Erosioncorrosion Testing of Materials for the use as Screw Materials in Twin Screw Multiphase Pumps in the Oil and Gas Production Industry
|Institut:||Laboratorium fuer Schweisstechnik / Prof. Dr.-Ing. T. Klassen|
|Hauptberichter:||Hoffmeister, Hans Prof. Dr.-Ing.|
|Tag der mündlichen Prüfung:||10.07.2007|
|Freie Schlagwörter (Englisch):||Erosion , corrosion , pumps , multiphase , oil , gas|
Kurzfassung auf Englisch:
Twin screw multiphase pumps are increasingly popular in the oil and gas production industry. They are used to boost the wellhead pressure in order to increase production in the early stages, prolong the overall production length, therefore resulting in greater recovery and to enable longer transport distances of hydrocarbons. The technology has been proven to be quite effective in onshore production facilities. The pumps are required to transport a mulitphase fluid containing corrosion enhancing elements such as formation water, carbon dioxide and Hydrogen sulphide, as well as erosion including hard particles and are therefore subjected to wear. The maintenance required due to this wear is easily accomplished in production areas with good infrastructures. Due to the worlds increasing energy demands and due to the fact that many onshore production sites are nearing depletion, the oil and gas production industry seeks to extend production in remote areas and in deepwater/ultradeepwater offshore sites. If multiphase twin screw pumps are to be used for these applications, they have to be able to run independently for long time frames since any kind of maintenance work in these locations is associated with high costs and a considerable logistical effort. As such, the pump materials that are subjected to wear have to be chosen very carefully. Since every hydrocarbon reservoir is different in its phase composition there is no one-for-all solution. The materials have to be optimised for every well and the multiphase composition of that well has to be carefully monitored during the production presents a compilation of the information on erosioncorrosion wear currently documented in literature as it is relevant to the wear phenomena found on the multiphase pumps. The wear characteristics of the multiphase pumps are documented and classified. As a result of the investigation of current literature, no sufficient information on the erosion and/or corrosion mechanism in small clearances, as they are typically for the space between rotating and stationary pump components is available. Also, no attempt has been made to experimentally simulate the effects of operational parameters on erosioncorrosion in such geometries. The purpose of this work was, therefore, to establish such an experimental setup and identify relevant parameters to be tested and to be compared to available results of operational experience. A new erosioncorrosion test cell is presented that is able to replicate the electrochemical and mechanical attack that the screws are subjected to. This test cell enables materials testing and selection in a laboratory environment. The effect of the multiphase fluid and operational paramenters on erosion, corrosion and erosioncorrosion will be discussed. In detail these are the effect of oil, water and sand fraction, temperature, clearace depth, rotational speed and formation water concentration. The fluid dynamics, as they are found in the clearance between screw and liner will be described regarding velocity and direction of flow as well as phase distribution and/or separation. Information on the influence of the fluid velocity on the boundary diffusion layer derived via rotating cylinder electrode experimentation will be supplied. As an example of application, a series of materials with different chemical compositions and a set of Tungsten carbide (WC) plating will be subjected to identical erosioncorrosion parameters and the resulting wear characteristics will be discussed. As a summarazing result it is demonstrated that the waer mechanisms observed in actual pump operation are reproduced and partially quantified by the developed test setup. The required further fields of work and respective experimental procedures are identified in order to establish a satisfying operational lifetime prediction procedure for multiphase pump components. This should also include further, advanced efforts in the numerical modelling of the erosioncorrosion mechanisms in smal clearances between moving and stationary pump components.
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