Butt Weld Symbol Explained: How to Read AWS Groove Weld Symbols on Drawings

A fabricator I once worked with cut, fit and welded an entire 40-foot plate girder before anyone noticed the single-V symbol he had read as a double-V — the scrap cost a full week of shop time. Butt weld symbols are small, quiet marks on a drawing, but misreading one turns steel into scrap, and this guide makes sure that never happens to you.

Why the Butt Weld Symbol on That Drawing Never Lies

The drawing is right. Every time. That is the uncomfortable truth that hits you the moment a stack of plate comes back from the plasma table with the wrong edge profile. I have watched a fitter trace a small V-shaped mark on a printed plan with one gloved finger, shrug, and send forty feet of flange plate to the bevel machine — only for the shop to discover later that the callout never asked for a bevel at all. Nothing on the page changed. Only the reader’s understanding of it did, and the steel paid the bill.

Butt weld symbols are the quietest marks on a fabrication drawing and the most expensive to misunderstand. They sit small, black and unassuming beside an arrow, yet they control edge prep, filler volume, weld pass count, inspection scope and the final cost of the joint. This guide exists so that the next time you see one, you read it with certainty instead of hope.

What You Are Really Looking For When You Search “Butt Weld Symbol”

Most people typing that phrase want three things, and this article gives you all three:

• A plain-English definition — what a butt weld symbol actually is, without a standards lawyer translating it for you.
• A picture in words — what the symbol looks like on a drawing, where every number sits, and what each element controls.
• Job-site confidence — the ability to walk up to a callout, read it aloud correctly, and know whether the joint you are about to weld matches the drawing.

Start with the joint itself. A butt joint is two members aligned in the same plane meeting edge to edge — plate against plate, pipe end against pipe end. It is one of the five basic joint types in the AWS welding symbol chart, alongside corner, T, lap and edge joints. Because that geometry carries full cross-section load with no overlap, it dominates structural steel, pressure-part and pipe drawings. Anywhere strength, leak-tightness or full thickness matters, engineers reach for a groove weld in a butt joint, and the symbol that calls it out is the one this article decodes. On pipe drawings in particular, the groove callout travels with the WPS, positions and inspection requirements that make the joint code-compliant. Mixed drawings also carry other families entirely, such as resistance spot welds, which follow completely different rules.

A Governed Language, Not a Sketch

Here is what separates welding symbols from handwriting: they are standardized. The governing document in the United States is AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. It first appeared in 1976 by combining and superseding two older documents — A2.0, Standard Welding Symbols, and A2.2, Nondestructive Testing Symbols — and it has been revised ever since. The current edition is A2.4:2020, the standard’s eighth edition, approved by ANSI on January 9, 2020, superseding A2.4:2012. AWS lists it at $165 for members and $220 for non-members, a price tag that reflects how broadly the standard is licensed by shops, EPC firms and engineering departments.

What that means practically is simple: if a symbol looks ambiguous, the answer already exists in print. There is no room for personal dialects, at least not on paper.

What This Article Covers

We build from the ground up, in the order you need it:

1. The anatomy of a welding symbol, and why a weld symbol is not a welding symbol.
2. Every groove glyph used in butt joints — square, V, bevel, U, J, flare and their double variants.
3. Decoding dimensions: root opening, groove angle, depth, size, length and pitch.
4. Arrow side versus other side, the single biggest source of scrapped steel.
5. CJP versus PJP, backing, backgouging and what the symbol quietly promises about strength.
6. Edge preparation behind the symbol, from ASME bevel standards to fit-up.
7. The ten most common mistakes, comparisons across AWS, ISO and IS conventions, and a field routine for checking callouts before the arc strikes.

By the end, a butt weld symbol will read like a sentence instead of a puzzle — and the drawing, as always, will still be right.

Welding Symbol vs. Weld Symbol: Know the Difference Before You Read Anything

Before you can read a butt weld callout with any confidence, you need one piece of vocabulary that trips up more apprentices than any glyph on the chart: a weld symbol is not a welding symbol. They sound interchangeable, they get used interchangeably in shop talk, and AWS A2.4 deliberately keeps them apart.

Clause 3.1 of the standard draws the line in plain terms. The weld symbol is the small graphic that indicates the type of weld: the V, the bevel, the square, the fillet, the U, the J. The welding symbol is the complete assembly you actually see on a drawing — the weld symbol plus the reference line, the arrow, any dimensions, any supplementary symbols, and an optional tail. One is a letter; the other is the whole sentence.

You can see the full anatomy in our welding-symbol glossary, but here is the working version.

