CPM CPM - Certified Plant Mechanic Welding and Fabrication Techniques 1 — Questions and Answers
Question 1: What does the acronym MIG stand for in the MIG welding process?
- Metal Inert Gas (Correct answer)
- Manual Iron Grind
- Magnetic Induction Gun
- Metal Ionization Gauge
Correct answer: Metal Inert Gas
MIG (Metal Inert Gas) welding, also called GMAW (Gas Metal Arc Welding), uses a continuously fed wire electrode shielded by an inert or semi-inert gas.
Question 2: What shielding gas mixture is most commonly used when MIG welding mild steel in a plant maintenance setting?
- Pure argon
- Pure CO2
- 75% argon / 25% CO2 (C25) (Correct answer)
- Helium and nitrogen blend
Correct answer: 75% argon / 25% CO2 (C25)
C25 (75% Ar / 25% CO2) provides a stable arc, good penetration, and reduced spatter, making it the most common choice for mild steel MIG welding.
Question 3: Which welding process uses a non-consumable tungsten electrode and is best suited for precision welds on stainless steel and aluminum?
- SMAW (Stick)
- FCAW (Flux-Cored)
- GTAW (TIG) (Correct answer)
- SAW (Submerged Arc)
Correct answer: GTAW (TIG)
GTAW (Gas Tungsten Arc Welding), commonly called TIG, uses a non-consumable tungsten electrode and filler rod added separately, allowing precise, high-quality welds.
Question 4: In SMAW (Stick) welding, what is the primary function of the flux coating on the electrode?
- Conduct electricity to the base metal
- Protect the weld pool from atmospheric contamination (Correct answer)
- Preheat the base metal
- Act as filler metal only
Correct answer: Protect the weld pool from atmospheric contamination
The flux coating melts and forms a slag that shields the molten weld pool from oxygen and nitrogen in the atmosphere, preventing porosity and oxidation.
Question 5: What is the purpose of preheating base metal before welding in plant maintenance applications?
- Increase electrode burn-off rate
- Reduce the risk of hydrogen cracking in high-carbon or thick materials (Correct answer)
- Speed up weld pool solidification
- Lower the required shielding gas flow rate
Correct answer: Reduce the risk of hydrogen cracking in high-carbon or thick materials
Preheating slows the cooling rate after welding, reducing thermal shock and the formation of hard, brittle microstructures that can crack in high-carbon or alloy steels.
Question 6: What does PWHT stand for and when is it typically required in plant fabrication?
- Post Weld Heat Treatment; used to relieve residual stresses and improve toughness after welding (Correct answer)
- Pre-Weld Handling Technique; used to clean metal before welding
- Partial Weld Heat Test; a non-destructive test method
- Pressurized Weld Hardness Test; used to measure weld hardness
Correct answer: Post Weld Heat Treatment; used to relieve residual stresses and improve toughness after welding
PWHT (Post Weld Heat Treatment) involves controlled heating and cooling of a completed weld to relieve residual stresses, temper hard zones, and meet code requirements.
CPM CPM - Certified Plant Mechanic Welding and Fabrication Techniques 1
What does the acronym MIG stand for in the MIG welding process?