Does UCS-66(b) (3) means: When the intended MDMT (not design MDMT) is between -55F to -155F and coincident ratio is less than or equal to the 0.35(lower threshold limit on UCS 66.1) than the component under evaluation can assume the value of MAT (or rated MDMT) to be -155F.
Is my interpretation correct?!
No, UCS-66 (b)(3), a sub paragraph of UCS-66 (b), provides the basis for not having to conduct impact testing for an MDMT between ?55°F and –155°F. I am confused when you say the component may “assume” the value of the rated MDMT of –155°F. There is more to be concerned with than just UCS-66 (b)(3). What is the vessel (or component) MDMT?
Is not it correct that the SA-105 material's MDMT is restricted to ?55°F (according to UCS-66(b) (1) (b)) without performing the impact testing?
No, when applying the provisions of UCS-66 (b)(1)(b), SA-105 only shows that the component is made of a Part UCS material. You need to evaluate and satisfy all requirements, not just the material specification requirement.
UCS-66 (b)(1) and subparagraphs (a), (b), and (c) address components with MDMT of ?55°F and warmer.
UCS-66 (b)(2) addresses components with MDMT colder than ?55°F and that do not satisfy paragraphs UCS-66 (b)(3) and UCS-68 (c).
UCS-66 (b)(3) addresses components with MDMT colder than ?155°F and with a coincident ratio less than .35.
Is not it correct when the Intended MDMT(worst condition during operation) is lower than design MDMT especially below -55F than impact testing of material(including SA-105) is required. Or use different material such as SA-350-LF3 for flange?
No, If the intended MDMT is supported by calculation using UCS-66(b), and exempts material impact testing requirements, it is acceptable. The following interpretation denotes this requirement.
Subject: Section VIII, Division 1 (2001 Edition); UCS-66, Marking MDMT on Nameplate
Date Issued: May 20, 2002
Question: In Section VIII, Division 1, is it permitted to list as the MDMT at MAWP on the nameplate a temperature which is warmer than the MDMT determined either by test or by application of the UCS-66 exemption rules?
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