Partial Penetration Weld Symbol Explained: How to Read, Draw, and Avoid Costly PJP Mistakes

A fabricator in the Midwest once built an entire stair stringer bay to the wrong weld size — the drawing called a 1/4-inch-deep bevel with a 3/16-inch PJP weld in parentheses, and the detailer read it as a full-penetration V-groove. The result was thousands of dollars in over-welded joints, grinding, and re-inspection, all because one small parenthetical number on a reference line was missed. That tiny number is the language of the partial penetration weld symbol, and once you can read it fluently, an entire category of shop-floor rework disappears.

The Little Number That Costs Big Money: Why the Partial Penetration Weld Symbol Matters

A fabricator in the Midwest once built an entire stair stringer bay to the wrong weld size. The drawing called for a 1/4-inch-deep bevel with a 3/16-inch PJP weld in parentheses, and the detailer read it as a full-penetration V-groove. The result was thousands of dollars in over-welded joints, grinding, and re-inspection, all because one small parenthetical number on a reference line was missed. Nobody falsified a measurement. Nobody used the wrong electrode. Someone simply misread a symbol.

That tiny number is the language of the partial penetration weld symbol, and once you can read it fluently, an entire category of shop-floor rework disappears.

What Exactly Is a PJP Weld?

A partial joint penetration (PJP) groove weld is a weld in which the weld metal does not extend through the full thickness of the joint. The joint is beveled or grooved to some depth, welded, and deliberately left short of the back side. This is the definition carried through structural practice in the AWS and AISC world, and it is not a defect or a shortcut. It is a design decision: the engineer determined that full fusion through the entire thickness was not structurally required at that location.

Compare that with a complete joint penetration (CJP) weld, where weld metal runs through the entire thickness of the joint. The two are dimensioned, inspected, and paid for very differently, which is exactly why confusing them on a drawing is so expensive.

PJP welds are typically specified when full fusion is not needed, and the savings are real: less filler metal, less labor, lower heat input, and noticeably less distortion than a CJP groove weld on the same joint.

What the Partial Penetration Weld Symbol Communicates

Welding symbols in the United States are standardized by AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination, the reference chart detailers keep pinned above the workstation. On a PJP callout, the symbol carries two numbers to the left of the groove symbol: first the depth of the bevel or joint preparation, and then the required weld size in parentheses. That parenthetical value is the heart of the callout. It tells the shop how far the weld metal must actually reach into the joint, which may be less than the full depth of the bevel shown.

The symbol exists because drawings have to communicate a design intent that a photograph or a note cannot: this joint is intentionally not welded through. Without the symbol, a welder who sees a big bevel will naturally fill it, and a welder who sees no bevel may run a fillet where a groove belongs. The symbol removes the guesswork in a few square millimeters of ink.

Who Reads the Symbol — And What Each Reader Needs

Everyone who touches a fabrication drawing reads the partial penetration weld symbol, but each reads a different part of it:

• Detailers draw it and must place the depth of preparation and the parenthetical weld size correctly on the arrow side or other side of the reference line.
• Fitters read the root opening, groove angle, and joint prep dimensions to cut and fit the joint the way the symbol assumes.
• Welders read the required size to know when to stop — how many passes, how deep, and whether a cover pass or contour is called for.
• QC inspectors verify that the completed weld meets the specified effective throat, and decide whether nondestructive examination is triggered by the joint type.
• Welding engineers reconcile the symbol with the WPS/PQR, because the qualified procedure must cover the exact PJP size shown.

Structural work in the U.S. ties this language back to AWS D1.1 for execution and inspection, and to AISC 360 and AISC 341 for design. Pressure piping work routes through ASME B31.1 and B31.3, which treat partial penetration welds and their examination requirements on their own terms. Same symbol family, different downstream consequences.

What You Will Learn in This Article

Two searches bring people here: how do I read a PJP weld symbol, and how do I draw one correctly. This article answers both. Over the next sections you will get the anatomy of the full AWS welding symbol, every groove type that can represent a PJP, a line-by-line comparison of PJP versus CJP, six worked reading examples, the ISO 2553 differences you will meet on international drawings, the design and inspection context behind the numbers, the seven mistakes that cause rework, and a shop-floor workflow that takes you from symbol to sign-off.

Read it once with a drawing in front of you. The stair stringer story stops happening.

Anatomy of a Welding Symbol: Where the Partial Penetration Information Lives

Before you can read a partial penetration weld, you need to know where to look. The AWS welding symbol is a compact little sentence built from a handful of parts, and every one of them sits in a fixed position. Move a number to the wrong side of the line and the instruction changes completely. This section walks through the whole anatomy so the PJP-specific pieces in the next section make sense at a glance.

