Duplex Tankers

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Factoras Vulcano S.A,Vigo, is a medium size ship-yard in the north of Spainproducing an extensive

range of civil and maritimeproducts, including chemi-cal carriers in both carbonand duplex stainless steel.Currently, the yard is final-ising the construction ofThe Primo, a duplex chemi-cal tanker for the Swedishshipping company Initia.The fabrication, from theindoor panel lines down to

the final outdoor blockassembly, is characterisedby wide scale use of ESABwelding solutions with a keyrole for ESAB OK Tubrodcored wires. This articlereviews the production ofchemical tankers at Vulca-no. Special attention isfocussed on the role ofFCAW.

Acknowledgement

We would like to thank FactorasVulcano for their excellent co-operation in preparing this arti-cle.A special word of thank weaddress to Ramn Prez Vzqu-ez, Production Manager, JessFernndez Iglesias, Steel SupplyManager, and Javier Perz, Weld-er Foreman. Their openness hascontributed greatly to this article.

In addition, we compliment ourspanish Esab colleagues Jos LuisSastre, Carmen Herrero and JosMara Fernndez Vidal on thegreat marketing success achievedat Factoras Vulcano.

IntroductionThe title Welding duplex chemi-cal tankers the Esab way, is per-haps a bit over-ambitious, but it isrightly chosen in the sense thatFactoras Vulcano apply ourwelding solutions in practicallyevery stage of the fabrication pro-cess of chemical tankers. Theshipyard has made intelligent useof ESABs capability to serve as atotal supplier for stainless steel

fabrication, selecting dependableand productive consumable/equipment combinations forpractically all fabrication steps.The yard possesses a high level ofpractical welding knowledge, pro-viding a solid basis for, sometimesdifficult, but often fruitful techni-cal discussions between our com-panies. Over the years, the co-operation in developing and im-plementing new techniques has

developed such that today we feelwe can rightfully claim thatEsabs mission statement to bethe preferred partner for weld-ing and cutting is fully valid forthis shipyard.

This article presents a bird-eye-view on the fabrication of chemi-cal tankers in duplex stainlesssteel at Factoras Vulcano.Avoid-ing too much technical detail, itwill step by step discuss the fabri-cation process as well as theESAB welding solutions that havebecome established. The FCAWwith rutile cored wires is empha-sised, because it plays a key role inthe fabrication and because these

products are relatively new for du-plex stainless steel welding.

Factoras Vulcano

Starting out with the repair ofrailway engines in 1919, FactorasVulcano widened their capabil-ities to what they are today; a fullscale fabricator of civil and mari-time constructions.Todays prod-uct range comprises civil engi-neering products like boilers, ma-

rine fresh water generators, re-fuse incinerators and sewagetreatment plants, whereas theshipbuilding segment fabricatescontainer ships, refrigerated ves-sels and chemical carriers.

Svetsaren No.1 1999 15

Welding duplex chemical tankers

the ESAB wayWide scale application of ESAB welding solutions at

Factoras Vulcano S.A., Spain

By Ben Altemhl, Svetsaren editor, interviewing Factoras Vulcano

production management.


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stainless steel assembly work in-volves the joints numbered 1,connecting the prefabricateddeck plates to construct the tankfloor. Here Factoras Vulcano ap-

ply a combination of manualFCAW on ceramic backing stripfor single sided root passes andSAW for the filling layers. ESABOK Tubrod 14.37 has been select-ed as the FCAW consumable, be-cause of its capabilities for down-hand work. With its slow freez-ing, fluid slag, it is designed toweld at high travel speed givinghigh productivity (Figure 3). Itgives good penetration and, after

slag removal, the back side of theroot requires no grinding orbrushing. The ceramic backingstrips to be used with this productrequire a rectangular groove toaccommodate the slag and to pro-mote a good bead appearance.OK 14.37 is welded in 85%Ar/15%CO2 gas protection, a mix-ture applied at Factoras Vulcanofor all FCAW (stainless and car-bon steel). Here, and for all otherFCAW, the yard uses simplistic

rectifiers without the need forpulsing.

