Ingemar Bjorklund, Trygve Blomster, Ilija Radeljic
Papers # 2016 Berlin
The S-bend installation method is the reason for the successful worldwide development of the market for marine PE pipelines over the last 50 years. Small and medium sized PE pipes can safely be installed using the S-bend installation method; however, difficulties increase as pipe sizes increase. In order to ensure a safe installation of pipes larger than 2000 mm, PE pipe and resin manufacturers must contribute to the development of the method, and supply expertise to contractors and the end user, as they did in the 1960s and 1970s when the S-bend method was originally developed. The technical support given to contractors and end users will be of utmost importance for the further growth of the market for large diameter marine PE pipelines.
PE pipes have been used for marine pipeline installations since the early 1960s. Today, solid wall PE pipes are by far the most frequently used material for marine pipelines. The main reason for the successful development of the market is the use of the S-bend installation method. This method involves floating the air-filled PE pipeline on the surface of the sea, and then submerging it by filling it with water from one end. During installation the pipe is significantly bent, and subjected to stresses and strains. For most pipelines, the stresses experienced during installation will be far higher than those experienced for the remainder of the pipe’s service life. Typically, the axial stress in a solid wall PE pipe may reach 6 -12 MPa during the installation phase. A solid wall PE pipe can accommodate such stresses, but for thin walled pipes (SDR>26) a significant out of roundness will occur when the pipe is bent. The out of roundness will highly influence the kinking risk for the pipe when bent. Today, solid wall PE pipes are manufactured in sizes up to 2500 mm in diameter, but the extrusion technology and PE material properties set limits for the wall thickness. These limits mean that large diameter pipes must be made to relatively high SDR ratings, and thus are more sensitive to kinking than smaller, more thick walled pipes. In order to safeguard the S-bend installation and avoid kinking failures of the pipes at installation the pipe supplier must be able to calculate the bending at installation, and be able to give technical support to designers, contractors and end users.
This paper highlights the experience of the S-bend installation method, how pipe bending can be calculated, and the necessity of accurate E-modulus data for PE100 materials at high stress levels. The latter is important for assessing safety margins at Sbend installations, and enables the pipe manufacturers to provide better design support to further develop the market for large diameter marine PE pipelines