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SA-welding-tips are useful information bits about Submerged Arc Welding (SAW).
This is the process where the arc is concealed and shielded from air under a blanket of granulated flux.
Under the arc, the flux evolves a protective atmosphere.
It also provides a cover of slag under which the weld bead cools down.
The flux cover prevents fumes, sparks, spatter and radiation from coming out from the weld location.
This process is therefore less harsh an environment for operators than comparable processes with visible arcs of the same energy.
The process, one more SA-welding-tip, is also protected against occasional
air drafts, much more than gas shielded methods, so that it can be performed outdoors.
Among SA-welding-tips, note that furthermore the flux can provide elements capable of controlling and improving the chemistry, by scavenging inclusions and oxides.
It can also modify the alloy with metallic additions if needed.
Flux must be compatible with base and filler metal as the success of the operation is determined by their mutual influences.
SA-welding-tips should recognize that, because of these capabilities, the selection of the proper flux for a given application may be more difficult.
The choice of consumables for other processes may be easier.
Here subtle interactions must be taken into account to obtain a weld metal of the correct quality.
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A short note on Filler Metal for SA-welding-tips was published (4) in issue 29 of Practical Welding Letter for January 2006. To read the note click on PWL#029.
These SA-welding-tips are intended to help those readers not specifically informed about all the technicalities, in the proper selection and conduction of this process.
First among the SA-welding-tips is a reminder of the main characteristics.
The arc, providing the heat input needed for welding, is struck between a continuously supplied (through a feeder) bare metal wire or strip consumable electrode, and the work.
The heat of the arc melts the electrode, some of the flux and a part of the base metal, providing a weld puddle to fill the joint.
Other SA-welding-tips include the notion that it is mostly used for relatively thick, long joints in flat position.
Mechanical and semiautomatic welding operations are usual, and also for surfacing large areas for proper corrosion or wear protection.
Note the SA-welding-tips reminder that materials welded include carbon and low alloy steels, stainless steels and nickel alloys.
SAW is not used for aluminum alloys, copper alloys and titanium.
- Simplified joint preparation
- High weld deposition rate potential
- High weld speed
- High productivity
- Screening of the arc under flux
- Active chemical control of weld pool
- Minimal operator training necessary
- Collection and utilization of unfused flux
- Controllable deep or shallow penetration
- Excellent weld quality
- Feasible in flat or horizontal position only
- High cost of equipment (power supply, electrode feeder, flux handling)
- High cost of accessories like positioners or boom carriage
- Slag removal necessary
Power supplies provide direct current of the preferred polarity, or alternating current as suitable, at high amperage levels.
The dc power can be either constant-current (CC) or variable current and constant voltage (CV).
Here are some additional, important SA-welding-tips.
At a given current level, a smaller electrode size gives a higher weld deposition rate than a larger size, because of higher current density.
If the size is changed to a larger one, however, the larger size electrode permits welding with a higher current, which can give a higher weld deposition rate.
Once the electrode diameter is selected, the parameters to set are:
- the power source (if alternating or direct current and in this case also the polarity),
- the voltage,
- the electrode extension (the length of electrode between the contact tube and the arc),
- the current (directly in CC systems or as a function of wire feed speed in CV systems) and
- the travel speed.
- Type, width and depth of flux layer are also important factors.
The current running in the circuit, as measured by an ampermeter, is determined by those selections.
For establishing the correct electrode extension, the following SA-welding-tips should be remembered.
The total current is split into two portions whose amounts are not known.
One part of the total current preheats, by resistance heating (proportional to the resistance times the square of the current), the portion of wire called electrode extension.
The other part maintains the arc determining heat input and penetration.
Power sources for Submerged Arc Welding are intended for continuous work at elevated current values.
As such they should be able to operate at 100% duty cycle to provide continuous welding without overheating.
Please remark the following SA-welding-tips.
The main difference is that constant voltage (CV) sources, are self regulating, therefore they can use fixed speed electrode feeders.
With CV sources, after the required arc length is established by preselected voltage, any occasional arc length change (causing a corresponding change in voltage) is promptly recovered through a current change that melts more or less wire (electrode) to restore the original arc length.
Direct current constant voltage (CV) power supplies are recommended for use with relatively thin steel at high welding speed, because constant voltage (CV) direct current provides smoother and more regular beads than alternating current.
Alternating current, a further SA-welding-tip, is preferred at elevated currents (over 1000 Amperes) because it reduces the effect of magnetic arc blow (erratic arc) that becomes important with direct current sources.
