In response to a growing industry trend toward corrosion- and maintenance-free natural-gas valves, Kerotest designed POLYBALL™™ 1/2" to 12" standard- and full-port valves made of medium- and high-density polyethylene. The valves also had to meet or exceed ASME B16.40, ASTM D-2513, and the U.S. Code of Federal Regulations (CFR), Part 192 standards.

Kerotest needed to trim excess material from the valve design while maintaining consistent structural integrity. An initial design was created with a standard outside diameter at the valve ends, which never changes because it must match standard pipe diameters. The inner and outer diameters of the valve center section, however, must be optimized in order to find a wall thickness that withstands necessary pressures. The company's goal was to create a valve to withstand higher pressures than the current industry standard - up to 125 PSI.

Figure 1. The Kerotest POLYBALL™ line includes 1/2'' to 12" standard- and full-port valves made from medium- and high-density polyethylene.

The valves were modeled in various sizes in a computer aided design (CAD) program. In addition to creating a full assembly for each valve, a simplified model was created representing only the parts that were of engineering interest. Sections of pipe were added to each end to simulate how the valve would be attached to a piping system. ALGOR's InCAD technology was used o capture the geometry from the CAD model, and a 3D solid finite element mesh was created.

Radial pressure loads were applied to the inside surface of the valves, and tensile loads were applied to the ends of the pipes. To facilitate the application of tensile loads, the ends of the pipes were modeled as if they were closed. Material properties obtained from the resin manufacturer were then applied. A linear static stress analysis was performed, and the stress results were viewed within ALGOR's FEMPRO Superview IV Results environment.

Figure 2. Kerotest engineers modeled the valve in Pro/ENGINEER and used ALGOR Linear Static Stress Analysis results to optimize parameters such as wall thickness.

The same process was used on models of various valve sizes. The findings were reviewed, and parameters such as wall thickness, shape of the transition into the piping, and the inside shape of the valve through which the gas flows were all optimized. The changes made reduced excess material and high stresses. Kerotest performed extensive prototype tests to ensure that the valves met the safety codes required for natural gas components. The valves are manufactured out of polyethylene, requiring the production of molds. FEA enabled the company to create a robust design that met all prototype testing requirements. The POLYBALL valves were released to market last year.

This work was performed by Kerotest Manufacturing Corp. of Pittsburgh, PA, in collaboration with ALGOR, Inc., also of Pittsburgh. For more information, contact Julie Halapchuk of ALGOR at 412-967- 2700, ext. 3029; e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.; or visit www.algor.com.