Ilija Radeljic, Ingemar Björklund
Papers # 2018 Las-Vegas
Installations of solid wall HDPE pipes are becoming more difficult and riskier with the increase in diameter (OD2000+ mm), length of strings (1000+ meters) and reduction in the wall thickness (SDR26-30). To gain a better understanding of the limits of the final pipe assembly prior to the sinking, a laboratory tests in scale were conducted. The results show the effect of SDR class, weight blocks at different spacings and internal pressure. Based on the obtained results of the behavior of pipe assembly, a much better understanding of the limits was obtained. These results and subsequent conclusions can lead to optimization of the assembly and safer installations.
Solid wall HDPE pipes have been used for marine applications in Europe since the 1960- ties. The sizes of solid wall PE marine pipes have been steadily increasing over the years and the maximum size is OD2500 mm at the time of writing.
Large marine HDPE pipes (OD>2000 mm) are usually of SDR-class 26 or 30 and design inputs may differ. Since large diameter HDPE pipes have relatively high SDR ratings, it will in principle be the risk of buckling failures at the installation which will set the design limitations. S-bend submersions of large diameter HDPE pipes are critical and thus require detailed studies to ensure a safe installation.
Several factors are crucial for the optimum choice of marine HDPE pipe and these include: pipe SDR, type of HDPE raw material, ballast blocks setup and internal pressure. The stiffening effect of the ballast blocks during the bending is of special interest since most of the existing data is based on the research done in 1930s on metallic pipes.
A test rig for bending of HDPE pipes was therefore developed with the goal to simulate the bending of the pipes and extract data related to different pipe setups in a smaller scale. The test setup can include various combinations of the above mentioned factors and tests can be performed on many different combinations. The results can then be scaled up to simulate performance of large diameter HDPE pipes.
Obtained test results gave a better understanding of the failure mechanisms as well as pipe behavior under different setups. Data obtained was: stress and strain in the pipe, creep modulus, out-of-roundness at bending, speed of failure, buckling radius at bending, influence of SDR-ratio, stiffening effect of ballast blocks and others.
The conclusions based on the obtained test data are presented in this paper.
The value of this testing is of particular importance to the marine contractors since design limits of the pipe are better known and uncertainties are reduced, which could result in a better optimization of installation processes and cost savings.
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