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Submerged arc welding with cored wires
By Juha Lukkari, Technical Manager, ESAB OY, Helsinki, Finland and Shaun Studholme, Group Product Manager, ESAB Group (UK) Ltd., Waltham Cross, U.K.
First published: Svetsaren 1-2/1996
Keywords: SAW, cored wires, OK Tubrod 15.00S, OK Tubrod 14.00S,OK Flux 10.71, membrane wall, box beams, process industry, power generation
Segment: Process industry, Power generation
Summary: The article describes the productivity increase that can be obtained in submerged arc welding by using cored wires in combination with standard SAW fluxes. It reviews three case studies of successful industrial applications.
The use of flux cored arc (FCAW) welding has increased dramatically in recent years and this growth has been well documented in the various international welding journals. The latest development in the field of cored wires is that of submerged arc welding and with it the transfer of the productivity benefits.
Submerged arc welding (SAW) is widely recognised as a very productive welding process which over the years has developed from the single wire approach to more productive variants such as twin wire, tandem and metal powder addition. Welding with cored wires continues the drive for increased productivity with the SAW process.
Cored wires for SAW are similar to those used in the gas shielded process with minor formulation modifications to take account of alloying contributions from the flux. Both metal cored and basic types are available in the size range 2.4 - 4.0 mm and can be used to weld a wide range of unalloyed or low alloy steels with excellent weld metal mechanical properties.
The range of cored wires currently available are:
Unalloyed
OK Tubrod 14.00S (metal cored) - ideally suited for fillet welding
OK Tubrod 15.00S (basic) - for applications requiring good notch toughness
Both these wires are approved to Grade 3, in combination with OK Flux 10.71, by the main Shipbuilding Approval Societies.
Low Alloy
OK Tubrod 15.24S (basic) - 1% Ni alloyed
OK Tubrod 15.25S (basic) - 2% Ni alloyed - designed for use with OK Flux 10.62 on applications requiring stringent mechanical properties i.e. offshore oil exploration.
Deposition rates with cored wires at the same welding current are between 20 and 30% higher than with the equivalent diameter solid wire. This increase can be utilised as faster welding speeds in the case of fillet welding, or, reduced arc times for multi run butt welding with both leading to increased productivity over conventional solid wire. The increase in deposition rate is due to the reduced current carrying cross sectional area available with the cored wire compared to a solid wire. The increased current density leads to a more rapid melting of the cored wire and hence a greater deposition rate. This difference between cored and solid wire is more pronounced than with gas shielded welding due to the high current levels used for SAW.
Cored wires for SAW may be used on standard equipment , however, at a given current the wire feed speed will be much greater than for the same size of solid wire and for this reason the gearing on the wire feed speed motor may need to be uprated. This becomes more important the smaller the diameter of cored wire used.
Typical applications in Finland for unalloyed wires are the welding of box beams and fin to tube welding of boiler membrane panels.
More difficult application where cored wires have been adopted include one sided welding in shipyards.
The following examples from Finnish fabricators highlight the benefits they have discovered when SAW with cored wires compared to solid wire.
Case Study 1.
Valmet Corporation welding of box beams
Valmet Paper Machine Works in Jyväskylä is the world’s leading manufacturer of paper machines with an order book at the end of 1995 standing at some 7500 million Finn marks. The Company also has other manufacturing operations in North America and Asia.
They replaced solid wire with OK Tubrod 14.00S (metal cored) in combination with OK Flux 10.71 for the welding of box beams on their gantry welding station (Fig. 2)
The 1 x 1 metre structural steel plates vary in thickness between 20 - 50 mm and are welded with a 45° single bevel preparation at the four corners with a typical depth of 12 mm. These four grooves are then welded in a single run to fabricate the box beam. When using 4 mm solid wire at 720 A, 36 V they achieved welding speed of 0.25 - 0.30 m / min. Changing to 4 mm OK Tubrod 14.00S they increased the speed to 0.35 - 0.40 m / min. An increase of approximately 30%. Where the increase in plate thickness requires deeper bevel preparations then the solid wire may require two passes whilst they can still maintain the use of single run welding with OK 14.00S. This is further evidence of the higher deposition rates of cored wires.
