Software helps ensure success of mixed-element design

Duren, Germany--In some petrochemical applications, butterfly valves control the flow of product. If a valve fails, the pressure downstream could rise to dangerous levels, potentially resulting in a catastrophic failure of a component. Workers' lives, millions of dollars, and public safety may be at stake.

Because of this risk, engineers at Zimmermann & Jansen need to ensure their valve designs will not fail in operation. "We depend on software from Algor Inc. (Pittsburgh, PA) to analyze how our valves will stand up under real-world conditions," says Michael Lemeshev, an engineer at Zimmermann & Jansen. "The cost of building and testing valve prototypes would be exorbitant because they are large and composed of expensive material," he adds.

Each butterfly valve has two plate-like structures (disks) attached along the rims. A shaft extends to opposite ends across the center of the disks. The valve fits into a pipe as a cross section, and rotates on the axis of the shafts. The valve's shell must withstand pressure in the flow line. The valve must also regulate pressure of the product moving toward the downstream components, and withstand temperatures up to 1,450F.

The geometry of the valve makes preparing a model for analysis difficult. The large shells of the disk are relatively flat, but the shaft and reinforcing blocks where the shaft meets the disk are solid pieces of material. "To obtain the most accurate analysis results, we need to use two different types of elements: plate/shell elements for the disk portions, and eight-node 'bricks' for the shaft and blocks," explains Lemeshev.

After making a wire frame model in AutoCAD, Lemeshev creates the surface meshing in Supersurf software. With the disk complete, Lemeshev creates the shaft of the valve using Algor's Superdraw II software. The shaft is then added to the block. To create the elements for the shaft and blocks, he uses Algor's Hexagen software, which automatically produces a solid mesh of eight-node "bricks." Lemeshev then uses Algor's COMBSST software to combine the brick and plate/shell sub-models into one model, and runs an initial analyses of the valve. "Having Algor software at my disposal has changed the way I design and test butterfly valves. The time it takes me to analyze a valve design has significantly dropped since I began using it,"says Lemeshev.