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Misunderstanding Welding Symbols: Part 1

Welding symbol detail drawing with pencil and eyeglass.

Sourced from AWS Learning

We’ve published several blogs over the years, and while we receive comments on all of them, we’ve noticed a steady stream of feedback on our blogs about welding symbols. Due to continued interest in these previously published blogs, we’ve decided to come back with a whole new set of common misinterpretations of AWS A2.4 Standard Symbols for Welding, Brazing, and Nondestructive Examination. Let’s dive right in.

Mistake No. 1: More Doppelgängers
In our blog entitled Welding Symbols Demystified: Part 2we discussed plug welds, slot welds, and their shared weld symbol. I’m here to tell you that there are a few more look-alikes plaguing your prints, and plug and slot welds find themselves in the thick of it yet again. There are many similar symbols on a print. A spot weld symbol is similar to a seam weld symbol, and so on. Some, however, are exactly the same.  As we discussed, the weld symbol for a plug weld is a rectangle. Slot weld? Also a rectangle. What about backing? Well, backing happens to be represented by a rectangle as well. And a spacer? I’ll give you three guesses, but you may only need one. The weld symbol for a spacer is a tried and true rectangle.

So what’s the key to telling one apart from the other? The answer is placement. In Welding Symbols Demystified: Part 2, we discussed how to differentiate between a plug weld and slot weld symbol. Now let’s look at backing and spacers. Backing is paired with a groove weld symbol. When a joint requires backing, the backing supplementary weld symbol is placed opposite the groove weld symbol on the reference line. If a spacer is required, a rectangle is centered on the reference line and the groove weld symbol is split in two and placed on either end of the spacer symbol. As a reference, take a look at the double bevel groove weld with a spacer pictured below. Simple enough, right?

Misunderstanding 1a

Mistake No. 2: Back vs. Backing
Back and backing welds also share a weld symbol, a semi-circle to be more precise. Let’s take a look at how to differentiate between the two. Since a semi-circle is used to communicate both back and backing welds, a tail is added to the welding symbol and the phrase “back weld” or “backing weld” is written within it. Two reference lines can also be used to indicate the very same thing. You see, when more than one reference line is attached to an arrow, the weld on the reference line closest to the tip of the arrow is applied to the joint first. The symbol pictured here depicts a backing weld symbol on the first line. Since it’s closest to the tip of the arrow, we know immediately that the symbol calls for a backing weld. This is because backing is always applied to the joint first. It’s as simple as that. No need to bring a tail into the situation.

Misunderstanding 2

Mistake No. 3: The Great Hierarchy of Lines
When looking at a print, you may notice solid lines, dashed lines, and segmented lines of varying lengths. With so many lines competing for pride of place on a plan, it’s hard to tell what each of them mean and which takes precedence. Let’s take a moment to sort them out. The three basic lines you’ll find on a print are object lines, hidden lines, and center lines. Object lines are solid and represent the edges of a part or joint. Hidden lines are dashed and represent the edges not visible to the eye. Centerlines, however, are comprised of long line segments followed by short line segments. They are used to indicate the very center of a symmetrical part or joint.  When all of these are present, they follow a hierarchy. An object line takes precedence over a hidden line and a hidden line takes precedence over a centerline.

Misunderstanding 3

Mistake No. 4: Flat vs. Flush
Weld faces can be finished using a number of different contours and finishing methods. The four contours include convex, concave, flat, and flush. Let’s focus on flat and flush. The difference between the two contours is this: flat simply means that the face of the weld must be, well, flat. Flush, however, requires that the weld be laid or finished in such a way that it rests flush against the part or base material itself. The supplementary weld symbol used to represent both of these contours is a straight line. Again, we find one symbol being used for two separate intentions. In order to indicate that a flat contour is desired, a tail is added to the symbol and the finishing method is written within it, i.e. “chip flat”, “grind flat”, and so on.

Misunderstanding 4

Mistake No. 5: Arrow Marks the Spot
Proper arrow placement on a print is very crucial. It must always touch the joint or part. You may notice that sometimes the arrow points at a joint and other times it points directly at the surface. The distinction depends on the type of weld. Below we’ve included a list to make it easy for you to determine when an arrow should be pointing at the joint or surface.

Misunderstanding 5

Misunderstang 5b

We’ll be back soon with five more of these tidbits. Until then, get better acquainted with the rules governing these symbols by checking out our course, Understanding Welding Symbols. Within the course, we cover all the mistakes that we’ve discussed in this blog series in addition to the rules that apply to all other welding symbols. From the outside, AWS A2.4 seems unassuming, but that little book packs in pounds and pounds of encrypted information within a very thin spine. With Understanding Welding Symbols at your disposal, deciphering prints will become second nature, making the confusion that comes with them a thing of the past.

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