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Potential savings in welding stainless steelsusing flux cored welding wires

BHLER


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Selection depends mainly on 3 factors that have essentially

equal significance in the decision-making process

Fig. 1: Deciding factors for the introduction of welding processes invarious welding shops

POTENTIAL SAVINGS IN WELDING STAINLESS STEELSUSING FLUX-CORED WIRES

H. Schabereiter, R. Drfler, J. Ziegerhofer

1. GENERAL

The use of high-alloyed flux-cored wires has undergone a remarkable upturn in recent years and moreparticularly in the very recent past.

For cost reasons the constant aim in welding fabrication shops is to substitute established welding pro-cedures with more up-to-date and above all more cost-effective processes. This is usually achieved bymeans of a close working relationship between the technicians, salesmen and welders. The factorsshown in Fig. 1 represent the main considerations for this.

Flux-cored welding wires are primarily measu-red on the properties of coated electrodes andsolid wires. For many years the consumption offlux-cored wires in Europe was less than 5 % ofthe overall potential for high-alloyed filler metalsand this has increased to almost 10 % in the lastfew years. An additional increase in the con-sumption of flux-cored wires is anticipated. Thiswill not be so much at the cost of coated elec-trodes but rather as substitution of solid wires.

The following sections will deal in greater detailwith the most significant deciding factors for sel-ecting welding processes and the possibilities ofreducing costs by using modern filler metals infabrication of corrosion resistant components.

2. SIGNIFICANT FACTORS FOR DECISION-MAKING

IN THE SELECTION OF WELDING PROCESSESGenerally speaking, the only welding processesand filler metals considered in practice are thosewhere the weld metal deposits satisfy the require-ments in the standards and the characteristicsspecified for mechanical properties and corrosionresistance.

Assuming these basic requirements, cost effi-ciency is compared with additional factors influen-

cing overall cost outlay in the manufacture ofwelded components.Fig. 2: Typical factors in the cost calculation

Filler metal

Weldingcurrent

Wireextension

Weldingvoltage

Duty cycle

Metal recovery

Weight of weld

Deposition rate

Joint area

Weight offiller metal

Filler metalcosts

Electricity costs

Gas costs

Labour costs

Capitalexpenditure

Total costof weld

Arc burningtime

Welddressing

Totalwelding time

CRITERIAFOR SELECTING

WELDINGPROCESSES

PRODUCTIVITY

PROFITABILITY

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Fig. 4 shows the comparable lengths of fillet welds with a specified throat thickness of 3 mm and thewelding time of 1 minute. The considerably faster travel speed using the flux-cored wire (800 mm) com-pared with the solid wire (670 mm) and the stick electrode (280 mm) speaks for itself.

a ... flux-cored wire 1.2 mm = 800 mm

b ... solid wire 1.0 mm = 670 mm

c ... stick electrode 3.2 mm = 280 mm

Fig. 5illustrates additional comparisons of travel speed. In this case different fillet weld thicknesses(3/5/7 mm) were produced using solid and flux-cored wire and the weld lengths achievable were mea-sured. The welds obtainable using the flux-cored wires are between 19 and 50 % longer with the samewelding time.

Gas: Argon +18 % CO2 for flux-cored wire

Argon +12 % CO2 for solid wire

Plate 5 mm for 3 mm fillet weldsthickness: 10 mm for 5 & 7 mm fillet welds

Severe bead oxidation with MAG solid wire,especially at 275 A. Wetting behaviour also notgood.

Only slight bead oxidation with MAG flux-coredwire even at 275 A!!

throat thickness 3 mm 5 mm 7 mm

Bhler EAS 4 M-FD, 1.2 mm 80 cm/min 48 cm/min 2 1 c m/min235 A, 33 V, 14 m/min (+ 19 %) (+ 33 %) (+ 23 %)

Bhler EAS 4 M-FD, 1.2 mm

54 cm/min 25 cm/min275 A, 35 V, 18 m/min (+ 50 %) (+ 39 %)

