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API-571 Exam - Topic 1 Question 121 Discussion

Actual exam question for API's API-571 exam
Question #: 121
Topic #: 1
[All API-571 Questions]

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

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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 Mar 06, 2026, 05:05 AM

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Lamar
12 days ago
I thought Monel 400 might be worse, interesting!
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Nieves
17 days ago
I totally agree, Inconel has a different expansion rate.
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Irving
22 days ago
A) Carbon steel to Inconel 625 is the most susceptible.
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Yuonne
27 days ago
High temps really mess with those dissimilar metals!
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Mose
1 month ago
Wait, I thought Monel was more resistant?
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Leonor
1 month ago
Definitely A, I've seen it happen too many times.
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Raymon
1 month ago
I disagree, I think D) Carbon steel to 316 stainless steel is more prone.
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Lenny
2 months ago
A) Carbon steel to Inconel 625 is the right choice.
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Ryan
2 months ago
If I recall correctly, 316 stainless steel is generally more compatible with carbon steel, so I’m leaning towards Inconel 625 being the most susceptible.
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Rory
2 months ago
I’m a bit confused about Monel 400 versus Incoloy 800. I feel like both could be problematic, but I can't remember the specifics.
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Markus
2 months ago
I think we did a practice question on this, and I recall that Inconel 625 has a reputation for being tricky with carbon steel.
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Trinidad
2 months ago
I remember studying that dissimilar metal cracking is often a concern with high-temperature applications, but I’m not sure which specific combination is the worst.
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