Constant current (CC) power supplies are not self regulating, they control the current level.
The variable electrode feed speed is set by a voltage sensing device that measures the voltage across the arc (depending on arc length).
The control then attempts to keep a constant arc length by varying the wire feed speed to restore the original arc length.
In other words, all constant current machines require voltage sensors to drive a variable speed electrode feeder.
These devices add to the equipment and maintenance costs, an important SA-welding-tip.
Constant current (variable voltage) sources are the usual choice for large weld puddles.
Some direct current power sources can be switched between constant voltage and constant current selectable modes.
Alternating current power supplies may be conventional welding transformers rated as constant current sources.
Open circuit voltage should be in excess of 80 V to assure re-ignition of the arc at every polarity reversal.
Constant voltage ac power sources supply approximate square wave output. These work with constant speed self-regulating feeders.
Certain types of power sources provide versatility of usage being suitable also for other welding processes, mainly GMAW.
In the past both types of dc suppliers where either of the motor-generator or of the transformer-rectifier type, and ac suppliers where simply transformers.
More recently inverter type suppliers have been developed for SAW, with digital solid-state controls and software regulation of power output.
Highly versatile equipment of this new design is characterized by the following main differences from older power supplies:
- Power input is always balanced on the three phases, irrespective of output,
- All modes (ac, dc-cc, dc-cv) can be supplied as selected,
- Switching between modes of supply is internal,
- Power sources can be connected in parallel for higher current output,
- dc output can be cc or cv upon selection,
- ac output with square waves (no arc extinction) can be balanced at will, controlling changes in penetration and deposition rate,
- Programmable logic controlled of external systems are compatible with these sources.
Flux Classification SA-welding-tips
While fluxes can be classified according to the methods of production (Fused or Bonded) more important is their action on the weld metal.
Neutral fluxes do not change the composition of weld metal as produced by the fusion together of base metal and electrode.
They contain little amounts of de-oxidizers (manganese and silicon) or none at all. These fluxes are used on de-oxidized, clean steel or for multiple passes on thick plates.
Active fluxes contain certain amounts of de-oxidizers (manganese and silicon) to help eliminating porosity and weld cracking in contaminated steel (by oxygen, nitrogen or sulfur).
They are used for single pass welds. Mechanical properties may be affected by manganese and silicon content in the weld metal.
Welding parameters, especially voltage, affect the flux to wire ratio consumption by weight, one more SA-welding-tip, which in turn influences composition and properties.
Because of the possible consequences, weld parameters must be strictly controlled when using active flux, much more than with neutral flux.
A further classification uses the basicity index (BI) that attempts to estimate the resulting oxygen content that will be found in the weld metal.
Basic fluxes tend to have lower oxygen content and better impact properties, especially in large multipass welds.
Acid fluxes, preferred for single pass deposition because of easier welding, have higher tolerance for contamination that could produce porosity.
A note on how to keep flux in place for root weld support in thin groove welds is available in the FAQ Page (Opens a new page).
Selection of consumables should be based on the base metal and its condition (clean or contaminated), and on the requirements for the final weld.
There is no AWS classification for fluxes or flux-electrode combination for stainless steels or for nickel alloys.
It must be noted that consumable manufacturers offer many more products that are not yet officially classified under proprietary brands.
The following SA-welding-tips give the Standards that specify Filler Materials for SAW:
ANSI/AWS A5.17/A5.17M-97 (R2007)
Specification for Carbon Steel Electrodes and Fluxes for Submerged Arc Welding
American Welding Society, 25-Sep-1997, 35 pages
Specification for Low-Alloy Steel Electrodes and Fluxes for Submerged Arc Welding
American Welding Society / 01-Nov-2011 / 60 pages
Specification for Bare Stainless Steel Welding Electrodes and Rods
American Welding Society / 17-Feb-2012 / 46 pages
Specification for Nickel and Nickel-Alloy Bare Welding Electrodes and Rods
American Welding Society / 01-Nov-2011 / 42 pages
Welding consumables - Solid wire electrodes, tubular cored electrodes and electrode/flux combinations for submerged arc welding of non alloy and fine grain steels - Classification
International Organization for Standardization / 01-Oct-2010 /
Parameter selection SA-welding-tips
Welding Current affects penetration, dilution and weld deposition rate. Direct Current Reverse Polarity (Electrode Positive) is generally used.
