Polyethylene (PE) pipes are widely used in natural gas transportation systems in urban areas nowadays. As landslide caused by earthquake would cause destructive damage to buried pipes, increasing attention is attracted to the safety of buried PE pipes under seismic load. In this paper, the deformation behavior of PE pipe subjected to seismic landslide was investigated and a related failure criterion due to yielding was proposed. Based on extensive uniaxial tensile tests, a rate-dependent constitutive model of PE was applied to simulate the mechanical behavior of PE pipes. The extended Drucker-Prager model was used for surrounding soil. In our proposed finite element model, a quartic polynomial bending deflection displacement normal to the pipeline was loaded along the axial direction of PE pipe. The numerical simulation results revealed that the main failure mode of buried PE pipe subjected to seismic landslide shifted from bending deformation to ovalization deformation with increasing bending deflection. On the basis of deformation behavior analysis, failure criterion curves were put forward, which depicts the maximum relative deflection of the pipe cross-section, and the maximum displacement of the pipe versus pipe length subjected to seismic landslide. The results may be referable for design and safety assessment of PE pipes due to seismic landslide.

The storage of hydrogen in a compressed gaseous form offers the simplest solution in terms of infrastructure requirements and has become the most popular and most highly developed hydrogen storage method. Hydrogen storage vessels are the key equipment of hydrogen refueling stations. Seamless pressure vessels made from high strength steel, which are now used in hydrogen refueling stations, are limited in volume, susceptible to hydrogen embrittlement, and difficult for online safety monitoring. In order to solve the aforementioned problems, the authors have developed a multifunctional steel layered hydrogen storage vessel with a volume of $5m3$ and a design pressure of $42MPa$ for the first demonstration hydrogen refueling station in the People’s Republic of China, which is flexible in design, convenient in fabrication, safe in use, and easy for online safety monitoring.

This technical brief proposes a defect recognition model to recognize four typical defects of phased array ultrasonic testing (PA-UT) images for electrofusion (EF) joints. PA-UT has been proved to be the most feasible way to inspect defects in EF joints of polyethylene pipes. The recognition of defects in PA-UT images relies on the experience of operators, resulting in inconsistent defective detection rate and low recognition speed. The proposed recognition model was composed of an anomaly detection model and a defect detection model. The anomaly detection model recognized anomalies in PA-UT images, meeting the requirement of real-time recognition for practical inspection. The defect detection model classified and located defects in abnormal PA-UT images, achieving high accuracy of defects recognition. By comparing detection models, optimizing parameters and augmenting dataset, the anomaly detection model and defect detection model reached a good combination of accuracy and speed.

Mathematical expression describing plastic behavior of steels allows the execution of parametric studies for many purposes. Various formulas have been developed to characterize stress strain curves of steels. However, most of those formulas failed to describe accurately the strain hardening behavior of steels in the full range which shows various distinct stages. For this purpose, a new formula is developed based on the well-known Ramberg–Osgood formula to describe the full range strain hardening behavior of steels. Test results of all the six types of steels show a three-stage strain hardening behavior. The proposed formula can describe such behavior accurately in the full range using a single expression. The parameters of the formula can be obtained directly and easily through linear regression analysis. Excellent agreements with the test data are observed for all the steels tested. Furthermore, other formulas such as Ludwigson formula, Gardner formula, UGent formula are also applied for comparison. Finally, the proposed formula is considered to have wide suitability and high accuracy for all the steels tested.