Analysis of the HAZ fracture resistance of HSLA steel weldments

Ispitivane su karakteristike otpornosti ka lomu u ZUT zavarenog spoja mikrolegiranog čelika povećane čvrstoće koji se koristi za izradu posuda pod pritiskom. S obzirom na namenu zavareni spoj treba da ima veliku otpornost ka pojavi i rastu prslina. Analiza je obuhvatila udarnu žilavost uzoraka simuliranih mikrostruktura koje su tipične za ZUT, žilavost loma nestandardnih uzoraka sa simuliranim mikrostrukturama i konačno standardne zavarene SENB uzorke. Analiza je pokazala da tip prsline (erozimatna i zamorna) na početak stabilnog rasta prsline ima veći uticaj kod duktilnijih mikrostruktura, a manji ili skoro nikakav kod krtijih. Takođe, komparativna analiza simuliranih uzoraka i zavarenih uzoraka pokazala je uticaj odnosa i veličine mikrostrukturnih regiona u ZUT-u na rast prsline t.j. uticaj mismeča na otpornost ka lomu.The HAZ fracture behavior of the weldments of HSLA steel for pressure vessels has been investigated. Having in mind the purpose of such structure, the welded joint should poses sufficient resistance towards crack occurrence as well its propagation. The analysis encompassed impact toughness testing of Charpy specimens and fracture toughness determination of SENB specimens of base metal and simulated microstructures of HAZ, and finally fracture toughness testing of welded specimens with crack located in the very narrow HAZ regions. The analysis revealed the effect of the crack tip (electro eroded or fatigued) on the onset of the stabile crack growth for the different microstructures. The comparative analysis between the testings showed the influence of the mismatch towards the fracture behavior of real welded joint in respect of simulated microstructures

Residual strength assessment of cracked welded spherical storage tank

Dva sferna rezervoara za amonijak (zapremine 1000 m3) su ispitana 1998. i 1999. tehnikama bez razaranja (NDT) u skladu sa Propisima za periodičnu kontrolu. Ovi rezervoari su izrađeni 1979. od čelika StE 460 prema DIN, mikrolegiranog Cr-Ni-Ti, debljine 30 mm. Uočen je veliki broj poprečnih prslina u metalu šava i uzdužnih prslina u zoni-uticaja-toplote (ZUT) i po liniji stapanja unutrašnjih zavarenih spojeva. Da bi se procenila zaostala čvrstoća oba rezervoara, ploče 500 x 500 mm, su isečene radi hemijskog, metalurškog i mehaničkog ispitivanja. Ova ispitivanja su obuhvatala detaljno određivanje žilavosti standardnih Šarpi epruveta na instrumentiranom klatnu i ispitivanja mehanike loma na standardnim SEN(B) epruvetama za ocenu žilavosti loma. Na osnovu rezultata Šarpi ispitivanja i ispitivanja mehanike loma ocenjena je preostala čvrstoća sfernih rezervoara sa prslinama.Two spherical storage tanks for ammonia (volume 1000 m3) have been tested in 1998 and 1999 by Non-Destructive Techniques (NDT) in accordance with the Periodic Inspection Regulations. These storage tanks have been constructed in 1979 of St.E460 steel according DIN, Cr-Ni-Ti microalloyed, 30 mm thick. The large number of transverse cracks in weld metal and longitudinal cracks in heat-affected-zone (HAZ) and along fusion line of inner welded joints have been detected. In order to assess the residual strength, of both storage tanks, plates 500 x 500 mm were cut for chemical, metallurgical and mechanical testing. These testing included detailed toughness testing of standard Charpy specimens on instrumented pendulum, and fracture mechanics testing on standard SEN(B) specimens for fracture toughness evaluation. Based on results of Charpy and fracture mechanics testing residual strength of cracked storage tanks has been assessed

Residual strength assessment of cracked welded spherical storage tank

Dva sferna rezervoara za amonijak (zapremine 1000 m3) su ispitana 1998. i 1999. tehnikama bez razaranja (NDT) u skladu sa Propisima za periodičnu kontrolu. Ovi rezervoari su izrađeni 1979. od čelika StE 460 prema DIN, mikrolegiranog Cr-Ni-Ti, debljine 30 mm. Uočen je veliki broj poprečnih prslina u metalu šava i uzdužnih prslina u zoni-uticaja-toplote (ZUT) i po liniji stapanja unutrašnjih zavarenih spojeva. Da bi se procenila zaostala čvrstoća oba rezervoara, ploče 500 x 500 mm, su isečene radi hemijskog, metalurškog i mehaničkog ispitivanja. Ova ispitivanja su obuhvatala detaljno određivanje žilavosti standardnih Šarpi epruveta na instrumentiranom klatnu i ispitivanja mehanike loma na standardnim SEN(B) epruvetama za ocenu žilavosti loma. Na osnovu rezultata Šarpi ispitivanja i ispitivanja mehanike loma ocenjena je preostala čvrstoća sfernih rezervoara sa prslinama.Two spherical storage tanks for ammonia (volume 1000 m3) have been tested in 1998 and 1999 by Non-Destructive Techniques (NDT) in accordance with the Periodic Inspection Regulations. These storage tanks have been constructed in 1979 of St.E460 steel according DIN, Cr-Ni-Ti microalloyed, 30 mm thick. The large number of transverse cracks in weld metal and longitudinal cracks in heat-affected-zone (HAZ) and along fusion line of inner welded joints have been detected. In order to assess the residual strength, of both storage tanks, plates 500 x 500 mm were cut for chemical, metallurgical and mechanical testing. These testing included detailed toughness testing of standard Charpy specimens on instrumented pendulum, and fracture mechanics testing on standard SEN(B) specimens for fracture toughness evaluation. Based on results of Charpy and fracture mechanics testing residual strength of cracked storage tanks has been assessed

