Air Welding Research Articles

AE Evaluation of Relationship between AE Signals and Fracture Mechanisms for the Weldment of Pressure Vessel Steel

The purpose of this study is to find out the AE characteristics and fracture mechanisms through AE signal analysis for the weldment, PWHT specimen and basemetal of the pressure vessel steel. Charpy sized specimens were taken from the multi-passed weld block. Specimens were given to four point bend and AE tests. Lots of AE signals were emitted from the weldment compared with the basemetal and PWHT specimen. Besides, amplitude for the weldment was the largest, followed by PWHT specimen and basemetal and more AE counts for the weldment were emitted in the process of deformation. Lots of microcracks around the notch for the weldment were formed so that more AE signals were produced. In addition, second phase particle such as MgO for the basemetal acts as AE source. However, in case of weldment, debonding mechanisms between matrix and hard oxides which are formed during welding in air attributed to the emission of AE signals and softened particles for the PWHT specimen cause to produce the low level AE signals.

Braze Pressure Welding (BPW) - A New Method for Joining Steel Pipes -

Braze Pressure Welding (BPW) with high frequency induction heating is a newly developed pressure welding technique using interlayer metals for welding the general steel pipes for pipe arrangement in buildings. BPW enables to make joints by solid-state welding in air using a flux sheet which is also developed for this technique. In this method, the interlayer metal is expected to play the primary role in making high performance joints. At a joining temperature, the melted interlayer removes contaminations from the joining surfaces of the base metals. Then the liquid filler is discharged from the joining interface by the joining pressure, and forms fillets at the gaps around the joint. In this stage, the joining pressure is relatively small, so the welding deformation can be restrained to a minimum. The fillets have the effects both on relaxing the stress concentration at the joint and on increasing the joining area, which contribute to the strengthening of the joint. Thus, the high quality pipe joining without the dispersion in joint properties due to welder’s skill can be performed. In this report, the concept and merits of BPW are explained, and the results of the investigation on the cleaning effect of the interlayer metal and the effects of fillet formation on strengthening the joint are discussed. The practical application of BPW in Japan is also introduced.

Butt Welding Joint of Aluminum Alloy by Space GHTA Welding Process in Vacuum

Aluminum alloys have been used widely in constructing various space structures including the International Space Station (ISS) and launch vehicles. For space applications, welding experiments on aluminum alloy were performed using the GHTA (Gas Hollow Tungsten Arc) welding process using a filler wire feeder in a vacuum. We investigated the melting phenomenon of the base metal and filler wire, bead formation, and the effects of wire feed speed on melting characteristics. The melting mechanism in the base metal during the bead on a plate with wire feed was similar to that for the melt run without wire feed. We clarified the effects of wire feed speed on bead sizes and configurations. Furthermore, the butt welded joint welded using the optimum wire feed speed, and the joint tensile strengths were evaluated. The tensile strength of the square butt joint welded by the pulsed DC GHTA welding with wire feed in a vacuum is nearly equal to that of the same joint welded by conventional GTA (Gas Tungsten Arc) welding in air.

真空中での宇宙ＧＨＴＡ溶接法によるアルミニウム合金の突合せ溶接

Aluminum alloys have been widely used in the constructing various space structures including the International Space Station (ISS) and launch vehicles. For space application, welding experiments of an aluminum alloy were conducted by the GHTA (Gas Hollow Tungsten Arc) welding processes using a filler wire feeder in vacuum. We investigated the melting phenomena of a base metal and a filler wire, bead formation phenomena and effects of wire feeding speed on melting characteristics. The melting phenomenon of melt-run welding with a filler wire was basically the same as that of without a filler wire. It was clarified that the effects of wire feeding speed on bead sizes and configurations. Furthermore the butt welding joints were welded by the optimum wire feeding speed and the tensile strengths of those joints were evaluated. The mean value of tensile strengths of butt welding joints that were made using d.c.-pulsed GHTA welding with filler wire in vacuum was almost same value as that was welded by GTA (Gas Tungsten Arc) welding in air.

