Application of preheat temperatures after welding pressure vessel steels

Technical Report · Mon Sep 01 04:00:00 EDT 1975

OSTI ID:7364702

Caplan, J S

Hydrogen-induced cracking occurs either in the heat-affected zone (HAZ) microstructure or in weld metal when four factors react simultaneously. These factors have been defined as (1) presence of hydrogen, (2) welding stresses, (3) a susceptible microstructure, and (4) a low temperature. Hydrogen can become available during welding from base and welding materials and extraneous contaminating matter. With the current processes of steel making where hydrogen is reduced to a low level, (in particular for critical applications within the nuclear industry where the hydrogen content in weld material is closely controlled) the presence of hydrogen in the starting metallic materials has been diminished, but not eliminated. However, the possibility of introducing hydrogen still exists to some degree, for example, from welding fluxes that have not been properly dried. Welding stresses are inevitably present and can only be minimized by consideration of joint geometry, fit-up, external restraint, and yield strength of the weld metal. The HAZ microstructure is dependent upon the cooling rate after welding, which, in turn, is governed by the weld heat input, preheat, thicknesses, composition, and hardenability of the steel. The one factor that is most subject to fabrication control is the preheat temperature and holding time after welding. Thus, dependence is placed on the control of preheat as an effective means of reducing hydrogen concentrations (if present) during welding and heat treatment. Data are presented to show the effects of preheat and postweld heat treatments. These data are principally concerned with the type of steels used for nuclear pressure vessels which, for classification purposes, usually have carbon equivalent values of 0.60 or less.

• Research Organization: Westinghouse Electric Corp., Pittsburgh, Pa. (USA)
• OSTI ID: 7364702
• Report Number(s): WCAP-8577
• Country of Publication: United States
• Language: English

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