API 571 Acidic Process Stream Corrosion

Question 1

At what Total Acid Number (TAN) does naphthenic acid corrosion typically become a significant concern in crude oil processing?

Accepted Answer

0.5 mg KOH/g

Answer

0.1 mg KOH/g

Answer

1.5 mg KOH/g

Answer

3.0 mg KOH/g

Question 2

What temperature range is associated with the highest naphthenic acid corrosion rates in refinery distillation equipment?

Accepted Answer

450°F–750°F (232°C–399°C)

Answer

100°F–200°F (38°C–93°C)

Answer

200°F–400°F (93°C–204°C)

Answer

800°F–1000°F (427°C–538°C)

Question 3

Which alloying element in stainless steel provides the greatest improvement in resistance to naphthenic acid corrosion?

Accepted Answer

Molybdenum

Answer

Chromium

Answer

Nickel

Answer

Silicon

Question 4

What is the primary corrosion mechanism in refinery amine treating units that causes attack on carbon steel equipment?

Accepted Answer

Acidic conditions from absorbed CO2 and H2S at elevated temperatures

Answer

Galvanic attack between lean and rich amine streams

Answer

Oxidation of amine degradation products forming organic acids

Answer

Microbiologically influenced corrosion in stagnant amine sections

Question 5

Carbon steel welds in amine service are susceptible to amine stress corrosion cracking when hardness exceeds which threshold?

Accepted Answer

HRC 22 (235 HB)

Answer

HRC 10 (187 HB)

Answer

HRC 30 (286 HB)

Answer

HRC 40 (371 HB)

Question 6

Caustic stress corrosion cracking (caustic embrittlement) in carbon steel is most likely to occur when NaOH concentrations exceed approximately:

Accepted Answer

10–30 wt%

Answer

1–3 wt%

Answer

5–7 wt%

Answer

50 wt%

Question 7

Which mitigation method is most effective for preventing caustic corrosion and caustic SCC in carbon steel equipment?

Accepted Answer

Limiting operating temperature and applying PWHT to welds

Answer

Using 304 stainless steel instead of carbon steel

Answer

Coating internal surfaces with phenolic epoxy lining

Answer

Injecting corrosion inhibitors into the caustic stream