Overview
Until recently, little thought was given to the concept of whether a plant had been over-designed. In many cases, the stress engineer could not change the plant design unless the analysis indicated a serious problem. If a plant layout passed the stress and equipment load analysis checks for the high temperature lines, many times the design was considered to be good enough. Adequacy was, and is, often accepted in place of excellence.
Operating companies are beginning to realize that over-design not only increases capital expenditures, it also raises operating costs. In today's highly competitive marketplace, cost savings, efficiencies, and quality designs can make the difference between a plant's success or failure.
CAD to Stress Integration
One of the most significant advances in plant design software technology is the integration of plant design CAD systems and stress analysis software. For example, several companies have taken advantage of the interface between AutoPLANT for plant design and AutoPIPE, piping stress analysis software. Currently, 90% of the data needed for piping stress analysis can be transferred directly from the AutoPLANT model into AutoPIPE for analysis.
This new technology not only saves time, it also allows for a "snapshot" or "thumbnail" analysis at the preliminary design stage. Designers that create plant layouts can now perform "run-of-the-mill" analysis in order to identify potential problems and evaluate alternatives early in the design cycle when changes can still be made more easily. The automated interface ensures that the plant CAD models and the stress models are identical. In this type of environment, expert stress analysts generally serve as trainers and mentors, helping designers use analysis tools effectively. With the designers performing most of the analysis workload, the expert analyst is able to spend more time on more complex and sophisticated analyses, which will improve design.
Outside the plant engineering marketplace, this kind of team approach to design is the modus operandi for most successful manufacturing companies. From bicycles to baby bottles, manufacturers of all types have made analysis tools an integral part of the design process. In response, CAD software vendors and stress analysis software developers have moved full speed ahead to integrate their technologies, thereby helping their customers improve design quality, save money, and shorten design cycles.
In recognition of the synergy between CAD and stress analysis, Parametric Technology, a major player in the mechanical CAD software marketplace, purchased Rasna Corp., a market leader in stress analysis optimization software, for an eye-opening 37 times earnings. Other mechanical CAD software vendors have rushed to integrate their software with leading general-purpose stress programs such as Ansys and Cosmos in order to compete.
However, engineering companies involved in plant design have generally been much slower in taking advantage of the CAD-analysis integration technology and have mostly not made analysis an integral part of the design process. This is partly the fault of the plant design CAD software vendors. Until recently, few plant design CAD systems offered any interface at all to stress analysis. Early interfaces to stress analysis provided difficult to use interface tools with limitations on the data that could be extracted.
Given the improvements in this technology, however, it is surprising how few plant engineering companies have integrated piping stress and structural analysis with CAD. As a result, only minimal piping stress analysis and structural analysis are often performed, typically later in the design cycle. In fact, most piping in a process plant is not analyzed at all except for the high temperature, large diameter piping. Dynamic analysis for consideration of upset conditions (such as resonance, waterhammer, slug flow, etc.) is almost never performed until a problem occurs. An engineer with a major plant engineering firm in Houston claim 90% of all their piping stress analyses involved the analysis of only one operating case scenario. No doubt expensive over-design has been the trade-off for a lack of analysis.
If a plant design CAD system such as AutoPLANT allows automatic transfer of piping and structural steel model data directly into the stress models, more analysis can be performed using fewer man-hours and earlier in the design cycle, to optimize the design while meeting or exceeding safety and reliability requirements. Companies that are slow to recognize the benefits of this technology will ultimately pay the price!
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