The Three Mandatory Parts (and One Optional Tail)

Per the AWS welding symbol chart, every welding symbol has exactly three mandatory components:

• The arrow — the leader line that points to the specific joint being called out. Its tip identifies the joint, and one end of that joint becomes the “arrow side.”
• The reference line — the horizontal bar that carries all the information. Everything else hangs off it.
• The weld symbol — the actual shape (fillet, V-groove, bevel, square, and so on) drawn on the reference line.

The tail is optional and appears only when you need to cite a specification, welding process, or other reference, such as “AWS D1.1” or “FCAW.” If there’s nothing to reference, there’s no tail. As TWI explains, a symbol without a tail is still a complete, valid callout.

Above or Below: The Rule That Is Never Negotiable

This is the single most important convention in the entire system, and it is where expensive mistakes are born:

• Symbol placed BELOW the reference line → applies to the arrow side of the joint.
• Symbol placed ABOVE the reference line → applies to the other side of the joint.

The arrow side is the side of the joint the arrow points to; the other side is the opposite face. Flip these and you weld the wrong face of the connection, or worse, you prepare a joint on a side that was never beveled. Fabricators have scrapped entire assemblies over this one reversal, which is why Structure Magazine lists misread arrow-side placement among the most commonly misapplied welding symbol errors. When symbols appear on both sides of the reference line at once, the joint gets a weld on each face — a very common PJP detail.

The Dimensional Zones: Left, Right, and Inside

Numbers on a welding symbol are not floating — their position tells you what they mean:

That left-hand zone is exactly where the partial penetration information lives. A PJP callout is not a special, unique glyph. It is a completely standard groove weld symbol — square, V, bevel, J, U, or flare — paired with a specific arrangement of dimensions on the left side of the symbol. The depth of the bevel preparation sits there, and the required weld size sits in parentheses right beside it. Same symbol as a CJP callout; different numbers, different job.

This is why the zones matter more than the shape. Two drawings can show an identical single-V symbol, yet one specifies full penetration and the other specifies a shallow 3/16-inch throat simply because a parenthetical value was added. According to National Board guidance, the dimensional arrangement, not the symbol outline, is what defines the required joint penetration — a point that carries real weight in pressure equipment work.

Get comfortable with these zones now, and the next section — where we break down each groove symbol that can carry a PJP — will read like plain English.

Groove Weld Symbols and How They Specify Partial Penetration

Every PJP callout on a shop drawing starts with a groove weld symbol. The groove symbol describes the shape cut into the joint; the numbers around it describe how far the weld must actually reach into that shape. Get the numbers in the wrong position and the meaning flips entirely, which is exactly what happened in the stair stringer story. So let’s walk through each groove symbol that can carry a PJP requirement, and then nail down the AWS dimensioning rule that makes it a partial penetration rather than a full one.

The Seven Groove Symbols That Can Represent a PJP

The AWS welding symbol chart shows the full family of groove welds. Seven of them routinely show up on PJP details:

Square groove welds deserve a second look. Because the edges are cut flat, fabricators often assume full penetration automatically. Not so. When the root opening is tight or the penetration is deliberately limited, a square groove weld is a perfectly legitimate PJP joint, and the specified weld size is what controls the required depth of penetration. TWI’s job-knowledge guide on weld symbols makes the same point: the symbol describes the joint preparation, while the dimensions describe the required fusion.

The AWS PJP Dimensioning Rule

Here is the rule that trips up detailers more than any other. Per AWS A2.4, for a partial joint penetration groove weld:

• The depth of joint preparation (bevel, J, or U depth) goes to the left of the groove weld symbol.
• The required weld size — effective throat for a groove weld, or depth of joint penetration — goes to the left as well, in parentheses, immediately before the preparation depth.

So a callout written as (3/8)-1 reads: a groove preparation 1 inch deep, with a required weld size of 3/8 inch. The parentheses are the entire signal. Without them, the two numbers lose their meaning, and a reader can easily mistake a PJP for a full-penetration groove.

Why Bevel and J Symbols Demand Extra Care

With a V-groove or square groove, both members look symmetric, so side placement is less critical. With a bevel-groove or J-groove, the shape of the symbol itself tells the fitter which member to prepare. If the symbol sits on the arrow side, the pointed bevel side of the symbol signals that this member gets cut; on the other side, the mirrored orientation tells the fitter the opposite member is prepared. Reading that backwards means the wrong plate gets beveled — a scrap-level mistake, not a rework-level one.

Flare Grooves Are Always Partial Penetration

Flare-V and flare-bevel grooves form naturally between rounded surfaces, such as rolled tube walls or the toe of a rolled shape. The concave surface limits how deep fusion can realistically reach, so these joints are partial penetration by definition — there is no such thing as a CJP flare groove weld. As AISC’s engineering FAQs confirm, flare groove welds are treated as a special class of PJP groove weld, with design strengths based on an assumed effective throat, typically taken as a fraction of the flare width rather than the full leg. That assumption matters enormously in design, and it starts with reading the symbol correctly.

