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  1. IDAC
19 January 2010

IDAC Provides Structural Elastic Analysis of Gas Vessel Design

Independent UK-based Zeta-pdm offers multiphase separation equipment often comprising of state-of-the-art separation internals. As part of their services for the oil and gas, water and petrochemical industries, the company offers flexible and entire solutions for separators, gas scrubbers, flash drums, degassers, slug catchers and enhanced oil recovery systems.

With a clientele that spans the globe, Zeta-pdm has sound expertise derived from an extensive background in production facilities troubleshooting, de-bottlenecking and revamping. Boasting an acknowledged capacity to provide operational designs, along with after-sales support, Zeta-pdm is committed to the “whole-life” concept.

Drawing from experience that has serviced names like BP, Chevron, Shell, Statoil and Maersk, to name a few, Zeta-pdm supplies equipment on applications for onshore and offshore static platforms together with those specifically developed for semi-submersibles, TLPs and FPSOs.

Research and development into new products and solutions is an essential part of the motivating force behind the company. In addition to design solutions, Zeta-pdm also provides clients with simulation services such as computational fluid dynamics (CFD) and finite element analysis (FEA).

FEA on a compressor suction scrubber vessel design

IDAC was approached by Zeta-pdm to conduct an independent FEA on a compressor suction scrubber vessel design. The primary objective of the analysis was to assess the structural integrity of the assembly under its own dead weight. The geometry consists of a vertical vessel, four holding clips and a support ring.

The inlet device rests on four clips while the gas outlet system is supported on a fully circumferential ring. Zeta-pdm was most interested in obtaining the von-misses stresses acting on the structure and total deformations caused due to these stresses.

The analysis was performed using ANSYS DesignModeler for the geometry
modifications and parameterization, while ANSYS simulation was used to set
up, solve and post process the linear static analysis.

Analysis method

The inlet device and the gas outlet system are not explicitly modelled, but instead point masses were added at their respective centres of gravity. Using ANSYS’ contact
technology, welded contacts were modelled in the geometry using fully bonded

To ensure that the stresses in the region of interest were most accurately
accounted for, the geometry was split in four different regions, each using a slightly
different mesh setting. A finer mesh was used in the area near the clips and the
supporting ring. The entire model was meshed using 3D higher order hexahedral and
solid shell elements.

Given the simplicity of the structure and the relative small mesh count as a result, a decision was made to model the entire model instead of using any natural planes of symmetry. To also reflect operating conditions accurately, IDAC used a combination of fixed, sliding and frictionless supports on the entire structure. For example, the bottom of the vessel sits on a skirt during daily operations. As a result, fixed supports were used on these surfaces.

In this particular analysis, hydrostatic and buoyancy forces were neglected, as they were determined to be minor in comparison to the operating loads. Gravity, however, was taken into consideration, as the assembly was being analysed under its own dead weight.

Upon review of the results, it was found that the maximum stresses do occur in the region of the pin supports. However, the design did not need to be edited as both the total deformation and maximum stresses were well under the yield limit of the material. As the material did not pass into the plastic part of the stress-strain curve,
the design has been verified for use in operation.

Design benefit

Given the successful completion of this project, Zeta-pdm and IDAC have now worked on numerous other projects together, where an independent analysis is sought, that cover varying designs and operating conditions. The use of finite element analysis in varying scenarios and under different loads has allowed Zeta-pdm to gain further confidence in their designs and also investigate ways for reducing manufacturing costs and turn-around times.

Paul Harker of Zeta-pdm says: “Working with IDAC has helped us to verify our designs, and has provided us with valuable feedback to assist us with further development. Also, the turnaround period from initial enquiry to completed report, and “quality of service” has been very impressive.”

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