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What does “continuous precipitates” mean in NACE MR0175?

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Question:

See A.2.3, MP inquiry #2005-13. The question is in regard to Appendix A.7 of NACE MR0175/ISO 15156-3. In A.7.3 third paragraph, it requires that “the microstructure … shall have grain boundaries with no continuous precipitates”. Is there any guidance as to what continuous means? For example, does it mean continuous throughout the microstructure? Our laboratory has reported suspected continuous precipitates “at some locations”.

Answer:

There is no definition of “continuous precipitates” in the standard. An acceptance criterion or other quantitative limit shall be agreed between the manufacturer/supplier and the equipment user.
As noted in the WARNING above ISO 15156-3, Scope, it is the equipment user’s responsibility to select the CRAs and other alloys suitable for the intended service. This responsibility includes the selection of specific quality requirements when none are given by the standard.

This question is in relation to NACE MR0175/ISO 15156-3 A.7.3

Reference: ISO 15156 Maintenance Panel Inquiry #2005-18

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