What Is Macro Examination?

Quick Answer

Macro examination (macrographic examination) is a destructive test that reveals the internal structure of a weld by cutting, polishing, and chemically etching a cross-section. The etched surface is examined at low magnification (up to 10x) to assess weld geometry, bead sequence, fusion line, heat-affected zone (HAZ) width, penetration profile, and the presence of defects such as porosity, lack of fusion, cracks, and undercut. Macro examination is mandatory for fillet weld procedure qualification under ASME Section IX QW-183 and for socket weld, branch connection, and overlay weld procedures.

Macro Examination Procedure

Step	Action	Details
1	Sectioning	Cut the weld transversely using a band saw or abrasive cutter; avoid overheating
2	Grinding	Grind the cut face progressively (80-320 grit) to remove saw marks
3	Polishing	Fine polish to 600 grit or finer for clear etch response
4	Etching	Apply chemical etchant to reveal weld structure
5	Examination	View at 1-10x magnification under adequate lighting (>500 lux)
6	Documentation	Photograph the etched cross-section with scale reference

Common Etchants

Etchant	Composition	Application
Nital (2-10%)	2-10% nitric acid in ethanol	Carbon steel, low-alloy steel
Ammonium persulfate	10% aqueous solution	Carbon steel (alternative to nital, less hazardous)
Aqua regia	HCl + HNO3 (3:1)	Stainless steel, duplex, nickel alloys
Marble\u0027s reagent	CuSO4 + HCl + water	Stainless steel, duplex (reveals ferrite/austenite phases)
Oxalic acid	10% aqueous, electrolytic	Austenitic stainless (sensitization test per ASTM A262 Practice A)

Etching time ranges from 10 seconds to several minutes depending on the etchant strength and material. Over-etching obscures detail; under-etching fails to reveal the fusion boundary.

What the Macro Reveals

Feature	What to Look For
Weld geometry	Root penetration depth, reinforcement height, bead width, throat thickness (fillet welds)
Fusion line	Complete fusion between weld passes and between weld and base metal
HAZ width	Extent of heat-affected zone (indicates heat input)
Bead sequence	Pass stacking, interpass overlap
Porosity	Gas pores visible as dark spots
Lack of fusion	Dark lines at fusion boundary or between passes
Cracks	Linear indications in weld, HAZ, or base metal
Undercut	Grooves at weld toe
Root concavity/convexity	Root profile shape and dimensions

Acceptance Criteria

Code	Application	Key Requirements
ASME IX QW-183	Fillet weld procedure qualification	No cracks; complete fusion at root; fillet weld leg size meets drawing requirements
ASME IX QW-184	Fillet weld performance qualification	Same as QW-183; macro from each qualified position
AWS D1.1	Structural welding	Minimum fusion, no cracks, convexity within limits
EN ISO 15614-1	Welding procedure qualification	Acceptance per EN ISO 5817 level B or C as specified
ASME B31.3	Process piping (socket welds)	Minimum 1.5 mm gap at socket bottom; full fillet leg

When Macro Examination Is Required

Weld Type	Code Requirement
Fillet welds	Mandatory for PQR qualification per ASME IX QW-183
Socket welds	Recommended/required per project spec to verify root gap and throat
Branch connections	Per project spec; verifies full penetration at set-on/set-in
Overlay/cladding	Verifies minimum overlay thickness and fusion to base metal
Groove welds	Optional (typically bend + tensile used instead)

Common Mistake

Cutting the macro specimen with a torch or plasma cutter. The thermal input alters the microstructure in the cut zone, producing misleading etch patterns and potentially masking heat-affected zone features. Always use mechanical cutting (band saw, abrasive wheel) with coolant to preserve the true weld microstructure.

Macro photographs are attached to the procedure qualification record (PQR) and archived with hardness test results, mill test certificates, and other qualification data per the inspection and test plan.

Read the full guide to non-destructive testing