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NACE MR0175 and elastic or plastic design criteria

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The question below was submitted to NACE MR0175 maintenance panel. At Oil & Gas Corrosion we can help you with materials selection to comply with NACE MR0175.

Question: Unfortunately answer #2011-08 left my organization at a loss. This answer does not address the fact that NACE MR0175-ISO 15156-1, Clause 5 states: This part of ANSI/NACE MR0175/ISO 15156 applies to the qualification and selection of materials for equipment designed and constructed using conventional elastic design criteria. For designs using plastic criteria (e.g. stain-based and limit-states designs), use of this part of ANSI/NACE MR0175/ISO 15156 might not be appropriate and the equipment/material supplier, in conjunction with the equipment user, shall assess the need for other requirements. This response does not address the issue that rupture discs plastically deform which is at the heart of and the basis of the previous inquiry.Metal rupture discs are made 8 to order product that plastically deform as part of the manufacturing process and will plastically deform when they burst (fail) when exposed to an overpressure process condition.

Answer: 

“The Maintenance Panel for NACE MR0175/ISO 15156 has reviewed your inquiry submitted May 4, 2012. You asked for further clarification of the answers to MP Inquiries #2009-05 and #2011-08.
Here is the Maintenance Panel’s response:
• The answer previously given has been confirmed to be correct by the Maintenance Panel (MP).
• The MP also confirms there is no conflict with the reply given for Inquiry 2009-05.
• Since the rupture disk is not a “Table A.1 exclusion,” it must either meet the material requirements in Annex A or be approved by the end user based on laboratory testing or field history. Confirming compliance with the material requirements in Annex A may be difficult for a rupture disk. However, it may be possible to demonstrate that the same raw material sheet with plastic deformation equivalent to worst-case locations on the rupture disk have metallurgical properties well within the material requirements in the standard.
Additional comments from other MP members:
1. On the issue of plastic deformation during manufacturing:
-Whether the material is plastically deformed in fabrication is not the issue here.
-Plastic deformation during manufacturing is irrelevant to clause 5, paragraph 9.
2. On the issue of deformation during rupture:
-Plastic deformation occurs when they burst, but then they’re intended to burst.
-The rupture disk functions within its elastic limit during the pressure-containing (bulk) of its service life. They are not designed to operate after additional in situ deformation (i.e., no strain-based design). Plastic deformation on failure is incidental to the function.
-The purpose of the wording in Part 1 Section 5 is to cover design criteria where the material is expected to function beyond the elastic limit in service without failing (strain-based designs for pipelines being a prime example). Bursting disks do not fall into this category, either being plastically deformed (cold worked) prior to service or suffering from plastic deformation incidental to failure (albeit failure is part of the function of the bursting disc in cases of over pressurization) in service.”

This question is in relation to NACE MR0175/ISO 15156-1 Clause 5

Reference: ISO 15156 Maintenance Panel Inquiry #2012-04

At Oil & Gas Corrosion we can help you with materials selection during design, whether you use elastic or plastic design criteria.

 

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