Fundamental Research On Underwater Welding - American Welding Society
Fundamental Research on Underwater Welding Effects of water environment structures of welds on metallurgical BY R. T. BROWN AND K. M A S U B U C H I ABSTRACT. The study on which this paper is based was conducted as part of a systematic research on f u n damentals of underwater welding. The entire program covered various subjects including the heat transfer and flow during underwater welding, the mechanisms of metal transfer and arc bubble formation, and the effects of water environment on the metallurgical structures and the properties of underwater welds. This paper primarily discusses the last subject. An experimental investigation was made of the welding metallurgy and microstructure of underwater shielded metal-arc welds. The paper discusses various topics including temperature histories and microstructural transformation, optimum welding current and speed, optimum weld bead shape, and optimum hardness profiles. Introduction Attempts to use underwater welding for the repair and salvage of ships and other ocean engineering structures have been marginally successful since the early part of this century. During the First World War period, bare electrodes wrapped with some waterproofing material were used. Shielded metal-arc electrodes were utilized in underwater welding soon after their introduction into the welding industry in the late 1920's. Problems of underwater visibility led to the adoption of a drag welding technique for most underwater welding applications in the early 1930's. Iron powder electrodes were developed in 1946 and were found to improve underwater drag welding. The quality of R. T. BROWN is Graduate Student and K. MASUBUCHI is Professor at the Department of Ocean Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139. Paper was presented at the 55th AWS Annual Meeting held at Houston, Texas, May fi-70, 1074 178-s i J U N E 1975 even the best of these underwater welds was still substantially less than that of similar air welds. Underwater welds were r e p o r t e d to p r o d u c e about 80% of the tensile strength and 50% of the ductility of corresponding air welds (Ref. 1). But these low weld quality properties still provided for joint integrity that was satisfactory for the t e m p o r a r y repair welds and salvage applications for which they were used. The expansion of the offshore oil drilling and production industry has led to the construction of large, permanent steel platforms, tanks, and pipelines in the ocean. Repairs or modifications requiring welded joints have been hindered by the poor quality of underwater welds. This poor weld quality has been especially limiting to pipeline welding. The need for high quality underwater welds has led to m u c h e x p e r i m e n t a t i o n and i n vestigation into both technical and practical aspects of underwater welding (Ref. 2). In addition to the metalarc process, several approaches to underwater welding have been investigated including chamber welding (Refs. 3-8), gas metal-arc welding (Refs. 9-13), gas metal-arc welding enclosed in a movable, diver held chamber (Ref. 14), plasma arc welding (Refs. 15, 16) and explosive b o n d ing (Ref. 17). Although several of these processes show potential for improving the quality of underwater welds, most research and investigation remains centered around the shielded metal-arc process. Chamber welding techniques are limited by the high cost of a suitable chamber and the relatively few joint configurations which can be enclosed in a chamber. Gas metal-arc welding processes have produced excellent u n derwater welds especially when used in c o n j u n c t i o n w i t h a m o v a b l e chamber. The primary limitation of these processes is their increased c o m plexity, both in equipment and tech- nique. It may be that these sophisticated systems will solve the problem of producing high quality welds for critical applications such as pipeline welding. However, for structural repair, modification, and construction, the shielded metal-arc process might be preferred because of