Underwater Joint Research Articles

UnitModule: A lightweight joint image enhancement module for underwater object detection

Underwater object detection faces the problem of underwater image degradation, which affects the performance of the detector. Underwater object detection methods based on noise reduction and image enhancement usually do not provide images preferred by the detector or require additional datasets. In this paper, we propose a plug-and-play Underwater joint image enhancement Module (UnitModule) that provides the input image preferred by the detector. We design an unsupervised learning loss for the joint training of UnitModule with the detector without additional datasets to improve the interaction between UnitModule and the detector. Furthermore, a color cast predictor with the assisting color cast loss and a data augmentation called Underwater Color Random Transfer (UCRT) are designed to improve the performance of UnitModule on underwater images with different color casts. Extensive experiments are conducted on DUO for different object detection models, where UnitModule achieves the highest performance improvement of 2.6 AP for YOLOv5-S and gains the improvement of 3.3 AP on the brand-new test set (URPCtest). And UnitModule significantly improves the performance of all object detection models we test, especially for models with a small number of parameters. In addition, UnitModule with a small number of parameters of 31K has little effect on the inference speed of the original object detection model. Our quantitative and visual analysis also demonstrates the effectiveness of UnitModule in enhancing the input image and improving the perception ability of the detector for object features. The code is available at https://github.com/LEFTeyex/UnitModule.

Rehabilitation Techniques for Offshore Tubular Joints

Exposure to load and offshore environment degrades the load-bearing capacity of tubular joints, necessitating reinforcement of these joints. Reinforcement is sometimes required for lifespan enhancement or qualification based on new requirements. Available reinforcement techniques include welded rings inside/outside the chord, doubler/collar plate at the brace-chord interface, grout filling, and clamp installation on the joints with/without cement. While these techniques increase the load-bearing capacity of damaged tubular joints, various practical limitations exist. Clamping may require heavy machinery, whereas welding stiffeners involves hot work and may not be permitted sometimes. Fiber-reinforced polymers (FRPs) have immense potential for reinforcing steel structures and are a viable alternative for rehabilitating tubular joints due to their exceptional mechanical and physical characteristics, offering competitive advantages over other methods. FRP reinforcement is becoming more feasible and economical for underwater joints. FRP reinforcement can be either precured, pre-impregnated, or wet layup. Aside from the significance of joint rehabilitation, a document covering the well-known options was lacking. This paper summarizes the advantages and limitations of these reinforcement methods, particularly FRP reinforcement. Possible research directions in FRP reinforcement of tubular joints are also discussed.

Underwater Local Cavity Welding of S460N Steel.

In this paper, a comparison of the mechanical properties of high-strength low-alloy S460N steel welded joints is presented. The welded joints were made by the gas metal arc welding (GMAW) process in the air environment and water, by the local cavity welding method. Welded joints were tested following the EN ISO 15614-1:2017 standard. After welding, the non-destructive—visual, penetrant, radiographic, and ultrasonic (phased array) tests were performed. In the next step, the destructive tests, as static tensile-, bending-, impact- metallographic (macroscopic and microscopic) tests, and Vickers HV10 measurements were made. The influence of weld porosity on the mechanical properties of the tested joints was also assessed. The performed tests showed that the tensile strength of the joints manufactured in water (567 MPa) could be similar to the air welded joint (570 MPa). The standard deviations from the measurements were—47 MPa in water and 33 MPa in the air. However, it was also stated that in the case of a complex state of stress, for example, bending, torsional and tensile stresses, the welding imperfections (e.g., pores) significantly decrease the properties of the welded joint. In areas characterized by porosity the tensile strength decreased to 503 MPa. Significant differences were observed for bending tests. During the bending of the underwater welded joint, a smaller bending angle broke the specimen than was the case during the air welded joint bending. Also, the toughness and hardness of joints obtained in both environments were different. The minimum toughness for specimens welded in water was 49 J (in the area characterized by high porosity) and in the air it was 125 J (with a standard deviation of 23 J). The hardness in the heat-affected zone (HAZ) for the underwater joint in the non-tempered area was above 400 HV10 (with a standard deviation of 37 HV10) and for the air joint below 300 HV10 (with a standard deviation of 17 HV10). The performed investigations showed the behavior of S460N steel, which is characterized by a high value of carbon equivalent (CeIIW) 0.464%, during local cavity welding.

