Pipelines buried in trenches and covered by soil are essentially under full axial constraint. Under such conditions, a temperature change resulting from the passage of hot oil coupled with high internal pressure can plastically deform the pipe. If the line is relatively thin the compression can induce axisymmetric wrinkling. Mild wrinkling is benign, but at higher strain levels it leads to collapse by localized wrinkling. During a lifetime of 20 or more years, lines experience many startup and shutdown cycles (-100). This work investigates whether a tube that develops small amplitude wrinkles can be subsequently collapsed by persistent cycling. The problem is investigated experimentally using SAF2507 super-duplex steel tubes with D/t of 28.5. The tubes are first compressed to strain levels high enough for mild wrinkles to form; they are then cycled axially under stress control about a compressive mean stress. This type of cycling usually results in material ratcheting. Here it is accompanied by accumulation of structural damage due to the growth of the amplitude of the initial wrinkles. The tube average strain initially grows nearly linearly with the number of cycles, but as a critical value of wrinkle amplitude is approached, wrinkling localizes, ratcheting grows exponentially and the tube collapses. The rate of ratcheting and the number of cycles to failure depend on the initial compressive pre-strain and on the amplitude of the stress cycles. However, collapse was found to occur when the accumulated average strain reaches the value at which the tube localizes under monotonic compression. A custom shell model of the tube with initial axisymmetric imperfections, coupled to a cyclic plasticity model is used to simulate successfully the series of experiments performed.


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    Titel :

    Progressive wrinkling and collapse of pipes due to axial cycling


    Weitere Titelangaben:

    Zunehmende Faltenbildung und Zusammenbruch von Rohren infolge zyklischer axialer Belastung


    Beteiligte:
    Jiao, R. (Autor:in) / Kyriakides, S. (Autor:in)


    Erscheinungsdatum :

    2009


    Format / Umfang :

    9 Seiten, 14 Bilder, 1 Tabelle, 16 Quellen




    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




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