Underwater Welding Research Articles

수중 용접봉으로 용접한 누수배관 용접부위의 부식 특성 평가

Leakage trouble on the sea water pipeline in engine room is often resulted from a localized corrosion due to severe corrosive environment caused by both high speed and high pressure of sea water flowing through the inner pipe. In addition, when the ship is in stand-by or emergency condition, underwater welding to control the leakage of sea water from a hole of its pipe is very important in an industrial safety point of view. In this study possibility of underwater welding to control leakage of sea water and corrosion property of its welding zone were investigated with the electrochemical methods by parameters of welding methods and welding electrodes when underwater welding is achieved with a such case that sea water is being leaked out with a height at 50㎜ from a hole of 2.5㎜ø of test pipe. Corrosion resistance of weld metal zone is better than the base metal and its hardness is higher than that of the base metal. However corrosion potential of weld metal zone showed a negative value than that of the base metal, therefore weld metal zone is preferentially corroded rather than the base metal by performance of galvanic cell due to difference of corrosion potential between weld metal zone and base metal. Eventually it is suggested that leakage of sea water is successfully controlled by underwater welding.

1553 溶融池振動モデルを用いた水中溶接の溶け込み制御に関する研究(S14 溶接・接合の動向とその展開,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Recently, welding process has been used under various environments. Under extreme environment such as vacuum, weightless and underwater condition, the need of automation technology of welding increases. In this research, the molten pool oscillation phenomenon in underwater welding was modeled. The calculated back bead width was obtained from the oscillation frequency and the dimension of the molten pool. Arc current was controlled using the difference between target and calculated back bead width. From the results of welding control experiments, the effectiveness of the system is confirmed.

洋上接合時の溶接変形を考慮した超大型浮体式海洋構造物の形状管理

Recently, the utility of VLFS (Very Large Floating Structures) attracts great deal of public attention. In order to construct VLFS, however, some technical problems remain. Because it is too large to build at any building dock or other site on the ground, the construction by joining floating units together on the sea is inevitable. Some advanced engineering for constructing operations on the sea are necessary, such as maintaining precise measurement of each unit, joining units in waves, underwater welding techniques.Demonstration with a large floating model was carried out by Technological Research Association of Mega-Float (TRAM) from 1995 to 2001. During construction of floating model, we found out it is important to estimate the welding distortion precisely, because it causes distortion of VLFS itself and the misalignment among units. Since complete restriction of the distortion at sea is impossible, precise estimation of the distortion become essential for super-sizing VLFS. In order to solve this problem, we had trial estimation by FEM analysis.In this paper, concerning on welding distortion, comparisons between experimental results and estimation by FEM analysis are shown. As a result, we show it is possible to estimate the welding distortion of VLFS under construction precisely. Moreover, we show FEM analysis can suggest the procedure to make geometrical inaccuracy and misalignment among units minimum by controlling the shapes of units and their placing position.

Vision-based seam tracking system of the underwater flux-cored arc welding

To track seam automatically during underwater flux-cored arc welding(UFCAW),a vision-based seam tracking system has been studied.This seam tracking system consists of a vision sensing system,an image processing and seam recog- nizing system,a control system and executive unit.The edge of the weld line is precisely detected by a wavelet transform method.The seam position error is calculated by a seam posi- tion recognition algorithm based on the binary image.Based on the theoretic analyze of the structure model of the vision-based seam tracking system,a control rule self-adjust fuzzy controller is designed.The factors of decreasing the precision of the seam tracking system are analysised,and some measures are adopted to improve the tracking precision.The tracking experiments results of the UFCAW confirm that the control rule self-adjust fuzzy controller meet the demand of the tracking precision.In the tracking trials of sidelong,reflex and curve weld line,the system can all meet the demand of the tracking precision.With the improved mini drain water cap,the tracking experiments of the underwater local dry welding are carried.The results indi- cate that this process can not only meet the demand of improve welding quality but also satisfy the tracking results.

Study of Underwater Laser Welding Repair Technology

IHI developed underwater welding process by using YAG laser and qualified the process to repair a thin wall stainless steel tank in a power plant in Japan. Important features of YAG laser welding are less welding distortion, and a small heat-affected zone (HAZ) due to the smaller heat input and higher cooling rate than with other conventional welding methods. In this study, we have conducted underwater laser welding of Ni-base alloy and stainless clad materials, such as Alloy 600 and E-309L / E-308L clad materials. Alloy 690 was selected as weld filler metal for a corrosion resistant overlay to prevent corrosion attack by the service environment. Welding trials were conducted on the surface of flat plates with simulated surface cracks, and the trial welds were assessed for soundness of welding. The preliminary results of the trial welds by using high power laser diode, and comparison between YAG laser and high power LD are reported.

