Inline IR-Cured XLPE Technology for Flexible Pipes

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractTo day Silane cross-linked HDPE is used as pressure sheath in unbonded flexible pipes for the offshore industry. This method is based on a two step process where the first step is the extrusion of the sheath and the second step the cross-linking using hot water or steam. However, this process is time consuming and it is difficult to cross-link the crystalline part of the polymer. Furthermore, it is required that the flexible pipe be finished with end fittings before hot water can be circulated in the pipe. Finally, it will not be possible to verify the actually obtained cross-linking of the pressure sheath unless re-terminating an end fitting.NKT has developed a new method to cross-link HDPE pressure sheath in flexible pipes using Peroxide in combination with infrared radiation (IR). This method is unique in the sense that it is an inline process where extrusion and cross-linking is done in one step. Thus, it is possible to measure the degree of cure as soon as the material has cooled down and no additional process is needed. Therefore, upon finalizing the extrusion of the pressure sheath test samples can be taken from the pipe to document the degree of cross-linking which can be as high as 90% compared to typically only 75% for the Silane-based process.The IR-cured XLPE technology will be described in this paper and results from the qualification programme which has been carried out according to API Spec 17J [1] and ISO 13628-2 [2] will be addressed.

Qualification of Polymer Materials for High Pressure CO2 Flexible Pipe Structures

“…The manufacturing process for XLPE inner liner is unique since it is based on a peroxide cross-linking process with inline curing [3], [4]. The cross-linking process of HDPE is initiated by free radicals creating very stable covalent carbon-carbon bonds between the polymer chains.…”