The Anatomy of a Welding Symbol

• Reference line. The horizontal line everything hangs from. Required on every welding symbol.
• Arrow. The leader that connects the reference line to the joint. Also always required. Clause 3.2 is blunt about why: the joint is the basis of reference for the entire system. The symbol describes what happens at that joint, not which plate happens to be nearer.
• Weld symbol(s). The type glyph, placed either above or below the reference line — and that placement carries meaning we unpack next.
• Tail. Optional. It forks onto the end of the reference line and identifies the welding process, specification, or other reference, such as a WPS number. If the drawing doesn’t need to name a process or procedure, there is no tail.
• Dimensions and supplementary symbols. Sizes, lengths, pitch, contour marks, and flags.

Arrow Side and Other Side: The Two Halves of the Line

Everything below the reference line applies to the arrow side — the side of the joint the arrow points at. Everything above applies to the other side — the side opposite the arrow. That is the entire rule, and it holds for every weld type, including butt and groove joints. Put a V below the line and the joint gets a single-V groove on the face the arrow touches. Put it above and the far face gets it. Put symbols on both sides, or use a double-V glyph, and you are welding both faces.

A simple example, drawn in text:

        V
  ─────────────
         \
          ▶  (arrow points to the joint)

Read it as: “single-V groove weld, arrow side.” The V sits under the reference line, so the bevelled V is cut and welded on the face the arrow points to. Nothing is called out on the other side.

For a printable reference, AWS publishes its weld symbol chart as a free PDF. Keep a copy at the print station. And if you are working from drawings issued in the last few years, it is worth reading about the changes A2.4:2020 made to the standard, because a surprising number of shops are still running charts from the previous edition.

Once this distinction is automatic, the rest of this guide gets much easier: every butt weld callout from here on out is a welding symbol carrying one or more weld symbols, anchored to a joint by an arrow, and read side-first before you ever look at a number.

The Butt Weld Symbol Family: Every Groove Symbol Used in Butt Joints

AWS A2.4 groups every groove weld used in a butt joint into one compact family: square, V, bevel, U, J, flare-V, flare-bevel and scarf. Each one is drawn in a single form (weld one side of the joint) and a double form (weld both sides). Learn to recognize those glyphs and their mirrored twins and you can decode the vast majority of butt weld callouts you will ever meet on a structural, pressure-part or pipe drawing. Here is the whole family: what each glyph looks like, when it gets specified, and what the fabricator has to cut into the steel to satisfy it.

Square Groove: The Simplest Member

The square groove glyph is two short vertical marks with an open gap between them, sitting flat on the reference line. Physically it asks for nothing more than square-cut edges butted together, sometimes with a small root opening and nothing else. No bevel machining, no torch cutting at an angle, no extra prep labor. It is the default for lighter plate where one or two passes will fill the joint, and for shop work where fit-up speed matters. Its ceiling is thickness: as plate gets heavier, a square groove becomes harder to fill with good penetration, which is exactly why the shaped grooves below exist.

V-Groove: Single and Double

The single-V glyph is a plain “V”. The double-V glyph stacks a V on top of an inverted V, which reads a bit like a sideways hourglass. Physically, the single-V means both edges are beveled toward each other to form a V with a root opening at the bottom, welded from one face. The double-V means both faces are beveled, creating a shallow V on each side of the plate so the joint is filled from both directions. That halves the deposited metal per side and lets you use less heat input on thick plate, provided you can flip the workpiece.

Bevel Groove: Single and Double

The single-bevel glyph has one vertical leg and one slanted leg, close to a leaning “1/”. The double-bevel mirrors that slant in both directions from a central stem. Here one edge stays square while the other is beveled, so only one member has to be cut. That matters when the parts are already fit up, when only one piece is accessible, or when beveling just one edge saves setup time. The slanted side of the glyph has to follow the break in the arrow, a rule we unpack in the arrow-side section.

U-Groove and J-Groove: Single and Double

U and J glyphs replace the sharp point with a curve: a rounded bottom for the U, a hooked curve for the J, each again available as a single or double version. The curved profile gives better root fusion with less filler metal than a deep V, which is attractive on heavy wall sections, but the preparation has to be machined or carefully gouged rather than simply torch-cut. As the National Board points out, V-, U-, bevel- and J-grooves are commonly specified to provide increased weld size in a given joint compared with a square-groove weld, and which one you pick usually comes down to the cost of the completed weld: prep labor on one side, versus deposited metal and passes on the other.

