ESAB TRAINING & EDUCATION · Submerged arc welding is carried out mainly in the flat position for...

ESAB TRAINING & EDUCATION

Submerged arc welding

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General informationContent

General information .............................................. 3The principles of submerged arc welding .............. 4Rules for welding .................................................... 4Parameters .............................................................. 5Setting welding data ................................................ 5Formulae ................................................................. 7Conversion table ...................................................... 7Submerged arc welding methods .......................... 8Single-wire welding ................................................. 8Twin-wire welding ................................................... 8Tandem welding ...................................................... 9Strip cladding ........................................................ 10Narrow gap welding .............................................. 11Cold wire addition ................................................. 11Iron powder ........................................................... 11

Joint preparation .................................................. 12Joint backing ........................................................ 13Consumables ......................................................... 14Electrodes .............................................................. 14Flux ........................................................................ 14ESAB fluxes and characteristics ......................... 15Iron powder .......................................................... 16Weld defects .......................................................... 19Action in the event of weld defects ..................... 21Welding data tables .............................................. 23Practical instructions ........................................... 27

Submerged arc welding (SAW) is a two component process using a flux and wire com-bination where the wire is melted in an arc under the flux that is deposited to the weld area. It is a process that is used on a variety of different objects, mainly heavy objects like ships, pressure vessels, the offshore industry, bridges, tanks and heavy duty pipes to name just a few. Submerged arc welding is carried out mainly in the flat position for butt and fillet joint configurations. Submerged arc welding is the most productive welding process where wires both non-and low alloyed and stainless steel types are utilised. Strip cladding using the submerged arc process is also a very popular way to deposit a layer of stainless weld metal on to a sheet of carbon steel substrate.

SAW is normally carried out in a workshop. Working outside with any type of welding can incur problems such as moisture being absorbed into the fluxes used. Although a substantial amount of welding is done outside, especially on large flat work pieces. SAW is most rational when the least amount of runs is required per joint and that all require-ments are fulfilled such as impact values.Welding is otherwise carried out from both sides of the work piece using a specific joint configura-

tion depending upon the thickness of the part to be welded. Some certain steels need to be welded using a multi run procedure to assure that impact and other requirements are accomplished. In cases where multi run procedures are uti-lised, costs increase but it is vital that the con-struction withstands the forces it is subjected to; therefore cost is not a priority. Welding defects can occur when SAW is used but on the whole, if all preparations are done in a correct manner the possibilities of defects de-crease.

4 5

Different electrode diameters at constant current.

Rules for welding

A wire feeder unit, welding power source, a flux delivery system and process controller are neces-sary to be able to weld SAW. The consumable is a bare continuous wire that is fed into a flux all of which is fed to the welding joint through a contact tube and flux hose. An electric cur-rent is transferred to the wire through a contact tube and contact jaws made of copper. The flux is delivered from a large hopper through a hose to a nozzle placed before the contact jaw in the direction of travel or through a flux funnel. An electric arc is formed once the wire makes con-tact with the work piece. The amperage and arc voltage needed to create an arc are supplied from the welding power source either with direct cur-rent or alternating current. The intense heat from the arc will melt the flux at the same time the wire melts into the work piece. The flux becomes molten as well as the wire. Due to its density the molten flux floats on the molten metal weld pool and will solidify. The flux can contain alloying elements or it can be neutral. The slag that forms from the flux during welding protects the molten pool from oxygen in the atmosphere and finally it will release from the weld bead and discarded. Not all flux is used in a single string and the sur-plus that hasn’t fused can be recycled back into the flux hopper using a flux recovery unit.

Basic principle of SAW

The slag that forms during welding has a heat insulating effect and reduces heat losses from the arc. This means that the energy produced in the arc is higher than would be in other open arc processes. The level of thermal efficiency is higher and as a result, faster welding speeds can be applied. The thermal efficiency in SAW is re-garded at being 60% compared to MMA or hand welding which is around the 25% mark. Either alternating or direct current can be used in the SAW process although direct current is the most common form of welding current.

Direct current versus alternating currentBoth direct current and alternating current are used for submerged arc welding, but direct cur-rent is used more frequently, with the electrode connected to the plus pole. The following advantages of direct current and the plus pole should be noted:• Less risk of pores in the weld metal with

direct current• Greater penetration in the joint. This is par-

ticularly important when welding I-joints• Arc stability is better with direct current than

with alternating current• Magnetic arc-blow is less apparent when

welding with AC current. • Direct current with electrode negative pro-

duces less penetration and a higher throat thickness. Electrode negative is an advantage when surfacing, increasing the deposition rate.

Parameters

This illustration shows how a change in arc voltage influ-ences the shape of the weld. Constant welding current.

Increasing the welding current results in deeper penetration.

Weld data settings

Welding parameters are set according to the dimen-sions and joint configuration of the work piece. They must be set so that the desired penetration and required bead appearance are obtained. From this standpoint the wire dimension, arc voltage, welding current and welding speed are carefully selected. The tables at the end of this compendium are for guidance only but are deemed good for basic settings.

Arc voltage

The arc voltage is an important parameter for the shape and width of the arc and in some aspect, the depth of penetration. Too high an arc voltage in a butt joint on a flat plate will result in a wide bead. In an X, V joint or fillet the result will be a concave bead with undercut, which reduces the slag detachability. If the arc voltage is too low the bead appearance on a butt weld becomes high and the penetration shallow. In X, V and fillets, the weld becomes convex and resulting in lack of fusion in the joint and extremely difficult to release slag.

