FEA software can virtually test and predict how industrial equipment designs such as pressure vessels, rotating machines, structural skids and piping systems will respond toenvironmental and operational loads when installed at heavy-duty facilities such as offshore platforms and power plants. This software combined with engineering support services helped Tolpa Techincal Services, LLC (TTS) handle projects for Atlantia, BP, Chevron, General Electric, Kinder Morgan and Rohm & Haas.
The Hempstead, Texas, consulting firm specializes in piping, plant design and stress analysis for clients mainly in the offshore oil and gas compression industries. Hubertina (Tina) Tolpa, principal engineer and owner of TTS, uses finite element analysis (FEA) software from Algor, Inc. of Pittsburgh.
For more than 25 years, Tolpa has integrated FEA software and 3-D modeling applications for design, detailing and numerical control (NC) manufacturing with dimensional control. She has used many commercial FEA and piping analysis systems including SAP, TRIFLEX, T-Pipe, Nu-Pipe, ADLPipe and CAESAR. “We had been using CADRE Pro to import AutoCAD 3-D CAD models for beam and plate analysis. The need to perform code checks drove us to look into Algor.”
TTS explores innovative engineering work while Algor’s customer support team aids her when necessary. “We developed a custom method for fatigue analysis of Floating Production, Storage and Offloading (FPSO) gas compressor skids,” said Tolpa. “Our Algor support engineer showed us how to put together all the stress load components in one analysis so we could find the maximum stress. This technique along with the ability to calculate the peak velocity and vibration responses for rotating machines were significant technical breakthroughs.
“Stress analysis of piping systems is our core application,” continued Tolpa, “but, we’ve also expanded to include nonlinear stress, linear dynamics, and mechanical event simulation (MES).”
TTS used Algor‘s PV/Designer modeling extender to construct a plate-type model of a compressor discharge bottle and pulsation damper. “Using PV/Designer’s modeling wizard for pressure vessels, we built the bottle with its three inlets and single outlet flange in about 30 minutes,” said Tolpa.
TTS performed linear dynamic analyses of a base frame that supports a gas compressor and its drive motor. Such frames require anti-vibration media underneath a machine, helping the machine run quieter and longer because it limits the amplitude of displacements and thus reduce fatigue effects.
The bottle was subjected to an 800 psi internal pressure and to nodal forces and moments at the center of the outlet flange. Beam elements were added to the outlet flange in FEMPRO to provide the center point for the nodal loads.
A linear static stress analysis determined the stress distribution. “The analysis results let us determine the right placement of supports for choke tubes passing through the bottle’s elliptical heads,” said Tolpa. “Pulsation bottles are sized to reduce the frequency response to the acoustic standing waves inside the pressure vessel.”
In another application, TTS performed linear dynamic analyses of a base frame that supports a gas compressor and its drive motor. “This type of support skid can require anti-vibration media underneath a machine,” explained Tolpa. “A well-designed skid allows the machine to run quieter and last longer by limiting the amplitude of displacements and thus reduce fatigue effects.”
TTS first performed a Modal with Load Stiffening analysis to determine natural frequencies. The modal results were then used in a Frequency Response analysis with load curves representing lateral, unbalanced, trip-level, rotating machine forces to calculate the shaking forces and peak velocities. “The idea here,” said Tolpa, “was to subject the base to excitations at the natural frequencies as well as at the principal vibration frequencies of the motor-compressor system to ensure that the operating stress levels were acceptable.” The analysis results confirmed the anti-vibration performance of the skid design.
Through Algor‘s PV/Designer modeling extender, TTS constructed a plate-type model of a compressor discharge bottle and pulsation damper. The bottle has three inlets and single outlet flange. The bottle was subjected to an 800 psi internal pressure and to nodal forces and moments at the center of the outlet flange.
PV/Designer was used to generate a model of the cylindrical tank and then additional plate elements (for the saddles) were added in FEMPRO. High transportation loads were represented by components of acceleration simultaneously acting in three different directions.
“We applied the loads in steps, searching for yielding in the supports. The MES results showed how much permanent deformation can occur, important to the manufacturer because, sometimes inexpensive repairs are a better investment than exceptionally heavy and stiff supports.”
PV/Designer was also used to generate a model of the cylindrical tank and saddle plate elements.
Loads were applied in steps to find areas of yielding. The MES results showed how much permanent deformation could occur.
TTS used MES to determine the amount of local reinforcement needed at a structure’s lifting point. “The structure was typical of the kind of equipment bases or frame weldments that we deal with,” said Tolpa. “We worked iteratively by adding plate elements as reinforcement on the bottom, front or back and then performed the simulation and examined the results to see the effect. The goal was to have the final displacement match the initial displacement, that is, no significant permanent deformation.” In the final design, stress levels were controlled while the residual displacement, following a lifting cycle, was reduced to a negligible level.
Tolpa plans to continue using Algor software for upcoming TTS projects. “We would like to
incorporate two- and three-dimensional fluid flow analysis for the prediction of definitive acoustic and flow-induced vibration in piping systems.”
Algor Inc., Tolpa Techincal Services
www.algor.com
www.tolpatechnical.com
: Design World :
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