5.2 Processing Discontinuities

ASNT NDT Level III Basic Examination Exam

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1 Introduction & Exam Overview

1.1 Current Exam Facts 1.2 Level III Role and Certification Path 1.3 Eligibility, Fees, Scheduling, and Retakes 1.4 Study Strategy and Exam-Day Approach

2 Chapter 2: Materials Fundamentals for NDT

2.1 Ferrous Metals and Iron-Carbon Phases 2.2 Non-Ferrous Metals and Alloys 2.3 Mechanical Properties and Crystal Structure

3 Chapter 3: Manufacturing Processes

3.1 Casting Processes and Cast Discontinuities 3.2 Forging, Rolling, and Forming 3.3 Extrusion, Drawing, and Machining 3.4 Heat Treatment Effects

4 Chapter 4: Welding and Joining Processes

4.1 Fusion Welding Processes 4.2 Weld Metal and HAZ Discontinuities 4.3 Brazing, Soldering, and Mechanical Joining

5 Chapter 5: Discontinuity Classification

5.1 Inherent Discontinuities 5.2 Processing Discontinuities 5.3 Service Discontinuities

6 Chapter 6: Specific Discontinuity Types

6.1 Cracks and Fracture Modes 6.2 Porosity, Inclusions, and Lack of Fusion 6.3 Laminations, Seams, Laps, and Undercut 6.4 Relevant vs Non-Relevant Indications

7 Chapter 7: NDT Method Selection and Inspection Planning

7.1 Method Selection Principles 7.2 Surface vs Volumetric Methods 7.3 Inspection Planning and Flaw Expectations

8 Chapter 8: Ultrasonic and Radiographic Testing

8.1 Ultrasonic Testing Principles and Applications 8.2 UT Limitations, Calibration, and Evaluation 8.3 Radiographic Testing Principles and Applications 8.4 RT Limitations, Image Quality, and Safety Basics

9 Chapter 9: Magnetic Particle, Liquid Penetrant, and Visual Testing

9.1 Magnetic Particle Testing 9.2 Liquid Penetrant Testing 9.3 Visual Testing

10 Chapter 10: Electromagnetic, Leak, Acoustic Emission, and Infrared Testing

10.1 Electromagnetic / Eddy Current Testing 10.2 Leak Testing 10.3 Acoustic Emission Testing 10.4 Thermal / Infrared Testing

11 Chapter 11: Specialty Methods and Method Comparison

11.1 Neutron Radiography 11.2 Magnetic Flux Leakage 11.3 Method Comparison and Supplemental Examinations

12 Chapter 12: SNT-TC-1A Recommended Practice

12.1 SNT-TC-1A Overview and Written Practice 12.2 SNT-TC-1A Training and Experience 12.3 SNT-TC-1A Examinations and Recertification

13 Chapter 13: CP-189 Standard Practice

13.1 CP-189 Overview and Scope 13.2 CP-189 Mandatory Requirements 13.3 SNT-TC-1A vs CP-189 Comparison

14 Chapter 14: CP-105 and NDT Training Programs

14.1 CP-105 Purpose and Topical Outlines 14.2 Developing and Approving NDT Training 14.3 OJT, Mentoring, and Instructor Oversight

15 Chapter 15: Building and Managing Certification Programs

15.1 Building Qualification and Certification Programs 15.2 Administering Examinations and Evaluating Competency 15.3 Program Audits and Managing Certifications

16 Chapter 16: Codes, Standards, Procedures, and Quality

16.1 Interpreting Codes, Standards, and Specifications 16.2 Developing and Approving NDT Procedures 16.3 Acceptance Criteria and Quality Control 16.4 External Audits and Inspection Documentation

5.2 Processing Discontinuities

Key Takeaways Explain This Topic AI

Processing discontinuities are introduced during manufacturing of the component: forming, machining, grinding, welding, heat treatment, plating, and related operations.

Map process → expected flaw: quench cracks after rapid cool, grinding burns/cracks after abusive grind, weld LOF/porosity/cracks in fusion joining, forming cracks at high strain locations.

