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
The digitization of todays 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
Improvement in the utility index is not only evident in the
project phase, but it is also visible in the entire lifecycle
of the plantsuch as commissioning, post-commissioning,
day-to-day operation, planned and unplanned shutdowns, maintenance, inspection and
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 boundariesreferred to as CAD
areasare discussed with piping, structural and electrical
design groups, as every discipline must follow the same model
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
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 classifications 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
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
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. 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 planti.e., commissioning,
maintenance and revampare
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
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.
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,
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.
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.