API 510 Chapter 16

API 510 Chapter 16 – The NDE Requirements of ASME Section V

Prepare for the API 510 Pressure Vessel Inspector certification exam with this API 510 Chapter 16 ASME Section V NDE study guide and free practice test.

ASME Section V, Nondestructive Examination, provides the methods, techniques, procedural requirements, calibration requirements, and documentation rules used when performing nondestructive examination on pressure equipment.

For API 510 candidates, the current examination scope concentrates on:

• Article 1 – General Requirements
• Article 2 – Radiographic Examination
• Article 6 – Liquid Penetrant Examination
• Article 7 – Magnetic Particle Examination
• Article 23, SE-797 – Manual Ultrasonic Thickness Measurement

The API 510 Body of Knowledge states that only the main body of each referenced Article is included unless specifically noted. Article 6 additionally includes Mandatory Appendices II and III, while Article 7 is limited to the yoke and prod techniques. 

After reviewing these topics, take the free API 510 Chapter 16 Practice Test to check your knowledge of ASME Section V NDE requirements.

What Is ASME Section V?

ASME Boiler and Pressure Vessel Code Section V – Nondestructive Examination provides requirements for performing different NDE methods.

It contains rules addressing subjects such as:

• Examination procedures
• Equipment
• Calibration
• Examination techniques
• Surface preparation
• Examination sensitivity
• Interpretation
• Documentation
• Records

An important API 510 exam principle is that ASME Section V primarily tells the examiner how to perform the NDE.

The referencing Code—such as ASME Section VIII Division 1 or API 510—determines when the examination is required and generally provides the applicable acceptance requirements.

A simple way to remember this is:

Section V = How to examine

Section VIII/API 510 = Why, when, extent, and applicable acceptance requirements

API 510 Chapter 16 Exam Scope

The current API 510 Body of Knowledge defines the ASME Section V examination scope very clearly. Candidates are expected to understand:

In addition, API expects candidates to understand the general NDE requirements found in ASME Section VIII Division 1 UG, UW, Appendices 4, 6, 8, and 12, together with the general NDE requirements in API 510.

ASME Section V Article 1 – General Requirements

Article 1 establishes the foundation for using Section V.

For the current API 510 exam, candidates should understand:

• Scope of Section V
• Rules for using Section V when it is referenced by another Code
• Responsibilities of the owner/user
• Responsibilities of subcontractors
• Calibration
• Meaning of inspection and examination
• Recordkeeping requirements

These subjects are specifically listed in the current API 510 Body of Knowledge.

Referencing Code Concept

Section V does not normally act alone.

For example, ASME Section VIII may state that a pressure-vessel weld requires radiographic examination.

Section V then provides the examination method.

Therefore, when solving an exam question, first ask:

Which Code is requiring the examination?

Then ask:

Which Section V Article tells me how the examination is performed?

Inspection vs Examination

Candidates should understand that inspection and examination are related but not identical concepts.

An examination is generally the performance of an NDE method to obtain information about a weld, material, or component.

Inspection is broader and may include:

• Reviewing examination results
• Evaluating vessel condition
• Comparing results with acceptance criteria
• Verifying Code compliance
• Reviewing records
• Making integrity decisions

An API Authorized Pressure Vessel Inspector may therefore use NDE results produced by qualified examiners as part of a larger inspection decision.

Calibration in ASME Section V

Calibration helps demonstrate that examination equipment is operating correctly and that examination results can be relied upon.

The calibration requirements vary by method.

Examples include:

Radiography: technique and image-quality controls.

Magnetic Particle: verification of equipment capability where required.

Ultrasonic Thickness Measurement: instrument calibration using suitable reference standards.

Calibration should not be confused with acceptance criteria.

Calibration answers:

“Is my examination system providing valid information?”

Acceptance criteria answer:

“Is the condition found acceptable?”

ASME Section V Article 2 – Radiographic Examination

Article 2 covers Radiographic Examination, commonly abbreviated RT.

