100+ Free NBBI Inservice Inspector (IS) Practice Questions

Pass your NBBI Inservice Inspector (IS) Commission Exam exam on the first try — instant access, no signup required.

✓ No registration✓ No credit card✓ No hidden fees✓ Start practicing immediately

~60-70% Pass Rate

100+ Questions

100% Free

1 / 10

Question 1

Score: 0/0

What is the primary purpose of the National Board Inspection Code (NBIC)?

To design new boilers and pressure vessels

To regulate the sale of pressure equipment

To establish manufacturing standards for new construction

To provide rules and guidelines for the installation, inspection, repair, and alteration of in-service pressure equipment

to track

2026 Statistics

Key Facts: NBBI Inservice Inspector (IS) Exam

Exam Questions

NBBI

60/85

Passing Score

NBBI

2 weeks

Course Length

NBBI

$3,500

In-Person Tuition

NBBI

Open

Book Policy

NBBI

300

Required Inspections (NB-380)

NBBI

The NBBI IS exam has 85 open-book multiple-choice questions with a passing score of 60 correct (~71%). Administered on the last day of the 2-week IS Commission Course. Key domains: NBIC Inspection (30%), Installation (20%), Repairs & Alterations (20%), Pressure Relief Devices (10%), Jurisdictional (10%), Condition Assessment (5%), Safety Controls (5%). Requires 5 credit points and employer sponsorship.

Sample NBBI Inservice Inspector (IS) Practice Questions

Try these sample questions to test your NBBI Inservice Inspector (IS) exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1What is the primary purpose of the National Board Inspection Code (NBIC)?

A.To design new boilers and pressure vessels

B.To regulate the sale of pressure equipment

C.To establish manufacturing standards for new construction

D.To provide rules and guidelines for the installation, inspection, repair, and alteration of in-service pressure equipment

Explanation: The NBIC (NB-23) provides rules and guidelines for the installation, inspection, repair, and alteration of boilers, pressure vessels, and pressure piping that are already in service. It is adopted by most US and Canadian jurisdictions as the standard for maintaining the safety and integrity of operating pressure equipment. Exam Tip: The NBIC is the in-service inspector's primary reference document — know its four parts and their scope.

2Which part of the NBIC covers the requirements for periodic in-service inspections of boilers and pressure vessels?

A.Part 1 — Installation

B.Part 4 — Pressure Relief Devices

C.Part 3 — Repairs and Alterations

D.Part 2 — Inspection

Explanation: NBIC Part 2 (Inspection) provides information and guidance needed to perform and document inspections of all types of pressure-retaining items, including information on personnel safety, NDE, tests, failure mechanisms, types of pressure equipment, and fitness-for-service evaluations. Part 1 covers installation, Part 3 covers repairs and alterations, and Part 4 covers pressure relief devices. Exam Tip: Part 2 is the core of the IS exam — study the inspection requirements for each type of equipment thoroughly.

3What are the two main types of in-service boiler inspections?

A.Fabrication and erection inspections

B.Hydrostatic and pneumatic inspections

C.Internal and external inspections

D.Radiographic and ultrasonic inspections

Explanation: The two main types of in-service boiler inspections are internal inspections (performed when the boiler is shut down, cooled, drained, and opened for entry or access) and external inspections (performed while the boiler is in operation). Internal inspections examine the waterside and fireside surfaces for deterioration, while external inspections evaluate external components, controls, safety devices, and operating conditions. Exam Tip: Internal inspections allow direct assessment of condition; external inspections verify safe operation — both are required at jurisdictional intervals.

4During an internal inspection of a firetube boiler, you observe thinning of the tube sheets around the tube holes. What is the most likely cause?

A.Corrosion caused by boiler water chemistry issues or galvanic action

B.Normal wear from steam flow

C.Impact damage from tube cleaning equipment

D.Paint peeling from the surface

Explanation: Thinning around tube holes in firetube boiler tube sheets is typically caused by corrosion, which may result from poor water chemistry (low pH, oxygen attack), galvanic action between dissimilar metals, or concentration of corrosive species in crevice areas. This area is particularly susceptible because of the crevice geometry between the tube and tube sheet. The inspector should measure remaining thickness and evaluate the cause. Exam Tip: Tube sheet ligament thinning is a critical finding — measure remaining ligament thickness and compare to minimum requirements.