Fatigue crack growth behavior of laser-processed 304 stainless steel in air and gaseous hydrogen

Fatigue crack growth test was performed to evaluate fatigue behavior of 304 stainless steel specimens with or without laser processing (welding and surface treatment) in air and gaseous hydrogen. As the crack propagation normal to the laser welding or scan direction, the laser-processed specimens exhibited a higher resistance to crack growth in the low stress intensity factor range (Δ K) than the as-received steel plates regardless of testing environments. However, the marked retardation of crack growth behavior vanished for welded specimens subjected to a 850 °C/h stress relief treatment or with a shorter distance from notch tip to the weld centerline in the test. Fatigue-fractured appearance of the steel plate tested in air was composed of mainly transgranular fatigue fracture and some flat facets, along with a small amount of intergranular fracture. While quasi-cleavage fracture and few twin boundary separations were observed for the same specimen in hydrogen. On the other hand, the lower crack growth rate of laser-processed specimens in both air and hydrogen was accompanied with rubbed areas on the fracture surfaces. It was found that the extent of quasi-cleavage fracture was related to the formation of strain-induced martensite, which would contribute to an increased fatigue crack growth rate of all specimens in gaseous hydrogen.

水中溶接における冷却過程の解析

Underwater welding techniques have been of growing importance as a number of new projects for offshore structures are underconsideration and some of them are being put into practice. Underwater“wet type”welding is especially useful for the repair and maintenance of those structures. In the previous paper, fundamental characteristics of wet welding such as heat transfer from plate to surrounding water have been evaluated using mixed gas shield welding, and the extent of heat transfer was quantitatively estimated in terms of coefficients of heat transfer. In addition, three dimensional Finite Difference Analysis was attempted to obtain temperature distributions within the plate. In this paper, cooling process for underwater welding is compared with that for welding in air, where the effects of welding conditions such as welding speed and plate thickness are discussed. It is also shown that the cooling rates for underwater welding could be analyzed within acceptable engineering accuracy using three dimensional FDM.

Welding sheet F-2M fluorinated plastic

Measurements have been made on the mechanical strength, microhardness, and morphology of welded joints in F-2M sheet plastic as affected by the temperature conditions during liquid welding. Liquid welding has advantages over hot air welding. Differential thermal analysis shows that destructive processes occur in the thermal welding of F-2M fluorinated plastic.

湿式水中アーク溶接に関する研究 ＩＩＩ 高張力鋼のインプラント試験

The cold cracking sensitivity of high strength steel in wet underwater welding was experimentally investigated by means of the implant weldability test with coated electrodes.The experiments were done with HT60 steel plates and D5003 covered electrodes, and the specimen6 mm in diameter having 1 pitch 40 degree spiral V notch with 0.5 mm depth, and 0.1 mm tip radius.The results are the following:(1) In the implant two pass welding in comparison to single pass welding, the lower critical stress for the cold cracking (σcr)imp increased by about 20 kgf/mm2 to about 55 kgf/mm2 in underwater welding and also by about 20 kgf/mm2 to about 75 kgf/mm2 in air welding: The lower critical stress ((σcr)imp in underwater welding was about 65-75 percentage of that in air welding.(2) By underwater two pass welding the columnar structure of the weld metal was transformed into a globular structure, and the martensitic structure of the heat-affected zone was transformed into the tempered structure. By air two pass welding the needle-like martensitic structure of the heat-affected zone was transformed into a bainite structure which was a fine pearlite.(3) In underwater welding, the micrography of the implant fracture surface showed mainly the quasi-cleavage of hydrogen embrittlement and the intergranular pattern near the notch in case of single pass welding. In air welding, it showed mainly the dimple fracture, and the quasi-cleavage of hydrogen embrittlement at lower stress.

