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.

The Influence of the Corrosion Product Layer Generated on the High Strength Low-Alloy Steels Welded by Underwater Wet Welding with Stainless Steel Electrodes in Seawater

The high strength low-alloy steels are welded by underwater wet welding with stainless steel electrodes. The microstructural and electrochemical corrosion study of base metal(BM), weld zone(WZ) and heat affected zone(HAZ) are carried out to understand the influence of the corrosion product layer generated on the high strength low-alloy steels welded by underwater wet welding with stainless steel electrodes, methods used including, potentiodynamic polarization, electrochemical impedance spectroscopy(EIS) and scanning electron microscope(SEM). The results indicate that the WZ acts as a cathode and there is no corrosion product on it throughout the immersion period in seawater. The HAZ and BM acts as anodes. The corrosion rates of the HAZ and BM change with the immersion time increasing. In the initial immersion period, the HAZ has the highest corrosion rate because it has a coarse tempered martensite structure and the BM exhibites a microstructure with very fine grains of ferrite and pearlite. After a period of immersion, the BM has the highest corrosion rate. The reason is that the corrosion product layer on the HAZ is dense and has a better protective property while that on the BM is loose and can not inhibit the diffusion of oxygen.

Study of pores produced in underwater wet welding

This paper deals with the effect of water depth in the range of 10 m to 80 m upon the formation of pores produced during underwater wet welding. The results show that it is easy for the inner pores to occur owing to the particularity of the molten metal solidification that the outer pores begin to appear when the water depth increases to about 60 m, that the porosity increases and pore grows up as the water depth increases, and that pores are all hydrogen-containing ones through the examination of the variation of number of pores with the residual hydrogen and oxygen content in the weld metal.

Microstructure and mechanical properties of E36 steel joint welded by underwater wet welding

The microstructure and mechanical properties of E36 steel joint welded by underwater welding using flux-cored wire are comprehensively investigated. The welding depth, welding current and welding voltage is 4 m, 130 A and 32 V, respectively. The weld metal is ferrite which varies in size, with carbide particles distributed on it, while the microstructure of HAZ is mixture of martensite of different size and some tempered structure. The microhardness of the weld metal is 190 HV. Almost all the tensile specimens fracture in weld metal and the average tensile strength of joint is 390 MPa, which is equal to 80% that of base metal. The tensile fracture morphology of joint presents obviously the characterization of brittle fracture, which displays the features of cleavage fracture and intergranular fracture.

Effects of process parameters on the depth-to-width ratio of flux-cored wire underwater wet welding

The effects of process parameters on the depth-to-width ratio （D/W） of flux-cored wire underwater wet welding with a certain type of homemade .flux-cored wire are studied. It is found that the welding .speed, wire feeding speed and torch oscillating amplitude hare significant effects on the dopth-to-width ratio （D/W） of welds. The D/W ratio of welds increases significantly with the increase of welding speed without the oscillating of welding torch. It increased （from 0. 14 to 0. 26 ） with the increase of wire feeding speed while the torch oscillating. And it decreased linearly with the increase of torch oscillating amplitude. However, the influelwe of oscillating speed, wire extension and welding voltage on the D/W ratio of welds was not obvious.

Development of underwater wet welding experimental and divers training system

Compared to traditional welding methods, the underwater wet welding is special with many different characteristics due to the unique aqueous environment. It is conducted completely under water by divers and unique welding technology is required in the special operation environment. The operating levels of the divers are the key factor to acquire high quality welded joints. In this paper, an underwater wet welding experimental and divers training system is developed to serve divers training and conducting welding experiments. The system consists of life support system, signals real-time monitoring system and communicating system, etc. An underwater butt welding experiment based on welding electrodes is conducted, and the system works well. It proves that the system can guarantee divers welding safely and successfully and high quality weld seam is expected to be acquired.

Analysis of the electrical conductivity of plasma during underwater wet welding

The electrical conductivity is indispensable for the underwater wet welding arc simulation. In order to get this parameter, the composition of the underwater arc is analyzed, and the electron content is obtained. Then the current formation mechanism in the arc and the effective collision cross-sectional area between the electron and ions is discussed. The calculation methods and results analysis are presented in this paper.

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

The thermal modeling of underwater friction stir welding （FSW） was conddcted 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.

