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API-571 Exam - Topic 1 Question 127 Discussion

Actual exam question for API's API-571 exam

Question #: 127
Topic #: 1

[All API-571 Questions]

Which of the following weldments is most susceptible to dissimilar metal cracking when operating at high temperatures?

ACarbon steel to Inconel 625

BCarbon steel to Monel 400

CCarbon steel to Incoloy 800

DCarbon steel to 316 stainless steel

Show Suggested Answer

Suggested Answer: D

Dissimilar Metal Cracking (DMC) is a form of high-temperature cracking that frequently occurs in weld joints between carbon steel and austenitic stainless steel (such as Type 316 SS) due to differences in thermal expansion coefficients and mechanical properties.

From API RP 571 Section 5.2.3.1 (Dissimilar Metal Weld Cracking):

''Cracking frequently occurs in weld joints between ferritic and austenitic materials such as carbon steel to 300 series stainless steels due to thermal expansion mismatch during high temperature operation.''

Therefore, Option D (Carbon steel to 316 stainless steel) is the most susceptible combination and the correct answer.

by Glenn at Jun 17, 2026, 11:30 AM

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Becky

D seems plausible. 316 stainless can crack under stress.

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Brandee

5 days ago

I’m leaning towards C. Incoloy 800 has its issues too.

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Chantell

10 days ago

I think A is the right choice. Inconel 625 is tricky at high temps.

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Jettie

15 days ago

Wait, is it really that bad with Inconel 625? Sounds surprising!

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Odette

21 days ago

Really? I thought it would be B) Carbon steel to Monel 400.

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Shaun

26 days ago

I've heard A) is definitely the most susceptible.

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Leonida

1 month ago

I disagree, I think D) Carbon steel to 316 stainless steel is more prone.

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Sherita

1 month ago

A) Carbon steel to Inconel 625 is the right choice.

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Peggy

1 month ago

I thought 316 stainless steel was more resistant to cracking, but I could be mixing it up with something else we studied.

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Tequila

2 months ago

I have a vague memory that Incoloy 800 can be problematic with carbon steel, especially at elevated temperatures.

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Sylvia

2 months ago

I feel like we discussed Monel 400 in class, but I can't recall its specific behavior with carbon steel under heat.

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Aileen

2 months ago

I think I remember that Inconel 625 is often used in high-temperature applications, but I'm not sure if it's the most susceptible to cracking.

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