Tack Weld Symbol: The Complete Guide to Reading, Drawing, and Applying Tack Weld Callouts (AWS A2.4 & ISO 2553)

Marco had one hour to close the shop, and the column splice he’d just tacked looked as square as a laser line. At 6 a.m. the next day that column leaned nine degrees out of plumb, and the culprit was three 3/4-inch tack welds that cracked overnight in the cold. Nobody had drawn them, nobody had specified them, and nobody had inspected them, because on the print they simply did not exist.

Why a Three-Quarter-Inch Tack Weld Can Sink a Six-Figure Fabrication Job

The morning after Marco walked away from that column splice, nobody went looking for a drawing note. Nobody pulled a WPS. The tacks looked clean, they held the pieces square under the shop lights, and that was good enough for everyone involved, including the inspector who signed off on fit-up at four o’clock. Three three-quarter-inch tacks, placed by feel, doing a job nobody had ever asked them to do. Overnight, in the cold, they cracked, the joint relaxed, and a column that had to be plumb to a fraction of a degree leaned nine degrees out of it.

That is the anatomy of a fabrication failure, and it has almost nothing to do with welding skill. Marco can run a bead. The problem was upstream: the tacks were never specified on the drawing, never referenced to a qualified welding procedure, and never inspected, because on the print they simply did not exist.

The Gap Nobody Talks About

Tack welds are the most-used and least-documented welds in metal fabrication. Every fit-up in every shop depends on them, yet they are routinely treated as a setup step rather than a weld. The tack weld symbol is where that gap starts, because most fabricators open a drawing expecting a dedicated symbol for tacks and never find one. What they find instead is a note, a tail reference, or nothing at all, and nothing at all is how nine-degree columns happen.

If you searched “tack weld symbol,” you are almost certainly asking four questions: Is there an actual dedicated symbol for a tack weld? How do you draw one on a print? How do you read one when it shows up in a callout? And what does the governing code say about it? This guide answers all four, in that order, then goes deeper into sizing, spacing, notation, code requirements, and inspection.

What You’ll Learn in This Guide

• What a tack weld is in AWS terminology, and when a “temporary” tack becomes a real, load-carrying weld.
• A fast refresher on welding symbol anatomy: arrow, reference line, dashed line, tail, size, length, pitch, and flags.
• How tack welds are actually called out on drawings, with worked examples of real shop notes and tail callouts.
• How to build a complete, unambiguous tack callout covering size, length, spacing, quantity, and removal.
• What AWS D1.1, ASME BPVC Section IX, and API standards require of tack welders and tack procedures.
• The seven costliest tack weld mistakes, and how to tell a tack apart from a stitch, intermittent, spot, or plug weld.

Underpinning all of it is a single American national standard: AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. First published in 1976, A2.4 consolidated two earlier documents, AWS A2.0, Standard Welding Symbols (1947), and AWS A2.2, Nondestructive Testing Symbols (1958). The current AWS A2.4:2020 is the 8th edition, approved by ANSI on January 9, 2020, superseding the 2012 version. The standard exists for one reason stated plainly in its own scope: welding cannot take its proper place as a fabricating tool unless a means exists to convey information from the designer to the welding personnel. A tack weld placed by feel, with no channel back to the engineer, is exactly the failure that sentence was written to prevent.

Before touching a tack callout, you need the underlying system, so the next section rebuilds the welding symbol from the arrow up, including the part of the symbol that does most of the work for tacks. Keep a copy of our complete welding symbols chart open while you read, and if you want the shape convention behind most tacks, start with the fillet weld symbol guide. Then, when you get to code, you will already understand why a reference to a qualified WPS in a symbol tail is not paperwork, it is the entire quality system in four characters.

What Exactly Is a Tack Weld? Definitions, Purpose, and Where It Sits in AWS Terminology

Before anyone can read a tack weld callout, everyone has to agree on what a tack weld is. The welding world is full of near-synonyms swapped on the shop floor, and those loose words are how Marco’s column splice ended up with three undocumented beads holding a structural joint together.

The Definition the Codes Use

AWS A3.0, the American Welding Society’s standard welding terms and definitions, gives the clean version: a tack weld is a weld made to hold parts of a weldment in proper alignment until the final welds are made. Two phrases carry the weight. Hold parts in proper alignment means the job is geometric, not structural. Until final welds are made makes the tack a placeholder with an expiry date, even when it is left in place. AWS A2.4, which governs welding symbols, treats tack requirements as notes and tail references rather than as a standalone symbol — a distinction we dig into next.