its relative simplicity. As the job depth increases, the need to use saturation diving and other engineering c o m plications will make it desirable to use only the simplest and most versatile welding processes and techniques (Refs. 18-20). Most of the developments and improvements in underwater welding have come from trial and error investigations by those who actually needed a more satisfactory underwater weld. But beginning in the early 1960's and continuing to the present time, several w o r k e r s have been studying the processes and phenomena of underwater welding on a more fundamental scientific and e n gineering basis. Several workers in Russia have r e p o r t e d on various aspects of both shielded metal-arc and thin wire (GMA) underwater welding processes (Refs. 21-35). A l though they have laid few theoretical foundations for the phenomena they have observed, their observations are many and precise. Dr. E. A. Silva has also done extensive work from this technical perspective (Refs. 36-39). During the last several years, a series of research programs has been c o n d u c t e d at the D e p a r t m e n t of Ocean Engineering of the Massachusetts Institute of Technology under the direction of Professor K. Masubuchi (Refs. 17, 40-47). The threeyear program on "Fundamental Research on Underwater Welding" was initiated on July 1, 1971. The objective of the program is to better understand fundamentals of underwater welding. The program covers the following phases: Phase 1: Survey of fundamental information on underwater
welding and cutting Phase 2: A study of heat flow during underwater welding Phase 3: Mechanisms of metal transfer in underwater arc welding Phase 4: Effects of water environment on metallurgical structures and properties of welds Phase 5: Development of new, i m proved underwater welding methods The program has been supported by the National Sea Grant Office of the National Oceanic and A t m o spheric Administration, Department of C o m m e r c e . The W e l d i n g Research Council and Ishikajima-Harima Heavy Industries have provided a portion of matching funds for the program during the second and the third year.* This paper presents primarily the work performed by R. T. Brown, and represents a significant portion of Phase 4. Details of the work are given in the M. S. thesis by Brown. A final report of the entire program is under preparation. Comparing Air and Water Welds Although the basic mechanisms of structural change are known and u n derstood, the highly transient and nonuniform nature of welding makes accurate microstructural prediction extremely difficult. Even if the weld microstructure were completely determined, it is doubtful that the resulting mechanical properties could be accurately predicted. Thus, experimental investigation and verification would be necessary. Similar uncertainties in the physical manipulation of the welding arc make a precise estimation of the welding heat input from specified welding conditions not possible. The specific nature of the links from the optimum welding c o n ditions to the heat input and temperature histories to the microstructural formations to the mechanical joint properties are not fully understood. The approach to determining how the heat transfer phenomena and microstructural transformations are affected by underwater welding — and thereby influence joint properties — has been to study the differences between air welding and underwater welding. Since the basic welding metallurgy in air has been well studied (Refs. 48-53), much unders t a n d i n g of u n d e r w a t e r w e l d i n g metallurgy can be gained by examining the dissimilarity between air and "Nine other Japanese companies provided additional matching funds during the third year to cover primarily the cost for printing the final report. water welds. Because most underwater welding has been performed under emergency conditions for salvage or temporary repair to ships and offshore structures, each situation has been s o m e w h a t u n i q u e and therefore not easily compared with other underwater welding efforts