Underwater laser welding for 304 stainless steel with filler wire

Underwater laser welding for 304 stainless steel with filler wire was successfully performed with a self-designed double-side gas-shielding nozzle. The effects of the back gas flow rate, travel speed and wire feed speed on the welding appearance, geometry characteristics of cross section, defects and mechanical property of butt joints were investigated. While the bottom surface of joint touched the water directly, the surface appearance was uneven and some small pores formed. With increasing the back gas flow rate to 50 L/min, the stable local dry cavity around welding zone was generated and an underwater laser welded joint without defects was obtained. After the optimization of process parameters, the tensile strength and impact toughness of the underwater laser welded joint approached those of in-air joint basically, and the using of filler wire improved the tensile strength of butt joint significantly. Compared to the in-air joint, the water cooling effect decreased both the area and width of fusion zone of underwater joint. This accelerated cellular dendrites grew up from fusion line to the bead center, which reduced the number of equiaxial grain and thus decreased the tensile strength slightly. In addition, the high cooling rate decreased the grain size, but increased the lathy ferrite content in fusion zone of underwater joint, decreasing the toughness of weld metal.

Dissimilar friction stir spot welding of AA2024-T3/AA7075-T6 aluminum alloys under different welding parameters and media

This paper studies the friction stir spot welding of AA2024-T3/AA7075-T6 Al alloys in the ambient and underwater environments by clarifying the nugget features, microstructure, fracture and mechanical properties of the joints. The results show that the water-cooling medium exhibits a significant heat absorption capacity in the AA2024-T3/AA7075-T6 welded joint. Nugget features such as stir zone width, circular imprints, average grain sizes, and angular inter-material hooking are reduced by the water-cooling effect in the joints. Narrower whitish (intercalated structures) bands are formed in the underwater joints while Mg2Si and Al2CuMg precipitates are formed in the ambient and the underwater welded joints respectively. An increase in tool rotational speed (600–1400 rpm) and plunge depth (0.1–0.5 mm) increases the tensile-shear force of the welded AA2024-T3/AA7075-T6 joints in both the ambient and underwater environments. The maximum tensile-shear forces of 5900 N and 6700 N were obtained in the ambient and the underwater welds respectively.

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.

Microstructure and properties of underwater laser welding of TC4 titanium alloy

Underwater local dry laser welding of TC4 alloy was carried out through a double-side gas-shielding nozzle, and the heat input and defocus distance were optimized by analysing the weld quality. With increasing heat input, the fusion zone (FZ) and heat-affected zone (HAZ) expanded, while the amount of vapour increased, resulting in an increase in the degree of oxidization of the underwater joint; the mechanical properties improved initially and subsequently deteriorated, influenced by bead oxidization and welding defects. With increasing defocus distance, the width of the FZ increased gradually, whilst the width of the HAZ remained largely unchanged. Excellent tensile strength and impact toughness were obtained when the laser beam was focused on the upper surface. In the FZ of the underwater laser welding (ULW) joint, the microstructure comprised full martensite α′ with an acicular morphology, whereas a small amount of grain boundary α-phase appeared in the FZ of the in-air joint, and the thickness of the α′ lamellae decreased compared to that of the in-air joint due to the higher cooling rate of the ULW joint. The impact toughness and tensile strength of the underwater joint reached ˜90% of the values for the in-air joint, and a mixed fracture mode was operative in the fracture surfaces.

An Experimental Study of Galvanic Corrosion on an Underwater Weld Joint

Kong, X.F.; Lv, J.; Gao, N.; Peng, X., and Zhang, J., 2018. An experimental study of galvanic corrosion on an underwater weld joint. In: Wang, D. and Guido-Aldana, P.A. (eds.), Select Proceedings from the 3rd International Conference on Water Resource and Environment (WRE2017). Journal of Coastal Research, Special Issue No. 84, pp. 63–68. Coconut Creek (Florida), ISSN 0749-0208.This study aimed to explore the galvanic corrosion behavior of an underwater weld joint using the polarization curve, galvanic current test, and microcurrent distribution test. The results revealed that galvanic corrosion evidently occurred in the area of the underwater weld joint, accelerating the corrosion process. The weld metal acted as the cathode, whereas the base metal (BM) and heat-affected zone (HAZ) acted as anodes. The maximum value of the cathode current in the weld region reached 3.5 μA. Corrosion current density was mainly decided by the diffusion process of dissolved oxygen (DO) in the seawater. As the immersion time increased, the oxygen diffusion process was hindered by the biofilm and sedimentary cover on the surface of the weld region, whereas the oxygen reduction reaction was suppressed. Therefore, the galvanic corrosion between the weld region and BM was further weakened.

