Discussion on the Causes of Cracking and Failure of Anticorrosion Layer of a Pipeline

Abstract

Abstract The cause of a rare cracking failure accident of the polyethylene (PE) anti-corrosion layers of a pipeline is analyzed and determined. The properties of the PE raw materials and the anti-corrosion layers were detected and analyzed according to the standard, and the micro-morphology of the anti-corrosion layers was characterized by the scanning electron microscope (SEM). The storage modulus and loss of the anti-corrosion layers at the range of -100~40 °C were tested by the dynamic mechanical analysis (DMA), and the stress of the anti-corrosion layers at low temperature (-40 °C) was calculated. The average thermal expansion coefficient of the anti-corrosion layers in the range of -40~60 °C was tested by the thermomechanical analysis (TMA), and the value at room temperature was obtained, which was compared with the value of the steel materials. The failure accidents caused by raw materials and anti-corrosion layers due to the quality problems, as well as aging and damage of anti-corrosion layers are excluded. The SEM results confirmed that the anti-corrosion layers with no obvious large-scale defects, there were microscopic defects less than 1 μm. At the low temperature (-40 °C), the storage modulus of the anti-corrosion layers is 2.58 GPa, and the corresponding stress is 23.99 MPa, which is higher than the tensile strength test value (22.21 MPa). The average thermal expansion coefficient of the anti-corrosion layers is 14.3×10-5/°C, which is higher than that of the steel material (1.2×10-5/°C). The high stress at low temperature (-40 °C) is one of the reasons for induced defects to cause cracks, and the huge difference in thermal expansion coefficient between the anti-corrosion layers and the steel material is another reason for that.