

  • Minimum preheat: per Table 5.8 (typically 50–100°F for thicknesses up to 1 in on Group I)
  • Maximum interpass: 500°F [260°C]
  • Method: contact thermocouple at the joint

Supporting PQR

The hybrid procedure requires a single PQR that qualifies both the GTAW root and the SMAW fill on the same test coupon:

  • PQR number: PQR-25-008
  • Date: 2026-04-15
  • Test coupon: 6 in NPS schedule 80 A106 Gr. B pipe, 6G position
  • Tests passed: 2 tensile (UTS > 70 ksi each), 4 side bends (no discontinuity > 1/8 in), VT acceptable

Common pitfalls on hybrid WPSs

  1. Claiming GTAW prequalified. GTAW is never prequalified under D1.1. Any GTAW WPS requires a PQR.
  2. Documenting only one process. Each process has its own essential variables. The WPS must fully document both.
  3. One PQR for GTAW + a different PQR for SMAW. Acceptable for some applications, but the test coupon should ideally combine both processes to qualify the transition.
  4. Purge gas omitted. Open-root GTAW on pipe requires back-purge to prevent oxidation. WPS must specify purge gas and flow.
  5. Position table mismatch. A 5G test coupon does not qualify 6G. Make sure the qualified position covers the production scope.

Hybrid WPSs are powerful but demand more documentation discipline than single-process procedures. A rule engine that supports multi-process WPSs and validates each process against its own essentials catches the common documentation gaps.