Solid wire, 1.2 mm60 cm/min 32 cm/min 1 5 c m/min

235 A, 28 V, 8 m/min

Solid wire, 1.2 mm 36 cm/min 18 cm/min

275 A, 31 V, 10.5 m/min

Solid wire, 1.0 mm67 cm/min 36 cm/min 1 7 c m/min

235 A, 31 V, 14 m/min

Fig. 5: Comparison of travel speeds for MAG solid wire and MAGflux-cored wire type 316L, welding position 2F

Fig. 4: Comparison of travel speed between stick electrode, solidwire and flux-cored wire (type 316 L) in fillet welds, welding

position 2F

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Post weld cleaning

The basic requirement for achieving optimum corrosion resistance with austenitic welds is the presenceof a completely clean bright metal surface. The passive layer responsible for corrosion resistance canonly form in the appropriate shape under these conditions. Thus the dressing of welds is equally avariable which determines quality during the fabrication of welding components.The cost saving benefits gained by welding with flux-cored wires as opposed to solid wires are listedbelow.

Minimum post weld cleaning due to:

Flat and smooth weld finish (minimum grinding expenditure), see Fig. 6 Minimum spatter formation Lower pickling expenditure (temper coloration is minimized), see Fig. 7 Less distortion due to increased travel speeds Lower repair rates (pores, slag inclusions, fusion defects)

Actual information regarding the overall costsavings achievable depend to some extent onthe cost structure and plant set-up of the indivi-dual company as well as on the particular wel-

ding work undertaken.

However, with a saving in welding time of bet-ween 19 and 50 % (see Fig. 5) and calculatedindustry rates of an average DM 100.-/hr forMIG/MAG welding in Western Europe, the flux-cored electrode, which is more expensive thansolid wire, usually makes savings of between10 and 30 % possible if the overall calculationincludes lower-cost weld dressing. Fig. 8graphi-cally illustrates this financial advantage when

using flux-cored wires in the flat or horizontalwelding position.

Fig. 7: Differences in weld oxidation between:a) flux-cored wireb) solid wire

a)

b)

Fig. 6: Component welding using flux-cored wire:smooth, notch-free welds with good wettingand uniform weld finish

Fig. 8: Cost savings when using flux-cored wire in the flat andhorizontal welding position

100

90

80

70

60

50

40

30

20

10

0

Solid wire Flux-cored wire

savings of

10 %to

30 %

100 %

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Statements from fabricators:

New filler metals are essentially developed by working closely with potential users. Following exten-sive laboratory testing, samples are used in practice to determine the products' suitability for large-scale production. Intensive discussions with consumers of stainless flux-cored wires then resulted inthe following practical knowledge.

Cost-effectiveness (quality and through put are decisive)

Productivity of the welding process Duty cycle Downtimes Post weld cleaning

Power Sources

Conventional MAG welding machines with 4-roll drive and water-cooled torches Average amperage when using flux-cored wires 1.2 mm can be 260 270 A. Higher than average

increase in productivity in this current range amperages compared with solid wire 1.2 mm (see Fig. 5)

Weld Dressing (pickling problems/costs)

Depends on design and plant set-up but still up to 30 % lower costs using flux-cored wire Pickling baths approx. DM 150.-/hr, waste disposal extremely expensive Spray pickling collection neutralisation disposal of liquid Glass bead blasting hourly rates DM 250.- to 350.-

The following additional benefits for the user of flux cored wires are worth mentioning:

Easier to operate than MAG solid wire No pulsed power source required (lower noise level) Lower gas costs (Argon + 18 % CO2 instead of Argon + 2 % CO2) Smooth bead appearance Less risk of fusion defects and thus lower repair rates Easier control of heat input due to higher welding speeds Good root pass welding characteristics with extra high productivity gains when using ceramic backing

2.1.2 Positional welding

Positional type flux-cored wires produce a rutile slag that solidifies rapidly and are therefore suitablefor all welding positions. Both, mixed gases and 100 % CO2, are used as shielding gases. The typicalcharacteristics of such FCAW wires are:

Rutile slag with rapid solidification (high melting point)Excellent backing effect for the weld pool

Use of high current intensities possible for out-of-position welding, e.g. 160 A instead of 100 120 Ausing solid wire (3G, 3F)

Up to 100 % higher travel speeds Excellent wetting behaviour, flat and smooth treat profile Powerful penetrating arc, spray transfer, minimum spatter formation Good mechanical properties

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In Fig. 11 it is easy to see the time saving andthe cost benefit gained by using a positionaltype flux-cored wire. Approximately 70 to 80 %higher travel speeds can be achieved in filletwelds compared with the solid wire electrode.This is many times higher than with manual arcwelding.

