Description:
<jats:p>Construction materials, traditionally used in process equipment, are today
successfully replaced by composite materials. Hence, many pipes are made of
these materials. The subject of this study was the influence of liquids on
the state of stresses and tensile strengths in the longitudinal and
circumferential direction of glass-polyester pipes of 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
(the ultimate tensile strength and the modulus of elasticity) 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 material composite
studied. Subsequently, the specimens were soaked in alkaline solutions:
sodium hydroxide (strong alkali) and ammonium hydroxide (weak alkali). These
solutions were selected because of their considerable difference in pH
values. The specimens and rings were left for 3, 10, 30 and 60 days in each
liquid at room temperature. Then, the samples were tested on tension by the
standard testing procedure. A comparison of the obtained 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 sample 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.</jats:p>