API 510 Material Evaluation and Selection 5

Question 1

When inspecting a weld overlay (cladding) applied for corrosion protection in a pressure vessel, the most critical metallurgical concern is:

Accepted Answer

Excessive dilution of the overlay by the base metal, which reduces corrosion resistance

Answer

High dilution of the overlay by the base metal reduces the alloy content (particularly chromium in stainless overlays), which can eliminate the corrosion protection the overlay was intended to provide.

Question 2

Post-weld heat treatment (PWHT) of carbon steel pressure vessel welds is performed primarily to:

Accepted Answer

Reduce residual welding stresses and lower HAZ hardness to improve toughness and SCC resistance

Answer

PWHT relieves thermally induced residual stresses and tempers hard martensite in the HAZ, reducing susceptibility to brittle fracture and environmentally assisted cracking.

Question 3

The risk of High-Temperature Hydrogen Attack (HTHA) in pressure vessels operating at elevated temperatures and hydrogen partial pressures is evaluated using:

Accepted Answer

API RP 941 (Nelson Curves)

Answer

API RP 941 provides the Nelson Curves that define temperature and hydrogen partial pressure limits for carbon and alloy steels to avoid HTHA in refinery hydrogen service.

Question 4

Austenitic stainless steel pressure vessels in service above approximately 140°F (60°C) in the presence of chlorides are most likely to fail by:

Accepted Answer

Chloride stress corrosion cracking (SCC)

Answer

Chloride SCC is the dominant failure mode for austenitic stainless steels in chloride environments above roughly 140°F, requiring only tensile stress, chloride ions, and elevated temperature.

Question 5

Chrome-moly alloy steels such as 2.25Cr-1Mo (P22) are selected over carbon steel for service above approximately 850°F (454°C) primarily because they offer:

Accepted Answer

Higher creep strength and greater oxidation resistance at elevated temperatures

Answer

Chromium and molybdenum additions significantly raise the creep strength and oxidation resistance, allowing these steels to sustain design stresses where carbon steel would fail by creep deformation.

(API 510) Certified Pressure Vessel Inspector Practice Test

(API 510) Certified Pressure Vessel Inspector Practice Test

API 510 Material Evaluation and Selection 5