API 510 Material Evaluation and Selection 3

Question 1

The Nelson curves published in API RP 941 define safe operating limits to prevent which damage mechanism?

Accepted Answer

High-temperature hydrogen attack (HTHA) in carbon and alloy steels

Answer

API RP 941 provides temperature versus hydrogen partial pressure curves that define the boundary above which HTHA becomes a risk for carbon and low-alloy steels.

Question 2

Sigma phase embrittlement in 316 stainless steel typically develops after extended exposure in which temperature range?

Accepted Answer

Between 1000°F and 1700°F (538°C and 927°C) during service

Answer

Sigma phase, an intermetallic compound that severely reduces toughness, precipitates from the ferrite phase of austenitic and duplex stainless steels within this temperature band.

Question 3

Which metallurgical damage mechanism reduces the impact toughness of 2.25Cr-1Mo steel after long-term service in the 650–1070°F (343–577°C) range?

Accepted Answer

Temper embrittlement due to tramp element grain-boundary segregation

Answer

Temper embrittlement results from grain-boundary segregation of tramp elements (P, Sn, As, Sb), raising the ductile-to-brittle transition temperature of the alloy steel.

Question 4

API RP 571 recommends which measure as the primary mitigation for alkaline stress corrosion cracking (caustic SCC) in carbon steel pressure vessels?

Accepted Answer

Applying PWHT to all carbon steel welds above caustic SCC threshold conditions

Answer

PWHT reduces residual welding stresses that, combined with caustic concentration and temperature, are the driving force for stress corrosion cracking in carbon steel.

Question 5

In wet H2S service, what is the maximum hardness specified for carbon steel weld heat-affected zones per NACE MR0175/ISO 15156 to prevent sulfide stress cracking?

Accepted Answer

HBW 237 (HRC 22)

Answer

NACE MR0175/ISO 15156 limits carbon and low-alloy steel hardness to HRC 22 (approximately HBW 237) to prevent sulfide stress cracking in sour service.

(API 510) Certified Pressure Vessel Inspector Practice Test

(API 510) Certified Pressure Vessel Inspector Practice Test

API 510 Material Evaluation and Selection 3