Understanding the symbol gets you halfway. The next question is what changes when that same joint is called out as complete joint penetration instead.

PJP vs. CJP: Reading the Difference on a Drawing and Why It Changes Everything

Two welds can look identical after they are ground flush and painted. One of them cost the fabricator $18 a linear foot; the other cost $52. The only difference was on the drawing, and it came down to a single pair of parentheses. Knowing how to tell a partial joint penetration weld from a complete joint penetration weld at a glance is the single most valuable reading skill you can build, because the two callouts trigger completely different preparation, filler volume, pass counts, inspection scope, and design strength.

The Visual Cue: Parentheses Tell You It Is PJP

Per the AWS welding symbol chart, a PJP groove weld is dimensioned by a required effective throat or depth of joint penetration placed in parentheses to the left of the weld symbol, alongside the depth of preparation. The parentheses are the tell. A CJP groove weld, by contrast, is typically specified with no parenthetical size at all: the weld is expected to extend through the entire member thickness, so there is no smaller number to write. Some drawings add a “Z” flag, a complete-fusion note, or a backgouge symbol on the reverse side of the joint to make the intent explicit, as described by the National Board.

Why Engineers Choose One Over the Other

PJP is the default when the joint does not need to develop the full strength of the base metal. It wins on economics, distortion control, and access: shallower bevels mean less groove volume, fewer consumable pounds, fewer passes, less heat input, and no backgouge. That is why the vast majority of gusset-to-beam flange connections, lap joints, and non-critical butt joints are PJP or fillet territory. The AISC fillet and PJP research report documents just how much economy is available when PJP is specified correctly.

CJP is reserved where the joint must carry the full yield force of the connected member: tension flanges in moment connections, members where the weld is the only load path, fracture-critical bridge details, and pressure-retaining joints. Seismic and cyclic demand make the choice stricter still. AISC 341 and AISC welding guidance require CJP, or specially detailed PJP with mandatory supplementary inspection, for highly ductile demand-critical joints, and TWI’s weld symbol reference makes the same distinction clear for international drawings.

The Cost of Confusing the Two

Misreading PJP as CJP over-welds the joint: extra groove prep, extra consumable, extra passes, sometimes a backgouge, plus expanded NDE. Practitioners routinely report that every unnecessary upgrade from PJP to CJP doubles or even triples the installed joint cost. Misreading CJP as PJP is worse. It leaves a load-carrying joint with a weld that never reached the root, and it usually surfaces as a rejection in Structure Magazine’s well-known list of misapplied welding symbols or, worse, in service.

A Mini Decision Framework

1. Is the joint a primary tension or fracture-critical load path? Yes → CJP, with mandatory NDE.
2. Is the connection cyclic or demand-critical per AISC 341 / AWS D1.1? Yes → CJP or specially qualified PJP with full inspection.
3. Is full member strength developed through the weld alone? Yes → CJP.
4. Is the joint governed by throat or leg capacity of an intentionally partial weld? Yes → PJP, dimensioned in parentheses.
5. Is it a flare groove on a rolled shape? It is PJP by nature; no upgrade is possible.

Reading Real Partial Penetration Weld Symbols: Six Worked Examples

Nothing makes welding symbols click faster than reading real callouts the way you would on a shop drawing. Below are six examples you will run into constantly on structural and fabrication drawings. For each one, we read the symbol left to right, then translate it into the plain-language instructions a welder would actually follow at the bench.

Example 1: The Single-V PJP Butt Joint — “(1/4)-1 30°, 1/4 root”

This is the classic PJP callout and the one that trips up beginners most often: a V-groove symbol sitting below the reference line, with dimensions stacked to its left as (1/4)-1 30°, 1/4 root.

• (1/4) — the parenthetical number is the required weld size, measured as depth of joint penetration. This is the number that matters for strength.
• -1 — the depth of preparation, meaning the groove is beveled 1 inch deep.
• 30° — the groove angle, 30 degrees included between the prepared faces (15 degrees per side).
• 1/4 root — the root opening at fit-up.

Shop-floor translation: “Bevel the member 1 inch deep at 15 degrees per side, fit up with a 1/4-inch root opening, and stop welding once you have 1/4 inch of penetration — not the full 1 inch.” That 3/4-inch gap between preparation depth and required size is exactly what makes this a partial penetration weld, and exactly the number the fabricator in our opening story missed.

Example 2: Single-Bevel PJP With Arrow-Side Preparation

Here a bevel-groove symbol (one vertical line, one slanted line) sits below the reference line, dimensioned (3/16)-3/4. Because it is below the line, it applies to the arrow side — the member the arrow points at.