湿式水中アーク溶接に関する研究 ＩＩ 高張力鋼溶接部の衝撃値および疲労強度について

The knowledge of notch toughness of welded joint-parts is very important for safety of welding structure. The welded parts have metallurgical discontinuity such as weld metal, bond and heat-affected zone, etc.; the Charpy impact test is often used for the valuation of notch toughness for the parts.It is well known that the fatigue strength of welded parts reduces to less than that of base metal. There are many factors reducing their fatigue strength: for example, geometrical effect of reinforcement, residual stresses and microstructural change in the heat-affected zone.In this paper, welding experiments are done by using HT60 steel plates and D5003 covered electrodes, and the specimens taken from welded joints in air and in underwater are examined by the impact and the fatigue tests. The results are the following:(1) In the impact test, the fracture transition temperature does not affect the oxygen and nitrogen absorption, but it does influence the hardness of the notch zone; the lower the hardness goes down, the lower the transition temperature does.(2) In air and underwater welding, the fatigue fractures occur in the weld metal; the fatigue limit of the joint parts is about 15 kgf/mm2 because of hydrogen embrittlement and blowholes in underwater welding, but 23 kgf/mm2 in air welding.(3) The micrography of the fatigue fracture surface shows mainly quasi-cleavage fracutre pattern of hydrogen embrittlement in underwater welding, and dimple fracture pattern in air welding.(4) In underwater welding, the structure in the neighborhood of the fatigue fracture consists of the ferrite and the pearlite, and the needle-like ones of the ferrite are of the widmanstatten-type. On the other hand, in air welding, it consists of the bainite where the columnar structure is made finer by the effect of the heat treatment due to the multi-pass welding.

湿式水中アーク溶接における鋼材のＴＲＣ試験 Ｉ

The initiation and propagation of root cracks in steel have been investigated with oblique y, straight Y and 45° single bevel grooves of the TRC test in the underwater wet welding process with covered electrode. Welding experiments are carried out by using HT 60 steel and D5003 covered electrode.The following results are obtained:(1) The diffusible hydrogen quantity reaches to the constant volume in about 2.4 x 104 min. (about 408 hrs.), where in air, it is about 30 cc/ 100 g Fe, and in underwater, about 70 cc/100 g Fe, i.e., the more root cracks occur in underwater welding.(2) The maximum hardness of the heat-affected zone is about Hv 350 in air, and Hv 440 in underwater, thus the crack sensitivity is higher in underwater welding.(3) In the TRC test, the lower critical stress of straight Y groove is higher than that of 45° single bevel groove in both air and underwater welding.(4) As for no-fracture specimens in the TRC test in underwater welding, there are many microfissure at the martensitic structure in the coarse grained zone near the bond.(5) The fracture surface shows predominantly the dimple pattern in air welding, while in underwater welding, the quasi-cleavage of hydrogen embrittlement pattern is widely observed there and near the root it shows many intergranular patterns.

１湿式水中アーク溶接に関する研究 Ｉ 被覆アーク溶接棒の適用性について

The feasibility of wet welding process in underwater with covered electrode is investigated. Welding experiments are done with HT 60 steel plate and D5003 covered electrode.The following results are obtained:(1) The hardness of heat-affected zone seems to be relatively low in case of two pass welding.(2) In underwater welding, weld metal seldom has blowholes, and no cracks are observed on the weld metal in X-ray inspection.(3) In underwater welding the oxygen absorption of weld metal is about 1.7 times of that in-air welding, the nitrogen absorption has about 0.25 times.(4) The quantity of diffusible hydrogen collected in mercury reaches to a constant volume in about 2.4 × 104 min. (408 hr).: In air welding, it is about 30 cc/100 g in case of one pass welding and about 25 cc/100 g in case of two pass welding; in underwater, it is about 70 cc/100 g in case of one pass welding and about 55 cc/ 100 g in case of two pass welding.(5) On two pass welding, the quantity of diffusible hydrogen is about 20% less than one pass welding.

Monitoring personnel exposure to stainless steel welding fumes in confined spaces at a petrochemical plant

This paper documents exposure to stainless steel welding fumes at a petrochemical plant. The situation evaluated may be separated into three categories: 1) evaluation of background concentration levels in a maintenance shop (area monitoring), 2) evaluation of personnel exposures during open air welding in a maintenance shop (personal monitoring), 3) evaluation of personnel exposures in confined space welding (personal monitoring). Thirty-five area samples and seventy-six personal samples were collected and analyzed for chromium (VI), total chromium, nickel, iron, copper, and total particulates. The background concentrations in the maintenance shop were found to be far below those felt to be harmful. Personnel exposures found in the maintenance shop during open air welding were also low, especially when compared to current OSHA permissible exposure levels. Contaminant levels found during confined space welding, as in distillation towers, were considered excessive. After several possible solutions to the problem were considered, it was decided to implement a mandatory air-line respirator program for all employees entering confined spaces during stainless steel welding operations.

