Macro Test in Welding: Procedure and Acceptance Criteria

Two fillet welds can look identical under a flashlight and both pass visual inspection — yet cut them open, polish them and etch them, and one shows a clean fusion line while the other has a dark seam of oxide running along the root. That single destructive examination, the macro test, is how code writers decide whether a fillet weld is genuinely qualified. Here is how the test actually works, what the etched face tells you, and where the acceptance criteria live.

What a Macro Test in Welding Actually Is, and What It Reveals

A macro test is a destructive examination: a welded coupon or production joint is cut in cross-section, ground flat, polished, chemically etched and studied at low magnification. The etchant attacks different microstructural regions selectively, so the interior paints itself in shades of grey and brown. The result is a macrograph, a printed or photographed picture of the weld’s internal architecture: fusion boundaries, heat-affected zone, penetration depth and any defects hiding inside.

The name comes from magnification. Macro means large scale. Where a micrograph might examine grain structure at 500x or 1000x, macro examination runs at low magnification, typically under 10x, where the whole cross-section fits one field of view. ASTM E381 describes etching specimens for macrostructural examination at low magnifications, usually less than 10x.

Not a new idea. Macroetching has served steel industry quality control for decades, well beyond welding, revealing structure, flow lines, grain size, segregation, inclusions and depth of carburization. Welding borrowed it for one question: did this weld actually join the metal?

The vocabulary you will meet in codes and labs

• Coupon — metal prepared to be welded and then tested: a machined test coupon, or a section cut from a real joint.
• Macro specimen — the cut cross-section of that coupon, a small block with the weld through the middle.
• Macrograph — the photograph of the etched face, shot straight-on with a scale bar.
• Fusion line — where molten weld metal met unmelted base metal and melted into it.
• HAZ (heat-affected zone) — base metal beside the weld heated enough to change properties without melting.
• Effective throat — weld metal depth from the face of a fillet weld to the root, the load-carrying dimension.
• Leg size — distance from the root of a fillet weld to its face, one of the two triangle sides.
• Etchant — the chemical that darkens different constituents so they separate visually.
• Base metal — the parent material being joined. Filler metal — the consumable wire, rod or electrode that becomes weld metal.

Why this test exists at all

Visual inspection sees only the outside. Study a fillet weld all afternoon and you still cannot tell whether the arc reached the root or a cold shut hides underneath. Radiography is better, but on a fillet weld it is awkward: corner geometry limits source and film placement, and even a clean radiograph cannot map the HAZ.

The macro test fills that gap, showing in a single image:

• Fusion to the root — whether weld metal bonded fully into the base metal;
• HAZ width — what it tells you about heat input and preheat;
• Bead and pass sequence — how many layers were deposited and in what order;
• Actual penetration depth — the real thing, not the drawing number;
• Internal defects — lack of fusion, cracks, porosity, slag or flux inclusions, cold shuts.

Those five items are why qualification codes insist on it. Macro examination is mandatory in fillet weld procedure qualification under ASME Section IX QW-183 and performance qualification under QW-184. Nusatek lists the standards welders actually see cited for macro work: ISO 9606-1:2013, BS 4515, AS 1210, AS/NZS 3992 and ASME Section IX:2015.

It is a living part of the code, not a footnote. The AWS D1.1/D1.1M:2025 edition revised the acceptance criteria for macroetch testing, confirming macroetch remains a code-governed qualification test. Qualify to D1.1 and work from the current edition, not a printout from a decade ago.

Where it sits in the weld quality chain

Four places:

1. Qualification — the PQR for a procedure and the performance test for a welder, where D1.1 and ISO 9606-1 rules come up most.
2. Production sampling — usually on sacrificial coupons or material that is already scrap, since the test consumes what it examines.
3. Failure analysis — when a joint has cracked or come apart in service, macroetch shows where the crack started and whether it followed the HAZ or fusion line.
4. Repair verification — after a repair weld, macroetch confirms the repair fused instead of just filling the gap visually.

If you are still building foundational paperwork, the macro test slots neatly alongside our guides to welder qualification records and procedure documentation. It is the evidence behind the numbers on those forms.

Plan for the fact that it destroys the part

Set one expectation early: the test is destructive, and the specimen is gone when you are done. It is never an improvised decision at the end of a shift. It is scheduled, cut in advance and budgeted for, and the equipment is what your shop already owns: a cut-off saw, a bench grinder, a polishing station and a sink. The chemistry is simple to learn, and once you recognize a sound fusion line you can read one in seconds. That skill is what the rest of this guide builds, from cutting the specimen to matching AWS D1.1 and ISO 9606-1 acceptance criteria.

How the Macro Test Works: Sectioning, Grinding, Polishing, Etching and Examination

Most failed macro tests are not failed welds. They are failed coupons. The joint gets judged on a face that somebody ground, polished, etched and dried, and every one of those steps can distort what the examiner sees. Get the bench work right and the macrograph practically reads itself; get it wrong and you can reject a perfect fillet or pass a defective one.

The sequence never really changes: section the specimen, grind it flat, polish it fine, etch it, rinse and neutralize, examine at low magnification, then document. Here is what each step actually involves.

Step 1: Sectioning the specimen

Cut transversely through the weld, through the center of the coupon, on a band saw or abrasive cut-off wheel with coolant running. Never use a torch or plasma cutter. A thermal cut leaves a recast, oxidized, heat-affected zone right where you are trying to observe one, and industry references are blunt about the consequence: flame-cut macro specimens produce misleading etch patterns and can mask genuine HAZ features. Coolant matters too. Let the wheel or blade run cool, keep the coupon from overheating, and give the cut a minute to cool before it goes to the grinder. A band saw with coolant preserves the true weld microstructure better than any thermal cutting method.

