Evaluation of the fatigue strength of bends of pipelines at high plastic strains

1988 ◽  
Vol 20 (8) ◽  
pp. 1072-1075
Author(s):  
D. L. Kostovetskii
Keyword(s):  
Fatigue Strength ◽  
Plastic Strains ◽  
High Plastic

Modification Strain-Based Failure Assessment Diagram for High Strength Pipeline Steel

2016 ◽  
Vol 853 ◽  
pp. 33-40
Author(s):  
Jun Lin Shi ◽  
Jian Ping Zhao ◽  
Wei Jie Jiang
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Pipeline Steel ◽  
High Strength ◽  
Plastic Strains ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
High Plastic

The strain-based failure assessment diagram (SB-FAD) has been developed to predict failure due to high plastic strains. This paper validates the SB-FAD by finite element results for high strength pipeline steel (X80, X80HD, and X90) with four representative specimens (CT, CCP, DECP, and SCEP) of different crack sizes, respectively. The influence of material properties, geometries and crack sizes on failure assessment curves were compared and analyzed. Meanwhile, the modified Option-1 curve of SB-FAD is given in this paper. The results showed that the modified Option-1 curve of SB-FAD is more accurate when the value of abscissais Dr small and more conservative when the value of abscissa Dr is large.

Fatigue strength of notched specimens with regard for cyclic plastic strains

1978 ◽  
Vol 10 (4) ◽  
pp. 381-385 ◽  
Author(s):  
V. T. Troshchenko ◽  
L. A. Khamaza ◽  
Yu. D. Mishchenko
Keyword(s):  
Fatigue Strength ◽  
Plastic Strains ◽  
Cyclic Plastic ◽  
Notched Specimens

Failure Prediction of Curved Wide Plates Using the Strain-Based Failure Assessment Diagram With Correction for Constraint and Notch Radius

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Anthony Horn ◽  
Mikhail Trull ◽  
Stijn Hertelé
Keyword(s):  
Fatigue Crack ◽  
Experimental Approach ◽  
Fatigue Cracks ◽  
Failure Prediction ◽  
Plastic Strains ◽  
Notch Radius ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Low Constraint ◽  
High Plastic

The strain-based failure assessment diagram (SB-FAD) has been developed for predicting failure from flaws in components subjected to high plastic strains. In this paper, a combined numerical and experimental approach is used to apply the SB-FAD to predict failure from a series of API 5L grades X80 and X100 curved wide plate (CWP) specimens with shallow notches machined into the pipe girth weld. For the CWP specimens tested in this work, the SB-FAD in its unmodified form resulted in over-conservative predictions of failure. This is attributed to the SB-FAD assuming high constraint conditions and the presence of a sharp fatigue crack, whereas the CWP specimens tested in this work were low constraint and contained a shallow machined notch without fatigue cracks. A modification of the SB-FAD is then proposed to account for nonsharp defects loaded to high plastic strains under conditions of low constraint. The resulting predictions of the modified SB-FAD show significantly reduced conservatism compared to the unmodified SB-FAD.

Failure Prediction of Curved Wide Plates Using the Strain-Based Failure Assessment Diagram With Correction for Constraint and Notch Radius

2013 ◽  
Author(s):  
Anthony J. Horn ◽  
Mikhail Trull ◽  
Stijn Hertelé
Keyword(s):  
Fatigue Crack ◽  
Experimental Approach ◽  
Fatigue Cracks ◽  
Failure Prediction ◽  
Plastic Strains ◽  
Notch Radius ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Low Constraint ◽  
High Plastic

The strain-based failure assessment diagram (SB-FAD) has been developed for predicting failure from flaws in components subjected to high plastic strains. In this paper, a combined numerical and experimental approach is used to apply the SB-FAD to predict failure from a series of API 5L grades X80 and X100 curved wide plate (CWP) specimens with shallow notches machined into the pipe girth weld. For the CWP specimens tested in this work, the SB-FAD in its unmodified form resulted in over-conservative predictions of failure. This is attributed to the SB-FAD assuming high constraint conditions and the presence of a sharp fatigue crack, whereas the CWP specimens tested in this work were low constraint and contained a shallow machined notch without fatigue cracks. A modification of the SB-FAD is then proposed to account for non-sharp defects loaded to high plastic strains under conditions of low constraint. The resulting predictions of the modified SB-FAD show significantly reduced conservatism compared to the unmodified SB-FAD.

