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12 3.35 23C Reference Temperature 3.3 100,000 hrs 3.25 Log Stress (psi) 3.2 50 yrs 3.15 3.1 1161 psi y = -0.0459x + 3.3237 1242 psi 3.05 2 R = 0.9528 3 2.95 0 1 2 3 4 5 6 7 8 Log Time (Hrs) Figure 13. Creep rupture master curve. The Long-Term Stress-Crack There is no notch, so failures occur at naturally occurring (Stage II) Resistance flaws. The results relate to the real world. The long-term stress-crack resistance of pipe formulations containing recycled content will certainly be the life-limiting There have been three different long-term stress-cracking property for properly installed corrugated pipes. The con- tests proposed for corrugated drainage pipe in the past few taminants present can be locations for stress cracks to grow. years (1, 3, 4). These are commonly known as the BAM Test, How quickly a crack grows will depend on the size, shape, and the FL-DOT junction test, and the pipe ring test. hardness of a particle along with the inherent stress-crack resistance of the resin or resin blend. In fact, it would not be an The FL-DOT Junction Test understatement to say that the resistance to slow crack growth is the critical property for the success of this project. The FL-DOT has sponsored a research project to develop The success that the gas pressure pipe industry has had test methods to determine if corrugated pipe can have a service reducing failures can be used as a model for creating a testing lifetime of 100 years (3). One of the tests involves stress-crack protocol to evaluate recycled contentcontaining pipe blends. tests without a notch on specimens taken from the pipe. The For pressure pipe, the long-term strength is determined first particular location tested is the junction between the liner and (Stage I) at room temperature, then a validation test is per- the corrugation. FL-DOT Test Method FM 5-572 covers the formed at 80C or 90C to ensure that brittle crack growth performance of the test and FM 5-573 covers the procedures (Stage II) will not occur during the service lifetime of the pipe. for extrapolation of the test results. The junction test specimen Validation can be performed two ways; one based on the is an ASTM Type IV dumbbell, which has a reduced area that Rate Process Method (RPM) (11) and one based on Popelar is 1/4 in. 1.3 in. The advantages for this test include the bi-directional shifting (POP) (12). These two methods of TTS following: are described in detail in Appendix D, Section D.8.2. It is performed on specimens from the finished pipe. A test similar to the long-term hydrostatic strength test It is related to field failures. for pressure pipe is needed and will be sought as part of It is more sensitive to the manufacturing process than to this study. the basic resin. The best features of the long-term hydrostatic strength test The well known RPM for data analysis can be applied. include the following: On the other hand, some disadvantages are The finished product can be tested. The thickness control of the test specimen is excellent. The thinnest part of the test specimen is often not the The applied stress is uniform throughout the specimen. junction but the liner on either side.