Effects of steel pipe segment straightening on tensile and fracture mechanical properties of resulting semiproducts

0507643 - ÚTAM 2020 RU A - Abstract
Gajdoš, Lubomír - Šperl, Martin
Effects of steel pipe segment straightening on tensile and fracture mechanical properties of resulting semiproducts.
XLVII International Conference “Advanced Problems in Mechanics". APM 2019. Book of abstracts. St. Petersburg: Polytech, 2019. s. 29-29. ISBN N.
[International Conference Advanced Problems in Mechanics. APM 2019 /47./. 24.06.2019-29.06.2019, St. Petersburg]
R&D Projects: GA TA ČR(CZ) TE02000162
Institutional support: RVO:68378297
OECD category: Composites (including laminates, reinforced plastics, cermets, combined natural and synthetic fibre fabrics

Fracture mechanics specimens relating to pressurized pipelines are usually produced from flat sheets obtained from press straightened pipe segments. There is however scepticism about the validity of fracture toughness values gained from straightened specimens due to the occurrence of plastic strains which may be induced in the straightened semiproducts during the press straightening process. In order to clarify a substantiation of this scepticism, we have carried out fracture mechanical tests on CT specimens manufactured from a CSN 411353 steel pipe 266 mm in diameter and 8 mm in wall thickness by a common procedure, i.e. from a pre-straightened sheet, as well as on curved CT specimens which to some extent simulate stress conditions in a pipeline wall loaded by internal pressure. Examination of R curves for flat (straightened) and curved CT specimens has shown that, besides differences in the curve slopes and a lower position of the R curve in the J-Δa diagram for the curved CT specimens, the fracture toughness parameters J0.2 and Jm for the curved CT specimens were smaller by less than 3% as compared to the flat CT specimens. Moreover, we have also performed basic stress-strain tests on circumferentially oriented straightened and non-straightened tensile specimens taken from L360NB steel pipe 530 mm in diameter and 8.6 mm in thickness. Examination of the stress-strain diagrams for the straightened and non-straightened tensile specimens has shown that press straightening does not influence the behaviour of steel above the yield stress, including the U.T.S., since the stress-strain curves practically coincide above the yield stress. The only change induced by straightening is the removal of the Luders region, and a subsequent change in the yield stress magnitude
Permanent Link: http://hdl.handle.net/11104/0298638