- How the NB-331 Outline Is Organized
- The 12 Domains at a Glance
- Domains 1-3: Roles, Equipment and Code Navigation
- Domains 4-5: Quality Control and Design
- Domains 6-7: Materials and Fabrication
- Domains 8-10: NDE, Testing and Calibration
- Domains 11-12: Data Reports and Record Retention
- Required References You Must Know
- Sequencing Your Preparation by Domain
- Frequently Asked Questions
- The National Board's NB-331-NC outline lists 12 numbered content areas, and the National Board publishes no percentage weight for any of them.
- Design and Fabrication carry the most sub-topics, from nozzle reinforcement and ligament efficiency to welding qualifications and out-of-roundness limits.
- Your references are ASME Sections I, IV, V, VIII Division 1 and IX, plus B31.1, QAI-1 and RCI-1/NB-263.
- The examination has 85 questions and follows attendance at the Authorized Inspector Commission course.
How the NB-331 Outline Is Organized
The National Board Authorized Inspector Commission (AI) is governed by The National Board of Boiler and Pressure Vessel Inspectors, and its content is defined in the detailed outline document NB-331-NC, Revision 6. That document is the authoritative source for what you are expected to know. If you are trying to understand what the exam covers, start there rather than with third-party summaries.
One detail trips up many candidates: the introductory summary in NB-331-NC groups the material into 11 objectives, while the detailed hierarchy beneath it is numbered across 12 headings. The 11-objective summary does not replace the detailed hierarchy. This guide follows the 12 numbered headings because that is where the specific topics, sub-topics and code references actually live.
The National Board does not publish percentage weights for these areas. Any site that quotes exact domain percentages for this commission is guessing. What you can do instead is judge relative depth from the outline itself: some headings contain a handful of items, while others, notably Design and Fabrication, are packed with dozens of distinct technical points.
For the broader picture of how the credential works, see our overview in AI Certification, and for eligibility details read AI Requirements 2026: Eligibility, Prerequisites & How to Qualify.
The 12 Domains at a Glance
The table below maps each numbered heading to its core subject matter so you can see the whole exam in one view. The detail for each domain follows in the sections after it.
| # | Domain | Core Focus |
|---|---|---|
| 1 | Responsibilities and Duties of the AI | RCI-1/ASME QAI-1 roles of agencies, supervisors and inspectors |
| 2 | Boiler and Pressure Vessel Types and Terminology | Identifying equipment types and their parts |
| 3 | Code Structure and Content | Navigating the ASME BPVC and related requirements |
| 4 | Quality Control System | Section I App. A-301, Section IV App. F, Section VIII Div. 1 App. 10 |
| 5 | Design | Shells, heads, nozzles, stayed surfaces, weld sizes, efficiencies |
| 6 | Materials | Specifications, markings, tolerances, certifications, defective-material repair |
| 7 | Fabrication | Forming, tolerances, attachments, welding and its qualifications |
| 8 | Nondestructive Examination | When required, permitted methods, qualification, reports |
| 9 | Testing and Heat Treatment | Impact tests, heat treatment, pressure tests, exemptions |
| 10 | Calibration of M&TE | Frequencies, methods, tolerances, standards, records |
| 11 | Data Reports and Stamping | Reports and stamping by construction type |
| 12 | Record Retention | Retention rules under Sections I, IV and VIII |
Domains 1-3: Roles, Equipment and Code Navigation
The first three domains establish who does what, what the equipment is, and where to find the rules. They are foundational, and weakness here undermines everything that follows.
Domain 1: Responsibilities and Duties of the AI
Responsibilities and Duties of the AI
This domain centers on RCI-1 and ASME QAI-1, which define the roles of authorized inspection agencies, supervisors and inspectors. The outline also notes that duties appear throughout the required references, not only in the documents dedicated to inspection.
- Distinguish the responsibilities of the agency, the supervisor and the inspector.
- Recognize duties the inspector must perform versus those belonging to the manufacturer.
- Expect to encounter inspector duties embedded in Sections I, IV and VIII as you read them.
A practical habit: whenever you study a code paragraph in another domain, ask yourself what the Authorized Inspector is expected to verify, witness or review. That turns Domain 1 into a running thread rather than an isolated topic.
