technical paper | Lifetime testing
Figure 3: Stress/strain curves for materials pre and post exposure
show there is no signifi cant change in the values measured and, as such, no loss in stabilization over the 20 year operation of the line.
Three-point fl ex testing Three-point fl exural testing was carried out in accord- ance with ISO 178. Due to the availability of suitably sized samples this testing was limited to the exposed material and the raw material properties are used for comparative purposes. As such, the degree of change from produced article to exposed article is not known. This comparison is, however, useful to address the overall change from raw material. From the data presented in Table 4 it is clear that there has not been any signifi cant change in properties from the initial that could be considered injurious to the performance of the insulation and fi eld joint systems.
Tensile test results Uni-axial tensile tests were performed on samples retrieved from both the exposed and unexposed specimens and in accordance with ASTM D638-03; type IV specimens, 50 mm/min at 21˚C. Tensile bars measuring 12 mm x 8 mm were used to reduce the impact of the foam structure on the ultimate elongation
24 PIPELINE COATING | May 2013
(elongation at break) of the materials. This is suffi cient for a comparative study. However, as can be seen in the right hand column in Table 5, the data is still associated with very high standard deviations relative to the mean, and graphical information is more informative. Tensile stress-strain curves are included for that reason later in Figure 3. From Table 5, it can be seen that the yield stress and
stress at break have reduced for both sets of samples post exposure. The fall is relatively small, but signifi - cant. As there is no evidence of chemical degradation in the polymer from the GPC study, this reduction may be a long term effect of the development of the thermody- namic phase/morphological structure of the material over time post-application. Elongation at yield is affected only slightly for both sets of samples over time, as is also the case for extension at break when the effects of premature failures are taken into consideration in the interpreta- tion of the results (Figure 3).
Thermal conductivity Thermal conductivity was measured for the exposed material and compared to the current design curve for BA202E at 660 kg/m3
. The results are shown in Figure 4,
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