Shop-floor translation: “The member the arrow touches gets a 3/4-inch-deep single bevel; the other member stays square. Weld to a required size of 3/16 inch.” On a T-joint only one plate gets beveled, so beveling the wrong plate is an expensive, irreversible mistake. A vertical line on the slanted side of the symbol tells you which side to prepare — a detail the Miller Electric guide to reading weld symbols flags as one of the most common misreads.

Example 3: Double-V PJP With Unequal Depths

A double-V-groove symbol appears on both sides of the reference line with different dimensions per side: below the line reads (1/2)-1, above the line reads (3/8)-3/4.

Shop-floor translation: “The arrow side gets a 1-inch-deep V preparation welded to 1/2 inch of penetration; the other side gets a 3/4-inch-deep preparation welded to 3/8 inch.” Groove symbols on both sides of the reference line mean the weld is required on both faces, and each side carries its own depth-of-preparation dimension. Total required penetration is 7/8 inch — still short of full depth on a thicker plate, which the engineer confirmed by calculation, not by eye.

Example 4: Flare-Bevel PJP on a Rolled Shape

A flare-bevel symbol (a slanted line meeting a half-circle curve) points at the rounded toe of a rolled shape, dimensioned simply 1/4. No parentheses appear — because flare-V and flare-bevel groove welds are always PJP by nature. The curved surface of a rolled shape can never be melted through predictably, so AWS treats these as partial penetration automatically.

Shop-floor translation: “Wet in the joint between the curved toe and the flat member to a 1/4-inch effective throat.” In design practice that throat derives from an assumed 5/8 of the flare radius, or from tabulated effective throat values in AISC’s engineering FAQs on welding. The welder doesn’t need that math — but the inspector checking fillet-gauge readings against the symbol does.

Example 5: PJP Groove Combined With a Fillet

One reference line carries a V-groove symbol below the line with (1/4)-1, plus a fillet symbol reading 1/4.

Shop-floor translation: “Run a 1/4-inch-deep PJP groove weld, then add a 1/4-inch fillet over the top.” This combined callout typically represents a partial penetration groove supplemented by a fillet for the remaining throat. The critical question is whether the required sizes add by throat or by leg size — as Structure Magazine’s article on commonly misapplied welding symbols warns, assuming leg-size addition is a frequent and costly error.

Example 6: PJP on Both Sides of a T-Connection

A double-bevel-groove symbol straddles the reference line, with (3/16)-1/2 on the arrow side and (3/16)-1/2 on the other.

Shop-floor translation: “Bevel both sides of the connecting member 1/2 inch deep and weld each side to 3/16 inch required size.” Total penetration is 3/8 inch plus root contact, sized by the engineer for the applied load. The official AWS welding symbol chart confirms the double-V, double-bevel, and double-J variants all follow this per-side dimensioning logic.

Read enough callouts this way and the pattern becomes automatic: parentheses mean required size, position on the reference line tells you which member gets prepped, and missing parentheses on a flare groove mean it was always partial penetration to begin with. With these six examples under your belt, you are ready to see how the ISO 2553 system handles the same joints — because international drawings read differently, and misreading those can be just as expensive.

AWS A2.4 vs. ISO 2553: How Other Standards Show Partial Penetration

A welding symbol only works if both ends of the drawing speak the same language. AWS A2.4 is the reference in the United States, but a large share of the world’s fabrication runs on ISO 2553, the international convention used across Europe, Asia, and anywhere else aligned with the ISO system. Buy a structural beam package from an overseas mill, or fabricate a skid for an international client, and the PJP callout in front of you may look familiar while still meaning something slightly different. Misreading ISO dimensioning as AWS dimensioning is a well-known cause of over- and under-welding on cross-border projects, which is why many multi-national fabricators simply add explicit text notes to remove any ambiguity.

The Bracket System: Which Side Gets the Weld

The first difference you notice is not in the weld symbol itself but in how AWS says which side and how ISO says it. AWS uses the reference line position rule: a symbol drawn below the line applies to the arrow side, and above the line applies to the other side. That rule is non-negotiable in the AWS system, and it is covered in detail in AWS’s official welding symbol chart.

ISO 2553 allows a more compact alternative: the bracket. Dimensions written inside a bracket apply to the arrow side, while dimensions outside the bracket apply to the other side. On a double-sided PJP butt joint, an ISO drawing can therefore carry two different weld sizes around a single symbol instead of repeating the symbol above and below the reference line. If you automatically apply the AWS “above = other side” rule to an ISO bracket drawing, you can easily swap the two sizes, weld the shallow side deep, and end up with a joint that fails both the drawing and the check.

