Application of Computer-Aided Design to Piping Layout
The piping industry today is very diverse in its use of computer-aided design. This diversity is shown by the various levels of sophistication of the CAD applications in use by different segments of the industry. Even within the same company, the sophistication of CAD use can vary widely from discipline to discipline, department to department. This diversity ranges from a surprisingly large portion of the industry in which there is little use of CAD to a few who claim to be approaching a paperless ofﬁce. Between these two extremes, most of the industry appears to be using CAD as computer-aided drafting. In this sense, CAD becomes an electronic pencil, not necessarily a design tool.
The meaning of the term CAD has evolved as quickly as the technology itself. From its original use as an acronym for computer-aided drafting, it has spawned a whole family of related acronyms: CADD (computer-aided drafting and design), CAE (computer-aided engineering), CAM (computer-aided manufacturing), and so on. Many of these terms have been applied when describing the design and layout of piping systems. In the minds of many people, CAD and its related acronyms are still envisioned as simply automated drafting, where CAD is basically the substitution of drawing boards with CAD terminals. While computer-aided drafting represents a signiﬁcant portion of the application of CAD to piping layout, this is changing rapidly. In this section, applications beyond simple drafting will be dis-cussed. Therefore the acronym CAD will mean computer-aided design and will refer to both design and drafting activities related to piping layout.
The entire ﬁeld of design automation, including CAD, is changing so rapidly that it would be of little value to make recommendations regarding speciﬁc hardware and software systems. What may be the best or most cost-effective system today may be out of the picture tomorrow. However, there are some fundamental issues associated with the selection and implementation of a CAD system which should be considered, regardless of the speciﬁc supplier of hardware and software.
Currently, as indicated previously, the most signiﬁcant use of CAD for piping layout is for drafting. Many software systems exist which can function on nearly every type of computer hardware available, including mainframe computers, minicomputers, workstations, and personal computers. Today, the use of CAD for two-dimensional drafting is dominated by CAD software for personal computers. In selecting a system for producing piping drawings, there are several issues which must be considered, regardless of the hardware to be used.
User-Deﬁnable Symbols and Menus. Any CAD software, if it is to be of long-term beneﬁt, must provide the capability to deﬁne its own drafting symbols and menus (e.g., tablet, on-screen) for selecting these symbols. Since piping drawings make extensive use of symbology, deﬁning symbols is of critical importance for signiﬁcantly increasing drafting productivity. This capability allows the user organization to create and manage libraries of its own symbols, standard details, and standard notes, which can be easily and automatically included in any drawing.
Use of Standard Hardware. Traditionally, many CAD systems were provided by the vendor as a turnkey system that included both hardware and software. In these cases, the CAD software was designed to operate speciﬁcally on the hardware provided by the vendor. Today, however, many vendors have decoupled the hard-ware and software, which allows the software to run on a number of hardware platforms. In fact, most of the major providers of CAD software for drafting provide only software, with the users acquiring the hardware and operating system independently. This is particularly true for the personal-computer-based CAD systems. By selecting software which can function on a number of types of hardware,the user has the ﬂexibility to more fully take advantage of rapid changes in the hardware market, i.e., decreasing prices with improved performance. If the CAD software can function only on the hardware from one speciﬁc vendor, then the user must rely on the hardware vendor to keep pace with the rest of the industry.
Availability of Third-Party Software. Certainly not every user can have the luxury of developing dedicated software, particularly beyond the development of symbol libraries and menus. Therefore, before selecting a CAD system, the user should determine how much application software is available from the vendor or from third parties. For piping layout, the most important applications to look for are those intended for generating orthographic piping drawings and piping isometric drawings. Application software, speciﬁc to piping layout, can signiﬁcantly increase the productivity of the application of CAD. If little or no applications software exists for the CAD system under consideration, then the user will likely have to develop his or her own applications software or fail to realize the full value of the CAD system.
Support of User-Developed Software. In cases where no applications software exists, perhaps due to the uniqueness of the user requirements, the user needs to ensure that application software can be developed for the speciﬁc CAD system. As a minimum, the system should support developing simple ‘‘macro’’ commands which execute a series of commands in response to a single command. Many systems have macro languages which offer much of the functionality of general-purpose programming languages. For more sophisticated applications, the system should provide interfaces to software written in other programming languages, such as Fortran or C++.
