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Characteristics of Metal Magnetic Memory Testing of 35CrMo Steel during Fatigue Loading

1
College of Mechanical and Transportation Engineering, China University of Petroleum-Beijing, Beijing 102200, China
2
China National Offshore Oil Corporation, Beijing 100029, China
*
Author to whom correspondence should be addressed.
Metals 2018, 8(2), 119; https://doi.org/10.3390/met8020119
Received: 29 December 2017 / Revised: 2 February 2018 / Accepted: 4 February 2018 / Published: 8 February 2018
(This article belongs to the Special Issue Advanced Non-Destructive Testing in Steels)
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Abstract

The fatigue fracture of a drillstring could cause drilling disturbances and some negative impacts (e.g., economic loss) will be brought when restoring the drillstring to functionality. In order to evaluate the effects of the fatigue damage of the drillstring during drilling, a new apparatus, which could monitor the load level in real-time, was built to perform the four-point bending fatigue test on 35CrMo steel, a typical material of drillstrings. Such an apparatus is based on metal magnetic memory (MMM) technology and can acquire the tangential and normal components of MMM signals. Based on the analysis of the change of surface morphology and MMM signals, it was concluded that the variation of MMM signals could be divided into four stages, which are used to accurately describe the fatigue damage process of the drillstring. Additionally, the MMM signal characteristics are introduced to especially evaluate the fatigue damage of the drillstring, including crack initiation. Furthermore, the scanning electron microscopy (SEM) results demonstrated that morphologies of fatigue fracture were related to the variation of MMM signals. Linear fitting results indicated that fatigue crack length had a good linear relationship with the characteristics, so it is feasible to monitor fatigue damage and predict the residual life of a drillstring by using MMM technology. View Full-Text
Keywords: fatigue fracture of drillstring; four-point bending fatigue test; surface morphology; MMM signal characteristics; SEM fatigue fracture of drillstring; four-point bending fatigue test; surface morphology; MMM signal characteristics; SEM
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Hu, Z.; Fan, J.; Wu, S.; Dai, H.; Liu, S. Characteristics of Metal Magnetic Memory Testing of 35CrMo Steel during Fatigue Loading. Metals 2018, 8, 119.

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