CRACK INITIATION, CRACK-GROWTH AND FRACTURE-BEHAVIOR OF LARGE-DIAMETER PIPES WITH CIRCUMFERENTIAL DEFECTS UNDER INTERNAL-PRESSURE AND SUPERIMPOSED ALTERNATING BENDING LOAD

Pipes made of steel 20 MnMoNi 5 5 and MnMoNiV-special melt having an e xternal diameter of 800 mm, wall thickness of 47 mm, and length of up to 5500 mm were provided with circumferential defects of defined lengt h and depth. They were loaded by internal pressure and a superimposed alternating bending moment. During the tests deformation and crack gro wth were determined in the wall thickness and circumferential directio n. Pipes with an outer diameter of 226 mm and a wall thickness of 20 m m were used to investigate the leak-before-break behaviour in the dyna mic sphere. These pipes were also made of steel 20 MnMoNi 5 5 and a Mn MoNiV-special melt and were loaded with internal pressure and an alter nating bending moment. The excitation took place at the resonance freq uency of the pipes. The pipes also contained circumferential defects o f defined length and depth.