Support for Multiple Users. Piping layout is not done in isolation and must inter-face design information and drawings from other piping designers as well as other disciplines. Therefore, the CAD system must support this type of activity. The CAD system should provide the capability for a designer to have read-only access to the CAD ﬁles of other designers for reference, interference checking, or use as background information for the piping drawings. Systems which have this capability often refer to it as a reference ﬁle capability. This allows one designer to see the ﬁle of another designer, as if it were part of his or her ﬁle; however, the data cannot be changed. For personal-computer-based CAD systems, this requires that they be part of some type of local or wide-area network. Without this capability in the CAD software or for personal computers which are not in a network, the data from other designers must be copied and incorporated into the designer’s ﬁle. This doesn't allow the designer to see the active data of other designers. In addition, it also greatly increases the storage requirements since many drawings are duplicated,perhaps numerous times. Most importantly, this introduces a more complicated ﬁle management problem, making it more difﬁcult to (1) know which ﬁle has the most up-to-date information and (2) ensure that everyone references the current data.
Database Capabilities. To utilize the CAD system for more than just drafting requires that the system have the ability to create drawings which, in addition to the drawing graphics, contain (or reference in database) other information which can be extracted from the drawing, such as valve numbers and/or line numbers. With this type of capability, bills of material can be generated automatically from the piping drawings. It is even possible to generate the input to the piping stress analysis program from a piping isometric. However, note that merely having a basic database capability does not mean that it can be effectively used for extracting data from piping drawings. This is the role of applications software developed speciﬁcally for piping which automatically generates and manages this information during the creation of the drawing. In the absence of piping applications software, the designer would be required to key in a signiﬁcant amount of data while generating the drawing. This not only dramatically decreases the productivity of the drawing production process, but also greatly increases the possibility of errors.
Training and Implementation. In the past, much of the cost of implementing the traditional turnkey CAD systems was in the hardware and software. Today, as the cost of hardware and software continues to decline, the majority of the cost is shifting from hardware and software toward training and support. Therefore, the costs associated with the training and implementation of a CAD system, even for two-dimensional drafting, should not be underestimated. In fact, experience has shown that the relative effectiveness of a CAD system is directly related to the amount of training and support the individual users receive.
The precise method of implementing a CAD system is dependent on the com-pany’s current organization and method of executing work. Centralized CAD groups working multiple shifts were often the norm with the installation of the large turn key systems. Now, however, as the cost continues to decrease and the piping design industry in general increases its sophistication in the use of CAD, more effective uses of CAD are being made by placing the workstations right in the piping design groups. Many companies started by training their drafting personnel. But again, experience has shown that even more effective use can be made of the CAD system by training senior-level piping designers. Instead of creating sketches which are then passed on to a drafter, the designer, using the CAD system and piping layout applications software, can create an electronic sketch which is very nearly a ﬁnished drawing, leaving very little to do in the way of drafting. This approach can greatly increase the productivity of the whole design and drafting cycle.
While the use of CAD for two-dimensional drafting in support of piping layout can provide a number of productivity beneﬁts, there are inherent limitations as to overall beneﬁts to the entire design, fabrication, and construction cycle. While providing beneﬁts in producing the piping drawings (e.g., drafting quality, drafting productivity) and possibly in generating bills of materials, it offers little in the way of improving design productivity. Also, the cost and effort required for interference detection are only marginally improved. Thus two-dimensional drafting, while improving drafting quality and productivity, does little for improving design qualityand productivity.
The use of three-dimensional (3D) modeling offers a signiﬁcant step forward in improving piping design productivity and quality. Systems for 3D piping modeling have existed since the 1970s in a variety of forms. The early systems were geared primarily toward interference detection and materials management and really were not used as design tools per se. Today, a number of systems exist which address the entire piping design cycle. In selecting one of these systems, all the issues which applied to computer-aided drafting apply to 3D piping design systems. However, there are a number of other issues which must also be considered.
Interactive Design. To truly improve piping design productivity, the software should provide the capability to interactively lay out the piping systems directly in the 3D computer model. This allows the piping designer to sit at the graphics workstation, viewing the 3D model, and directly add new piping or modify existing piping. Without this capability, the system can provide other beneﬁts, such as in interference detection, but will not necessarily improve the piping design productivity. In fact, without interactive design capabilities, another step is added to the process for entering the data into the 3D model from the 2D design drawings. Many CAD systems provide interactive 3D modeling capabilities, but these are not usually sufﬁcient for 3D piping design. Applications software, speciﬁcally aimed at piping design, is required to realize gains in design productivity. Without this type of applications software, 3D modeling is probably only effective for early conceptual design and perhaps detailed modeling of very speciﬁc problem areas.