The principles that apply to heat partition between electrode and work were explained for other processes (See Tig Welding Tips) and are repeated here:
In DCEP (Electrode Positive):
- 30% of the heat is concentrated in the workpiece
- 70% of the heat in concentrated in the electrode
- Shallow penetration
- Wide weld area
In DCEN (Electrode Negative):
- 70% of the heat is concentrated in the workpiece
- 30% of the heat is concentrated in the electrode
- Some penetration and more buildup
- Narrow weld area
It may be misleading to compare the overall performance of SAW in both polarities at the same current level, because of the different partition of the heat generated as explained above.
One should remember that in order to sustain the higher current level in DCEP a larger size electrode might be required so that the comparison becomes even more difficult if not impossible.
Straight Polarity (Electrode Negative) tends to give narrow beads with less penetration and more buildup therefore contributing to reduce base metal dilution, preferred sometimes, but not always, for surfacing applications.
Straight Polarity (Electrode Negative) is also preferred for poor fitup or larger than optimum root gap, and at comparable current gives higher deposition rate.
At comparable current level Reverse Polarity (Electrode Positive) will give lower weld deposition rate, wider beads with increased penetration.
Electrode size affects current density. At a given current level smaller size electrode has higher current density, producing narrower beads at higher penetration than larger size wires. The smaller electrode will also permit higher deposition rate.
In cases where it may be important to limit the heat input rate, this may be obtained by increasing the weld travel speed, by reducing current or both.
Here is the last, for the time being, of our SA-welding-tips. If you obtained in your regular work with SAW, unacceptable warping or distortion, it would pay to look for the real causes.
Don't be tricked to think that you will solve the problem by changing electrode and/or flux. Nothing could be farther from the truth.
You may have a look at the short note on Controlling Distortion, published (3) in Issue 104 of Practical Welding Letter for April 2012.
Click on PWL#104 to see it.
Summing up, the most important of all SA-welding-tips is the following one.
Because of complexity and interactions of all parameters involved there is no better method of determining their suitability for any given application than performing welding tests and examining visual aspect, shape, and dimensions of the weld bead in metallographic sections of test pieces.
An Article on Tandem GMA Welding and Surfacing was published (11) in Issue 52 of Practical Welding Letter for December 2007.
Click on PWL#052 to see it.
An Article on Submerged Arc Welding Optimization was published (7) in Issue 73 of Practical Welding Letter for September 2009. Click on PWL#073 to read it.
An Article on the Importance of Welding Flux Composition and Particle Size in SAW was published (7) in Issue 74 of Practical Welding Letter for October 2009. Click on PWL#074 to read it.
Both Articles are also available in our collection on Welding Talk.
For Technical Services on Submerged Arc Welding see:
Raya Technical Services
If you are involved with Submerged Arc Welding, it might benefit you to inquire on the use of CERAMIC Electrode Extension Nozzles at this link above.
An Article on Submerged Arc Welding Electrode Extension Nozzles was published (11) in Issue 88 of Practical Welding Letter for December 2010. Click on PWL#088 to see it.
An Article on Submerged Arc Welding (SAW) on Cr-Mo-Ni Steels was published (11) in Issue 104 of Practical Welding Letter for April 2012.
Click on PWL#104 to see it.
An Article on Filler Metals for SAW cladding with 309LMo was published (4) in Issue 110 of Practical Welding Letter for October 2012.
Click on PWL#110 to see it.
Two Articles by Naddir M. Patel on Submerged Arc Welding Fluxes - A Primer, Part 1 and Part 2, were published (2) in Issues 126 and 127 of Practical Welding Letter for February and March 2014.
Click on PWL#126 and on PWL#127 to see them.
An Article on Submerged Arc Welding Optimization was published (2) in Issue 134 of Practical Welding Letter for October 2014.
Click on PWL#134 to see it.
An Article on New SAW Technology was published (7) in Issue 137 of Practical Welding Letter for January 2015.
Click on PWL#137 to see it.
An Article on How to use Submerged Arc to weld Creep Resistant Steels was published (4) in Issue 142 of Practical Welding Letter for June 2015.
Click on PWL#142 to see it.
An Article on Distortion Control was published (3) in Issue 162 of Practical Welding Letter for February 2017.
Click on PWL#162.
Find also a rich list of Online Resources on Submerged Arc Welding Flux.
Click on Bulletin 93.
* * *
|Watch the following Lincoln Electric Video on|
FABTECH 2011: Submerged Arc Welding Demo https://www.youtube.com/watch?v=j-hfExEmGsE
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SA-welding-tips are essential bits of information that, by explaining causes and effects in this complex welding process, help in preventing problems and in looking for possible solutions when facing unexpected difficulties in qualifying procedures.