or with air welding results. Although some workers have provided c o m parisons between air and water welds (Refs. 16, 37, 41), the research reported here attempts to provide more fundamental material upon which to base general conclusions and insights into underwater welding metallurgy. The first useful i n f o r m a t i o n to emerge from this investigation concerns the optimum welding parameter values during underwater SMA (shielded metal-arc) welding with different types and sizes of electrodes. A comparison between these underwater optimum values and the corresponding optimum values in air indicate that underwater welding requires a higher current for the same arc voltage. The welding speed shows no general trend between air welding and water welding. Another portion of the investigation involves the weld bead shape characteristics of underwater welds compared with air welds. The largest variation in weld bead shape is caused by changing the welding current from nonoptimum to optimum values. Penetration remains a function of the welding current and is not strictly dependent on the electrode size or the welding medium. Undercutting is a problem for many of the underwater welds. The weld bead size is quite similar for corresponding air and water welds, a l t h o u g h water welds tend to be narrower with a higher reinforcement. The general shape of underwater welds does not appear to be significantly different for air welds. This suggests that the most critical effects of the water do not begin to affect the weld until the weld puddle has formed and begins to solidify. The remainder of this investigation covers the microstructure and hardness of u n d e r w a t e r S M A welds. H a r d e n i n g b e c o m e s very critical following welding. However, underwater welding does not result in a weld metal quench that is beyond modification and control. Larger weld beads, resulting from a higher heat input, will give less hardening. Thus, welding with a 1/8 in. electrode will cause more severe hardening than will a 3/16 in. electrode. Similarly, higher heat inputs will decrease the hardening effects. Localized martensite transformations appear in a l most all underwater welds i m m e d i ately adjacent to the fusion line and extending for less than 0.5 m m . The Fig. 1 — Correlation of the maximum temperature with regions in the heat-affected zone 3000 2500- - 2000 I 500- I 000- 500 TIME Fig. 2 — Possible microstructural transformations during welding WELDING RESEARCH SUPPLEMENT! 179-8
extent of the HAZ in underwater welds is reduced by 30-50%, indicating a more rapid dissipation of heat from the weld bead into the base metal. Although many of the observations and conclusions of this investigation were perhaps expected from previous intuitive reasoning, their documentation and quantification is important and necessary to the future development of underwater welding technologies. Temperature Histories and Microstructural Transformation The solidification and microstructural transformations of any weld are determined by the temperature history of that welded joint. The maximum temperature of a region in the HAZ will govern the recrystallization and grain growth phenomena. Figure 1 illustrates the correlation between the maximum temperature, Tm, and the distance from the fusion line. The cooling rate from Tm will determine the type of transformation process that occurs. Slow cooling rates will result in the equilibrium crystal structure of pearlite within a ferrite matrix. More rapid cooling will induce none q u i l i b r i u m t r a n s f o r m a t i o n struc- tures of bainite and martensite or mixed products such as Widmanstatten structures. Figure 2 illustrates the basic transformations and modifications to the grain size and crystal structure that may occur during a welding cycle. Underwater welding is subject of very severe quench conditions and therefore, often results in the formation of the less desirable nonequilibrium transformation p r o d ucts of m a r t e n s i t e a n d b a i n i t e . Figures 3A and 3B show the differences in cooling rates