Significance and Use
The data obtained by this test method are useful for establishing stress versus failure-time relationships in a controlled environment. The long-term strength (LTS) is determined primarily for materials used in molding applications. The LTS categorized in accordance with Table 1 of ASTM D2837 is known as the SDB (strength design basis).
Note 1—These SDB values will be published in PPI TR-4 for materials used in molding applications only.
The test method can also be used on an experimental basis for pipe-grade materials as an indicator of stress-rupture performance. The long-term strength or SDB values obtained by this test method are not intended to replace the HDB determined for pressure pipe tested in accordance with Test Method D1598.
In order to determine how plastics will perform in pipe fitting applications, it is necessary to establish the stress-failure time relationships over four or more decades of time (hours) in a controlled environment. Because of the nature of the test and specimens employed, no single line can adequately represent the data, and therefore the confidence limits should be established.
Note 2—Some materials may exhibit a nonlinear relationship between log-stress and log-failure time, usually at short failure-times. In such cases, the 105 – hour stress value computed on the basis of short-term test data may be significantly different than the value obtained when a distribution of data points in accordance with Test Method D2837 is evaluated. However, these data may still be useful for quality control or other applications, provided correlation with long-term data has been established.
Scope
1.1 This test method covers the requirements to determine the time-to-failure of thermoplastic resins for piping applications by uniaxial loading of a grooved tensile test specimen. This grooved tensile specimen achieves a multi-axial stress condition, which mimics the stress condition found in pressurized solid-wall plastic pipe. The ratio of the stress in the axial direction to the transverse direction approximates that for a pressurized solid-wall pipe specimen.
1.2 It is intended that the data generated on these specimens be analyzed according to the methodology set forth in Test Method D2837 to generate a long-term strength design value for the material.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