The “S” Prefix and Penetration Depth

ISO-influenced drawings also have their own shorthand for penetration. As TWI’s job knowledge article on weld symbols explains, in a butt joint an “S” followed by a number placed to the left of the symbol refers to the depth of penetration. That looks nothing like the AWS convention you learned, where the depth of preparation sits to the left of the groove symbol and the required weld size sits beside it in parentheses. An “S3” on an ISO drawing is telling you the specified penetration depth; seeing only a bare “S” means the penetration depth is the full thickness of the thinner part joined.

y or a: What the Number Actually Measures

ISO symbols state explicitly whether the dimension is throat thickness, marked “y”, or leg length, marked “a”. AWS, by contrast, leans on the effective-throat convention for groove welds and lets position and symbol type carry much of the meaning. This distinction matters enormously for a PJP callout: a number marked as an “a” leg on a partial penetration groove is measuring something different than an AWS effective-throat value, and translating one straight into the other will give you the wrong throat, wrong weld volume, and wrong inspection criterion. Open Oregon’s welding symbols chapter offers a good side-by-side orientation if you are teaching this to a mixed-standard crew.

Flags, Rings, and Small Graphic Differences

Even the supplementary symbols differ slightly. ISO 2553 uses its own conventions for the field weld flag and the weld-all-around indicator, with graphic details that do not map one-for-one onto AWS A2.4. The intent behind them is the same: a flag means the weld is made on site rather than in the shop, and a circle at the junction means weld all the way around. But small drawing differences can hide big execution differences, and Structure Magazine’s article on commonly misapplied welding symbols documents how routinely even familiar symbols are misapplied in practice.

They Are Not Interchangeable by Eye

It is worth knowing that AWS anticipated this problem. AWS A2.4 itself includes a supplementary comparison so that AWS-symbol drawings can be translated for ISO-based shops. That inclusion is the clearest official acknowledgment that the two systems are related but not interchangeable by eye. On a mixed-standard project, the practical workflow is simple:

• Identify the governing standard in the drawing notes before reading any symbol.
• Confirm whether dimensions are throat (y) or leg (a), and whether a penetration prefix such as “S” is present.
• Confirm which side each dimension applies to using the bracket, not the AWS above/below rule.
• Where anything is unclear, request a note from the engineer of record rather than guessing.

For pressure and boiler work specifically, the National Board’s references are a useful reminder that welding symbols never stand alone: they must be reconciled with the construction code, the WPS, and the inspection plan. Treat the symbol as the starting sentence of a conversation, not the final word, and cross-border PJP drawings stop being a trap.

Design and Code Context: What the PJP Symbol Means for Engineering and Inspection

A weld symbol is not decorative. Behind every parenthetical number on a reference line sits an engineering decision that controls throat thickness, weld cost, required NDE, and ultimately whether the joint passes inspection. Once you can read the partial penetration weld symbol fluently, the next question is what that symbol actually obligates you to do.

Effective Throat: The Number Behind the Number

For a PJP groove weld, the design effective throat is not the full thickness of the plate and not the depth of the bevel either. It is the thickness of the thinner part joined minus the depth of joint preparation that remains unwelded. If a 1-inch plate carries a 3/8-inch-deep bevel with a required weld size of 5/16 inch in parentheses, the unwelded 5/16 inch below the fusion line stays there by design, and the throat you are paid for, designed for, and inspected against is the 5/16 inch specified. That logic is the backbone of AISC’s engineering FAQ guidance on welding, which walks through exactly how these dimensions are interpreted.

Flare groove welds deserve special attention because the joint is formed by the convex surface of a rolled shape rather than a machined bevel. The effective throat is derived from that convex geometry, and TWI’s job-knowledge write-up on weld symbols reinforces the same point: flare-V and flare-bevel welds are partial penetration by nature. You cannot order full fusion out of a symbol that never promised it.

What AISC Says About PJP Strength

AISC 360 Table J2.5 sets the available strength of PJP groove welds by the effective throat, and the NCSEA/AISC Research Report on fillet and PJP welds compiled the strength and ductility data behind those provisions. The takeaway for the shop floor is reassuring: conservatively designed PJP welds perform reliably as long as the effective throat is actually achieved. The failures start when the throat on paper and the throat in the joint diverge.

ASME Pressure Piping: Where NDE Gets Tied to the Symbol

In pressure piping, ASME B31.1 and B31.3 permit PJP groove welds in many services, but the required extent of examination follows the weld type and the service category. This is where the symbol stops being a drawing convention and becomes an examination plan. A PJP in normal service may need only spot or sample examination; a PJP in severe cyclic service can demand the same rigorous examination as a CJP. Calling it “partial” does not automatically make it a lighter inspection load.

AWS D1.1 Inspection Implications

Under AWS D1.1, visual inspection applies to every weld, while UT or RT for groove welds is invoked by the code or by the engineer of record. Choosing PJP instead of CJP can reduce the volume of volumetric NDE required, but it never removes the visual obligation, nor does it excuse poor fit-up. The symbol tells the inspector which acceptance criteria apply, and Structure Magazine’s list of commonly misapplied welding symbols documents how often that chain of reasoning breaks down in the field.

Practically speaking: the deeper the specified size in parentheses, the more passes, the more heat input, and often the more NDE. Read the number, then price the joint accordingly.

