Osjetljivost čelika X70 na hladne pukotine pri mokrom podvodnom zavarivanju

U ovom radu obrađena je problematika podvodnog mokrog zavarivanja čelika za cjevovode API 5L X70 s aspekta osjetljivosti na nastanak hladnih pukotina. U uvodnom dijelu obrazložena je motivacija istraživanja te je dan presjek dosadašnjih spoznaja i provedenih istraživanja na području mokrog podvodnog zavarivanja, dodatnih materijala, mehanizama nastanka hladnih pukotina, utjecaja katodne zaštite i razvoja čelika za cjevovode. Definirane su hipoteze te je osmišljen plan eksperimenta za dobivanje relevantnih informacija nakon čije statističke obrade će biti moguće donijeti određene zaključke te odbaciti ili prihvatiti hipoteze. Eksperimentalni rad proveden je u Laboratoriju za zavarivanje, Fakulteta strojarstva i brodogradnje. Iz osnovnog materijala API 5L X70 izrađene su epruvete za određivanje difundiranog vodika i Implant test. Primijenjena su tri postupka zavarivanja-REL, zavarivanje praškom punjenom žicom u plinskoj zaštiti i zavarivanje samozaštićujućom praškom punjenom žicom , svaki na tri razine unosa topline. Epruvete su prije zavarivanja držane u katodnoj zaštiti na tri razine potencijala. \Nakon zavarivanja izmjereni su difundirani vodik, određeno je kritično Implant naprezanje te su izmjerene tvrdoće HV10. Analiza rezultata je pokazala da postupak zavarivanja, ovisno o unosu topline, kao i potencijal katodne zaštite imaju utjecaja na difundirani vodik i na kritično Implant naprezanje. Također je pokazano da se unosom topline može utjecati na mikrostrukturu u ZUT-u što se direktno očitava na vrijednostima tvrdoća i smanjenju rizika od pojave hladnih pukotina. Mikrostrukturna analiza ukazala je da su kod većine uzoraka u grubozrnatom ZUT-u detektirane hladne pukotine te da postoji značajan utjecaj nehomogenosti na pojavu hladnih pukotina. Statističkom analizom potvrđeno je da su unos topline i potencijal katodne zaštite značajni faktori koji utječu na difundirani vodik i kritično Implant naprezanje. Metodom odzivnih površina dobiveni su matematički modeli koji su provjereni i uspoređeni sa postojećim podacima i modelima te je ustanovljena dobra korelacija. \Na osnovi provedenog ekperimentalnog rada i analize podataka dobivenih mjerenjem difundiranog vodika i kritičnog Implant naprezanja zaključeno je da je moguće podvodno mokro zavarivanje na čeliku X70 uz postizanje zavara određene kvalitete i bez pojave hladnih pukotina. Međutim, pri tome za svaki postupak zavarivanja postoji određeno područje parametara čija primjena daje optimalne rezultate. Uz to, pokazano je da potencijal katodne zaštite ima utjecaja na cjelovitost podvodnih cjevovoda s gledišta pojave hladnih pukotina

Numerical Modelling and Experimental Investigation of a Buried Arc Welding Process

This paper presents a numerical and experimental study of residual stresses induced by the buried arc welding process in a butt-welded plate sample. Within the framework of numerical investigations, a thermo-mechanical finite element analysis is performed by applying the element birth and death technique in the thermal analysis, while the mechanical analysis is performed simultaneously in one step to reduce simulation time. To validate the numerical model, a series of experiments using a fully automated welding process are conducted. The temperature and residual stress measurements are performed by using thermocouples and hole-drilling stress relaxation method. Furthermore, the heat input efficiency for the buried arc welding process is determined by using a parametric analysis

Determination of ballistic properties on ARMOX 500T steel welded joint

In this paper, the effect of different hardness filler materials and sequence of welding on the ballistic performance has been investigated. Also, besides the optimization of the ballistic properties, other mechanical testing was carried out in order to achieve wanted mechanical properties along the entire welded joint. The experimental work includes macrostructure analysis, ballistic testing, and hardness testing of steel welded joint. The base material used in the experiment were ARMOX® 500T plates. In this experiment 3 different filler materials were used. Based on the testing results, it was found out that best ballistic performance of the welded joint is achieved if capping layer is welded with a hardfacing filler material.  This distributes the impact energy to a greater area and transfers it to the lower hardness weld layer underneath which then absorbs the rest of the energy

