Defect Inspection Of Inner Tube In Steam Injection Boiler Based On Metal Magnetic Memory Method

The steam injection boiler is one of the major equipments used in steam process technology in the current world. In China, it is widely used in Shengli and Liaohe oilfield. Because radiation section tubes in stream injection boiler bear high temperature (about 350℃), high pressure (about 18Mpa) and pressure fluctuation from reciprocal pump, stress concentration occurs in this area commonly, resulting in failure and accident eventually. Therefore, it's necessary to detect tubes fault early. This subject focus on the core issue how to detect fault of inner tube in stream injection boiler based on metal magnetic memory (MMM) method.Tensile test and fatigue test on wet steam generator 20G tubes were carried out and the metal magnetic memory (MMM) signals were detected. Though the analysis of MMM signals from different loading stages and different fatigue cycles, the variation of the MMM signals and the quantitative evaluation of MMM technology were obtained, and used in oilfield test finally.This subject refers to several key issues as follows:in depth study of MMM theory, investigation of steam injection boiler tube failure, tensile test and fatigue test on steam injection boiler 20G tubes and detection and analysis of MMM signals, field test and comparison MMM method with other non-destructive detections.Though laboratory test and field test, evaluation criterion of MMM is obtained. The results showed that:(1) the value of magnetic gradient K basically stays the same with the load increasing in the load of the elastic stage. When the load reaches intensity degree, the K value is 4.6 A/(m·mm). The maximum value of K is about 10A/(m·mm) when the load reaches intensity degree. (2) The K value of stress concentration zone (SCZ) increases slowly with the cycle increasing in the initial stage of fatigue test. When the sample is closing to damage, the K value of SCZ increases to 12A/(m·mm). (3) Through laboratory test and field test, when the K value is larger than 12A/(m·mm) steam injection boiler 20G tubes are closing to damage. When the K value is greater than 7A/(m·mm) and less than 12A/(m·mm), the tube has obvious stress concentration, and this zone should be taken seriously. Therefore, MMM technology which can detect the location of SCZ and diagnostic early faults is a very effective detection method.