For the API 510 exam, candidates should understand the scope and general requirements of Article 2 and pressure-vessel radiography subjects including:

• Required marking
• IQI type
• IQI selection
• Number of IQIs
• IQI placement
• Allowable radiographic density
• Backscatter control
• Location markers
• Records

These topics are specifically identified in the current API 510 Body of Knowledge.

How Radiographic Testing Works

Radiographic testing uses penetrating radiation that passes through the material being examined.

Depending on the examination system, radiation may come from:

• X-ray equipment
• Gamma-ray sources

Differences in material thickness or density cause different amounts of radiation to reach the detector.

This creates an image that can reveal certain internal discontinuities.

What RT Is Good at Detecting

Radiography is especially useful for many volumetric discontinuities, such as:

• Porosity
• Slag inclusions
• Certain incomplete-penetration conditions
• Some fusion-related imperfections

However, RT should not automatically be considered the best method for every discontinuity.

Defect Orientation and Radiography

One of the most important radiography principles for API 510 candidates is:

Detection of planar defects depends strongly on their orientation relative to the radiation beam.

A rounded gas pore changes the effective thickness/density regardless of orientation.

A tight crack or lack-of-fusion plane may produce little radiographic contrast if it is poorly aligned with the radiation beam.

Therefore:

RT is generally strong for volumetric imperfections but can be less reliable for unfavorably oriented planar discontinuities.

Image Quality Indicators – IQIs

An Image Quality Indicator, or IQI, is used to demonstrate that the radiographic technique has achieved the required image quality.

Common forms include:

• Wire-type IQIs
• Hole-type IQIs

Important exam concepts include:

• Correct IQI selection
• Correct placement
• Required number
• Visibility
• Relationship to examination sensitivity

An IQI is not an artificial weld defect.

Its purpose is to demonstrate radiographic quality and sensitivity.

IQI Placement

IQI placement is important because image quality is affected by geometry.

The applicable Section V requirements determine where the IQI should be placed and what conditions must be satisfied.

Candidates should avoid memorizing a simplified statement such as:

“The IQI is always placed on one particular side.”

Instead, learn the Code logic and permitted arrangements.

Radiographic Density

For conventional film radiography, density indicates the degree of film darkening.

Radiographs must satisfy the applicable density requirements so that:

• Weld details can be interpreted
• Relevant indications can be seen
• Required image quality is demonstrated

A film that is too light or too dark may not provide adequate examination quality.

For exam preparation, use the current Article 2 requirements when a question asks for exact limits.

Backscatter Radiation

Backscatter occurs when radiation passes through the examination object and is scattered back toward the detector by surrounding material.

Excessive backscatter can degrade radiographic image quality.

Section V therefore includes requirements for controlling or identifying backscatter.

Candidates should understand:

Backscatter can produce misleading or degraded radiographic images and therefore must be controlled.

Location Markers

Location markers allow an indication visible on a radiograph to be related to the actual physical location on the weld or pressure vessel.

This is critical for:

• Repair
• Re-examination
• Documentation
• Traceability

Without proper location identification, a rejectable indication may be difficult to find on the actual vessel.

Radiographic Identification and Marking

Radiographs require appropriate identification so that the examination can be traced to the correct:

• Vessel
• Component
• Weld
• Location
• Examination record

Identification should not obscure the examination area.

Good radiographic traceability is particularly important when the image becomes part of the vessel’s permanent inspection history.

RT Records

Radiographic records may include information such as:

• Component identification
• Examination location
• Technique
• IQI information
• Examination results
• Date
• Examiner information
• Required supporting documentation

Recordkeeping is explicitly included in the API 510 Article 2 exam scope.

ASME Section V Article 6 – Liquid Penetrant Examination

Article 6 covers Liquid Penetrant Examination, commonly abbreviated PT.

For the current API 510 exam, the scope includes the Article 6 main body plus Mandatory Appendices II and III. Candidates should understand subjects involving:

• Procedures
• Contaminants
• Techniques
• Examination
• Interpretation
• Documentation
• Records

API specifically identifies these subjects in the Body of Knowledge.

How Liquid Penetrant Testing Works

PT detects discontinuities that are open to the examined surface.

The method relies on capillary action.

Liquid penetrant enters a surface-breaking discontinuity and is later drawn back toward the surface by developer, creating a visible indication.

