Underwater Wet Flux-cored Arc Welding Research Articles

Effect of water flow on the arc stability and metal transfer in underwater flux-cored wet welding

The influences of flow rate and direction on metal transfer mode and molten pool shape in underwater wet flux-cored arc welding (FCAW) process were studied. Real-time electric signal data, metal transfer images and weld appearances at different flow rates and directions were obtained. The electric signal results showed that the increase of flow rate would deteriorate stability of the wet welding process. Two typical modes of metal transfer, globular repelled transfer mode and surface tension transfer mode were observed. Their proportion would change with increasing of flow rate. When flow rate increased from 0m/s to 2.5m/s, the proportion of globular repelled transfer mode increased from 71.5% to 100%. When welding direction was downstream, the proportion of spatter increased from 4.23% to 56% with the flow rate adding to 2.5m/s. The variation of flow direction would change position of molten pool, which result in the change of spatter lose rate. The depth-to-width radio of weld bead which was welded upstream increased from 0.13 to 0.8 with the increase of flow rate. As welding downstream, the depth-to-width radio didn’t change obviously. The method to overcome adverse effects of flow was discussed, and an acceptable appearance of welding seam was obtained.

Porosity and Microstructure of Underwater Wet FCAW of Duplex Stainless Steel

Flux-cored arc welding (FCAW) of duplex stainless steels has been widely used in offshore engineering, nuclear power engineering, and petroleum pipe lines. But underwater wet welding repair technology is still impossible for avoiding pore defects in welds. To study how pores perform in underwater wet welds, underwater wet flux-cored arc welding of S32101 duplex stainless steel was carried out in a hyperbaric chamber. The evolution of porosity and microstructure with welding parameters in 20 and 60 m water depth was analyzed for comparison. The relationship between porosity and austenite morphology in microstructures was discussed. Decreased welding parameters can increase the cooling rate. As a result, the ferrite to austenite transformation can be promoted and the resultant microstructures can be refined. Lower welding speed prolongs the high-temperature retention time, which is helpful to gas escaping from the molten pool. As a result, the porosity of the welds decreases. Reduced welding voltage with finer microstructure prevents the porosity in both water depths. It was found that the coarser the austenite microstructure was, the higher the porosity was. Additionally, the welds conducted with bigger welding current in 20 m water depth have lower porosity, the same as the welding speed, while the situation is reversed in 60 m water depth for a coarser austenite microstructure.

Investigation on dynamic behaviors of bubble evolution in underwater wet flux-cored arc welding

Bubble evolution behavior has a significant effect on the process stability and weld joint quality in underwater wet flux-cored arc welding (FCAW). In this study the visual sensing of bubble evolution behaviors based on high-speed camera method have been explored in attempt to accomplish the study of the wet welding process. The effects of preset welding parameters on the bubble evolution behaviors are investigated in detail. Four typical bubble evolution modes during the wet welding process and their corresponding welding electric information are determined to describe the bubble behaviors along with arc characteristics. Results indicated that the bubble evolution of underwater wet welding is unstable and complicated, necessitating control by adjusting the welding parameters to obtain a more stable protective effect. And there is a matching relationship between the coefficient of variation, weld appearance and bubble evolution mode for certain welding parameters. For underwater wet FCAW, a stable welding process can be acquired with a lower floating frequency and a larger maximum diameter of the bubble without arc extinguishing.

Microstructure and mechanical properties of underwater wet welded high-carbon-equivalent steel Q460 using austenitic consumables

Underwater wet flux-cored arc welding of Q460 steel using specially developed Ni-based filler and commercially obtained ER308 were investigated. Wet welded joints using Ni-based filler were of high performance with high ultimate tensile strength (518MPa) and impact toughness of the weld metal (128.9J/cm2). ER308 failed to acquire sound welded joints due to extensive slag remained in the bottom of groove. The highest microhardness (450 HV) was recorded on the coarse-grained heat-affected zone of the base metal for both joints. TypeⅡboundaries existed in the interfaces between austenitic weld metal and ferritic base metal. Compared to austenitic stainless steel weld metal, nickel-based weld metal possessed the ability to be significantly diluted by Q460 base metal.

The effect of alumino-thermic addition on underwater wet welding process stability

Real-time electric signal data, metal transfer images and weld appearances at different alumino-thermic additions in underwater wet flux-cored arc welding (FCAW) were obtained. The electric signal results showed that the thermite addition would improve the stability of the wet welding process while the weld appearances at larger content of thermite displayed numerous tiny spatters. The shock in weld pool due to metallurgical reaction was responsible for the tiny spatters. Two typical modes of metal transfer process, globular repelled transfer mode and surface tension transfer mode, were observed. The aluminum flux addition changed the droplet diameter, transfer time and relative proportion of metal transfer mode. When the thermite addition increased from 0 to 50%, the weld penetration depth increased from 2mm to 4mm, and the weld dilution rate increased from 22% to 37%.

Study of underwater wet welding stability using an X-ray transmission method

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 (32V). When the arc voltage is less than 32V, 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 1Hz and the bubble diameter is larger than 24mm.

Sensitivity model for prediction of bead geometry in underwater wet flux cored arc welding

To investigate influence of welding parameters on weld bead geometry in underwater wet flux cored arc welding (FCAW), orthogonal experiments of underwater wet FCAW were conducted in the hyperbaric chamber at water depth from 0.2 m to 60 m and mathematical models were developed by multiple curvilinear regression method from the experimental data. Sensitivity analysis was then performed to predict the bead geometry and evaluate the influence of welding parameters. The results reveal that water depth has a greater influence on bead geometry than other welding parameters when welding at a water depth less than 10 m. At a water depth deeper than 10 m, a change in travel speed affects the bead geometry more strongly than other welding parameters.

Spectroscopic analysis of the arc plasma of underwater wet flux-cored arc welding

Experiments in air and under water (0.4m depth) were conducted and the spectrum signals collected. The width of the weld under water was about two-thirds of the width in air, suggesting that the arc plasma was compressed by the water environment. The two sets of spectrum signals were largely similar except for the ultraviolet spectrum, from where the environmental effects were inferred. The analysis identified a unique peak at 656.2793nm in the underwater spectrum, consistent with H atomic transitions, suggesting that H atoms become involved, although without affecting the overall spectral similarity of the two environments. In either environment the arc plasma was mainly composed of self-shielding gas and evaporated metals, with only minor effects stemming from the interaction with water.