Underwater Robotic Welding of Lap Joints with Sandwiched Reactive Multilayers: Thermal, Mechanical and Material Analysis

ABSTRACTUnderwater welding using reactive materials pre-deposited at the junction surfaces as a self-contained, in-situ ignitable heat source mitigates external power and gas supply requirements. Consequently, lending itself to robotic implementation eliminating the cost along with health and safety hazards of human welder-divers. This project reports on lap joining of aluminum sheets with sandwiched commercial reactive Ni-Al multilayers that are perforated to allow for melt fusion under compression upon ignition, in saline and deionized water as well as air for comparison. Finite-element thermal simulations are employed to study the resulting welding temperature field and melt conditions. Infrared pyrometry and thermocouple measurements during welding were used to validate the computational simulations. The lap joints are subjected to standard shear testing, and comparable compliance, strength and toughness values of the welds are assessed for underwater and dry joints. Scanning electron (SEM) of the weld sections reveal rapidly melting and solidifying microstructures of the parent metal, with minimal melt flow and perfusion of nickel aluminide aggregates from the reacted multilayers, and no signs of cavitation.

Numerical and experimental study on the effects of welding environment and input heat on properties of FSSWed TRIP steel

In this paper, the effect of input heat and welding environment on microstructure and mechanical properties of friction stir spot welded TRIP steel sheets were investigated. Six types of joints produced in both air and water environments and under rotational speeds of 900, 1350, and 1800 rpm. Then, the microstructure and mechanical properties of them were studied. The thermal histories, strain, and strain rate distributions of cases obtained by finite element modeling. According to the temperature and strain distribution and microstructural observations, four different zones determined in welding region: stir zone, thermomechanically affected zone, and high and low temperature heat-affected zones. It is obtained at in-air welds by increasing the rotational speed, the strength of joints increase to a maximum value because of higher strain rate and more recrystallization of prior austenite grains. The strength then decreases due to high amount of heat input and growth of recrystallized grains. Thermal history of underwater welds showed lower peak temperature and rapid cooling rate. Also, by increasing rotational speed in underwater joints, the strength and hardness increased because of microstructure refinement. The fracture surfaces of joints showed a dimple pattern ductile fracture in all cases except 1800 rpm in-air joint that the fracture was less ductile which agrees with lower tensile elongation of it.

The strengthening mechanism of spray forming Al-Zn-Mg-Cu alloy by underwater friction stir welding

Spray forming Al-Zn-Mg-Cu alloy has been welded successfully by underwater Friction Stir Welding (underwater FSW). The joint is defect-free with tensile strength of 406.06MPa and improved elongation (1.96%). Microstructure of underwater joint has been improved in which the hard-etched area is eliminated compared with traditional joint. The microstructure of joints was observed by OM and SEM. EDS, DSC, XRD and TEM were applied to do further study on the evolution of strengthening phases. The results show that water cooling method has improved the thermal cycle of welding. The microstructure of joint and the strengthening mechanism of underwater joint had a close relationship with the effect of water cooling method. The system analysis of underwater FSW process has been illustrated. Water cooling method creates rapid cooling process to introduce GPII zone and reserve a large amount of needle-like semi-coherent structure MgZn2 which is {0001}η(η′) ∥{111}Al dispersing in the matrix. The strength of joint has been enhanced by coherency strengthening.