Seven Common Partial Penetration Weld Symbol Mistakes (and How to Catch Them)

Even seasoned detailers, welders, and inspectors slip up on the partial penetration weld symbol. The difference between a correct PJP callout and a costly misread often comes down to small details hidden on the reference line. Below are the seven most frequent errors pulled from real shop experience and documented by industry sources, along with simple ways to catch each one before cutting, fitting, or welding.

1. Reversing Arrow Side and Other Side

The most frequent reading error is swapping which side of the joint gets the PJP groove. Per AWS A2.4, a symbol placed below the reference line applies to the arrow side, while a symbol placed above the reference line applies to the other side. This rule sounds simple, but under production pressure, it’s easy to flip. Always trace the arrow to the actual joint member first. If the arrow points to a plate edge or bevel face, confirm that face matches the side shown before prepping.

2. Forgetting the Parentheses Convention

For most groove welds that call out partial penetration, AWS shows two numbers to the left of the groove symbol: the required weld size in parentheses, followed by the depth of preparation. Skipping the parentheses and welding to the larger number is one of the biggest sources of over-welding. The parenthetical value is the effective throat or specified PJP depth the designer wants achieved, not just how far you beveled. Treat that number as the “must meet” value for the joint. When in doubt, check the exact callout against TWI’s breakdown of weld symbols to lock in the correct order.

3. Treating Flare Grooves as Full Penetration

A very common trap is looking at a flare-bevel or flare-V groove symbol and assuming full fusion is required. In reality, Structure Magazine’s “Commonly Misapplied Welding Symbols” points out that flare groove welds are always partial joint penetration by nature, due to the curved radius of the rolled or formed surface. You cannot obtain uniform complete penetration into that radius without special, impractical preparation. For this reason, the PJP size in parentheses must be used to control the weld, not an assumed CJP.

4. Omitting Root Opening or Groove Angle

Many PJP symbols show the groove type but leave out a root opening (R) or groove angle. While some values may be covered by a qualified WPS, the drawing always takes priority for the fit-up shown. Missing these dims forces the shop to guess. A tighter root opening than intended can choke access and limit penetration, while an open root with no angle can lead to excess buildup. Cross-check every PJP groove for R and included angle. If either is blank, get written clarification before tacking.

5. Assuming a Fillet-Plus-Groove Symbol Means Leg-Size Addition

It’s tempting to read a fillet symbol placed next to a groove symbol on the same side and just add leg sizes. That is incorrect. When both appear together on one joint face, the governing design is the effective throat of the combined weld. As outlined by AISC research on fillet and PJP welds, the load-carrying capacity must be based on effective throat, not a simple arithmetic of two leg dimensions. Blindly “stacking” leg sizes leads to serious over-welding with no code basis.

6. Ignoring Field-Weld Flags

The small flag pointing away from the arrow on the reference line means the PJP weld is a field weld. This single mark changes everything from fit-up sequencing and access to scaffolding, preheat control, and final inspection. Field conditions rarely match the controlled jig of the fab bay. For jobs governed by National Board inspection guidance, missing a field flag can also throw off hold points. Treat every flag as a red-light reminder to adjust your plan.

7. Failing to Reconcile the Symbol with WPS/Qualification

The partial penetration weld symbol tells what is required, but the WPS/PQR tells how it’s proven. A callout for a specific PJP size is only valid if your qualified procedure covers that groove type, process, position, thickness, and the required effective throat. This is especially critical for flare grooves and for PJP on both sides. Before releasing work, run a symbol-to-WPS cross-check. Lean on resources like Open Oregon’s Welding Symbols textbook to train new hands on this habit.

From Symbol to Shop Floor: Applying the Partial Penetration Weld in Practice

A weld symbol is only a set of instructions. Turning it into a sound joint takes a deliberate sequence of steps, and on PJP joints the margin for error is thinner than most crews expect. Because the weld is intentionally stopped short of the joint root, a small deviation in fit-up, current, or travel speed can push you past the specified penetration and turn a partial weld into an accidental full one, or leave you short of the required throat. Here is the workflow that keeps the drawing and the finished joint in agreement.

Step 1: Read the Dimensions Backward

Start by pulling the numbers off the reference line in the order AWS A2.4 defines them: required weld size in parentheses first, then the depth of preparation, then root opening and groove angle if shown. That gives you the target effective throat, not just the bevel depth. Cut only as deep as the preparation calls for, and plan the weld to land on the parenthetical size. If the symbol shows a 1/4-inch bevel with a 3/16-inch weld size in parentheses, a 1/4-inch-deep groove welded full is over-welded, while a shallow 1/8-inch pass is a reject. The AWS welding symbol chart is worth keeping laminated at the fit-up table for exactly this reason.