SAW filling is done with theESAB wire/flux combination OK16.86/OK Flux 10.93, a combina-tion widely applied in duplexstainless steel fabrication, andwith an excellent reputation. Theflux is a low-hydrogen, non-alloy-ing, basic agglomerated type(AWS: SA AF 2 DC). OK Autrod16.86 is of the 23Cr-9Ni-3Mo type

alloyed with 0.15%N to obtain aweld metal with sufficiently over-matching mechanical properties, agood austenite/ferrite balance,and excellent corrosion resistancewhen welding standard UNS

In 1990 the company com-menced a three year plan to re-structure and modernise the ship-yard, involving a 1200M Pesetasinvestment.What results today is

a modern medium-size shipyardwith advanced FORANCAD/CAM design facilities, anESAB NUMOREX NXB9000under water plasma cutting instal-lation connected to the CAD/CAM system.Also, a panel fabri-cation line with two ESAB A6-LAE1250-TAC1000 submergedarc welding machines, mechan-ised welding stations for stiffenerattachment and various systems

for mechanised SAW and FCAWapplied in sub-assembly and finalassembly. The yard lay-out guar-antees an efficient flow of workthrough production.Along withthe modernisation, the yard im-plemented the ISO 9001 qualityassurance system.Together withan orderbook of specialised pro-jects that reaches well into thenext century, the yard is well posi-tioned to compete in todays de-manding market.

Construction of chemi-

cal tankers at Factoras

Vulcano

Although fabricated out of twocompletely different base materi-als, carbon steel and duplex stain-less steel, the construction of

chemical tankers at Factoras Vul-cano takes place according to es-tablished, modern shipbuildingpractices involving panel fabrica-tion, the construction of sub-sec-

tions, the assembly of block sec-tions, and the final connecting ofblock sections in the dock.Weshall focus on the role of duplexstainless steel cored wires. Sincethese are applied primarily in thedock assembly, we describe thefabrication of The Primo in re-versed order.

Figure 1 gives a schematic viewof a 16000DWT chemical carrierfrequently built by Vulcano, and

very much resembling the Primo.The vessel has 12 tanks in duplexstainless steel and two small tanksserving for storage of cleaningwaste. Parts in duplex stainlesssteel are highlighted in red. Verti-cal assembly welds are indicatedwith yellow dots.

Figure 2 shows the Primosomewhere half way during theassembly of the chemical cargotanks. Prefabricated sections arehighlighted with individual

colours and all assembly weldsare visualised by yellow lines,numbered 1 to 9, and described inthe margin.

For a good understanding ofthe construction, we recommendto first have a look at Figure 4. Itshows the next block section tobe assembled, comprising a decksection and tank assembly, thecorrugated bulkheads. As such, itwill be turned and placed in the

construction. The yellow lines inFigure 2 may, therefore, indicateready welds or welds to be madewhen the next block section hasbeen positioned.

The first step in the duplex

16 Svetsaren No.1 1999

Figure 1: Top-side view of a chemical tanker with 12 duplex

stainless steel tanks.Yellow dots in the magnification represent

vertical assembly welds.

Figure 3: Root pass in deck joint with

OK Tubrod 14.37 seen from above.


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S31803 types of duplex stainlesssteel. Vulcano use ESAB A2 Mul-titrac SAW machines, guided byrails attached parallel to thejoints. The same machine-consu-mable solution is used all over

the yard, providing a dependablewelding method in many produc-tion steps (see later).

The same method as describedfor the tank floors is used for theconnection of the tank floor tothe carbon steel hull of the bot-tom (2), be it with 309L typewelding consumables. The flux-cored wire for welding theroot pass on ceramic strip isOK Tubrod 14.22, also a rutile

type for all positional use, where-as the wire/flux combinationapplied for filling is OK Autrod16.53/OK Flux 10.93.

The next assembly step in-volves the placement of the twoside wall sections to the bottomof the vessel where first the car-bon steel parts are connected, fol-lowed by weld type number 3between subsequent block sec-tions. Basically, this is the sametype of joint as between the cor-rugated bulkheads (6), but weld-ed with a slight angle. It is a V-joint welded vertically-up, manu-ally or mechanised with rail-trackequipment, with OK Tubrod

14.27. This rutile cored wire withfast freezing slag system is by farthe most productive solution formaking these kinds of assemblywelds, with deposition rates thatreach up to 3kg/h. Single-sided

root passes are again made on ce-ramic backing strips with a rec-tangular groove

Assembly welds type 4 and 5connect the tank walls to the tankfloor. Both types are treated assemi-positional welds, primarilyperformed with FCAW. Rootpasses are welded on rectangularceramic strips in the case of weld4 and on cylindric ceramics in thecase of weld 5. The back side ofweld 5 has poor accessibility dueto the geometry of the construc-tion. SMAW with ESAB OK67.50, an established acid- rutileelectrode for standard duplexgrades, was found to provide themost practical and secure solutionfor sealing the root.