Analysis of Underwater Repair Technology on the Jack-Up Platform Spud Can

Underwater welding has been used widely in construction and maintenance of off-shore facilities. With state-of-the-art equipment and fi ller materials it is possible to achieve high quality of welded joints, particularly if underwater dry welding is applied. On the other hand, wet underwater welding has several advantages from the aspects of fl exibility and cost effi ciency, but some serious problems could emerge due to weld quality and safety of divers. In this paper analysis of applicable technologies of underwater repair of a jack-up platform spud can is made, including description of possible problems that may occur. Also, a comment on specifi c details of proposed techniques has been given and a comparative analysis of considered techniques focused on the economic and technological aspects of repair has been made

Pojava hladnih pukotina pri zavarivanju visokočvrstog čelika S960 QL

The paper presents the study of weldability of micro-alloyed high-strength S960 QL steel with the application of experimental methods and mathematical models from the aspect of cold cracks occurrence. In the experimental part of the research RD (Research Department) test was applied to estimate the steels susceptibility to the occurrence of cold cracks. For the analysis of the impact of heat input on the mechanical properties of the welded joint the test steels were welded with one, two or more runs, out of which samples were made for the production of specimens in order to measure the hardness and impact strength in HAZ (heat affected zone). Based on the obtained results an estimate was provided regarding the weldability of S 960 QL steel as well as the proposal for further research.U ovom radu provedeno je istraživanje zavarljivosti mikrolegiranog čelika visoke čvrstoće S960 QL uz primjenu eksperimentalnih metoda i matematičkih modela s aspekta pojave hladnih pukotina. U eksperimentalnom dijelu istraživanja primjenjen je RD test za procjenu sklonosti čelika na pojavu hladnih pukotina. Za analizu utjecaja unosa topline na mehanička svojstva zavarenog spoja, zavarene su ispitne ploča s jednim, dva i više prolaza od kojih su načinjeni uzorci za izradu epruveta za mjerenje tvrdoća i udarne radnje loma u ZUT- u. Na osnovi rezultata dana je ocjena zavarljivosti čelika S 960 QL

METHODE DER NUMMERISCHEN SIMULATION VON SWEISSARBEITEN ALS EINE UNTERSTÜTZUNG IN DER INDUSTRIE

U ovom članku opisana je prikazana metodologija rješavanja numeričkih simulacija zavarivanja,kao i proveda validacijskih pokusa koji se koriste za provjeru rezultata simulacija te uklanjanje pogrešaka u odabranim ulaznim parametrima. Pokazani su primjeri eksperimenata koji ilustriraju podatke,kao na primjer temperaturni ciklusi,deformacije u izabranim točkama,procjene veličine zone taljenja i ZUT-a,tvrdoća itd. Rezultati dobiveni u realnim pokusima u različitim granama primjene,uporabljeni su za kalibraciju numeričke simulacije te su postignuti rezultati simulacija koje se dobro podudaraju sa stvarnim proizvodima. Uz takav pristup i definirane parametre,provjerena i potvrđena numerička simulacija u cijelosti je vjerodostojna te se postižu vrijedni podaci koji mogu unaprijediti proizvodnju,čak i za složene sklopove.This articles describes and outlines the methodology of solving numerical welding simulations and the implementation of validation experiments used to check the results of simulations and removal of errors in selected input parameters. Examples of experiments are shown to illustrate data as for example temperature cycles,deformations in selected spots,estimation of the size of the melting zone and HAZ,hardness etc. The obtained results in real experiments in different applications sectors have been applied for calibration of numerical simulation and the achieved simulation results match well with real products. With such an approach and defined parameters,the verified and confirmed numerical simulation is fully credible and enables to obtain valuable data that can improve manufacturing even of complex assemblies.In dieser Arbeit ist die Methode der numerischen Simulationen von Schweißarbeiten beschreiben zusammen mit den Validation-Prozess,der sich für die Resultatnachprüfung und für die Behebung von Fehlern in gewählten Parametern verwendet. Es sind Exemplare der Beispiele gezeigt die Daten wie z.B. den thermischen Zyklus,die Defoormationen in gewählten Punkten,die Großenschätzung der Schmelz- und Wärmeeinflusszone,den Härtewert usw.anzeigen. Für die Kalibration der numerischen Simulation waren die Daten von realen Prozessen übernommen worden. Die Simulation stimmt mit den realen Prozessen überein. Mit so einen Zugang und definierten Parametern,die durchprüfte und bestätigte numerische Simulation ist zuverlässig und die Daten können sich in einer Produktion als Verbesserung,sogar für sehr komplexe Teile,benutzen

