Long-term durability of large-diameter polyester composite pipes

Introduction. The paper deals with relaxation and creep coefficients, long-term ultimate bending deformation under long-term exposure to moisture and chemically active environment (10,000 hours) of sewer pipes.

Materials and methods. 400, 1,200 and 1,400 mm diameter sewer pipes made of glass-reinforced polyester. A compressive load was applied to the specimen at a constant rate until a specific annular strain of (3.0 ± 0.5) % was achieved in (60 ± 10) s. The obtained specific annular strain was kept constant for 2 minutes, after this time the compressive load and annular strain were determined and recorded. The essence of the method is to load a test specimen, placed horizontally and immersed in water, at a given temperature, with a diametrically compressive load for a time during which the annular strain remains constant. The load is measured at specified intervals until 10,000 h is reached. According to the test results, the long-term specific annular stiffness and relaxation coefficient under the influence of moisture are determined in accordance with the methodology of GOST R 57008–2016. Two specimens shall be used for testing, unless otherwise specified in the normative document. Long-term specific ring stiffness and relaxation coefficient are the arithmetic mean obtained for two specimens.

Results. It was found that the performance characteristics (long-term ultimate bending deformation, relaxation and creep coefficients when exposed to moisture) of the investigated sewer pipes are determined by the specific ring stiffness and their diameter. For polyester pipes with initial ring stiffness of 5,000 N/m2 increasing their diameter from 400 to 1,400 mm leads to linear increase of relaxation coefficient (from 0.79 to 0.96) and decrease of long-term ultimate bending strain (from 0.84 to 0.75 %) when exposed to moisture during 10,000 hours.

Conclusions. The durability of the investigated sewer pipes made of glass-reinforced polyester exceeds 50 years.

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