between air welding and underwater w e l d i n g . While air welds may cool from melting to 200 F in 60 seconds, an underwater weld will cool down to 200 F within 5 seconds. Thus, underwater cooling rates are 10 to 15 times more rapid than those in air. Predicting the microstructure of metal subjected to a particular heat treatment (temperature history) has been the theme of extensive metallurgical research. Isothermal Transformation (IT) diagrams record the crystal transformations from austenite that will occur isothermally at a specified temperature. The value of \ -A F \ (A ) Isotfrermol Tronsf or mol ion Diagram ( 2 % C ) 200- \ \ -a- \ Cooling rate a i 2 5mm from the fusion Una 400- . X V Underwaler welding conditions j - " \ (E60I3 5/32") \ —-Air welding conditions \ \ T I M E I Seconds) 100 IOOO * \ Me ng (6) Underwater o \ 500 - / /(2 IOO0O0 Weld (2) - A j tr 1 , /( )\ IOOO - IOO0O (B) Continuous Cool.ng Trgnsformotio O.agram I 2 % C ) Ro id Cooling Rotes — sX I i 25 Fig. 3 — Temperature histories of air welds compared to those of underwater welds Experimental Procedure and Results A series of bead-on-plate welds were made on 4 X 6 X % in. plates of 1020 steel u s i n g E 6 0 1 3 , E 7 0 1 4 , E6027, and E7024 electrodes of 1/8, 5/32, and 3/16 in. diam. The objective of the weld bead series was to: 1. Determine the optimum welding conditions in air and underwater for the electrodes studied; 2. C o m p a r e these c o r r e s p o n d i n g sets of optimum welding conditions and obtain conclusions or make observations about the effect of underwater welding on these conditions; 3. C o m p a r e the g e o m e t r i c a l and microstructural properties of the resulting weld beads and determine those characteristics which are changed or modified as a result of underwater welding; 4. Attempt to correlate the modified geometrical and metallurgical properties of the underwater weld beads with fundamental mechanisms of underwater welding. Optimum Welding Current i 20 such a chart is limited in welding metallurgy because the metal is undergoing continuous cooling. C o n tinuous Cooling Transformation (CCT) diagrams have been developed to aid metallurgists in predicting the microstructure of a metal sample which is continuously cooled from a specific maximum austenitizing temperature, Tm . These diagrams are more useful than IT diagrams, but their value for predicting the microstructure of a weld HAZ is still incomplete because of the nonuniform maximum temperatures across the HAZ and because of the extremely short time at this maxi m u m t e m p e r a t u r e . Their relative predictive power is illustrated by Fig. 4. Fig. 4 — Relationship between T and CCT diagrams for 0.2% C steel A 300 A ac-dc drooping characteristic welding machine was used along with a strip-chart recorder to AIR ISP) S m i . l G I X AMPS jjjjjjf l \ 20 jm/fj. SETT inn MO AVS nvfrt*' ff taff 5SBS. Mre II) TIME ISECMIDS) Fig. 5 — Voltage and current recordings during air and underwater welding. (A) E7014 (1/8 in.) electrode: (B) E6027 (3/16 in.) electrode 180-s I J U N E 1975
measure and record the voltage and the current during welding. The current ranges for the air weld specimens were approximated by c o n sulting the manufacturer's suggested values. The current ranges for the u n derwater welds were assumed to be 10-20% higher based on previous published information. These previously suggested current values are summarized and compared with the values obtained from this study in Table 1. The optimum welding current was obtained for each electrode by examining the weld beads as they appeared on the plate and by examining the geometrical characteristics of the cross sections. Visual inspection of the welded plates involved examining the regularity and consistency of the weld beads. The cross-section analysis involved m a x i m i z i n g the p e n e t r a t i o n to w i d t h ratio and minimizing undercut and reinforcement. The welding current ranges for air welds recommended in this study tend to be in the manufacturer's suggested ranges. The underwater current ranges are in all cases