The next fabrication step con-cerns the placement of the thirdprefabricated block section com-prising a deck section and a crossof longitudinal and transverse

tank walls; the corrugated bulk-heads. This section can be seenisolated, and upside down, in Fig-ure 4. The prefabrication of thiscomponent will be described later.

After turning and positioning

this section between the sidewalls of the ship, a number of as-sembly welds remain to be made.

Assembly welds type number 6are the ones indicated with yel-low dots in figure 1.They connectthe corrugated longitudinal bulk-head with the previous tank sec-tion, and the transverse bulk-heads with the corrugated partsattached perpendicular to theside walls.The welding methodand consumable used are exactlythe same as described for weldtype number 3 (OK Tubrod14.27), but the welding position istruly vertical-up.

To obtain optimal weldingeconomy, Factorias Vulcano applymechanised welding with railtrack systems for the filler layers.

Figure 5 shows a typical exampleof a vertical assembly weld madein this way. Deposition ratesamount to 3kg/h when calculatedat 100% duty cycle, which is high-ly productive for this kind of un-avoidable assembly welds.

Assembly weld 7, between cor-rugated bulkheads and the tankfloor, is carried out manually, be-cause the geometry of the joint istoo complicated to allow mechan-isation (Figure 6). Moreover, theroot gap may show misalign-ments, requiring the welder tomanually build-up the root with avarying number of beads. OKTubrod 14.27 proves to be a ver-satile and dependable consum-able for this kind of demandingwork. Root passes are made al-most twice as fast as with stickelectrodes, using cylindrical ce-ramic backing, with excellent ab-lity to compensate for misalign-

ment of the joint.


Figure 4: Fabrication of a block section consisting of a tank cover with vertical

corrugated walls in duplex stainless steel.

Figure 5: Vertical weld between corru-

gated tank walls; mechanised welded

with OK Tubrod 14.27


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Connection between

corrugated bulkheads and

tank floor

Position: PC/2GRoot: FCAW with OK Tubrod 14.27,

manually welded onto cylindric

ceramic backing.

Filling: FCAW with OK Tubrod 14.27,

welded manually.


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Figure 2: Principal dock assembly welds

Tank floor from

pre-fabricated plates.

Position: PA/1G

Root & 1st pass: FCAW with OK

Tubrod 14.37, welded manually ontoceramic backing strip.

Filling: SAW with

OK Autrod 16.86/OK Flux 10.93

4 Connection between vertical

tank wall and angled side

wall

Position: PC/2G

Root: FCAW with

OK Tubrod 14.27,

welded manually

onto ceramicbacking strip.

Filling: FCAW with

OK Tubrod 14.27,

welded manually .

3

6

Connection between

corrugated bulkheads and

between tank side walls

Position: PF/3G

Root: FCAW with OK Tubrod 14.27,

welded manually onto ceramic

backing stripFilling: FCAW with OK Tubrod 14.27,

welded manually.

72 Connection between tank

floor and carbon steel hull

Position: PA/1GRoot & 1st pass: FCAW with OK

Tubrod 14.22, welded manually onto

ceramic backing strip.

Filling: SAW with

OK Autrod 16.53/OK Flux 10.93

5Connection between angled

side wall and tank floor

Position: PC/2G

Multi-layer T-joint; full penetration.

FCAW with OK Tubrod 14.27,manually.

Sealing: SMAW with OK67.50

1

2

3

3

6

5

74

89

9

9


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Connection between

corrugated bulkheads and tank

cover

Position: PC/2GRoot: FCAW with OK Tubrod 14.27,

manually welded onto cylindricceramic backing.Filling: FCAW with OK Tubrod 14.27,welded manually.

duplex stainless steel

8

9Connection between tank

cover and between tank

covers and side walls

Position: PA/1GRoot & 1st pass: FCAW with OKTubrod 14.37, manually welded ontoceramic backing strip.Filling: FCAW with OK Tubrod 14.37

3

4

Assembly weld 8, connecting asmall, extending part of the cor-rugated bulkhead to the deck ofthe subsequent tank section, is

done in a semi-overhead positionwith exactly the same weldingprocedure. OK Tubrod 14.27 isone of the best cored wires avail-able for overhead work, becausethe stiff, fast freezing slag pre-vents sagging of the weld metal.

