The expansion joint that was the subject of this work is a 60in pipe diameter joint, which will be attached to a flue gas pipeline in a Brazilian refinery. The structure was designed for an environment of 750oC flue gas temperature, 2.75 barg internal pipe pressure as well as sustaining pipe thrust end loads and pipe torsional displacements. The structure is manufactured from stainless steel.
Senior Flexonics required a finite element analysis to be conducted for the expansion joint in order to provide evidence of thermal and structural integrity of the design under the various loading requirements of pipe temperature, internal pressure, end thrust and torsion. A finite element model was produced for both transient thermal and non-linear contact stress analyses. The analyses were conducted with the ANSYS general-purpose finite element analysis program.
A finite element model was produced for both transient thermal and non-linear contact stress analyses.
The geometric model of the expansion joint was constructed within the ANSYS pre-processor. Advantage was taken of symmetry in the joint. Therefore, a quarter model of the joint was constructed.
Having created the geometric model the finite element mesh was created with the ANSYS automatic swept mapped meshing capability. The finite element mesh was initially created with the 20-noded thermal SOLID90 element and latterly these elements were changed to the 20-noded structural SOLID95 element. The active degrees of freedom in the SOLID90 element is temperature and for the SOLID95 element translatory displacement in the x, y and z directions.
The transient thermal analysis solves for the temperature degrees of freedom as a result of both conduction and convection effects. The effects of radiation were ignored. Non-linear temperature dependent material data for thermal conductivity were incorporated into the analysis.
Having obtained the temperature distribution, due to the thermal effects, this data was used along with the other operating conditions in a non-linear contact analysis. Non-linear contact was used to simulate the interaction between the various parts in the expansion joint assembly. Non-linear temperature dependent material properties were used during this simulation.
The design team at Senior Flexonics were very impressed with the response time of the analysis to verify their conceptual designs. The project engineer said: "The analysis provided us with an accurate representation of the behaviour and stresses of the expansion joint during operation. This enabled us to reduce material cost, weight and perform minor modifications prior to manufacturing."
As these components are largely manufactured to order it is not viable for the company to conduct physical testing of high-value but low-volume designs. However, the use of ANSYS allows engineers to conduct simulations of their conceptual design models in a cost effective manner.