API 510 Material Evaluation 5

Question 1

An inspector is evaluating a vessel that operates in polythionic acid service during shutdowns. Which material is most resistant to polythionic acid stress corrosion cracking (PASCC)?

Accepted Answer

Type 347 stainless steel (stabilized grade)

Answer

Type 347 SS, stabilized with niobium, resists sensitization and is therefore the most resistant grade to PASCC among standard austenitic grades.

Question 2

A vessel exhibits localized corrosion in a pattern corresponding to the original weld bead geometry. The base metal shows minimal attack but the weld metal is heavily corroded. What type of corrosion is occurring?

Accepted Answer

Galvanic corrosion due to electrochemical potential difference between weld and base metal

Answer

Galvanic corrosion occurs when the weld metal has a different electrochemical potential than the base metal in the same electrolyte, causing preferential attack of the anodic member.

Question 3

When performing a material evaluation for a pressure vessel in cyclic thermal service, which material property is most critical to assess for resistance to thermal fatigue?

Accepted Answer

Coefficient of thermal expansion and thermal conductivity

Answer

Thermal fatigue is driven by differential thermal strains; materials with lower thermal expansion coefficients and higher thermal conductivity (reducing temperature gradients) are most resistant.

Question 4

An API 510 inspector reviews a vessel data report and finds the design code listed is ASME Section VIII, Division 1, Edition 1965. The vessel requires a major repair using current materials. What is the material evaluation requirement?

Accepted Answer

Use current ASME Section II materials that are acceptable under current code and were permissible under the original code

Answer

API 510 requires repairs to use current ASME Section II materials; the material should be acceptable under the current code and equivalent to what was allowable under the original construction code.

Question 5

A material evaluation for a new vessel nozzle fabricated from SA-105 (carbon steel forging) reveals a hardness of 165 HB. The vessel will operate in wet H2S service. Is this material acceptable per NACE MR0103?

Accepted Answer

Yes; 165 HB is well below the 200 HB limit and acceptable for wet H2S service

Answer

NACE MR0103 permits carbon steel with hardness ≤200 HB (22 HRC) in wet H2S service, so 165 HB is acceptable for the base metal.

(API 510) API 510 Inspector Certification Practice Test

(API 510) API 510 Inspector Certification Practice Test

API 510 Material Evaluation 5