Flare-V and Flare-Bevel: The Grooves Nobody Prepares

Flare grooves are the exception in the family: the joint geometry creates them, not the fabricator. A flare-V appears wherever two curved surfaces meet, such as two pieces of round bar, pipe or tube laid side by side. A flare-bevel appears where a flat edge meets a curved one, the classic case being hollow structural section (HSS) welded to a plate or to another section. Because no edge preparation is called for, these symbols often get skimmed past, but they still carry size and throat requirements. AWS A2.4:2020 added detailed usage guidance for flare groove welds for the first time, and research published by AISC clarifies how to calculate effective throat on them, since the theoretical throat of a curved joint does not behave like a sharp-V groove. If you fabricate HSS moment connections or tube frames, this is the part of the standard worth reading twice. Our pipe welding procedures guide covers how these callouts carry through to WPSs and inspection on round stock.

Scarf: The Brazing Symbol in the Groove Family

The last glyph is a single diagonal slash, and it belongs to brazed joints rather than fusion-welded ones. The scarf joint cuts both members at a matching angle so the braze filler spreads over a long area instead of a point. You will see it on light-gauge material, small-diameter piping and tube-to-tubesheet work, where a full groove weld would simply burn through. It shares the groove symbol family because the geometry looks the same on paper, but the process behind it is brazing, and the filler, temperature and cleaning rules are entirely different.

Read the family in this order and recognition gets fast: identify whether the glyph has a point, a curve or no cut at all, then check whether it appears once or mirrored for the double version, then look for the numbers that tell you how deep and how wide. The next section puts those numbers on the page.

Reading Dimensions on a Butt Weld Symbol: Root Opening, Angle, Depth and Size

The glyph tells you the shape of the groove. The numbers tell you exactly how much metal to remove, how wide to open the joint, and how far the weld has to go. This is where a butt weld symbol stops being a drawing convention and becomes a set of shop instructions. Misread a dimension and you don’t get a slightly different weld, you get an under-strength joint or a plate that has to be re-cut. The positions are fixed by the standard, so once you learn where each number lives, you can read any callout without guessing. AWS lays out the fixed positions for length of weld, pitch (center-to-center spacing) and specification or process reference on its welding symbol chart, and Open Oregon’s groove welding symbols chapter walks through the same layout with annotated examples.

Where Each Number Lives on the Symbol

Think of the reference line as a shelf with designated slots. Nothing floats:

A Worked Example You Can Read Aloud

Picture a standard AWS callout: a single-V groove symbol sitting below the reference line, with 1/2 in to the left of the symbol, 1/16 tucked inside it, and 90° written across the middle. Reading it properly, in shop language:

Notice what that script does: it forces you to name the side before anything else. Most dimension errors start as side errors. For a fuller breakdown of how these callouts are written and issued on fabrication drawings, see our guide to weld callouts and pipe welding procedures.

The 2020 Contour Change That Caught People Out

Two details in AWS A2.4:2020 changed how contour is handled. First, the flat contour symbol is now limited to fillet welds; groove, plug and slot welds use the flush symbol instead. Second, the standard now allows the contour of a weld to be achieved by any method — welding or mechanical — as seen fit at the work site, rather than implying one prescribed route. The ANSI blog breakdown of the A2.4:2020 changes explains why this matters: a flush groove can now be finished by grinding, machining or a controlled final pass without the drawing over-specifying the technique.

Numbers That Come From the Fitting, Not the Symbol

Not every dimension appears on the welding symbol. Edge preparation standards fill the gaps. For buttwelding ends, ASME B16.9 specifies a plain bevel of 37.5° ± 2.5° with a root face (land) of 1.6 mm (0.06 in) ± 0.8 mm for standard end preparation. That ± 2.5° tolerance is your fit-up allowance; a bevel cut at 40° still conforms, but one cut at 45° does not, and the drawing’s 90° included angle for a two-sided joint means 45° per member — so check which number you are actually holding the bevel protractor against.

Keep a printed copy of the AWS chart at the bench. Numbers placed one slot to the left or right of where they belong change the job entirely, and the chart is the fastest authority to settle it.

Arrow Side vs. Other Side: The Single Most Misread Part of a Butt Weld Symbol

If there is one place where a butt weld symbol quietly costs a shop money, it is here. Not the glyph, not the numbers — the side. The reference line on a welding symbol has two halves, and which half your groove symbol sits on decides which face of the steel gets cut, beveled and welded. Get it backwards and you have often welded the one face that was never supposed to be touched.

