Boiler Inspector Certification
Examination Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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Question 1
A fire-tube boiler is rated at 200 boiler horsepower. What is the approximate
heating surface area required if the boiler operates at a maximum allowable
working pressure (MAWP) of 150 psig and uses the standard rule of 10 square feet
of heating surface per boiler horsepower?
A) 1,500 sq ft
B) 2,000 sq ft
C) 2,500 sq ft
D) 3,000 sq ft
Answer: B) 2,000 sq ft
Rationale: Standard rule: 1 boiler horsepower = 10 sq ft of heating surface for
fire-tube boilers. Therefore, 200 hp × 10 = 2,000 sq ft. This is a fundamental
calculation for inspectors when verifying nameplate data against actual
measured surface.
Question 2
During an internal inspection of a water-tube boiler, you observe severe pitting on
the water side of the lower drum. Which of the following is the most likely
primary cause?
,A) Oxygen corrosion
B) Caustic embrittlement
C) Hydrogen embrittlement
D) Fatigue cracking
Answer: A) Oxygen corrosion
Rationale: Pitting on the water side, especially in the lower drum, is classic
dissolved oxygen corrosion. Oxygen pitting is localized and occurs where oxygen
concentration cells form. Caustic embrittlement causes intergranular cracking,
not pitting. Hydrogen embrittlement is associated with high-temperature
hydrogen attack. Fatigue cracking is mechanical.
Question 3
What is the minimum required thickness for a carbon steel boiler shell subjected
to an internal pressure of 300 psig, with a shell diameter of 48 inches, joint
efficiency of 0.85, and allowable stress of 15,000 psi? Use the ASME BPVC formula
for cylindrical shell thickness.
A) 0.375 in
B) 0.500 in
C) 0.625 in
D) 0.750 in
Answer: C) 0.625 in
Rationale: Using t = (P × R) / (S × E – 0.6P) for pressure vessels. R = 24 in. t = (300
× 24) / (15,000 × 0.85 – 0.6×300) = 7200 / (12750 – 180) = 7200/12570 = 0.573 in.
The next standard nominal thickness is 0.625 in (5/8 inch). Inspectors must
round up to the nearest standard plate thickness.
Question 4
Which non-destructive examination (NDE) method is most suitable for detecting
subsurface flaws in thick boiler drum welds during a shutdown inspection?
A) Liquid penetrant testing
,B) Magnetic particle testing
C) Ultrasonic testing
D) Eddy current testing
Answer: C) Ultrasonic testing
Rationale: Ultrasonic testing (UT) penetrates deep into thick sections and
detects internal flaws like inclusions, lack of fusion, and cracks. Liquid penetrant
and magnetic particle are surface-only. Eddy current is limited to near-surface
and conductive materials.
Question 5
A boiler has a safety valve set to pop at 250 psig. The accumulated pressure during
a full-flow test must not exceed what percentage of the MAWP, per ASME Section
I?
A) 3%
B) 5%
C) 6%
D) 10%
Answer: C) 6%
Rationale: ASME Section I requires that for power boilers, the accumulated
pressure during safety valve discharge must not exceed 6% of the MAWP (or 3%
for certain cases, but the standard maximum accumulation for boilers is 6%). For
a 250 psig set, accumulation limit = 250 × 1.06 = 265 psig.
Question 6
What is the primary function of a staybolt in a fire-tube boiler?
A) To support the furnace crown
B) To reinforce flat surfaces against internal pressure
C) To attach the boiler to the foundation
D) To provide a mounting point for gauges
, Answer: B) To reinforce flat surfaces against internal pressure
Rationale: Staybolts are tension members used to brace flat or curved plates
(like the shell and tube sheets) to prevent bulging or rupture due to internal
pressure. They do not support the crown primarily—that is done by crown stays
or arch tubes.
Question 7
When conducting a hydrostatic test on a boiler that has been repaired, the test
pressure is typically:
A) 1.5 × MAWP
B) 1.25 × MAWP
C) 2.0 × MAWP
D) Equal to MAWP
Answer: A) 1.5 × MAWP
Rationale: ASME Code and NBIC require a hydrostatic test at 1.5 times the
MAWP for new construction or major repairs, but at least 1.25 times for minor
repairs. However, the standard for a complete hydro test after major alteration
is 1.5 × MAWP, with temperature and stress considerations.
Question 8
Which type of boiler water treatment is most effective at preventing caustic
embrittlement?
A) Phosphate treatment
B) Chelant treatment
C) Coordinated pH/phosphate control
D) Sodium sulfite scavenging
Answer: C) Coordinated pH/phosphate control
Rationale: Caustic embrittlement occurs when free caustic soda concentrates in
crevices. Coordinated pH/phosphate control maintains a phosphate-to-caustic
Examination Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
Question 1
A fire-tube boiler is rated at 200 boiler horsepower. What is the approximate
heating surface area required if the boiler operates at a maximum allowable
working pressure (MAWP) of 150 psig and uses the standard rule of 10 square feet
of heating surface per boiler horsepower?