5What is the primary purpose of an in-service inspection of a pressure vessel?

A.To assess the current condition and determine continued fitness for service at the operating pressure and temperature

B.To verify the vessel meets original construction code requirements

C.To redesign the vessel for higher pressure

D.To determine the resale value of the vessel

Explanation: The primary purpose of an in-service inspection is to assess the current condition of the pressure vessel and determine whether it remains fit for continued service at its current operating pressure and temperature. This includes identifying deterioration mechanisms, measuring remaining wall thickness, evaluating defects, and determining if repairs or re-rating are needed. Exam Tip: In-service inspection focuses on CURRENT condition versus REQUIRED condition — always compare actual measurements to minimum requirements.

6Which of the following is the most common form of deterioration found during in-service inspections of boilers?

A.Fatigue cracking

B.Hydrogen embrittlement

C.General corrosion and wastage

D.Radiation damage

Explanation: General corrosion and wastage (uniform metal loss) is the most commonly encountered deterioration mechanism in boilers and pressure vessels during in-service inspections. It results from the interaction between the metal and its environment (water, steam, flue gases) and is influenced by water chemistry, temperature, and operating conditions. Other mechanisms such as fatigue, caustic embrittlement, and pitting are also found but less frequently. Exam Tip: Corrosion is the number one enemy of in-service equipment — always take thickness readings at known corrosion-prone areas.

7What instrument is most commonly used to measure remaining wall thickness during in-service inspections?

A.A caliper

B.A ruler

C.An ultrasonic thickness gauge

D.A pressure gauge

Explanation: Ultrasonic thickness gauges are the most commonly used instruments for measuring remaining wall thickness during in-service inspections. They use high-frequency sound waves to measure the distance from the external surface to the internal surface, providing accurate thickness readings without requiring access to the inside of the vessel. The readings are compared to the minimum required thickness to determine continued fitness. Exam Tip: UT thickness readings should be taken at multiple points, especially at known corrosion-prone areas — document locations for trending.

8What is the minimum required thickness of a pressure vessel component?

A.The thickness calculated using the original code of construction formulas for the current MAWP at the operating temperature, excluding corrosion allowance

B.The original as-built thickness minus the corrosion allowance

C.Half of the original thickness

D.The thickness determined by the manufacturer only

Explanation: The minimum required thickness (t_min) is calculated using the design formulas from the original code of construction for the current MAWP at the operating temperature, without any corrosion allowance. The actual measured thickness must equal or exceed this minimum. If the actual thickness is less than t_min, the vessel must be repaired, re-rated to a lower MAWP, or retired from service. Exam Tip: t_min is calculated at CURRENT conditions — if the vessel has been re-rated, use the current MAWP, not the original design pressure.

9During an external inspection of an operating boiler, which of the following should the in-service inspector check?

A.Only the boiler nameplate data

B.Only the fuel supply

C.Safety valves, operating controls, low-water cutoffs, combustion conditions, piping connections, insulation condition, and structural supports

D.Only the electrical connections

Explanation: During an external inspection of an operating boiler, the in-service inspector should examine safety valves (for proper operation and sealing), operating controls (pressure, temperature, water level), low-water cutoffs, combustion conditions (flame, flue gases), piping connections (leaks), insulation condition, structural supports, and general housekeeping. The goal is to verify safe operating conditions. Exam Tip: External inspections cover everything visible while operating — develop a systematic approach to avoid missing items.

10What is the purpose of the low-water cutoff device on a steam boiler?

A.To regulate the water flow rate into the boiler

B.To control the steam quality

C.To prevent overpressure conditions

D.To shut down the burner if the water level drops below a safe minimum to prevent overheating and potential dry firing

Explanation: The low-water cutoff (LWCO) device automatically shuts down the burner if the water level in the boiler drops below the safe minimum level. This prevents the boiler from operating with insufficient water, which can cause overheating of the heating surfaces, thermal stress, and potentially catastrophic failure. ASME CSD-1 and jurisdictional requirements specify LWCO testing frequencies. Exam Tip: LWCO devices must be tested regularly — the exam frequently tests LWCO testing requirements and CSD-1 provisions.