Basic PT Examination Sequence

A useful study sequence is:

Clean → Apply penetrant → Dwell → Remove excess penetrant → Apply developer → Examine → Interpret → Record → Post-clean

The exact requirements depend on the selected penetrant system and applicable Article 6 procedure.

Surface Preparation for PT

Surface preparation is critical.

Contaminants such as:

• Oil
• Grease
• Paint
• Scale
• Dirt
• Moisture

can prevent penetrant from entering a discontinuity.

Poor cleaning can therefore cause relevant discontinuities to remain undetected.

Penetrant Dwell Time

Penetrant must remain on the examination surface long enough to enter open discontinuities.

Insufficient dwell time can reduce examination sensitivity.

Excessive or inappropriate processing can also interfere with results.

For specific examination values, candidates should use the applicable Article 6 requirements.

Excess Penetrant Removal

After dwell time, penetrant remaining on the surface must be removed appropriately.

The goal is:

Remove background penetrant without removing penetrant trapped in discontinuities.

Excessive cleaning can remove relevant penetrant.

Insufficient cleaning can produce excessive background and make interpretation difficult.

Developer

Developer helps draw penetrant from discontinuities back to the surface and improves contrast.

It therefore helps make surface-breaking discontinuities easier to see.

Candidates should understand the developer’s function rather than treating it simply as another cleaning material.

---

Visible and Fluorescent PT

Penetrant systems can use:

Visible penetrant

which is normally viewed under suitable visible-light conditions,

or

Fluorescent penetrant

which is examined under specified UV-A conditions.

The applicable examination procedure determines the technique.

What PT Can Detect

PT can reveal surface-breaking conditions such as:

• Fine cracks
• Surface porosity
• Seams
• Laps
• Other open-to-surface discontinuities

The material does not need to be magnetic.

This makes PT particularly useful for materials such as austenitic stainless steels.

What PT Cannot Detect

PT cannot reliably detect:

• Completely subsurface cracks
• Internal porosity with no surface opening
• Internal slag inclusions
• Hidden laminations

Remember:

If the discontinuity does not break the examined surface, penetrant cannot enter it.

PT Indication vs Defect

A visible penetrant indication is not automatically a rejectable defect.

The correct sequence is:

Indication → Interpretation → Characterization → Compare with acceptance criteria

The referencing Code determines whether the indication is acceptable.

ASME Section V Article 7 – Magnetic Particle Examination

Article 7 covers Magnetic Particle Examination, commonly abbreviated MT.

For the current API 510 examination, Article 7 is specifically limited to:

Yoke technique

and

Prod technique

Candidates should understand:

• Procedures
• Yoke and prod techniques
• Calibration
• Examination
• Interpretation
• Documentation
• Records

The API Body of Knowledge explicitly limits detailed Article 7 exam coverage to these two techniques.

How Magnetic Particle Examination Works

MT is used on suitable ferromagnetic materials.

The component is magnetized.

A discontinuity can interrupt the magnetic field and produce a leakage field at or near the surface.

Magnetic particles are attracted to the leakage field and form an indication.

What MT Can Detect

MT is highly effective for:

• Surface cracks
• Near-surface cracks
• Weld-toe cracking
• Heat-affected-zone cracking
• Fatigue cracks
• Other suitable planar discontinuities

Compared with PT, MT can detect certain discontinuities slightly below the surface.

Material Limitation of MT

MT requires material capable of being magnetized.

Therefore, it is commonly applicable to:

• Carbon steels
• Many low-alloy steels
• Other ferromagnetic materials

Many austenitic stainless steels are not suitable for conventional MT.

For surface cracking on those materials, PT may be more appropriate.

Yoke Technique

The yoke technique uses a magnetizing yoke positioned on the examination surface.

The magnetic field passes through the material between the poles of the yoke.

Magnetic particles are then applied to reveal leakage fields associated with discontinuities.

Yokes are commonly used for localized examination of:

• Welds
• Repair areas
• Heat-affected zones

Prod Technique

The prod technique uses electrical contacts placed against the examination surface.

Current passes through the material between the prods, producing a magnetic field.

