Pipefitter Pipe Fabrication Methods 4 — Questions and Answers
Question 1: What is the minimum preheat requirement purpose when welding on high-carbon or alloy steel pipe during fabrication?
- To speed up welding travel speed
- To reduce the risk of hydrogen-induced cracking in the heat-affected zone (Correct answer)
- To increase the weld bead width
- To eliminate the need for post-weld heat treatment
Correct answer: To reduce the risk of hydrogen-induced cracking in the heat-affected zone
Preheat slows the cooling rate of the weld and HAZ, reducing the risk of hydrogen-induced (cold) cracking in hardenable steel alloys.
Question 2: In shop fabrication, what is the primary advantage of using a pipe positioner (turning roll) during welding?
- It eliminates the need for filler metal
- It keeps the weld in the flat (1G) position throughout the joint (Correct answer)
- It preheats the base metal automatically
- It measures wall thickness during welding
Correct answer: It keeps the weld in the flat (1G) position throughout the joint
A pipe positioner rotates the pipe so the welder can maintain the flat 1G position, producing higher-quality, faster welds.
Question 3: Which pipe end preparation is required for a standard butt weld joint on pipe with wall thickness greater than 3/16 inch?
- Plain square cut end
- Beveled end at approximately 37.5 degrees (Correct answer)
- Threaded end with sealant
- Socket end with 0.062-inch shoulder
Correct answer: Beveled end at approximately 37.5 degrees
ASME B31 codes require pipe ends thicker than 3/16 inch to be beveled at approximately 37.5 degrees to allow full penetration groove welds.
Question 4: What is a 'spool' in the context of pipe fabrication?
- A reel used to store welding wire
- A pre-fabricated pipe assembly consisting of pipe, fittings, and flanges ready for field installation (Correct answer)
- A type of pipe hanger support
- A threaded pipe connector
Correct answer: A pre-fabricated pipe assembly consisting of pipe, fittings, and flanges ready for field installation
A spool is a shop-fabricated pipe assembly — a sub-section of piping complete with fittings and flanges — transported to the field for installation.
Question 5: When using an oxy-fuel torch to cut pipe for fabrication, what is the function of the cutting oxygen lever?
- It controls the preheat flame temperature
- It releases a high-pressure stream of oxygen that oxidizes and blows away the molten metal (Correct answer)
- It adjusts the fuel gas flow rate
- It ignites the torch tip
Correct answer: It releases a high-pressure stream of oxygen that oxidizes and blows away the molten metal
The cutting oxygen lever opens a valve that directs a high-pressure oxygen stream onto the preheated metal, causing rapid oxidation and blowing the slag away.
Question 6: Which type of pipe flange is typically used as a companion flange on equipment nozzles and allows for slight angular misalignment during assembly?
- Weld neck flange
- Lap joint flange with stub end (Correct answer)
- Slip-on flange
- Blind flange
Correct answer: Lap joint flange with stub end
A lap joint flange pairs with a stub end and can rotate freely around it, allowing bolt holes to be aligned and accommodating minor angular misalignment.
Question 7: What does 'center-to-center' (C-C) dimension mean on a piping isometric drawing?
- The outer diameter of the pipe
- The distance measured from the center of one fitting or component to the center of another (Correct answer)
- The wall thickness of the pipe
- The gap between two pipe flanges
Correct answer: The distance measured from the center of one fitting or component to the center of another
Center-to-center is the dimension from the centerline intersection of one fitting to the centerline intersection of another, used to lay out piping runs.
Pipefitter Pipe Fabrication Methods 4
What is the minimum preheat requirement purpose when welding on high-carbon or alloy steel pipe during fabrication?