API 653 Material Evaluation 4 — Questions and Answers
Question 1: The carbon equivalent (CE) formula is used during material evaluation primarily to assess:
- Corrosion resistance of the plate
- Weldability and susceptibility to heat-affected zone cracking (Correct answer)
- Tensile strength of the material
- Suitability for low-temperature service
Correct answer: Weldability and susceptibility to heat-affected zone cracking
Carbon equivalent quantifies the combined effect of alloying elements on hardenability, which directly affects weldability and HAZ cracking risk.
Question 2: During material verification of an older tank with unknown plate specifications, which field test can provide a preliminary indication of the steel grade?
- Brinell hardness testing (Correct answer)
- Magnetic particle inspection
- Dye penetrant testing
- Hydrostatic pressure test
Correct answer: Brinell hardness testing
Brinell or portable hardness testing can provide an approximate correlation to tensile strength, helping to identify unknown steel grades in the field.
Question 3: API 653 allows the use of existing shell material for fitness-for-service if it meets minimum thickness requirements, even if the original mill certification is unavailable, provided:
- The tank was built before 1970
- Chemical and mechanical tests confirm suitability (Correct answer)
- The product stored is non-hazardous
- The inspector has 10+ years of experience
Correct answer: Chemical and mechanical tests confirm suitability
Without mill test records, API 653 requires that representative samples be tested chemically and mechanically to confirm the material meets the required specification.
Question 4: What type of non-destructive examination is most effective for detecting laminations in rolled steel plate used for tank shells?
- Magnetic particle testing (MT)
- Dye penetrant testing (PT)
- Ultrasonic shear-wave testing
- Straight-beam ultrasonic testing (UT) (Correct answer)
Correct answer: Straight-beam ultrasonic testing (UT)
Straight-beam (compression wave) UT is sensitive to planar discontinuities parallel to the plate surface, such as laminations.
Question 5: A tank shell plate is identified as ASTM A573 Grade 70. The minimum yield strength of this material is:
- 30 ksi
- 42 ksi (Correct answer)
- 50 ksi
- 70 ksi
Correct answer: 42 ksi
ASTM A573 Grade 70 has a minimum tensile strength of 70 ksi and a minimum yield strength of 42 ksi.
Question 6: When reviewing corrosion rate data for a tank bottom, the short-term corrosion rate is calculated using measurements from:
- Original construction thickness and the most recent inspection
- The last two consecutive inspections (Correct answer)
- All inspection data averaged over the tank life
- Only the most recent inspection reading
Correct answer: The last two consecutive inspections
The short-term corrosion rate uses thickness loss between the two most recent inspections divided by the time interval, capturing recent corrosion trends.
Question 7: Hydrogen blistering in tank shell plates is most commonly found in tanks storing:
- Light distillates such as gasoline
- Produced water with high H₂S content (Correct answer)
- Fresh water for fire suppression
- Ethanol blends
Correct answer: Produced water with high H₂S content
Hydrogen blistering occurs when atomic hydrogen generated by sulfide-promoted corrosion diffuses into the steel and recombines at internal voids, a common problem in H₂S-containing produced water service.
API 653 Material Evaluation 4
The carbon equivalent (CE) formula is used during material evaluation primarily to assess: