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What are the NACE MR0175 limits for ferritic ductile iron ASTM A395?

A395 NACE: Acceptability of Ferritic Ductile Iron for Pressure-Containing Parts

Question 1:

Does Section A.2.4.1, part 2 (ANSI/NACE MR0175/ISO 15156-2:2015) stating “”Ferritic ductile iron in accordance with ASTM A395 is acceptable for equipment unless otherwise specified by the equipment standard”” imply that its use is acceptable for pressure-containing parts?

Answer 1:

ANSI/NACE MR0175/ISO 15156-2 does not restrict the use of ferritic ductile iron in accordance with ASTM A395 for pressure-containing components. However, it is important to note that other standards, such as API standards, may have specific restrictions on the use of this material beyond the scope of ANSI/NACE MR0175/ISO 15156-2.

Question 2:

Are there any partial pressure limits that would apply to the use of ferritic ductile iron in accordance with ASTM A395?

Answer 2:

There are no partial pressure limits regarding H₂S for cast iron, but it is important to note the warning preceding the Scope of ANSI/NACE MR0175/ISO 15156-2. The warning states: “”Carbon and low-alloy steels and cast iron selected using this part of ISO 15156 are resistant to cracking in defined H₂S-containing environments in oil and gas production, but not necessarily immune to cracking under all service conditions. It is the equipment user’s responsibility to select the carbon and low-alloy steels and cast iron suitable for the intended service.””

Reference: MP Inquiry 2017-02 (NACE MR0175 Part 2 A.2.4.1)

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