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Eng. Rev. 30-2 (2010) 101-109 101 _______________________________________________________________________________________________________________________

UDK 621.79152:621.643.41:658.562

AUTOMATIZIRANO ZAVARIVANJE CIJEVIAUTOMATIC PIPE WELDING

Vedran MILO Dubravka BILI Duko PAVLETI

Saetak: Automatizacija zavarivanja predstavlja nunost posebice u offshore industriji i naftnoj industriji gdje je potrebno u inkovito izvo enje zavarivanja uz udovoljavanje visokim zahtjevima za kvalitetom zavarenih spojeva. Uradu je prikazan primjer automatiziranog zavarivanja cijevi vanjskog promjera 48'' (1,21 m) , te stjenke debljine 30,9 mm izra ene od elika poviene vrsto e, oznake X65.

Kljune rijei: cijevi

automatizirano zavarivanje off shore industrija ispitivanje kvalitete zavarenih spojeva

Abstract: Welding automation is a necessity, especially in the offshore and oil industry where the welding should beeffective and high quality of the welded joint should be achieved. The paper describes an example of automated pipeswelding with an outside diameter and 48'' (1.21 m) , wall thickness of 30.9 mm , made of higher strength steel X65.

Keywords: piped automated welding offshore industry welded joint quality inspection

1. UVOD

U suvremenojoff shore industriji i naftnoj industrijispajanje cijevi velikih promjera zavarivanjem predstavljaizazovan zadatak, posebice s aspekta koliine, kvalitete irokova izvedbe. Stoga se neprestano razvijaju nove, teusavravaju postojee metode automatiziranogzavarivanja kao i provjere kvalitete zavarenih spojeva.Takoer, nove pristupe i postupke izvedbe zavarivanjazahtijevaju i materijali od kojih su graene cijevi. Isprvasu to uglavnom bili ugljini elici, no postupno se svevie koriste slitine otporne na koroziju, nehr ajui elici,

duplexmaterijali itd. Suvremeno stanje u tome podru judonosi i nove zahtjeve: usavravanje strunog osoblja,

razvoj i unapreivanje procesa zavarivanja, kao i opremeza zavarivanje. Inenjeri neprestano rade na rjeavanju problema spajanja materijala zavarivanjem kao primjer takva rada mogue je navesti provoenje opsenihistraivanja poboljavanja orbitalnog zavara kako bi se postigao zavar otporan na dinamika optereenja koja se pojavljuju prilikom polaganja cijevi u more.U radu e biti prikazan primjer automatiziranogzavarivanja cijevi vanjskog promjera 48'' (1,21 m) , testijenke debljine 30,9 mm izraene od elika povienevrstoe, oznake X65, slika 1.

1. INTRODUCTION

In the modern offshore and oil industry, weld joining oflargediameter pipes is a challenging task, especially interms of quantity, quality and completion deadlines.Therefore, continual development of new improvementsof existing methods of automated welding and qualitycontrol of welded joints are in place.Furthermore, new materials in pipes production requirenew approaches and welding procedures. In the beginning, pipes were mostly made from carbon steels, but gradually corrosion resistant alloys, stainless steels,

duplex materials, etc. were used in pipes production.Changes in the conditions and requirements in pipeswelding requires further training of professional staff anddevelopment of welding processes and equipment.Engineers are constantly dealing with challenges thatnew materials bring into welding engineering. For example, extensive studies have been conducted toimprove the orbital weld in the sense that it will be moreresistant to dynamic loads during the laying of pipes ontoseabed.The paper describes an example of automated pipeswelding with outside diameter and 48'' (1.21 m) , wallthickness of 30.9 mm, made of higher strength steel X65,

Figure 1.

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102 V. Milo, D. Bili , D. Pavleti : Automatizirano zavarivanje ______________________________________________________________________________________________________________________

2. PRIPREMA CIJEVI ZA ZAVARIVANJE

Priprema cijevi za zavarivanje vri se rezanjem imehanikom obradom. Rezanje se vri pomouautomatiziranog nosaa plamenika koji putuje po prstenu.Prsten je ujedno i ozubljena letva, dok je na pominomdijelu nosaa plamenika zupanik preko kojega seostvaruje orbitalno gibanje. Najprije se na cijev postavlja prsten, odnosno zupasta letva, kako je prikazano na slici2, koji se potom zatee dok se ne priljubi uz vanjskustijenku cijevi.

