Abstract

In insulation joints, elastomeric U-shaped monolithic seals (UMSs) are replacing O-ring systems because of their enhanced sealing capabilities for the oil and gas industries. UMSs are compressed axially during assembly and radially when pressurized in operation. The reliability of UMSs due to the displacement imposed during assembly and the internal pressure in operation is influenced by the axial compression ratio, thickness ratio (TR), and geometric complexity. In this study, the hyperelastic behavior of elastomeric UMSs under axial and radial compressions is investigated using axisymmetric finite-element analysis. Twelve examples of UMSs with three geometric restraints (open grooves on both sides (type 1), an open groove on one side only (type 2), and no groove (type 3)) and four thickness ratios (TR = 0.25, 0.50, 1.00, and 1.50) are evaluated. To analyze nonlinear elastomeric materials, neo-Hookean constitutive equations are applied and the UMSs are considered as being a nearly incompressible hyperelastic material with a Poisson’s ratio of 0.499. The failure and detachment risks of UMSs are analyzed in terms of the equivalent stress, gap distance, contact pressure, and strain energy density. It is advantageous that the smaller the TR, the smaller the stress distribution. However, the generation of broader detachment regions is observed. Type 1 symmetrically shows the lowest stress distribution and the smallest detachment region, whereas type 3 symmetrically shows the highest values. Type 3 (TR = 0.25) shows the broadest detachment region in the arc-length range from −15.7 to 15.7 mm, whereas the largest gap of 0.7 mm is observed in type 2 (TR = 0.5). For all types, the detachment region disappears completely at TR = 1.0 or higher, which implies that full sealing is occurring. The average contact pressure increases exponentially during axial compression (in assembly) and linearly during radial compression (in operation). The largest contact pressure of 31.5 MPa is observed in type 3 (TR = 1.5), while the lowest is observed in type 1 (TR = 0.25). As for the strain energy density, type 3 at TR = 0.25 shows the largest increase in the strain energy density with 1.75 MJ/m3, while type 1 shows the most stable values of all cases. In conclusion, the lowest risk of failure of a nonlinear hyperelastic UMS was investigated numerically with minor equivalent stress and detachment region with higher contact pressure, which can be taken into account to ensure the reliability of the UMS.

Highlights

  • An unexpected failure of the sealing system in an insulating joint can create serious problems in unexpected failure of the sealing an insulating installed joint can create serious problems in oil and gasAn pipelines.Insulating joints are system criticalincomponents in underground natural-gas oil and gas pipelines.Insulating joints are critical components installed in underground natural-gas and oil pipelines

  • The U-shaped monolithic seals (UMSs) housed in its surrounding parts was subjected to axial compression by the displacement of the pipe pups

  • Mises equivalent stress distributions with the deformed shape of the UMS due to the applied axial displacement up to 8 mm from the left and right pipe pups, which corresponds to a compression ratio of 40%

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Summary

Introduction

An unexpected failure of the sealing system in an insulating joint can create serious problems in unexpected failure of the sealing an insulating installed joint can create serious problems in oil and gasAn pipelines.Insulating joints are system criticalincomponents in underground natural-gas oil and gas pipelines.Insulating joints are critical components installed in underground natural-gas and oil pipelines. Installed at pipelines appropriate intervals between the pipes, insulation joints canbetween reduce pipe amount ofoil current flowing in the and maintain the electrical potential difference the amount of current flowing in the pipelines and maintain the electrical potential difference sections, thereby preventing pipe corrosion due to electrical or chemical reactions and increasing the between pipe sections, thereby preventing pipe corrosion due to electrical or chemical reactions and serviceincreasing life of pipelines. They can provide electrical protection from the riskfrom of explosion the service life of pipelines

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