Activating flux tungsten inert gas welding for enhanced weld penetration

Operating experience in the nuclear power industry has shown that dissimilar metal welds joined with Inconel 82/182 (ERNiCr-3/ENiCrFe-3) filler metal in the primary loop of pressurized water reactor (PWR) plants are susceptible to primary water stress corrosion cracking (PWSCC). Repair of these dissimilar metal weld joints by weld overlay (WOL) using the PWSCC resistant 52 M (ERNiCrFe-7A) filler metal has been successfully applied in numerous PWRs. The typical dissimilar metal joint consists of a low alloy steel vessel nozzle welded to an austenitic stainless steel safe end. The WOL extends from the low alloy steel nozzle over the safe end and most often onto the adjoining wrought or cast stainless steel pipe. Recent experience shows that 52 M is susceptible to hot cracking when welded over specific heats of centrifugally cast stainless steel pipe. The cracking was attributed to unexpectedly high dilution caused by a synergistic influence of Silicon (Si) and Sulfur (S) on weld pool behavior and bead shape. This paper presents the cause and mechanism of 52 M hot cracking when welding over cast stainless steel, and discusses the synergistic influence of Si, S and other trace elements on the weld bead shape and dilution. In addition, the influence of gas tungsten arc (GTA) welding parameters is discussed in relation to the successful application of 52 M WOL on cast austenitic stainless steel base metals.

Behavior and Hot Cracking Susceptibility of Filler Metal 52 M (ERNiCrFe-7A) Overlays on Cast Austenitic Stainless Steel Base Materials

A method of forming an optical device comprises applying a laser beam to a target area of the surface so as to selectively heat material of the surface thereby to provide transfer of material due to a surface tension gradient, wherein the surface is such that, when liquid, parts of the surface at higher temperatures have a higher surface tension than adjacent parts of the surface at lower temperatures.

Method of forming an optical device

CHAPTER 7 – Metal Transfer and Mass Flow in the Weld Pool

Weld bead center line shift during laser welding of austenitic stainless steels with different sulfur content

Following difficulties with heat–to–heat variation in weld penetration enountered during GTA welding of stainless steel tubing, a program was undertaken to identify the cause of the problem and to develop remedial techniques. The variation in weld penetration was attributed primarily to differences in sulphur and, to a lesser extent, oxygen content, in broad agreement with a published model for such effects based on surface tension. The incorporation of copper alloy heat sinks into the standard welding head was successful in overcoming the problem. Both argon − 1% oxygen shielding gas and multipass welding procedures have been demonstrated to be promising alternative solutions, but these techniques have not been fully developed. To prevent the recurrence of the problem in future construction, a limit of 100–200 ppm sulphur has been included in the material specification for tubing purchases.

C. Gluck

Papers

Welding 304l stainless steel tubing having variable penetration characteristics