Joint preparation is the foundation of a good weld. A poorly prepared joint leads to defects: lack of fusion, incomplete penetration, porosity, and slag inclusion. AWS D1.1, the structural welding code for steel, defines prequalified joint configurations that have been proven through decades of testing and field experience. Using a prequalified joint simplifies WPS qualification and provides confidence that the joint will perform as designed.
This guide covers the standard prequalified groove joint configurations, explains when to use CJP versus PJP, walks through the groove geometry parameters, and provides guidance on filler metal estimation. It is written for weld engineers, fabricators, and quality inspectors who need to specify, verify, and estimate groove weld joints.
CJP vs PJP: When to Use Each
Complete joint penetration (CJP) welds develop the full strength of the base metal. The weld extends through the entire cross-section of the joint. CJP welds are required when the joint must carry the full design load of the connected members in tension, such as moment connections in seismic frames, pressure vessels, and fatigue-loaded structures.
Partial joint penetration (PJP) welds have a specified effective throat that is less than the full material thickness. They are acceptable for many static-load connections where the full strength of the base metal is not needed: column splice connections, stiffener-to-flange welds, and some bracing connections. PJP welds are cheaper to produce because they require less filler metal and welding time.
The choice between CJP and PJP is a structural design decision, not a fabrication decision. The structural engineer specifies the weld type on the drawings. The fabricator's job is to prepare the joint and execute the weld to match the specification. If a drawing calls for a CJP weld, substituting a PJP weld is a code violation regardless of how much filler metal you put in the joint.
One important difference: CJP welds in butt joints do not require a weld size callout on the drawing because the weld, by definition, extends through the full thickness. PJP welds must specify the effective throat or weld size.
Prequalified Joint Configurations
AWS D1.1 Table 3.2 defines prequalified CJP groove joints. Table 3.3 defines prequalified PJP groove joints. A prequalified joint does not require WPS qualification testing (bend tests, macro-etch) if it is used within the specified parameters. This saves significant time and cost in WPS development.
The most common prequalified CJP butt joints are: Single-V groove (B-U2): 60-degree included angle, 0-1/4 inch root opening, 0-1/8 inch root face. This is the default CJP joint for structural steel. Double-V groove (B-U3): Same angle but grooved from both sides. Uses 40-50 percent less filler metal than single-V on thick plate. Single-bevel groove (TC-U4): Simpler to prepare (only one plate beveled) but harder to weld because of the sharp corner at the root.
For PJP joints, the groove depth determines the effective throat. AWS D1.1 Table 2.2 provides the effective throat as a function of groove depth and groove angle. Steeper angles provide better penetration for a given groove depth.
Using a non-prequalified joint configuration (different angle, different root opening, or a configuration not in the tables) requires WPS qualification testing per AWS D1.1 Clause 4. This adds cost and lead time but may be justified for specialty applications.
Weld Joint Prep Calculator
AWS D1.1 prequalified groove weld joint dimensions. Bevel angle, root opening, root face, groove angle, and effective throat for V, bevel, J, and U groove joints.
Groove Geometry: Angle, Root Opening, Root Face
Three parameters define the groove: included angle, root opening (gap), and root face (land). Each affects weld quality, filler metal consumption, and production efficiency.
Included angle (the total angle of the groove) determines access for the welding torch or electrode. Wider angles provide better access and penetration but consume more filler metal. The standard 60-degree included angle (30 degrees per side) is a compromise. Narrower angles (45 degrees) save filler metal but risk lack-of-fusion defects at the root. Wider angles (90 degrees) waste filler metal.
Root opening (gap) provides space for the root pass to achieve full penetration. Too narrow and the root pass cannot penetrate through the joint. Too wide and the root pass falls through. For a standard single-V CJP with backing, the root opening is typically 1/4 inch. For open root (no backing), 1/16 to 1/8 inch is common.
Root face (land) is the ungrooved portion at the root of the joint. It provides a platform for the root pass and prevents burn-through. A thicker root face reduces the risk of burn-through but increases the risk of incomplete penetration. Typical root face: 0-1/8 inch for CJP joints with backing, 1/16-3/32 inch for open root.
