API 571 Acidic Process Stream Corrosion 2

Question 1

CO2 corrosion ('sweet corrosion') of carbon steel produces what primary corrosive species when CO2 dissolves in water?

Accepted Answer

Carbonic acid (H2CO3)

Answer

Sulfuric acid (H2SO4)

Answer

Hydrochloric acid (HCl)

Answer

Formic acid (HCOOH)

Question 2

What protective corrosion product can form on carbon steel during CO2 corrosion and reduce corrosion rates under certain conditions?

Accepted Answer

Iron carbonate (FeCO3)

Answer

Iron sulfide (FeS)

Answer

Iron oxide (Fe3O4)

Answer

Iron hydroxide (Fe(OH)3)

Question 3

Below which temperature does protective iron carbonate (FeCO3) scale typically fail to form during CO2 corrosion, leaving carbon steel unprotected?

Accepted Answer

Below 140°F (60°C)

Answer

Below 60°F (16°C)

Answer

Below 212°F (100°C)

Answer

Below 300°F (149°C)

Question 4

In HF alkylation units, which material is the preferred choice for many components due to its resistance to hydrofluoric acid?

Accepted Answer

Monel 400 (Ni-Cu alloy)

Answer

304 stainless steel

Answer

Carbon steel with Alonized coating

Answer

Titanium Grade 2

Question 5

What flow velocity limit is typically imposed on carbon steel piping in anhydrous HF acid service to prevent erosion of the protective iron fluoride scale?

Accepted Answer

3 ft/s (0.9 m/s)

Answer

1 ft/s (0.3 m/s)

Answer

10 ft/s (3.0 m/s)

Answer

20 ft/s (6.1 m/s)

Question 6

Sour water corrosion in refinery overhead systems is primarily caused by which corrosive species?

Accepted Answer

Ammonium bisulfide (NH4HS)

Answer

Ammonium chloride (NH4Cl)

Answer

Sodium hydroxide (NaOH)

Answer

Hydrogen fluoride (HF)

Question 7

Above what NH4HS concentration in refinery overhead water systems does carbon steel corrosion rate increase significantly, per API 932-A guidance?

Accepted Answer

2 wt%

Answer

0.5 wt%

Answer

8 wt%

Answer

15 wt%