API 571 Corrosion Mechanisms 3

Question 1

Naphthenic acid corrosion primarily occurs above what temperature threshold?

Accepted Answer

450°F (232°C)

Answer

Naphthenic acid corrosion becomes significant above 450°F (232°C) in crude distillation units where organic acids in crude oil react aggressively with steel.

Question 2

The Total Acid Number (TAN) of crude oil is used to assess risk of which damage mechanism?

Accepted Answer

Naphthenic acid corrosion

Answer

A higher TAN value indicates greater naphthenic acid content in crude, correlating directly with corrosion potential in high-temperature crude processing units.

Question 3

Chloride stress corrosion cracking (Cl-SCC) in austenitic stainless steel requires what combination of conditions?

Accepted Answer

Tensile stress, chlorides, and temperature above ~140°F

Answer

Cl-SCC requires simultaneous presence of tensile stress, chloride ions, and temperatures typically exceeding 140°F to initiate and propagate.

Question 4

Which alloy provides the best resistance to naphthenic acid corrosion in high-temperature crude service?

Accepted Answer

316L stainless steel with molybdenum

Answer

Molybdenum-containing stainless steels such as 316L exhibit significantly better naphthenic acid resistance than carbon or low-alloy steels.

Question 5

How does corrosion fatigue differ from pure mechanical fatigue?

Accepted Answer

A corrosive environment eliminates the normal fatigue endurance limit

Answer

Corrosion fatigue involves the synergistic effect of cyclic stress and corrosive environment, which removes the normal endurance limit seen in air fatigue.

API 571 - API 571 Corrosion and Materials Practice Test

API 571 - API 571 Corrosion and Materials Practice Test

API 571 Corrosion Mechanisms 3