Step 2: Grinding away the saw marks

Progressively remove the saw or wheel marks, typically starting around 80 grit and stepping down through the grades. The goal is not a shiny surface yet, it is a flat one. Any waviness left in the face will distort your leg size and effective throat measurements and will make the etched pattern look lopsided. Keep the wheel flat, use light pressure, and work the whole face evenly rather than digging a groove into the coupon.

Step 3: Polishing to a clean finish

Fine polish to roughly 600 grit or better for a clear, even etch response. The Michigan Tech materials science SOP for macro-etching goes further and specifies polishing samples down to 1200 grit, which is a good target for cleanest contrast. Coarse scratches do not just look bad, they hold etching solution in their valleys and later read as false indications. Struers’ guidance on etching prep makes the same point about preparation quality driving etch contrast.

Step 4: Etching

Apply the selected etchant by immersion or with a cotton swab, working the face evenly. For most carbon and low-alloy steels, room temperature is right. For macro-etching with hydrochloric acid, the Michigan Tech SOP calls for a hot bath, roughly 70 °C, monitored with a thermometer, because temperature changes the attack rate and therefore the contrast. A third option, electrolytic etching, is standard for austenitic stainless sensitization checks under ASTM E381 practice.

Step 5: Rinse and neutralize

Wash promptly with cold water as soon as the etch is complete, then neutralize the residual acid so the attack stops. Skipping this is how a good specimen ends up pitted, stained or blotchy, and the damage can be mistaken for porosity. Neutralize the spent solution slowly with a base such as sodium hydroxide or sodium bicarbonate until bubbling stops before disposal.

Step 6: Examination at low magnification

Examine at 1x to 10x under good lighting. Industry guidance places the illumination requirement at more than 500 lux, and it is not a detail to skip. A macrograph is read by color and line, so dim or uneven lighting turns a subtle indication in the HAZ into something you miss. A macroetch examination reference is also clear on handling: pick the specimen up by the edges and never touch the etched face, because fingerprints and smears obscure the very features you are there to document.

Step 7: Documentation

Photograph the macrograph straight-on with a metric scale bar in the frame, and record the measured values: leg size, effective throat, HAZ width, penetration depth, and the location and nature of every indication. In aerospace TIG qualification work, where fillet coupons are routinely macroetched, the macrograph is part of the permanent record, not a side note. This guide to aerospace TIG welding standards covers the wider qualification picture for those shops.

Step	What you do	What it controls
1. Section	Band saw or abrasive cut-off wheel, transversely, with coolant	Avoids thermal damage that masks HAZ features
2. Grind	About 80 grit, stepping finer, keep the face flat	True leg and throat measurements
3. Polish	600 grit minimum, 1200 grit for best contrast	Removes scratches that mimic defects
4. Etch	Immersion or swab, room temp or hot HCl at ~70 °C, thermometer	Contrast and definition of the microstructure
5. Rinse and neutralize	Cold water wash, then neutralize residual acid	Stops pitting and staining
6. Examine	1x to 10x, lighting above 500 lux	Reliable reading of fine indications
7. Document	Straight-on photo with scale bar, record all measurements	A defensible, comparable result

Choosing an Etchant: Nital, Hot Hydrochloric Acid and Other Macroetch Chemistry

Pick the wrong etchant and a good coupon becomes unreadable, or reads as defective when it is not. The reagent is the biggest variable in a macro test, and it is a chemistry decision made before the specimen is cut.

What an Etchant Actually Does

Etching is a controlled, very shallow corrosion reaction. Different microstructural constituents react at different rates, so the etchant darkens some areas and barely touches others. That contrast separates weld metal, fusion line, heat-affected zone and base metal into bands you can measure and photograph. The mechanics are covered in Struers’ guide to etching, and the low-magnification framework is ASTM E381.

Nital: The Carbon Steel and Low Alloy Default

Nital is 2 to 10 percent nitric acid in ethanol, the classic macro etchant for carbon and low-alloy steels, also used on tin and nickel alloys. It works at room temperature, with a dwell from seconds to several minutes. Published macro examination guidance notes that nital is often taken as roughly one part acid to three parts water for routine coupon work, keeping the boundaries crisp.

It gives clean grain contrast and a sharply defined fusion line. Its weakness is chemistry mismatch: on stainless or a heavily scaled surface the result is uneven, so clean the scale off rather than etching through it. On low-alloy work, filler and HAZ chemistry drive the response, so check your filler choice against our guide to alloy steel welding electrodes first.

If nitric acid is a headache to store, 10 percent aqueous ammonium persulfate is a less hazardous alternative for carbon steel. It develops good weld and HAZ contrast, and it is a powder mixed with water rather than a concentrated acid on a shelf.

Hot Hydrochloric Acid: The Lab Workhorse

Hot hydrochloric acid, or muriatic acid, is what many university and industrial labs reach for on carbon steel because the contrast it produces at temperature is strong and the weld, HAZ and base metal separate unmistakably. The procedure in Michigan Tech’s macro-etching standard operating procedure is representative: bring the bath to roughly 70 degrees Celsius, hold the specimen about 15 minutes, then rinse and neutralize promptly.

That result comes with obligations. Hot acid is a severe burn hazard, it fumes, and it needs a fume hood, a thermometer, tongs and controlled disposal. It is sensitive to technique, so a lab that runs it well has rehearsed it. Without a chemistry bench, nital is an easier place to start.