Finite element analysis of the angular distortion and residual stress in underwater wet welding

In underwater environment, the shape, voltage, and energy density of the welding arc vary because of the high pressure and there are notable changes in workpiece cooling conditions due to the strong cooling effect of water. As a result, there are clear differences between the residual stress and thermal distortion in underwater wet welding and those in conventional welding （in air）. Considering these process features, a thermo-mechanical finite element model of underwater wet bead-on-plate welding was established. The influences of the water compressing action to the arc and the enhanced heat losses caused by the surrounding water on the residual stress and the angular distortion of the workpiece were analyzed. Results show that the angular distortion gets smaller in deeper water, and that the longitudinal residual stress gets smaller as water flows faster.

Modeling of underwater wet welding seam forming based on support vector machines

Underwater welding is developing fast because of the exploration of marine resources, and underwater wet welding automation is urgently needed because of the rigorous environment. To control the welding process automatically, the model of the process should first be built to predict the current welding process status. In this paper, arc and visual sensors were used simultaneously to obtain the electrical and visual information of underwater wet welding, and support vector machines （SVM） were used to model the process, experiment results showed that the method could effectively use the information obtained and give precise prediction results.

Review on underwater friction stir welding: A variant of friction stir welding with great potential of improving joint properties

Friction stir welding（FSW） is a solid-state welding process which is capable of joining materials which are relatively difficult to be welded by fusion welding process. Further, this process is highly energy-efficient and environmental-friendly as compared to the fusion welding. Despite several advantages of FSW over fusion welding, the thermal cycles involved in FSW cause softening in joints generally in heat-treatable aluminum alloys（AAs） due to the dissolution or coarsening of the strengthening precipitates leading to decrease in mechanical properties. Underwater friction stir welding（UFSW） can be a process of choice to overcome these limitations. This process is suitable for alloys that are sensitive to heating during the welding and is widely used for heat-treatable AAs. The purpose of this article is to provide comprehensive literature review on current status and development of UFSW and its importance in comparison to FSW with an aim to discuss and summarize different aspects of UFSW. Specific attention is given to basic principle including material flow, temperature generation, process parameters, microstructure and mechanical properties. From the review, it is concluded that UFSW is an improved method compared with FSW for improving joint strength. Academicians, researchers and practitioners would be benefitted from this article as it compiles significantly important knowledge pertaining to UFSW.

Seam Tracking Technology for Hyperbaric Underwater Welding

Automatic weld seam tracking technology to be used in hyperbaric underwater damaged pipeline repair welding is much more important, because of poor bevel preparation and severe working condition. A weld seam tracking system based on digital signal processing（DSP） passive light weld image processing technology has been established. A convenient charge coupled device（CCD） camera system was used in the high pressure environment with the help of an aperture and focus altering mechanism to guarantee overall image visibility in the scope of pressure below 0.7 MPa. The system can be used in the hyperbaric environment to pick up the real welding image of both the welding arc and the welding pool. The newly developed DSP technology was adopted to achieve the goal of system real time characteristics. An effective weld groove edge recognition technique including narrow interesting window opening, middle value wave filtering, Sobel operator weld edge detecting and edge searching in a defined narrow area was proposed to remove the guide error and system accuracy was ensured. The results of tracking simulation and real tracking application with arc striking have proved the validity and the accuracy of the mentioned system and the image processing method.

Underwater Laser Welding/Cladding for High-performance Repair of Marine Metal Materials:A Review

With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must be performed in underwater environments.The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment.The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique.First,we elaborated recent advances and key issues of drainage nozzles all over the world.Next,we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials.Then,the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed.The differences between the convection,conduction,and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated.After that,several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed.Finally,suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided.The present review will not only enrich the knowledge in the underwater repair technology,but also provide important guidance for the potential applications of the technology on the marine engineering.

Underwater friction stir welding of ultrafine grained 2017 aluminum alloy

2017 aluminum alloy plates with an ultrafine grained （UFG） structure were produced by equal channel angular processing （ECAP） and then were joined by underwater friction stir welding （underwater FSW）. X-ray diffractometer （XRD）, transmission electron microscope （TEM）, scanning electron microscope （SEM） and microhardness tester were adopted to investigate the microstructural and mechanical characteristics of the FSW joint. The results indicate that an ultrafine grained microstructure with the mean grain size of-0.7 Ixm is obtained in the weld nugget by using water cooling. However, The FSW joint exhibits softening compared with the ultrafine grained based material and the heat affected zone （HAZ） has the lowest hardness owing to the coarsening of the strengthening precipitates.

