Subsea composite flexible pipeline plays a vital role in the offshore oil and gas transportation process.Heat sources and fluid ingress in the flexible pipes operating environment can cause aging and degradation of the liner material.Since material aging is related to the change in its dielectric constant,coplanar capacitance sensors can measure the capacitance in situ to reflect the degree of material aging.The measurement principle and finite element simulation analysis of coplanar capacitance sensors are presented,and the changes in the dielectric properties of two PE materials,i.e.,cross-linked polyethylene(XLPE)and temperature resistant polyethylene(PERT),during thermal aging,are investigated.For the aged and unaged samples,the parallel capacitance values are measured in the frequency range of 1 kHz～1 MHz and the effects of aging temperature,aging environment and aging time on the dielectric properties of the materi-als are investigated.The results show that the dielectric properties of PE materials increase slightly with the increase of aging tempera-ture,with a change of about 0.005 pF per 10℃.Accelerated aging in diesel-infiltrated environment has a greater effect on the dielectric properties of PE materials compared to water-infiltrated environment.The longer the accelerated aging time,the greater the dielectric properties of PE materials.The amount of change in XLPE is smaller than that of PERT under the same aging conditions,and PERT is more sensitive to changes in aging conditions.The experimental results prove the feasibility of the aging degree measurement method of PE materials proposed.
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