Senior Flexonics is owned by Senior plc. Flexonics is Senior's clear global leader in the design, manufacture and marketing of thin walled flexible tubing and related high technology products to the world's major aerospace, automotive and specialised industrial companies. Senior Flexonics strives to provide creative precision engineered solutions of the highest quality, supported by immaculate and committed service, to meet the most demanding technical and environmental needs of its customers.

The company is based in the UK and has operations worldwide. This particular piece of consultancy work was conducted for the Expansion Joint Division based in Waltham Cross in the United Kingdom.

The expansion joint that was the subject of this work is a 60” 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 bar internal pipe pressure as well as sustaining pipe thrust end loads and pipe torsional displacements. The structure is manufactured from ASTM A240 GR 304H stainless steel 18Cr-8Ni.

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 Revision 5.5 general-purpose finite element analysis program. The photograph above illustrates the construction of the expansion joint.

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. A graphic showing the temperature distribution obtained from the analysis is shown to the right.

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 resulting displacement and stress contour plots are shown below. All the analyses were run using Intel Pentium based PC’s.

The design team at Senior Flexonics, led by their Project Engineer Nadeem Nuruddin, was very impressed with the response time of the analysis to verify their conceptual designs. “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”, says Nadeem.

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. The company now uses the ANSYS DesignSpace finite element analysis system, embedded within their computer aided design system Mechanical Desktop from Autodesk, to conduct basic simulations of their conceptual design models.