Research of chamber local dry underwater welding system and drainage properties

Because of relatively large protective area and good underwater welding quality, chamber underwater welding has a great using prospect in spent fuel pool maintenance at nuclear power plant. A chamber local dry automatic underwater welding test system with a data acquisition platform is developed, drainage seal tests in a water tank are carried out and the data acquired from the tests are analyzed. The results show that the chamber local dry underwater welding test system can achieve good drainage seal, the drainage effect is enhanced with the increase of the drainage gas flow rate and the drainage time. The results establish the foundation of the research of chamber local dry underwater welding.

Underwater robot local dry welding system

To satisfy the demand for good quality underwater welding and maintenance of nuclear power stations,a set of local dry automatic welding systems has been developed.These systems were based on an underwater robot that consisted of a special high-power underwater welding power supply,diving wire feeder,mini drain cap,welding robot,and special underwater welding torch.With a digital signal controller microprocessor as its core and combined with a dual inverter topology,the welding power supply was characterized by full-digital construction and multi-waveform flexible output.A compact diving wire feeding device was designed,based on the armature voltage negative feedback and high-frequency chopping pulse width modulation.This device yielded a high-efficiency seal of the driving motor with the help of dynamic and static sealing technology.To overcome the difficulty of local protection and deslagging in the welding area,a mini drain cap(with a duplexgas structure)based on the principle of the convergent nozzle was designed.The practical tests and the underwater welding experiments revealed that the underwater robotic local dry welding system is quite feasible.That is,the system could strike the arc stably and reliably in the shallow water environment,and formed beautiful welding seams.

Study of gas shielding stability for underwater local dry welding based on FLUENT

The research of gas shielding stability technology, playing a key role in underwater local dry welding, was introduced in this paper. The study includes shielding cup design, gas flow simulation, draining and welding experiments. The commercial computational fluid dynamics （ CFD ） software FLUENT was applied to get and compare the speed and pressure contour images of gas in the three kinds of cup with different intake mode. The computed results show that the cup with stilling chamber on the top has the best shielding performance. The underwater welding experiment of 15 meters proves that the shielding cup with stilling chamber can offer a good dry space, the welding arc can burn stably in it and the weld quality is perfect. The research will facilitate the application of underwater local dry welding technology in the maintenance of nuclear power station widely.

Finite element simulation of three-dimensional temperature field in underwater welding

Mathematical models of three-dimensional temperature fields in underwater welding with moving heat sources are built. Double ellipsoid Gauss model is proposed as heat sources models. Several factors which affect the temperature fields of underwater welding are analyzed. Water has little influence on thermal efftciency. Water convection coefftcient varies with the temperature difference between the water and the workpiece , and water convection makes molten pool freeze quickly. With the increase of water depth, the dimensions of heat sources model should be reduced as arc shrinks. Finite element technology is used to solve mathematical models. ANSYS software is used as finite element tool, and ANSYS Parametric Design Language is used to develop subprograms for loading the moving heat sources and the various convection coefftcients. Experiment results show that computational results by using double ellipsoid Gauss heat sources model accord well with the experimental results.

Short-circuit process model in underwater welding using rotating arc sensor

In order to detecting and tracking along the weld seam with rotating arc sensor in underwater welding,the highpressure water environment rotating arc welding hardware platform is established and welding experiments using rotating arc sensor is done. Different radius of rotating arc sensor is used. And the corresponding welding current and voltage is obtained,which is compared with the results of rotating arc sensor short-circuit process simulation model under high-pressure water environment established in this article. The results show that under high-pressure water environment,rotating arc radius should be optimized,otherwise the short-circuit-arcing cycle will transit to a short-circuit-arcing-abruption cycle,making the welding quality poor. At last the critical radius between the short-circuit-arcing cycle and short-circuit-arcing-abruption cycle under high-pressure water environment is obtained.

A novel wavelet method for electric signals analysis in underwater arc welding

Electric signals are acquired and analyzed in order to monitor the underwater arc welding process. Voltage break point and magnitude are extracted by detecting arc voltage singularity through the modulus maximum wavelet （MMW） method. A novel threshold algorithm, which compromises the hard-threshold wavelet （HTW） and soft-threshold wavelet （STW） methods, is investigated to eliminate welding current noise. Finally, advantages over traditional wavelet methods are verified by both simulation and experimental results.