Determining the creep behavior of thermoplastic pipes

ISO 9967

Underground pipes are subject to largely constant compressive loading following installation. Experience shows that increases in deformation have largely ceased after a relatively short time.
From a technical point of view the creep test to ISO 9967 is based on the standard for determination of ring stiffness, ISO 9969. As in practice deformation has ended after two years at the most, sufficiently accurate property values can be achieved by measurements performed over a period of 42 days.
During the test a section of pipe is loaded with a constant radial force at a level which produces a ring cross-section deformation of 1.5%. Ring deformation under this load is read off at defined intervals. With modern testing machines, however, continuous recording of ring deformation is now also possible.
The assumed deformation after two years is calculated by extrapolation of a regression line of the measured values. With ZwickRoell testing machines this is carried out by testXpert III testing software, which also displays the logarithmically scaled deformation-time diagram. Intervention by the operator is not therefore necessary during measurements.

ISO 899-2	Flexural creep with three-point loading
ISO 7684	Glass-reinforced thermosetting plastic (GRP) pipes - determination of creep factor under dry conditions
EN 761	Glass-reinforced thermosetting plastic (GRP) pipes - determination of creep factor under dry conditions
EN 1862	Glass-reinforced thermosetting plastics (GRP) pipes. Determination of the relative flexural creep factor following exposure to a chemical environment