The last step in the assemblyprocess involves the connectionof the tank cover (weld type 9).This is done in the downhand po-sition with OK Tubrod 14.37

(root passes on rectangular ce-ramic backing strips.

Subassembly

Going back to Figure 4, it can beseen that this prefabricated blocksection consists of two major parts;the tank cover and a cross of twocorrugated bulkheads placed per-pendicular to the tank cover.

Starting with the tank top, it isclear that it is composed of agreat number of plates. The smallyellow lines represent weldsmade indoor on the panel lines(described later) to form thepanels out of which the deck iscomposed.The thick yellow lines

are the pre-assembly welds con-necting the panels to form thetank cover.They are made ac-cording to exactly the same weld-

ing procedure as described forthe tank floor in Figure 2 (weldtype 1). FCAW is used for theroot and first pass (OK Tubrod14.37 on rectangular ceramicbacking strip) and SAW (OK Au-trod16.86/ OK Flux 10.93) is usedfor filling and capping.

The sketch of Figure 7 de-scribes the basic component ofthe corrugated bulkheads.Assuch, they are supplied by the

steel fabricator, bent to the rightgeometry with welds connectingthe three areas of increasing platethickness. To form a completelongitudinal bulkhead nine weldsare required. Figure 8 shows thefabrication of these welds.Againthe combination of OK Tubrod14.37 on ceramic backing for theroot pass and OK Autrod 16.86/OK Flux 10.93 is applied for thefilling layers.

Two pre-assembly welds re-main to form the block section.The transverse corrugated bulk-heads are connected to the longi-tudinal ones by means of K-jointswelded mechanised in vertical-up

Figure 6:Attachment of a vertical corrugated tank wall to the tank floor; manually

with OK Tubrod 14.27 (PC position).

Plate thickness

24 mm 15 mm18 mm

19Svetsaren No.1 1999

Figure 7: Corrugated wall segment as purchased from the steel works.


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position with OK Tubrod 14.27using cylindrical ceramic backingto allow fast root pass deposition.The cross of bulkheads created inthis way is attached to the tankcover in PB position with OK Tu-brod 14.27 using the same weld-ing procedure as applied in the

dock assembly for weld type 7.Panel fabrication

Panel fabrication is carried out in-doors on a panel fabrication linewith two ESAB A6-LAE1250-TAC1000 submerged arc weldingmachines. Panels for the tankfloor, the tank cover and for theside walls of the tanks are all pre-fabricated according to the samewelding procedure.The number ofplates comprising a panel varies.

At the moment of our visit,there was no duplex fabricationin progress, so we describe the

welding procedure by means ofthe sketch in figure 9a. Duplexplates are bevelled to a Y-jointwith a land of 4mm and posi-tioned on the panel line with aminimal root gap.To avoid con-tamination of the duplex materi-al, AISI 316L plates are placed

between the duplex plates andthe carbon steel rollers of thepanel line.

SAW with OK Autrod 16.86and OK Flux 10.93 is applied forthe complete joint.The first layeris carried out with a tandem sys-tem; the two filling layers withsingle-wire SAW. After completingthe above, the panels are turnedand sealed with single wire SAW.

At this moment, Factorias Vul-cano are experimenting with a

new ESAB solution aiming atsingle-sided welding of the pan-els, which would provide a sub-


The ESAB OK Tubrod series of cored wires for standardduplex stainless steel consist of an all-position type, OKTubrod 14.27 and one for downhand use, OK Tubrod 14.37.They provide fabricators with optimal welding characteris-

tics and productivity for manual or mechanised welding.OK Tubrod 14.27 is a very versatile consumable, suited

for truly all welding positions, including pipe welding incombination with the TIG process for rooting. Very fastvertical-down welding of fillet welds is possible for partsthat allow to be attached without secure root penetration.Many fabricators standardise on this type only,when themajority of the work involves positional welding.

Both types have very clear advantages compared withMMA and GMAW, reviewed below.

