Underwater Wet Welding Research Articles

Current Research and Recommended Development on Fatigue Behavior of Underwater Welded Steel

Underwater welding is the process of joining materials in the underwater. This process carried out to maintain or improve the structure of the material in water environments such as rivers and the sea. The underwater welding process consists of dry and wet welding. Underwater dry welding (UDW) is a welding method using a chamber that conditioned in the air environment. Whereas underwater wet welding is the welding process using a particular waterproof stick electrode, which directly water environments. UWW does not require a specific area during the welding process so that the operation is more accessible than other methods. So, the cost required is cheaper. However, the UWW technique has a disadvantage due to the water waves whose magnitude is always changing around the welding area. Cyclic loads that occur continuously can cause defects in the underwater welding results, such as inclusions. If there are several inclusions, so it will cause an increase in the rate of fatigue crack propagation. Fatigue behavior in the underwater joint can be a significant problem that must resolve. Therefore, this review article can be a reference in determining the steps to improve and increase the fatigue resistance of underwater welding joints.

A novel underwater submerged-arc welding acquires sound quality joints for high strength marine steel

The serious interferences from the surrounding water severely limit the process stability and joint quality of the current underwater welding technologies. To effectively isolate the welding area, a mixture of epoxy resin and submerged-arc flux was innovatively prepositioned in the welding area during underwater welding process. Butt welding experiments of a typical high strength marine steel were conducted to verify the advantages of this technique. Compared with the traditional underwater wet welding, underwater submerged-arc welding significantly optimized the arc burning environment due to the covering and isolation, which effectively improved the stability of welding process. Defectless joints with microstructure that full of fine acicular ferrite and high-quality mechanical properties, especially, outstanding performance of ultimate strength and plasticity were obtained. The results are expected to positively widen the practical application of underwater welding in many water related industries.

Investigation of Arc Bubble Affecting the Arc Stability and Improvement of Weld Appearances Using Bubble Constraint Device in Underwater Wet Welding

The generating, floating and collapsing of arc bubble is a special phenomenon in underwater flux-cored wet welding. The configuration changing process of bubble will change the stress on droplet and influence the droplet transfer process. In this study, the shape changing of bubble is captured in graphic and the real-time electric signal data is obtained. The impact of bubble floating and collapsing results in the globular repelled transfer mode, which also reduces the arc stability. A self-designed gas-shield cover is used as a bubble constraint device to improve the welding process stability and weld appearances by limiting the free floating and expansion of arc bubble. The relationships between the cover diameter and the characteristics of weld appearance are studied.

Effect of Parameters Change on the Weld Appearance in Stainless Steel Underwater Wet Welding with Flux-Cored Wire

The underwater wet welding (UWW) technology is rapidly developing as a crucial method in the maintenance work of marine equipment and offshore platform. The rapid development of UWW technology has also exposed the problems to be solved urgently. Therefore, the influence of welding parameters on the weld appearance and welding spatters was investigated in this paper. The main welding parameters used in the study are welding current, arc voltage, welding speed and the contact tip-to-work distance (CTWD). Through the orthogonal test, it is found that, as each welding parameter increases within a certain range, the amounts of welding spatter decreases first and then increases, and the weld forming effect first becomes better and then deteriorates. The amount of wet welding spatter is mainly affected by the welding speed. When the welding speed is low, the splash is more, and the change of the welding current and the arc voltage has a little effect on the number of spatters. When the welding speed is large, the spatter is most with a small welding current and a large arc voltage. After evaluating the weld morphology obtained by welding under various parameters, a set of optimal parameters was obtained. The best parameters for the underwater wet welding of stainless steel with self-shielded flux-cored wire are determined to be 200 A-29 V-2.0 mm/s-15 mm (CTWD).

