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Intelligent indexing is key to 3D CAD plant modeling

12.01.2012  |  Saha, S.,  Reliance Refinery, Jamnagar, IndiaNair A.,  Reliance Ports and Terminals Ltd., Reliance Refinery, Jamnagar, India

Indexing is a key activity in CAD modeling. Arbitrary indexing of the models invariably leads to problems, as discussed in this article.

Keywords: [engineering and design] [modeling] [software] [CAD] [engineering and construction]

Modeling a plant in a three-dimensional (3D) computer-aided design (CAD) environment and digitizing of the existing setup are becoming trends due to the immense benefits these features provide to owners and plant operators. They not only bring visualization, but they also provide ample opportunities to all contributors to the project to take preventive actions through model reviews and data analysis.

Indexing is a key activity in CAD modeling. Arbitrary indexing of the models invariably leads to problems, as discussed in this article.


CAD supports the entire workflow of all functional groups. Historically, it has benefited the engineering and construction contractor. The benefits come from improved accuracy and constructability, fewer engineering work-hours, lower material surpluses and shorter schedules.1

The utility of the CAD plant is not limited to engineering and construction. Its benefits can be extended to other functional groups like operations, inspection, etc. This article attempts to create awareness of plant indexing methods and explore opportunities for contribution by all functional groups to improve the utility of plant digitization.

The digitization of today’s plant is not limited to assigning location coordinates to graphical components of the plant (Fig. 1). Various developments occur when linking the databases of other functional groups, which eventually increases the utility index of the digital plant.

  Fig. 1.  CAD plant model.

Improvement in the utility index is not only evident in the project phase, but it is also visible in the entire lifecycle of the plant—such as commissioning, post-commissioning, day-to-day operation, planned and unplanned shutdowns, maintenance, inspection and revamps.

Organize with indexing

Indexing is the process of organizing the physical area or components of the plant into logical parts. These logics are developed during the initial stages of CAD. Model boundaries are finalized based on process systems and the mobilization of modelers. These boundaries—referred to as CAD areas—are discussed with piping, structural and electrical design groups, as every discipline must follow the same model boundaries.

In a complex containing many plants, it is common to find rack areas with different CAD names beginning with the letters D, H, J, etc. (Fig. 2). However, there are benefits in standardizing the rack CAD areas of all plants to begin with the letter “R” (Fig. 3). In this way, a project manager can focus on these areas to prioritize engineering and procurement efforts and to clarify the design for the construction team. A construction manager can easily identify the rack isometrics from the lot for prompt distribution. 

  Fig. 2.  Sample CAD index in a typical ISBL unit.

  Fig. 3.  Refined CAD index with rack in R-series.

Importance of the indexing method

Once the CAD area is finalized and deliverables commence, it is not practical to make changes to the CAD area, as this could result in undesirable revisions to deliverables. Therefore, the optimization process for the CAD area must be carried out well in advance. Instead of finalizing CAD area classification based on process systems and mobilized modelers, it is prudent to consider this classification’s influence on all functional groups at various lifecycle stages of the plant.

Plant design and layout are conceptualized and developed in the CAD development stage (Fig. 4). Job division and mobilization of skilled modelers for design development activities are considered major factors for CAD area classification. A small number of CAD areas may result in model allocation difficulties, thus limiting CAD modeler mobilization and ultimately affecting progress. A large number of CAD areas may result in increased clashes and interfaces, as well as in design-check instances requiring relevant management tools. Optimization on the number of CAD areas is necessary for efficient CAD development activity.

  Fig. 4.  Number of CAD model files in CAD
  areas of a typical inside-battery-limits unit.

In the procurement stage, cost benefits are realized from discounts for bulk purchases. Materials are grouped irrespective of their CAD areas to attain maximum discounts. The ideal situation is to begin procurement after engineering completion; however, this is not a practical approach most of the time. The project team must prioritize engineering activities and optimize procurement actions to provide a relevant construction front and make planned progress. A well-thought-out CAD area classification can help the project team set priorities and envisage the construction front.

In the construction stage, the work front depends on the availability of drawings and materials. The available work front is generally divided into various construction work areas (CWAs). These areas require different types of skilled labor (e.g., rack, compressor, pump, column and reactor area). A carefully developed CAD area classification that takes CWAs into consideration avoids the need to split isometrics into two or three parts. This can save substantial construction efforts and prevent compilation problems.