Stainless, Duplex and Nickel Alloys

Stainless and nickel alloys need their own chemistry, and published macro etch guidance for these materials points to three standard options:

• Aqua regia, hydrochloric plus nitric acid commonly mixed 3 parts to 1. It etches stainless, duplex and nickel alloys well and will destroy a coupon if you overdo it. Fresh mix, short immersion, proper disposal.
• Marble’s reagent, copper sulfate with hydrochloric acid and water. The classic reagent for revealing ferrite-austenite phase balance in stainless and nickel alloys, so it is the right pick when the question is phase balance rather than weld geometry.
• 10 percent aqueous oxalic acid used electrolytically, the standard sensitization test for austenitic stainless steels under ASTM A262 Practice A. A grain-boundary reveal rather than a general macro etch, but the same family of techniques.

Shops qualifying stainless or nickel work, from Alloy 20 welding procedures to aerospace TIG welding qualification, will find those reagents worth stocking. Aluminum needs its own, usually alkaline or nitric based.

Etching Time: The Line Between Too Little and Too Much

Every reagent has a window. Under-etch and the fusion boundary never develops, so you can miss real lack of fusion or misread a sound weld. Over-etch and the detail goes soft and smeared, edges look ragged, and you can talk yourself into believing a defect that is not there. Published macroetch guidance is blunt about both failure modes.

Work in short increments instead of guessing one long bath. Swab, rinse, dry and look before committing to another ten seconds. Hot solutions etch faster, so a bath that looked right at 20 degrees can over-etch at 70 degrees in a fraction of the time.

Etchant	Typical material	Method and conditions	Main hazard
Nital, 2-10% nitric acid in ethanol	Carbon steel, low alloy, tin, nickel alloys	Room temperature; seconds to minutes	Nitric fumes, skin contact
Dilute nital, about 1 acid to 3 water	Carbon steel coupons	Room temperature; frequent inspection	Same as nital, lower concentration
10% aqueous ammonium persulfate	Carbon steel, low alloy	Room temperature; rinse well after	Oxidizer, dust and skin irritation
Hydrochloric acid, heated	Carbon steel, low alloy	About 70 C, roughly 15 minutes	Severe burns and fumes; fume hood required
Aqua regia, HCl:HNO3 at 3:1	Stainless, duplex, nickel alloys	Fresh mix; brief room-temperature immersion	Extreme oxidizer, toxic fumes
Marble’s reagent, CuSO4 + HCl + water	Stainless and nickel alloys	Room temperature; swab or immersion	Acid and copper salts; waste handling
10% aqueous oxalic acid	Austenitic stainless steel	Electrolytic, per ASTM A262 Practice A	Electrical hazard, acid handling

Reading the Macrograph: Fusion, HAZ, Penetration and the Defects You Can See

A macrograph isn’t just a photograph of an etched coupon, it’s a map. With the right polish and etch, it shows the weld’s geometry, heat history, and any indications worth recording. Knowing how to read that map is what separates a recorded test from a useful one, and it’s exactly why macro examination is built into many qualification clauses.

The Fusion Line and Heat-Affected Zone

The first thing to trace is the fusion line: the boundary where melted weld metal met unmelted base metal. On a sound weld, this line is continuous, with no smeared oxide along it. It’s only visible due to the etchant reacting differently to the two materials, so any imperfection in polishing will obscure it.

Just beyond that boundary sits the heat-affected zone (HAZ). This is base metal that was never melted, but was heated enough to change its microstructure. After etching, it appears as a distinct band between the fusion line and the unaffected base metal. Its width is a direct read on heat input. A narrower HAZ generally points to lower heat input, while a wider one points to higher heat input. This is a change in structure, not a discontinuity, which is why it’s often best measured by macroetching rather than radiography or UT. As Nusatek notes, macro-etching is the method of record for HAZ depth and weld penetration for this exact reason.

Weld Metal, Bead Sequence and Penetration

Moving into the weld metal, you’ll see columnar grains growing from the fusion line towards the center of the pool. With multi-pass welds, these layers become the most important thing to count. Each pass should melt into the one below it, creating one fused mass. A coupon that clearly shows its bead sequence allows a second look for interpass lack of fusion, something that is especially important for precise joints such as those found in aerospace TIG qualification.

From there, focus on penetration: how far the weld metal traveled into the groove or under the root. Look for these common root profiles:

• Reinforcement: Metal standing proud of the parent surface. Normal for a sound weld.
• Convexity: A crowned root or face, often from excess heat in a pass.
• Concavity: A hollowed root profile, often tied to travel speed or arc placement. More of a fatigue concern than a strength concern.

Defects You Can See on the Etched Face

Once the geometry is known, indications become much easier to identify. Shape is the key to separating them from one another.

Indication	How it appears after etching
Lack of fusion	A dark, irregular line at the fusion boundary or between passes, often at a toe or root.
Slag or flux inclusions	Dark, sharp-edged pockets trapped within the weld metal.
Porosity	Round gas voids, either scattered or clustered throughout a bead.
Cracks	Sharp, linear indications, sometimes branching. They often run through the HAZ into the base metal.
Cold shuts	A distinct line where two weld pools met without fusing, with no grain continuity.
Undercut	A groove melted into the parent metal at the weld toe, below the toe line.

This level of visibility is especially useful on trickier materials. For example, with aluminum flux core welds, the macrograph is often the fastest way to confirm each layer is fusing cleanly to the one below it.