Domain 2: Boiler and Pressure Vessel Types and Terminology
You must be able to identify boiler and vessel types and name their parts correctly. Questions in this area reward precise vocabulary. Know the difference between power boilers, heating boilers and pressure vessels, and be comfortable naming components such as shells, drums, headers, nozzles and heads, since these same terms recur through the design and fabrication domains.
Domain 3: Code Structure and Content
This domain tests whether you can navigate the ASME Boiler and Pressure Vessel Code and related requirements efficiently. Knowing which section governs which type of construction, and how the parts of each section are laid out, saves enormous time on every other domain. Candidates who treat the Code as a book to be memorized struggle; candidates who treat it as a structure to be navigated do far better.
For a compact reference to the facts you will reach for most often, keep our AI Cheat Sheet 2026: One-Page Review of Must-Know Facts alongside your Code books.
Domains 4-5: Quality Control and Design
Domain 4: Quality Control System
Quality Control System
The outline ties this domain to three specific code locations, one for each construction section:
- Section I, Appendix A-301 (power boilers)
- Section IV, Appendix F (heating boilers)
- Section VIII, Division 1, Appendix 10 (pressure vessels)
Learn what a manufacturer's quality control system must contain and how the three appendices compare. A useful exercise is building your own side-by-side comparison of the three, since exam questions often hinge on a requirement that differs between sections.
Domain 5: Design
Design is one of the densest domains in the outline. It spans power boilers, heating boilers, external piping and vessels, and breaks down into many distinct technical subjects.
Design: Topics You Must Master
- Shells and drums, piping, headers and nozzles
- Formed and flat heads
- Braced and stayed surfaces
- Weld sizes and nozzle reinforcement
- Preformed and prefabricated pressure parts
- Flanges
- Joint efficiencies and ligament efficiency
Expect calculation-oriented questions here. You should be comfortable applying code formulas, reading the correct figures and tables, and understanding why a given joint efficiency or reinforcement requirement applies. Because this domain is broad, plan to return to it more than once rather than trying to finish it in a single sitting.
Domains 6-7: Materials and Fabrication
Domain 6: Materials
The materials domain covers construction-section rules, product-form tolerances, markings and marking methods, pressure versus nonpressure parts, non-ASME standards, repair of defective material, and certifications. Pay particular attention to how material rules differ depending on whether a part is a pressure part, since that distinction drives many questions. Understand also what documentation must accompany material and what the inspector should verify before it is used.
Domain 7: Fabrication
Fabrication is the other large domain, and it divides naturally into forming and welding.
Fabrication: Forming and Fit-Up
- Cutting and edge preparation
- Cold-forming limits
- Out-of-roundness limits for cylindrical, conical and spherical shells
- Formed-head tolerances
- Attachment of lugs and fittings
- Holes for screwed or threaded stays and tubes
Fabrication: Welding
- Welding responsibilities and processes
- Procedure qualification and welder/operator qualification (tied to Section IX)
- Surface cleaning and alignment tolerances
- Spin holes and finished joints
- Fillet welds
- Defect repair, peening and surface weld-metal buildup
Welding questions connect heavily to Section IX, so make sure your understanding of qualification is solid before you tackle the fabrication paragraphs in Sections I and VIII. If you want a sense of how demanding this material is relative to the rest of the exam, our piece on How Hard Is the AI Exam? Complete Difficulty Guide 2026 discusses where candidates tend to struggle.
Domains 8-10: NDE, Testing and Calibration
Domain 8: Nondestructive Examination
NDE questions revolve around Section V and the NDE requirements in the construction sections. The outline emphasizes when NDE is required, which methods are permitted, the advantages and limitations of each method, procedure and personnel qualification, and reports. A strong approach is to build a matrix of methods against what each can and cannot detect, so you can answer method-selection questions quickly.
Domain 9: Testing and Heat Treatment
This domain groups impact testing, heat treatment and pressure tests, including exemptions and alternatives. The exemptions are the exam-friendly part: many questions ask whether a requirement applies at all, so you need to know the conditions that exempt a part from impact testing or postweld heat treatment, and when an alternative is permitted.