Four Words People Use Interchangeably but Shouldn’t

Related terms overlap enough to cause confusion, so they are worth separating:

• Tack weld — a small weld that positions and restrains the joint until final welding. It may stay or may be removed.
• Temporary weld — any weld installed only for the duration of fabrication or erection and never intended for the finished structure. Most temporary welds are tacks, but not every tack is temporary.
• Construction aid weld — the formal term AWS D1.1 uses for temporary attachments such as lifting lugs, alignment tabs, and brace anchors that are not part of the finished structure. D1.1 Clause 5 handles “Tack Welds and Construction Aid Welds” together for exactly this reason.
• Fit-up tack — shop slang for a tack placed during assembly to lock a fit-up. Same weld, different vocabulary.
• “Tack” as a verb — to tack means to place those welds. A note reading “TACK AS REQUIRED” asks for something far vaguer than one reading “TACK WELD, 2 IN. LONG.”

The Four Jobs a Tack Actually Does

Every tack on every job falls into one of four roles:

1. Alignment and positioning — pulling two members into the correct relationship and holding them there while fit-up is verified.
2. Restraint against distortion — resisting the shrinkage forces of the final weld sequence. The more restrained the joint, the more stress the tacks themselves carry as the real beads cool.
3. Gap control — maintaining root opening and land across the length of a joint so the root pass doesn’t wander from open to tight.
4. Handling stability — keeping assemblies safe and square during rigging, transport, and field erection.

Three of those four are load-bearing before the structure ever sees service, and a tack is no harmless dab of metal. Each one is a full heat-cycle event: it melts base metal, creates its own heat-affected zone, and locks residual stress into the joint before the final weld starts. On crack-sensitive steel, a small tack with a steep cooling rate can crack on its own and then get welded right over. If you have chased spatter and surface damage around a finished joint, our guide on weld defects and undercut walks through how that damage gets accepted, rejected, and repaired.

Process and Material Change the Tack, Too

Tacks are not one-size-fits-all across processes:

• SMAW with E6010 is a classic root tack on structural steel — deep penetration, forgiving on fit-up gaps, and easy to cut out later.
• GMAW short-circuit transfer is the default tack method in most shops because it is fast, low-heat, and easy to start in position. Our step-by-step MIG tack weld guide covers spacing, settings, and tack sizes for this process.
• FCAW tacks are common on heavy structural steel where the shop is already running flux core for production welds.
• GTAW (TIG) is preferred on stainless and aluminum, where heat input control and cleanliness decide whether the joint survives. See our TIG sheet metal guide for settings that translate well to tacking thin material.
• Aerospace work frequently prohibits permanent tacks outright, or requires them to be fully removed and dressed, because an uncontrolled tack in a fatigue-critical part is an inclusion waiting to happen.

Scale matters. The U.S. Bureau of Labor Statistics counts roughly 430,000 welders, cutters, solderers, and brazers working across the country. When a small-definition error — what counts as a tack, when it needs a procedure, when it must be removed — repeats across that many people on that many joints, tiny ambiguities get expensive fast.

Anatomy of a Welding Symbol: A Fast Refresher Before You Read a Single Tack Callout

Before you can understand how a tack weld gets communicated on a drawing, you need to read the sentence it lives inside. In AWS terms, that sentence is the welding symbol — a compact grammar of lines, shapes, and numbers that tells a fabricator what weld to make, where to make it, how big it should be, and what process to run. Skip this refresher and the rest of this guide reads like sheet music to someone who never learned the staff.

The governing American document is AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. That standard defines the welding symbol as a composition of an arrow, reference line, tail, and weld symbols, with the tail reserved for supplementary information such as process, specification, or reference. Here is how to parse each piece.

The Core Parts of a Welding Symbol

• Arrow — points to the joint or member being welded. Where it touches determines which side is the arrow side.
• Arrow line — the leader connecting the arrow to the reference line.
• Reference line — the solid horizontal line everything hangs from. Weld symbols sit above or below it.
• Dashed line — used when symbols are needed on both sides of the joint; it represents the other side.
• Tail — the fork at the far end, holding supplementary data: process, specification, WPS number, or a note.
• Weld symbol — the shape itself: a triangle for a fillet, a V or U for a groove, a circle for a spot weld.
• Dimensions — size to the left of the symbol, length and pitch to the right.
• Contour and finishing marks — the arc or straight line plus a letter indicating grinding, machining, or as-welded condition.
• All-around circle — the weld wraps the entire joint.
• Field weld flag — the weld is made on site, not in the shop.

A visual reference such as the AWS weld symbol chart puts each shape in context.

Welding Symbol vs. Weld Symbol

These two terms get swapped freely on the shop floor, and it causes real confusion. The welding symbol is the entire callout: arrow, lines, tail, dimensions, flags, everything. The weld symbol is only the shape — the triangle, the V, the circle. When a fitter asks what symbol that is, they mean the shape. When a drawing note says “see welding symbol,” it means the whole assembly, tail included.

Arrow Side vs. Other Side

AWS convention is fixed and worth committing to memory: anything drawn below the reference line applies to the arrow side, and anything drawn above it applies to the other side. Flip the arrow to the opposite member and the sides swap with it. That is why a careful inspector checks which member the arrow touches before anything else.