Measuring Fillets: Leg and Effective Throat

For fillet welds, the macrograph allows direct measurements. The leg is measured from the root corner to the face of the weld along the parent metal. For a 90 degree fillet, the theoretical effective throat is taken as 0.707 times the leg size, as it’s the shortest distance from the root corner to the face and the dimension that carries load.

Codes can add additional requirements. For unequal-leg fillets, AWS D1.1 requires the smaller leg to be not less than 1.25 times the effective throat for that throat to be considered effective. This is exactly why AISC’s 2016 research on weld clearances relied on sectioned specimens to measure actual leg sizes and effective throats, rather than relying on drawings alone. A 6 mm leg can have a theoretical throat of 4.24 mm, but if the smaller leg is undersized against its required minimum, the throat may not be effective despite looking generous.

Macro Test Acceptance Criteria: AWS D1.1, ASME Section IX and ISO 9606-1

Every macro test ends in a pass or a fail, and where that line falls is not a matter of shop opinion. It is written into the welding code, and judging a weld against the wrong edition can turn an entire qualification into an argument at the worst possible time. Here are the three criteria sets you are most likely to meet.

AWS D1.1: Table 6.2 macroetch criteria

In AWS D1.1/D1.1M, the macroetch acceptance criteria for qualification test specimens sit in Table 6.2. The classic requirements are simple, and they explain most rejections:

• Fusion to the root of the joint is required, but fusion beyond the root is not. A fillet weld with complete fusion along the root that stops there passes.
• The minimum leg size shall meet the specified fillet weld size. No lower leg is acceptable, even when the weld looks full and smooth in every other respect.
• Cracks are not permitted. Any crack visible on the etched face fails the coupon.

These criteria have backed structural fillet weld qualification for years, and the AWS D1.1/D1.1M:2015 preview is handy for the older wording. They are not the final word for anything you are doing today.

Why macro results differ from visual results

Table 6.1 of AWS D1.1 sets the visual inspection criteria for the same coupons, and the two tables are easy to conflate. Visual inspection is forgiving by design: a fillet weld leg may be up to 1/8 in. (3 mm) under the specified size, provided this occurs over no more than 10% of the weld length, and undercut is tolerated up to 1/32 in. (1 mm).

Those allowances cannot be confirmed by eye. A weld can measure short at the surface because of bead contour while the actual leg is fine, or look generous because of reinforcement and still be genuinely undersized. Research published by AISC on sectioned specimens found measured legs below the specified 1/4 in. still acceptable under the Table 6.1 visual criteria, which is exactly why visual and macro results do not always tell the same story.

One procedural point catches people out: AWS D1.1 requires the coupon to be visually examined first, and if the coupon fails visual inspection, further mechanical testing and nondestructive examination shall not be performed. A coupon that already fails on appearance is not a candidate for macroetch.

ASME Section IX: QW-183 and QW-184

ASME Section IX reaches the fillet weld macro test through two routes. QW-183 covers the procedure qualification test, QW-184 covers welder performance qualification on fillet welds. The coupon is cut transversely to give a centre section of about 4 in. (100 mm) long for macro examination.

Acceptance comes down to three things: no cracks, complete fusion to the root of the joint, and a fillet weld leg size that meets the drawing requirement. Section IX is not generous here. If the drawing calls for a specific leg, the macro section has to show that leg, and fusion has to reach the root without a dark oxide seam breaking the boundary.

ISO 9606-1 and the record trail

Internationally, ISO 9606-1 governs welder qualification, using macro examination of fillet welds alongside bend tests, with the examination method described in ISO 15614. The criteria follow the same logic: fusion to the root, correct leg and throat geometry, no cracking. Where a job falls under a sector-specific regime, the governing standard changes with it, which is why the aerospace welding standards guide is worth a read if that is your market.

Record keeping matters as much as the cut. The AWS D1.1 welder, welding operator or tack welder qualification test record form lists macroetch as a distinct reported result, alongside appearance, fillet size, fracture test and root penetration. A visual pass does not paper over a failed macroetch line on that form.

The retest philosophy

A failed macroetch is a failed test. Where a code allows a retest, it means repeating the complete qualification, not re-sectioning a second piece of the same coupon and calling it a pass. If the failure points at the procedure rather than the welder, a WPS review is the honest next step, not another attempt with the same settings.

Standard	What the macro section must show	Key dimensional requirement	Watch out for
AWS D1.1 Table 6.2	Fusion to the root (not necessarily beyond), no cracks	Minimum leg shall meet the specified fillet weld size	Clause 6 revised in the 2025 edition; check the current edition
ASME Section IX QW-183 / QW-184	Complete fusion to the root, no cracks	Leg size meeting the drawing requirement; centre section about 4 in. long	Visual examination of the coupon comes first
ISO 9606-1	Fusion to the root, correct leg and throat geometry, no cracking	Macro method per ISO 15614, used with bend tests	Sector rules may replace the base standard

When You Actually Need a Macro Test: Welder Qualification, WPS Qualification and Production QA

A macro test is cheap, fast and uniquely revealing, but it destroys the part it is performed on. The question is never “can we macroetch this?” It is “does this weld have to be opened up to be believed?” Answer that correctly and macroetch becomes one of the most cost-effective tools in the shop; answer it wrong and you section a good weld for nothing.

Clause 4 and Clause 6 Use the Same Etch for Different Jobs

AWS D1.1 splits qualification in two. Clause 4 qualifies the welding procedure specification: can this WPS, with this filler metal, preheat and joint detail, produce sound weld metal? Clause 6 qualifies the welder or welding operator: can this person make that weld, in the positions and with the process called for?

