Pitch in welding is the distance between the centers of consecutive weld segments in an intermittent weld. It’s not the gap between welds, but rather the center-to-center spacing measured along the joint. This distinction matters because misreading pitch on a welding symbol can result in welds that are too far apart or too close together, directly affecting the strength of the joint.
How Pitch Is Measured
When you see a welding symbol on an engineering drawing, pitch appears as the second number after a hyphen. For example, a notation like “2-5” means each weld segment is 2 inches long with a pitch of 5 inches. That 5-inch pitch is measured from the center of one weld segment to the center of the next, not from the end of one to the start of another.
The gap between weld segments (the unwelded space) is simply the pitch minus the weld segment length. In the example above, the clear space between welds would be 3 inches. This is the quickest way to figure out your actual spacing when you’re working from a print.
One important note: ISO standards define pitch differently from American Welding Society conventions. Under the ISO system, pitch refers to the clear distance between segments rather than the center-to-center distance. If you’re reading drawings that follow international standards, the same number means a shorter overall spacing. Always check which standard the drawing follows before laying out your welds.
Chain vs. Staggered Intermittent Welds
Pitch applies the same way whether you’re doing chain intermittent welds or staggered intermittent welds, but the layout on the joint looks different.
- Chain intermittent welds have weld segments on both sides of the joint that line up directly across from each other. The pitch is the same on both sides, and the segments mirror each other.
- Staggered intermittent welds offset the segments so that welds on one side fall between the welds on the other side. The ideal offset is half the pitch, placing each weld segment on one side directly centered in the gap on the opposite side.
Staggered layouts distribute stress more evenly across the joint because there’s always a weld segment resisting load somewhere along the length. Chain layouts are simpler to lay out but concentrate heat and stress at the same points on both sides.
Why Pitch Matters for Joint Strength
Pitch controls how much of a joint is actually welded versus left open. A shorter pitch means more weld segments per foot of joint, which increases overall strength but also adds weight, time, and heat input. A longer pitch reduces those factors but leaves more of the joint relying on the base metal alone.
Engineers specify pitch based on the load the joint needs to carry. Structural applications like beams and frames often call for tighter pitch to handle dynamic or heavy loads. Lighter assemblies like enclosures or guards can use wider pitch because the welds primarily hold parts in position rather than resist major forces. The pitch you see on a drawing isn’t arbitrary; it reflects a calculated balance between strength, weight, and cost.
Pitch in Spot Welding
Pitch isn’t limited to arc welding. In resistance spot welding, pitch refers to the center-to-center distance between individual spot welds. Here, though, pitch has an additional engineering concern called the shunting effect.
When spot welds are placed close together, electrical current from the welding electrode can travel through the previously completed weld instead of flowing entirely through the new weld location. This diverts energy away from forming the new weld nugget. Research has shown that as weld pitch decreases, the nugget diameter and weld quality both drop because of this increased shunting. The effect becomes significant at pitches of 40 mm or less.
Despite this tradeoff, shorter pitch in spot welding can meaningfully increase the strength of an assembly. Studies on automotive body panels found that short-pitch spot welding, even at 40 mm or below, was effective in increasing vehicle body strength. Manufacturers balance these competing factors by adjusting welding parameters like current and squeeze time when working at tighter pitches.
Reading Pitch on Welding Symbols
On an AWS-standard welding symbol, pitch information sits on the same side of the reference line as the weld symbol itself. The format is always: weld size, then segment length, then a hyphen, then pitch. So a fillet weld symbol showing “3/16” with “3-6” to its right means a 3/16-inch fillet weld applied in 3-inch segments at a 6-inch pitch (center to center).
If the symbol shows dimensions on both sides of the reference line, that indicates welding on both sides of the joint. When the segments are directly aligned, it’s a chain intermittent weld. When one side is offset, the symbol will include a stagger indicator, and the pitch still applies independently to each side.
The welding symbol system, governed by AWS A2.4, provides a standardized way to communicate these requirements on drawings. It specifies location and extent of welds but does not dictate tolerances or design requirements. Any additional details beyond what the symbol conveys, like surface finish or inspection criteria, need to be noted elsewhere on the drawing.