Pipefitter Pipe Fabrication and Joining 5 — Questions and Answers
Question 1: What does the term 'centerline to end' (CL-E) dimension represent in pipe fabrication?
- The overall installed length of a pipe spool
- The distance from the center of a fitting to the end of its connecting pipe or hub (Correct answer)
- The pipe wall thickness measured from the bore centerline
- The offset distance in an isometric drawing
Correct answer: The distance from the center of a fitting to the end of its connecting pipe or hub
CL-E (centerline to end) is the measured or calculated distance from the center of a fitting to the face or end of the pipe connection, used in pipe layout and spool fabrication.
Question 2: Which type of gasket is most appropriate for a raised-face flange operating in 600-psig high-temperature steam service?
- Full-face rubber sheet gasket
- Spiral-wound metallic gasket with inner and outer rings (Correct answer)
- Compressed non-asbestos fiber sheet gasket
- Ring-type joint (RTJ) soft iron gasket
Correct answer: Spiral-wound metallic gasket with inner and outer rings
Spiral-wound metallic gaskets with inner and outer rings are the industry-standard choice for high-temperature, high-pressure steam on raised-face flanges due to their resilience and leak resistance.
Question 3: A pipefitter is fabricating a 45-degree offset using two 45-degree elbows. The offset distance (rise) is 12 inches. What is the travel (pipe cut length between fittings)?
- 12.00 inches
- 16.97 inches (Correct answer)
- 14.14 inches
- 8.49 inches
Correct answer: 16.97 inches
For a 45-degree offset, travel = offset ÷ sin(45°) = 12 ÷ 0.7071 ≈ 16.97 inches; this is the pipe length between the two elbow centers.
Question 4: Which pipe joining method uses a roll-groove cut into the pipe OD and a mechanical coupling to create the joint?
- Victaulic (grooved mechanical) coupling (Correct answer)
- Compression fitting
- Swage nipple connection
- Dresser coupling
Correct answer: Victaulic (grooved mechanical) coupling
Victaulic (grooved mechanical) couplings engage a roll groove machined or cut into the pipe OD, allowing fast assembly and some pipe deflection without welding.
Question 5: When performing a butt weld on pipe in the 6G (inclined fixed) position, what is the primary challenge for the welder compared to the 1G (flat) position?
- Greater heat input is required because the pipe is inclined
- The weld must be completed in all positions simultaneously without rotating the pipe (Correct answer)
- Preheat requirements are eliminated in the inclined position
- The root opening must be doubled in the inclined position
Correct answer: The weld must be completed in all positions simultaneously without rotating the pipe
The 6G position requires the welder to weld in all positions (flat, vertical, overhead) continuously around a fixed, inclined pipe without rotation, making it the most comprehensive test position.
Question 6: A carbon steel pipe isometric shows a 90-degree elbow with a 'long radius' (LR) designation. For a 4-inch nominal pipe size, what is the centerline radius of this elbow?
- 4 inches
- 6 inches (Correct answer)
- 8 inches
- 3 inches
Correct answer: 6 inches
For long-radius elbows, the centerline radius is 1.5 times the nominal pipe size; for 4-inch pipe, 1.5 × 4 = 6-inch centerline radius.
Question 7: What is the correct sequence of steps when making up a bolted flange joint to ensure even gasket compression?
- Tighten bolts in a clockwise spiral pattern to full torque in one pass
- Tighten bolts in a cross (star) pattern through multiple torque passes (Correct answer)
- Tighten the top bolt first, then work downward to the bottom bolt
- Apply full torque to opposing bolts only until all bolts are snugged
Correct answer: Tighten bolts in a cross (star) pattern through multiple torque passes
Bolts must be tightened in a cross (star) pattern through at least three incremental torque passes to achieve even gasket seating and prevent joint leakage.
Pipefitter Pipe Fabrication and Joining 5
What does the term 'centerline to end' (CL-E) dimension represent in pipe fabrication?