In Clause 4 the macroetch is one piece of evidence alongside bend tests, confirming fusion to the root, real penetration and an acceptable profile. If it fails, the problem belongs to the WPS, so you change the procedure, not the welder.

In Clause 6 the question is human skill. The Fillet Weld Break and Macroetch Test Plate lets the examiner break out the welder’s fillet and etch it, so root fusion and leg size are judged from the inside, not the outside contour. The Plug Weld Macroetch Test Plate does the same for welders qualifying through plug welds. Results land on the AWS N-4 qualification test record form, where macroetch appears as its own result alongside appearance, fillet size, fracture test and root penetration.

Tubular Work: Where Macroetch Is Often the Only Way In

For pipe and box structures, D1.1 provides a dedicated macroetch test for T-, Y- and K-connections, listed as clause 9.22.1 in the 2015 edition with acceptance criteria in 9.22.1.1, plus a Corner Macroetch Test Joint for T-, Y- and K-connections welded without backing on box tubing for CJP groove welds.

The reason is geometry. At a corner joint on box tubing there is no straight line of sight for a radiography beam, so RT is difficult and often not feasible, while UT needs access, a calibrated setup and a skilled operator. A macroetch on a cut-off corner coupon shows root fusion and penetration directly, making macro testing the practical qualification route for tubular corner work rather than a fallback.

ASME Section IX and ISO 9606-1

ASME Section IX qualifies procedures under QW-183 and welders under QW-184, and in both the fillet weld coupon is macroetched to confirm complete fusion to the root, the absence of cracks and a leg size that meets the drawing. ISO 9606-1 works the same way, with macro examination of the fillet weld test piece supplementing the fracture and bend tests to confirm root fusion and throat dimensions, showing what surface inspection cannot (macro etch examination in practice, and what macro examination is used for).

Where Macroetch Earns Its Keep in Production

• Sacrificial coupons and first-of-a-kind welds. Trial welds during new construction, where the part is expendable and the question is whether the procedure behaves as written.
• Repair welds. A cut from a repair, sectioned to confirm the welder fused into existing material rather than just laying bead on it.
• Failure analysis. Whether cracking ran through weld metal, the HAZ or base metal, and where the lack-of-fusion boundary actually sits.
• Special geometry. Tube-to-tubesheet and overlay welds in power plant and pressure equipment are sectioned to verify minimum weld thickness and fusion to base metal, which radiography cannot measure.

The Cost Logic

A macroetch costs a few dollars in consumables and an hour of bench time. Radiography and UT cost orders of magnitude more per unit and still will not show the HAZ or the pass sequence. Macroetch when you need the internal metallurgical condition of a weld; use RT or UT when you need to inspect the production member without destroying it.

Three Scenarios

1. A shop qualifying a new FCAW fillet procedure. The coupon is cut and etched to prove root fusion and leg size, then each welder runs their own Clause 6 test. If the procedure passes but the welder fails, the fix is training, not paperwork. Some shops qualify the same fillet more easily with SMAW (the case for stick welding) or with an all-position rod and electrode selection suited to the position tested.
2. A repair weld on a bridge girder. The production member stays intact and gets UT or MT. A sacrificial offcut from the same repair procedure is macroetched to prove the repair weld fused to the parent metal, the question the owner cares about.
3. A tube-to-tubesheet overlay in a power plant. There is no practical way to radiograph an overlay on a tubesheet and read its thickness, so a cut section is macroetched to confirm fusion to base metal and deposited thickness, with consumable selection handled through an alloy steel welding electrode guide and the applicable overlay procedure.

Macro Test vs. Radiography, Ultrasonic, Penetrant and Other Inspection Methods

Choosing an inspection method is not about finding a best one, it is about matching the tool to the question. A macroetch answers a metallurgical question: did this weld fuse to the root, how deep did it penetrate, how wide is the heat-affected zone? RT and UT answer a different one: is there a discontinuity inside this weld that will get it rejected? Conflating the two is the most common mistake shops make.

Method	What it detects	What it cannot show	Destructive?	Relative cost	Typical use
Visual (VT)	Surface contour, size, length, visible cracks, slag, spatter	Anything internal: fusion to root, porosity, HAZ	No	Lowest	Mandatory first pass (AWS D1.1 Table 6.1)
Magnetic particle (MT)	Surface and near-surface cracks and seams in ferromagnetic metal	Aluminium, austenitic stainless, non-magnetic alloys; no depth	No	Low	Carbon and low-alloy steel, incl. after repair
Liquid penetrant (PT)	Fine surface-breaking cracks and porosity on clean non-porous material	Anything subsurface; no fusion, penetration or HAZ data	No	Low	Stainless, aluminium, non-magnetic alloys; welds, castings
Radiography (RT)	Porosity, slag, inclusions, cracks oriented to the beam	HAZ; fillet fusion to root not reliably proven; no leg size; subjective	No	High	Pressure butt welds (AWS D1.1 Part E, ISO 17637)
Ultrasonic (UT)	Planar and volumetric flaws; sensitive to lack of fusion and cracks, gives depth	Dead zone under probe; unreliable in laminated plate; orientation sensitive	No	High	Thick-plate butt welds (AWS D1.1 Part F, ISO 17640)
Macroetch	Fusion line, HAZ, penetration depth, bead sequence, lack of fusion, slag, cracks, porosity, undercut	The production member’s own condition; anything off the sectioned plane	Yes	Low	Qualification coupons, repair verification, failure analysis

Macroetch is the only method in shop use that directly shows the heat-affected zone. RT and UT can flag a flaw in that region, but neither renders the widened, tempered or coarsened grain band, because the HAZ is a change in microstructure, not a void. MT and PT are surface methods only, and MT will not work on aluminium or austenitic stainless. If your question is what happened to the base metal beside the weld, the ASTM E381 low-magnification examination convention is the reference point, and no NDT substitute exists.

