Unexpectedly, numerous stress corrosion cracking failures of production tubing have occurred from the external surface (annular side), rather than from the internal (production side). This problem is encountered frequently in HPHT (high pressure/high temperature) wells and is termed annular environmentally assisted cracking (AEAC). Studies of these failures have pointed to an incompatibility between the metallurgy of the tubing and the completion/packer fluid placed in the annulus. Simplistic causative factors such as a chloride ion-metal interaction are insufficient to explain the AEAC failure mechanism. In contradistinction, our research studies on the compatibility of martensitic stainless steel production tubing with a large variety of completion/packer fluids have implicated specific fluid contaminants as key causative factors. Of these contaminants, CO2 and/or its aqueous counterparts (carbonate, bicarbonate or carbonic acid) play a major role. Quite unexpectedly, the presence of bicarbonate/carbonate ion produces cracking in sodium bromide brines, which are often believed to be free of cracking issues. Similarly, occurrences of stress corrosion cracking on the external surface of pipeline have been reported since the late sixties. In these instances the bicarbonate ion in groundwater has also been assigned a major role. This paper focuses on the important role of CO2 chemistry in explaining the observed cracking for the two different environments. The unique interactions of CO2 and its basic counterparts HCO3(-) and CO3(2-) with the completion/packer fluid (high salt concentration, divalent cations, etc.) and its relevance to the tubing failures are discussed. Comparison is made to the fluid chemistry responsible for pipeline cracking. Chemical mechanisms to explain the role of bicarbonate/carbonate in the observed tubular cracking are presented. The study describes the importance of fluid and CO2 chemistry in localized corrosion and stress cracking of diverse metallurgy, advancing our knowledge of the ubiquitous CO2 corrosion issues.


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    Title :

    Carbon dioxide corrosion when least expected: Importance of carbonate chemistry in stress corrosion cracking on the external surfaces of martensitic stainless steel production tubing and low-alloy carbon steel pipeline


    Additional title:

    Unerwartete Kohlendioxidkorrosion: Die Bedeutung der Carbonatchemie bei der Spannungsrisskorrosion der äußeren Oberfläche von Betriebsleitungen aus martensitischen nichtrostenden Stählen und Pipelines aus niedriglegiertem Kohlenstoffstahl


    Contributors:


    Publication date :

    2010


    Size :

    10 Seiten, 55 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English








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