Because electrical current enters the material directly at the prod contacts, proper technique is important to avoid surface damage.

API 510 candidates should recognize that prod examination and yoke examination are different magnetization methods, even though both are covered by Article 7.

Direction of Magnetization

MT sensitivity depends strongly on the relationship between:

Magnetic field direction

and

Discontinuity orientation

A discontinuity that crosses the magnetic field at a favorable angle generally produces a stronger indication.

A crack nearly parallel to the field can be difficult to detect.

For this reason, an effective examination may require magnetization in more than one direction.

Visible and Fluorescent Magnetic Particles

MT can use:

• Visible particles
• Fluorescent particles

Fluorescent particles are viewed under appropriate UV-A lighting.

The procedure and examination conditions must match the selected particle system.

MT Calibration and Equipment Checks

Article 7 includes calibration and equipment-verification requirements.

The purpose is to ensure that the magnetizing equipment produces adequate examination capability.

Candidates should understand the general concept and learn where the exact requirements are located in the current Code.

MT Interpretation

Not every magnetic-particle indication represents a rejectable crack.

Indications can result from:

• Real discontinuities
• Geometry
• Changes in section thickness
• Magnetic permeability changes

The examiner must distinguish relevant indications from nonrelevant indications and evaluate relevant conditions according to the referencing Code.

PT vs MT Quick Comparison

A simple exam memory aid is:

Nonmagnetic material + surface crack → think PT

Ferromagnetic steel + surface/near-surface crack → think MT

ASME Section V Article 23 – SE-797 Ultrasonic Thickness Measurement

The current API 510 exam does not require the entire ultrasonic-testing body of Section V.

The official scope is specifically:

Article 23, SE-797 only – measuring thickness by the manual ultrasonic pulse-echo contact method.

Candidates should understand:

• Scope of SE-797
• General rules for applying the ultrasonic method
• Specific ultrasonic thickness-measurement procedures in paragraph 7

This limitation is explicitly stated in the API 510 Body of Knowledge. 

How Ultrasonic Thickness Measurement Works

An ultrasonic transducer sends a high-frequency sound pulse into the material.

The pulse travels through the material, reflects from the back surface, and returns to the transducer.

The instrument uses the travel time and acoustic velocity to determine thickness.

Conceptually:

Thickness = Velocity × Round-Trip Travel Time ÷ 2

The division by two accounts for the sound traveling to the back wall and returning.

Why Couplant Is Required

Air is a poor transmitter of ultrasonic energy between the probe and test surface.

A couplant is therefore applied between the transducer and material.

Its purpose is to:

• Remove the air gap
• Improve sound transmission
• Produce reliable back-wall echoes

Poor coupling can result in unreliable or missing thickness readings.

UT Calibration

Before measuring vessel thickness, the instrument must be properly set up and calibrated.

Factors can include:

• Material acoustic velocity
• Probe
• Known reference thickness
• Expected thickness range
• Surface condition
• Temperature where relevant

An inaccurate calibration can result directly in an inaccurate thickness measurement.

That error can then affect:

• Corrosion rate
• Remaining life
• Inspection interval
• MAWP evaluation

This makes UT calibration especially important for API 510 inspectors.

Surface Condition and UT

Surface condition can affect ultrasonic measurements.

Potential problems include:

• Heavy corrosion scale
• Rough pitting
• Thick coatings
• Curvature
• Poor probe contact
• Elevated temperature

Suspicious readings should be evaluated rather than automatically accepted.

UT Thickness Measurement and Corrosion

UT thickness measurement is widely used to evaluate:

• General corrosion
• Erosion
• Wall thinning
• CMLs
• Remaining wall thickness

The readings can support calculations such as:

Corrosion Rate

and

Remaining Life

which were covered earlier in API 510 Chapter 4.

Spot Readings vs Scanning

One of the most important practical principles is:

A spot thickness reading represents only the area immediately beneath the probe.

If corrosion is highly localized, a few widely spaced readings can miss the thinnest location.

Where localized deterioration is expected, inspection may require:

• Additional measurements
• Grid mapping
• Scanning
• Other appropriate techniques

Do not assume that one acceptable thickness reading proves the entire vessel area is acceptable.

