In this work, an analysis of the residual fatigue life of X70-grade pipeline steel with a semi-ellipse defect was carried out. The results show that the maximum stress intensity factor under the influence of the flow field to be higher than the value under a simple pressure load at the defect site and a parameter analysis of flow field and stress makes it clear that pressure fluctuations should be minimized to increase residual fatigue life of high-strength steel pipes. For instance, increasing defect length to 30 mm from 10 mm in the axial direction decreases the residual fatigue life of the above pipe to 60% of original life. Therefore, long defects in the axial direction of the pipe should be paid close attention to during on site monitoring. The probability of defects on the internal pipeline surface increases over time because of the mechanical effect of the flow field and abrasion on the pipe. Defects can propagate rapidly in an unstable manner, eventually leading to pipe failure and economic losses. Changing flow conditions and loads on the inner pipe wall lead to structural deformation. Pipe status in turn affects the flow field to a certain degree, creating a fluid-structure interaction (FSI) with feedback inside the pipe. This article highlights FSI, defect propagation, and finite-element analysis of FSI using the natural gas pipeline model from a section of the West-to-East Natural Gas Transmission project (X70-grade steel pipeline). The stress distribution of high-strength steel pipe calculated by FSI was applied to analyze and compare residual fatigue life with the residual fatigue life calculated under a simple internal pressure load. In addition, maximum stress and stress intensity factors for different axial lengths of semi-elliptical defects were analyzed. The stress-intensity factor increases with increasing maximum stress in the defect and leads to decreased residual fatigue life of the high-strength steel pipe.
Flow-field stress intensity exceeds simple pressure load at defect
Oil and Gas Journal ; 112 , 1 ; 94-101
2014
7 Seiten, 8 Bilder, 2 Tabellen, 17 Quellen
Aufsatz (Zeitschrift)
Englisch
Belastungsfaktor , Druck (Mechanik) , Druckschwankung , Fehlerabschätzung , Fehlercharakterisierung , Fehlergröße , Fehlerorientierung , Finite-Elemente-Analyse , Fluid-Struktur-Wechselwirkung , hochfester Stahl , mathematische Methode , mechanische Beanspruchung , mechanische Spannungsverteilung , Modell , Pipeline-Betrieb , Restlebensdauer , Rohrleitungsschaden , Spannungsintensitätsfaktor , Stahlrohr , Strömungsfeld , Fehlerausbreitung
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