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?

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 Mar 06, 2026, 05:05 AM

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Rory

7 hours 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

5 days 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

10 days 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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