Fig. 13: Macro-section and side bend test specimenfrom a thick-walled pipe joint.

Fig. 12: Example of practical application

Fig. 11: Comparison of weld lengths achievable in the sameamount of time

Flux-cored wire Solid wire Stick electrode

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Fig. 12illustrates a particular example of a prac-tical application. Here dished boiler ends withwall thicknesses of 38 mm are manufacturedfrom material AISI 316L. The double-V butt weldsare produced by automatic welding in the verti-cal-up position. Bhler EAS 4 PW-FD 1.2 mmwas used as the flux-cored wire. The self-pee-ling slag and smooth weld finish with only slightoxidation (can be removed by brushing easily)are clearly visible.

Joining pipes in the Offshore industry gives riseto almost all the welding positions possible inpractical use. As an example, Fig. 13 shows amacro-section and a side bend test specimenoriginating from a thick-walled 1.4462 pipe joint.The pipe dimensions are 508 x 49 mm.Bhler CN 22/9 PW-FD 1.2 mm was used asthe flux-cored wire with optimum results regar-ding welding characteristics, mechanical pro-perties and corrosion resistance.


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2.1.3 Sheet metal fabrication using 0.9 mm FCAW wires

1.2 mm is the most commonly used diameterof flux-cored wire employed in practice forwall thicknesses above 3 mm. Flux-coredwires of 0.9 mm diameter are especiallysuitable for joining thin metal sheets above1.5 mm.

They are ideal for welding small, well-wettedweld cross-sections at high travel speed andwith less heat input. This is one aspect thathas an effect on costs since there are fewerdistortion problems and less post-weldstraightening at the same time as visualbenefits, Fig. 14.

2.1.4 Lower-priced shielding gases

Stainless steel flux-cored wires are welded using the commercially available shielding gasesArgon + 1525 % CO2. At approx. 16 litres per minute the gas flow rate is the same as when weldingsolid wires using argon + 2 % CO2. The use of shielding gas containing higher levels of CO2 for slag-forming flux-cored wires is rendered possible since every single metal droplet transferred in the arc iscompletely covered with slag. This prevents any reaction with the shielding gas.

Fig. 15 shows a metal droplet completely coveredwith slag at the end of the FCAW wire. Thus there isno carburisation or burn-off of elements with an oxy-gen affinity, such as chromium, which would be unac-ceptable for corrosion reasons.

The cost benefits for the user result on one hand from the lower gas costs and also from the lower gasconsumption which follows on from the shorter welding time.

2.2 Reliable and consistent weld quality

The basic requirement for proper performance of welding work is the use of suitably trained weldingstaff. In many cases a requirement is made for certified welders for the production of welded compo-

nents and in certain regulations this requirement is mandatory. On the European market the proce-dure for testing welders is specified in standard EN 287. There is reference to the individual weldingprocesses, such as metal active gas (MAG) welding using flux-cored wires.

Fig. 14: Welded joints produced on 2 mm thick metal sheets using flux-

cored wire 0.9 mm

Butt weld Fillet weld

Complete covering of the Partially peeled slagdroplet with rutile slag after cooling off

Lap joint Corner joint

Fig. 15: Metal droplet on a flux-cored electrode

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Training, testing and maintaining the validity of test certificates for the welding staff represents a con-siderable amount of time and money for the welding shop. Welding processes that allow the trainingtime to be shortened and that reduce possible weld defects therefore represent a cost reduction factorfrom the quality management point of view.

Easy to operate and reliable in processing

Flux-cored wires ensure a very wide range ofpossible setting parameters. This makes the sel-ection of optimum welding data significantlyeasier see Fig. 16.