higher than the air welding ranges. For the E6013 ( 1 / 8 , 5 / 3 2 , 3/16 in.) electrodes, this increase is 10-20 A. For the E7014 (1/8, 5/32, 3/16 in.) electrodes, the increase is 20-30 A. For the E7024 (1/8, 5/32 in.) electrodes, the increase was not determined because actual welding currents above the air welding current range of 170220 A were not obtainable due to the limiting effect of the elongated arc length which occurred. Similarly, it was impossible to specify the o p timum underwater welding current for the E6027 (5/32, 3/16 in.) electrodes. The effect of an elongated arc length on the actual welding current can be demonstrated by noticing that, for air w e l d i n g with E6013 electrodes, there is no difference between the machine setting and the m e a s u r e d current values. Underwater welding with E6013 produces only slightly elongated arc lengths and the differences between the machine settings and the m e a s u r e d values are 10-20 A. For E7014 air welds, the actual current is identical to the machine setting values. For u n derwater E7014 welds, the decrease in observed current is 10-30 A, with larger current lags for the larger electrode (3/16 in). This effect becomes more noticeable for E7024 and E6027 electrodes which both have a much thicker flux covering. For E7024 (1/8 in.) electrodes welded in air at a machine setting of 190 A, the observed current was 170 A, a decrease of 20 A. For the same electrode welded u n derwater at 200 A machine settings, the observed currents are only 150 and 100 A for straight polarity and reverse polarity, respectively. TABLE I SUMMARY OF RECOMMENDED WELDING PARAMETERS Air Welding Underwoter Current ( amps) I/8" E60II E60I3 E70I4 E7024 General 8/32" { Airco) ( R.T. Brown , 1974 ) I I - 1 6 , p m (Westinghouse) ( R.T B r o w n , 1974) 1 3 - 1 5 i p m (Westinghouse) ( R.T. B r o w n , 1974 ) 1 2 - 1 4 ipm I/8 E60I I E60I3 1 2 0 - 190 ( W e s t i n g house) 150-170 120-190 170-190 E7024 1 8 0 - 2 5 0 240-280 1 70-210 E6027 180-250 250-300 1 30 General 5 / 3 2 " ( R.T B r o w n , 1974 ) (Airco ) ( R.T B r o w n , 1974) ( Westinghouse) ( S i l v a , 1971) ( R.T B r o w n , 1 9 7 4 ) ( West mg house ) ( S i I V O , 197 1) (R, T B r o w n , 1 9 7 4 ) E70I4 5/16" E60I3 100-210 E70I4 190-260 220-260 E6027 250-325 12 - 1 3 I pm 1 1 - 1 5 ipm 1 0 - 11 ipm (Westinghouse) 190-210 3/16 1 5 - 1 9 ipm ( W e s t i n g house ) ( R.T B r o w n , 1 9 7 4 ) 1 5 - 1 7 ipm ( Westing house ) ( R.T B r o w n , 1 9 7 4 ) I I - 13 ipm 180-200 General Speed (ipm) (amps) 1 60 50-120 95-125 1 15-150 150-170 140-180 130-170 (R.T Brown,1974) ' 1 0 - 1 3 ipm Welding Current Speed (ipm] ---- ( B u r k e s , 1950) 1 15-150 ( R. T B r o w n , 1974 ) 1 7 -24 1 5 0 - 170 ( R.T. B r o w n , 1974) 11-15 .pm 170 140-150 (R.T. Brown, 1974) (Levin , K i r l e y , 1972) 200 170-190 200-260 2 0 0 - 250 190-210 160-190 200-250 170-210 (Burkes, 1950) ( N a v y , 1968) 13-16 ipm (Silva, 1971) (Brown, 1973) (Meloney , 1973) 1 2 - 1 5 ipm ( R. T B r o w n , 1 9 7 4 ) 1 4 - 2 3 ipm ( Brown, 1973) ( R.T. B r o w n , 1 9 7 4 ) 1 1 - 1 7 ipm 200-260 170 ( S i l v a , 1971 ) ( R.T. B r o w n , 1974) II 2 4 0 - 280 140 180-200 200-220 ( S i l v a , 1971 ) ( R. T, B r o w n , 1 9 7 4 ) ( Levin, Kirley, 1972) ( A v i l o v , 1955) 220-260 200-240 ( N a v y , 1968) ( R.T. B r o w n , 1974) 220 ( R.T. 180 ( R.T ipm 15 - 1 6 ipm - 13 ipm ' 12-14 ipm 15-16 ipm Brown, 1 974) 7 - 8-Hpm Brown , 1974) 8 —1 0 ipm ( A v i l o v , 1955) (Craf tweld) 220-270 225-280 TABLE 2 rlLLD BEAU WIDTH VARIATIONS FROM THE OPTIMUM OR 3EST CONDITIONS ELECTRODE WATER (S?) AIR (S?) 33 3.2-6.4 5,5-8 5.6-8,6 53 80 75 6.4-3 6.4-9,6 6,4-12,8 80 78 6.4-8 4.8-8 9,6-12,8(0) 89 4.8-12.8 37 6,4-9.6 7 57 3,2-4 6,3-3 6,3-8 80 83 E7014 3/16" 3-9.6 8-9,6 11,2-14.4 E7024 1/8" 12,8-14.4 E5013 3/16" E7014 1/8" E7014 5/32" m 1,6-4,8 4-6,4 6.4-9.6 W i DTK VARIATION E6013 5/32" ! % WIDTH tll.H 7 MAX E60I3 1/8" WATER (RP) WIN % WIDTH VARIATION 80 80 83 62 65 60 70 64 67 50 E7Q24 5/32" 9.5-12,8 85 8-11.2(0) 72 6.4-11.2 E6027 5/32" 9.6-12.8 75 6.4-9,6(0) 67 9,6-14.4 65 29 6.4-11.2 57 E6027 3/16" 12,8-17.6 