Weld Positions Field Guide
AWS D1.1 / ASME Sec IX Welding Metallurgy & Geometry
WELD JOINTS & TYPES
Technical Reference
SHEET 01 / 03
Welded assemblies rely on standardized joint geometries and two primary weld forms: Groove Welds and Fillet Welds. Joint configuration dictates bevel prep, penetration depth, and load-bearing performance.
1 Butt Weld (Butt Joint)
B-Joint
Base Metal Base Metal Weld Face Reinforcement Root Penetration
Definition: Members positioned edge-to-edge in approximately the same plane.
- Requires square, bevel, V, U, or J groove preparation on heavy sections.
- Engineered for direct axial tension and dynamic cyclic fatigue loads.
- Grinding flush yields 100% joint efficiency with minimal stress risers.
Primary Weld: Groove Weld Prep: Beveled Edges
2 Lap Weld (Lap Joint)
L-Joint
Base Plate Overlapping Member Fillet Bead
Definition: Members joined along overlapping parallel planes.
- Welded along overlapping edges using single or double fillet welds.
- Eliminates edge-preparation costs; provides highly forgiving fit-up.
- Loads in eccentric shear; crevice can trap moisture (corrosion risk).
Primary Weld: Fillet Weld Stress: Longitudinal Shear
3 Corner Weld (Corner Joint)
C-Joint
Outside Bead Inside Fillet (opt) Base Plate
Definition: Members positioned at approximately 90° meeting at their outer edges.
- Classified as Flush (Closed), Half-Open, or Full-Open.
- Standard choice for structural tanks, boxes, cabinets, and hollow sections.
- Full-open corner forms a natural V-groove requiring minimal edge preparation.
Joint Angle: 90° Perpendicular Style: Open vs Closed
4 Fillet Weld (Weld Form)
Tee / Cross-Section
Face Base Plate
Definition: Triangular cross-section weld joining surfaces at roughly 90°.
- Most prevalent weld in industry; forms Tee, lap, and inside corner joints.
- Requires no costly beveling; sized by leg length (\(z\)) and throat (\(a\)).
- Load capacity is calculated entirely across the theoretical throat dimension.
Beveling: Square Edge Profile: Flat / Convex
Critical Engineering Anatomy: Fillet Weld Geometry AWS Standard Sizing Formula
1. Leg Length (\(z\))
Distance from joint root to fillet toe along each plate surface.
2. Throat (\(a\))
Minimum design thickness: \(a = z \times \cos(45^\circ) \approx 0.707 \cdot z\).
3. Weld Toe
Boundary line where weld face meets base metal; stress riser zone.
4. Joint Root
Deepest point of intersection where parts met prior to welding.
Welding Technology Reference Series Section 1: Joint Geometries & Classifications Page 1 of 3
AWS D1.1 Table 4.1 Position Nomenclature & Gravity Dynamics
PLATE POSITIONS: 1F–4F & 1G–4G
Technical Reference
SHEET 02 / 03
Key: Digits: 1=Flat, 2=Horizontal, 3=Vertical, 4=Overhead
F = Fillet G = Groove
Fillet Positions (F) Tee & Lap Seams
1F — Flat Fillet Highest Deposition
Orientation: Plates tilted 45° to form a horizontal V-trough; weld face horizontal.
Technique: Gravity retains puddle; supports maximum electrode size and rapid travel speeds.
2F — Horizontal Fillet Most Common
Orientation: Bottom plate horizontal, upright plate vertical. Seam runs horizontally.
Technique: Torch angled 40°–45° pointing upward toward vertical wall to counteract puddle sagging/undercut.
3F — Vertical Fillet Uphill vs Downhill
UP
Orientation: Plates vertical; weld axis is vertical (travels vertically).
Technique: Vertical-Up for structural depth; pause at toes with inverted-V weave. Vertical-Down for sheet metal.
4F — Overhead Fillet Severe Gravity Sag
Orientation: Underneath overhead joint. Horizontal plate is positioned above.
Technique: Ultra-short arc, reduce amperage 10–15%, stringer beads to prevent dripping molten metal.
Groove Positions (G) Butt & Edge Grooves
1G — Flat Groove Baseline Position
Orientation: Plates horizontal; weld axis horizontal; filler metal deposited from top side.
Technique: Highest allowable heat input; uniform bevel fill; straightforward root control with backing or keyhole.
2G — Horizontal Groove Asymmetric Gravity
Orientation: Plates vertical in plane; weld seam/axis is horizontal.