A) 1,500 sq ft
B) 2,000 sq ft
C) 2,500 sq ft
D) 3,000 sq ft
Answer: B) 2,000 sq ft
Rationale: Standard rule: 1 boiler horsepower = 10 sq ft of heating surface for
fire-tube boilers. Therefore, 200 hp × 10 = 2,000 sq ft. This is a fundamental
calculation for inspectors when verifying nameplate data against actual
measured surface.
Question 2
During an internal inspection of a water-tube boiler, you observe severe pitting on
the water side of the lower drum. Which of the following is the most likely
primary cause?
,A) Oxygen corrosion
B) Caustic embrittlement
C) Hydrogen embrittlement
D) Fatigue cracking
Answer: A) Oxygen corrosion
Rationale: Pitting on the water side, especially in the lower drum, is classic
dissolved oxygen corrosion. Oxygen pitting is localized and occurs where oxygen
concentration cells form. Caustic embrittlement causes intergranular cracking,
not pitting. Hydrogen embrittlement is associated with high-temperature
hydrogen attack. Fatigue cracking is mechanical.
Question 3
What is the minimum required thickness for a carbon steel boiler shell subjected
to an internal pressure of 300 psig, with a shell diameter of 48 inches, joint
efficiency of 0.85, and allowable stress of 15,000 psi? Use the ASME BPVC formula
for cylindrical shell thickness.
A) 0.375 in
B) 0.500 in
C) 0.625 in
D) 0.750 in
Answer: C) 0.625 in
Rationale: Using t = (P × R) / (S × E – 0.6P) for pressure vessels. R = 24 in. t = (300
× 24) / (15,000 × 0.85 – 0.6×300) = 7200 / (12750 – 180) = 7200/12570 = 0.573 in.
The next standard nominal thickness is 0.625 in (5/8 inch). Inspectors must
round up to the nearest standard plate thickness.
Question 4
Which non-destructive examination (NDE) method is most suitable for detecting
subsurface flaws in thick boiler drum welds during a shutdown inspection?
A) Liquid penetrant testing
,B) Magnetic particle testing
C) Ultrasonic testing
D) Eddy current testing
Answer: C) Ultrasonic testing
Rationale: Ultrasonic testing (UT) penetrates deep into thick sections and
detects internal flaws like inclusions, lack of fusion, and cracks. Liquid penetrant
and magnetic particle are surface-only. Eddy current is limited to near-surface
and conductive materials.
Question 5
A boiler has a safety valve set to pop at 250 psig. The accumulated pressure during
a full-flow test must not exceed what percentage of the MAWP, per ASME Section
I?
A) 3%
B) 5%
C) 6%
D) 10%
Answer: C) 6%
Rationale: ASME Section I requires that for power boilers, the accumulated
pressure during safety valve discharge must not exceed 6% of the MAWP (or 3%
for certain cases, but the standard maximum accumulation for boilers is 6%). For
a 250 psig set, accumulation limit = 250 × 1.06 = 265 psig.
Question 6
What is the primary function of a staybolt in a fire-tube boiler?
A) To support the furnace crown
B) To reinforce flat surfaces against internal pressure
C) To attach the boiler to the foundation
D) To provide a mounting point for gauges
, Answer: B) To reinforce flat surfaces against internal pressure
Rationale: Staybolts are tension members used to brace flat or curved plates
(like the shell and tube sheets) to prevent bulging or rupture due to internal
pressure. They do not support the crown primarily—that is done by crown stays
or arch tubes.
Question 7
When conducting a hydrostatic test on a boiler that has been repaired, the test
pressure is typically:
A) 1.5 × MAWP
B) 1.25 × MAWP
C) 2.0 × MAWP
D) Equal to MAWP
Answer: A) 1.5 × MAWP
Rationale: ASME Code and NBIC require a hydrostatic test at 1.5 times the
MAWP for new construction or major repairs, but at least 1.25 times for minor
repairs. However, the standard for a complete hydro test after major alteration
is 1.5 × MAWP, with temperature and stress considerations.
Question 8
Which type of boiler water treatment is most effective at preventing caustic
embrittlement?
A) Phosphate treatment
B) Chelant treatment
C) Coordinated pH/phosphate control
D) Sodium sulfite scavenging
Answer: C) Coordinated pH/phosphate control
Rationale: Caustic embrittlement occurs when free caustic soda concentrates in
crevices. Coordinated pH/phosphate control maintains a phosphate-to-caustic