3.2-11,2(0) 73 Figure 5a is the strip chart recording for E7014 (1/8 in.) electrodes and shows the initial underwater current readings equal to the machine setting but the s u b s e q u e n t decrease to values limited by the long arc lengths (due to the elongated flux barrel). Figure 5b further illustrates this effect with E6027 (3/16 in.) electrodes. Even in air, the elongated arc column results in a significant current difference of 130 A at a machine setting of 300 A. Underwater welding intensifies this effect and the chart recordings show the accompanying variability in the arc length. This difficulty in maintaining a constant arc length at a sufficiently high current results in very WELDING unsatisfactory weld deposits when underwater welding with either E7024 (5/32 in.) or E6027 (5/32 in. and 3/16 in.) electrodes. The variability in arc length induces inconsistencies in the weld bead deposit. The weld bead size and penetration become irregular. This effect is easily observable by comparing various 5/32 in. electrode weld deposit widths. The minimum weld bead width for the best E6013 (5/32 in.) air weld is 80% of the maximum width. But for underwater welds, this width variability increases so that the minimum width is only 64% of the maximum width. Values for E7014 width variations increase from 83% in RESEARCH SUPPLEMENT! 181-8
TABLE 3 WELDING SPEED, CURRENT, AND POWER INPUT ELECTRODE CURRENT (AMP) VOLTAGE (VOLT) (KILO POWER WATTS) SPEED (IPM) HEAT INPUT (KJ/ IN) 9-10 9-10 9 6013 AIR 1/8" SP RP 9 0 - II 0 1 30-150 1 30-140 20-23 25 - 27 26-27 2-2 5 3 4 -4 3 4 12-16 24 - 2 5 1 7 -22 6013 AIR 5/32"SP RP 1 30-170 1 60-190 1 50-180 23 - 2 7 25 - 29 2 1-24 3.5 - 4 . 2 4-5 3 6-4 17-19 20-25 19-23 11-13 11-12 10-1 1 6013 AIR 3/l6"SP RP 160-180 18 0 - 2 1 0 160-180 20-23 23 - 3 0 27-28 3 4 -3.8 4.6-5 4 4 6 - 4.8 15-17 16 - 18 22-23 14-17 13- 18 15-24 7014 AIR 1/8" SP RP 1 3 0 - 150 1 50-160 140-150 24 - 2 6 27 - 2 8 27 - 2 8 3.5 4 - 45 4.3 - 4 . 7 13-15 19-21 22 - 2 5 14-1 5 11-12 13-15 7014 AIR 5/32"SP RP 160-180 1 70-190 1 30-170 23-26 27 27-30 4-43 4 6-5 4-4 8 12-13 12-17 1 1 -13 17-19 18-23 20-23 7014 AIR 3/l6"SP RP 200-240 160-190 120-180 23 - 26 28-35 30 - 4 5 4 8-5 8 5.8 4. 5 - 5. 5 11-13 12 7-8 23-26 34-36 38-48 6 0 2 7 AIR 5/32"SP RP 1 20-180 32 - 42 10-11 28-32 80-130 38-42 4 3-54 4 5-55 5 -5.5 6 0 2 7 AIR 3/16" SP RP 140-170 1 50-190 100-160 34 - 3 9 35 - 4 5 34-40 5-5.5 4 - 5,5 4-5.5 7 0 2 4 AIR 1/8" SP RP 120-150 1 50-160 50-100 26-31 3 0 - 35 37-43 7 0 2 4 AIR 5/32"SP RP 140-160 130-180 8 0-200 30-35 35-40 35-45 air to 60% underwater. E7024 electrodes are exceptionally smooth in air (86%) but become irregular underwater (57%). E6027 electrodes are not as steady in air (75%), but become quite inconsistent underwater where the arc may actually stop and have to be reignited. (Table 2). Optimum Welding Speed When employing the drag technique, the welding speed is almost entirely a function of the welding current. The power input of the arc will result in a specific "digging power" which is the ability of the arc to penetrate the base plate and to cut the weld crater. It is best to keep the tip of the electrode resting on the lip of the weld crater. Slowing down the electrode may cause it to fall into the weld crater and result in melt through. Speeding up the electrode will cause it to move ahead of the weld crater and result in a discontinuous weld bead. Data from E7014 electrodes show the effects of increased power to increase the 'natural d r a g ' welding speed and of larger electrode diameters to decrease the 'natural drag' welding speed in air and underwater. The most obvious effect is the decreasing speed with larger electrode diameters. An E7014 (1/8 in.) electrode with a 3.5 kW power input will give a speed in air of 15 i p m . An E7014 (3/16 in.) electrode welded 182-s I J U N E 1 9 7 5 7 28-42 10 9 8 29-36 36-44 36-52 3.5-4.3 3 5-55 3 7 12-14 15-16 4- 9 18-30 2 1 -22 23-32 5-5.2 3 6-6.3 4-5 3 1 3-15 1 3 7 24-27 33-36 35-44 with 5-6 kW will result in a speed of 12 ipm in air. Underwater welding induces two modifications. The power