The rule itself is short enough to memorize in a breath:

• Below the reference line means the arrow side — the side the arrow points to.
• Above the reference line means the other side — the side opposite the arrow.
• Symbols on both sides (or a single double-groove symbol straddling the line) mean weld both sides of the joint.

That is the whole contract. The arrow points at the joint, and the line tells you which member of that joint the callout belongs to.

The Break in the Arrow: Who Gets the Bevel

A plain arrow is enough for a single-V, because both members are symmetric — both edges get beveled. But a bevel-groove or J-groove joint is asymmetric: one member stays square, the other is cut. So AWS uses a break (a kink) in the arrow to identify the member to receive the bevel, and the bevel symbol must be drawn to match that member. If the break points at the lower plate, the slanted leg of the bevel glyph leans the same way. As the ANSI write-up on AWS A2.4:2020 and the free AWS weld symbol chart both show, the arrow break and the glyph direction are one piece of information, not two.

Three Scenarios, Read Out Loud

Scenario 1 — single-V below the line. Two plates butted square, arrow pointing at the joint, a single-V symbol hanging below the reference line with 1/2 in. to the left. Read it aloud: “Groove weld on the arrow side, single-V, half-inch deep, this side only.” The welder bevels the face the arrow touches and leaves the far face alone.

Scenario 2 — double-V above the line. The same joint, but the double-V glyph sits above the reference line. Now it reads: “Other side.” The arrow-side face stays square; preparation and welding happen from the far side. Physically the joint looks identical to Scenario 1 on the fit-up table — only the symbol distinguishes them, which is exactly why this is where scrap happens.

Scenario 3 — a skewed joint with no clear reference side. On a mitred or oddly angled butt joint there is often no natural “front.” AWS A2.4:2020 answered this by introducing multiple subreference lines, used to designate a groove weld that extends around a joint where there is no clear point where the joint transitions from one joint type to another. Instead of guessing, the drafter stacks subreference lines so each segment of the joint carries its own symbol. If you see stacked lines, read each level as its own callout.

The Story of the Nozzle Welded Backwards

A welder I knew was fitting a pressure-nozzle stub into a vessel head. The bevel-groove callout was below the line, arrow on the stub — the stub was the member to bevel. He read the arrow as merely “indicating the joint,” beveled the head instead, and ran a full pass on the wrong face. The joint passed a visual look but failed fit-up verification, the stub was cut out, and the head was repaired under a qualified procedure. One symbol, one side, one afternoon gone. The habit that prevents it is trivial: before you cut, say the side out loud — “arrow side” or “other side” — and point at the face you mean.

Rule of thumb: find the arrow first, name the side second, read the glyph third. Do it in that order every time and the arrow side versus other side mistake simply cannot happen.

CJP vs. PJP: What a Butt Weld Symbol Really Says About Strength

Every butt weld symbol carries a hidden contract. The glyph tells you the shape of the joint, the numbers tell you the geometry, but what the symbol really promises is penetration — how far through the thickness the weld metal is supposed to travel. Get that contract wrong and you get a weld that looks perfect on the surface and fails where nobody can see it.

Two Words That Decide Everything: CJP and PJP

Complete joint penetration (CJP) means the weld fuses the joint through the entire thickness of the members, root to top, one continuous metallurgical bond. When a CJP groove weld is properly made, the joint is effectively as strong as the base metal around it. That is why structural tension members, pressure-boundary pipe and plate, and most heavy beam flange splices are specified as CJP.

Partial joint penetration (PJP) means the weld is only required to reach a specified depth. The remaining thickness at the root stays unfused by design, not by accident. That is not a defect — it is a deliberate, money-saving decision, appropriate where the loads do not demand full fusion.

How the Drawing Tells You Which One You Have

Here is the trap: a groove weld symbol never says “CJP” or “PJP” in words. You read penetration from the dimensions.

– The dimension placed to the left of the groove symbol is the depth of groove (and, in most cases, the required weld size). If that depth equals the full thickness of the thinner member, you are looking at a CJP detail.
– If the depth of groove is less than full thickness, you have a PJP groove weld. The remaining metal is land, not weld.
– When both a groove depth and a different finished weld size are required, AWS shows the weld size first with the groove depth in parentheses — for example, 3/8 (1/4). That is a weld smaller than the groove, a classic PJP signature.

AWS A2.4 also gives you a toolbox of symbols describing what happens on the root side of the joint, which is exactly where CJP is won or lost:

The standard carries dedicated categories for back and backing welds, joints with backing, and joints with spacers precisely because root-side reinforcement is the difference between “penetrated” and “hoped for.” The AWS A2.4:2020 preview lays out these categories in full.