A second advantage matters more in a small shop than a heavy plant. Macroetch needs no film or scan interpretation, no calibrated NDT equipment and no certified operator. Bench technique is teachable in an afternoon, while RT or UT technician certification is a formal process with a formal report. Because AWS D1.1 treats visual inspection as the baseline and NDT as the added layer, macroetch is a cheap way to get metallurgical answers when a coupon cannot be justified at a radiography house.

The Combination Strategy Codes Actually Expect

In practice, inspection is a sequence, not a menu. Visual inspection comes first on every weld, catching gross errors like bad profile, spatter and visible cracking. NDT is then added where design or code demands it: RT for pressure butt welds, UT for thick plate, MT or PT for surface cracks. On qualification coupons the macroetch takes over, since what needs proving is fusion to the root, leg size and the absence of cracks, which surface inspection cannot show. After a repair the sequence restarts: visual, then the required NDT, then macroetch on the cut sample to confirm the repair fused. The macroetch sits at both ends of the quality chain, which is why it keeps appearing in code paperwork.

Where the Trade-Offs Actually Land

Macroetch is low cost, fast and metallurgically rich, but destructive: every macroetch consumes the coupon it examines. That is why it is paired with documented criteria and a written report, not used as a stand-alone opinion, and why shops macroetching a production member run a sacrificial coupon alongside the real weld. RT and UT preserve the part but cost more and take longer, and the record still depends on an interpreter’s judgement. A radiograph shows what the film shows, not how deep the penetration went or where the fusion line stopped.

Macroetching is also broader than weld testing. The same bench skills behind the macro-etch examination of a fillet coupon are used for material condition: electrolytic etching with 10% oxalic acid under ASTM A262 Practice A is the standard macro-style electrolytic etch for detecting sensitization in austenitic stainless steel, and it reveals grain structure on un-welded parts. This is how a mill cert becomes a metallurgical opinion.

Pick the method that answers your question, then pay for it honestly. Is the weld interior metallurgically sound? Macroetch. Does the member you are shipping hold a rejectable flaw? RT or UT. Most shops need both, in the right order.

Common Macro Test Mistakes, and How to Avoid Them

Most rejected coupons do not fail because the weld was bad. They fail because of what happened on the bench after welding. A hot cut, a coarse grind, an over-long etch or a misread measurement can turn a sound fillet weld into a “failure” that gets charged to the welder and the procedure. The cleanest macro results come from shops that run the metallurgical bench with the same discipline as the welding bay.

Preparation errors

1. Cutting the specimen with a torch or plasma cutter. Symptom: a mottled, heat-tinted band along the cut face, a fusion line that seems to fade at the edge, or an HAZ that appears to stop short. Cause: thermal input from the cut alters the microstructure in the cut zone, so the thing you need to read has already been changed. Fix: use a band saw or abrasive cut-off wheel with coolant, let the saw cool, and keep the cut clear of the region you intend to examine.
2. Stopping the polish too early. Symptom: a hazy, half-visible fusion boundary and unreliable crack detection. Cause: saw marks and coarse scratches hold etch residue and mimic fine linear indications. Fix: step grit progressively and finish at 600 grit as a minimum. Michigan Tech’s macro-etching SOP calls for a final polish at 1200 grit, which gives noticeably cleaner contrast on carbon and low-alloy steels.
3. Grinding the HAZ or a shallow fusion line off the coupon. Symptom: a perfectly etched coupon with nothing on it. Cause: aggressive grinding to “get a flat face” removed the features you needed to read. Fix: section slightly deeper into the joint, keep the ground face flat without removing material past the HAZ, and confirm before etching that the region of interest still exists.

Etching errors

4. Wrong etchant for the base metal. Symptom: no contrast on stainless or aluminium, blotchy attack on heavily scaled carbon steel. Cause: nital will not develop stainless grain structure, and mill scale blocks the etch entirely. Fix: match the etchant to the material and clean the specimen before it goes into the bath. Degreasing and surface preparation are covered well in our guide to how to prep aluminum before welding, and the same discipline applies to any coupon you etch.
5. Over-etching. Symptom: a washed-out macrograph where the fusion boundary has faded and a dark gap appears that reads as lack of fusion. Cause: too long in the bath. Etching time runs from about 10 seconds to several minutes depending on etchant strength and material, so no single safe number exists. Fix: etch in short increments, rinse and inspect between dips, and remember that over-etching and under-etching both ruin the result, as explained in Struers’ guidance on etching practice.
6. Etching a specimen that is still hot. Symptom: uneven dark patches and pitting on one side of the face. Cause: residual grinding heat accelerates attack locally. Fix: wash the coolant and grinding heat off, let the coupon reach room temperature, then etch.
7. Failing to rinse and neutralize. Symptom: pits and stains that appear only after the specimen has dried, sometimes hours later. Cause: residual acid keeps attacking the surface. Fix: rinse promptly in cold water and neutralize before drying.
8. Touching the etched face. Symptom: grey smears across the image where fingers or gloves dragged the pattern. Cause: oils and grit on hands. Fix: handle specimens by the edges with tongs and never touch the etched surface. A single fingerprint can spoil a coupon you paid for.