Welding current

The welding current has the greatest effect on the amount of penetration into the work piece. The choice of current is based on plate thickness and joint ge-ometry. The welding current has little or no effect on the bead width but to high a current will lead to burn through and to low a current will lead to lack of fusion

in the weld. The welding current is proportional to the wire feed speed, which also has an effect on the weld metal deposition rate in kg/h. At a given welding cur-rent with the electrode on straight polarity (electrode negative) the deposition rate will be somewhat higher but the penetration will be less. Welding speed

Travel speed will also affect the penetration depth. If the travel speed is increased at a given current and arc voltage the penetration will decrease, the bead will ap-pear restricted and vice versa if the welding speed is decreased. If the welding speed is reduced to a much lower speed at a given current/voltage the opposite effect will happen where the penetration is reduced because energy in the form of heat cannot be trans-ferred correctly to the work piece due to the fact that an overly large molten pool has been formed. If the welding speed is to be altered then both welding cur-rent and voltage must be tuned accordingly.

Electrode diameter

For a given current, changing the electrode diameter will affect the current density. (Amperage per mm2 of wire cross section) therefore a larger electrode will penetrate less and reduce the risk of burn through in the root run. At the same time striking the arc becomes more difficult and arc stability is also reduced with the likelihood of root failures occurring in a V joint.

d = 4mm 3,25 3,0 2,5 2.0

S = 32A/mm 48 56 82 120

24 28 32 36 40V

200 300 400 600 800A

Principles of submerged arc

welding

Feedrollers

Contacttable

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Penetration is reduced when electrode stick-out increases.

Electrode extension is the length of electrode from the contact jaw or contact tip to the work piece. This measurement is an important pa-rameter that affects the pre heating of the electrode tip. Should the electrode extension be too short, the pre heat will be less and the penetration deep. If the electrode extension is longer then the resistance in the wire is greater and the electrode heats up more. This implies that penetration is reduced and the deposition rate increases.

When welding low alloyed steels a normal electrode extension is between 22 and 27 mm. When cladding with wire the electrode exten-sion can be up to 40 mm with certain wires and with straight polarity (electrode negative) the deposition rate can be increased at the same time as dilution with the parent metal is reduced. The flux height should be adjusted according to the size of the molten pool.

Electrode extension (stick out) Electrode angle

The angle between the electrode and the work piece will determine the amount of penetration of the electrode into the joint.

The most suitable electrode angle when welding with single or twin wires for joining two plates is 90 degrees. In welding submerged arc using the tandem process the trailing head, normally on al-ternating current is angled towards the leading head so that the electrode meets the trailing edge of the molten pool.

Electrode angle Trailing Vertical Stick-out

Penetration Large Normal Small

ThroatNarrow (large)

Normal Wide (small)

Tendency towards undercut

Normal Small

Formulae

Tensile energy (heat input)

Q = tensile energy in kJ/mmU = voltage in voltsI = current in AmperesV = travel speed in mm/minη = efficiency (for submerged arc welding = 0,90)

Carbon equivalentThe material must be pre-heated if Ec> 0,40 %

Shape factor

F = width:height ratioB = width of the weldD = height/depth of the weld

F should be at least 1-1.5, as there is otherwise a risk of hot cracking.

Deposition rateAn approximation of the deposition rate can be calculated using the following formulae:

Deposition rate (kg/h) = Amp/(50 x Diam0,3) single wire, plus pole

Deposition rate (kg/h) = Amp/(40 x Diam0,3) single wire, alternating current

The electrode feed speed (m/min with the plus pole) can be calculated more exactly using the following formula:

• ηQ =U • I • 60

V

Ec = cEv = C+Mn + cr+Mo+v + ni+ cu

6 5 15

B

DF =

AMP + 221,41

44,7 x diam1,79WFS = ))

Conversion table for welding speedMetres Per hour m/h

CentimetresPer minutcm/min

English figuresPer hour ´/h

English tumPer minute´/min

10 17 33 7

20 33 66 13

30 50 98 20

40 67 131 26

50 83 164 33

60 100 197 39

70 116 230 46

80 133 262 52

90 150 295 59

100 167 328 65

120 200 394 79

140 233 459 92

160 267 525 105

180 300 590 118

200 333 656 131

220 367 722 144

240 400 787 157

260 433 853 170

280 467 918 183

300 500 984 197

Conversion factorsm/h x 1,66 = cm/min metres x 3,281 = feetmeter x 39,37 = inches cm/min x 0,6 = m/hfot x 0,305 = metres inches x 25,4 = mm

Temperature conversion

Celcius C = F (F-32) x 5 9Fahrenheit F = (C x 9) + 32 5

30mm 45mm 60mm 80mm

Electrode stick-out is normally measured as the dis-tance from the contact nozzle to the surface ofthe workpiece.

Släpande Vertikal StickandeStick- out distance

The effect of electrode angle on penetration.

Dragging angle Vertical Electrode pushing angle

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Submerged arc welding methods

Single wire welding

Electrode diameters ranging from 1.2 to 6.0 mm can be used with current ranges from 120 am-peres for small diameters up to 1 500 amperes for the larger diameter wires. To enable higher production the single wire method can be easily modified into a twin wire or tandem system. Both solid wires and metal or flux cored wires can be used with submerged arc welding.

Twin-wire welding

Instead of welding with one single 3 mm Ø wire the feed mechanism of the wire feeder can be mod-ified enabling welding with two wires each having a diameter of 2.4 mm. The wires protrude 8 mm from each other from the contact jaws and can be inline or traversing the joint to be welded. Advan-tages are increased deposition and deeper penetra-tion. One power source is used and the welding current is travels through both wires. The electrode polarity is positive. This type of modification is simple and economically viable.