The adjustment strategy of welding parameters for spray formed 7055 aluminum alloy underwater friction stir welding joint

In present work, the adjustment strategy of Underwater Friction Stir Welding (UFSW) parameters for spray formed 7055 aluminum alloy has been discussed by 3 groups welding experiment by changing rotation or traveling speed. The thermal cycles, microstructures, especially Reentrant Zone (RZ), tensile properties and micro-hardness of joints have been compared. The results show that the underwater joint which presents good properties has full weld nugget with wider and deeper RZ. It proves that the rotation speed has a wider adjustment range than traveling speed for UFSW process. In the water cooling environment, the fluidity of metal is weakened sharply. High rotation speed can ensure the fluidity of metal till the joint is filled completely that shows better properties. SEM&EDS and XRD results show that these joint keeps most of MgZn2. It indicates that a high rotation speed can be applied to UFSW process without worrying about overheating the joint. In the cooperation of high rotation speed and water environment, the joint is under a dynamic heat remedy process which makes the joint under a balance thermal cycles so that achieves better property. The parameter of high rotation speed and high traveling speed is recommended for UFSW.

Corrosion behavior of spray formed 7055 aluminum alloy joint welded by underwater friction stir welding

Abstract Friction stir welding with water cooling method had modified the microstructure of spray formed 7055 aluminum alloy but the corrosion behavior of alloy had been affected as well. Despite the tensile property having increased 15%, the corrosion behavior of underwater joint was more complex than base metal and traditional joint. Underwater joint characterized with an atypical pattern of intergranular corrosion (IGC) that its corrosion paths were not along the grain boundary though it still suffered a rank 4 IGC. At the same time, underwater joint was slightly sensitive to exfoliation corrosion (EXCO) and crossed 3-level-leap of corrosion rank within 24 h. Tafer curves illustrated more negative corrosion potential and lower corrosion current density for underwater joint than base metal and traditional joint. High potential phase MgCu 2 in traditional joint blocked corrosion process to some extend but non-uniform distribution of MgCu 2 led to weak zone for corrosion. In comparison with traditional joint, underwater joint avoided the formation of MgCu 2 and kept a large quantity of efficient strengthening particles (MgZn 2 ) in the matrix. Though MgZn 2 with more negative potential than that of MgCu 2 would lead to a higher sensitivity to corrosion, underwater joint still showed better corrosion resistance compared with base metal. In the process of underwater friction stir welding, MgZn 2 had been stirred into grains leaving grain boundary a high potential zone. Since corrosion paths were discontinuous and not along with the grain boundaries, corrosion process was blocked so it performed better resistance to corrosion and corrosion rate of underwater joint had decreased a lot compared with traditional joint and base metal.

Microstructure and mechanical properties of spray formed 7055 aluminum alloy by underwater friction stir welding

Ultra-high strength spray formed 7055 aluminum alloy in which Zn is supersaturated solid solution requires strict control of heat input in welding process. In this paper, underwater friction stir welding is carried out in order to reduce heat input comparing with traditional friction stir welding and further improve the joint performances by varying welding temperature history. Through comparing the thermal cycle curves and distribution of residual stress of the plate welded in different media, the reason why the joint welded underwater shows a better performance is figured out. The result shows that tensile strength, hardness and plasticity of underwater welded joint are better than that welded in air. The underwater joint has a fine grained microstructure without “S line” defect, a typically distinct boundary between the weld nugget zone and the thermal mechanically affected zone and a narrow heat affected zone. The main strengthening phase in underwater joint is MgZn2 .

Thermal modeling of underwater friction stir welding of high strength aluminum alloy

The thermal modeling of underwater friction stir welding (FSW) was conducted with a three-dimensional heat transfer model. The vaporizing characteristics of water were analyzed to illuminate the boundary conditions of underwater FSW. Temperature dependent properties of the material were considered for the modeling. FSW experiments were carried out to validate the calculated results, and the calculated results showed good agreement with the experimental results. The results indicate that the maximum peak temperature of underwater joint is significantly lower than that of normal joint, although the surface heat flux of shoulder during the underwater FSW is higher than that during normal FSW. For underwater joint, the high-temperature distributing area is dramatically narrowed and the welding thermal cycles in different zones are effectively controlled in contrast to the normal joint.