Why CJP Usually Comes With an NDE Callout

CJP butt welds on pressure parts and tension members are normally examined, because visual inspection alone cannot prove root fusion. The welding symbol’s tail is where the drawing points you to the contract behind the weld: a WPS number, a specification, or an examination requirement. And AWS A2.4:2020 rewrote and expanded the nondestructive-examination clause, so the symbol can now carry the examination method, its frequency and its extent — for example, radiography of 100 percent of a butt weld, or spot RT at stated intervals. The National Board reinforces this on pressure-part work, where CJP groove welds in pressure boundaries are the norm rather than the exception.

Two Real Joints, Side by Side

Picture a 6-inch Sch 80 carbon steel process line. The isometric calls a single-V-groove butt weld, both sides, with the tail referencing the WPS and an RT symbol calling 100 percent radiography. That is CJP: full thickness fusion, examined, documented. Our pipe welding procedures guide walks through exactly how that WPS, pass sequence and inspection plan fit together.

Now look at the HSS handrail frame beside it. The square tube ends meet in a flare-V groove, dimensioned with a groove depth well under the wall thickness. No backing, no insert, no NDE tail. That is a textbook PJP butt joint. As AISC’s research on flare-groove welds documents, these welds depend on the angle between the fusion faces and the outside corner radius of the HSS — which is exactly why you size them by effective throat, not by hope.

The Takeaway

Read the depth first, check the root-side symbols second, and read the tail last. Three glances tell you whether that butt weld symbol is promising a full-thickness, examined joint or an economical, partial-depth fusion. That is the invisible contract — and now you can read it.

Edge Preparation Behind the Symbol: Root Face, Bevel Angles and Joint Design

The small groove glyph for a butt weld symbol on a print carries far more weight than it appears. No matter how skilled the welder may be, the joint will fail to reach its intended strength if the edge preparation does not match what that symbol is calling for. These dimensions dictate how the plates or pipes will be machined, fit up, and fused, making them just as important as the process used to weld them.

The Building Blocks of Groove Preparation

To read these callouts correctly, it’s important to know the core elements that go into a grooved butt joint:

• Square edges: Best for thinner materials, square groove preparations require little to no machining. However, they severely limit penetration on thicker sections.
• Bevels: A sloped edge cut into one member allows for deeper penetration on thick workpieces, while also reducing the amount of filler metal required.
• Root face (land): The small, flat surface left at the bottom of a bevel helps support the root pass, prevents burn-through, and creates a more consistent tie-in.
• Root opening: The gap between the two members at the root. A properly sized opening allows for full penetration, especially for precise processes like TIG welding.
• Groove angle vs. bevel angle: The bevel angle is the angle of a single beveled edge, while the groove angle (included angle) is the total angle between the two opposing beveled faces.
• Compound bevels: Common on thick-walled components, these use two different bevel angles on a single edge. This reduces the total groove volume, minimizes distortion, and saves filler metal.

What the Codes Say: ASME B16.25 and ASME B16.9

For piping systems and fittings, edge preparation is guided by strict codes. ASME B16.25 Buttwelding Ends governs the preparation of buttwelding ends. It specifies welding bevels, the shaping of heavy-wall components, and requirements for joints with or without backing rings, split or continuous backing rings, consumable inserts, and GTAW root passes. These specifications are crucial for maintaining code-compliant pipe welding procedures.

For wrought steel fittings, ASME B16.9 Table 1 provides a thickness-based breakdown for end preparation:

This tiered approach reduces weld volume on thick walls without sacrificing full fusion. When paired with the correct selection of electrodes in welding, it helps create a joint that is both strong and economical.

Practical Fit-Up and Shop Standards

With so many variables, it’s easy to over-detail a print. For this reason, The National Board suggests that details like root opening, groove angle, and finish contours are often best specified by a shop standard, rather than on every drawing. This prevents conflicting callouts, streamlines tack welds, and improves quality control across the board.

Cost in the Real World: Single-V vs Double-V

These principles become clear when prepping a 1-inch (25.4 mm) carbon steel plate. Single-V grooves can be machined from one side, making them useful for limited-access joints. However, they require a large groove volume to fill, leading to excess filler metal, higher labor costs, and increased distortion.

Double-V grooves split the bevel between both sides, cutting the depth per side in half. This drastically reduces filler metal, allows for balanced passes to control distortion, and is far more economical for thick plates with two-sided access. The trade-off is simply needing access to both sides of the joint.

For most two-sided, 1-inch plate fabrications, the double-V is the smarter route. It’s a decision that directly impacts everything from the duty cycle of your welding connectors, all the way down to your project’s bottom line.