Vision based seam tracking system for underwater flux cored arc welding

Manual underwater welding is usually time consuming, expensive and hard to perform because of the rigorous underwater environment. Automatic underwater welding can be performed faster at less cost and with higher quality. An automatic seam tracking system for underwater flux cored arc welding has been developed. It consists of a vision sensing module, a seam recognition module, a fuzzy controller (FC) and an X–Y travel platform. The vision sensing module can capture clear seam images during welding, successfully resolving the problem of welding arc interference during underwater flux cored arc welding. The seam recognition module filters, enhances and thresholds the seam images and then recognises the seam deviation angle with a three layer back propagation neural network. The FC outputs the control parameters according to the seam deviation angle and then controls the X–Y platform to drive the torch to the centre of the seam. In this study, three different welds were considered: a straight line, a kinked straight line and an S curved line. These welds were tracked real timely during underwater flux cored arc welding. The results show that this seam tracking system can meet the requirements of the automatic underwater flux cored arc welding.

Relationship between weld quality and optical emissions in underwater Nd: YAG laser welding

In underwater laser welding (LBW), the weld quality is very dependent on the shielding conditions of the local dry cavity when other welding parameters are fixed. Thus, diagnosing the stability of the local dry cavity is the key to monitoring of underwater LBW. In this work, a sensing system containing two optical sensors was set up to detect the infrared and ultraviolet waveband of the optical emissions induced in the welding. The effect of water on the laser welding was studied first by conducting direct underwater welding, which was performed without any method to exclude the water from the welding zone. A kind of plasma that has strong ultraviolet emission formed if the water depth was more than several millimeters, which considerably reduced the penetration depth. Then a gas-shielding nozzle was used to form a local dry cavity for underwater LBW. The relationship between the optical signals and the weld quality with various shielding conditions were investigated. The results show that the detected signal well reflects the shielding condition variations of the local dry cavity. The optimal shielding condition could be determined by signal stability.

Special features of the effect of hydrogen on the weldability of structural steels in underwater welding by the ‘wet’ method

(2003). Special features of the effect of hydrogen on the weldability of structural steels in underwater welding by the ‘wet’ method. Welding International: Vol. 17, No. 3, pp. 221-225.

６０６１アルミニウム合金の水中摩擦圧接

The some characteristics of the underwater friction welded joints of 6061 aluminum alloy, which were made by using a brake type friction welding machine, were examined with different welding conditions. The highest temperature of the friction welding process on the underwater welding was considerably lower than that of the atmospheric welding, and both friction pressure and friction time did not hardly affected to the temperature on the friction welding process. The total loss of the underwater welded joint became smaller compared with atmospheric welded joint, moreover the width of softening area on the underwater welded joint reduced and the softening ratio also decreased. The maximum joint efficiency of the underwater welded joint could be obtained 86%, it was slightly lager than that of the atmospheric welded joint which was 82%. The elongation of the underwater welded joints were lower than that of the atmospheric welded joint. Both the underwater and atmospheric welded joints fractured in the softened area under the tensile load.

Recent developments in underwater wet welding

Recent developments in underwater wet welding

Newly Undertaken Inspections and Repairs for Aged Nuclear Power Generators

Some of the Japan's oldest nuclear generation plants are now entering their 30th year, which is close to their designed lifespan. The Rules on fitness-for-service for nuclear power plants undertaken by utilities are to extend the lifetime of plants to 60 years. Upon lifetime extension new rules must be applied and JSME (Japan Society of Mechanical Engineers) issued new rules in May 2000. These rules define allowable flaw sizes in operating plant components. In these circumstances, in-situ flaw sizing and repairs are urgently needed. Accordingly, laser inspections such as laser UT and laser holography and low heating repairs such as underwater laser welding and friction surfacing are being developed.

Reuse of Shielding Gases in Underwater Welding by Pressure Swing Adsorption

Reuse of Shielding Gases in Underwater Welding by Pressure Swing Adsorption

331 溶接技術情報データベース構築を目的とした画像処理技術の開発(OS 加工・検査のロボット化・知能化)

Authors have been accumulating many experimental data of underwater welding process for offshore construction, maintenance and repair. Arc welding is the most basic technology in industry, however, physical analysis of arc welding process is still an outstanding issue. We analyze motion pictures of arc phenomena to understand actual arc welding process. Recent advancement of Information Technology makes it possible to provide this dynamic information of arc welding process as a multimedia database. We describe summary of the welding process information database in XML and the technique to reduce data size.