Tandem welding

The ultimate in reaching high deposition rates is to use the tandem submerged arc method. This system is really two separate systems working together as one unit. The required com-ponents are:

1. Two separate welding power sources, one direct current and one alternating current.2. Two separate process controllers3. Two separate wire feeding systems

The leading electrode is carrying direct current and the trailing electrode is carrying alternating current. The trailing welding head is angled to-wards the leading head so that the electrode enters the trailing edge of the molten pool. Even tandem systems can be equipped with twin wire configu-rations. This enables a maximum of 4 wires to be fed into the joint to be welded. Deposition rates with these systems reach up to 30 kg per hour. When welding a butt joint, electrode diameters can vary between 2 x 2, 2 x 2.4 and 2 x 3 mm. The distance between the twin wires is 8 mm. Di-rect current is the preferred type welding current, which gives the best arc stability. Straight polarity or electrode negative, as it is also known as, is used in hard facing applications. Penetration is less and deposition is higher.

Electrode positioning, advantages and disadvantages

• Twin wire welding makes possible the position-ing of the electrodes between transverse to paral-lel to the joint. This is made possible by rotating the contact tube between zero and 90 degrees.• Having the electrodes parallel to the joint improves penetration and reduces the risk of un-dercut and porosity. As the molten pool is longer in this case gases within the pool have more time to escape.• When the electrodes are transverse to the weld-ing joint penetration decreases. Joints having large angles can be filled much quicker once the root runs are concluded. The root runs can be done with the electrodes parallel and the fill runs and capping can be done using the wires trans-verse to the joint.• Electrodes can also be placed diagonally across the joint too in cases where smaller joint angles are used.

Type of electrode

Diametermm

Area mm2

Welding current A max

Deposition ratekg/h

Single electrode

3,0 7,06 650 8,0

4,0 12,56 850 11,5

5,0 19,62 1100 14,5

Double electrode2,0 6,28 1000 14,0

2,5 9,81 1200 17,0

Comparison between single and twin wires

Tandem twin 4 electr. – 2 welding heads

Tandem + tandem, twin

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Placing electrode, arc voltage and welding current

Strip cladding

The equipment used for submerged arc welding with different variants of wire can also be convert-ed for strip cladding. Instead of wires a strip to-gether with special fluxes is used as the electrode. Strip dimensions are usually 30, 60 or 100 mm wide and 0.5 mm thick. Strip cladding is a slow process. The strip feed speed is very slow so feed-ers must have the appropriate gear ratios and drive

motors that allow for slow feeding. The advantage of strip cladding is the low level of dilution ob-tained between the weld and parent metals. Weld-ing currents can range from 600 to 1500 amperes. Strip cladding is used to surface thick walled vessels with a liner of stainless steel. This makes possible vessels to be built in carbon manganese steels bring down the cost substantially.

Narrow gap welding

The ESAB Narrow Gap submerged arc welding method is designed to work on pressure vessels having a wall thickness up to 350 mm. The joint width is approximately 18 mm at the top and the joint angle no more that 3 degrees. If convention-al joints were to be used having this thickness it would take a very long time to fill. Costs for la-bour, consumables, manpower and energy would soar. This is where narrow gap welding has its ad-vantages. It makes welding thick walled vessels so much easier and above all more economic. After the root run has been deposited, narrow gap welding is then carried out by alternating the weld bead from the left side to the right side of the joint after each revolution of the vessel. NGW can naturally be carried out on circumferential and longitudinal narrow joints. Because the weld bead is deposited on the alternately on each side the slag detachability does not become a problem because the beads are narrower that the joint itself. Using highly basic welding fluxes ensures that the weld is tough. In all, the following points are the advantages with NGW.

• Reduced arc time• Less consumables• Reduces stresses in the weld• Narrower heat affected zone HAZ• Low heat input• High quality• Economic

Synergic cold wire systems

In addition, a cold wire attachment can be added to the current bearing welding head. The idea is to be able to feed a non current bearing electrode into the molten pool thus significantly augmenting dep-osition rates. The cold wire is fed into the molten pool simultaneously as the current bearing wire. The same feed motor is used together with a gear box with two axles. One will feed the hot wire and the other will feed the cold wire. The most success-ful ratio of wire diameters is where the cold wire is one or two dimensions smaller than the hot wire.

Iron powder

Another way of increasing deposition rates is to add iron powder. Special iron powder dispensers are available that feed out iron powder into the molten pool. When using DC current, the wire be-comes magnetic and the iron powder sticks to it and is feed into the molten pool.

Deposition rates for different SAW methods.

900 A=+

700 A~

90 mm

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850 A~

800 A~750 A~

15 mm15 mm

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750 A~1150 A

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750 A~

50 mm

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800 A ~

600 A~

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1100 A=+

800 A=_

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900 A~

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100 mm

100 mm

FCB + GRAIN FCB

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Joint preparation

To take full advantage of the economic benefits of automatic welding, joint preparation must be performed with the greatest accuracy. The edges of the plate must be machined or cut with narrow tolerances to obtain optimal penetration. The root face of a V-joint or double Y-joint must be suf-ficient to achieve the desired root run and avoid perforation. The edges of the metal must be abso-lutely clean – in other words, free from moisture, grease, oil, paint, mill scale and rust to avoid po-rosity and cracking. If plasma cutting is used, the joint edges must be cleaned by grinding.

