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Numerical and experimental investigation of the influence of HAZ on the fracture behavior of longitudinal welded linepipes

  • The present paper deals with the influence of heat affected zone (henceforth HAZ) on the fracture performance of longitudinal welded linepipes in dependence on constraint level. It has been shown that toughness values of HAZ obtained from standard fracture mechanics tests lead to uneconomic linepipe design for two reasons. The first reason is that laboratory specimens with higher constraint level generally exhibit lower fracture resistance compared to flawed linepipes. The second one has to do with a higher probability of cleavage failure occurrence in the laboratory specimen than in the linepipes due to larger areas of lower toughness (so called local brittle zones (LBZ)) intersected by crack front. In recent years numerous studies have been initiated with the objective to quantify the constraint level and thus to allow for less conservative linepipe safety assessment by applying constraint corrected toughness values. However, the main focus of these studies has hitherto been on the homogeneous materials, failing to account for the possible effects of different microstructures within the heterogeneous HAZ. This paper seeks to close this gap by reporting on results from tests on fracture mechanics specimens of a high strength X80 steel, i.e. SENB and SENT specimens as well as results from ring expansion tests. Both, deep and shallow cracks are inserted in the fracture mechanics specimens and rings targeting the fusion line (FL). By varying the initial crack size and sample type, different constraint levels are achieved and subsequently quantified using numerical methods. Besides constraint observations, post metallographic analyses are performed to identify exact HAZ microstructure involved at the crack tip. Finally, the influence of HAZ properties, flaw size and geometry on the failure behaviour of the linepipes has been demonstrated and assessed. Based on the combination of the results from constraint studies and the post metallographic analyses, the methodology is proposed which enables simple quantitative prediction of toughness values for safe and economic design of linepipes with flaws located in HAZ.

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Metadaten
Author:Aida NonnORCiDGND, Marion Erdelen-Peppler, Christoph Kalwa
URL / DOI:https://www.gruppofrattura.it/ocs/index.php/esis/ECF18/paper/viewFile/6273/2143
Parent Title (English):18th European Conference on Fracture, Fracture of Materials and Structures from Micro to Macro Scale, Dresden, Germany
Document Type:conference proceeding (article)
Language:English
Year of first Publication:2010
Release Date:2021/03/23
Tag:HAZ; LSAW linepipe; X80; constraint analysis; finite element modeling; linepipe safety; local brittle zones
Institutes:Fakultät Maschinenbau
Technologie-Campus Neustadt an der Donau
Fakultät Maschinenbau / Computational Mechanics and Materials Lab (CMM)
Publication:Externe Publikationen
research focus:Produktion und Systeme