Impeding effect of bubbles on metal transfer in underwater wet FCAW

Aiming at the complicated physical process of underwater wet welding, two background light sources, laser and dysprosium lamp, are combined with high-speed camera to realize synchronous visual sensing of metal transfer, bubble evolution and arc behaviors. The dynamic changes of droplets and bubbles under different arc voltage conditions are investigated. Their interaction relationships are described in detail. From the perspective of the bubble impeding the metal transfer, the reason for the large droplet diameter and low transfer frequency under low arc voltage conditions is analyzed. The gas flow drag force (FL) is the largest at the neck of the bubble separation stage, which greatly affects the stability of the metal transfer process. When the droplet is located above the neck, it is easy to be carried away by separated bubbles to form a spatter. At the same time, the bubbles rising away from the axis of the wire can easily cause the droplet to deviate from the wire.

Experimental study of arc bubble growth and detachment from underwater wet FCAW

The bubble around the arc burning zone, defined as arc bubble, is the key factor to affect the process stability and joint quality in underwater wet welding. In this study, visual sensing of the bubble growth and detachment based on a high-speed camera in conjunction with a dysprosium lamp was realized. The extracted boundaries of a growing arc bubble were obtained via an image processing of the captured raw images. The bubble geometries were then calculated and determined. The relationships between the bubble geometries and welding heat input were experimentally investigated. Three distinct stages, including the formative stage, the elongation stage, and the detachment stage, were defined to describe the bubble growth along with a neck’s evolution. The variation trends of bubble geometries under different heat inputs were discussed to elucidate the bubble dynamic effect. For underwater wet welding, this provides a new orientation to promote the development of wet welding technology by sensing bubble growth.

Dynamic control of current and voltage waveforms and droplet transfer for ultrasonic-wave-assisted underwater wet welding

Ultrasonic vibration can change the dynamic behavior of the bubble and improve the process stability in underwater wet welding (UWW); thus, it has been attempted to profitably control metal transfer process. Arc signals about welding current and arc voltage together with the high-speed imaging detected in conventional UWW and ultrasonic-wave-assisted UWW (U-UWW) were used as information source for determining the droplet transfer mode. The results show that the change in the characteristics of bubble motion affects the droplet transfer process in U-UWW. During the short-circuiting transfer process in small arc voltage, the frequency of arc extinction and the peak of short-circuiting current are both decreased. During the droplet repelled transfer process in middle arc voltage, the droplet repulsive phenomenon is weakened, and the transfer frequency is increased from 7.9 Hz to 10.5 Hz at 34 V. Meanwhile, the droplet diameter is reduced and its transfer stability is improved. During the droplet repelled transfer process in high arc voltage, the frequency and duration time of arc extinction are both reduced. The underlying difference of droplet transfer process between conventional UWW and U-UWW was investigated by the two aspects including ultrasonic wave effect and dynamic bubble effect.

Influence of CaF2 on microstructural characteristics and mechanical properties of 304 stainless steel underwater wet welding using flux-cored wire

Underwater wet welding (UWW) of 304 stainless steel was performed using a set of wires with various calcium fluoride contents. The appearances, compositions, microstructural characteristics and mechanical properties of welding joints were analyzed. As the proportion of CaF2 rose, the welding appearances had been improved owing to the increasing coverage of slag. The depth-width ratio descended from 33.5% to 15.7% with an increase of CaF2 from 0% to 65% due to the reduction of the molten pool heat. Microstructural observations showed that the fully austenitic weld metal was consisted of four regions and the proportion of each region varied with the content of CaF2. The t8/5 cooling times of the heat affected zone were prolonged from 4.4 s to 6.1 s as the CaF2 content increased from 0% to 65%, which contributed to the microstructure variation. Besides, the uppermost element in the welds was Ni (at least 65%) whose content gradually went up with more and more CaF2 in the wire. Under the same conditions, the concentration of the solutes in the Ni-based welds lowered, encouraging the dislocation to be smaller and more dispersive. It was 20% CaF2 that the wire contained when the weld reached the best mechanical property with 522 MPa tensile strength and 132.74 J/cm2 impact toughness.