Sensors and their classification in the fusion weldingtechnology

U radu su navedeni i opisani najčešće korišteni senzorski sustavi u suvremenoj zavarivačkoj industriji koja u današnje vrijeme podrazumijeva robotizirane sustave. Predstavljene su podjele senzora u ovisnosti o mehanizmima djelovanja te mjerenim parametrima, a prvenstveno se pozornost posvetila robotiziranim postupcima zavarivanja (MIG/MAG, elektrootporno i lasersko zavarivanje). Ukratko su objašnjeni mehanizmi djelovanja pojedinih senzorskih sustava skupa s njihovim mogućim ograničenjima, prednostima ili specifičnostima.In this paper the most commonly used sensing systems in modern welding industry, which nowadays includes robotic systems, are listed and analysed. According to mechanisms of action and measured parameters, several classifications of sensor systems are presented. MIG/MAG, resistance and laser beam welding processes are the most commonly robotized ones in the industry and therefore special attention is given to them. Several characteristics, limitations and advantages of sensor systems are presented and mechanisms of action are briefly described

ANALYSE DER SCHWEISSTECHNOLOGIE AN SCHIENENPROFIL 60R1 MIT FüLLDRAHTSCHWEISSEN

U ovome radu opisana je problematika zavarivanja tračnica samozaštitnom praškom punjene žicom ( HRN EN ISO 4063:114 ) kao i svojstva dobivenih zavara. Prema planu eksperimenta na osnovnom materijalu kvalitete R200 profila 60R1 varirane su različite opcije pripreme i temperatura predgrijavanja kako bi se utvrdila optimalna tehnologija. Uzorci su ispitani nerazornim metodama te su prvenstveno utvrđene nepravilnosti naljepljivanja koje upućuju na nedostatnu tehniku rada zavarivača. Analizom makroizbrusaka ustanovljene su razlike u strukturi i širini ZUT-a,ovisno o primjenjenoj tehnici rada i temperaturi predgrijavanja. Također,mjerenjem tvrdoće utvrđeno je da za manje temperature predgrijavanja dolazi do povećanja tvrdoće u zoni ZUT-a što može inicirati pojavu krhkog loma u zoni zavarenog spoja.In this paper some aspects of application of self shielded flux cored arc process ( HRN EN ISO 4063:114 ) are described as well as properties of welded joints. According to experimental work on rails of grade R200 and 60R1 profile different options of joinrt preparation and preheat temperatures are applied in order to define optimal technology. Samples are investigated with NDT methods and generally lack of fusion is determined what points out on poor welding technique. MAcroetch analisys showed that there is significant difference in heat affected zone width and structure depending on applied welding technique and heat temperature. Furthermore,it is shown that lower preheat temperatures will generate higher hardness in heat affected zine and therefore increase susceptibility to brittle cracking in weld joint.In dieser Arbeit wird die Problematik der Schweißtechnologie für Schienenschweissen mit Fülldraht ( HRN EN ISO 4063:114 ),zussamen mit den Schweißnaheigenschaften,bearbeitet. Nach dem Experimentplan,am Grundmaterial der R200 Qualität Profil 60R1,wurden verschiedene Vorbereitungsoptionen und Vorwärmetemperaturen variiert damit man eine optimale Schweißtechnologie erschaffen kann. Die Proben wurden mit zerstörungfreien Methoden geprüft und am meisten hat man die Fehler des Aufklebens von Material entdeckt,wozu der Grund dafür die Schweißtechnologie war. Mit der Makroprobenanalyse wurden Differenzen in der Struktur und der Wärmeeinflusszone festgestellt,die abhängend von der Technik und der Vorwärmetemperaturen zu einer Vergrößerung der Härtewerte in der Wärmeeinflusszone kam,was nachträglich zu einen Kalltriß führen kann

Numerical Modelling and Experimental Investigation of a Buried Arc Welding Process

This paper presents a numerical and experimental study of residual stresses induced by the buried arc welding process in a butt-welded plate sample. Within the framework of numerical investigations, a thermo-mechanical finite element analysis is performed by applying the element birth and death technique in the thermal analysis, while the mechanical analysis is performed simultaneously in one step to reduce simulation time. To validate the numerical model, a series of experiments using a fully automated welding process are conducted. The temperature and residual stress measurements are performed by using thermocouples and hole-drilling stress relaxation method. Furthermore, the heat input efficiency for the buried arc welding process is determined by using a parametric analysis