Piping Pipe Welding and Fabrication 1 — Questions and Answers
Question 1: What welding process is most commonly used for root pass welding on carbon steel process piping?
- Gas Metal Arc Welding (GMAW)
- Shielded Metal Arc Welding (SMAW) or Gas Tungsten Arc Welding (GTAW) (Correct answer)
- Submerged Arc Welding (SAW)
- Flux-Cored Arc Welding (FCAW)
Correct answer: Shielded Metal Arc Welding (SMAW) or Gas Tungsten Arc Welding (GTAW)
SMAW (stick) and GTAW (TIG) are most commonly used for root passes on process piping due to their precision and ability to produce high-quality root beads.
Question 2: What is the purpose of preheat in pipe welding?
- To increase welding speed
- To reduce the risk of hydrogen-induced cracking and improve weld quality (Correct answer)
- To remove mill scale before welding
- To soften the base metal for easier cutting
Correct answer: To reduce the risk of hydrogen-induced cracking and improve weld quality
Preheating reduces the cooling rate of the weld, minimizes hydrogen cracking risk, and reduces thermal shock in the heat-affected zone.
Question 3: What is a Welding Procedure Specification (WPS)?
- A document listing the welder's qualifications
- A document prescribing the variables to be used when making a production weld (Correct answer)
- A record of production weld repairs
- A material certification for filler metal
Correct answer: A document prescribing the variables to be used when making a production weld
A WPS specifies the welding variables (process, filler metal, preheat, interpass temperature, etc.) required to produce a weld meeting code requirements.
Question 4: What does PWHT stand for in pipe fabrication, and why is it performed?
- Pre-Weld Heat Treatment — done before welding to anneal the base metal
- Post-Weld Heat Treatment — done to relieve residual stresses and improve material properties (Correct answer)
- Partial Weld Heat Treatment — used on partial penetration welds only
- Pipe Wall Heat Treatment — to normalize pipe wall thickness
Correct answer: Post-Weld Heat Treatment — done to relieve residual stresses and improve material properties
PWHT is performed after welding to reduce residual stresses, improve ductility, and prevent stress corrosion cracking in susceptible materials.
Question 5: What type of joint preparation is most commonly used for butt welds on pipe with wall thickness greater than 3/16 inch (4.8 mm)?
- Square groove
- Single-V groove bevel (Correct answer)
- Fillet weld
- J-groove
Correct answer: Single-V groove bevel
Single-V groove preparations are standard for pipe butt welds, allowing full penetration and access for root, fill, and cap passes.
Question 6: What is 'interpass temperature control' in pipe welding?
- Controlling the temperature of the welding rod before use
- Limiting the maximum temperature of the weld between passes to prevent metallurgical damage (Correct answer)
- Monitoring ambient temperature during welding
- Setting the preheat temperature for each pass
Correct answer: Limiting the maximum temperature of the weld between passes to prevent metallurgical damage
Interpass temperature is the temperature of the weld area between weld passes; exceeding the maximum can degrade mechanical properties, especially in stainless steels and chrome-moly alloys.
Piping Pipe Welding and Fabrication 1
What welding process is most commonly used for root pass welding on carbon steel process piping?