technical paper | Lifetime testing
Table 5: Tensile testing of exposed and unexposed samples Specimen
Stress at Exposed FJ Unexposed FJ Exposed foam
Average StDev
Average StDev
Average StDev
Unexposed foam Average StDev
Yield (MPa) 15,96 1,57
17,14 0,35
16,32 3,14
12,30 1,74
with the upper and lower measurement tolerances (1% level) included for reference. As can be seen, the data points generated from the exposed material lie within the design envelope. The gradient of the relationship of k-value with temperature is different for the two data sets. The reason for this departure is that the design curve is generated on a large number of precisely machined, stress relieved samples, whereas the data points from the retrieved material were generated on non-stress relived material in order to avoid infl uencing the results.
Some warpage of non-stress relieved samples is
expected at elevated temperatures. This leads to imperfect thermal contact in the experiment and artifi cially low values.
Conclusion
From the analysis performed there is no evidence of signifi cant degradation of the materials used in the Thermotite polypropylene foam applied on pipes used in
15,0 3,28
18,24 1,11 12,8 7,85 12,3 1,65
Elongation at Yield (%)
Stress at
Break (MPa) 14,86 0,97
19,42 1,18
15,48 2,99
12,48 1,61
Elongation at Break (%)
50,41 7,53
47,70 20,62 27,24 11,28 31,67 11,02
the Tordis project in 1992 and subsequently used in the subsea environment for 20 years. In particular: GPC and MFI measurements indicate that no signifi cant change in the build-up of the materials at the molecular level has taken place and the results of IOT measurements also confi rm that the material remains adequately protected from potential oxidative effects; Mechanical property measurements confi rm that no signifi cant change in mechanical properties has taken place during the 20 years of exposure; Thermal conductivity measurements made on exposed material are within the range used as the basis for thermal system design for the end of life density reached. It is clear from the data presented that the Thermo- tite polypropylene foam system used on the Tordis fi eld has performed excellently during 20 years of service and even after this time is showing no signifi cant indications of property change.
In the absence of change it is impossible to predict a failure case and the only lifetime conclusion that can be reached is that the coating system, under the conditions applied, can be expected to display a lifetime in excess of the initial 20 year design.
About the authors:
This technical article is based on a paper titled ‘Long term ageing of polypropylene foam; results of testing performed after 20 years of exposure in a subsea environment’, which was presented by Bredero Shaw vice president of fl ow assurance products Adam Jackson at the Oilfi eld Engineering with Polymers 2012 conference. The full set of conference proceed- ings, including all 21 presentations, is available here
http://bit.ly/10TBKNY
Figure 4: k-value of foamed BA202E after subsea exposure for 20 years 26 PIPELINE COATING | May 2013
The paper was co-authored with E Simonsen at Bredero Shaw AS, T Stark and R Nixon at Borealis Group AG, and B Melve and D Ali at Statoil ASA.
www.brederoshaw.com
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