Many processing flaws are surface-connected at introduction; others (subsurface weld defects, internal forging bursts) need volumetric methods.

Inspection sequence matters: inspect after the process that creates the risk (e.g., after quench and finish grind) when procedures require it.

Last updated: July 2026

5.2 Processing Discontinuities

Quick Answer: Processing discontinuities are introduced while manufacturing the component —forming, machining, grinding, welding, heat treating, plating, and similar operations. They are not primary solidification features of the stock (inherent) and not in-service damage (service). Classic examples include machining cracks , grinding burns and cracks , weld defects , forming cracks , quench cracks , and plating-related cracking . Level III judgment is process → flaw → method → when to inspect .

If inherent flaws answer “what did the mill put in the metal?”, processing flaws answer “what did the shop do to the part?” Domain 4 of the Basic exam repeatedly tests that distinction with manufacturing scenarios.

Definition and Boundaries

A discontinuity is processing-related when the essential free surface, crack, fold, or volumetric defect is created by a fabrication or finishing process applied to stock or a semi-finished product.

• Not processing Why
• Ingot pipe, primary inclusions Formed in material production → inherent
• Fatigue crack after 10 years of cycling Formed in use → service
• Weld incomplete fusion Formed during joining → processing
• Quench crack after hardening Formed during heat treatment → processing

Some defects look like service cracks under a microscope. Classification still follows when the crack formed relative to the life cycle, not only fracture-surface appearance.

Process → Flaw Map (High-Yield Table)

Process Typical discontinuities Morphology / location cues Primary NDT tendencies

Forging Laps, folds, bursts, flashes, seams from scale Surface folds; internal bursts in heavily worked zones VT, MT/PT for surface; UT for bursts

Rolling / forming Seams, laps, forming cracks, orange-peel tears Aligned with working direction; tight bends crack on outer fiber MT/PT/VT; UT if midwall

Machining Chatter marks (nonrelevant risk), tool gouges, machining cracks (esp. hard materials) Follow tool path; sharp roots act as stress raisers VT, PT, MT; ET on conductive surfaces

Grinding Grinding cracks, grinding burn (temper/re-harden) Network or transverse cracks on ground face; burn discoloration MT/PT after grind; hardness/etch for burn

Welding (fusion) Porosity, slag, LOF, LOP, undercut, solidification cracks, HAZ cracks Along weld/HAZ geometry VT + method suite (RT/UT/MT/PT per code)

Heat treatment (quench) Quench cracks Often from sharp corners, holes, section changes; may be deep MT/PT; UT for deep cracks; inspect after quench/temper per procedure

Plating / coating Hydrogen-assisted cracks (high-strength steel), coating blisters, interface delamination Underplate or at high-stress sites after plate Bake-out process control; MT/PT after plate when required

Drawing / extrusion Chevrons, surface scoring, central bursts (severe draws) Longitudinal or internal centerline VT, UT, ET depending on product

Memorize the left two columns for scenario questions; use the right columns for method selection.

Machining Cracks and Surface Integrity

Machining removes metal. When feeds, speeds, tool wear, or material hardness are wrong, the surface can develop:

Cracks from excessive tensile residual stress or thermal shock at the tool tip

Deep tool marks that act as notches for later fatigue (processing origin of a stress raiser even if the crack opens in service)

Smeared metal that hides underlying flaws from PT

High-hardness alloys, quench-and-temper steels, and some cast irons are especially sensitive. Level III procedures often require surface NDT after final machining of critical features (threads, seal diameters, bearing journals) because machining both creates and reveals discontinuities.

Grinding Burns and Grinding Cracks

Abusive grinding —too aggressive a wheel, inadequate coolant, or glazed wheel—creates localized overheating :

• Temper burn : over-tempered soft spots (dark etch response)
• Re-hardening burn : thin martensite layer that can crack

Grinding cracks : typically shallow , often perpendicular to the grinding direction or in a network on the ground surface

For NDT:

• MT (wet fluorescent on steel) is classic for grinding cracks after finish grind of hardened parts
• PT for nonmagnetics or when MT is unsuitable
• Visual color change is a clue , not proof of crack depth
• Timing: many aerospace and gear procedures mandate inspection after final grind , not only after rough machine

Grinding cracks are processing even if the part later fails in fatigue from that crack—the origin class follows introduction during manufacturing.