Technique: Metal tends to roll down. Multi-pass stringers required; place bottom bead first to create shelf for upper beads.
3G — Vertical Groove Major Qual Test
Orientation: Plates vertical; weld axis vertical. Typically vertical-up progression.
Technique: Pause momentarily at groove sidewalls to tie in and prevent undercut; sweep across center rapidly to avoid bulging.
4G — Overhead Groove Highest Skill Grade
Orientation: Plates horizontal overhead; weld deposited into joint from underside.
Technique: Surface tension and arc force hold puddle. Keep puddle small, travel fast, avoid wide weave manipulation.
Welder Qualification Hierarchy (AWS D1.1 Code Rule)
Welder qualifications are hierarchical: passing tests in more challenging positions qualifies lower positions. Qualifying in 3G & 4G Plate qualifies the welder for 1G, 2G, 3G, 4G, and all Fillet (1F–4F) positions on plate. Note: plate tests do not qualify for fixed pipe (5G/6G).
Welding Technology Reference Series Section 2: Plate Position Standards & Techniques Page 2 of 3
ASME Sec IX / API 1104 Fixed Pipe Dynamics & Shop Summary
5G PIPE POSITION & MATRIX
Technical Reference
SHEET 03 / 03
5G
HORIZONTAL FIXED PIPE POSITION
Non-Rotated / 360° Circumference
PIPE AXIS (FIXED) 12:00 (Flat 1G) 6:00 (Overhead 4G) 3:00 (3G Vert) 9:00 (3G Vert) Uphill Travel: 6:00 → 12:00
Dynamic Position Transition
In 5G, the pipe is placed horizontally and held stationary (cannot rotate). The welder must adapt body angle, travel speed, and puddle control around the full circumference:
1. Overhead (6:00) Root start; risk of drop-through or suckback. Keep tight arc.
2. Vertical (3:00/9:00) Weave transition; risk of gravity sag and edge undercut.
3. Flat Cap (12:00) Crown tie-in; danger of high buildup and excess heat.
Progression Codes: Structural piping (ASME/AWS) requires Uphill for full penetration. Cross-country pipelines (API 1104) typically use fast Downhill cellulosic passes.
Complete Weld Positions & Joint Types Master Reference
| Code / Type | Category | Joint Axis / Orientation | Gravity Impact | Critical Technique & Defect Prevention |
|---|
| 1F / 1G | Flat Fillet / Groove | Horizontal plane, top side | Favorable (pulls down) | High travel speed; uniform fill; watch for slag inclusions in deep grooves. |
| 2F / 2G | Horizontal Fillet / Groove | Plates vertical, seam horizontal | Moderate sag toward bottom | Torch 40°-45° up; stack stringers bottom-to-top; eliminate upper undercut. |
| 3F / 3G | Vertical Fillet / Groove | Plates vertical, seam vertical | Heavy downward pull | Inverted-V weave; pause at sides to tie in sidewall, cross center swiftly. |
| 4F / 4G | Overhead Fillet / Groove | Horizontal plates overhead | Severe dripping risk | Short arc length; reduce amperage 10-15%; maintain narrow stringer passes. |
| 5G | Fixed Horizontal Pipe | Pipe horizontal; continuous seam | Continuous 360° variation | Body repositioning; smoothly transition from overhead root to flat cap. |
| Butt Joint | Primary Joint Type | Edge-to-edge coplanar | Depends on position | Ensure 100% root penetration, proper root opening (gap), and root face land. |
| Lap Joint | Primary Joint Type | Parallel overlapping plates | Typically horizontal (2F) | Fillet size matches thickness of thinner plate; avoid melting top corner edge. |
| Corner Joint | Primary Joint Type | 90° angle at edge junction | Inside/outside profiles | Tight root gap control to prevent burn-through on open corner joints; clamp well. |
| Fillet Weld | Triangular Weld Profile | Corner of T, lap, or corner | Affects leg balance | Aim for flat to slight convex face; avoid acute concave throat (cracking risk). |
Undercut Prevention
In 2F, 2G, and 3G, pause at the sidewall toes to allow filler metal to fill the gouge cut by the arc.
Heat Input Control
Vertical-up (3G/5G) deposits thicker beads with higher heat per inch; lower amperage prevents puddle sag.
Fit-up & Tack Welds
Accurate root face and gap are mandatory. Feather tack ends to feather into the incoming root pass.
Welding Technology Reference Series Section 3: 5G Pipe Dynamics & Shop Reference Matrix Page 3 of 3