Step 2: Control Fit-Up Before the Arc Strikes

The root opening printed on the symbol is the single biggest determinant of whether the required PJP throat is actually achieved. A root opened up by an extra 1/16 inch, or closed tight by tack distortion, shifts how far the arc reaches into the joint. Check the root opening with a gauge after tacking, not just before. Alongside fit-up, AWS D1.1 requires groove faces and the prepared area to be cleaned of mill scale, oil, and paint regardless of penetration depth, so a bevel cut weeks ago and stored outside needs wire brushing before it goes together.

Step 3: Qualify the Procedure for the Size You Are Welding

This is where shops get cited. AWS D1.1 requires welding procedures to be qualified for the range of joint penetration and weld sizes actually used, so a PJP made outside the qualified WPS range is a code violation even when the finished weld looks acceptable. Confirm that your PQR supports the groove type, thickness range, and effective throat on the drawing before production starts. If the detailer changes the weld size mid-job, that is a requalification conversation, not a field decision.

Step 4: Position, Sequence, and Hold the Penetration

• Positioning: Set work position and torch angle so the arc points at the groove face, not straight down the root. Flat position gives the most consistent penetration control.
• Pass sequencing: Stringer beads, cleaned between passes where required, keep heat input predictable. Chasing a wide weave into a shallow PJP is how accidental full penetration happens.
• Penetration control: Hold voltage, travel speed, and stick-out within the qualified WPS window. PJP joints are more forgiving than CJP on access but less forgiving on consistency.
• Heat and distortion: PJP joints deposit less filler and take lower heat input than equivalent CJP joints, measurably reducing angular distortion in plate assemblies. Balanced sequencing and skip welding amplify that advantage.

Step 5: Dress to Contour, Then Sign Off

If the symbol carries a contour mark, the job is not finished when the arc stops. Flush, convex, and concave contours appended to the PJP symbol require grinding or machining to the specified contour after welding. Once dressed, inspection follows the drawing: verify effective throat against the parenthetical size, check for undercut and profile, and confirm any NDE required by the code or specification has been completed. Per the National Board and ASME practice, the extent of examination is tied to the joint type the symbol declares, so a PJP callout and a CJP callout can trigger very different inspection loads on the same assembly.

The habit worth building is simple: treat every PJP symbol as a short checklist rather than a single instruction. Read the size, verify fit-up, confirm the WPS, control the passes, dress the contour, and document the sign-off. Miss one link and the joint either costs you in rework or fails inspection. Handle all six and the partial penetration weld comes out exactly as the detailer intended.

Comparisons, Quick-Reference Tips, and What to Do Next

You have now walked the full length of the partial penetration weld symbol, from the reference line to the code that governs its inspection. What makes that knowledge stick on a busy shop floor is a single page you can glance at between fit-up and arc strike. Below is that page.

Side-by-Side: PJP, CJP, Fillet, and Flare Groove

These four symbols get confused more than any others, and the confusion is almost never harmless. Use this table as your first filter when a drawing lands on the bench:

Your 60-Second PJP Reading Checklist

1. Find the arrow side. Symbols on the arrow side of the reference line are arrow side, the rest are other side. Get this wrong and every number after it is wrong.
2. Identify the groove shape. Square, V, bevel, J, U, flare-V, or flare-bevel. The shape tells you the required edge preparation.
3. Read left of the symbol. First number is the depth of preparation; the number in parentheses is the required weld size.
4. Check length and pitch to the right of the symbol. Intermittent PJP is unusual and should always be questioned.
5. Look at the tail for the process, specification, or WPS reference that governs the weld.
6. Check for flags — the field-weld flag at the reference line break, the weld-all-around circle at the arrow break.
7. Reconcile with the WPS. A symbol is only as good as the qualified procedure behind it.

Build a Shop Symbol Crib Sheet

The best shops do not just hang a chart — they build their own: one page per joint type they actually run, with the symbol on top, a photo of a sectioned or finished weld beside it, the qualified WPS number below, and the effective throat the welder should see on a gauge. Shops that maintain this format consistently report fewer weld-size disputes at inspection, because the argument ends before it starts. Start with the joints you run weekly: the bevel-groove butt joint, the T-joint with a PJP bevel, the rolled-shape flare-bevel, and the fillet-plus-groove combination.

Where to Keep Learning

For a clean, beginner-friendly walk through square, V, bevel, J, and U groove symbols using the same dimensional conventions as AWS A2.4, Open Oregon’s open textbook chapter on groove welding symbols is free and genuinely well drawn. For the one-page shop reference, the AWS welding symbol chart published by AWS sections shows every basic weld symbol and every element of the welding symbol in one frame. When you are ready to move from reading symbols to reading drawings confidently, Miller Welds’ guide to reading and understanding welding symbols is the practical next step, and the standard itself, AWS A2.4, remains the authoritative reference you should own a copy of.

