API 653 Welding & Metallurgy 5 — Questions and Answers
Question 1: What is the purpose of a 'temper bead welding' technique when PWHT cannot be performed on an in-service API 653 tank?
- To increase deposition rate and reduce welding time
- To refine and temper the HAZ grain structure using the heat from successive weld passes, substituting for furnace PWHT (Correct answer)
- To apply multiple weld beads for cosmetic appearance improvement
- To prevent porosity by controlling travel speed on each pass
Correct answer: To refine and temper the HAZ grain structure using the heat from successive weld passes, substituting for furnace PWHT
Temper bead welding uses carefully controlled successive passes so each bead's heat cycle refines and tempers the coarse-grained HAZ of the previous pass, improving toughness without a furnace heat treatment.
Question 2: In API 653, which destructive test is used on a weld procedure qualification test coupon to verify adequate fusion and verify resistance to cracking at the weld root?
- Charpy V-notch impact test
- Guided bend test (Correct answer)
- Rockwell hardness test
- Macro-etch test
Correct answer: Guided bend test
The guided bend test bends the weld coupon around a prescribed die to open and reveal lack-of-fusion, incomplete penetration, or cracking at the root or face of the weld.
Question 3: When API 653 requires a Charpy V-notch (CVN) impact test for a weld procedure, what property is being verified?
- Tensile strength at elevated temperature
- Notch toughness (fracture energy) at a specified low temperature (Correct answer)
- Fatigue resistance under cyclic loading
- Creep resistance at sustained elevated temperature
Correct answer: Notch toughness (fracture energy) at a specified low temperature
CVN tests measure the energy absorbed when a notched specimen is broken at a specified temperature, verifying that the weld and HAZ have adequate toughness to resist brittle fracture at minimum design metal temperature.
Question 4: Which type of corrosion preferentially attacks carbon steel welds in crude oil tanks due to differential aeration between the weld and base metal?
- Crevice corrosion beneath the weld cap
- Galvanic corrosion driven by weld-to-base-metal potential difference
- Microbiologically influenced corrosion (MIC) at the weld root
- Concentration cell corrosion at the weld toe where oxygen is depleted (Correct answer)
Correct answer: Concentration cell corrosion at the weld toe where oxygen is depleted
Oxygen concentration cells form at geometric transitions like weld toes, where the restricted geometry limits oxygen replenishment, making that area anodic relative to well-aerated base metal and accelerating corrosion.
Question 5: According to API 653, when a tank shell repair weld is made on a shell that originally required impact testing, what additional requirement applies to the repair weld procedure qualification?
- The repair WPS requires only a hardness test to be considered qualified
- The repair WPS must also be qualified with CVN impact tests meeting the original specification requirements (Correct answer)
- Impact testing is waived for repair welds because the repair area is small
- The repair WPS is automatically qualified if the original construction WPS is on file
Correct answer: The repair WPS must also be qualified with CVN impact tests meeting the original specification requirements
API 653 requires that repair welding procedures meet all original construction requirements, including impact testing, when the base material specification mandated impact testing.
Question 6: What is the metallurgical significance of the 'fusion line' (bond line) in a steel weld, and why is it often the location of cracking?
- It is where the weld metal fully melted and has the highest ductility
- It is the interface between fully melted weld metal and partially melted base metal, with coarse grain structure and potential for high residual stress concentration (Correct answer)
- It is where flux inclusions accumulate and reduce mechanical properties
- It is the centerline of the weld where solidification shrinkage is greatest
Correct answer: It is the interface between fully melted weld metal and partially melted base metal, with coarse grain structure and potential for high residual stress concentration
The fusion line has the coarsest grain size (grain growth region), the highest cooling rate, and the greatest residual tensile stress, making it the most common location for heat-affected zone cracking.
Question 7: Per API 653, which condition would require that a completed weld repair be radiographed rather than ultrasonically tested as the sole volumetric NDE method?
- The repair weld is longer than 12 inches
- The engineer of record specifies radiography as required by the original construction code or due to access limitations for UT (Correct answer)
- The weld was made using GMAW (MIG) process
- The tank was built after 1990
Correct answer: The engineer of record specifies radiography as required by the original construction code or due to access limitations for UT
The choice of volumetric NDE method (RT vs. UT) is governed by the applicable code, the engineer's specification, and practical access; for some joint configurations and code requirements, RT is specifically required.
API 653 Welding & Metallurgy 5
What is the purpose of a 'temper bead welding' technique when PWHT cannot be performed on an in-service API 653 tank?