水中溶接における冷却過程の評価

Underwater welding technologies are of growing importance with increasing of waterfront projects. Underwater welding technique also provides effective means for repairing many kinds of offshore structures. It should be pointed out, however, that such important properties as the cooling cycle and the joint strength in the underwater welding are not fully understood. In the previous studies, cooling cycle of underwater welding conducted in the water at rest was investigated. From a site welding point of view, it is necessary to elucidate how a tidal current and a wave affect the welding operations and the strength of welded joint.In this paper, underwater welding is performed in the running water, and the effects of water flow velocity on the cooling process are studied. The experiments are conducted in a water tank especially designed for this purpose, where the flow velocity is varied up to 30cm/sec. Accordingly, significant characteristics of the cooling curves and cooling rates are estimated.

Image Processing for Automatic Welding in Turbid Water

Wet underwater welding is a key to improving offshore construction and maintenance cost performance. Automatic wet welding with local dry space provided by a water curtain provides high-quality mechanical properties on weld metal. The most important factor in maintaining high weld quality is precise nozzle positioning. Light cutting by slit laser beam shows potential for shape recognition in air. Waterproof containers for the laser emitter and video camera are used for underwater seam tracking of weld line in turbid water. Acrylic windows on the laser emitter and video camera shortened the total light path length in turbid water and improved image quality. Laser light was dimmed by scattering in turbid water but detected groove geometry, enabling good seam tracking. A trial to get a clear image used a fiberscope camera in the welding nozzle and detected root gap width precisely. Welding conditions such as molten pool geometry were also detectable.

Current state of underwater welding and cutting

Current state of underwater welding and cutting

On the influence of wet underwater welding on CTOD-δ5

The influence of wet underwater welding on the crack tip opening displacement CTOD-δ5 is investigated in this paper. The welding process is numerically simulated. The instationary temperature field and welding residual stresses are calculated using the finite element method (FEM). The crack tip opening displacement for a sharp, stationary crack on the surface of a bead-on-plate weld under bending is determined. The results for an underwater wet welded specimen and a dry welded specimen are compared. The welding residual stresses are considered in the 3D fracture mechanics FE calculation as well as the material heterogeneity due to the different material properties of weld metal, heat-affected zone and base metal.

Underwater Wet Repair Welding and Strength Testing on Pipe-Patch Joints

The underwater wet welding method for repairing of submerged structural members has been intensively developed during the last years. It is an economical and especially more time-independent procedure. The shortened repair duration is a major advantage in regions with rough sea climate as the North Sea area. During research projects the weldability and fatigue performance of pipe-patch connections have been tested. These joints are in use for repairing of collision indents. The shape of the actual used repair patch was optimized to the requirements of underwater wet welding at high tensile strength steels as BS4360 Gr 50D. Steel materials in this grade show problems in regard to high hydrogen susceptibility, and therefore cold cracking. The fatigue behavior of the patch-welded pipe structural member has been investigated. First test series were carried out using as-welded joints. In a second part of the project, post-weld-treated connections were tested. The weld seams on these joints were partially ground or hammer peened. The test results have been evaluated by means of the hot-spot concept and then faced with actual code requirements. Extensive strain gage measurements and finite-element calculations have been carried out to provide the stress state in the structural details.

High power laser welding in hyperbaric gas and water environments

A hyperbaric laser welding facility has been constructed and the feasibility of high power CO2 and Nd:YAG laser welding in both high pressure gas and water environments, to simulated water depths of 500 m, has been established. From initial trials on welding through water at atmospheric pressure, it was found that the different absorption characteristics of water to 10.6 μm (CO2 laser) and 1.06 μm (Nd:YAG laser) radiation proved crucial. The Nd:YAG laser was totally unsuitable as the beam was largely diffused in the water, whereas the CO2 beam was readily absorbed and, using high speed video equipment, was found to form a high irradiance channel and a dry region around the weld area. Welding under a high pressure gas environment produced a highly energized plume which prevented keyhole welding at pressures over 1 × 106 Pa. An investigation carried out into the efficacy of a gas jet delivery system to alleviate the extent of the plume showed that argon blown horizontally across the weld was the optimum configuration, extending the welding range up to 5 × 106 Pa. A limited investigation into high pressure underwater welding showed porosity to be a problem although sound welds were produced at pressures up to 2 × 106 Pa.

水中溶接における冷却過程の解析

Recently, the importance of underwater welding has been increasing as a number of waterfront projects are progressing. Underwater “wet type” welding is considered to be particularly useful for repairing offshore structures so built. It has essential drawbacks, however, that the weld portions are rapidly cooled due to high rates of heat dissipation into surrounding water, which decreases the strength of welded joints. In the previous paper, three dimensional Finite Difference Method has been applied to evaluate the cooling rates of underwater welding. In this report, the numerical method is improved to obtain better results to simulate the specific characteristics of cooling rates in underwater welding. The amount of heat transferred into surrounding water is evaluated by following calculation procedures proposed for corresponding heat transfer mechanism, such as free convection, nucleate boiling, etc., with surface temperatures of plates measured by thermocouples. The validity of numerical method presented here is ascertained by comparing experimental results.