Lifetime prediction pump rods

Pumping rods are central components of pumpjack systems in crude oil production. They move in an up and down cycle to pump the oil out of the bore hole using a piston mechanism.

During operation of the pump rod, corrosion-related damage occurs which, depending on the notch geometry, can significantly reduce the lifetime of the pump rods.

Pumpstange 2

As part of the project, the influence of corrosion-related notches on the lifetime of pump rods was investigated using the finite element method (FEM) in order to calculate the local stress concentrations at different notch radii and shapes. This made it possible to identify critical notch shapes and take suitable steps to increase the lifetime.

The determination of the notch factors was based on the assumption of a uniaxial stress condition. During operation of the pumping rod, in addition to the oscillating tensile load due to the upward and downward movement and the dead load, which is significant for boreholes with a depth of 2000 – 3000 m, bending stresses can be overlaid due to the borehole geometry (boreholes with deflection radii). Furthermore, the rod guides of the pump rod and the geometry of the screw connection between two pump rods (couplings) cause local stress increases. These two influencing factors were integrated into a 3D FE model of a 50 m long drilling section and the effects on the lifetime were investigated.

The picture on the left shows the overall model in the area of a pump rod deflection (black line), as well as a detail with the corresponding rod guides and couplings.

Ansprechperson

krach neu web

Dr. Wolfgang Krach

+43 1 974 89 91-11