SPED Piping Math & Dimensional Calculations

Question 1

What is the center-to-end dimension of a 6" NPS long-radius 90° butt-weld elbow per ASME B16.9?

Accepted Answer

9 inches

Answer

For NPS 3/4 and larger, a long-radius 90° elbow has a center-to-end dimension of 1.5 × NPS, so 1.5 × 6 = 9 inches. A short-radius elbow is 1.0 × NPS.

Question 2

A 45° offset has a set (offset) of 24 inches. What is the travel (center-to-center length along the 45° run)?

Accepted Answer

33.94 in

Answer

For a 45° offset, travel = set × 1.414 (the cosecant of 45°). So 24 × 1.414 ≈ 33.94 inches.

Question 3

A rolling offset has a roll of 9 inches and a rise of 12 inches. What is the true offset?

Accepted Answer

15 inches

Answer

True offset = √(roll² + rise²) = √(81 + 144) = √225 = 15 inches. This is a 3-4-5 right triangle scaled by 3.

Question 4

Two 4" NPS long-radius 90° elbows are 60 inches apart center-to-center. Allowing a 1/8" root gap at each weld, what is the cut length of the straight pipe between them?

Accepted Answer

47.75 in

Answer

Each 4" LR elbow takes out 6" (1.5 × 4). Cut length = 60 − 6 − 6 − (2 × 0.125) = 47.75 inches.

Question 5

A 40-foot gravity drain line must slope 1/8 inch per foot. What is the total drop?

Accepted Answer

5 inches

Answer

Total drop = slope × length = 0.125 in/ft × 40 ft = 5 inches.

(SPED) Society of Piping Engineers and Designers Certification Practice Test

(SPED) Society of Piping Engineers and Designers Certification Practice Test

SPED Piping Math & Dimensional Calculations