Case Study 2.
Tampella Power fabrication of boiler membrane panels.
Tampella Power manufactures boilers for both the power generation and the pulp paper industry. This Finnish company is one of the world leaders in the design and manufacture of black liquor recovery boilers. The company employs 1500 people in both Finland and the USA.
The main application for submerged arc welding is the fabrication of membrane panels which constitute the walls of the boilers. The panels are made up of tubes fillet welded to fins in the Tampere Works of Tampella Power this is accomplished by using four large SAW installations each equipped with four welding heads (Fig.1). As the panels pass through the station two heads weld one side of membrane using 2.0 mm solid wire and OK Flux 10.81. The panel is then turned over and reversed through the machine to weld the second side with the remaining two heads. Using 380 A and 29 V they achieve a welding speed of 1.4 m / min.
Late last year trials began with 2.4 mm OK 14.00S and OK Flux 10.81 replacing the 2.0 mm solid wire with exceptional results. At the same welding parameters they produced the equivalent fillet weld dimensions at a speed of 1.7 m / min. Further optimisation of the parameters by increasing the current to 480 A and the voltage to 31 V resulted in a further increase in speed to 1.8 m / min. This 20 - 30 % increase in welding speed has been achieved without compromising weld quality (Fig 3). Efforts to increase speeds using solid wire have resulted in unacceptable weld profiles with undercut being the main concern.
Case Study 3.
One sided welding
One Finnish Shipyard using a multi wire technique with its one sided welding station has found that replacing the lead solid wire with 4 mm OK 15.00S basic cored wire has improved the root bead profile and has reduced the tendency for excess penetration into the copper backing bar.
The dramatic increase in the use of cored wires for semi-automatic welding has resulted from productivity improvements over solid wire; this was brought about, in part, by increased deposition rate. In the final analysis it is the deposition rate and the other attributes which collectively have the most impact on production performance.
With regards to the SAW process, the stated 20 to 30% higher deposition rate over the equivalent size of solid wire will ultimately lead to a disproportionately even greater performance with increased current.
First published: Svetsaren 1-2/1996
Keywords: SAW, cored wires, OK Tubrod 15.00S, OK Tubrod 14.00S,OK Flux 10.71, membrane wall, box beams, process industry, power generation
Segment: Process industry, Power generation
Summary: The article describes the productivity increase that can be obtained in submerged arc welding by using cored wires in combination with standard SAW fluxes. It reviews three case studies of successful industrial applications.
The use of flux cored arc (FCAW) welding has increased dramatically in recent years and this growth has been well documented in the various international welding journals. The latest development in the field of cored wires is that of submerged arc welding and with it the transfer of the productivity benefits.
Submerged arc welding (SAW) is widely recognised as a very productive welding process which over the years has developed from the single wire approach to more productive variants such as twin wire, tandem and metal powder addition. Welding with cored wires continues the drive for increased productivity with the SAW process.
Cored wires for SAW are similar to those used in the gas shielded process with minor formulation modifications to take account of alloying contributions from the flux. Both metal cored and basic types are available in the size range 2.4 - 4.0 mm and can be used to weld a wide range of unalloyed or low alloy steels with excellent weld metal mechanical properties.
The range of cored wires currently available are:
Unalloyed
OK Tubrod 14.00S (metal cored) - ideally suited for fillet welding
OK Tubrod 15.00S (basic) - for applications requiring good notch toughness
Both these wires are approved to Grade 3, in combination with OK Flux 10.71, by the main Shipbuilding Approval Societies.
Low Alloy
OK Tubrod 15.24S (basic) - 1% Ni alloyed
OK Tubrod 15.25S (basic) - 2% Ni alloyed - designed for use with OK Flux 10.62 on applications requiring stringent mechanical properties i.e. offshore oil exploration.