The Tail: Where Tack Information Lives

For this article, the tail is the star. It is deliberately the least standardized and most flexible part of the symbol — a designated parking spot for information geometry cannot express. Process callouts (GTAW, SMAW, FCAW), procedure references (WPS-04), and tack weld instructions all end up there. When a drawing reads “TACK PER D1.1” or “TACK WELD, 2 IN. LONG @ 12 IN. O.C., REMOVE BEFORE FINAL WELD,” the text sits in the tail or in a general note the tail points to. Understand the tail and you understand most of how tacks are specified.

Dimensions: Size, Length, Pitch

Standard placement puts size to the left of the weld symbol and length plus pitch to the right. For an intermittent fillet, “1/4 – 2 @ 12” reads as a 1/4-inch leg, 2 inches long, on 12-inch centers. Pitch means center-to-center distance, not the gap between increments — a detail that trips up new readers constantly. Contour symbols ride above the weld symbol; finishing method goes in the tail or a note. Tack spacing is dimensioned with the same logic, which is why confusing the two can produce a joint nobody ordered.

Inches, Millimeters, and the ISO 2553 Counterpart

A2.4 dual-unit practice puts the inch value first with the metric equivalent in parentheses — 1/4 in. (6 mm). Drawings produced to ISO 2553, the international standard for symbolic representation of welded joints, follow a different grammar: the weld symbol sits on a continuous line for arrow-side welds and a dashed line for other-side welds, with its own dimensioning rules and supplementary symbols. The shapes look familiar; the rules are not interchangeable.

Two A2.4:2020 changes also catch people out. Flash and upset welding symbols are no longer supported, and the plug weld symbol no longer carries the diameter symbol as part of the symbol itself. Older charts still pinned to shop walls show both, which is a good reason to check the current edition instead of the laminated poster.

Get Fluent Before You Go Further

Two references make the rest of this guide easier to follow: a complete weld symbol chart for the shapes themselves, and a closer look at the groove weld symbol for the joint types most often held with tacks on structural work. With the anatomy settled, we can ask the real question: is there a tack weld symbol at all?

So, Is There a Tack Weld Symbol? How Tacks Really Get Called Out on Drawings

Let’s answer the question the way a shop foreman would: no. There is no dedicated tack weld symbol. Not in AWS A2.4, not in the AWS weld symbol chart, and not in any edition of ISO 2553. If you’ve been flipping through symbol libraries looking for a dotted triangle or a short zigzag labeled “tack,” you can stop. It was never drawn, and that omission is deliberate.

AWS A2.4:2020 gives construction and interpretation rules for groove, fillet, plug, slot, spot, seam, edge, stud, and surfacing weld symbols, plus brazing and NDE symbols. That is the complete catalog. The basic weld symbols in the A2.4:2007 chart are fillet, square groove, V-groove, bevel, U, J, flare-V, flare-bevel, plug, slot, spot, seam, stud, and surfacing. A tack weld doesn’t appear because it isn’t a weld type in the symbolic sense. Tack two plates together and you have still made a fillet or a groove. The symbol describes the shape; the tack-ness is a job requirement, and requirements get written, not drawn.

Where Tack Requirements Actually Live

Once you see that split, the rest follows. Per ANSI, the tail of the welding symbol and the supplementary symbols are used to designate supplementary information, and that tail is precisely where tack instructions belong. On real drawings you’ll find them in four places:

• General notes on the sheet, applying to everything printed on it
• Tail notes on a single welding symbol, scoping the instruction to one joint
• Leader notes with an arrow placed directly on the short weld
• Detail views and weld schedules that dimension fit-up welds next to the production welds

If those terms are still fuzzy, our guide on how to read welding symbols walks the anatomy from arrow to tail first.

Worked Examples: How It Actually Reads on the Paper

Example 1 — leader note. A leader arrow touches a two-inch bead at a web-to-flange junction, with this text above the reference line:

TACK WELD, 2 in. LONG @ 12 in. O.C., TYP., PER WPS-04, REMOVE BEFORE FINAL WELD

Read it left to right. It is a tack. It is two inches long. It repeats every twelve inches on center. That spacing is typical. It follows WPS-04. It comes out before the production weld goes in. Every clause a welder needs, and not one of them requires a symbol.

Example 2 — tail note. The weld symbol is a plain fillet triangle with a leg size to its left, and the tail reads TACK PER D1.1 CLAUSE 5 or simply TACK PER WPS-04. The triangle gives the shape. The tail gives the instruction.

Example 3 — general note. “ALL FIT-UP TACKS TO BE MADE BY QUALIFIED WELDERS, CLEANED TO SOUND METAL, AND FUSED INTO THE FINAL WELD UNLESS NOTED OTHERWISE.” This is the clause that stops Marco from leaving a hard-start crack in the back of a column.