The welding behaviour remains constant through-out broad ranges of current intensity and volta-ge. The large parameter box tolerates uninten-tional changes to the operating point by the wel-der without loss of quality. Welding with asmooth, non-spatter spray arc is possible as lowas 150 Amps, 25 Volts and 6.5 m/min wire feedwith 1.2 mm FCAW wires and 0.9 mm wiresoperate in the spray arc transfer already at 110 A, 26 V and 9.5 m/min. By comparison solid wire onlytolerates a very narrow operating range. This requires a high level of concentration from the welderregarding correct torch positioning especially since relatively small deviations lead to impairment of thewelding behaviour.

The greater independence of parameter setting and the lower risk of welding defects compared withwelding using solid wires speak for the reliability of flux-cored wires.

Fig. 17 illustrates the characteristic penetration profiles of the wires mentioned. Using the flux-coredwire provides more even penetration with excellent side wall fusion and a good weld profile due prima-rily to the wider arc. The solid wire on the other hand exhibits very deep penetration in the middle butin this case it is possible to see poor fusion of the lower side wall due to torch manipulation being a littletoo flat. In practical application the problems caused by lack of fusion continue to give rise to diffi-culties even when working with the most vigilant and experienced solid wire welders.

Flux-cored wire 1.2 mmGas: Argon + 18 % CO2

Excellent penetrationGood bead appearance

Solid wire 1.2 mmGas: Argon + 2.5 % CO2

Deep penetration at the

bead centre, however,the lower plate is hardlypenetrated

Fig. 16: Possible parameter ranges in the spray transferfor flux-cored and solid wires

Formation of spatters

Solid wire1.2 mm

Solid wire1.0 mm

FCAW wire 1.2 mm

Poor bead appearance

38

36

34

32

30

28

26

24

22150 200 250 300

Amperage (A)

Fig. 17: Comparison of penetration profiles of solid wire and flux-cored wires

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2.3 Product quality and constancy

Years ago there was some scepticism regarding the use of flux-cored wires. This was due to the factthat the flux core was sometimes variable in quality or possibly even missing. Today this scepticism isno longer appropriate since flux-cored wires from well-known companies are manufactured in modernproduction plants. They consist of high-alloy austenitic precision steel strips and a filling of variousmineral and metallic components exhibiting a special composition depending on the type of alloy. AtBhler Welding the infills are agglomerated prior to filling to ensure uniform filling and to preventdecomposition of the different raw materials during filling due to their different specific weights.

A specially installed control system using up-to-date monitoring technology constantly and efficientlychecks the consistance of filling. The whole production process satisfies the criteria of EN ISO 9001.

At Bhler Welding every production lot is checked for the welding characteristics, feed properties andchemical composition of the weld metal during quality assurance.

Increased precautions when storing partly used spoolsand spools removed from their original packaging areparticularly important for today's users. As is the casewith high-alloyed rutile-coated stick electrodes, all rutileslag-forming flux-cored wires must also be protectedfrom atmospheric moisture and the formation of con-densation on the wire surface if the dew point falls.They are more sensitive to the formation of worm-holesthan solid wires. The reason for this is that an excessof hydrogen of humid wires is unable to effuse in timeprior to solidification of the weld pool due to the slagprotection of the weld on one hand and the high travelspeeds and simultaneously lower heat input on theother too. Therefore care must always be taken tostore partly used spools correctly and always to usewires which have acclimatized. Wires which havebecome humid can be rebaked at 150C.

Today thousands of tons of high-alloyed flux-cored wires are successfully used for production weldingthroughout the world. The wires have proven and established themselves in the construction ofchemical and petrochemical plants, offshore engineering, tanker construction, the paper and pulp indu-stry, plant construction in the food, drinks or textile industries up to the welding of highly corrosion-resistant flue gas desulphurisation plants.