Deposition rates with cored wires at the same welding current are between 20 and 30% higher than with the equivalent diameter solid wire. This increase can be utilised as faster welding speeds in the case of fillet welding, or, reduced arc times for multi run butt welding with both leading to increased productivity over conventional solid wire. The increase in deposition rate is due to the reduced current carrying cross sectional area available with the cored wire compared to a solid wire. The increased current density leads to a more rapid melting of the cored wire and hence a greater deposition rate. This difference between cored and solid wire is more pronounced than with gas shielded welding due to the high current levels used for SAW.
Cored wires for SAW may be used on standard equipment , however, at a given current the wire feed speed will be much greater than for the same size of solid wire and for this reason the gearing on the wire feed speed motor may need to be uprated. This becomes more important the smaller the diameter of cored wire used.
Typical applications in Finland for unalloyed wires are the welding of box beams and fin to tube welding of boiler membrane panels.
More difficult application where cored wires have been adopted include one sided welding in shipyards.
The following examples from Finnish fabricators highlight the benefits they have discovered when SAW with cored wires compared to solid wire.
Case Study 1.
Valmet Corporation welding of box beams
Valmet Paper Machine Works in Jyväskylä is the world’s leading manufacturer of paper machines with an order book at the end of 1995 standing at some 7500 million Finn marks. The Company also has other manufacturing operations in North America and Asia.
They replaced solid wire with OK Tubrod 14.00S (metal cored) in combination with OK Flux 10.71 for the welding of box beams on their gantry welding station (Fig. 2)
The 1 x 1 metre structural steel plates vary in thickness between 20 - 50 mm and are welded with a 45° single bevel preparation at the four corners with a typical depth of 12 mm. These four grooves are then welded in a single run to fabricate the box beam. When using 4 mm solid wire at 720 A, 36 V they achieved welding speed of 0.25 - 0.30 m / min. Changing to 4 mm OK Tubrod 14.00S they increased the speed to 0.35 - 0.40 m / min. An increase of approximately 30%. Where the increase in plate thickness requires deeper bevel preparations then the solid wire may require two passes whilst they can still maintain the use of single run welding with OK 14.00S. This is further evidence of the higher deposition rates of cored wires.
Case Study 2.
Tampella Power fabrication of boiler membrane panels.
Tampella Power manufactures boilers for both the power generation and the pulp paper industry. This Finnish company is one of the world leaders in the design and manufacture of black liquor recovery boilers. The company employs 1500 people in both Finland and the USA.
The main application for submerged arc welding is the fabrication of membrane panels which constitute the walls of the boilers. The panels are made up of tubes fillet welded to fins in the Tampere Works of Tampella Power this is accomplished by using four large SAW installations each equipped with four welding heads (Fig.1). As the panels pass through the station two heads weld one side of membrane using 2.0 mm solid wire and OK Flux 10.81. The panel is then turned over and reversed through the machine to weld the second side with the remaining two heads. Using 380 A and 29 V they achieve a welding speed of 1.4 m / min.
Late last year trials began with 2.4 mm OK 14.00S and OK Flux 10.81 replacing the 2.0 mm solid wire with exceptional results. At the same welding parameters they produced the equivalent fillet weld dimensions at a speed of 1.7 m / min. Further optimisation of the parameters by increasing the current to 480 A and the voltage to 31 V resulted in a further increase in speed to 1.8 m / min. This 20 - 30 % increase in welding speed has been achieved without compromising weld quality (Fig 3). Efforts to increase speeds using solid wire have resulted in unacceptable weld profiles with undercut being the main concern.
Case Study 3.
One sided welding
One Finnish Shipyard using a multi wire technique with its one sided welding station has found that replacing the lead solid wire with 4 mm OK 15.00S basic cored wire has improved the root bead profile and has reduced the tendency for excess penetration into the copper backing bar.
The dramatic increase in the use of cored wires for semi-automatic welding has resulted from productivity improvements over solid wire; this was brought about, in part, by increased deposition rate. In the final analysis it is the deposition rate and the other attributes which collectively have the most impact on production performance.
With regards to the SAW process, the stated 20 to 30% higher deposition rate over the equivalent size of solid wire will ultimately lead to a disproportionately even greater performance with increased current.