For tacks laid with wire feed, spacing and setting conventions are covered in our MIG tack weld guide.

The ISO 2553 Approach

ISO 2553 runs on the same philosophy with different architecture. The weld symbol sits on a continuous line for the arrow side and a dashed line for the other side, a tail carries reference information, and the standard supports both System A and System B dimensioning. There is still no tack symbol. International practice splits the job exactly as AWS does: the conventional symbol defines geometry, and the notes define the increment as a fit-up tack, its length, its spacing, and whether it stays. One caution — check the drawing notes for which dimensioning system is called out before you lay a single dimension string. Mixing System A and System B is its own expensive mistake, and our welding codes explained article covers how the governing standard gets picked in the first place.

The Field Weld Flag and the All-Around Circle Do Not Mean Tack

Two symbols get misread constantly, so let’s be blunt. The field weld flag where the reference line meets the arrow means the weld is made on site instead of in the shop. The all-around circle means the weld runs around the entire joint. Neither one says anything about length or about being temporary. A flagged symbol with a “TACK PER WPS-04” tail is a field tack. A flagged symbol with no note is a field production weld. The flag told you where. The note tells you what.

That distinction matters, because erectors routinely treat a flagged tack as informal field fit-up that no drawing governs. It isn’t. Once a tack appears in a note or a tail, it is a documented requirement with an owner, a procedure, and an inspection trail behind it. The only tack that escapes that treatment is the one nobody wrote down, and that is the one that fails overnight in the cold.

Building a Complete Tack Weld Callout: Size, Length, Spacing, Pitch, and Notes

A tack weld instruction is only as good as its weakest word. “Tack as required” on a shop drawing looks harmless, but it hands every fitter a different answer: different length, different spacing, different filler, and sometimes a different opinion on whether the tack ever gets removed. This section walks through every field of a fully dimensioned tack callout so you can write one that cannot be misread, and read one without guessing.

The Seven Fields of a Complete Tack Instruction

Think of a tack callout as a sentence with seven slots. Leave one blank and someone downstream will fill it in with a guess.

• Size. If the tack is fillet-shaped, give the leg size, exactly as you would for a fillet weld. If the shop is working from a rule of thumb tied to material thickness, write the rule down rather than assuming everyone learned the same one.
• Length. A tack is an increment with a length, not an indefinite blob. “2 in. LONG” is a dimension; “small tack” is not.
• Spacing or pitch. The center-to-center distance between tacks. This is where tack layout quietly borrows the logic of intermittent welds.
• Quantity. “6 TACKS PER SIDE” removes any argument about when to stop.
• Location. “AT CORNERS AND MIDSPAN, TYP.” tells the fitter where restraint actually matters.
• Process and filler metal. Reference the WPS by number, or name the process and classification directly.
• Disposition. State plainly whether the tack stays, gets removed before final welding, or must be ground flush.

Why Tack Spacing Uses Intermittent Weld Notation

Tack layout and intermittent fillet welding share the same three-part format: size, length, pitch. In intermittent fillet weld notation, the pitch is the center-to-center distance between the increments of the weld. So a callout reading 1/4 in. fillet weld 2 in. long on 6 in. centers describes a 1/4-inch leg, each increment 2 inches long, with the start of one increment 6 inches from the start of the next. In practice, a MIG tack weld spacing and sizing guide uses the same center-to-center logic when laying out fit-up tacks on sheet and light structural work.

The tricky part is telling a specified intermittent fillet weld apart from a fit-up tack, because the numbers can look identical. Three cues separate them:

1. Position of the information. A production intermittent weld sits on the reference line with the triangle symbol and the size-length-pitch values. Tack requirements almost always live in the tail, in a leader note, or in a general note.
2. Language. The word TACK, plus removal or incorporation language, appears only on tacks.
3. Contour and finish symbols. Under AWS A2.4:2020, the flat contour symbol is restricted to fillet welds, while the flush symbol is used for other welds such as groove, plug, and slot welds. A finish mark is therefore a production-weld instruction, not a hint that something is temporary. Similarly, on spot and seam welds, the dimension placed to the left of the symbol designates the size of the weld.

Shop Floor Conventions Are Not Code

Fitters often lay tacks at regular intervals by feel, and experienced crews produce good joints this way. But common practice numbers for structural steel are conventions, not code mandates, and the responsible engineer has to confirm them for the job at hand. The moment tacks are incorporated into the final weld, they inherit the requirements of that weld, including the qualified procedure. A WPS and procedure documentation guide shows how the tack, the root pass, and the production passes all trace back to the same qualified paper trail.

Writing Notes That Cannot Be Misread

Ambiguity hides in three places: vague qualifiers, mismatched units, and unstated tolerances.