Numerical analysis of tensile specimen fracture with crack in HAZ

Numeričkim rešenjima se omogućava istraživanje složenijih problema, uključujući analizu pojedinačnih uticaja, posebno u slučajevima kada izostaju odgovarajući eksperimenti i matematička rešenja usled visoke cene, složenosti problema, itd. U ovom radu se razmatra numeričko modeliranje i analiza ponašanja loma zavarenih zateznih epruveta sa prslinom u ZUT, na primer, uticaj heterogenosti zavarenog spoja na raspodelu napona i deformacija ispred vrha prsline, kao i uzroci pojave loma. Analizirana su dva slučaja: vrh prsline lociran u finozrnom ZUT i vrh prsline lociran u grubozrnom ZUT. Eksperimentalna istraživanja, u oba slučaja, su pokazala dejstvo prepreke mismečinga zavarenog spoja, nakon inicijalnog širenja prsline u finozrnom ili u grubozrnom ZT, što je prouzrokovalo skretanje rasta prsline u oblasti duktilnijeg osnovnog materijala, čime se smanjila i brzina rasta prsline. U ovom članku su opisana razmatranja ovakvog ponašanja uz primenu numeričke simulacije eksperimenta. .Numerical solutions enable investigation of complex problems, including analysis of various influences, especially in cases when experimental research and mathematical solutions are not appropriate, such as high price, problem complexity, etc. In this article, numerical modeling and analysis is presented, concerning fracture behavior of HAZ cracked welded tensile specimens i.e. the influence of welded joint heterogeneity on the distribution of stress and strain in front of the crack tip and the reasons causing failure. Two cases are analyzed: crack tip located in fine-grained HAZ and crack tip located in coarse-grained HAZ. Experimental research in both cases exhibited that the barrier act of welded joint mismatch, after the initial propagation of crack in fine-grained or coarse-grained HAZ, has brought to a turn of crack propagation into more ductile base metal, thus decreasing the crack propagating speed. The article brings some observations regarding such behavior by applying numerical simulations to the experiment.

STRUCTURAL INTEGRITY ASSESSMENT OF SPHERICAL STORAGE TANKS

Abstract Two spherical storage tanks for ammonia (volume 1000 m 3 ) have been tested in 1998 and 1999 by Non-Destructive Techniques (NDT) in accordance with the Periodic Inspection Regulations. These storage tanks have been constructed in 1979 using microalloyed steel St.E460 according to DIN, with thickness of 30 mm. The large number of transverse cracks in weld metal and longitudinal cracks in heat-affected-zone and along fusion line of inner welded joints has been detected. In order to estimate the residual strength, from both storage tanks, plates 500x500 mm were cut for the chemical, metallurgical and mechanical investigations. These investigations encompassed detailed toughness testing, including standard Charpy specimens, tested on instrumented pendulum, and fracture mechanics testing on standard SENB specimens for fracture toughness evaluation. Using data obtained by Charpy and fracture mechanics testing, the structral integrity of cracked storage tanks has been assessed

Crack tip fields effects on crack propagation through the heat affected zone in an overmatched welded joint

The mismatching constraint effect on crack propagation through the heat-affected zone (HAZ) in a welded joint is presented in this paper. It is shown that due to this effect, the fracture behavior of an overmatched welded joint depends on the mechanical properties and the size of the region of the crack tip location, as well as on the properties and the size of surrounding regions. The finite element analysis of high-strength low-alloyed (HSLA) steel welded joints with crack tips in the heat-affected zone is performed based on previous experimental work. Two locations of the crack tip are analyzed: fine-grained HAZ (FGHAZ) and coarse-grained HAZ (CGHAZ). In both cases, after the initial propagation of the crack in FGHAZ or CGHAZ, its propagation is directed toward more ductile base metal, thus increasing the fracture resistance of a welded joint. Some new observations about the reasons for such behavior due to crack tip strain fields are presented as well