Measurement errors during joint preparation cause defective welds thus making automatic welding more difficult to achieve. The result of a poor fit up in the joint is burnt through or lack of penetration, i.e. root defects. Submerged arc welding demands a more elab-orate joint preparation compared to welding with manual metal arc coated electrodes. Nothing can be gained if optimal joint preparation for sub-merged arc welding is not performed.

Joint backing

The advantage of using backing is to ensure that correct penetration is secured and that an accept-able appearance of the root run is acquired.

Backing bar

Defining the backing bar can be expressed as a support for the root run when the root gap is wide. A backing bar is common in most static longitudinal welding stations. Other types of backing are ceramics or fibreglass tapes used si-multaneously with a copper backing bar.

Backing strip

Backing strip takes the form of a flat metal bar or a profile, normally of the same grade as the workpiece, which is tack-welded under the joint and is allowed to remain a part of the structure.

Backing

An easily applied backing in the form of ceram-ics designed for use with welding objects that cannot be turned, such as ship’s decks, fixed struc-tures and so on. The use of backing bars saves air gouging and subsequent welding.

I joint

V joint

I joint

Double Y joint

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In submerged arc welding, the consumables are made up of two components, an electrode and flux. More recently, a third component, iron powder, has been used on an increasing scale.

Electrodes for SAW

Most carbon steel electrodes are coated with a few micrometers of copper. The copper coating does several things. It creates an optimal current transfer between the welding head and the elec-trode itself and partially protects the wire from rusting. One must keep in mind though that this coating does not inhibit rusting of the wire and the wire must be stored according to the manu-facturers instructions. Several different types of electrode are avail-able on the market, solid wire, tubular types and strips. All of these types of wires are used for joining and surfacing. Tubular wires are from a development point of view much easier to attain optimal alloying elements. This means that neu-tral fluxes can be used instead of alloying fluxes.

Flux type Advantages Disadvantages

FusedNon-hygroscopic

Alloying elements like Cr and Ni cannotbe included via the flux

High grain strength High volume weight (approx. 1.6 kg/l)

SinteredRelatively high hygroscopicity

Alloying elements cannot normally beincluded via the flux

Relatively low volume weight (ca 1,3 kg/l) Relatively low grain strength

Agglomerated

Alloying elements like Cr and Ni can be included via the flux

Hygroscopic

Low volume weight (approx. 0.8 kg/l) Relatively low grain strength

Consumables

Fluxes for SAW

Different steels demand different wire and flux combinations. Therefore a multitude of different fluxes exist. Some fluxes are designed to accom-modate good mechanical properties and others to provide less stringent weld qualities. As men-tioned before there are fluxes with alloying prop-erties and neutral fluxes that provide protection to the molten pool from atmospheric oxygen and other impurities. Therefore welding consumable manufacturers produce fluxes depending upon the type of steel to be welded. Combinations of fluxes and wires are com-mon in acquiring special properties needed for the steel type in question to be welded. Combi-nations can take three different configurations, namely all alloying elements can be added to the weld metal through the wire, the flux or both wire and flux. Fluxes come in three different forms, agglom-erated, fused and sintered. Fused fluxes are ho-mogeneous where the components of the flux are fused to form a glass like mass which is crushed, ground and finally sieved to obtain a suitable grain size. Agglomerated fluxes can absorb moisture (hy-groscopic). They are made in a completely dif-ferent manner than fused fluxes. The components in agglomerated fluxes are bonded together with potassium or sodium silicate and rotating the compound in a cone shape or drum and finally dried in a rotating tubular kiln at temperatures between 800 and 900 °C. When dry the granules are sieved to the required grain size. Sintered fluxes are form baked and dried into discs that are later crushed to the required grain size. Fused fluxes are non hygroscopic meaning that they do not absorb dampness from the at-mosphere and are ideal for welding outdoors and in environments having high relative humidity. Agglomerated fluxes are hygroscopic and do absorb moisture. These fluxes must be handled in a manner where moisture is kept from them by storing in a special flux drier. Agglomerated fluxes should always be dried before use.

ESAB fluxes and characteristic properties

From a chemical point of view, fluxes are nor-mally divided into the following groups: • Acid and neutral fluxes (with basicity

B = < 1.2) • Basic fluxes (B = 1.2-2.0) • High-basic fluxes (B = > 2.0) • Special fluxes

Special fluxes are not defined chemically; they are defined by application for example for weld-ing of stainless steel and hard facing.

A. Acid and neutral fluxes

Some fluxes in this group are neutral and others al-loying types. In other words the neutral fluxes do not add any alloying elements to the weld metal where the alloying types do e.g. Mn, Cr, Si, Mo to name a few. ESAB has several fluxes available in this group two of them being OK Flux 10.80 which is a neu-tral flux and OK Flux 10.81 which adds silicon and manganese to the weld metal. OK Flux 10.80 is specifically developed to be used with high current and slow welding speeds where is possible to weld butt joints in plate thick-ness up to 30 mm. The basicity index for this flux is 1.1.

OK Flux 10.81 is an acid agglomerated alloying flux adding both Mn and Si to the weld metal. It is designed to weld at higher speed on thinner plates using moderate amperage settings. The basicity index for OK Flux 10.81 is 0.6. High basic fluxes produce purer and stronger weld metal. All agglomerated fluxes are hygroscopic. This means that they absorb moisture and they must be stored in a dry place and dried before use. After use and at the end of the day they must be stored in a heated container to keep it dry.

B. Basic fluxes

Fluxes within the basicity range of 1.2 to 2.0 are generally characterized by:• Excellent welding characteristics• Excellent mechanical properties

(grade III approvals with impact strength re-quirements down to -20 degrees Celsius

• They can be both alloying and non alloying• Designed to be used with low alloyed elec-

trodes.