Measurement and interpretation errors

9. Measuring the wrong dimension. Symptom: a sound fillet weld reported undersize. Cause: leg size and effective throat are different dimensions, and in an unequal-leg fillet the smaller leg is not the one the code calls for. Fix: confirm which dimension the governing code requires, measure that one, and record both. This confusion is one of the most common sources of false rejections, and it is why AWS D1.1/D1.1M:2025 should be read rather than paraphrased from memory.
10. Calling a scratch, a grinder mark or undercut a crack. Symptom: a “crack” that turns out to be a directional grinding trace, or an undercut groove reported as an indication. Cause: all three are linear. Fix: genuine cracks are sharp, linear, often branching and open at the surface; grinding scratches are rounded and follow the tool direction; undercut is a groove at the weld toe and is not automatically a defect, since AWS D1.1 visual criteria permit up to 1/32 in. (1 mm) undercut.

Record and process errors

11. Skipping the documentation. Symptom: a result that cannot be defended months later. Fix: photograph straight-on with a metric scale bar, label with weld identification, procedure, welder, date and etchant, and record every measurement and indication. A macrograph without a scale is an opinion, not a record.
12. Assuming a failed macroetch proves the weld is bad. Symptom: a procedure condemned on a coupon that was actually damaged during preparation. Cause: preparation errors masquerade as weld defects. Fix: review the bench record first, then repeat on a fresh specimen. If the failure is real, treat it as a process problem rather than a welder problem.

None of these mistakes is exotic. Every one has been made in a shop with the right equipment, the right code book and a qualified welder at the bench. The difference between shops that pass macro tests cleanly and shops that argue about them is a written procedure, a checklist form, and the discipline to follow both.

Bench Setup, Chemical Safety and Documenting the Result

The macro test itself costs almost nothing. A saw, a grinder, a bottle of etchant and an afternoon of bench time produce more metallurgical information about a weld than any other test a typical shop can afford. What separates a shop that runs macroetch as a controlled process from one that runs it as a favour for the occasional inspector is the setup around it: a clean bench, disciplined chemical handling and a paper trail that survives a dispute.

Setting up the bench

You do not need a metallurgical laboratory. You need a defined, repeatable corner of the shop with a few things in fixed places.

• Cutting area: a band saw or abrasive cut-off wheel with a coolant tray, so the section is cut cool and square.
• Grinding and polishing station: a bench grinder with coolant, plus abrasive steps from roughly 80 grit through 600 grit and finer for the final polish.
• Fume hood or ventilated enclosure for any hot acid work, positioned away from the cutting area so grinding dust and acid vapour never mix.
• Rinse sink with a neutralizing agent stored within reach, and a separate thermometer for the hot hydrochloric bath.
• Tongs and glass or plastic bath containers, marked so the etched side is always known.
• Camera and scale: any camera that shoots square to the surface, plus a printed metric scale bar.

Stocks of PPE, gloves, tongs and grinding consumables can be ordered alongside routine welding supplies and safety gear, so the lab kit stays stocked with the same reorder cycle as the rest of the shop.

Chemical safety and PPE

Chemical splash goggles are the minimum. Add a face shield whenever you pour acid, acid-resistant gloves, a lab coat or apron, and closed shoes. The Michigan Tech macro-etching SOP is explicit about this: lab coats, nitrile gloves and tongs for handling any specimen that has been in contact with acid, with waste rinsed down the sink under the fume hood followed by several minutes of cold water.

The mixing sequence is the part people get wrong under time pressure. Always pour water into the vessel first, then add acid slowly with constant stirring. Never add water to concentrated acid. The reason is heat: adding acid to water releases heat gradually and safely, while the reverse creates a sudden boiling splash. The same reverse-of-mixing logic governs disposal. Spent acid is neutralized slowly with a base such as sodium hydroxide or sodium bicarbonate, added little by little, until the bubbling stops. Only then does the solution go down the sink with copious cold water running.

Finally, dry etched specimens belong outside the fume hood area, protected with a clear coating if you need to keep them for long-term retention. Acid trapped under a stacked coupon will keep working on it.

Documenting the result

Photograph the macrograph straight on with a metric scale in frame. A scaled image is evidence that can be re-measured months later during an audit or a dispute over weld size, and it is far harder to argue with than a note saying “leg OK”.

Label each image with the weld identification, the procedure, the welder, the date and the etchant used. Then record the measured values in writing: leg size, effective throat, HAZ width, penetration depth, and the location and nature of every indication you see. Those same results get transcribed onto the AWS D1.1 welder, welding operator or tack welder qualification test record form, which carries dedicated lines for macroetch results. That is where the record becomes defensible paperwork rather than a note on a bench scrap.

Calibration and repeatability

The reason two labs can disagree on the same weld is rarely chemistry. It is lighting, magnification and scale. Standardise all three. Use the same lighting setup, the same magnification range, a calibrated scale and a written laboratory procedure, and your results become comparable with anyone else’s who works the same way.

Conclusion: Making the Macro Test Work for You

Two fillet welds can look identical to the naked eye, but only one cut, polished, and etched reveals the truth underneath. That is where the macro test in welding earns its place: cheap, fast, uniquely informative. Because it is destructive, though, the result is only as good as the preparation and the person carrying it out.