Repeatability of UT Measurements

Corrosion-rate calculations compare measurements taken at different times.

For reliable trending, inspectors should try to maintain consistency in:

• Measurement location
• Calibration
• Probe
• Surface preparation
• Technique

Condition Monitoring Locations help make repeat measurements more meaningful.

ASME Section V vs ASME Section VIII Acceptance

This distinction is extremely important for Chapter 16.

Suppose an examiner performs PT on a pressure-vessel weld.

ASME Section V Article 6 tells the examiner how to conduct the penetrant examination.

But the acceptance requirements for that particular pressure-vessel weld come from the applicable referencing Code.

Similarly:

Section V Article 2 → RT technique

Section VIII → Applicable RT requirements and acceptance

This is one of the most useful Code-navigation concepts for API 510.

ASME Section VIII NDE References for API 510

The current API 510 Body of Knowledge also requires candidates to understand general NDE rules in:

• UG
• UW
• Appendix 4
• Appendix 6
• Appendix 8
• Appendix 12

of ASME Section VIII Division 1.

These references connect Section V examination methods with pressure-vessel construction and acceptance requirements.

For example, candidates may need to know:

Which method applies?

How is it performed under Section V?

Which Section VIII appendix contains the applicable acceptance requirements?

This cross-Code navigation is a major part of API 510 exam preparation.

Indication, Discontinuity and Defect

These three terms should not be treated as identical.

Indication

A response produced during an NDE examination that requires interpretation.

Discontinuity

An interruption in the normal structure or configuration of the material.

Defect

A discontinuity that exceeds the applicable acceptance criteria and is therefore rejectable.

The correct thought process is:

Find an indication → interpret it → identify the discontinuity → compare with Code acceptance criteria → determine whether it is a defect.

Linear and Rounded Indications

Some NDE acceptance rules classify indications according to their shape.

Linear Indication

Generally associated with an elongated response and can be significant when related to crack-like discontinuities.

Rounded Indication

May be associated with volumetric conditions such as porosity.

However, shape alone does not determine acceptance.

The applicable Code criteria must be used.

Selecting the Correct ASME V Article

A simple exam-navigation method is:

Do not search the entire Section V Code when the examination method already tells you which Article applies.

ASME Section V Exam Strategy

When answering an NDE question, use this sequence:

Step 1 – Identify the Examination Method

RT?

PT?

MT?

UT thickness?

Step 2 – Go to the Correct Article

Article 2?

Article 6?

Article 7?

SE-797?

Step 3 – Identify What the Question Is Asking

Is it about:

• Procedure?
• Technique?
• Calibration?
• Examination?
• Interpretation?
• Records?

Step 4 – Apply Section V

Find the examination-method requirement.

Step 5 – Check the Referencing Code if Acceptance Is Asked

Do not automatically assume that Section V contains the final accept/reject requirement.

A useful memory sequence is:

Method → Article → Technique → Examination → Interpretation → Referencing Code → Acceptance

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Common API 510 Chapter 16 Exam Mistakes

Studying All of ASME Section V

The current API 510 exam is limited to specific Articles and portions. Concentrate on the official Effectivity Sheet and Body of Knowledge.

Treating Section V as the Construction Code

Section V principally provides NDE methods and requirements. Section VIII/API 510 establishes the broader pressure-vessel requirements.

Assuming RT Detects Every Crack

Planar-discontinuity orientation can significantly affect radiographic detectability.

Treating an IQI as an Artificial Defect

An IQI demonstrates image quality and examination sensitivity.

Assuming PT Can Find Subsurface Defects

PT requires the discontinuity to open to the examined surface.

Using MT on Nonmagnetic Material

MT requires a suitable ferromagnetic material.

Forgetting the Direction of Magnetization

MT sensitivity depends on the relationship between the discontinuity and the magnetic field.

Studying Every MT Technique

For the current API 510 exam, Article 7 detailed coverage is limited to yoke and prod techniques.

