Pressure equipment design specialist achieves reliable results using Simcenter Femap with Nastran

Verifying designs of pressure equipment

Ener Consulting – Integrated Technical Services (Ener Consulting), founded in 2002 and with headquarters in Prato, Italy, offers engineering consulting to industrial customers. The company’s mission is to work with dedication, to stay abreast of technological developments and to provide customers with reliable results. One of the core services of Ener Consulting is the verification of pressure equipment, exchangers, piping and vessels in the oil and gas, power and chemical industries. Over the years, the business has been gradually extended to other industries, including pharmaceuticals, food, pulp and paper, waste processing and many others.

“The design of pressure equipment has evolved over time for the type and complexity of analysis, requiring high-level specialization and analysis skills,” says Stefano Milani, finite element modeling (FEM) manager at Ener Consulting. “Until the mid-1990s, finite element analysis was regulated by loose standards; there were just a few guidelines with no proven procedures. Customers did not have extensive know-how, and without clear procedures, virtually all verifications of pressure vessels were based on manual calculations.”

Automated analysis with Simcenter Femap

In the 2000s, the pressure vessel sector made quick progress with the introduction of standards and technology tools to automate analysis tasks. In this context, Ener Consulting started to collaborate with a Siemens Digital Industries Software Solution Partner for Simcenter 3D, Simcenter Femap with Nastran solutions.

After using basic FEA software that could not perform accurate analysis and delivered unreliable results, Ener Consulting identified Simcenter™ Femap™ with Nastran® software from Siemens Digital Industries Software as a suitable solution for implementing engineering, analysis and design services, and keeping up with the requirements of target markets.

“Traditional FEA tools that are integrated in 3D CAD software are very simple and intuitive,” Milani says, “but they have limited capabilities and are inadequate to execute accurate analysis in conformity with the strictest standards or in-depth verification. Simcenter Femap offers clear and tangible benefits in terms of speed, ease of use and reliability of results.”

Ener Consulting, developed an add-on module for stress linearization in Simcenter Femap. “With this plug-in, engineers need only a couple of clicks on the screen to get the results they are looking for,” says Francesco Palloni, business development manager at a Siemens Digital Industries Software Solution Partner.

“The end customers in our reference markets need to check products with a quick and reliable method,” Milani says. “Simcenter Femap helps us deliver the desired results following either a traditional approach or a more modern and advanced method.”

The benefits of nonlinear analysis

For the structural verification of pressure vessels, a traditional design-by-analysis approach (stress categorization) often results in component oversizing, because the conventional linear static analysis approach, while proven and easy to apply, is conservative. Engineers must also consider that the linear analysis procedure is articulated and time-consuming when applied to complex geometry. Currently, pressure equipment regulations allow the application of more accurate analysis methods, including using tools such as Simcenter Femap with Nastran for nonlinear calculations.

“The ASME boiler and pressure vessel standard, for instance, allows for checking pressure vessels using a nonlinear constitutive equation,” Milani explains. “On one hand, it forces the analyst to introduce a more complex constitutive equation in the mathematical model; on the other it requires a tool like Simcenter Femap with Nastran to solve this type of analysis,” Milani explains.

“The Simcenter Femap nonlinear approach offers a wider admissibility range,” Palloni adds. “With the same geometry and materials, a component can offer higher performance than those predicted with elastic linear analysis. Another benefit is obtained in the postprocessing phase, which is faster and immediate.”

The effectiveness of the Simcenter Femap nonlinear approach was proven in the case of a vessel with a flat bottom of variable thickness. When analyzed with a conventional linear analysis procedure, the component did not pass the elastic test; however, it proved suitable and compliant with applicable standards when it was checked with a nonlinear approach.

The linear approach to pressure vessel verification is constrained by significant design loads which, combined with linear stress analysis methods, results in the noncompliance of the design.Consequently, the initial geometry has to be modified or the load values have to be reduced to fit into the admissible range. Using Simcenter Femap with a nonlinear analysis approach requires more computing power than linear calculations and greater attention to plastic collapse, but offers a more immediate verification of the structural integrity of the pressure equipment.