Investigation on mechanical behaviour of pigging robot passing through T-type tee pipe in subsea automatic launching system

Pipelines serve as the primary method for offshore natural gas transportation, where pigging operations are essential for maintaining pipeline efficiency and safety. To enable pigging robot launching and receiving between offshore platforms and subsea manifolds through a single pipeline, subsea automatic pigging robot launchers are typically employed, with the offshore platform functioning as the receiving terminal. This approach facilitates pigging operations without interrupting production, thus enhancing economic benefits. This study used finite element simulation to investigate the mechanical behaviour of an monoethylene glycol (MEG) fluid-driven pigging robot as it traverses a T-type tee without interrupting production. A Coupled Eulerian-Lagrangian (CEL) method was used to develop a fluid-structure interaction (FSI) simulation model, analysing the motion of the pigging robot in natural gas production pipelines as they traverse T-type tee under MEG driving conditions. The mechanical behaviour of hyperelastic polyurethane was simulated using the third-order Ogden model, while the fluid response was characterized by the Mie-Grüneisen equation of state in a linear Us-Up form. The results demonstrate that the pigging robot’s average velocity increases significantly with rising inlet pressure within the 0.15–0.25 MPa range. A distinct reduction in frictional resistance occurs when the inlet pressure reaches 0.3 MPa. This study established a FSI simulation model using the CEL method to evaluate the effects of different launching pressures on pigging robot movement through tee junctions. The findings provide references for pigging operations in natural gas pipelines.