Interference Detection. A major advantage of using 3D computer modeling for piping layout is the ability to automatically check for interferences. This alone can provide a signiﬁcant improvement in design quality by making it possible to issue a ‘‘provable’’ design, i.e., an interference-free design. Many CAD systems, particularly those originally developed for mechanical design, can detect interferences between two 3D objects; but this is not sufﬁcient for checking plant models for interferences in a production environment. As a minimum, the software should provide the following capabilities:
The software should be able to check interferences for all or part of the plant in a batch mode. This check should include not only piping but all other disciplines as well. The software should have a method of reporting interferences which is easy to interpret and makes it possible to quickly locate the interferences in a large and complex model. Some systems also offer the capability to check for interferences as the piping is being designed. This is especially useful for designing pipe in very congested areas.
The software should check for not only ‘‘hard’’ interferences, i.e., metal-to-metal, but also ‘‘soft’’ interferences, such as personnel access areas, equipment removal spaces, insulation, and construction access.
The software should provide some capability for managing interference resolution over the life of the project. This includes the ability to suppress certain types of interferences and ﬂagging certain speciﬁc interferences as acceptable which will not be reported in the future.
Drawing Generation. To fully realize the beneﬁts of 3D modeling, the system should provide the capability to automatically or semi-automatically produce the piping drawings, both orthographic and isometric, directly from the 3D piping model. These drawings should be generated in the form of 2D CAD drawings so that they can be managed along with the 2D drawings not generated from the 3D model. For orthographic drawings, the system should be able to represent the piping in the format required by the user, e.g., single-line; it should be able to automatically remove hidden lines from the model; and it should have some basic capability to automatically place annotation, such as component call outs, into the drawing. For piping isometrics, it is not unreasonable to expect the software to generate the piping isometric automatically.
Bills of Material. As a minimum, the software should have the capability to produce a bill of materials for any of the components included in the model. If a user requires stringent control of piping materials, the system should also provide a piping materials control system or an interface to a third-party materials control system.
Interface to Other Systems. Since many disciplines utilize 3D geometry data, the software should have the ability to interface the 3D geometry data with other computer systems. For piping design, this would include the piping stress analysis systems. This could also include interfaces to fabrication equipment, such as numerically controlled pipe-bending systems.
Design Review. The use of 3D modeling for piping design impacts the design process in a number of ways. First, the design evolves in the 3D model—not on the drawings, as in the case of 2D design. The drawings are not usually produced until the design is completed. This means that the drawings cannot be used as a means of reviewing the design while the design is in progress. Second, since in some companies the use of 3D design has virtually eliminated the plastic model, the plastic model is also no longer available as a design review tool. Thus the 3D software system should provide, either directly or through an interface, the means of reviewing the 3D computer model on a high-performance graphics terminal. These types of systems provide the capability to ‘‘walk through’’ solid shaded models in real time for the purposes of design review.
Training and Implementation. Once again, the issues related to computer-aided drafting apply here as well. The primary difference is one of degree. Systems for 3D computer modeling of piping require more training, more support, and a longer learning curve. Also, these types of systems are more pervasive than simple 2D CAD drafting in that they require a higher level of integration between disciplines and departments and thus a higher level of management attention and support. For these systems to be effective, it is imperative that senior-level design personnel are trained in the use of the system and can use it effectively for piping layout.
Computer-aided drafting and computer-aided design have been used effectively and productively for piping design for a number of years. One of the most important lessons learned from the application of CAD to piping layout, particularly the use of 3D modeling, is that design ﬁrms are no longer tied to the same design process and design documentation as when the design was performed manually. The use of 3D piping design provides a number of opportunities for improving the way in which plant design is performed, over and above simply the increase in design productivity. In fact, experience has shown that force-ﬁtting 3D piping design into a project organization and design process geared to manual design actually leads to some inefﬁciencies.
There appear to be several factors which are important to the continued effective application of this technology. Perhaps most important is the fact that being able to effectively apply this type of software requires training—not only for the individual designers and engineers but also for the supervisors, project engineers, and project managers who control the project work. This type of software opens up new possibilities for improving the way project work is performed, but being able to take advantage of these requires that people at all levels of the project understand the software capabilities as well as its limitations.