Advantages over MMA

higher productivity in general due to higher duty cycle productivity for positional welding almost 3 times

higher through increased deposition rates very economic deposition of root passes, with less

welder skill needed no stub-end waste and therefore higher efficiency

Advantages over GMAW

up to 150% higher productivity in positional welding excellent performance with conventional power sour-

ces; no expensive pulsed arc equipment needed. use of normal 80%Ar/20%CO2 shielding gas; use of

expensive high Ar mixtures is avoided. Fabricatorshave an option to standardise on one gas when weld-ing both unalloyed and stainless steels.

less oxydation of weld surface due to protective action

of slag no grinding or sealing needed for the back side of root

passes easy parameter setting

ESAB OK Tubrod rutile cored wires for duplex stainless steel

Product dataClassifications

AWS A5.22:

OK Tubrod 14.27 E2209T1-1/E2209T1-4OK Tubrod 14.37 E2209T0-1/E2209T0-4

Approvals

OK Tubrod 14.27 ABS, Controlas, DNV, GL, LR,RINA, TV

OK Tubrod 14.37 DNV, GL, LR,TV

All weld metal composition (weight %)

OK Tubrod 14.27 OK Tubrod 14.37

C: 0.03 C: 0.03Si: 0.50-0.90 Si: 0.60-1.00Mn: 0.50-1.00 Mn: 0.70-1.20

Cr: 21.0-23.0 Cr: 21.0-23.0Ni: 8.0-10.0 Ni: 8.0-11.0Mo: 2.75-3.25 Mo: 2.75-3.25N: 0.11-0.17 N: 0.10-0.16P: 0.025 P: 0.035S: 0.025 S: 0.025

FN: 30-50 FN: 30-50

Mechanical properties in Ar/CO2OK Tubrod 14.27 14.37

Rp0.2% (MPa) 500 480Rm (MPa) 690 690A5d (%) 25 25

ISO-V 20C (J)

60

40Shielding gas: Ar/CO2 or CO2

Polarity: DC+

stantial time saving. Successfultests have been carried out with abacking rail filled with fine grainOK Flux 10.93 enabling to depos-it a good quality root pass that re-quires no sealing (Figure 9b). Ap-plication of this system, however,requires an investment in stain-

less steel rollers, because it doesnot allow protection of the du-plex material in the way utilisedpresently. The feasibility studyhas not yet been completed.

Steel grade and mecha-

nical properties

All duplex stainless steel used forthe construction of the Primo ispurchased from Avesta under thebrand name Avesta 2205. It is astandard, molybdenum alloyedgrade.

Mechanical properties of thewelds are overmatching with all


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Figure 8: Welding of a corrugated

bulkhead. Root (below) made with

FCAW; filling and capping with SAW.

Figure 9a: Double sided SAW panel

fabrication.Figure 9b: Single-sided SAW panel

fabrication. Root pass on gutter filled

with fine grain OK FLUX 10.93

ESAB consumables used for this

project.The Ferrite number ofthe weld is required to be bet-ween 2570 which is a normal re-quirement for duplex stainlesssteel welding, and sufficientlywide for construction practice.The Ferrite number is checked bymeans of a representative se-quence of weld samples in vari-ous stages of the construction, us-ing the same welding procedureand consumables as for the actual

welds. From the same samples,confirmation of mechanical prop-erties are obtained.

Preheating is not applied, al-though a minimal temperature of16C is prescribed; sufficient toavoid condensation under themild climatic conditions of the re-gion. The interpass temperature islimited to a maximum of 150C.

Appendix I shows a full WPSfor OK Tubrod 14.27 prescribing

the manual or mechanised assem-bly welding in PF position, as de-scribed in Figure 2 (weld type 6).It contains useful information forreaders that have become inter-ested in this product, as well as afree lesson in welding terminolo-gy in the rich and beautiful Span-ish language.

To conclude

When having the privilege of vis-iting this modern, yet cosy ship-yard in Galicia, I fell at homefrom the start, enjoying the warmand open atmosphere I encoun-tered. It was very rewarding tosee that Esabs commitment to be

a total supplier works out so wellat Factoras Vulcano, and that ourproducts are being applied to the

full satisfaction of the yard.To avoid leaving behind the

impression that it is fun to be aneditor for Svetsaren, I will refrain

from describing the short boattrip across a beautiful bay, afterthe interview, to the small family

restaurant where I received valu-able lessons in seafood dining.Disfrutaba de toda forma y unda regresar.

Figure 10: Welding Procedure Specifications.

Duplex Tankers

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