Weld Defects as Processing Discontinuities

Fusion welding is a manufacturing process ; weld discontinuities are therefore processing (unless the weld was sound and a service crack later initiates at the toe). Core families:

• Weld discontinuity Brief cause cue
• Porosity Gas entrapment in solidifying weld metal
• Slag inclusions Trapped flux/slag (SMAW/FCAW etc.)
• Lack of fusion (LOF) Incomplete bonding of weld to base or bead to bead
• Incomplete penetration Root not fully filled/fused as required
• Undercut Groove melted into base metal at toe
• Solidification / hot cracks Weld metal tears during freezing
• HAZ / cold cracks Hydrogen + hard HAZ + stress (often delayed)

Method suites are code-driven, but Level III Basic logic remains: surface weld cracks and undercut → VT + MT/PT; volumetric porosity/slag/LOF → RT and/or UT depending on joint access and thickness. Chapter 4 deepens welding processes; here the classification point is origin = processing .

Forming Cracks

Cold or hot forming (bending, stamping, spinning, expanding) can crack material when strain exceeds local ductility:

• Outer fiber tensile cracks on bend radii
• Orange-peel surface rupture on coarse-grain material
• Luders or stretcher strains (more cosmetic, but can confuse VT)

Forming cracks are often surface-breaking and elongated parallel to the free edge of the bend or transverse to the principal stretch direction. MT/PT/VT dominate; UT is secondary unless thickness and access support subsurface checks at severe formed zones.

Heat-Treat Quench Cracks

Quench cracks form when rapid cooling produces tensile surface stresses (or internal stresses) that exceed the material’s strength while it is hard and brittle. Favored sites:

• Sharp corners, keyways, holes, and abrupt section changes
• High-hardenability steels quenched too severely
• Delayed cracking when hydrogen and residual stress combine after quench

NDT implications:

• Cracks may be deep relative to grinding cracks
• MT is highly effective on ferromagnetic parts once scale is controlled

Procedures often specify inspection after quench and temper and again after final grind if grind is used to restore dimensions

Residual stress and permeability changes after heat treat affect MT technique variables—Level III must approve parameters for the as-heat-treated condition

Plating and Related Processes

Electroplating , especially of high-strength steels , can introduce hydrogen that promotes hydrogen-assisted cracking . Process controls (baking after plate) are primary; NDT may be required after plating on fracture-critical parts. Coating processes can also create blisters or delamination at the coating–substrate interface—surface methods for open defects, and specialized approaches when interface integrity is critical.

Inspection Timing and Method Selection

Level III thinking for processing discontinuities:

• Identify the last process that can create the flaw of concern
• Inspect after that process (and after surface preparation that reveals the surface)
• Match surface vs volumetric methods to whether the flaw is expected open to the surface
• Do not rely on receiving inspection of raw stock alone if welding, quench, or grind follows

• Situation Weak strategy Strong strategy
• Hardened gear after finish grind Only billet UT at mill MT/PT of ground teeth/journals after grind
• Full-penetration weld VT only Code-required volumetric + surface methods
• Quenched shaft before temper Skip NDT until shipping MT after quench/temper per procedure; recheck after grind
• Exam Traps

Calling a quench crack “inherent” because the steel chemistry was high-carbon — chemistry is material; the crack is processing.

Calling weld porosity “service” because the vessel is already installed — if it formed during welding, origin remains processing (discovery time ≠ origin class).

Using only RT for suspected tight grinding cracks — wrong morphology/method match; surface methods first.

Ignoring orientation : forming and grind cracks have preferred directions relative to tools and strain.

Processing discontinuities close the manufacturing half of the origin triad. Section 5.3 covers what happens after the part enters service.