Study On Burst Pressure Of Plastic Pipe Reinforced By Cross-Winding Steel Wires

Plastic pipe reinforced by cross-winding steel wires (PSP) is composed of two layers of thermoplastic high density polyethylene(HDPE) matrix and the high strength steel wires mesh sheleton. They are cohered together with high-performance hot melt adhesive. Combining the high strength of steel wires and flexibility and corrosion resistance of high density polyethylene, PSP can work under hard pressure, and keep high toughness. With the excellent performance of PSP, there has been a growing interest in the bad environment, such as high pressure, corrosion and large deformation of PSP.However, up to now, the short-term burst pressure only can be calculated under the normal temperature. In order to raise the standard of design, expand the application field and ensure safety of PSP, it needs to develop a method of predicting short-term burst pressure under different temperature. Owing to the difference in the structure and load-bearing mechanism between PSP and PE pipe, PSP needs to establish a distinctive long-term performance predicting method, which is different from PE pipe. Thereforce, study on the method of predicting burst pressure under different temperature and time has an important effect on safe operation of PSP.In order to keep PSP running safely, research on burst pressure of PSP is conducted in this paper. This research is supported by National High Technology Research and Development Program (863program, Number:2009AA044801), the main work of this paper is as follows:(1) Based on mechanical properties analysis of PSP, the prediction model of burst pressure was established. It was revealed that the main factors of influenced stress of steel wires were modulus of HDPE and elastic constants of composite layer. The modulus of HDPE was effected by temperature and time. Then elastic constants of composite layer were calculated on the method of macro elastic modulus of multi-layer boards. By combining the main factors and criterion failure based on fracture of steel wires, the burst pressure under different temperature and time was studied systematically.(2) Study indicated that steel wires were the main load-bearing structure of PSP, and HDPE only bear a small part of load, which showed the viscoelastic characteristic. The influence of temperature on initial modulus and the relation between relaxation modulus and time were studied by theory and test research. Based on data of the tension test and dynamic mechanical analysis (DMA), the correlation between initial modulus and temperature was obtained. It was indicated that the initial modulus decreased linearly with increase of temperature from20℃to80℃. Results also showed that the relationship between the relaxation modulus and time was a power function. At first, relaxation modulus dropped swiftly, then it declined softly as the time increased, however, farther prolongation of the time resulted in slow decrease of relaxation modulus.(3) In order to verity the accuracy of the theoretical model, short-term burst test at different temperature and long-term hydraulic test under20℃were carried out. The experimental study showed that calculated results were close to test data, and their relative error were within3.1%～16.1%from20℃to80℃and-0.83%-17.2%less than2500h, respectively. It can be used for predicting the burst pressure and advancing the engineering application of PSP. Through theoretical analysis and experimental results, the temperature coefficient based on the existing standard can be modified.