Effect of alkaline and acidic solutions on the tensile properties of glass-polyester pipes

Abstract

The influence of liquids on the state of stresses and tensile strengths in the longitudinal and circumferential direction of glass-polyester pipes is the subject of this paper. The pipes were manufactured in Corporation "Poliester" Priboj, and had a definite structure and known fabrication process. These analyses are of great importance for the use of glass-polyester pipes in the chemical industry. The tensile properties were tested and determined for specimens cut out of the pipes; flat specimens for the tensile properties in the longitudinal direction and ring specimens for the tensile properties in the circumferential direction. First, the tension test was performed on virgin samples (without the influence of any liquid), to obtain knowledge about the original tensile properties of the studied composite material. Subsequently, the samples were treated by water, as well as alkaline and acidic solutions: sodium hydroxide (strong alkali), ammonium hydroxide (weak alkali), phosphoric acid (weak acid) and nitric acid (strong acid). The solutions were selected because of considerable differences in their pH values. The pipe segments were exposed to each liquid for 3, 10, 30 and 60 days, at room temperature. Then the specimens cut from these segments were subjected to tension testing by the standard procedure. A comparison of the results was made based on the pH values of the aggressive media in which the examined material had been soaked, as well as based on the original tensile properties and the number of days of treatment. Micromechanical analyses of specimen breakage helped in the elucidation of the influence of the liquids on the structure of the composite pipe and enabled models and mechanisms that produced the change of strength to be proposed.