About the NBBI Inservice Inspector (IS) Exam

The NBBI Inservice Inspector (IS) Commission certifies individuals to perform inspections of installed boilers and pressure vessels, covering installation, inservice operation, and maintenance under the National Board Inspection Code (NBIC). The open-book exam covers NBIC Parts 1-3 (Installation, Inspection, Repairs & Alterations), pressure-relieving devices, jurisdictional requirements, condition assessment, and safety controls. This credential is essential for state and insurance company boiler inspectors.

Questions

85 scored questions

Time Limit

Last day of 2-week course

Passing Score

60/85 correct (~71%)

Exam Fee

$3,500 in-person / $4,200 virtual (National Board (NBBI) / Prometric)

NBBI Inservice Inspector (IS) Exam Content Outline

30%

NBIC Part 2 — Inspection

Inservice inspection procedures, condition assessment, inspection intervals, documentation

20%

NBIC Part 1 — Installation

Installation requirements, jurisdictional requirements, piping connections, safety devices

20%

NBIC Part 3 — Repairs and Alterations

Repair methods, alteration requirements, R-stamps, welding procedures, documentation

10%

Pressure-Relieving Devices

Safety valve inspection, relief device testing, set pressure verification, capacity

10%

Jurisdictional Requirements

State and local boiler laws, registration, operating permits, inspection frequencies

Condition Assessment

Corrosion evaluation, thickness measurements, remaining life calculations, fitness for service

Safety Controls and Instrumentation

Low water cutoffs, flame safeguards, pressure controls, combustion controls

How to Pass the NBBI Inservice Inspector (IS) Exam

What You Need to Know

Passing score: 60/85 correct (~71%)
Exam length: 85 questions
Time limit: Last day of 2-week course
Exam fee: $3,500 in-person / $4,200 virtual

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

NBBI Inservice Inspector (IS) Study Tips from Top Performers

1Tab and index your NBIC Parts 1-3 — the exam is open-book but time management is critical

2Focus on NBIC Part 2 (Inspection) — it accounts for the largest portion of the exam

3Know the differences between repairs and alterations, and when R-stamps are required

4Study safety valve testing intervals, set pressure tolerances, and capacity requirements

5Understand jurisdictional boiler laws and how they interact with NBIC requirements

Frequently Asked Questions

What is the NBBI Inservice Inspector (IS) Commission?

The NBBI IS Commission qualifies individuals to inspect installed boilers and pressure vessels for installation compliance, inservice condition, and repairs/alterations under the National Board Inspection Code (NBIC). The 85-question open-book exam is given on the last day of a 2-week course.

What is the NBIC?

The National Board Inspection Code (NBIC), also known as NB-23, is the standard for installation, inspection, and repair of boilers and pressure vessels. It has three parts: Part 1 (Installation), Part 2 (Inspection), and Part 3 (Repairs and Alterations). The IS exam is heavily based on NBIC content.

How does the IS Commission differ from the AI Commission?

The IS Commission covers inspection of installed and operating equipment under the NBIC — installation, inservice inspection, and repairs. The AI Commission covers inspection during manufacture of new equipment under the ASME Code. Many inspectors eventually hold both.

What is the NB-380 training program?

NB-380 is the National Board Inservice Inspector Training Program. It requires candidates to complete 300 inspections under the instruction of a National Board Commissioned Inspector in addition to passing the IS Commission exam.

Who employs NBBI Inservice Inspectors?

IS Commissioned Inspectors typically work for state or jurisdictional boiler inspection agencies, insurance companies that provide boiler and machinery coverage, or owner-user inspection organizations. Employer sponsorship is required for the commission.

Is the NBBI IS exam open-book?

Yes. The IS exam is open-book. You may reference the NBIC (Parts 1-3) during the exam. The NBIC is included with your course tuition. Practice navigating the code quickly since the exam is timed.

What experience do I need for the IS Commission?

You need a minimum of 5 credit points from education and experience. Technical degrees and training earn education credits. Each year of boiler/pressure vessel experience earns 1 credit. Employer sponsorship by a jurisdiction or authorized inspection agency is also required.