2. PIPES EDGES PREPARATION

Pipes edges preparation is done by oxyfuel cutting andmachining. Oxyfuel cutting is supported by anautomated torch carrier mounted on a circular rigid rail.The carrier is equipped with a gear wheel allowing for the motion along the rail. Firstly, the circular rail ismounted on the pipe, Figure 2, which is then tightened upto the pipe wall.

Slika 1. Primjer cijevi Figure 1. Pipe example Slika 2. Montirani prsten zup asta letva Figure 2. Circular rigid rail mounted on a pipe

Potom se postavlja nosa plamenika na prsten na nainda se zupanici na nosau plamenika namjeste nazupastu letvu te se dre na pripadajuoj poziciji uz pomo komprimiranog zraka. Na slici 3 prikazan je postavljeni nosa s plamenikom.Kada je pomini dio privren, potrebno je odrediti brzinu gibanja, odnosno brzinu rezanja, koja priblinoiznosi 20 cm/min. Rezanje se vri plinskim plamenom.Omjer kisika naprama acetilenu je 4 naprema 1. Za taj primjer potrebno je priblino 15-20 minuta da se rezanjeizvede u potpunosti. Odrezana cijev prenosi se u sljedeufazu u kojoje se izvriti priprema lijeba.Pripremanje se vri na posebnim tokarilicama glodalicama (slika 4), bez sustava za hlaenje. Ovisno o promjeru cijevi razlikuje se i tokarilicaglodalica. Ureajse sastoji od hidraulikih ventila pomou kojih se cijev sunutarnje strane pozicionira (slika 5), te obradnogsustava s tri doetiri tokarska noa od kojih svakiobrauje jednu povrinu lijeba. Pozicioniranje cijevi vrise na nain da se cijev navue na tokarilicuglodalicu tese pomou hidraulike sile priljubljuje uz ureaj pocijelom svojem opsegu. Rotaciju noeva vri hidraulikimotor visokog tlaka. Za automatsko zavarivanje koristi seUlijeb s kutom od 3, a za runo Vlijeb s kutom od

Then the torch carrier is mounted on to the rail, set into position and locked into place by compressed air.The torch and torch carrier mounted on the rail are shownin Figure 3.When the torch carrier is in place and fixed, it isnecessary to set the cutting speed, which is approximately20 cm/min. Cutting is done with oxyfuel gas. The ratioof oxygen compared to acetylene is 4:1. In the exampleshown, the duration of cutting is approximately 1520minutes. Cut pipe is transported to the next phase inwhich groove preparation will be made.The grove preparation is done by a special lathemillingmachine, Figure 4. Different lathemilling machines fitdifferent pipe diameters. The machine incorporateshydraulic valves that are used for pipe centering, Figure5, and machining systems with three to four lathe knives,each of which machine a different groove surface. Pipes positioning is carried out in such a way that the pipe ismounted on the lathemilling machine and tightlyclamped onto it by hydraulic force. The high pressurehydraulic motor rotates machining knives. A narrow gapUgroove, set at an angle of 3, is used for automatic pipes welding, while the Vgroove, with a grove openingangle of 30, is used for hand welding. When the

Prstenzupasta letva/Circular rigid rail

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Eng. Rev. 30-2 (2010) 101-109 103 _______________________________________________________________________________________________________________________

30. Nakon izrade lijeba na jednoj strani cijevi, cijev serotira za 180, te se postupak ponavlja. U promatranom primjeru izvodio se Uspoj s dimenzijama kako je prikazano na slici 6. Nakon obrade lijeba dobivene sedimenzije kontroliraju pomou pominog mjerila. Tedimenzije moraju biti unutar zadanih tolerancija, kako je prikazano na nacrtu.

required grooves are prepared on the one side of the pipe,the pipe is rotated on the other side and the process isrepeated. In the observed example, the Ugrove is prepared in accordance with dimensions shown in Figure6. When the grooves preparation is finished, the groovesdimension control is carried out.

