In the long history of technical drawings, it has been necessary to depict designed objects in multiple views, simply because 3-D things cannot be effectively described in 2-D space. At minimum, usually two views of the objects are required — think of architectural house drawings, which typically include floor plans as well as side views.
Using models, the general arrangement of the facility to be built can be easily conveyed without relying on multiple drawings and documents. Whether virtual or physical, one major advantage of engineering models over engineering drawings is ease of visualization.
Prior to the now ubiquitous use of 3-D modeling software to generate engineering drawings for process plants, scale models were often constructed to assist for visualization of the designed facility.
All equipment, piping and structures in the plastic process plant were color-coded according to process fluid service and were built to plastic design model specifications and procedures provided by engineering companies in order to standardize and control the workflow and presentation of the plastic model. Handmade sketches, fully dimensioned and annotated, were made from the model and used for fabrication of pipe spools. After the model was completed in the office, it was shipped to the construction site where it was used as a reference to put fabrication spools together and to assist construction and installation planning.
While today’s 3-D computer-aided design (CAD) models are physically intangible and require powerful computer hardware and software to create and use, they offer many more useful features than their physical predecessors, such as automatic documentation generation.
As the digital model is being “built,” each component is either created from scratch or selected from a digital catalog (of geometric shapes) and then inserted into the model as well as automatically added to the associated model database (information file cabinet).
The database allows for automatic generation/extraction of orthographic drawings of plant areas, bills of materials, line designation tables, equipment lists, work packages, characteristics and geometry for pipe and structural stress analysis, piping isometrics, plot plans, etc. — deliverables that had to be produced by hand either before or after the plastic model was built. The 3-D model-database also minimizes the possibilities of error while transposing information from the model to deliverable documents.
Some limitations and caveats regarding digital models
While 3-D CAD models offer the ability to easily reuse previously designed equipment, components and common assemblies, the concept of GIGO (garbage-in, garbage-out) still applies.
This is especially true for vendor-sourced equipment models created from 2-D supplier drawings by the engineering firm. As opposed to pipe fittings, valves and other inline piping components, which are standardized in dimensions, major equipment is most often custom-designed for each process facility. If these components are inaccurately modeled, the interconnecting piping between equipment will not fit, resulting in expensive field fixes, schedule delays and the use of profanity on-site during construction.
The use of component catalogs by the modelers also tends to eliminate the need of the modelers to know such details as standard dimensions and material makeup of the inserted components. To some this may not be a concern, but it tends to minimize the nuts-and-bolts-level detailed knowledge of the designer.
Another phenomenon that can occur is overconfidence in the digital model, simply because they tend to project precision and there is a “wow factor” associated with the visualization technology.
The compatibility of the format of the information files can also be an issue if a project was designed utilizing one software application package and a subsequent upgrade to the project needs to be performed using a different software application package. There are data translators and convertors, but typically the conversion process will not function 100-percent correctly, leaving unwelcome (and possibly hidden) surprises to be discovered at the most inopportune moment.
Similar to file format incompatibility is the issue of hiring trained and experienced modelers who are familiar with the software used on a new project.
One advantage of “the good old days” was designers could get up to speed and draw just as fast and accurately with mechanical pencils — no training needed or learning curves to overcome. At one time you instinctively knew how to use your hand to draw and now you have to learn how to tell a machine to do it for you!
For more information on SPED, visit www.spedweb.com or call (832) 286-7678.
