SPED Pipe Fabrication & Welding Standards 3 — Questions and Answers
Question 1: What is the significance of the 'essential variable' concept in ASME Section IX welding qualifications?
- It defines the variables that require welder re-qualification only
- It identifies variables whose change requires requalification of the WPS (Correct answer)
- It lists variables that may be freely adjusted without documentation
- It specifies the variables that affect only the visual appearance of the weld
Correct answer: It identifies variables whose change requires requalification of the WPS
Essential variables are those welding parameters where a change beyond specified limits is believed to affect the mechanical properties of the weld, requiring a new PQR and revised WPS.
Question 2: According to ASME B31.3, what type of joint must be used for all fluid services in Category M (highly toxic) service?
- Socket-weld joints up to 2-inch NPS
- Threaded joints for sizes 1-inch and smaller
- Butt-welded joints for all sizes (Correct answer)
- Flanged joints with full-face gaskets
Correct answer: Butt-welded joints for all sizes
ASME B31.3 Chapter VIII for Category M service requires butt-welded joints throughout to minimize leakage risk for highly toxic fluids.
Question 3: During hydrostatic pressure testing of a piping system per ASME B31.3, the test pressure must be at least:
- 1.0 times the design pressure
- 1.25 times the design pressure adjusted for temperature
- 1.5 times the design pressure adjusted for temperature (Correct answer)
- 2.0 times the design pressure at ambient conditions
Correct answer: 1.5 times the design pressure adjusted for temperature
ASME B31.3 paragraph 345.4.2 requires hydrostatic test pressure of at least 1.5 times the design pressure, adjusted by the ratio of allowable stress at test temperature to allowable stress at design temperature.
Question 4: What is the maximum allowable mismatch (high-low) between pipe wall interiors at a butt weld per ASME B31.3 for normal fluid service?
- 1/16 inch (1.6 mm)
- 1/8 inch (3.2 mm) or 25% of wall thickness, whichever is less (Correct answer)
- 3/16 inch (4.8 mm)
- 1/4 inch (6.4 mm)
Correct answer: 1/8 inch (3.2 mm) or 25% of wall thickness, whichever is less
ASME B31.3 paragraph 328.4.3 limits weld joint internal misalignment to 1/8 inch or 25% of the thinner component wall thickness, whichever is less.
Question 5: Which welding process is classified as a 'low hydrogen' process, making it preferred for welding higher-strength and thicker carbon steel pipe?
- SMAW with EXX10 cellulosic electrodes
- GMAW (MIG) with ER70S-6 wire
- SMAW with EXX18 low-hydrogen electrodes (Correct answer)
- OFW (oxy-fuel welding)
Correct answer: SMAW with EXX18 low-hydrogen electrodes
EXX18 electrodes have a low-hydrogen flux coating that limits diffusible hydrogen in the weld deposit, reducing the risk of hydrogen-induced cracking in susceptible steels.
Question 6: In pipe spool fabrication, what is the purpose of a 'weld map'?
- A diagram showing the travel speed and heat input for each weld pass
- A document that identifies weld joint locations, weld numbers, and applicable WPS for each weld on a spool (Correct answer)
- A quality checklist for post-weld heat treatment activities
- A drawing showing the preheat zone dimensions around each weld
Correct answer: A document that identifies weld joint locations, weld numbers, and applicable WPS for each weld on a spool
A weld map is an isometric or orthographic drawing that assigns unique weld numbers to each joint, cross-referencing the applicable WPS, welder ID, and NDE requirements for full traceability.
Question 7: What does the AWS classification 'ER308L' designate for stainless steel filler metal?
- An electrode/rod for welding P-No. 8 austenitic stainless with low carbon content (Correct answer)
- An electrode for high-temperature chromium-moly alloy steels
- A bare rod used exclusively for gas tungsten arc welding of duplex stainless
- A flux-cored electrode for welding 9% nickel cryogenic service pipe
Correct answer: An electrode/rod for welding P-No. 8 austenitic stainless with low carbon content
ER308L is an electrode/rod (ER) matching 308 stainless composition with low carbon (L ≤0.03%) to minimize sensitization, used to weld 304/304L base material.
SPED Pipe Fabrication & Welding Standards 3
What is the significance of the 'essential variable' concept in ASME Section IX welding qualifications?