Slika 3. Nosa s gorionikom za rezanje Figure 3. Oxy fuel cutting torch carrier

Slika 4. Tokarilicaglodalica Figure 5. Lathemilling machine

Slika 5. Pozicioniranje cijevi na tokariliciglodalici pomo u ventila

Figure 5. Pipe positioning on the lathemilling machine

Slika 6. Prikaz dimenzija Ulijeba Figure 6. Ugroove dimensions

3. POZICIONIRANJE I ZAVARIVANJE

Nakon pripreme lijeba par cijevi postavlja se u poloajza zavarivanje i orbitalno zavaruje. Za pozicioniranje

cijevi koristi se unutranja pneumatska stezaljka koja seekspanzijom ventila priljubljuje uz cijevi, poravnava ih i

3. POSITIONING AND WELDING

Prepared pipes are placed into position for welding andare orbitally welded. For pipes positioning, the inner

pneumatic clap is used. The pneumatic clamp places pipes in a line and holds it during welding. Another

Cijev/Pipe Hidrauliki cilindar /Hydraulic cylinder

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fiksno pozicionira. Druga vana funkcija unutarnjestezaljke su bakrene podloke koje slue kao podloga zaednostrano zavarivanje. Stezaljka se moe unutar cijevi

pomicati naprijednatrag kako bi mogla zauzeti potrebnu poziciju. Slike 7 i 8 prikazuju unutarnju stezaljku za pozicioniranje cijevi.

important function of the pneumatic clamp is as a supportof the welds root, by a copper backing, in onesidewelding. The pneumatic clamp can be repositionedwithin a pipe in order to be placed in the right positionfor welding. The pneumatic clamp used in automatic pipewelding is shown in Figure 7 and Figure 8.

Slika 7. Unutarnja stezaljka Figure 7. Pneumatic clamp

Slika 8. Pozicioniranje cijevi pomo u unutarnje stezaljke

Figure 8. Pipes positioning with the help of the pneumatic clamp

Primjer lijeba za zavarivanje prije samog zavarivanja prikazan je na slikama 9 i 10.

An example of the weld groove before welding is shownin Figure 9 and Figure 10.

Slika 9 Prikaz Ulijeba Figure 9. Ugroove

Slika 10. Pozicionirane cijevne sekcije Figure 10. Pipes positioning for welding

Na tako pripremljenu cijev potrebno je stavitiodgovarajui prsten odnosno zupastu letvu po kojojese gibati orbitalna glava za zavarivanje. Prsten senamjeta i pozicionira jednako kao i kod rezanja cijevi. Nakon pozicioniranja i stezanja prstena uz cijev potrebnoe, prije montiranja zavarivake glave, izvriti

predgrijavanje cijevi na priblino 100 C, kako bi sezavarivanje kvalitetnije izvelo. Predgrijavanje se vri

plamenom plina propana. Montiran prsten i

On a pipe prepared in such way, a rail for orbital weldingand automated head are mounted. The bent rail ismounted and positioned in the same manner as for oxy fuel cutting. After rail positioning and before a weldinghead is mounted, the pipes are preheated to a temperatureof approximately 100 C in order to facilitate betterwelding results. Preheating is carried out by propane gasflame. Mounted guiding rail and preheating are shown in

Figure 11.

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Eng. Rev. 30-2 (2010) 101-109 105 _______________________________________________________________________________________________________________________

predgrijavanje prikazani su na slici 11.Kada se izvri predgrijavanje, potrebno je montiratizavarivaku glavu. Zavarivaka glava montira se tako dase zupanici postave na zupastu letvu. Glavu zazavarivanje na prstenu dri komprimirani zrak. Unosom parametara zavarivanja u elektroniku ureaja, cijevi suspremne za zavarivanje.U prikazanom primjeru koriste se dva sustava zazavarivanje koje je patentirala tvrtka Saipem S.p.A. To sumehanizirani sustav PASSO* te automatizirani sustavSWS*. U osnovi su obaju postupaka MIG/MAGzavarivanja punom icom u zatitnom plinu, razlika jesamo u stupnju mehanizacije, odnosno automatizacije.Zavarivaki sustav PASSO sastoji se od izvora struje zazavarivanje, elektronskog sklopa, mjeaa plina, spojnihkablova i vozila za zavarivanje. Izveden je za zavarivanjecjevovoda u horizontalnoj ili vertikalnoj poziciji. Naponzavarivanja daje izvor struje, a parametri brzineorbitalnog zavarivanja i brzine ice unose se prekoelektronskog sklopa i mogue ih je mijenjati automatski, putem promjene programa na zavarivakoj glavi. irinu ivrijeme osciliranja regulira sam zavariva kao i promjenu parametara za vrijeme promjene poloaja zavarivanja.Slika 12. prikazuje zavarivaku glavu PASSO.