• “TYP.” versus “AS REQUIRED.” TYP. (typical) means the same instruction applies at every similar location, which is a real instruction. AS REQUIRED is usually a bad sign on a drawing; it means the detailer deferred a decision to the floor, and you should request a dimension before welding.
• Dual dimensions. A2.4 dual-unit practice puts inches first with the metric equivalent in parentheses, for example 2 in. (50 mm). Keep the whole drawing consistent so nobody converts a pitch twice.
• Tolerances and rounding. Round in one direction and state it. A note that says “MINIMUM” for tack size and length is far stronger than a nominal number that invites rounding down.

Read a callout that way before you strike an arc, and the argument about whether a tack is “just a tack” never starts.

The Code Behind the Symbol: What AWS D1.1, ASME, and API Actually Require for Tacks

A tack weld callout on a drawing is only an instruction. What turns that instruction into an enforceable requirement is the code named in the contract documents. The general notes, the specification section, and the fabrication standard referenced on the print work together to decide whether your tack is acceptable, who was allowed to make it, and whether anyone has to look at it afterward. If the drawing says nothing, the governing code still applies. Silence on a print is not an exemption.

Why AWS D1.1 Is the Code That Shows Up Most Often

For structural steel in the United States, the default reference is AWS D1.1, Structural Welding Code – Steel. The current version, AWS D1.1/D1.1M:2020, is the 24th edition of the standard, approved by ANSI on December 9, 2019, and it supersedes AWS D1.1/D1.1M:2015. You will also see D1.1 called out indirectly through a structural specification that adopts it by reference, which is why detailers should read the notes block before they assume a shop-floor convention carries over.

D1.1 does not treat tack welds as an afterthought. Two clauses matter most:

• Clause 4 (Qualification). The qualification provisions extend to tack welders, and the standard includes a method of testing and acceptance criteria specifically for tack welder qualification. The person placing tacks on a D1.1 joint is not outside the qualification system just because the welds are small.
• Clause 5 (Fabrication). This is where tack welds and construction aid welds are addressed in practice: tacks must be cleaned before final welding, tacks that will not be incorporated into the finished joint must be removed, and any tack that will become part of the final weld must be made in accordance with a qualified welding procedure specification.

That last point is the one shops get wrong most often. A 2-inch tack sitting in the root of a full-penetration groove weld is not a preliminary step; it is part of the weld that gets x-rayed, and it was produced under whatever filler, polarity, preheat, and conditions the welder happened to choose. D1.1 also permits non-code welds to be used as construction aids, including temporary attachment of brackets and lugs, provided the tack is later removed and the base metal underneath is not damaged. Base metal damaged by a removed tack has to be repaired under the code, not filled over and forgotten.

Low-Hydrogen Steel, Cracking, and Welding Over Tacks

Tacks are where hydrogen cracking starts on crack-sensitive steel. They are small, they cool fast, they are often made last thing at the end of a shift, and they are frequently made with whatever electrode is closest to the bench. On low-hydrogen-controlled work, that habit is exactly backwards: tacks in restraint-heavy joints should come from the same low-hydrogen filler and the same controlled conditions as the final weld, with preheat and interpass temperature observed and consumables handled and baked correctly. Getting the settings right on a low-hydrogen electrode such as E7018 is part of that discipline, which is why we walk through the numbers in our 3/32 E7018 amperage guide.

Before anyone welds over a tack, the tack gets inspected like any other deposit: slag removed, surface cleaned, visually checked for cracks. A cracked tack left in place and buried under a cover pass is a crack in the finished weld, and no amount of downstream NDT will make it go away. The same applies to tacks laid over trapped mill scale, slag, or galvanized coating. And the practical rule worth repeating to every fitter on the floor: a tack weld is not exempt from inspection because it is “just a tack.” If it is in the joint, it is in the code’s scope.

ASME Section IX and API Work: Different Rulebooks, Same Logic

Move off structural steel and the authority shifts. For pressure equipment, ASME Boiler and Pressure Vessel Code Section IX covers qualification of welding and brazing procedures, welders, brazers, and welding operators. On a Section IX code weld, tack welding performed by unqualified personnel, or outside the qualified procedure, can invalidate the joint before the real welding begins.

API documents follow the same pattern with their own rules. Field standards such as API 650 for storage tank fabrication and API 1104 for pipeline construction set out their own tack provisions, including when tacks must be removed, ground, or made with matched filler by a qualified welder to an approved procedure. Because these requirements vary by standard and by edition, the welder’s source of truth is the WPS and the applicable code, not memory. Our pipe welding procedures guide breaks down how a WPS, weld map, and inspection plan fit together on pressure line work.

That is the through-line of every code in this section. The symbol tells you what the engineer wants. The code tells you what makes it legal.

