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 D 2837 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 D 1598.

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 D 2837 is evaluated. However, these data may still be useful for quality control or other applications, provided correlation with long-term data has been established.