When preheating is completed, the welding head ismounted onto the guiding rail. The welding head ismounted so that the gear wheels on the head set are set ona jagged rail. The welding head, mounted on the rail, iskept in position by compressed air. By setting thewelding parameters onto the command panel of thewelding machine, the welding can start.In the example shown, two welding systems are used, both patented by the Saipem SpA company. These are themechanized system PASSO*, and the fully automatedsystem SWS*. Basically, both are based on MIG/MAGwelding processes with solid wire and shielded gas. Thedifference between these two systems is only in thedegree of mechanization or automation.The PASSO welding system consists of a welding powersource, electronic circuit, shielding gas mixing device,connecting cables, and a carriage for welding. ThePASSO welding system is designed for pipes welding ina horizontal or vertical position. Welding voltage is provided by the power source, while the speed for orbitalwelding and wire speed are set via an electronic control board and can be automatically changed by changing preset programs on the welding heads. The parameters oftorch oscillation, e.g. width and time of oscillation, aswell as changes of parameters due the welding position,set the welding operator. Figure 12 shows a PASSOwelding head.

Slika 11. Predgrijavanje cijevi na 100 C Figure 11. Pipes preheating at the temperature of 100 C

Slika 12. PASSO zavariva ka glava Figure 12. PASSO welding head

Zavarivaki sustav SWS je potpuno automatskizavarivaki sustav, baziran na MIGMAG postupkuzavarivanja. Sastoji se od izvora struje za zavarivanje,sofisticiranoga elektronikog sklopa koji upravlja svim parametrima zavarivanja, mjeaa plina, spojnih kablovai vozila za zavarivanje s jednim ili dva gorionika. Koristise za orbitalno zavarivanje cjevovoda na kopnu i na morui to izraenih od svih vrsta ugljinih elika i ostalih

zavarljivih materijala. Parametri zavarivanja unose se usustav preko raunala, uz pomo posebnoga programa

The SWS welding system is a semiautomatic weldingsystem based on the MIGMAG welding process. Itconsists of a welding power source, a sophisticatedelectronic system that controls all welding parameters,shielding gas mixing device, connecting cables and acarriage for welding with one or two torches. The SWSwelding system is used for orbital welding of carbon steel pipelines as well as for pipelines made from other

weldable materials, both on land and at sea. Welding parameters are entered into the system via computer with

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razvijenog za tu namjenu. Vaan dio automatiziranogsustava je automatsko centriranje gorionika u lijebu.Orbitalno zavarivanje podijeljeno je u krune segmentekako bi se svakom dijelu kruga mogli dodijeliti optimalni parametri. Svi se parametri pohranjuju u memorijiraunala za kasniju jednostavnu uporabu. Kako je cijeli postupak automatski, prilikom svakog prolaska zavar jekonstantno iste kvalitete. Ureaj je programiran na nainda takoer prati i razmak izmeu dvaju vozila zazavarivanje kako ne bi dolo do njihova sudara. Ulogaoperatora je u nadgledanju i pozicioniranju ureaja. Na slikama 13 i 14 prikazani su karakteristiniupravljaki zasloni programa za SWSzavarivanje.

specialized software developed for this purpose. Animportant part of the automated welding system is torchselfcentring within a groove. Orbital welding is dividedinto circular segments that enables that optimal parameters are set for each part of the circle individually.All welding parameters are electronically stored. Sincethe entire welding process is computer controlled, theweld quality is continuously at the same high level. Thewelding system is programmed in a way that alsomonitors spacing between the two carriages for weldingand to avoid their possible collision. The role ofoperators is to monitor and position the carriage forwelding. In Figure 13 and Figure 14 are shown typicalscreens of the SWS welding system.

Slika 13. SWSprogram Figure 13. SWS welding program screen

Slika 14. SWSprogram Figure 14. SWS welding program screen

Da bi sustav funkcionirao, inenjer zavarivanja mora u program unijeti niz parametara, od opih (dimenzijecijevi: promjer, debljina stjenke; naziv projekta; vrsta plina, vrsta dodatnog materijala za zavarivanje, debljinaice itd.) do specifinih kao to su udaljenost prstena odlijeba, dimenzije lijeba, dubina lijeba, kut nagibalijeba itd. te parametara zavarivanja (napon, struja, brzina dodavanja ice, irina i vrijeme osciliranja, brzinazavarivanja itd.). Na ovome primjeru orbitalnozavarivanje izvodila su dva vozila za zavarivanje svaki sasvoje strane cijevi. Na svakom vozilu zavarivala su dvagorionika tako da su se izvodila dva prolaza odjednom.Slika 15 prikazuje orbitalno zavarivanje cijevi.Kako je debljina stijenke 30,9 mm, potreban je vei broj prolaza. Za svaki se prolaz posebno definiraju parametrizavarivanja. U ovom primjeru potrebno je napraviti 14 prolaza da bi se ispunio cijeli lijeb. U tablici 1 prikazanisu parametri za svaki pojedini prolaz, koriteni prilikomzavarivanja cijevi.

