scope:

Aspects of Construction Covered by These Rules

(a) This Case contains rules for the selection of materials and for the design of Class 2 and 3 components, parts, and appurtenances that are expected to experience metal temperatures that exceed those covered by the rules and stress limits of Subsection NC, Subsection ND, and Tables 1A, 1B, and 3 of Section II, Part D.

(b) The rules of this Case are independent of the type of non-lethal fluid contained by the component. However, if the Owner (or his agent) specifies in the Design Specifications that the component will contain lethal substances,(Footnote 1) then the acceptable weld types and weld examinations shall also comply with requirements (1)-(5) listed below.

Footnote 1 - By "lethal substances" are meant poisonous gases or liquids of such a nature that a very small amount of the gas or of the vapor of the liquid mixed or unmixed with air is dangerous to life when inhaled. For purposes of this Division, this class includes substances of this nature which are stored under pressure or may generate a pressure if stored in a closed vessel.

(1) All butt welded joints at the pressure boundary shall be fully radiographed. An exemption is allowed for the weld seam in heat exchanger tubes and pipes, provided the seam is butt welded without the addition of filler metal, and, provided the tube or pipe is totally enclosed within a shell of a vessel which meets the requirements for vessels containing lethal substances.

(2) The component shall be postweld heat treated when the pressure boundary material includes either carbon or low alloy steels.

(3) Category A weld joints in vessels and similar weld joints in other components shall be Type No. (1), (see NC-4262 for definitions).

(4) Categories B and C weld joints in vessels and similar weld joints in other components shall be Type No. (1) or No. (2).

(5) Category D weld joints in vessels and similar weld joints in other components shall be full penetration welds extending through the entire thickness of the pressure boundary wall.

(c) Those portions of the Class 2 (or Class 3) component, part or appurtenance which are at all times experiencing temperatures within the range covered by Tables 1A, 1B, and 3 of Section II, Part D may be designed to the rules of NC-3000 (or ND-3000) using the material rules of NC-2000 (or ND-2000).

(d) Design procedures and material data not contained in this Case may be required to ensure the structural integrity or continued functioning of the stuctural part during the specified service life. For example, the rules do not provide methods to evaluate deterioration which may occur in service as a result of corrosion, mass transfer phenomena, radiation effects, or other material instabilities. Nor do the rules ensure continued functional performance of deformation-sensitive structures such as valves and pumps.

(e) This Case is not applicable to storage tanks constructed in accordance with NC-3800, NC-3900, ND-3800, and ND-3900. This Case is not applicable to internal structures outside the scope of (f) below.

(f) The rules of this Case apply to those permanent attachments as described in the Design Specifications and to portions of components covered by the Code, as explained in:

NCA-3252(e) (Code Boundary description in Design Specification)

NCA-3254.1 (Limits on Code Boundaries of attachments)

NCA-1130 (Parts excluded from Code coverage)