The Biggest Takeaways

Before the next qualification, keep these points locked in:

1. It reveals what NDT cannot. Macro testing is the only routine destructive method that documents fusion to the root, the heat-affected zone, penetration depth, and internal weld geometry at once. Neither radiography nor ultrasonics displays the fusion line with this clarity.
2. Know your acceptance criteria and your edition. They live in AWS D1.1 Table 6.2, ASME Section IX QW-183 and QW-184, and ISO 9606-1. Because AWS D1.1/D1.1M:2025 revised macroetch acceptance criteria, checking the edition in front of you is essential for anyone specifying or accepting a result.
3. Match the etchant to the base metal. Nital for carbon and low-alloy steel, hot hydrochloric acid for stronger contrast on carbon steel, aqua regia for stainless and nickel alloys. Etching chemistry decides what you can even see, and the Struers etching reference shows what attacks which microstructure.
4. Cut mechanically and polish fine. A torch or plasma cut alters the very zone you are reading. Step the grit progressively to at least 600, and 1200 for the cleanest response, exactly as the Michigan Tech macro-etching procedure sets out. These are non-negotiable steps, not refinements.
5. Measure the dimension the code asks for. For a fillet weld that is the leg, not the throat, and the throat counts as effective only when the smaller leg is at least about 1.25 times it. Measuring the wrong dimension makes a sound weld look undersized.
6. Document everything with a scale. A straight-on photo with a metric scale bar, weld ID, procedure, welder, date, and etchant, plus recorded leg size, throat, HAZ width, and penetration depth. Carry it onto the AWS N-4 qualification test record form so the paperwork holds up months later.
7. Treat a failure as a review trigger. A failed macroetch should send you back to the WPS, not straight to a re-run. And disputed results most often trace back to preparation quality rather than weld quality.

Where to Go Next

Three practical moves deliver most of the value:

1. Run one fillet weld macro coupon on your own procedure. Nothing exposes a WPS problem faster than seeing your own fusion line.
2. Write a one-page lab SOP with a checklist form. Cutting method, grit sequence, etchant, timing, neutralising, scale. It turns a good result into a repeatable one.
3. Pair macroetch on qualification coupons with RT or UT on production members. That combination is standard, cost-effective inspection practice, and it keeps destructive testing where it costs you nothing.

If you are still assembling qualification records, our all-position welding rod guide explains what each position demands of a welder. The aerospace welding standards overview shows how qualification and NDT stack up on critical structures. For the processes producing the fillet welds you are about to section, why SMAW still wins is a practical place to start.

Cut the coupon. Etch it. Read it properly. Done well, this method tells you more about your weld than anything else you can put on the shop floor.

Frequently Asked Questions

What is a macro test in welding?

A macro test, also called a macroetch or macrographic examination, is a destructive test in which a welded coupon or joint is cut, ground, polished, chemically etched and then examined at low magnification. It reveals the internal architecture of the weld, including the fusion line, heat-affected zone, penetration depth, bead sequence and defects such as lack of fusion, cracks, slag and porosity.

Which etchant is used for a macro test on carbon steel?

For carbon and low-alloy steel, nital (nitric acid in ethanol) at roughly 2 to 10% is the standard choice, and 10% aqueous ammonium persulfate is a less hazardous alternative. Hot hydrochloric acid at around 70 degrees Celsius for about 15 minutes gives strong contrast in a lab setting. The etchant must always be added to water, never the reverse.

What magnification is used to examine a macroetched specimen?

Macro specimens are examined with the naked eye or under low magnification, typically 1x to 10x, which is why the technique is called macro rather than micro examination. ASTM E381 describes macroetching as examination at low magnifications, usually under 10x, while some metallographic references permit up to 25x with a hand lens.

What are the AWS D1.1 acceptance criteria for a macroetched fillet weld?

Under AWS D1.1 Table 6.2, a fillet weld on a qualification coupon must show fusion to the root of the joint (not necessarily beyond it), the minimum leg size must meet the specified fillet weld size, and cracks are not permitted. AWS D1.1/D1.1M:2025 updated the macroetch acceptance criteria, so always confirm against the current edition of the code and the project specifications.

Can a macro test replace radiography or ultrasonic testing?

No. Macroetch is destructive, so it can only be applied to coupons, test pieces or joints you are prepared to sacrifice, while RT and UT inspect the actual production member non-destructively. The methods are complementary: macroetch proves fusion to the root and shows the HAZ, whereas RT and UT detect volumetric and planar internal discontinuities in the installed weld.

How long does a macro test take from cutting the coupon to the final report?

Allow roughly 30 to 60 minutes for a typical fillet weld coupon including cutting, progressive grinding, polishing to 600 or finer grit, etching, rinsing, measuring and photographing. Stainless, stainless dissimilar or hot hydrochloric acid work can take longer because of extra polishing and etch dwell time, and a full WPS qualification with multiple coupons takes considerably longer than a single macro.

Why does my macroetch look too dark or completely washed out?

A washed-out macrograph is usually over-etched, meaning the specimen spent too long in the bath or the etchant was too strong for the material. An over-dark or blotchy result usually means the etchant was applied to a hot surface or that the polish was too coarse. Etch in short increments, watch the surface, and start with a weaker solution.

Is macro testing required for welder qualification?

In many cases, yes. ASME Section IX QW-184 requires macro examination for fillet weld performance qualification, and ISO 9606-1 requires macro examination of fillet weld test pieces in all positions. AWS D1.1 uses macroetch as one of the options for fillet weld break-and-macroetch test plates and for tubular corner macroetch joints, so the exact requirement depends on the joint type and the governing code.

What is the difference between a macro etch and a micro etch?

A macro etch reveals features at low magnification, typically weld geometry, the fusion line, the HAZ, penetration depth and gross defects such as cracks, slag and porosity. A micro etch is applied to a fine-polished, often mounted specimen and is examined at 100x to 1000x to reveal grain structure, phases and microscopic metallurgical details such as martensite, sensitization or ferrite content.