The 10 Most Common Butt Weld Symbol Mistakes (and How to Fix Them)

Most scrapped-girder stories start the same way: someone trusted an assumption instead of the standard. Here are the ten errors that show up most often in shops, on site, and in QA reports, with what each one looks like on paper and the fix that stops it.

1. Confusing the weld symbol with the welding symbol. Read in isolation, the V glyph gets treated as the whole callout, so the reference line, arrow side, dimensions, and tail all get skipped, and the joint gets welded from the wrong direction or left unwelded. Fix: read the full assembly in order, arrow, reference line, glyph, numbers, then tail.
2. Reading arrow side and other side backwards. A single-V below the reference line gets called “the far side” because it sits on top of the line in the reader’s mental model. The welder plates the wrong face, and on a one-pass fit-up that means cutting it out and starting over. Fix: below the line means arrow side, above the line means other side, no exceptions. Drill it until it is automatic.
3. Ignoring the break in the arrow. A bevel symbol with a bent arrow is read as if the arrow were straight, so the bevel gets cut on the wrong member and the vertical leg of the glyph also points the wrong way, leaving the prep and the symbol in disagreement. Fix: the break points at the member that gets beveled, and the vertical side of the bevel symbol must follow that break.
4. Assuming double-V when the drawing shows a single-V with a root opening. The small root opening dimension inside the symbol is misread as a second, mirrored groove. The fitter preps both edges instead of one, wasting beveling time and adding fill passes nobody paid for. Fix: a double-V symbol has two glyphs mirrored about the reference line. One glyph means one groove, no matter what the root opening says.
5. Mixing ISO and AWS conventions on the same drawing. A dashed ISO-style reference line appears next to AWS-style symbols, or a welder trained on ISO 2553 applies dashed-line logic to a solid line. Side-of-joint interpretation flips, and the whole joint can end up welded on the wrong face. Fix: identify the governing standard in the drawing header before the first cut, and never blend conventions inside one callout.
6. Forgetting that the size to the left of the symbol overrides assumed thickness. A groove depth or weld size of 1/2 in sits left of the glyph, but the operator sizes the weld to the plate because “it’s a full-penetration joint anyway.” The result is over-welding, distortion, and filler cost, or under-welding when the number is smaller than expected. Fix: the number left of the symbol governs. Read it first, then confirm against plate thickness. This kind of mismatch is exactly what leads to rework and profile defects such as undercut.
7. Missing the weld-all-around or field-weld flag. A small circle at the junction of the arrow and reference line, or a flag pointing away from the line, gets overlooked because it is tiny. A plate is welded on three sides in the shop and shipped, or a field weld is attempted with shop equipment. Fix: check the junction of arrow and reference line before you read anything else on the symbol.
8. Assuming CJP when only a groove depth is given. A single-V with a depth dimension and no mention of complete joint penetration gets loaded as though it were CJP, or it skips the NDE the designer intended, and the shortfall surfaces in service. Fix: groove depth alone says nothing about penetration. Look for backing, backgouging, melt-through, or an explicit CJP note, and confirm the governing procedure, as covered in pipe welding procedures.
9. Ignoring the tail reference. The forked tail carrying a WPS number, specification, or examination requirement is treated as decoration and never opened. The welder runs the wrong process or the wrong position, and the NDE requirement is discovered at inspection instead of at setup. Fix: an empty tail is fine; a populated tail is an instruction. Resolve it before arc strikes.
10. Using outdated symbols. Old shop drawings carry symbols that no longer exist in the current standard, so fabricators and inspectors disagree about what the mark means and checkers flag the drawing as nonconforming. Fix: know what changed. AWS A2.4:2020 removed support for flash and upset welding symbols, dropped the diameter symbol from the plug weld symbol (the diameter symbol is still needed when designating the plug dimension on the welding symbol), added a combination groove symbol that can draw one groove glyph backward to show the real joint configuration, and now lets a value to the left of spot and seam weld symbols designate only the weld size. Details are in the ANSI write-up of the A2.4:2020 changes and the standard itself.

None of these mistakes require bad luck, only hurry. A habit of reading the whole welding symbol, in order, from arrow to tail, is the cheapest quality control in the shop.

Butt Weld Symbols Compared: Fillet, Plug and Slot — and AWS vs. ISO vs. IS

A butt weld symbol rarely travels alone. The same structural drawing that carries a single-V groove callout also carries fillet symbols on the stiffeners, plug or spot callouts on the gussets, and a row of examination symbols in the notes. Reading the groove callout correctly is only half the job. You also need to know which symbol family belongs to which joint, and which drafting standard the sheet was produced under, or you will size a fillet for a groove joint or flip an ISO drawing upside down.