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Single-run welding with the separate addition of iron powder calls for backing or root runs in or-der to prevent the iron powder sipping through the joint. Iron powder is normally fed from hopper with a dispenser unit attached to it. The dispenser sup-plies the desired amount of iron powder through tubes to the welding wire. When welding with DC current the wire is magnetic and the iron powder is attracted to the wire and is fed into the joint with the wire. Iron powder is normally alloyed with manga-nese (approx. 1.8%), but nickel-alloyed powders are also available. OK Grain 21.85 is made up of low-alloy iron granules measuring 0.5-0.7 mm. If it is added to the weld joint, it helps to facilitate welding in thick plate or in situations where large throats in horizontal fillet joints are needed, as the joint can be filled with a smaller number of runs. Penetra-tion is reduced, reducing the risk of burnthrough at gap openings or root faces that are too small. In some cases, the reduced penetration of the parent metal is an advantage.

Flux consumption Ψ(flux consumption per weight unit of molten electrode)

In fabrication welding, it is most important to choose a consumable that produces a weld met-al that matches the analyis of the parent metal. Needless to say, it is not always possible to expect complete analysis similarity. It also needs to be generally balanced to enable it to be used for com-paratively large groups of similar steels. In spite of this, the main principle is that consumables should produce a weld metal which, in terms of mechanical strength, is at least equivalent to the rest of the material. Over the years, in-depth ex-perience of the characteristics of dissimilar weld metals has been acquired by both manufacturers and users of consumables. It is always a good idea to conduct tests in advance to ensure that the selected consumable in the steel in question will produce a weld joint with the desired properties. Weld defects can occur in connection with any kind of automated welding. They are basically the same as those occuring during handwelding.

Within this group, ESAB has two fluxes available, OK Flux 10.70 and OK Flux 10.71. OK Flux 10.70 has a basicity of approximately 1.7 and can be described chemically as being of the aluminate-basic type. This flux is of the alloy-ing type and is characterised among other things by the fact that its basicity has been chosen to en-able welding to be performed with both direct and alternating current. It is also characterised by good slag detach-ability, run formation, pore resistance and current resistance. As a result of these characteristics, this flux can be used for welding vertical and horizon-tal fillet welds using both single- and multi-elec-trode systems and for normal butt welding. As a result of its good storage characteristics, this flux is designed eventually to replace OK Flux 10.80. OK Flux 10.71 has a basicity of approximately 1.6 and can be described chemically as being of the aluminate-basic type. This flux separates itself from OK Flux 10.70, by compensating or weakly alloying in terms of its alloying elements and it should therefore be welded in combination with alloying electrodes. The general welding characteristics of this flux are identical to those of OK 10.70. But the actual difference is for metallurgical reasons, is more suitable for multilayer welding in thicker material, such as fine-grain-treated steel.

C. High-basic fluxes

This group, which has a basicity between 2.0-3.5, is generally characterised by: • Moderately good welding characteristics (can normally only be welded on DC+) • Excellent mechanical properties (this flux type is used for welding LPG material with impact strength requirements down to –55°C) • These fluxes are neutral – in other words, they are designed to be welded using alloying elec-trodes (OK Autrod 12.34)

Within this group, ESAB supplies OK Flux 10.61 and OK Flux 10.62. OK Flux 10.61 has a basicity of approximately 2.8 and can be described chemically as being of the calcium-basic type. This flux is compensating or produces a slight burn-off in terms of alloying elements. OK Flux 10.62 has such good welding

characteristics that tandem welding with the elec-trode connected to direct current is possible. The slag removal, run formation, aversion to porosity and current resistance of this flux can be regarded as being among the most optimum for fluxes of this type. OK Flux 10.62 has a higher basicity than OK Flux 10.61 and better welding characteristics with direct and alternating current.

D. Special fluxes

As the introduction stated, these fluxes are gener-ally only defined according to their applications. ESAB sells the following fluxes. OK Flux 10.92 is intended for welding stainless steel and is alloyed with Cr to compensate for Cr burn-off during welding. It is neutral and has a ba-sicity of around 0.8. The reason for this is because it is designed for surfacing with stainless strips and therefore the welding characteristics need to be optimal. OK Flux 10.92 is most suitable for welding with austenitic strip electrodes as well as 308L, 367, 316C and 318 wires. OK Flux 10.96 is of the alloying type and is designed for hardfacing. With an unalloyed elec-trode (OK Autrod 12.10), it produces a hardness of approximately 36 HRC. OK Flux 10.16 is designed for surfacing with Inconel strips and is also used for joint welding with duplex electrodes and solid wire. To our knowledge, nothing corresponding to this flux is currently available on the market.

Iron powder

To increase productivity when welding materi-als of a thickness more than 20 mm or more, iron powder or cold wire is added to the filling runs. With the same heat input, the addition of iron powder produces a narrower HAZ than conven-tional SAW, which is an advantage when it comes to the strength of the welded structure. The heat input is reduced in relation to the amount of iron powder added. Productivity can be improved by almost 50%. This means that the labour cost of welding is re-duced accordingly, the throughput time of the welded object in the workshop is shorter.