Research and Application of Underwater Wet Welding Technology

Underwater wet welding has the characteristics of simple equipment and flexible operation. This paper introduces the basic principle of underwater wet welding, focusing on wet welding by welding materials, welding methods and the influence of water environment.

In situ X-ray imaging of melt pool dynamics in underwater arc welding

The dynamic behavior of the underwater melt pool was firstly in-situ observed with the X-ray transmission method. A method for quantitatively characterizing the melt pool stability was pioneered. Comparing with conventional melt pool composing metal liquid, the pool was filled with bubbles in underwater environment. By observing the X-ray images and charactering the weld pool waveform, it is confirmed that the underwater melt pool was more volatile than onshore melt pool, which was mainly caused by the evolution of large bubble in the pool. Violent fluctuation of melt pool was the basic reason gaining poor weld and multiple defects in the underwater wet welding. To mitigate pool fluctuations by reducing the size of bubble, the ultrasonic vibration was applied directly on the workpiece, which improved the melt pool stability, uniformized the weld formation, and decreased the weld porosity.

Control of Droplet Transition in Underwater Welding Using Pulsating Wire Feeding.

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.

Arc stability indexes evaluation of ultrasonic wave-assisted underwater FCAW using electrical signal analysis

Ultrasonic wave-assisted underwater flux-cored arc welding (FCAW) has the potential to control the dynamic bubble and then improve arc stability. In this study, the four indexes evaluation methods to determine arc stability, i.e., oscillograms, cyclograms, probability distribution, variation coefficients of the welding current and arc voltage, were conducted to study the effect of ultrasonic wave on the arc stability. Results show that it is reasonable to evaluate the variation in arc stability with the welding parameters including wire feed speed and arc voltage, or without/with an ultrasonic wave by using the four indexes evaluation methods. Further, the control of the dynamic bubble induced by the exertion of ultrasonic wave can be used to explain why the arc stability is improved. The key points to excellent arc stability depend on both the designation of the welding parameters and reasonable control of the bubble with structural integrity. Therefore, through the novel method which combines optimized welding parameters with a stable bubble environment, the achieved welding process can effectively reduce the bubble disturbance and enhance the arc stability. Results presented in the paper aim to understand the combined influence mechanism of welding parameters and ultrasonic wave on the arc stability in underwater wet welding.

Advantages of the Application of the Temper Bead Welding Technique During Wet Welding.

Thermo-mechanically rolled S460ML steel was chosen for welding in underwater wet welding conditions by covered electrodes. The main aim of this study was to check the weldability for fillet welds in a water environment by controlled thermal severity (CTS) tests and to check the influence of temper bead welding (TBW) on the weldability of the investigated steel. Non-destructive and destructive tests showed that S460ML steel has a high susceptibility to cold cracking. In all joints, hardness in the heat-affected zone (HAZ) was extended to the 400 HV10 values. Microscopic testing showed the presence of microcracks in the HAZ of all welded joints. TBW was chosen as the method to improve the weldability of the investigated steel. This technique allows for the reduction of the maximum hardness in the HAZ below the critical value of 380 HV10, as stated by the EN-ISO 15614-1:2017. It was determined that for S460ML steel, from the point of view of weldability, the pitch between two beads should be in the range 75%–100%. Also, if the pitch between two beads increases, the hardness, grain size, and number of cracks decreases. In all specimens where the hardness of the HAZ was below 380 HV10, there were no microcracks.

