CPM CPM - Certified Plant Mechanic Welding and Fabrication Techniques 2 — Questions and Answers
Question 1: What is the operating principle of a plasma cutter used in plant fabrication and maintenance?
- Uses a high-frequency laser beam to melt metal
- Uses an ionized high-velocity gas jet to cut electrically conductive metals (Correct answer)
- Uses a rotating abrasive wheel to cut through metal
- Uses oxy-acetylene combustion to oxidize and cut metal
Correct answer: Uses an ionized high-velocity gas jet to cut electrically conductive metals
Plasma cutting passes an electrical arc through a gas (air, nitrogen, or argon) to create a plasma jet hot enough to melt and blow through conductive materials.
Question 2: In oxy-acetylene cutting, what is the minimum safe oxygen concentration that must be maintained in a confined work area?
- 15%
- 17%
- 19.5% (Correct answer)
- 22%
Correct answer: 19.5%
OSHA requires a minimum of 19.5% oxygen in a work environment; below this level the atmosphere is oxygen-deficient and dangerous to workers.
Question 3: What type of weld joint is formed when two pieces of metal are placed end-to-end in the same plane?
- Lap joint
- T-joint
- Corner joint
- Butt joint (Correct answer)
Correct answer: Butt joint
A butt joint joins two pieces in the same plane along their edges and is commonly used on pipe, plate, and structural members.
Question 4: What is the primary cause of porosity in a completed weld bead?
- Excessive preheat temperature
- Gas trapped in the weld pool during solidification (Correct answer)
- Too slow a travel speed
- Undersize electrode diameter
Correct answer: Gas trapped in the weld pool during solidification
Porosity results when hydrogen, oxygen, or nitrogen gas becomes entrapped in the solidifying weld metal, forming voids that weaken the weld.
Question 5: What is the purpose of back purging with inert gas when welding austenitic stainless steel pipe?
- Cool the exterior weld bead quickly
- Protect the inside (root) of the weld from oxidation and sugaring (Correct answer)
- Increase weld pool fluidity
- Reduce arc voltage requirements
Correct answer: Protect the inside (root) of the weld from oxidation and sugaring
Back purging displaces oxygen from the pipe's bore so the root pass is not oxidized, preventing 'sugaring' and maintaining corrosion resistance in the HAZ.
Question 6: In welding terminology, what does the term 'penetration' refer to?
- Distance the electrode extends beyond the contact tip
- Speed at which the weld pool travels along the joint
- Depth to which fusion extends into the base metal from the weld surface (Correct answer)
- Angle of the electrode relative to the base plate
Correct answer: Depth to which fusion extends into the base metal from the weld surface
Penetration describes how deeply the weld fusion zone extends into the base metal; insufficient penetration creates a weak joint that may fail under load.
CPM CPM - Certified Plant Mechanic Welding and Fabrication Techniques 2
What is the operating principle of a plasma cutter used in plant fabrication and maintenance?