r e q u i r e d for o p t i m u m w e l d bead appearance is increased, and the resulting 'natural d r a g ' speed is higher. Underwater, an E7014 (1/8 in.) electrode with 4 kW results in a speed of 20-23 ipm. Underwater, an E7014 (3/16 in.) electrode with 5-6 kW will result in a speed of 8-11 ipm. This suggests that the optimum current was not achieved for the 3/16 in. electrodes, as this would have given a more efficient (lower) power/speed ratio. This inability to reach the optimum welding current is further illustrated by examining data from the E6027 underwater electrodes. Because the elongated arc barrel in underwater welding limited the current to 150-175 A, which was less than the air values, the power input was limited to below 5.5 kW and the speed in underwater welding was limited to below the o p t i m u m . The natural tendency to lower the welding speed when the power input is limited acts to maintain a constant heat input, but does not fully compensate for the decreased heat input due to the elongated arc length and r e d u c e d current w h e n using E6027 and E7024 electrodes underwater. Optimum underwater welding speeds are 5-10 ipm faster for 1/8 in. electrodes while they are only 2-5 ipm faster for 3/16 in. electrodes. The higher optimum power input in underwater welding is a stronger effect than the increase in speed and so the net effect is to increase the heat input to an optimum underwater weld. Table 3 summarizes this data. Optimum Weld Bead Shape Underwater welds have previously been reported to be more spread out and less penetrating than air welds, due in part to the rapid cooling rates in underwater welding (Ref. 39). The present experiments provide more data for evaluating these shape characteristics in underwater welds. M a c r o p h o t o g r a p h s of the underwater and air weld beads were made and c o m p a r e d . The following shape factors were considered in addition to the bead size: 1. The weld penetration-shape factor (width divided by penetration) indicates the degree of relative penetration obtained. 2. The percentage of reinforcement (% filler metal divided by total weld bead) indicates the relative amount of fusion that has taken place. 3. The relative depth of penetration (penetration divided by total bead height) indicates the relative height of reinforcement and depth of penetration. In measuring these shape characteristics, it must be remembered that there are three separate factors influencing changes in the weld bead shapes: 1. The weld bead shapes are changing as a result of moving from a nonoptimum welding current to the o p t i m u m or best o b t a i n e d welding current. 2. There are changes due to varying electrode size and due to different flux c o v e r i n g c o m p o s i t i o n and thickness. 3. Finally, there are various changes which result in switching from air welding to underwater welding conditions. The effects from underwater welding conditions are masked behind these other two factors. However, by c o m paring the weld beads obtained at or near the optimum welding current, it appears that the shape of air and underwater weld beads are very similar for the same welding current. For an E6013 (5/32 in.) air weld at 175 A and 13 k J / i n . heat input, the penetration was 2.2 mm (Fig. 6). For an E6013 (5/32 in.) underwater (SP) weld at 180 A with a heat input of 11 kJ/in., the penetration was 2.3 m m . An E6013 (5/32 in.) water (RP) weld at 175 A with a heat input of 11 k J / i n . had a penetration of 2.3 m m . Thus, for the same current, the penetration was identical between air and water welds. For this same electrode, the air speed was 17 ipm while the two un-
