API-571 Exam - Topic 1 Question 119 Discussion

Actual exam question for API's API-571 exam

Question #: 119
Topic #: 1

(Which three residual alloy elements are of most concern when it comes to corrosion of carbon steel in HF Alkylation process units?)

ACr / Mo / Ni

BC / Nb / V

CCr / Cu / Ni

DCu / S / V

Show Suggested Answer

Suggested Answer: C

Comprehensive and Detailed Explanation From Exact Extract:

In HF Alkylation units, API RP 571 identifies certain residual alloying elements in carbon steel that can significantly increase corrosion rates in HF acid service.

The most detrimental residual elements are:

Chromium (Cr)

Copper (Cu)

Nickel (Ni)

These elements:

Disrupt formation of protective iron fluoride films

Increase general and localized corrosion rates

Are tightly controlled in carbon steel specifications for HF service

Referenced Documents (Study Basis):

API RP 571 -- Section on Hydrofluoric Acid Corrosion

by Naomi at Jan 05, 2026, 05:16 AM

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Alex

4 months ago

I’m with B) C / Nb / V. Carbon and niobium play a role too.

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Wade

4 months ago

D) Cu / S / V seems right. Sulfur is notorious for corrosion.

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Kimberlie

4 months ago

I lean towards C) Cr / Cu / Ni. Copper can be a big issue.

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Nakisha

4 months ago

I think it's A) Cr / Mo / Ni. They really affect corrosion.

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Leota

4 months ago

I always thought Ni was more of a friend than a foe in this context!

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Pilar

4 months ago

Wait, are we really worried about Cu in D)? That seems off.

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Ettie

5 months ago

A) is correct, no doubt about it!

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Jean

5 months ago

I thought it was B) C / Nb / V? Seems like a tricky one.

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Renay

5 months ago

Definitely A) Cr / Mo / Ni. Those are the usual suspects.

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Delmy

5 months ago

Cr, Mo, and Ni? More like the Three Musketeers of corrosion resistance in HF Alkylation! That's the way to go, folks.

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Onita

5 months ago

Haha, who would even think Cu, S, and V are the answer? That's like asking for trouble in an HF plant. Gotta be Cr, Mo, and Ni all the way!

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Johnson

6 months ago

Hmm, Cu, S, and V? Sounds like a recipe for disaster in that HF environment. I'll stick with the Cr, Mo, and Ni option.

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Marylou

6 months ago

C, Nb, and V? Nah, that's not gonna cut it in an HF Alkylation process. Gotta go with the classic Cr, Cu, and Ni.

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Casie

6 months ago

Cr, Mo, and Ni are definitely the culprits here. Gotta watch out for those pesky residual alloy elements!

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Linsey

7 months ago

I believe Cr and Ni are definitely involved, but I’m uncertain about the third element. Could it be Cu?

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Marya

7 months ago

I practiced a similar question, and I feel like Cu was mentioned as a concern, but I can't remember the others.

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Xuan

7 months ago

I think it might be Cr, but I can't recall if Mo or Ni is more relevant.

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Rosenda

7 months ago

I remember studying corrosion issues in HF Alkylation, but I'm not sure which elements are the most critical.

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Alayna

7 months ago

This is right up my alley. Identifying critical alloy elements for corrosion resistance is a classic exam question. I've got a good strategy for working through the options systematically.

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Wenona

7 months ago

I'm a bit unsure about this one. I know corrosion is a big issue in these units, but I'm not totally clear on which specific elements would be the biggest problem. Time to do some quick reviewing.

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Lindy

8 months ago

Alright, I've got this. The question is asking about the most concerning residual alloy elements, so I'll need to consider how each of those could impact corrosion in this specific process.

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Laurene

8 months ago

Okay, let me see. I know carbon steel is commonly used, so the residual alloy elements are probably the main concern. I'll need to review my notes on corrosion mechanisms.

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