Effects of arc bubble behaviors and characteristics on droplet transfer in underwater wet welding using in-situ imaging method

The effects of arc bubble behaviors and characteristics on droplet transfer are observed with an in-situ X-ray imaging method. The changes in the force acting on the droplet are analyzed at three distinct stages of arc bubble in one life cycle. The maximum gas flow drag force acting on the droplet exists in the moment that bubble just contacts the droplet. The deviation angle between droplet and wire axis increases with the bubble expansion rate, which increases the probability of welding spatter, and then reduces welding stability. The deviation angle of droplet is reduced by limiting the expansion of arc bubbles at a certain hydrostatic pressure. A new kind of arc bubble constraint device is designed and applied to limit the free expansion and floatation of arc bubble, which improves the metal transfer stability and the weld appearance.

Microstructure and mechanical properties of dissimilar welds between 16Mn and 304L in underwater wet welding

ABSTRACTDissimilar joint between 304L austenitic stainless steel and low-alloy steel 16Mn was underwater wet welded using self-shielded nickel-based tubular wire. Microstructure, mechanical properties and corrosion behaviour of dissimilar welded joints were discussed. Ni-based weld metal was fully austenitic with well-developed columnar sub-grains. Type II boundary existed between Ni-based weld metal and ferritic base metal in underwater welds similar to that in air welds. Major alloying elements distributed non-uniformly across the austenitic weld metal/16Mn interface. Maximum hardness values in wet welding appeared in a coarse-grained heat-affected zone at the 16Mn side, which possessed very low impact toughness. Underwater Ni-based welded joints fractured at Ni-based weld metal under tensile test. Ni-based weld metal had favourable corrosion resistance similar to 304L base metal.

Investigation of acoustic radiator affecting bubble-acoustic interaction in ultrasonic wave-assisted UWW at shallow water

The evolution mode of the dynamic bubble around the arc burning zone plays an essential role in adversely affecting the stability of underwater wet welding (UWW) process. Ultrasonic wave-assisted UWW (U-UWW) provides such a promising approach to control the bubble evolution and achieve a large and stable bubble. In fact, the enhancement of bubble-acoustic interaction capabilities by optimization of acoustic radiator also provides chances for the development of U-UWW. In this work, acoustic radiator with a concave surface has been designed in order to investigate the effect of curvature radius on the bubble-acoustic interaction. Analysis of the high-speed imaging in conjunction with welding current and arc voltage waveforms was carried out to understand the variation in bubble evolution for process control and how the bubble evolution was affected by varying curvature radii. The study indicated that stable bubble can be more easily achieved in U-UWW because it minimizes the extent of the undesirable bubble evolution occurring in an erratic and time-variant behavior. The difference in the shape and motion track of the bubble is also observed in different curvature radii. Acoustic field simulations confirm the acoustic pressure changes with curvature radius, consistent with experimental result that the maximum degree of ultrasonic control of the bubble indeed appears in practice. Observations and analysis of arc stability and weld morphology revealed that the addition of ultrasonic wave in UWW contributes to an improvement in the welding process. Due to varying curvature radii, the degree of improvement also produces significant differences. Furthermore, in terms of bubble evolution, arc stability, weld morphology and acoustic field simulation, the degree of bubble-acoustic interaction follows the order: R = 38 mm > R = 30 mm > R = 46 mm > conventional UWW, suggesting that curvature radius of 38 mm exhibits a better interaction performance.

Correlation between wire feed speed and external mechanical constraint for enhanced process stability in underwater wet flux-cored arc welding

It is a great challenge to improve the process stability in conventional underwater wet welding due to the formation of unstable bubble. In this study, mechanical constraint method was employed to interfere the bubble generated by underwater wet welding, and the new method was named as mechanical constraint assisted underwater wet welding. The aim of the study was to quantify the combined effect of wire feed speed and condition of mechanical constraint on the process stability in mechanical constraint assisted underwater wet welding. Experimental results demonstrated that the introduction of mechanical constraint not only suppressed the bubble without floating but also stabilized the arc burning process. The degree of influence of mechanical constraint, which changed with wire feed speed, played an important role during the mechanical constraint assisted underwater wet welding process. For all wire feed speeds, the fluctuations of welding electrical signal were decreased through introduction of mechanical constraint. The difference in the proportion of arc extinction process between underwater wet welding and mechanical constraint assisted underwater wet welding became less with increasing wire feed speed. At wire feed speed lower than 7.5 m/min, the improvement of process stability was very significant by mechanical constraint. However, the further improvement produced limited effect when the wire feed speed was greater than 7.5 m/min. The observation results showed that a better weld appearance was afforded at a large wire feed speed, corresponding to a lower variation coefficient.