To make the welding system functional, the weldingengineer must enter a number of parameters into the program, ranging from general (pipe dimensions:diameter, wall thickness, project name, type of shieldinggas, filler materials specification, filler wire diameter,etc.) and specific parameters, such as distance of theguiding rail from the groove, groove dimensions, groovedepth, groove angle, etc., and the welding parameters(voltage, current, wire speed, latitude and period ofoscillation, the speed of welding, etc.). In the describedexample, orbital welding was performed by two carriagesfor welding, each on opposite sides of pipes. On eachcarriage for welding there were two torches so that thetwo passes are performed at once. Orbital pipes weldingare shown in Figure 15.Since pipe wall thickness is equal 30.9 mm, several passes are required. Welding parameters are defined foreach pass separately. In the example, it is necessary tomake 14 passes to fill the entire groove. Welding parameters for each weld pass are shown in Table 1.

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4. ISPITIVANJE KVALITETE ZAVARENIHSPOJEVA

Nakon zavarivanja pristupa se kontroli zavarenog spojametodama bez razaranja i to vizualnom metodom,rendgenskom i ultrazvunom metodom. Vizualna metodai rendgenska metoda klasine su metode koje se primjenjuju i kod uobiajenog nadzora kvalitetezavarivanja, dok se ultrazvuna metoda izvodi sautomatskim ureajem namijenjenim upravo primjenikod zavarenih cijevnih spojeva, slika 16. Ako ispitivanje pokae da zavar ne zadovoljava zadane kriterije kvalitete potrebno ga je lijebiti te ponovo runo zavariti. Nakonizvrenog popravka zavareni se spoj ponovno ispituje.Sam princip rada automatiziranog ureaja za ispitivanjeultrazvukom zasniva se na istim principima kao ikonvencionalni ureaji za ultrazvuno ispitivanje. Ovisno

o koritenoj ultrazvunoj sondi taj ure

aj moe slati i primati ultrazvune valove, pod odreenim kutom,

fokusirano, itd. Nakon primljenih signala dekoder obrauje podatke i alje ih na raunalo. Na raunalu sezavareni spoj prikazuje u obliku odreenih valova kao toe prikazano na slici 17. Prikaz je podijeljen u zone po

dubini i po prijeenom putu od poetne toke. Svakazona u dubinu je od 1 do 3 mm.

4. WELDED JOINT QUALITY INSPECTION

Upon successful pipes welding follows a quality controlof welds. Quality control is carried out by non destructive methods, e.g. visual method, Xray andultrasonic methods. The visual method and the Xraymethod are classical methods that are applied, while theautomatic ultrasonic method is designed specifically forapplication on welded pipes joints, Figure 16. If theinspection results show that the weld does not meet therequired quality criteria, the weld has to be removed andrepaired by hand welding. Upon repair, the welded jointis again submitted to quality control.The principle of automated ultrasound inspection is basedon the same principles as for conventional ultrasoundinspection. Depending on the applied ultrasonic probes,the ultrasound waves can be send and receive at a certainangle, focused, etc. A decoder processes the receivedsignals and sends them to a computer. On the computerscreen, the weld is shown in wave form, as seen in Figure17. The inspection result representation is divided intozones, depending on depth and travelling path from thestarting point. Each zone is 1 to 3 mm in depth.