Seven Costly Tack Weld Mistakes (and Exactly How to Fix Each One)

Walk any busy fabrication floor and you will find the same pattern: the final weld gets a WPS, a preheat check, a visual inspection, and a sign-off. The tack that held everything together for the first two hours gets none of that. Below are the seven failures that cost shops the most money, each with a corrective action you can put in a work instruction tomorrow, plus the kind of exchange you will actually hear between a fitter and a CWI.

Mistake 1: The Tack Never Made It Onto the Drawing

Fix: Put the requirement in the symbol tail or a general note, with a WPS reference and an explicit statement: REMAIN or REMOVE BEFORE FINAL WELD. If it is not written down, no one owns its quality.

Fitter: “There’s no tack callout, so we’re freehanding it.” CWI: “Freehand means undocumented. Add the note, then we both know who signs for it.”

Mistake 2: Tacks Too Small or Too Short for the Job

Fix: Size the tack for the restraint it must survive, not for convenience. A 1/4 in. tack holding a cambered beam against shrinkage will crack, and the crack will be blamed on the fit-up crew. If the detailer has not specified size, length, and spacing, request an RFI before striking an arc.

Mistake 3: Tack Placement Interferes With Fit-Up, NDT, or the Final Profile

Fix: Keep tacks out of the ultrasonic scan path, out of the stop-start zone of the final weld, and away from chamfered edges that the mill will later grind. Tacks belong where they can be incorporated or cleanly removed without gouging the base metal.

Fitter: “I tacked the corner so it wouldn’t walk.” CWI: “That corner is the UT gate. Move it 3 in. left or mark it for removal.”

Mistake 4: Wrong Filler or Process on Crack-Sensitive Steel

Fix: Tacks on thick or high-strength steel are prime real estate for hydrogen-induced cracking, because small, fast-cooling welds chill quickly and lock in restraint stress. Use the qualified low-hydrogen process and filler, control preheat, and keep consumables dry. Our guide to hydrogen cracking in welds explains why a 3/4 in. tack on a cold morning can fail overnight. For stick tacks, dial settings with our 3/32 E7018 amperage chart; for wire, start with a proper MIG welder setup and check out our MIG tack weld guide for spacing and settings.

Mistake 5: Dirty Tacks Buried Under the Final Pass

Fix: Wire-brush or grind every tack before the covering pass. Trapped slag, mill scale, or galvanized coating is a documented cause of porosity and incomplete fusion. AWS D1.1 requires tack welds that become part of the final weld to be cleaned and inspected, not simply covered up (AWS D1.1:2020). See our porosity causes and fixes guide and the rules in weld cleaning between passes.

Mistake 6: Tacks Never Removed, or Removed Destructively

Fix: If the note says REMOVE, remove it, and use a method that does not nick or gouge the parent metal. Overzealous grinding that leaves a 1/8 in. crater is worse than the tack it erased, and it invites the undercut and profile rejection you were trying to avoid.

Fitter: “It’s ground, good enough.” CWI: “That’s a gouge. Fill it per the repair procedure, then re-inspect.”

Mistake 7: Treating Tack Welding as a Free Skill

Fix: Anyone who tacks is welding, and tack welders fall under the same qualification and continuity requirements as production welders. A helper who “just puts tacks on” while the certified welder is on break is a code violation waiting for an audit. Confirm qualification records before the shift starts, and make sure PPE and hot-work controls cover tack crews too.

None of these seven problems are exotic. All of them start where Marco’s column did: with a tack nobody wrote down, sized, cleaned, or checked.

Tack Weld vs Stitch Weld vs Intermittent Fillet vs Spot Weld: Clearing Up the Confusion

Ask five fabricators what a “stitch weld” is and you will get five slightly different answers, and one of them will be describing a tack. Words that sound interchangeable on the shop floor carry different meanings on a drawing, and the difference decides which weld gets made, inspected, and rejected. The organizing principle is simple: look at the symbol shape and the intent behind it. A tack is a fit-up instruction, a stitch is a production weld, and a spot weld is a different process with its own geometry.

Seven Terms, Seven Different Jobs

Read down the “dimensioned fields” column and the pattern jumps out. Every real weld has a place on the symbol for its geometry, while a fit-up tack has no standard symbol field of its own. That asymmetry is why tack requirements end up in notes, in the symbol tail, or in a general drawing note instead of a boxed dimension line. AWS A2.4 provides dedicated symbols for groove, fillet, plug, slot, spot, seam, edge, stud, and surfacing welds, and tacks are conspicuously absent from that list.

Why a Loose Vocabulary Costs Money

Here is the scenario that burns jobs. An engineer writes “STITCH WELD 3/8 – 2 – 6” on a gusset detail, meaning a permanent intermittent fillet with a real throat to calculate. The fitter reads it as a request to hold the gusset in place and puts on four small tacks. Come inspection, the joint is under-welded by a wide margin and the assembly goes back to the fit-up station. Run the error the other way and it is just as bad: a fitter asks for “a few stitches” on a pipe spool, the welder lays in production-quality beads that now interfere with root opening and alignment, and the fit has to be gouged out before the real root pass can go in. For context on how fit-up tacks are actually run on sheet and small tube, our MIG tack weld guide walks through spacing, settings, and sensible tack sizes.