Studying Full Ultrasonic Flaw Detection Under Section V

The current API 510 Article 23 scope is specifically SE-797 manual pulse-echo contact thickness measurement, not the entire range of ultrasonic examination techniques.

Confusing an Indication With a Defect

An indication must first be interpreted and compared with the applicable acceptance criteria.

Take the Free API 510 Chapter 16 Practice Test

Now take the free API 510 Chapter 16 ASME Section V NDE Practice Test.

Practice questions should focus on the current exam scope:

Article 1 – General Requirements

• Scope
• Referencing Code
• Responsibilities
• Calibration
• Inspection vs examination
• Records

Article 2 – Radiographic Examination

• Marking
• IQIs
• Density
• Backscatter
• Location markers
• Records

Article 6 – Liquid Penetrant Examination

• Procedure
• Contaminants
• Techniques
• Examination
• Interpretation
• Documentation
• Records

Article 7 – Magnetic Particle Examination

• Yoke technique
• Prod technique
• Calibration
• Examination
• Interpretation
• Records

Article 23 / SE-797

• Manual ultrasonic thickness measurement
• General UT principles
• Coupling
• Calibration
• Measurement procedure

For each incorrect answer, return to the applicable Article and identify the paragraph that controls the answer.

That approach develops the Code-navigation skill required for open-book API 510 questions.

Current ASME Section V Reference for API 510

For candidates taking the September 2026, January 2027, or May 2027 API 510 examination, the official Effectivity Sheet specifies:

ASME Boiler and Pressure Vessel Code – 2025 Edition

Section V – Nondestructive Examination

Included portions:

• Article 1
• Article 2
• Article 6
• Article 7
• Article 23 – SE-797 only

The current API 510 Body of Knowledge further limits Article 7 to yoke and prod techniques and specifies the examination knowledge expected from each Article. 

Candidates should always verify the Effectivity Sheet for their exact examination date because Code editions and exam coverage can change.

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UpWeld offers an API 510 Exam Learning Package containing more than 5,000 independently developed practice questions covering theory, Code navigation, practical scenarios, welding, NDE, and numerical calculations.

API 510 Question Bank – 5,000+ Practice Questions

The practice bank covers topics such as:

• API 510
• ASME Section V
• Article 1
• Radiographic Examination
• Liquid Penetrant Examination
• Magnetic Particle Examination
• Ultrasonic Thickness Measurement
• ASME Section VIII
• ASME Section IX
• API RP 571
• API RP 572
• API RP 576
• API RP 577
• API RP 578
• Welding
• NDE
• WPS/PQR/WPQ
• PWHT
• Impact testing
• Pressure-vessel calculations
• Corrosion rate
• Remaining life
• MAWP
• Inspection intervals
• Repairs
• Alterations
• Rerating
• Pressure testing
• Practical scenarios
• Numerical questions
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• Closed-book style practice

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Use the UpWeld learning package as a practice and revision resource alongside the official API and ASME references applicable to your exam date.

UpWeld practice questions are independently developed for educational purposes. They are not official API examination questions, and no specific practice question can be guaranteed to appear on an API certification exam.

Continue Your API 510 Exam Preparation

After completing the API 510 Chapter 16 ASME Section V NDE Practice Test, do not simply memorize the answers.

For each question, ask:

Which examination method is involved?

Which Section V Article applies?

Is the question about procedure, calibration, technique, examination, interpretation, or records?

Does Section V answer the question, or do I need to return to the referencing Code for acceptance?

A strong revision sequence is:

NDE Method → Section V Article → Procedure → Technique → Calibration → Examination → Interpretation → Referencing Code → Acceptance → Records

This approach will help you navigate ASME Section V quickly and accurately during API 510 preparation.

Disclaimer

UpWeld is an independent educational and exam-preparation platform. UpWeld is not affiliated with, sponsored by, authorized by, or endorsed by the American Petroleum Institute, ASME, or their certification programs.

API, API 510, ASME, ASME BPVC Section V, and associated publication names belong to their respective owners.

UpWeld practice questions are independently developed for educational purposes and are not official API examination questions. Examination editions and requirements may change. Candidates should always verify the current API 510 Body of Knowledge and Publications Effectivity Sheet for their examination date.