Document: NUREG-0800
Document ID: d8b522d4-dee5-4122-89d4-b2b45d0ca729
Document Type: srp
Title: REACTOR COOLANT PRESSURE BOUNDARY MATERIALS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070420.pdf
Revision Date: 2023-06
Chapter: 5
Section ID: 5.2.3
CFR Part: 
CFR Title: 

Content:
the thermal insulation may be leached by spilled or leaking liquids and deposited on the stainless steel surfaces. The controls on the use of nonmetallic thermal insulation are reviewed. d. Austenitic stainless steel is subject to hot cracking (microfissuring) during welding if the weld metal composition or the welding procedure is not properly controlled. Because cracks formed in this manner are small and difficult to detect by nondestructive testing methods, welding procedures, weld metal compositions, and delta ferrite percentages that minimize the possibility of hot cracking must be specified. As a part of achieving this control, Regulatory Guide 1.31, "Control of Ferrite Content in Stainless Steel Weld Metal," contains recommendations for 5.2.3-5 DRAFT Rev. 3 - April 1996 process control through the testing of weld test pads. The staff recommendations will provide assurance that the ferrite content will be adequate to prevent microfissuring. The adequacy of the proposed welding procedures, weld metal compositions, testing of weld metals, and delta ferrite content is reviewed. 21 The assurance of satisfactory electroslag welds for austenitic stainless steel components can be increased by maintaining a weld solidification pattern with a strong intergranular bond in the center of the weld. The welding variables that have a significant effect on the weld solidification pattern must be controlled. A number of electroslag welding process variables, such as, slag pool depth, electrode feed rate and oscillation, current, voltage, and slag conductivity, have been shown to influence the weld solidification pattern. If the combination of process variables produces a deep pool of molten weld metal, the crystal (dendritic) growth direction from the pool sides will join at an obtuse angle at the center of the weld, and cracks may develop because of the weaker centerline bond between dendrites. A proper combination of process variables promotes a dendritic growth pattern with