Creep Behaviors of HDPE Applied in Composite Flexible Pipes
DAI Zhi-shuang, WANG Hong-xuan, LU Cheng-lin, SONG Ping-na, CHEN Xing, YUAN Xiao-yan
1. School of Material Science and Engineering, Tianjin University, Tianjin 300072, China; 2. Neptune Offshore Engineering Development Co.,Ltd., Tianjin 300384, China
Abstract：The creep of inner liner material for subsea composite flexible pipe may result in the over-reduction of its thickness, which may consequently lead to structural failure. The radial compression stress of high-density polyethylene (HDPE) is studied by using finite element analysis (FEA) method. Under 20 MPa inner compression load, the radial compression stress is 11 MPa when the interaction of structural layers is ignored, while the radial compression stress is 19.9 MPa when the real contact status between HDPE and flat steel is considered. The compression creep properties at 11 MPa under different temperatures are measured. According to the timetemperature equivalence principle, the predicted compression creep deformation of HDPE during 30 years at 60 ℃ is 17.5%. A groove clamp with a gap span for side restrained compression creep is designed, and the side restrained compression creep properties under different temperatures are investigated. The results indicate that the reduction of thickness of HDPE during 30 years at 60 ℃ is 6.6%. The filling volume in the gap span can be calculated according to the thickness of inner liner and the size of gap span of the armour layers, which can be the guidance of construction design for the flexible pipe.
