Determination of fatigue crack growth parameters in welded joint of HSLA steel

Abstract

The structural integrity and operational safety of welded pressure vessels primarily depends on the behaviour of weldments. In spite of all efforts in material production and improvements in welding techniques, including strict codes, requirements and directives, the crack occurrence in welded structures cannot be completely excluded. This is why fracture mechanics analysis is inevitable in the structural integrity assessment of all welded structures. Examples of practical application of fracture mechanics parameters in cracked pressure vessel structural integrity are considered. This paper shows the determination of parameters of the fatigue crack for constituents of welded joints produced of high strength low alloyed steel Nionikral-70 (yield strength 700 MPa). Results have shown that the position of notch and crack initiation affect the values of the stress intensity range of fatigue threshold ΔKth and parameters in the Paris’ equation.

Integritet konstrukcije i sigurnost u radu zavarenih posuda pod pritiskom uglavnom zavisi od ponašanja zavarenih spojeva. Pored svih uloženih napora u proizvodnji i poboljšanja postupaka zavarivanja, uključujući i stroge standarde, zahteve i smernice, pojava prslina u zavarenim konstrukcijama se ne može u potpunosti izbeći. Zato je analiza mehanike loma neophodna u proceni integriteta svih zavarenih konstrukcija. Razmotreni su primeri praktične primene parametara mehanike loma u integritetu posuda pod pritiskom sa prslinom. Rad prikazuje određivanje parametara zamorne prsline za konstituente zavarenih spojeva izrađenih od niskolegiranog čelika povišene čvrstoće Nionikral-70 (napona tečenja 700 MPa). Rezultati pokazuju da položaj zareza i inicijacija prsline utiču na vrednosti raspona napona za granicu zamora ΔKth i na parametre Parisove relacije.