derwater speeds were 22 ipm (SP) and 19 ipm (RP). Thus, the underwater speed was slightly increased. The air weld had a width of 8.5 mm, and thus a width/penetration shape factor of 3.9. The underwater SP weld was narrower (5.5 mm) and gave a shape factor of 2.4. The underwater RP weld was not as narrow as the underwater SP weld (7.5 mm), and thus gave a shape factor very similar to the air weld of 3.3 The % reinforcement values for these weld beads were 35%, 42%, and 49%, respectively. This indicates that the air weld was \(2024) Curvent i HeatVnput; Penetration Width.\ Reinforcement Shape f a c t o * WM a r e a : \ Max. h a r d n e s s CurrE Heat Penet Widt Reinforcement Shape factor W M area ; Max h a r d n e s s 9 0 amps a. 2 KJ/m mm Q5.2 mm LJ 1.7 mm 2.2 I- I 6 mm 4 3 0 KHN 2 2 mm 2 y / 23 mm2 I 9 5 \ a r r * s \ . 19 V j / i n 1 9/r\m SJS m\n / l m i /5.0 \ / 39 mmn / 221 KHN\ Curren Heat tn Penetra Width : Reinforcement Shape factor W M ar ea ; M a x hardness ' / 05amp4 1 9 Kj/n 2.7 m A 8 . 7 ohm 2. 1 / n m 3.2/ 4 0 mm2 20pKHN o " -, « 2.0 4.0 24 mm' 3 2 5 KHN J20I3) 7 mm Current H e a t inp Penetra Wid th' Reinforcement Shape factorWM a r e a ; Max. h a r d n e s s Current\ Heat input - \ . Penet ration "*-» Width Rein f o r c e m e n t ; Shape factor WM a r e a : Max. hardness : 2.4 3 3 30 590 KHN Fig. 6 — Weld bead shape characteristics for E6013 (5/32 in.) electrodes. X 7.5, reduced 51% I4 CuXrent ; — Hea K i n p u t : PenetYation Width \
affected by underwater welding — and thereby influence joint prop erties — has been to study the differ ences between air welding and under water welding. Since the basic weld ing metallurgy in air has been well studied (Refs. 48-53), much under standing of underwater welding metallurgy can be gained by examin
the limited depth of underwater welding. Welding equipment transformed from manual welding to underwater automatic welding. The efficient and low-cost underwater welding was achieved[7]. In order to study the automatic welding technology under larger deep-water environment, the underwater automatic welding system was designed in this paper. The
3. Classification of Underwater Welding Underwater welding may be divided into two main types: a) Wet welding b) Dry welding Fig. 3.1 Classification of underwater welding 3.1 Wet welding 3.1.1. Wet welding with coated electrode Wet welding is performed at ambient pressure with the welder-diver in the water and no physical barrier
¾ The effects of heat input, underwater welding depths and composition of shielded gases on welds toughness. Key words: underwater welding, wet welding, dry welding, local cavity, weldability of steel INTRODUCTION For nearly thirty years underwater welding techniques have been investigated at Department of Materials Technology and Welding at GUT.
5000 m. Explosive welding underwater can significantly reduce noise pollution. Some researchers have welded plates underwater using the explosive welding technique [12-17]. Nonetheless there are very few references about underwater explosive welding of cylindrical members. Figure 1. Schematic diagram of explosive welding process in planar geometry
BS 499: Pt 1 1991 states, "any welding process in which the weld is made between surfaces brought together to a molten state, without hammering or pressure". Keywords: Underwater welding, Electric arc welding, weld ability of steel, Electric arc welding in underwater, Electric arc welding in air, mild steel.
6.3 Mechanised/automatic welding 114 6.4 TIG spot and plug welding 115 7 MIG welding 116 7.1 Introduction 116 7.2 Process principles 116 7.3 Welding consumables 130 7.4 Welding procedures and techniques 135 7.5 Mechanised and robotic welding 141 7.6 Mechanised electro-gas welding 143 7.7 MIG spot welding 144 8 Other welding processes 147 8.1 .
surface welding and underwater welding is not significantly different. This means the critical effect of the water only begins when the weld pool begins to form and solidify. The HAZ in underwater welding is reduced by 30 to 50% when compared to surface welding, indicating that heat dissipates rapidly from the weld bead into the base metal. The
System as the Army’s personnel accountability automation system with the electronic Military Personnel Office (throughout). o Deletes Personnel Transaction Register (AAC-P01) (throughout). Headquarters Department of the Army Washington, DC 1 April 2015 Personnel-General Personnel Accounting and Strength Reporting *Army Regulation 600–8–6 Effective 1 May 2015 H i s t o r y . T h i s p u b .