Which Symbol Families Belong to a Butt Joint

The groove family is the only family that actually describes a butt joint: square, V, bevel, U, J, the flare-V and flare-bevel variants, plus the scarf symbol used for brazed butt joints. Everything else you meet on the same sheet is answering a different question:

• Fillet symbols serve T-joints, corner joints and lap joints. A fillet never specifies a butt joint, no matter where it sits on the reference line.
• Plug and slot welds join overlapping members through a prepared hole or slot. The members are not butted against anything.
• Spot and seam welds are resistance welds made across faying surfaces. Our explainer on how a spot welder works covers the physics, but on a groove drawing these symbols simply do not apply.
• Edge welds fuse the exposed edges of stacked plates, and surfacing welds build up a face. Neither is a joint-preparation callout.

The official AWS welding symbol chart makes this explicit: several cells in its grid are printed “Not Used”, showing that symbols such as spot, plug and seam cannot appear in the arrow-side or other-side position for butt-joint applications. Pull the free chart and the empty cells are obvious at a glance.

AWS A2.4 vs. ISO 2553: The Dashed Line That Changes Everything

AWS A2.4:2020 is the current ANSI-approved edition and supersedes A2.4:2012. Under AWS there is one reference line: a symbol placed below the line applies to the arrow side, a symbol above it applies to the other side, and there is no visual cue other than position.

ISO 2553-style drawings add a dashed reference line beneath the solid one. That dashed line is the tell. It marks the other side, and the solid line always sits on the arrow side. A welder trained on AWS habits who ignores the dashed line will weld the correct symbol to the wrong face of the joint.

One more AWS advantage worth knowing: A2.4 covers welding, brazing and nondestructive examination symbols in the same document. A single drawing callout can therefore carry the groove weld, its size, and the radiography requirement together, which is why pipe and pressure drawings often look dense but are actually self-contained.

How India’s IS 813:1986 Names the Same Joints

National schemes use their own vocabulary for identical geometry. India’s IS 813:1986 prescribes the rules for symbolic representation of welds on drawings and lists designations such as square butt weld, single-V butt weld, single-bevel butt weld, single-U butt weld, single-J butt weld and their double variants. The shapes are familiar; the labels and placement rules are not identical to AWS, so a drawing issued under IS 813 must be read by IS 813 rules.

Why a Mixed-Standard Shop Needs a House Rule

Plenty of fabricators receive AWS sheets from US engineers, ISO sheets from European clients and IS-marked drawings from Indian projects in the same week. The fix is a written house rule: identify the governing standard before reading a single glyph, annotate the drawing set with its standard, and never mix conventions within one detail. On pipework especially, where crews move between specs, our walkthrough of pipe welding procedures shows how the symbol, WPS and inspection plan must line up.

The takeaway is simple. Butt joints get groove symbols, everything else on the sheet belongs to another joint family, and the standard behind the drawing decides how the arrow side is read. Check the chart, check the standard, then strike the arc.

Practical Tips for Reading and Checking Butt Weld Symbols in the Field

All of the theory means little until you are standing at the joint with your prep tools in hand. One rushed glance is all it takes to repeat the fabricator from our opening story and scrap a girder. The fix is a short, repeatable routine.

Your Go-To Field Routine

Run these steps in order before you strike an arc. It catches the most common errors without derailing your Pipe Welding Procedures: The Complete Guide to WPS, Positions, Passes & Inspection.

1. Find the arrow: Locate the reference line and arrow, then check for a “break” in the arrow, which points to the member that must be beveled on bevel, J, and U groove callouts.
2. Identify the joint: Two plates, a nozzle to a vessel, or two pipes? The answer dictates access, restraint, and edge prep.
3. Split arrow side from other side: Symbols below the line apply to the arrow side, symbols above to the other side. Both sides means a weld on both sides. This is the single biggest cause of scrap, so confirm it first.
4. Read the glyph: Square, V, bevel, U, J, or flare determines exactly how you prep the steel. When unsure, check your shop copy of the free AWS welding symbol chart PDF, which notes that “weld symbols shall be contained within the length of the reference line and shall not be placed at either end of the line”.
5. Read the numbers left to right: Groove depth and weld size sit to the left of the symbol; root opening and groove angle sit adjacent to it. Length, pitch, contour, and finishing designators appear when specified.
6. Check the tail: The tail carries the process, specification, or WPS reference, and on critical joints it can also call out NDE (nondestructive examination).
7. Check supplementary flags: The field weld flag, weld-all-around circle, contour marks, backing, and melt-through indicators all change the scope of the weld.
8. Confirm WPS and thickness: Cross-check every dimension against the assigned WPS for material, thickness, and position. It is also the moment to verify consumables, such as the correct rod for 5/32 E7018 Amperage: Settings, Polarity & Technique.
9. Verify against edge prep: Measure root face, bevel angle, root opening, and land against the callout before tacking. If anything is out of tolerance, fix the prep first.

