Pipefitter Pipefitting Math and Calculations 5 — Questions and Answers
Question 1: A pipe drops 3 inches over a 10-foot horizontal run. What is the slope expressed as inches per foot?
- 0.25 in/ft
- 0.30 in/ft (Correct answer)
- 0.33 in/ft
- 0.50 in/ft
Correct answer: 0.30 in/ft
Slope = 3 inches ÷ 10 feet = 0.30 inches per foot.
Question 2: How many threads per inch (TPI) are on a 2-inch NPT pipe thread?
- 8 TPI
- 10 TPI
- 11.5 TPI (Correct answer)
- 14 TPI
Correct answer: 11.5 TPI
2-inch NPT pipe threads have 11.5 threads per inch per the ASME B1.20.1 standard.
Question 3: What is the circumference of a pipe with an outside diameter of 10.75 inches (10-inch nominal)?
- 31.42 inches
- 33.77 inches (Correct answer)
- 35.11 inches
- 38.24 inches
Correct answer: 33.77 inches
Circumference = π × OD = 3.1416 × 10.75 ≈ 33.77 inches.
Question 4: A 5-piece equal-spread 45° offset uses 4 fittings and covers a 24-inch set. What is the spread between each fitting center?
- 4 inches
- 6 inches (Correct answer)
- 8 inches
- 10 inches
Correct answer: 6 inches
In a 5-piece equal-spread offset with 4 fittings, each fitting covers 24 ÷ 4 = 6 inches of set.
Question 5: A hydrostatic test requires pressurizing a system to 1.5 times the design pressure of 400 psig. What is the test pressure?
- 500 psig
- 550 psig
- 600 psig (Correct answer)
- 650 psig
Correct answer: 600 psig
Test pressure = 1.5 × 400 psig = 600 psig, which is the standard hydrostatic test multiplier.
Question 6: The flow velocity in a 3-inch pipe (ID = 3.068 in) is 8 ft/s. If the pipe transitions to a 6-inch pipe (ID = 6.065 in), what is the approximate velocity in the larger pipe?
- 1.0 ft/s
- 2.0 ft/s (Correct answer)
- 4.0 ft/s
- 6.0 ft/s
Correct answer: 2.0 ft/s
Using continuity (A₁V₁ = A₂V₂): area ratio ≈ (3.068/6.065)² ≈ 0.256, so V₂ ≈ 8 × 0.256 ≈ 2.05 ft/s.
Question 7: A pipefitter calculates that 3 inches of pipe is needed per degree of bend on a 2-inch pipe. How long a pipe section is needed to fabricate a 30° bend?
- 60 inches
- 90 inches (Correct answer)
- 30 inches
- 45 inches
Correct answer: 90 inches
Required length = 3 inches/degree × 30 degrees = 90 inches of pipe.
Pipefitter Pipefitting Math and Calculations 5
A pipe drops 3 inches over a 10-foot horizontal run.
What is the slope expressed as inches per foot?