Consider a case where piping modeled in a single CAD area is to be constructed from a column overhead to the receiver over the rack (Fig. 5). In such cases, the construction team typically splits the drawings to respective CWAs and distributes them to various contractors.

  Fig. 5.  Concept of construction work area

Such situations end in responsibility distribution problems, especially during hydrotesting or mechanical completion of the system. Commercial justification is needed when the single drawing is billed by more than one contractor. However, a carefully developed CAD area that takes these issues into account will avoid such situations and allow construction managers to focus on priority activities.

Improper indexing can cause a number of difficulties. Cases of arbitrary indexing include the following:

  • A large number of CAD areas without proper model boundaries. Process logics are usually difficult to memorize, and this results in confusion and drawing splits for construction.2
  • CAD areas in multiple physical locations, usually observed in outside-battery-limits racks, with multiple bridges to process units. In such cases, the identification of physical location becomes difficult. Continuation drawing numbers must be reviewed to find the exact location.
  • Drawings modeled in different CAD areas. This happens due to a modeling error or overlapping CAD areas, as model boundaries are not always “straight lines.”2 Such cases are usually seen in the incoming and outgoing lines of the rack.

CAD index case study

In one case study, the plant inspection group called for a database structure for tagging the inspection history of lines as a way of developing a future inspection strategy. The plant was experiencing problems with the existing CAD index due to CAD area overlaps and the same area in multiple locations (Fig. 6).

  Fig. 6.  Rack area with CAD indexing issues.

A breakthrough was achieved by restructuring the indexing of the racks with unique index names (UINs). Negative effects on existing deliverables were avoided by mapping the new UINs with the existing CAD index. This approach not only resolved the problem, but it also opened avenues for other functional groups to link their databases to the digital plant.

The entire lifecycle of the plant—i.e., commissioning, maintenance and revamp—are affected by CAD area classification. A refined CAD area classification can simplify data tagging of all functional groups in the digital plant map. This process may lead to new data interpretation approaches, which may help in structured work plans and controlled job distribution to third-party experts. Safety and value-addition initiatives can be easily incorporated at all plants, and information exchange across functional groups creates opportunities to dissolve barriers between them.


Indexing the digital plant is critical for all contributors to the project, and it has substantial influence on the entire lifecycle of the plant. The active participation of all stakeholders during the process is encouraged to improve the utility indexing of the digital plant. Utility indexing by all functional groups in the lifecycle of the plant indicates that pivotal information exchanges are taking place, thus helping to avoid the side effects of departmentalization.

Proper indexing not only improves the ability to respond to opportunities and challenges, but it also provides the possibility of exploring untapped areas of improvement to achieve accuracy and encourage competitiveness. HP 


1 Bausbacher, E. and R. Hunt, Process Plant Layout and Piping Design, Prentice Hall, Upper Saddle River, 1994.
2 Beale, R. J., P. Bowers and P. Smith, The Planning Guide to Piping Design, Gulf Publishing Company, Houston, 2010.

The authors
Dr. Subrata Saha is head of the engineering division of Reliance Ports and Terminals Ltd., which is the engineering wing of the Reliance Refinery at Jamnagar, India. He has a wide range of experience in engineering design in the power and hydrocarbon industries. Dr. Saha holds a BTech degree in mechanical engineering from the Indian Institute of Technology in Kharagpur, India, and a PhD from the Indian Institute of Technology in Kanpur, India.

Ajay Nair is the lead piping engineer at the engineering division of Reliance Ports and Terminals Ltd. at the Reliance Refinery in Jamnagar, India. He has 15 years of industry experience, particularly in refinery and petrochemical CAD environments. Mr. Nair holds a mechanical engineering degree from the L.D. College of Engineering in Gujarat, India.

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David Walsh

Hey there . Im currently doing my architectural thesis at victora university of New Zealand looking at onshore oil and gas sites around new Zealand and looking into the architectural benefits of using the hydrocarbons and geothermal benefits that exists once the sites are abandoned. What I am after is a Cad 3d model of a onshore and gas site and I was wondering where would be the best place to get this from? the ones youve drawn here look incedible and they would be really help if I could get hold of part of the model or the whole thing or if you could even direct me to another contact that could lend me a 3d model of a site.

Thanks David

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