The fix is boring and effective: use the code term in conversation, not the slang. Say “tack” when you mean temporary. Say “intermittent fillet” when you mean the finished, dimensioned weld. Pipe work is especially unforgiving here because root tacks sit inside a weld that later becomes the pressure boundary, which is one reason pipe welding procedures spell out tack length, placement, and grind-back requirements so explicitly.

What Changed in AWS A2.4:2020

Two updates are worth knowing because they show up on newer prints. First, the diameter symbol is no longer part of the plug weld symbol itself, though it is still used when designating the plug dimension on the welding symbol. Second, A2.4:2020 now permits a combination groove weld symbol designating two different edge shapes, with one symbol drawn backward so the drawing shows the actual joint configuration. Neither change adds a tack symbol, which reinforces the point: tacks are conveyed by notes, and the weld shape is still conveyed by the conventional symbol. The ANSI summary of the A2.4:2020 revision is a quick read if you want the full list of changes.

Spot work deserves one extra caution. Resistance spot welds on coated or conductive material behave nothing like arc tacks, and a mis-set electrode stack will happily produce a cosmetically perfect, structurally empty weld. Practical parameter control for that process is covered in our guide to spot welding copper, where margin for error is thinnest.

Practical Playbook: Writing, Making, and Inspecting Tack Welds That Hold

Everything in the previous sections only matters if it shows up in someone’s hands at the right moment. A tack weld callout has three audiences: the person who draws it, the person who makes it, and the person who signs off on it. When all three do their job, tacks quietly hold a joint in tolerance until the real weld locks it in. When one drops out, you get Marco’s leaning column. Here is the role-by-role playbook.

For Engineers and Detailers

Your job is to make the tack impossible to ignore and impossible to misread:

• Put the requirement where the welder looks. Tack instructions belong in the symbol tail or in a general note on the sheet, not buried in a specification chapter nobody opens. If the tail says TACK PER WPS-04, the requirement travels with the callout.
• Name the WPS explicitly. A tack that will be incorporated into the final weld must be made to a qualified procedure. Write the number.
• State the disposition. Say REMOVE BEFORE FINAL WELD or INCORPORATE INTO FINAL WELD. Never leave it to the fitter’s judgment.
• Delete “AS REQUIRED.” That phrase means the drawing is unfinished. Replace it with a size, a length, a spacing, and a quantity.
• Use one unit system per sheet. Follow the AWS A2.4 (dual-dimension convention) practice used everywhere else on the drawing, so nobody has to guess whether a tack spacing is 12 inches or 12 millimeters.
• Coordinate with NDT. A tack parked across a radiographed corner or where ultrasonic testing will run creates a reject before the weld is even placed. Mark tack zones as exclusion areas on the NDT plan.

For Fitters and Welders

The tack is a weld, so work it like one:

• Follow the qualified procedure, including the WPS requirements for positions, passes, and inspection, and use the qualified process and filler metal rather than whatever rod is nearest the fixture.
• Keep tacks clean and dry. Oil, mill scale, paint, and moisture under a tack become porosity and hydrogen cracking in the finished joint.
• Place tacks away from high-stress weld terminations and from areas that will be NDT-scanned.
• Control heat on thick sections: maintain the specified preheat, and don’t quench a tack with a rag because the fit-up crew is in a hurry. Details are in our guide to running E7018 filler correctly, where arc starts and stops are handled the same way.
• Avoid arc strikes outside the joint. Stray strikes are base-metal damage and are grounds for rejection.
• Never grind a tack to “hide” a defect. If a tack cracks, remove it properly and tell the inspector.

For Inspectors and QA

Verify, don’t assume: confirm tack welder qualification for the process being used, measure tack size and spacing against the drawing, examine tacks for cracks before final welding begins, confirm that tacks marked for removal were actually removed and ground correctly, and document everything in the report with photos where the code allows.

Safety: The Tack Is Where Hot Work Starts

Tacking is often the first arc of the day and the most casually treated, and it carries the same hazards as production welding. OSHA’s general requirements for welding, cutting, and brazing live under 29 CFR 1910.252 and cover fire prevention, protection of personnel, and ventilation; the agency’s welding, cutting, and brazing topic page collects the related standards. Fire watch and hot work controls follow NFPA 51B, Standard for Fire Prevention During Welding, Cutting, and Other Hot Work. NIOSH identifies welding fume as a mixture of metal fumes and gases, including manganese and hexavalent chromium in some processes, and recommends exposure controls. And tacking inside a vessel or pit falls under the permit-required confined space standard at 29 CFR 1910.146. Coated or galvanized steel raises fume risk further, so know your welding PPE and respiratory protection requirements before the first tack goes in.

