• A new stiffness model of the hydraulic cylinder was established, which incorporated factors of the compressibility of the oil, the axial deformation of the piston rod, the volume expansion of cylinder barrel, and the volume expansion of flexible hoses. • The level of each impacting factor on the hydraulic cylinder stiffness was analysed: the compressibility of the oil is about 80 %, the volume expansion of the cylinder barrel is about 10 %, the axial deformation of the piston rod is about 6 %, and the volume expansion of flexible hoses is about 3 %. The impact of either the volume expansion of metal pipes or the sealing deformation is very small. • Experimental tests proved that the content of the air in the hydraulic oil influences both the hydraulic cylinder stiffness andthe bulk modulus significantly, but only at a low pressure level (P < 6 MPa).• Tests proved that the change of the hydraulic cylinder stiffness is nonlinear. When the pressure P < 6 MPa, the degree of nonlinearity is relatively high. However, when the pressure is P > 6 MPa, the stiffness approaches to linearity.

Girth weld cracking of long-distance oil and gas pipelines yields substantial harm to pipeline safety and may cause serious accidents. As of today, non-destructive testing has been one of the most common methods for predicting potential faults and ensuring safe operation. Classical pipeline non-destructive testing methods include magnetic flux leakage testing and the use of ultrasonic testing by electromagnetic acoustic transducers. However, they are incapable of identifying the defects in complex surfaces like girth welds. Magnetic flux leakage testing exhibits poor anti-interference abilities and low space resolution. Ultrasonic testing by electromagnetic acoustic transducers suffer from low conversion efficiency and poor signal quality. In order to overcome the disadvantages of conventional pipeline non-destructive testing methods, we propose an embedded eddy current testing system by leveraging image processing and neural networks. Hough transform and the contour extraction technique are employed to extract the characteristic features from the two-dimensional (2D) eddy current impedance image. Experiment results show that the system can effectively identify the girth weld defects, featuring an accuracy of up to 92%. The low power consumption and compactness of the proposed system makes it a great candidate for pipeline inner inspection.

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Rubber bearings are used widely in small and medium-span highway bridge structure. In this paper the transient dynamics of the plate rubber bearing and the pot rubber bearing which are widely used in practical engineering is analyzed. And the fatigue life of bridge bearing is estimated using reliability theory