Choice of consumable

18 19

The effect of flux type on different welding characteristics and welding quality

CharacteristicsOK Flux 10.40

OK Flux 10.80

OK Flux 10.81

OK Flux 10.70/10.71

OK Flux 10.61

OK Flux 10.62

Current resistance XXX XXX XX XX X X

Alternating currentwelding

X (X) XX

Fillet weld properties XXX XX XX XX XX XX

Gap bridging ability X XX XXX XX X X

Slag removal X XX XXX XX XX XX

Welding speed X XXX XXX XX XX XX

Run appearance XX XX XXX XX X X

Crack resistance XXX XXX XXX XX X XXX

Spricksäkerhet X X X XX XXX XXX

Mechanical properties X X X XX (X) XXX XXX

Applications for different fluxes and electrode types

Flux Elektrode typ Application

OK Flux 10.70 OK Autrod 12.10General structural steel, pressure vessels, steel with increased strength (max. approx. 600 N/mm2 class)

OK Flux 10.71 OK Autrod 12.20

OK Flux 10.80

OK Flux 10.81

OK Flux 10.61 OK Autrod 12.20 Low-alloy steel Domex,

OK Flux 10.62 OK Autrod 12.24 Ox etc

OK Flux 10.71 OK Autrod 12.34

OK Flux 10.91 OK Autrod 16.10 18/8-steel

OK Flux 10.92 OK Autrod 16.30 18/8-Mo-steel

OK Band Surfacing

OK Flux 10.96 OK Autrod 12.10 Surfacing HRC 32/40

OK Autrod 12.40 Surfacing HRC ca 46

OK Flux 10.71 OK Tubrod 15.40 Surfacing HRC 27/34

OK Tubrod 15.42 Surfacing HRC 35/44

OK Tubrod 15.52 Surfacing HRC 55/60

OK Flux 10.61 OK Tubrod 15.74Surfacing HRC 45/65Cr=11,5-14,5 %

OK Flux 10.16 Inconel

OK Flux 10.69 Backing powder for Cu bar

The following table lists the most important types of OK fluxes and electrodes for SAW, their combinations and the materials with which they are used.

Weld defects

X = normal, XX = good, XXX = very good

Welding defects cannot be ruled out when us-ing automated welding. The defects that occur resemble those that are found in manual metal arc welding. Defects that occur on the surface are easily detected but defects like slag inclusions, lack of fusion and sub surface porosity can only be detected through radiographic and ultra sonic testing of the welded object. To maintain defect free welds the welding procedure specifications (WPS) must be adhered to under all circumstanc-es. Weld defects can be summarised as follows:• Root defects• Hot cracking• Pipes• Surface porosity• Sub surface porosity• Slag inclusions• Undercut• Lack of fusion

Root defects

A root defect is quite simply incomplete penetra-tion of a joint cross-section. They appear on X-rays as clear, straight lines. In automatic weld-ing, penetration in the joint is an important factor and in cases where root defects occur, penetration is described as incomplete. If the welding is performed from two sides and the root runs do not converge, an explana-tion could be that the root face of the joint is too thick, the joint angle is too small or both. Other explanations could be that the current was too low, the travel speed was too high, or the weld runs were not performed symmetrically. The current is the welding variable that has the greatest impact on penetration depth.

Hot cracking, pipes

Hot cracks generally occur in the centre of a welded bead and they then run in a straight line in the longitudinal direction of the weld head. Hot cracks can occur in butt welds and fillet welds. Hot cracks occur at approximately 1200°C and

are caused by segregation which occurs when the molten pool solidifies. Carbon and sulphur then concentrate in the centre of the bead and at high temperature the strength of the material is considerably reduced. However, the cause of hot cracks in automatic welding is the formation of a pipe, combined with the segregation of carbon and sulphur. Pipes occur in a weld bead in com-bination with segregation of carbon and sulphur.Pipes also occur when the bead form factor or ratio between the width of the bead and the pene-tration depth are not acceptable. In this situation, it is in fact a case of shrinkage and not cracking. Hot cracking can be eliminated by forcing the molten pool to cool from the bottom to the sur-face, so that the primary crystals are forced to grow upwards at an angle towards the surface of the run – in other words, by welding against a cooling base. When welding heavier gauge metals, hot cracking occurs if the cooling rate is too fast. Pre-heating can be utilised to combat this.

Surface porosity

Surface porosity occurs due to the fact that there could be impurities in the flux, rusty electrodes, oil, paint or grease in the joint and hydrogen due to moisture in the flux. The gases that form po-rosity have not been able to exit the molten pool and become entrapped when the molten metal is in the solidification phase. Pores that escape the molten pool become trapped beneath solidified slag and become so called surface pores. They migrate to the centre of the weld bead and ap-pear as a string of pin holes along the solidified weld metal. Surface porosity can be eliminated by decreasing the welding travel speed making sure that the joint is clean and preheating thicker work pieces. Other defects that occur on the sur-face of the weld are pockmarks or indenta-tions and wormholes where gases have not been able to escape through the slag before it solidifies.

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Pores

Sub-surface porosity is not visible from the sur-face. These pores are formed by gas pockets held in the solidifying weld metal. There are two main types of sub-surface porosity. One type occurs when the two root beads do not meet in an appro-priate manner. Rest slag from previous runs can cause porosity and release gases if not properly removed before welding. Slag inclusions

Slag inclusions can occur in submerged arc welding but are rare in single passes. Mainly in multi-run joints slag inclusions will occur. Slag removal is an important factor that must not be overlooked. Undercut

Undercut is due to high arc voltage in compari-son to wire feed speed. Undercut is when there are small grooves adjacent to the weld bead. Undercut should always be eliminated either by reducing the arc voltage to the required level or by decreasing the travel speed.

Other defects

If the welding current is too high in relation to the diameter of the wire, uneven beads will be the result as the arc will break through the flux covering the slag and cause uneven ripples in the bead appearance.

