Double-V groove
The X-groove is a double-sided beveled groove with two opposing V-welds. It is welded from both sides and halves the weld volume. Distortion remains significantly lower than with a single-sided V-groove. Suitable for thick plates from about 15 mm.
Physico-Chemical Mechanism of Action
In a single-sided V-groove, the arc melts a large, asymmetric weld pool. During solidification, the metal shrinks toward the weld root, creating significant angular distortion. The X-groove divides the cross-section into two smaller, symmetric weld pools. The two welds face each other. Their shrinkage forces act in opposite directions and largely cancel out. Additionally, only half as much filler metal is melted, so the total heat input into the part decreases.
Metallurgical Relevance & Welding Risks
The biggest danger lies in the center of the weld at the root. If the first side is not melted deep enough or not properly cleaned before welding the second side, lack of fusion or slag inclusions remain. These defects act as sharp notches. Under dynamic loads or at low temperatures, they can open up and lead to cracks. Uneven welding sequences, such as too many passes on one side, also cause residual distortion. For high-strength steels, too high interpass temperature can reduce toughness.
Shop Practice & Action Instructions
From about 15 mm plate thickness, the X-groove is worth it. Bevel both sides exactly the same depth, typically flank angle per side 30 to 35 degrees. Weld the first side, then grind the root from the opposite side with a carbon arc gouge or grinder to bare metal. Only then weld the second side. For thick plates, alternate layers symmetrically, never filling more than 50 percent of the groove cross-section on one side. Measure interpass temperature and keep it below 250 degrees Celsius for mild steels.