Key Takeaways, a One-Page Cheat Sheet, and What to Do on Your Next Job

Tack welds are the most-used and least-documented welds in fabrication, and that gap almost always starts at the drawing. Ten sections later, the whole story compresses into four sentences you can carry to the shop floor tomorrow: AWS A2.4 gives tack welds no dedicated symbol, so their requirements live in the symbol tail and the drawing notes; the weld shape itself is still drawn with a conventional symbol; the governing code, not shop custom, defines what is acceptable; and any tack that becomes part of the final weld is a real weld with real consequences.

If You Only Remember Three Things

• No symbol, no excuse. There is no unique tack weld callout in AWS A2.4:2020, the current U.S. standard (ISO 2553 is its international counterpart). If tacks matter, write them into the tail or a general note.
• Tack welders qualify separately. AWS D1.1 carries its own tack welder qualification provisions, and an unqualified tack is an unqualified weld.
• Documented tacks are the cheapest insurance you will ever buy. A one-line note referencing a WPS costs seconds; an undocumented tack that cracks overnight costs a re-erection.

The One-Page Cheat Sheet

Your FAQ, Answered Fast

How do you show a tack on a drawing? With a note or tail entry, plus the conventional fillet or groove symbol for the tack’s shape. Do tacks need a WPS? Yes, whenever they will be incorporated into the final weld, carry load during erection, or the governing code says so. Can tacks be welded over? Only if the note or code allows it, and only after they are clean, sound, and verified crack-free. Do tacks need inspection? A tack is not exempt because it is small; look at it before the production weld buries it. How do tacks differ from intermittent welds? An intermittent fillet is a dimensioned production weld; a tack is a fit-up aid you are supposed to notice and plan for.

Marco’s column did not fail because anyone was careless with a torch. It failed because three small welds existed on the shop floor and nowhere else. The fix was never skill; it was a note on a print, a WPS number, and somebody’s initials.

Frequently Asked Questions

Is there an official tack weld symbol in AWS A2.4?

No. AWS A2.4 does not define a dedicated tack weld symbol the way it defines fillet, groove, plug, spot, seam, or stud symbols. Instead, tack weld requirements are conveyed through drawing notes, general notes, or the tail of the welding symbol, while the weld shape used for the tack is still shown with a conventional symbol such as a fillet triangle.

How do I put a tack weld on a drawing?

Draw the weld shape you intend (usually a fillet) and add a note or leader specifying tack size, length, spacing, quantity, process, whether the tack is incorporated or removed, and the governing WPS or code clause. Many detailers also add ‘TYP.’ or a detail balloon so the requirement is not overlooked in the shop.

Do tack welds need a WPS?

In code work, yes, in effect. AWS D1.1 and similar codes require that welding, including tack welds that become part of the finished weld, be performed in accordance with a qualified welding procedure by qualified personnel. Always check the governing code and contract documents for your project.

Can you weld over a tack weld?

Often yes, provided the tack was made with a compatible qualified procedure and filler metal, is clean and sound, and the governing code permits incorporation. Tacks must be free of slag, porosity, and cracks before they are covered, because defects trapped under a final pass are costly to find and repair.

Do tack welders need to be qualified?

Under AWS D1.1, tack welders are addressed in the qualification requirements, with method of testing and acceptance criteria specified for tack welder qualification. In practice this means the person placing production tacks should be qualified for the process, position, and thickness involved.

What is the difference between a tack weld and a stitch weld?

A tack weld is a short fit-up weld used to hold parts in alignment until final welding, and it is usually called out with a note. A stitch weld is generally a chain intermittent fillet weld that is a final production weld, dimensioned using size, length, and pitch notation. One holds the assembly; the other is part of the permanent joint.

How big should a tack weld be?

There is no single universal number. Common shop practice ties tack size and length to material thickness and to the restraint the joint needs, and the applicable code or engineer’s note governs. What matters most is that the tack is specified, made to a qualified procedure, and inspected rather than left to chance.

Should tack welds be removed before final welding?

It depends on what the drawing and code specify. Tacks that will be incorporated into the final weld are typically left in place, cleaned, and welded over, while tacks that will not be incorporated are usually required to be removed without damaging the base metal. The instruction should be explicit on the drawing, not decided in the field.

Why do tack welds crack?

Common causes include rapid cooling of a small weld on thick or cold steel, hydrogen from moisture or a non-low-hydrogen filler, high restraint, and insufficient size or length for the load the tack is asked to carry. Cracks in tacks must be removed before final welding, not welded over.

Does ISO 2553 use a different tack weld notation?

ISO 2553 governs symbolic representation of welded joints internationally and, like AWS A2.4, does not provide a distinct standalone tack weld symbol. In practice, tacks are conveyed through notes and general drawing requirements, with the weld shape shown using the standard ISO symbol conventions.