Characteristics and Formation Mechanisms of Welding Defects in Underwater Friction Stir Welded Aluminum Alloy

Underwater friction stir welding (FSW) has been demonstrated to be a promising method for strength improvement of heat-treatable aluminum alloy joints. However, when improper welding parameters are utilized, welding defects, such as voids can be produced in the joints, leading to dramatically deteriorated mechanical properties. Thus to obtain high-quality underwater joints, it is necessary to understand the variables that promote the formation of these defects. In this study, the characteristics of welding defects in underwater joints were examined, and the formation mechanisms of the defects were investigated by analyzing the material flow patterns during underwater FSW. The results indicated that welding defects can occur at both low- and high-rotation speeds (HRS). The defects formed at HRS can be divided into two types according to the welding speed. When a HRS and a low welding speed are chosen, the material beneath the tool shoulder tends to be extruded into the pin stirred zone (PSZ) after flowing back to the advancing side. This results in a turbulent flow condition, creating void defects in the PSZ. When a high welding speed is coupled with the HRS, a large amount of material from the thermo-mechanically affected zone is dragged into the pin hole, which causes the material of the shoulder stirred zone to fill the pin hole in a downward flow direction. This leads to turbulent flow in PSZ, and creates voids or even groove defects in the as-welded joints.

Effect of Water Cooling on Grain Structures and General Mechanical Properties of 2219-T6 Friction Stir Welded Joint

Regarding the friction stir welding (FSW) of heat–treatable aluminum alloys, although the thermal flow does not cause any material fusion, it can still deteriorate the local mechanical properties of the joints due to coarsening or dissolution of the strengthening precipitates. Therefore, it is of significance and possible to improve the joint properties by controlling the temperature level. For this purpose, a 2219-T6 aluminum alloy was underwater friction stir welded in the present study, and the temperature histories, grain structures and the general mechanical properties of the joints were investigated in order to illuminate the effect of water cooling. The results reveal that the water cooling action can effectively control the temperature level in the joint. The recrystallized grains in the weld nugget zone (WNZ) are significantly refined under the water cooling effect. The mechanical analysis indicates that the tensile strength of the joint can be improved by 6% through the external water cooling action. Additionally, the underwater joint also exhibits superior bend and impact properties to the normal joint, indicating the positive effect of water cooling on the general mechanical properties of the joints.

Homogeneity of Mechanical Properties of Underwater Friction Stir Welded 2219-T6 Aluminum Alloy

Underwater friction stir welding (FSW) has been demonstrated to be available for the improvement in tensile strength of normal FSW joints. In order to illuminate the intrinsic reason for strength improvement through underwater FSW, a 2219 aluminum alloy was underwater friction stir welded and the homogeneity of mechanical properties of the joint was investigated by dividing the joint into three layers. The results indicate that the tensile strength of the three layers of the joint is all improved by underwater FSW, furthermore, the middle and lower layers have larger extent of strength improvement than the upper layer, leading to an increase in the homogeneity of mechanical properties of the joint. The minimum hardness value of each layer, especially the middle and lower layers, is improved under the integral water cooling effect, which is the intrinsic reason for the strength improvement of underwater joint.

Microstructural evolution and its effect on mechanical performance of joint in underwater friction stir welded 2219-T6 aluminium alloy

Underwater friction stir welding (FSW) has been demonstrated to be an effective method to improve the mechanical properties of joints. To illuminate the characteristics of underwater FSW, the microstructural evolution and its effect on mechanical performance of an underwater joint were investigated in the present paper. The weld nugget zone (WNZ) is characterised by the homogeneity of refined grain structures in the direction of thickness. The precipitate deterioration is gradually strengthened from the heat affected zone (HAZ) to the WNZ. The dislocation movement featured by different types of grain boundaries suggests that continuous dynamic recrystallisation has occurred in the WNZ during FSW. The evolutions of strengthening precipitates and grain structures have significant influence on hardness distributions and the tensile fracture features of the underwater joint.

Microstructure and mechanical properties as a function of rotation speed in underwater friction stir welded aluminum alloy joints

A 2219-T6 aluminum alloy was underwater friction stir welded at a fixed welding speed and various rotation speeds in order to illuminate the influence of rotation speed on the performance of underwater joints. With increasing rotation speed, the hardness of the stir zone (SZ) gradually increases due to the increase in dislocation density. The tensile strength first increases from 600 to 800 rpm and then reaches a plateau in a wide rotation speed range. After that a remarkable decrease in tensile strength occurs owing to the formation of void defect. The joint welded at lower rotation speed tends to be fractured in the SZ. At higher rotation speeds, the hardness increase in the SZ makes the fracture locations of defect-free joints move to the thermal-mechanically affected zone (TMAZ) or heat affected zone (HAZ).