高圧ふん囲気下のアーク溶接について

Argon gas is useful for conventional gas shielded arc welding in air, but it is harmful to diver/welder's health in pressurized atmosphere such as underwater hyperbaric welding. Although helium gas is more expensive than argon gas, it is the safest among other inert gases in pressurized atmosphere. Accordingly, this report describes the effects of ambient pressure up to 10 kg/cm2abs., shielding gases and welding parameteres on welding arc behaviors in pressurized atmosphere, that is, simulated underwater hyperbaric welding.The results obtained are summerized as follows;1) Arc voltage during TIG, MIG and SMA welding becomes higher with an increase in ambient pressure.2) Arc voltage during TIG and MIG welding with helium gas shielding is higher than that with argon gas shielding.3) Arc voltage during TIG and MIG welding is elevated by an increase in welding current.4) Penetration depth of welded bead becomes deeper as ambient pressure increases.5) Number of short circuiting transfer per second during MIG and SMA welding increase with an increasing in ambient pressure when weldingparameters are the same.* Kawasaki Heavy Industries, Ltd.

Mechanisms of Rapid Cooling and Their Design Considerations in Underwater Welding

Rapid cooling is an inherent problem in underwater welding. This paper discusses the basic understanding of cooling mechanisms during underwater welding and the effectiveness of various methods of reducing the cooling rate. Numerical results obtained from a computer analysis are used to discuss the design criteria and the effect of various parameters on the cooling rate. Introduction During the last several years, systematic research efforts on underwater welding have been made at the Dept. of Ocean Engineering of the Massachusetts Inst. of Technology. Most of the research programs were funded by the National Sea Grant Office of the National Oceanic and Atmospheric Admin. Some of the reports, theses, and papers have been published. The research programs have covered various subjects including basic research on mechanisms of underwater welding as well as development of new, improved processes. This paper discusses one subject: rapid cooling during underwater wet arc welding.* This paper has been prepared primarily from results obtained in research by Tsai.The major portion of Tsai's research is composed of extensive mathematical analyses of heat flow during underwater wet arc welding. A series of mathematical equations has been developed to analyze all pertinent phenomena involved: dynamics of bubble formation, heat-loss mechanisms, etc. Experiments were made to examine the validity of the analyses. Studies were made to investigate effects of various parameters (welding conditions, plate thickness, etc.) on cooling rates in weldments, especially in the heat-affected zone (HAZ). Studies also were made to evaluate the effectiveness of various methods of reducing the cooling rate.Since details of analytical and experimental results are included in Ref. 4, this paper presents a brief summary of the analysis and some experimental results. The emphasis of this paper is placed on information of practical importance. Brief Summary of Cooling Mechanisms in Underwater Welding The mode of heat transfer in underwater welding is quite different from that in air welding. The existence of dynamic bubbles during underwater welding induces a flow field around the welding arc. This water flow along with the agitation of bubbles carries the heat away quickly from the base material and causes the rapid cooling phenomenon. In this section, buble dynamics and heat-loss mechanisms are discussed. Underwater Bubble Dynamics Bubble generation due to the high concentration of heat in the arc and its departure and final collapse during the underwater arc welding process in the wet condition was investigated by a high-speed cinematography study at the Massachusetts Inst. of Technology. JPT P. 1825＾

