Mechanisms of Rapid Cooling and Their Design Considerations in Underwater Welding

Abstract

Rapid cooling is an inherent problem in underwater welding. This paper discusses the basic understanding of cooling mechanisms during underwater welding and the effectiveness of various methods of reducing the cooling rate. Numerical results obtained from a computer analysis are used to discuss the design criteria and the effect of various parameters on the cooling rate. Introduction During the last several years, systematic research efforts on underwater welding have been made at the Dept. of Ocean Engineering of the Massachusetts Inst. of Technology. Most of the research programs were funded by the National Sea Grant Office of the National Oceanic and Atmospheric Admin. Some of the reports, theses, and papers have been published. The research programs have covered various subjects including basic research on mechanisms of underwater welding as well as development of new, improved processes. This paper discusses one subject: rapid cooling during underwater wet arc welding.* This paper has been prepared primarily from results obtained in research by Tsai.The major portion of Tsai's research is composed of extensive mathematical analyses of heat flow during underwater wet arc welding. A series of mathematical equations has been developed to analyze all pertinent phenomena involved: dynamics of bubble formation, heat-loss mechanisms, etc. Experiments were made to examine the validity of the analyses. Studies were made to investigate effects of various parameters (welding conditions, plate thickness, etc.) on cooling rates in weldments, especially in the heat-affected zone (HAZ). Studies also were made to evaluate the effectiveness of various methods of reducing the cooling rate.Since details of analytical and experimental results are included in Ref. 4, this paper presents a brief summary of the analysis and some experimental results. The emphasis of this paper is placed on information of practical importance. Brief Summary of Cooling Mechanisms in Underwater Welding The mode of heat transfer in underwater welding is quite different from that in air welding. The existence of dynamic bubbles during underwater welding induces a flow field around the welding arc. This water flow along with the agitation of bubbles carries the heat away quickly from the base material and causes the rapid cooling phenomenon. In this section, buble dynamics and heat-loss mechanisms are discussed. Underwater Bubble Dynamics Bubble generation due to the high concentration of heat in the arc and its departure and final collapse during the underwater arc welding process in the wet condition was investigated by a high-speed cinematography study at the Massachusetts Inst. of Technology. JPT P. 1825＾