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The effects of arc voltage on the stability of the underwater wet flux-cored arc welding (FCAW-S 114) process are explained based on studying the droplet transfer process using the X-ray transmission method. The mode of metal transfer and the protective bubble effect, which vary with voltage, affect the stability of the welding process. The results indicate that there is a critical arc voltage (32 V). When the arc voltage is less than 32 V, an unstable welding process occurs because of the high proportion of short-circuit transfer and limited bubble size. Increase in the arc burning zone must be protected, and the proportion of repelled metal transfer caused by the high arc voltage decreases the stability of the welding process. In this study, stable welding process is acquired when the proportion of repelled metal transfer is less than 20%, the short circuit frequency is lower than 1 Hz and the bubble diameter is larger than 24 mm. [ABSTRACT FROM AUTHOR]

Underwater wet welding is a crucial repair and maintenance technology for nuclear plant. A boric acid environment raises a new challenge for the underwater welding maintenance of nuclear plant. This paper places emphasis on studying the influence of a boric acid environment in nuclear plant on the underwater welding process. Several groups of underwater wet welding experiments have been conducted in boric acid aqueous solution with different concentration (0-35000 ppm). The viscosity of the welding slag and the mechanical properties of welds, such as the hardness, strength, and elongation, have been studied. The results show that with increasing boric acid concentration, the viscosity of the slag decreases first and then increases at a lower temperature (less than 1441 °C). However, when the temperature is above 1480 °C, the differences between the viscosity measurements become less pronounced, and the viscosity tends to a constant value. The hardness and ductility of the joints can be enhanced significantly, and the maximum strength of the weld metal can be reached at 2300 ppm. [ABSTRACT FROM AUTHOR]

Underwater wet welding technology is widely used. Because the stability of droplet transfer in underwater wet welding is poor, the feasibility of improving the droplet transfer mode has been discussed from various technical directions. In this work, the characteristics of pulsating wire feeding were studied in the pulsating wire feeding mode by investigating the effects of changing the pulsating frequency, the wire withdrawal speed, and the wire withdrawal quantity on the droplet transfer process and the welding quality. With the aim of improving weld forming and welding stability, the authors selected the coefficient of variation and the ratio of unstable droplet transfer as the indexes to evaluate the effect of droplet transfer control. The pulsating wire feeding process of underwater wet flux-cored wire was analyzed in depth, and the following conclusions were drawn: using the pulsating wire feeding mode and after comparing and analyzing the pulsed wire feeding process under the same frequency condition, the authors found that the forming and stability were better under the conditions of slower withdrawal speed and smaller withdrawal quantity. The short-circuit transition ratio decreased steadily with the increase of pulsating wire feeding frequency, the rejection transition ratio first rose and then decreased, and the splash ratio first decreased and then rose. [ABSTRACT FROM AUTHOR]

For obtaining high quality of underwater welding repairing for nuclear power equipments, the influence of boric acid on metal transfer process of underwater flux-cored wire wet welding in boric acid solution is explored by an X-ray transmission system. The research results show that the mixed repelled globular transfer and solid short circuit transfer mode and the mixed repelled globular transfer and surface tension transfer mode are two kinds of main metal transfer modes during underwater welding in boric acid solution. The proportion of the mixed repelled globular transfer and surface tension transfer mode is increasing with the increasing of concentration of boric acid solution, which is caused by the difference of force condition of the droplet. [ABSTRACT FROM AUTHOR]

Metal transfer process in underwater flux-cored welding are investigated by X-ray transmission method for welding velocity from 0.5 mm/s to 9.5 mm/s. The metal transfer mode of underwater flux-cored wire welding is the mixed transfer mode mainly composed of four fundamental transfer modes i.e. wide-angle globular repelled transfer mode, small-angle globular repelled transfer mode, surface tension transfer mode and short-circuit transfer mode. The category and proportion of fundamental modes constituting the mixed mode depend strongly on the welding velocity owing to the variation of force condition on droplet. With increasing welding velocity, the proportion of the wide-angle globular repelled transfer mode increases continually while that of the surface tension transfer mode and short-circuit transfer mode decreases, and the proportion of the small-angle globular repelled transfer increases firstly and then decreases gradually. The welding appearance and cross-sectional macrostructure of weld specimens at different welding velocities are also investigated. When the welding velocity increases from 0.5 mm/s to 3.5 mm/s, the weld width decreases from 20 mm to 12 mm and the weld penetration increases rapidly from 0.8 mm to 3.7 mm, completely different from in-air welding. [ABSTRACT FROM AUTHOR]