Slika 15. Orbitalno zavarivanje cijevi Figure 15. Orbital pipes welding

Tablica 1. Prikaz koritenih parametraTable 1. Welding parameters

ProlazPass

Brzinarotacije glaveHead rotationspeedcm/m

Brzina iceWire speedcmm/min

JakoststrujeCurrentA

NaponVoltageV

Oscilacija plamenikaTorchoscilationmm

1 80-100 13,50 240-250 27 0,002 80-100 15,00 220-230 29 1,503 55-67 12,50 230-242 29 1,504 55-68 12,50 230-243 29 2,005 55-69 12,50 230-244 29 2,506 55-70 12,50 230-245 29 2,807 55-71 12,50 230-246 29 3,008 55-72 12,50 230-247 29 3,209 55-73 12,50 230-248 29 3,5010 55-74 12,50 230-249 29 3,8011 55-65 11,00 225-235 27 4,0012 55-66 11,00 225-236 27 4,2013 55-67 11,00 225-237 27 4,5014 25-35 8,00 180-200 25 8,00

Slika 16. Ultrazvu ni mjerni pretvara Figure 16. Ultrasonic probe

Slika 17. Prikaz o itanja automatskog ultrazvuka Figure 17. Representation of reading of automatic

ultrasonic inspection

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Nakon izvedene kontrole zavarenih spojeva uzorci sealju na mehanika ispitivanja. Ako su dobiveni rezultatiu skladu s propisanim standardima i normama tezahtjevima naruitelja, izdaje se dokument koji definiratehnologiju zavarivanja na ispitanim uzorcima.Odobrenom tehnologijom pristupa se procesu proizvodnje cjevovoda na terenu.

5. ZAKLJUAK

Zavarivanje cijevnih spojeva, posebice promjera veih od300 mm, u suvremenoj se praksi sveee izvodi pomou mehaniziranih, automatiziranih pa i robotiziranihsustava za zavarivanje. Takvi postupci zahtijevaju visoku

razinu pripreme lijeba za zavarivanje to obinoukljuuje mehaniku obradu stranica lijeba kao i precizno pozicioniranje elemenata koji se spajaju. U radue prikazan jedan postupak pripreme za zavarivanje,

automatiziranog zavarivanja te principa kontrole kvaliteteizvedenog zavara za cijev promjera 48'' (1,21 m) , naeliku povienevrstoe.

LITERATURAREFERENCES

[1] Meden, G., Paveli, A., Pavleti, D., Osnove zavarivanja , Tehniki fakultet, Rijeka, 2000.

2 orda D.,Orbitalno zavarivanje , FSB, preuzeto sinterneta, 11.12.2008.

ZAHVALA

Rad je nastao na temelju diplomskog rada studentaVedrana Miloa pod nazivom Automatiziranoavarivanje i navarivanje cijevi . Posebnu zahvalnost

autori duguju tvrtkiSaipem Mediterranean Service Rijeka , odnosno njihovu laboratoriju za zavarivanje,ijisu podaci koriteni u nastanku ovoga rada.

Primljeno / Received: 24.03.2010.

Strukovni prilog

Adresa autora / Authors addressVedran MiloBrodogradilite VIKTOR LENAC d.d.Branimira Markovia 151000 [email protected]

When quality control confirms that inspected weldedoints are of acceptable quality, the specimens taken from

the joint are sent for mechanical testing. If the resultsobtained from the mechanical testing are in accordancewith applicable standards and norms, and clientrequirements, a document that defines the technology ofwelding on the tested samples is issued. Finally, weldingtechnology can be approved and the piping production process in the field can take place.

5. CONCLUSION

The welding of pipe joints, especially of diameters largerthan 300 mm, in modern practice is increasingly performed using mechanized, automated and evenrobotic welding systems. Such procedures require a high

level of welding groove preparation quality, whichusually includes groove machining, and the precise positioning of elements that are going to be joined. The paper presents the procedure of welding preparation,automated welding and principles of welded join qualitycontrol for welded joint of pipes with a diameter of 48''(1.21 m) , in increased strength steel.

3 Dokumentacija tvrtke Saipem, 2009.

ACKNOWLEDGMENTS

The paper is based on student Vedran Milo diplomathesis named Automated pipes welding and surfacewelding. The authors owe special gratitude to theSaipem

editerranean Service Rijeka company, and theirWelding laboratory, which kindly proved data used in thecreation of this paper.

Prihvaeno / Accepted: 23.04.2010.

Technical note

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Eng. Rev. 30-2 (2010) 101-109 109 _______________________________________________________________________________________________________________________

Dubravka Bili Saipem Mediterranean Services Llc.Welding Laboratory RijekaM. Baraa 5451 000 [email protected]

Izv. prof. dr. sc. Duko Pavleti, dipl. ing.Tehniki fakultet Sveuilita u RijeciVukovarska 5851000 [email protected]

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