Tips for Drafters Issuing Butt Weld Callouts

A clean drawing saves a shop from headaches. Keep dimensions consistent, avoid duplicating details already covered by a shop standard, and issue callouts that comply with AWS A2.4:2020. When a groove runs continuously around a joint, use subreference lines to say so clearly. Most importantly, be explicit about penetration: never leave CJP to assumption, because it changes inspection, cost, and safety requirements.

Verification, Inspection, and Safety

For critical joints, especially complete joint penetration (CJP) butt welds, visual examination is almost always paired with volumetric NDE such as RT or UT as the code requires. Those requirements can hang directly off the symbol’s tail, so never skip it.

Compliance also extends past the metal. General industry falls under OSHA’s welding, cutting, and brazing rules in 1910 Subpart Q (1910.251 through 1910.255), while construction falls under 1926 Subpart J (1926.350 through 1926.354). Specifically, OSHA 1926.352 and OSHA 1926.353 cover fire prevention and ventilation, including a fire watch lasting at least 30 minutes after welding or cutting. These are commonly bundled with ANSI Z49.1 (Safety in Welding, Cutting and Allied Processes) and AWS A3.0.

Protecting yourself matters just as much. Gear up with Welding PPE: The Complete Guide to Protective Gear Every Welder Needs (2026) and MIG Welding Safety Precautions: The Complete Guide to Staying Safe in 2026.

That brings us back to the scrapped 40-foot plate girder. A few extra seconds running this checklist costs nothing and prevents weeks of lost time. Bookmark the AWS welding symbol chart, lock the routine in, and never let a small mark on a drawing cut into your work again.

Frequently Asked Questions

What is a butt weld symbol?

A butt weld symbol is the groove-type weld symbol (square, V, bevel, U, J, flare or scarf) placed on the horizontal reference line of an AWS welding symbol to describe a weld made in a butt joint, where two members meet edge to edge in the same plane. It communicates the weld type, groove dimensions and which side of the joint to weld.

What is the difference between a butt weld symbol and a groove weld symbol?

They are effectively the same family of symbols. AWS classifies them as groove weld symbols because the same glyph can also appear in corner or T joints, but when the glyph sits against a butt joint it is read as the butt weld symbol for that joint.

How do you know which side of the joint a butt weld symbol applies to?

In AWS convention, a symbol placed below the reference line applies to the arrow side — the side the arrow points at — while a symbol above the line applies to the other side. A symbol on both sides, or a double-groove symbol, means weld both sides.

What do the numbers around a butt weld symbol mean?

Numbers to the left of the symbol give the depth of groove and, when different, the weld size. Values inside or around the symbol give the root opening and the groove (included) angle, while values to the right give length and, for intermittent welds, the pitch between segments.

Does a butt weld symbol tell you whether the weld is full penetration?

Not by itself. Complete joint penetration (CJP) versus partial joint penetration (PJP) is implied by the callout details, the drawing notes, and often a tail reference to a specification or WPS. If the drawing does not call out CJP, do not assume it.

What does a break in the arrow of a butt weld symbol mean?

The break points to the member that is to receive the bevel. When you see a bevel or J-groove symbol, the glyph must be drawn to match the beveled member, so the break tells the fabricator which plate to cut.

Which standard governs butt weld symbols in the United States?

ANSI/AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. The current edition is A2.4:2020 (8th edition), which superseded A2.4:2012 and itself built on a lineage that began in 1976.

How do AWS butt weld symbols differ from ISO and other national symbols?

AWS uses a single reference line with symbols above and below it, while ISO-style conventions add a dashed reference line to indicate the other side. National standards such as India’s IS 813 use their own designation tables, so shops working to both systems should set an explicit house rule per drawing.

Where can I get a butt weld symbol chart for free?

The American Welding Society publishes a welding symbol chart based on AWS A2.4 as a downloadable PDF, and the standard itself is sold through AWS and the ANSI Webstore. Bookmark one chart in the shop and verify it against the edition your drawings cite.