Domain 10: Calibration of Measurement and Test Equipment (M&TE)
Calibration covers frequencies, methods, tolerances, master standards, identification and records for both working and master measurement and test equipment. It is a compact domain with clear rules, which makes it a good place to secure dependable points. Distinguish carefully between working and master equipment, because the requirements differ.
Key Takeaway
Domains 8, 9 and 10 are rule-heavy rather than calculation-heavy. Build short comparison tables (methods, exemptions, calibration intervals) and review them repeatedly; this is efficient points-per-hour study.
Domains 11-12: Data Reports and Record Retention
The final two domains are administrative in character, but they are exactly where an inspector's day-to-day work lands. Domain 11 covers data reports and stamping for the type of construction involved, so you must know which report and which stamp apply to power boilers, heating boilers and pressure vessels. Domain 12 covers record retention under ASME Sections I, IV and VIII, including what must be kept and how the requirements compare across the three sections.
Because these domains reward accurate recall of specific requirements, they are good candidates for flashcards and quick tables. Treat them as an easy win, not an afterthought.
Required References You Must Know
The outline identifies the documents you are expected to work from. Having the right editions and knowing your way around each is half the battle.
| Reference | Primary Domains It Supports |
|---|---|
| ASME Section I | Power boiler design, fabrication, quality control, reports |
| ASME Section IV | Heating boiler requirements and quality control |
| ASME Section V | Nondestructive examination |
| ASME Section VIII, Division 1 | Pressure vessel design, fabrication, testing, records |
| ASME Section IX | Welding procedure and personnel qualification |
| ASME B31.1 | Power piping, including external piping topics |
| QAI-1 | Qualifications for authorized inspection |
| RCI-1 / NB-263 | Rules for commissioned inspectors and inspection agencies |
Our AI Study Guide 2026: How to Pass on Your First Attempt covers how to tab and annotate these references so you can find answers quickly when it counts.
Sequencing Your Preparation by Domain
Rather than studying the domains in numerical order, sequence them by dependency. The structure below is a suggested ordering, not a published requirement.
Orientation (Domains 1-3)
- Read NB-331-NC and map each heading to its code location.
- Learn the equipment vocabulary and the layout of each ASME section.
Technical core (Domains 5-7)
- Work Design calculations repeatedly, since they are the most demanding.
- Pair Fabrication welding topics with Section IX qualification rules.
Rule-based domains (Domains 4, 8-12)
- Build comparison tables for quality control appendices, NDE methods, exemptions, calibration and retention.
- Finish with practice questions across all 12 domains.
Placing the calculation-heavy domains in the middle gives you time to revisit them, while saving the table-driven domains for the end, when they are easiest to consolidate. To test your readiness across the full outline, try the questions on our AI practice test site, and use the domain-by-domain practice sets to find your weakest areas before exam day.
Once you know the content, the practical questions are cost, timing and results. Review AI Certification Cost 2026: Complete Pricing Breakdown, AI Exam Dates 2026: Testing Windows, Deadlines & Scheduling and AI Passing Score 2026: Exactly What You Need to Pass. If you are weighing whether to pursue the commission at all, Is the AI Certification Worth It? Complete ROI Analysis 2026 and AI Salary Guide 2026: Complete Earnings Analysis are good next reads.
Frequently Asked Questions
The detailed outline, NB-331-NC Revision 6, has 12 numbered headings. The introductory summary groups the content into 11 objectives, but the 12-heading hierarchy is the detailed breakdown candidates should study from.
No. No percentage weights are published, so you should prepare for all 12 areas. Design and Fabrication contain the most sub-topics, but smaller domains can still appear on the exam.
The National Board's examination information confirms 85 questions, with the exam following attendance at the Authorized Inspector Commission course and a passing examination. The exact timer, current fee and numerical pass mark should be confirmed directly with the National Board.
The required references are ASME Sections I, IV, V, VIII Division 1 and IX, ASME B31.1, QAI-1, and RCI-1/NB-263. Each domain draws on specific parts of these documents.
Start with Responsibilities and Duties, equipment terminology and Code structure, since they give you the vocabulary and navigation skills for everything else. Then spend the most time on Design and Fabrication before consolidating the rule-based domains.