PFDs and P&IDs: Dos and Don’ts (Part One – Definitions and Uses)


This post outlines the purpose of Block Flow Diagrams (BFDs), Process Flow Diagrams (PFDs), Piping and Instrumentation Diagrams (P&IDs), the inputs required, tips and tricks, dos and don’ts when developing these diagrams, the use of them and the required status of completion throughout process design development of the metallurgical plant process design and mining projects phases (i.e. Concept, Scoping, Pre-feasibility, Feasibility, Detail Design, Installation, Commissioning and Start-up).


The extraction, beneficiation, and processing of metals, concentrates, and minerals through mineral processing and hydrometallurgical plants is dependent on the selection of an appropriate and economically viable process. BFDs provide a complete overview of the whole process in block diagram form. They summarise the major unit operation between process block units. PFDs characterize all the process flows to and from all the equipment required to perform the process within the boundaries set by the BFD. The PFD is a schematic representation of the total production process. P&IDs provide a detailed schematic representation of the connectivity/network between all equipment, fittings, pipes, valves, and instruments. More specifically they identify all equipment and characterize (size, materials & type) and sequence all pipe, pipe fittings, valves and in-line instrumentation. They also incorporate the plant control and operating philosophy and hence are the foundation documents for all HAZOP processes.

Generally there is a clear distinction between PFDs and P&IDs:

  • PFDs are the foundation control documents for the process design, incorporating the mass, water, and energy balance.
  • P&IDs are the foundation control documents for engineering design.


Block Flow Diagram: A BFD generally starts the process design sequence. It shows the process units as blocks together with major streams interacting with these process units. A BFD is a schematic representation of the whole process.

Process Flow Diagram: A PFD is the first drawing created to show the items of major equipment and their relation to one another in the process scheme. It shows the relationships between the major process units in the whole system. A PFD is a schematic representation of the fundamental plant design. It therefore includes associations between drawing elements, major process equipment, and engineering information from the process and discipline design definition phase and the control / operating strategy. The PFD includes key data relationships concerning process equipment and streams. Text elements on the PFD may contain process design properties (e.g. flowrates, etc.) and key equipment design attributes associated with the major process equipment shown on the PFD.

Piping and Instrumentation Diagrams: As it mentioned above, PFDs define the inputs and outputs for a process system and serve as control documents for the process design and plant configuration. PFDs serve as the initial tool used to create the specifications and data sheets for all the process related equipment; P&IDs further enhance the specifications and data sheets. They initiate the definition of all piping, instrumentation, control valves, and electrical components. The P&IDs therefore become the control documents for engineering design. P&IDs are also the documents that are used for HAZOP reviews and therefore incorporate all the fundamentals of process control configuration and plant operating philosophy. A P&ID is a schematic diagram that shows associations between the drawing elements and engineering details of the equipment, instrumentation, piping, valves, their connectivity, materials of manufacture, and sequence.

Information Required to Produce BFDs, PFDs and P&IDs

The information required to produce block flow diagrams includes the following:

  • Major unit operation.

The information required to produce process flow diagrams includes the following:

  • Scope and battery limits.
  • Process flow description and process design criteria.
  • Basic Equipment List for the process.

The information required to produce P&IDs includes the following:

  • Scope and battery limits.
  • Process, mechanical & electrical design criteria, and specifications.
  • Equipment list and specifications (sizes, capacities, design pressures, design temperatures etc.).
  • Process control philosophy and configuration.
  • Motor list.
  • Pump list.
  • Instrument list.
  • Master line list including preliminary valve list.
  • Piping, valve, instrument, and equipment design standards.
  • Vendor data.
  • General plant arrangement and layouts.
  • Calculations / models.

Uses of BFDs, PFDs and P&IDs

Generally, BFD’s are used to establish the interactions between the major process units.

The PFDs start with the feed materials into ROM (Run of Mine) and end with a final product as well as by-products and mine waste. PFDs not only track the product / materials through the process but also allow the process engineer to obtain quantitative information on the raw material usage, major bypass and recirculation lines, mass and water balance, and sequencing. Flow data specified on PFDs should represent maximum flows, minimum flows, and normal flows.

PFDs should be used as the basis for process selection, optimisation and identification of viable or non-viable (technical and economical) process options.

The uses of PFDs are summarized as follows:

  • Process selection and optimisation.
  • Process design criteria.
  • Mass, water, and energy balances.
  • Process stream characterisation.
  • High level process control philosophy and control system configuration.
  • Preliminary equipment and motor lists.
  • Equipment datasheets (process equipment but excluding piping and valves).
  • Basis of preliminary HAZOP.
  • Generation of P&IDs.
  • Preliminary capital cost (Capex) estimating.

The uses of P&IDs are listed as follows:

  • Equipment list / motor list / instrument list generation.
  • Equipment specifications and data sheets.
  • Piping, valves, instrumentation, and hoses specifications / piping installation.
  • Instrumentation equipment, controls, and loops.
  • Architectural and HVAC (Heating, Ventilation and Air Conditioning).
  • Final master line list / valve list.
  • HAZOP’s.
  • Capital cost estimating.
  • Basis of master drawing register.
  • Single Line Diagram (SLDs).

What each Mining Project Phase Needs?

PFDs and P&IDs are developed through different phases of a mining project. Development status of the PFDs and P&IDs during these phases and their application for capital cost estimates at various levels of required accuracy are summarised in the below table:

Project Phase PFDs P&IDs Others
Conceptual Study (± 30% to +35% Accuracy) Preliminary Not Required
Pre-Feasibility Study (± 20% to +25% Accuracy) Preliminary for options Preliminary for complex process only
Feasibility Study (± 10% to +15% Accuracy) Final optimised Detailed for major process
Detail Design (± 5% to +10%) Finalised and approved Finalised and approved Vendor data included

In Part two of this post we will talk about Tip & Tricks; Dos & Don’ts while developing and working with PFDs and P&IDs.

Meanwhile if you need to develop BFD, PFDs, or P&IDs for any phase of your mining project, update or make “as built” drawings for your processing plant or want to educate and train your engineers and operators on how to read and use these drawings OreVenture Training and Technical Services is pleased to offer these services.