Pipefitter Pipe Fabrication Methods 5 — Questions and Answers
Question 1: What is the purpose of a 'line-up clamp' (internal lineup clamp) used during pipe spool fabrication?
- To hold the grinding wheel in place during bevel preparation
- To align two pipe ends concentrically and hold them at the correct root gap before welding (Correct answer)
- To measure the internal diameter of the pipe
- To support the pipe on rolling stands
Correct answer: To align two pipe ends concentrically and hold them at the correct root gap before welding
An internal lineup clamp is inserted into both pipe ends to ensure they are concentric and at the correct root gap, preventing misalignment during the root pass.
Question 2: When fabricating a lateral (Y-branch) fitting, the branch pipe intersects the header at an angle typically less than 90 degrees. What is the most critical layout challenge?
- Selecting the correct pipe schedule
- Developing the accurate compound saddle cut profile on both the header and branch pipe (Correct answer)
- Choosing the correct flange rating
- Determining the pipe insulation thickness
Correct answer: Developing the accurate compound saddle cut profile on both the header and branch pipe
The compound saddle cut must accurately match the curvature of the header on the branch pipe end so the joint fits tightly with minimal gap before welding.
Question 3: In fabrication, what is 'back-purging' and when is it required?
- Cleaning the weld bead with a wire brush after each pass
- Filling the inside of a pipe with inert gas to protect the weld root from oxidation, required for stainless steel and reactive alloys (Correct answer)
- Reversing the shielding gas flow direction
- Applying flux paste inside the pipe joint
Correct answer: Filling the inside of a pipe with inert gas to protect the weld root from oxidation, required for stainless steel and reactive alloys
Back-purging floods the pipe interior with argon or nitrogen to exclude oxygen from the weld root, preventing oxidation (sugaring) in stainless steel and titanium welds.
Question 4: Which ASME standard governs the dimensional requirements for butt-welding fittings used in pipe fabrication?
- ASME B16.5
- ASME B16.9 (Correct answer)
- ASME B31.3
- ASME B16.11
Correct answer: ASME B16.9
ASME B16.9 covers factory-made wrought buttwelding fittings, specifying dimensions, tolerances, and ratings for elbows, tees, reducers, and caps.
Question 5: When calculating the cut length of pipe between two 90-degree long-radius elbows in the same plane, what must be subtracted from the face-to-face dimension?
- The pipe outer diameter only
- The takeout (end-to-center) of each elbow — one for each end (Correct answer)
- The pipe wall thickness times two
- The weld gap for each joint only
Correct answer: The takeout (end-to-center) of each elbow — one for each end
The cut length equals the face-to-face distance minus the takeout of each elbow (one at each end), ensuring the assembled spool matches the drawing dimension.
Question 6: What is the function of a 'swage nipple' (swaged nipple) in pipe fabrication?
- To repair a cracked pipe section
- To reduce from one pipe size to a smaller size in a short face-to-face dimension, used where space is limited (Correct answer)
- To increase pipe wall thickness at a weld joint
- To provide a threaded branch outlet on a header
Correct answer: To reduce from one pipe size to a smaller size in a short face-to-face dimension, used where space is limited
A swage nipple is a compact concentric or eccentric reducer used where a standard reducing fitting would not fit, available in threaded or plain ends.
Question 7: During hydrostatic testing of a fabricated pipe spool, what is the standard hold time required by ASME B31.3 at the test pressure before inspection?
- 5 minutes
- 10 minutes (Correct answer)
- 30 minutes
- 60 minutes
Correct answer: 10 minutes
ASME B31.3 requires a minimum hold time of 10 minutes at hydrostatic test pressure before inspection for leaks begins.
Pipefitter Pipe Fabrication Methods 5
What is the purpose of a 'line-up clamp' (internal lineup clamp) used during pipe spool fabrication?