Back to the Stair Stringer

Remember the Midwest fabricator from the start of this article. The callout read ‘(3/16)-1 30°’. Read slowly, it says: a 1-inch-deep bevel preparation, a 30-degree included groove angle, and a required weld size of 3/16 of an inch in parentheses. That is a partial penetration weld — not a full-penetration V-groove. Reading the parentheses correctly would have produced the right weld on the first pass, saved the grinding and re-inspection bill, and kept the stringer bay on schedule.

That is the whole point of the partial penetration weld symbol. It is not a technicality; it is an instruction with a dollar figure attached to it. Learn to read it, teach your crew to read it, and keep the crib sheet within arm’s reach of the bench.

Quick Tips and Next Steps

• Print the AWS symbol chart at full size and tape it inside the fitting station, not the office.
• Train detailers and welders together. Symbol errors are communication errors, and communication errors need both sides in the room.
• When in doubt, ask the engineer before the arc is struck. Once the metal is deposited, a PJP misread becomes a CJP correction, and that is a very expensive fix.
• Re-read Structure Magazine’s article on commonly misapplied welding symbols every few months; the same seven errors keep showing up across the industry.

Read the parentheses. Verify the throat. Confirm against member thickness. Do those three things on every PJP callout and the category of rework that started this article simply disappears from your shop.

Frequently Asked Questions

What does a partial penetration weld symbol look like on a drawing?

It is a standard groove weld symbol (square, V, bevel, J, U, or flare) on the reference line, with the required weld size written in parentheses to the left of the symbol and the depth of preparation placed next to it. The parentheses are the key visual cue that the joint is partial penetration rather than complete joint penetration.

How is a PJP weld different from a CJP weld in AWS symbols?

A CJP groove weld symbol typically carries no parenthetical weld size because the weld must run through the full member thickness, and it may include a backgouge or complete-fusion note. A PJP symbol carries a required size in parentheses plus the depth of preparation,, meaning the full thickness must be fused. If you see parentheses around a size, treat it as PJP and verify the required throat against the member thickness.

Which groove weld symbols can specify partial penetration?

Square, V-groove, bevel-groove, J-groove, and U-groove symbols can all specify PJP when dimensioned with a required size less than full thickness. Flare-V-groove and flare-bevel-groove welds are always PJP by nature, because the convex surface of the connected part limits how deep fusion can realistically reach.

How do you dimension a partial penetration V-groove weld per AWS A2.4?

Write the required weld size in parentheses to the left of the V symbol, followed by the depth of preparation — for example, (1/4)-1, meaning a 1-inch deep bevel with a required 1/4-inch weld size. The groove angle and root opening are placed on or above the weld symbol itself, such as 30° included angle and a 1/4-inch root opening.

What is the difference between AWS A2.4 and ISO 2553 for PJP welds?

AWS A2.4 places symbols below the reference line for the arrow side and above for the other side, while ISO 2553 uses a bracket system with arrow-side dimensions inside the bracket. ISO also explicitly marks throat thickness (y) or leg length (a), and some ISO-influenced drawings use an ‘S’ prefix for penetration depth, so the two systems should never be read interchangeably.

Why are flare groove welds always considered partial penetration?

The natural concave profile of a rolled beam flange, rounded bar, or formed section creates a groove whose depth varies across the joint, so full through-thickness fusion is not achievable or required. AISC treats flare groove welds as a special class of PJP with effective throat values derived from the flare geometry, typically a fraction of the flare width or radius.

When should an engineer specify CJP instead of PJP?

CJP is specified where the connection must develop the full strength of the member or where fracture and fatigue resistance govern: tension flanges, fracture-critical and cyclic-loaded seismic or bridge connections, and many pressure-piping butt joints. PJP is appropriate when the required load can be carried by a smaller effective throat, saving preparation, filler, labor, distortion, and NDE scope.

Does a partial penetration weld still require inspection?

Yes. AWS D1.1 requires visual inspection of all welds, and PJP groove welds may also require NDT when the code, specification, or engineer’s drawing calls for it — especially in cyclic or severe service. Choosing PJP instead of CJP can reduce the volume of required NDE in some services, but it never removes the visual inspection obligation or the need to verify the required throat.

What is the most common mistake when reading a partial penetration weld symbol?

Missing the parentheses convention — reading the required weld size and the depth of preparation as interchangeable — which leads to welding to the wrong depth. The second most common error is reversing the arrow-side and other-side placements, so the weld or the member preparation ends up on the wrong side of the joint.

How does a PJP symbol interact with a fillet weld symbol on the same reference line?

When a fillet symbol accompanies a groove symbol on the same reference line, the required effective throats of the two welds add together to meet the specified total throat, unless the drawing states otherwise. Welders and detailers should confirm whether addition is on a throat basis (standard AWS interpretation) or explicitly on a leg basis, since assuming leg-size addition over-welds the joint.