Formation of submicrometre-grained structure in magnesium alloy due to high plastic strains

1990 ◽  
Vol 9 (12) ◽  
pp. 1445-1447 ◽  
Author(s):  
R. Z. Abdulov ◽  
R. Z. Valiev ◽  
N. A. Krasilnikov
Keyword(s):  
Magnesium Alloy ◽  
Plastic Strains ◽  
High Plastic

Application of Separated Die Design to Production of Ecap Dies

2012 ◽  
Vol 445 ◽  
pp. 120-124 ◽  
Author(s):  
Huseyin Erol Akata
Keyword(s):  
Metal Forming ◽  
Die Design ◽  
Shear Stresses ◽  
Notch Effect ◽  
Plastic Strains ◽  
Alloy Specimen ◽  
Equal Channel Angular Processing ◽  
High Plastic ◽  
5083 Aluminum Alloy ◽  
Very High

Metal forming processes with principally shear stresses that very high plastic strains are obtained in one pass are defined as severe plastic deformation (SPD) processes. Strain values can additionally be increased with additional passes throughout the process. Equal channel angular processing (ECAP) is the most applied method among the SPD processes due to relative ease of die manufacturing. On the other hand, die failures like corner cracking are frequently observed due to high notch effect and therefore use of the dies is limited. In the presenting study multi element die design (separated die design) approach was applied to production of ECAP dies in order to eliminate die failures and 5083 Aluminum alloy specimen were deformed with several passes. Although some additional development for die arrangement and fixation are needed, corner cracking was never observed and dies could be used safely.

Fracture Control in Pipelines Under High Plastic Strains: A Critique of DNV-RP-F108

2008 ◽  
Author(s):  
Andrew Cosham ◽  
Kenneth A. Macdonald
Keyword(s):  
Fatigue Loading ◽  
Practical Experience ◽  
Ground Movement ◽  
Plastic Strains ◽  
Offshore Pipelines ◽  
Fracture Control ◽  
Offshore Industry ◽  
Girth Welds ◽  
Pipeline Design ◽  
High Plastic

Offshore pipelines experience strains greater than yield during pipelay and in service. Installation by reeling introduces high levels of plastic strain, typically on the order of 2 percent for a 12 in. flowline. Controlled lateral buckling in offshore pipelines, due to high operating pressures and/or temperatures, may also give rise to high strains and large cyclic loads. Similarly, frost heave or ground movement in onshore pipelines can cause high strains. To date, most of the cases involving high strains are to be found in offshore pipelines, in terms of both design and the assessment of accidental states. However, some of the experiences in the offshore industry have relevance to onshore pipelines. Fracture control in this context is designing pipelines to address the implications of these high static and cyclic strains during installation/construction and operation. Pipeline design codes such as DNV-OS-F101 and DNV-RP-F108 give guidance. Two issues to consider are: the degradation of the material properties, and the failure of the girth welds. High strains may cause failure or the growth — by stable ductile tearing — of preexisting flaws in the weld. Subsequent fatigue loading may cause pre-existing flaws to grow to failure. Engineering critical assessments (ECAs) are conducted during pipeline design to determine tolerable sizes for weld flaws. Standards such as BS 7910 and API 579 are primarily stress-based and it is not straightforward to apply them to strain-based situations. DNV-RP-F108 addresses this gap by providing additional guidance derived from UK and Norwegian research programmes. Assessing flaws subject to high strains is at the ‘cutting-edge’ of applied fracture mechanics. ECAs often have a reputation of being ‘over-conservative’. ECAs of pipelines subject to high strains may indicate that only very small flaws would be acceptable, whereas practical experience has shown that the girth welds are highly tolerant to the presence of flaws. It is therefore instructive to consider under what situations might ECAs be too conservative, and when they may be non-conservative. The available guidance for ensuring fracture control in pipelines under high plastic strains is discussed in this paper, and the wider issues are addressed.

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