API-571 Exam - Topic 2 Question 129 Discussion

Actual exam question for API's API-571 exam

Question #: 129
Topic #: 2

Which type of corrosion is most likely to occur in hydroprocess reactor effluent streams in units producing alkaline sour water?

AAmine

BAmmonium bisulfide

CCaustic

DAmmonium chloride

Show Suggested Answer

Suggested Answer: B

From API RP 571 and RP 932-B:

''In hydroprocessing reactor effluent systems, the most common corrosion mechanism is ammonium bisulfide (NHHS) corrosion, which forms in the presence of hydrogen sulfide and ammonia.''

''NHHS attacks carbon steel aggressively under turbulent flow and at low pH.''

Correct answer is B -- ammonium bisulfide corrosion.

by Kenny at Jul 16, 2026, 03:02 AM

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Abel

3 days ago

Wait, I thought caustic was the main issue?

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Janey

8 days ago

I’m not so sure about that, could be A) Amine too.

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Sharan

13 days ago

Definitely agree with that!

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Theodora

18 days ago

I think it's B) Ammonium bisulfide.

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Tamesha

24 days ago

Amine corrosion seems less likely here, but I’m not confident about the others. I wish I had reviewed more before the exam!

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Florinda

29 days ago

I feel like caustic corrosion was mentioned in a similar practice question, but I can't recall the specifics.

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Ilda

1 month ago

I think ammonium bisulfide could be a strong candidate since we discussed it in relation to sour water treatment in class.

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Laurel

1 month ago

I remember studying about corrosion types, but I’m not entirely sure which one is most common in alkaline sour water.

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