A major advance in high-power electron-beam welding in air

A major extension of the capabilities of nonvacuum electron-beam welding follows from the development of a machine with higher beam power. Tests with a new atmospheric electron gun operating at 60 kW have shown that the advantages of nonvacuum electron-beam welding must be reevaluated. Gas heating produced by the beam itself becomes very pronounced, so that electron scattering is reduced causing the high-power density of the beam to be retained over larger working distances. Single-pass butt welds with a depth-to-width ratio of 4 : 1 can be made in 3.8-cm-thick steel at a speed of 0.77 cm/sec, while the ultimate welding depth exceeds 5 cm. Medium thick material, e.g., 1.3-cm steel, can be welded at a 5-cm work distance, with a depth-to-width ratio of 3 : 1. The large work distance permits access to more complex structures and interior corners such at T sections, which can now be fabricated from a plate, 1.3 cm thick, at a speed of 2–3 cm/sec, making a full through weld from one side. Also, seam welds of two 3-mm-thick hot-rolled steel sheets can be produced at speeds of up to 15 cm/sec. High-power machines need not be significantly larger or costlier than low-power guns, and the present 60 kW does not represent any technical limit. Welding efficiency improves with higher power; when welding steel of 2 cm thickness or more the energy efficiency of the process at 60 kW is better than 50%, while at 40 kW it is merely 30%. In addition, the high power permits greater welding speed. These developments translate directly into improved cost justification for electron-beam welding and a broad expansion of its possible applications.

Phosgene formation during welding in air contaminated with perchloroethylene.

The formation of phosgene caused by short-wave radiation from welding arcs in air contaminated with perchloroethylene has been studied experimentally, and compared with theoretical calculations. There is some agreement between the methods and it is concluded that welding in air contaminated with perchloroethylene is more hazardous than welding in air containing trichloroethylene or methylchloroform and should be avoided.

On the formation of phosgene by photo-oxidation of methyl chloroform in welding.

The formation of phosgene caused by short wave radiation from metal-inert gas welding in air contaminated with methyl chloroform has been studied experimentally, and by a calculation method. The results agree quite well and lead to the conclusion that methyl chloroform is not a safe solvent in welding environments.

Special Characteristic of the Steel Bare Electrode in Relation to the Motion of Molten Tip Under the Welding in Air

Special Characteristic of the Steel Bare Electrode in Relation to the Motion of Molten Tip Under the Welding in Air

Abridgment of cathode energy of the iron arc

For purposes of study, the available energy at the cathode of the iron arc for welding in air, and the disbursement of this available energy to the cathode processes, are set up in balance-sheet form. The energy as heat at the cathode includes that from (1) ionic bombardment, (2) ohmic resistance of cathode tip, (3) radiation from the anode, and (4) combustion. Since the division of total arc energy between anode and cathode is nearly an equal one, the sum of the first three should approximate one-half of the total energy input to the arc. Heat Disbursement at Cathode: The principal consumption of heat at the cathode is by (5) melting of cathode, (6) evaporation of atoms at cathode, (7) evaporation of electrons at cathode, (8) dissociation of arc vapors, (9) radiation to anode and to air. Of the total heat disbursed by the arc more than half is consumed, as shown by measurement, by the melting of the electrode. The heat consumption for this melting is greater than the calculated value of total heat received at the cathode. The latter value is therefore incorrect and needs to be revised, using higher values of V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> or φ + or both. On the other hand, the calculated total energy consumption at the cathode corresponds closely to one-half the measured total electrical input to the arc and is therefore approximately correct.

Cathode Energy of the Iron Arc

The available energy at the cathode of the iron arc for welding in air, and the disbursement of this available energy to the cathode processes, are set up in balance-sheet form for purposes of study. Since many of the constants involved are not accurately known the results obtained are approximate only and indicate the probable order of magnitude of the quantities involved rather than the exact quantities themselves. The paper thus represents a preliminary survey. The energy as heat at the cathode includes that from: (1) Ionic bombardment, (2) Ohmic resistance of cathode tip, (3) Radiation from the anode, (4) Combustion. The sum of the first three items should approximate one-half of the total energy input to the arc, (since the division of total arc energy between anode and cathode is nearly an equal one). Item (1) is by far the largest heat source. But using values of f = 0.625 (fraction of current at cathode which is carried by electrons) as determined by Compton and by Gunther-Schulze, and taking the cathode voltage drop V c = 9.0 volts which is higher than V 1 the ionizing potential, (= 7.83 volts, Mohler) this quantity, together with the smaller items (2), (3), and (4), is still too small to account for the observed rate of melting of the cathode. Possibly ?? + , the heat of condensation of incoming ions, is not zero for this arc as Compton has shown for the tungsten arc.