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Conveyer screw from AISI 316 Ti for the pulp industry welded withBhler EAS 4 M-FD

Pressure vessel with heating coil from AISI 316L welded withBhler EAS 4 M-FD

Pipe segment from duplex steel UNS S 31803 for the offshoreindustry welded with Bhler CN 22/9 PW-FD

Part segment of a scrubber & separator made ofUNS S 31803 welded with Bhler CN 22/9 N-FD

Dissimilar joint weld, 3G,welded with Bhler CN 23/12 Mo PW-FD

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High-alloyed flux-cored wires are available for the most commonly used stainless CrNi and CrNiMosteels as well as for dissimilar joints or weld cladding and are standardised in the European standardEN 12073 and the American standard AWS 5.22 respectively.

3. SUMMARY

The present report investigates in depth the basic factors such as productivity, processability and qua-lity in the selection of welding processes. The significant advantages of using flux-cored wires for wel-ding stainless steels become perfectly apparent. Despite the higher product price of flux-cored wires,there are remarkable time savings, productivity gains and potential cost savings to be made if all thecost factors relevant to fabrication are taken into consideration.

Users who already have extensive practical experience of production welding using high-alloyed flux-cored wires have given the following factors as reasons for changing over:

High deposition rate and increased productivity

Easy to operate

Smooth welding characterisitcs & weld finish

Radiographically sound weld deposit

Lower costs for the shielding gas

Simple and more cost effective post weld cleaning

Less repair work

Decreased overall fabrication costs

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RANGE OF PRODUCTS

For flat and horizontal welding positions

* size 0.9 mm can be operated in all welding positions

For positional welding

If you have special questions or if you need expert consultation and

competent advice, please feel free to contact us.A team of Bhler welding experts with special knowledge

in every sphere of welding engineering is at your disposal.

DESIGNATION EN 12073 AWS A 5.22

BHLER EAS 2 PW-FD T 19 9 LPM (C) 1 E 308 LT 1-4 (1) 1.2

BHLER EAS 4 PW-FD T 19 12 3 LPM (C) 1 E 316 LT 1-4 (1) 1.2

BHLER CN 22/9 PW-FD T 22 9 3 NL PM (C) 1 E 2209 T 1-4 (1) 1.2

BHLER CN 23/12 PW-FD T 23 12 LPM (C) 1 E 309 LT 1-4 (1) 1.2

BHLER CN 23/12 Mo PW-FD T 23 12 2 LPM (C) 1 E 309 L Mo T 1-4 (1) 1.2

BHLER E 308 H PW-FD TZ 19 9 HPM (C) 1 E 308 HT 1-4 (1) 1.2

size

in mm

sizein mmDESIGNATION EN 12073 AWS A 5.22

BHLER EAS 2-FD T 19 9 LRM (C) 3 E 308 LT 0-4 (1) 0.9* 1.2 1.6

BHLER SAS 2-FD T 19 9 Nb RM (C) 3 E 347 T 0-4 (1) - 1.2 -

BHLER EAS 4M-FD T 19 12 3 LRM (C) 3 E 316 LT 0-4 (1) 0.9* 1.2 1.6

BHLER E 317 L-FD TZ 19 13 4 LRM (C) 3 E 317 LT 0-4 - 1.2 -

BHLER CN 22/9 N-FD T 22 9 3 NL RM (C) 3 E 2209 T 0-4 (1) - 1.2 -

BHLER CN 23/12-FD T 23 12 LRM (C) 3 E 309 LT 0-4 (1) 0.9* 1.2 1.6

BHLER CN 23/12 Mo-FD T 23 12 2 LRM (C) 3 E 309 L Mo T 0-4 (1) 0.9* 1.2 1.6

BHLER A 7-FD T 18 8 Mn RM (C) 3 E 307 T 0-G - 1.2 -

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Bhler Schweitechnik

Aust r ia GmbH

Bhler Welding St. 1A-8605 Kapfenberg

Tel.: ++43 (0) 3862-301-0

Fax: ++43 (0) 3862-301-95193

e-mail: [email protected]

http://www.boehler-welding.com

Forwarded by:


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hlerSchweitechnik

ustriaGmbH

Bhler-Welding-St. 18605 Kapfenberg/ AUSTRIATel.: ++43 (0) 3862-301-0Fax: ++43 (0) 3862-301-95193e-mail: [email protected]://www.boehler-welding.com

Forwarded by:

BSGA

03/2001

E2500

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