Wire feed speed controls the amperage. High current means high wire feed speed. For a given diameter of wire a certain arc voltage is neces-sary. If the arc voltage is insufficient in compari-son to the amperage an unstable arc will be the result.

Action in the event of weld defects

Undercut• Reduce arc voltage• Reduce welding speed• Increase electrode diameter

Cracks in fillet joints• Reduce arc voltage• Reduce welding speed• Increase electrode diameter• Pre-heat• Change to another electrode, perhaps a

different flux

Cracks in butt-joints• Reduce welding speed• Check the fixation and gap opening of the

plates• Make sure no copper is being extracted from

the root support

Poor penetration• Increase welding current• Change the electrode to positive polarity• Check stick-out length• Increase joint angle

Transverse cracks in multi-run welding• Increase inter-pass temperature• Reduce welding speed• Reduce arc voltage• Reduce current and voltage• Change consumable

Cracks in root runs• Reduce current and voltage• Do not use an electrode dimension that is too

small, in comparis on to the rootface• Pre-heat• Make sure that back gouging is not too nar-

row and deep

Difficulty removing the slag in butt joints and I-joints• Change electrode dimension• Increase arc voltage in I-joints• Reduce welding speed• Remove rolling mill scale, corrosion and

contaminants• Check to see if joint geometry is sufficient

Slag trapped in deep or narrow joints• Reduce arc voltage• Reduce current and voltage• Reduce the effect of flux bed height

Root porosity• Change electrode, twin-arc• Reduce welding current• Change the electrode to positive polarity• Use gas flames in front of the arc• Clean the joint very carefully• Reduce welding speed

Organic porosity• Change electrode• Change the electrode to positive polarity• Reduce welding speed• Remove all grease from the joint very carefully

Porosity caused by magnetic arc blow• Change electrode• Change the electrode to positive polarity• Reduce arc voltage and welding speed• Reduce current and voltage• Make sure the earth lead is in the right place• Use alternating welding current

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Finding and rectifying mechanical and electrical defects

Symptom Defect Action

Varying, unstable values on the volt-meter and ammeter

The contact jaws are worn or the wrong size, which results in poor contact. Too little pressure on the pressure and feed rollers.

Fit new contact jaws.

Difficult to adjust arc voltage and welding current.

Oxidised rheostat.Turn the rheostat repeatedly in both directions. This removes oxide from the contact surfaces.

Abnormally fast wear and run-out in the contact jaws for bare or covered electrodes.

The clamping screw in the clamping sleeve has lost its clamping effect. This results in poor contact pressure and the formation of sparks between the elec-trode and contact jaws.

Fit a new clamping screw.

There is play in the welding wire as it passes through the contact jaws.

The contact jaws are worn or have the wrong dimensions.

Fit new contact jaws of adjust the ex-isting ones.

Burned or internally verdigris-cov-ered contact jaws.

Poor electrical contact between the con-tact jaws.

Clean the contact jaws. If they are badly burned, fit new ones.

Uneven, irregular electrode feed. The pressure on the feed roller is too high or too low. Wrong roller dimension or worn electrode groove in the feed roller.

Adjust to normal pressure. Check the roller dimension or change the roller if necessary.

When welding with an electrode with a smalldiameter electrode, the electrode wanders and becomes twisted.

The brake hub in the wire drum has not been tightened sufficiently..

Tighten the adjustable washer on the brake hub so that sufficient braking effect is obtained.

Overheating of the welding current cables.

Oxidised or loose connections. The welding cables have the wrong dimen-sions for the welding current.

Clean and tighten the connections. If the welding current requires it, change to two cables

Welding data tables

Butt joint welded from both sides

Plate thickness mm

Elektrode diameter mm

Weld run no Arc voltage VWelding current A

Welding speed cm/min

6 3-4 1 30-32 350-400 50-70

2 31-33 400-450 50-70

8 3-4 1 30-32 450-500 60-70

2 30-33 500-550 50-60

10 4 1 30-32 450-500 60-70

2 31-33 550-600 60

12 4-4 1 32-35 600-650 60

2 33-35 700-750 60-65

14 4-4 1 33-35 650-700 50-60

2 33-35 750-800 40-50

Welding data, butt joints

Applies for direct current (plus pole). If alternat-ing current is being used, the arc voltage should be about two volts higher. Typical welding data for the SAW of C-Mn steel using OK Flux 10.70, OK

Flux 10.71, OK Flux 10.80 and OK Flux 10.81. With OK Flux 10.40, the arc voltage should be slightly higher, about two volts.

Weld metal strength, typical values for all-weld-metal samples

OK Flux 10.40/OK Autrod

Tensile yield limitN/mm2

Ultimate tensile strength N/mm2

Impact strengthJ

Charpy V°C

12.10 370 470 60 -20

12.20 410 510 50 -20

Approval


ABS LR2 DnV BV GL RS

12.10 2TM 2TM IITM A2M 2TM 2TM

12.202T, 3M3YM

2T, 3M3YM

IITIIIYM

A2TA3YM

2T3YM K2T3M

Welding data, butt joints

Typical welding data for SAW of low-alloy steel with OK Flux 10.61 and 10.62.

