The plot plan is one of the key documents produced during the engineering phase in any processing facility. It is used to locate equipment and supporting infrastructure and to establish the sequence of major engineering and construction activities. Plot plans are used by almost every engineering group within a project task force from estimating and scheduling through construction. Standardization of plot plans is difficult, however a few basic rules are applied.

Plot plans developed with three dimensional CAD modeling have the advantage of producing multiple plans, elevations, and isometric views with no additional effort.

Plot plans are used for

Piping Design: The plot plan is used to produce equipment arrangement studies that facilitate the interconnection of above and below ground process and utility piping systems and to estimate piping material quantities.

Civil Engineering: The plot plan is used to develop grading and drainage plans, holding ponds, diked areas, foundation and structural designs and all bulk material estimates.

Electrical Engineering: The plot plan is used to produce area classification drawings, to locate switchgear and the incoming substation and motor control center, to route cables and to estimate bulk materials.

Instrument Engineering: The plot plan is used to locate analyzer houses and cable trays, assist in the location of the main control house, and estimate bulk materials.

Systems Engineering: The plot plan is used to facilitate hydraulic design , line sizing and utility block flow requirements.

Scheduling: The plot plan is used to schedule the orderly completion of engineering activities.

Construction: The plot plan is used to schedule the erection sequence of all the plant equipment, which includes rigging studies for large lifts, constructability reviews, marshaling, and lay-down areas throughout the entire construction phase.

Estimating: The plot plan is used to estimate the overall cost of the plant.

Client use: The plot plan is used for safety, operator, and maintenance reviews and to develop an as-built record of the plant arrangement.

To develop a plot plan, a designer must assemble the following information

1. Equipment list

2. Process flow diagram

3. Block flow diagram

4. Specifications

5. Process design data

6. Equipment sizes

7. Materials of construction

Types of Plot Plans

The grade mounted horizontal inline arrangement: Usually located within a rectangular area, with equipment placed on either side of a central pipe rack serviced by auxiliary roads.

The structure mounted vertical arrangement: has equipment located in a rectangular multilevel steel or concrete structure.

Various requirements dictate the location of equipment and supporting facilities within the conventional operating plant, and many factors must be considered when designer is locating the equipment. They are:

Plant Layout Specification highlights the spacing requirements for equipment and access widths and elevation clearances for operator and maintenance access.

Economic Piping: The major portion of the piping within most process units is used to interconnect equipment and support controls between equipment. To minimize the cost, the equipments must be located in the process sequence and close enough to suit safety needs, access requirements, and piping flexibility.

Process Requirements: Equipments must be located in a specific position to support the plant’s process operation.

Common operation: Equipment that requires continuous operator attention or shares common utility and maintenance facilities should be located in the same area.

Real estate availability:

Equipment sizes: Equipment sizes vary in a process plant and hence care must be taken to ensure that large cumbersome pieces of equipment first and then plan the remainder of the unit around them.

Underground facilities: Depending on soil conditions, the foundations are either piled or spread footings. Instruments, electrical cabling can be located above or below grade along with underground piping, cooling system which the designer need to investigate.

Climatic conditions: Weather conditions influence the location of certain equipments, which may require them to be housed.

Pipe Racks: Most inline plant arrangements are furnished with a central pipe rack system that acts as the main artery of the unit supporting process interconnection feeds, product and utility piping, instrument and electrical cables and sometimes air coolers and drums.

Roads, Access Ways and Paving: For maintenance and safety, the principal access to and from most process units is by auxiliary roads. Clearance according to project specifications should be provided. Most clients require that the equipment areas, the areas beneath the pipe rack and the areas around buildings be paved with concrete for housekeeping.

Buildings: Apart from buildings that house equipment, it is often necessary to position control houses, substations, analyzer houses, and operator shelters within the process unit battery limits.

Equipment spacing for operator and maintenance access, safety, piping flexibility and support and platforming requirements.