Included angle: 60° (30° per side)
Root opening: 1/4" (with backing) or 1/16-1/8" (open root)
Root face: 0-1/8" (with backing) or 1/16-3/32" (open root)
These are the most commonly specified values for structural steel fabrication.
Estimating Filler Metal Consumption
Filler metal consumption depends on the groove cross-sectional area, the deposition efficiency of the welding process, and allowances for reinforcement, spatter, and waste.
The groove cross-sectional area for a single-V CJP joint is approximately: A = (t x tan(angle/2) x t / 2) + (root_opening x t), where t is the plate thickness and angle is the included groove angle. For a 1-inch plate with 60-degree groove and 1/4-inch root opening: A = (1 x 0.577 x 0.5) + (0.25 x 1) = 0.539 in2.
Add reinforcement (cap): Typically 1/16 to 1/8 inch above the plate surface, adding approximately 0.05-0.10 in2 per side.
Total cross-sectional area x joint length x steel density (0.283 lb/in3) = weight of weld metal deposited. Divide by deposition efficiency: SMAW 63 percent, GMAW solid wire 93 percent, FCAW 83 percent, SAW 98 percent. The result is the weight of filler metal consumed.
For quick field estimates: A single-V CJP weld on 1-inch plate with GMAW solid wire consumes approximately 2.0 lb of wire per linear foot. On 3/4-inch plate, approximately 1.2 lb per foot. On 1/2-inch plate, approximately 0.6 lb per foot. These are approximations. Use the calculator for precise values.
Weld Joint Prep Calculator
AWS D1.1 prequalified groove weld joint dimensions. Bevel angle, root opening, root face, groove angle, and effective throat for V, bevel, J, and U groove joints.
Backing Bars and Backgouging
CJP welds can be made with or without backing. With backing, a steel bar is tack-welded to the back side of the joint before welding. The root pass is deposited against the backing bar, which supports the weld pool and simplifies achieving full penetration. The backing bar is typically 3/8 or 1/2 inch thick and at least 1 inch wide.
Without backing, the welder must achieve full penetration through an open root. This requires higher skill and is slower. After completing the weld from the first side, the root is backgouged (using carbon arc gouging or grinding) to remove any defects, and a back weld is applied from the second side to complete the CJP.
AWS D1.1 specifies that permanent steel backing left in place is acceptable for most structural applications. However, for cyclically loaded structures (bridges, cranes), backing must be removed and the back side ground smooth to eliminate the stress concentration at the backing bar edge. AISC 341 seismic provisions also require backing removal for demand critical welds.
When estimating filler metal for backgouged joints, add 15-25 percent to the groove weld volume to account for the backgouge cavity that must be filled with the back weld. This volume is frequently omitted from estimates.
Joint Preparation Methods
The bevel can be cut by several methods, each with different cost, quality, and equipment requirements:
Oxy-fuel torch: The most common method for carbon steel in the shop and field. Fast, inexpensive, and adequate for most structural work. The cut surface has a rough texture with drag lines and may have a thin heat-affected zone (HAZ). Grinding is required to remove any adhered slag or notches before welding.
Plasma cutting: Faster than oxy-fuel with a narrower kerf and smaller HAZ. Good for thinner material and stainless steel. The cut quality is generally better than oxy-fuel, requiring less grinding.
Mechanical beveling: Using a plate beveling machine or clamshell pipe beveler. Produces a clean, consistent bevel with no HAZ. Preferred for pipe welding and when metallurgical considerations prohibit thermal cutting (some stainless and high-alloy steels).
Grinding: Used for cleanup and for preparing J-groove and U-groove profiles that cannot be cut with a torch. Slow for full-depth bevels but necessary for achieving the smooth, curved profiles of J and U preparations.
CNC plasma or laser: For production fabrication, CNC-cut bevels provide the best consistency and can cut compound angles (Y-bevels) in a single pass. The initial equipment cost is high but per-piece cost is low for volume work.