Butt joint welded from both sides with a gap opening

Plate thickness mm




6 3 1 29 300-350 60-67

2 30-31 375-425 60-67

8 3 1 30-31 450 60-67

2 31-32 500 65-67

10 4 1 30-31 500 60-67

2 30-32 575-600 60-67

12 4 1 30-32 600 60

2 30-32 600 60

23

24 25

Weld metal strength, typical values for all-weld-metal samples


Tensile yield limitN/mm2

Ultimate tensile strength N/mm2

Impact strengthJ

Charpy V°C

12.22 420 510 100/50 -40/-60

12.24 520 600 50/- -40-

12.32 470 570 100/70 -40/-60

12.34 580 660 100/60 -40/-60

13.10 430 560 200 +20

13.20 450 590 100 +20

13.21 470 560 120/60 -40/-60

13.27 500 570 120/80 -40/-60

13.40 630 700 60/40 -40/-60

13.43 710 800 70/50 -40/-60

One welding head

Plate thickness mm




6 3 3 26-28 450 75

8 4 4 28-30 575 70

10 4 5 28-30 650 60

Welding data, fillet welds

Reference values for SAW fillet joints in unal-loyed and low alloyed structural welding steel OK Flux 10.70 and OK Flux 10.81.

One welding head, positional welding, horizontal fillet

Plate thickness mm


Weld run no

Arc voltage VWelding current A


8 4-5 4 26-28 450 83

12 5 6 32-34 850 60

15 5-6 7 33-35 850-875 42-45

Double wire (twin-arc)

Plate thickness mm


Weld run no



– 2x2,5 4 26-28 800 110

– 2x2,5 5 26-28 800 75

Two welding heads +~

Plate thickness mm


Weld run no



– 4 4 +29 550 125

~34 630

– 4 5 +29 550 120

~34 630

N.B. 30 mm should be welded with two runs from either side to take account of impact strength etc. Welding pa-rameters other than those given in the table then apply.

Welding data, butt joints, V-joints, X-joints

Typical welding data for the SAW of C-Mn steel using OK Flux 10.40, OK Flux 10.70, OK Flux 10.71, OK Flux 10.80 and OK Flux 10.81.

V-joint 60° with a root face of 8 mm

Plate thickness mm




16 5-6 NA 32-34 700-750 40-45

NA 33-36 650-750 40-45

18 5-6 NA 32-34 800-850 37-40

NA 36 850 45

20 5-6 NA 32-34 925 30

NA 34-36 850 42-46

X-joint 70° with a root face of 6-8 mm

Plate thickness mm




18 5-6 NA 3-34 700-750 60-67

NA 34-36 800-850 60-67

20 5-6 NA 34-36 750-800 60-67

NA 34-36 800-850 65-67

25 5-6 NA 34-36 750-850 60-67

NA 34-36 900-950 60-67

30 5-6 NA 32-36 900 60

NA 34-36 1000 60

Welding data for stainless steel

Typical welding data for SAW in stainless “18/8” steel. Joint types and reference values. Consuma-bles OK Autrod 16.10, OK Flux 10.91 and OK Flux 10.92.

I-joints

Plate thickness mm


Weld run no



6 3 1 30-32 350 60-70

2 32 400-450 60-70

8 4 1 32-33 400-450 60-70

2 34 550 60

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V-joint 60° with a handwelded bottom run, gap 0-2 mm, root face 2 mm

Plate thickness mm


Weld run no



10 3-4 1

2

12 3-4 1

2-3

20 4 1

2

3-5

• Check that the feed rollers, contact jaws and contact tips have the correct dimensions. • Make sure that the wire is correctly straight-ened to avoid abnormal wear and tear on the con-tact jaws and tips. Worn contact jaws result in an unstable welding process and unstable instru-ment readings. If the grooves in the feed roller are worn, wire feed will be uneven.• In joint welding with direct current, the elec-trode should be connected to the plus pole. • The distance between the workpiece and the contact jaws should be kept between 25 and 35 mm. • To ensure good arc striking at the start of weld-ing, the electrode should be cut at an angle, re-ducing electrical resistance in the wire for trou-ble free start. • The return leads must have good contact with the workpiece. • All the cables should be organised in such a way that they do not disrupt the welding process.

X-joint 70° with a root face of 4-5 mm

Plate thickness mm


Weld run no



12 4 1 32-34 500 60

2 32-34 600 60

14 4 1 32-34 550 50

2 32-34 600 50

X-joint 60° with a handwelded bottom run, gap 0-2 mm, root face 2 mm

Plate thickness mm


Weld run no



25 4 1 28-30 550-600 60

2 32-34 550-600 50

3-4 32-34 550-600 50

5 28-30 550-600 50

6 30-32 550-600 50

7-8 32-34 550-600 50-60

Practical instructions

• The air pressure that is used to recycle flux should not be higher than necessary. If the air pressure is too high, the flux will become pulver-ised. • The contact jaws and nozzles must be regarded as wear parts. • When welding cylindrical objects with a small diameter, a flux support should be used. This produces improved control of the flux bed and reduces the unwanted loss of flux around the wire. • The same care should be given automatic welding equipment as is given to the other costly equipment.• To obtain the best welding results, mill scale and the like should always be removed from the area to be welded.

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Notes

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Notes

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30 31

Notes

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Notes

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ESAB AB

Box 8004, SE-402 77 Göteborg, Sweden

Phone: +46 31 50 90 00. Fax: +46 31 31 50 93 90

[email protected] www.esab.com

Content

• General information • The principles of submerged arc welding • Rules for welding • Parameters • Setting welding data• Formulae • Conversion table• Submerged arc welding methods • Single-wire welding • Twin-wire welding • Tandem welding • Strip cladding • Narrow gap welding

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001

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• Cold wire addition • Iron powder • Joint preparation• Joint backing • Consumables • Electrodes • Flux • ESAB fluxes and characteristics • Iron powder • Weld defects• Action in the event of weld defects • Welding data tables• Practical instructions

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