Comparison of underwater wet welding performed with silicate and polymer agglomerated electrodes

Conventional basic electrodes varnished and basic electrodes agglomerated with polymer in underwater wet welding in a simulated depth of 10 m were compared. A hyperbaric tank was used for depth simulation and a gravity welding device for making the bead on plate welds. Bead on plate welds were deposited with welding currents of 100, 120, 140, 160 and 180 A with DCEN and DCEP polarities, in order to evaluate the arc stability through a non-dimensional statistical index. The welding current which showed better stability level in both polarities was chosen to evaluate weld bead morphology, weld metal porosity, weld metal oxygen and diffusible hydrogen levels. A methodology was used to correlate the heat input and short-circuit frequency with the weld bead morphology. It was observed a direct relation with the weld metal oxygen and penetration and an inverse relation of the weld metal oxygen with the diffusible hydrogen. Electrodes agglomerated with polymer showed higher penetration values than conventional electrodes in both polarities and lowest diffusible hydrogen levels in the DCEP polarity. It was observed lower levels of weld metal porosity for the electrodes agglomerated with polymer in comparison to conventional electrodes. This result was related to lower levels of porosity found in the droplets formed at the tip of the electrodes agglomerated with polymer.

Effects of welding speed on bubble dynamics and process stability in mechanical constraint-assisted underwater wet welding of steel sheets

Dynamic behavior of the bubble was investigated by high-speed camera and using the dysprosium lamp method for welding speed ranging from 1.0 mm/s to 6.0 mm/s during conventional underwater wet welding and mechanical constraint-assisted underwater wet welding. Process stability analysis was conducted by welding electric signal to predict the evolution of bubble features. For conventional underwater wet welding, the variation in bubble geometry over time is visually observed and its track morphology changes from a vertically upward track to a deflected track with increasing welding speed. The stable and sustained bubble with its structural integrity benefits from mechanical constraint for all welding speeds. Mechanical constraint can compensate for the insufficient bubble protection and successfully prevent further bubble-induced perturbation on welding arc. In comparison to onshore welding and underwater wet welding with mechanical constraint, conventional underwater wet welding indicates the most variation of welding electric signal. The variation coefficient exhibits similar result with welding speed for the exertion of mechanical constraint, whereas the difference in variation coefficient exists for conventional underwater wet welding. The direct observation over weld morphology is also demonstrated to show the feasibility of bubble control using the developed process. Discernible difference in weld penetration appears, displaying higher value with mechanical constraint than without mechanical constraint.

Influence of calcium fluoride on underwater wet welding process stability

To explore the influence of calcium fluoride on underwater wet welding process stability, the relevance of calcium fluoride in the flux to metal transfer mode and arc stability was discussed in the process of underwater wet welding using a set of wires with various calcium fluoride contents. The metal transfer images were obtained using X-ray imaging system and the electric signal detection system was used to collect arc voltage and welding current signals synchronized with the film frames. Three metal transfer modes, i.e., repelled globular transfer, surface tension transfer, and spatter-like metal droplet transfer, were observed during the underwater wet welding process. The spatter-like metal droplet transfer mode was put forward firstly. Increasing the contents of calcium fluoride in the wire from 0 to 65%, the proportion of surface tension transfer mode steadily climbed from approximately 15 to 40% while that of spatter-like metal droplet mode declined from 53 to 35%. The arc stability of the welding process firstly deteriorated and then ameliorated with the increasing calcium fluoride content.