Chapter 1 Understanding the basics of piping and instrumentation diagrams (P&IDs)

In this chapter, the introduction, importance, skeleton, comparison with block flow, process flow diagram, different tools, common rules, types, and steps involved in developing piping and instrumentation diagrams (P&IDs) are discussed in detail. Understanding the P&IDs is the first step in the development of critical equipment, instruments, and pipelines on the P&IDs. Once there is a good understanding of the basics of P&ID, the engineer can contribute efficiently towards the scope development of a project or participate in the P&ID meetings.

1.1 Introduction to P&ID

A Piping and instrumentation diagram (P&ID) is a detailed representation of a process showing piping and valves, instrumentation, process equipment, and note details required to design, construct, and safely operate a process plant. P&IDs are control documents for any process plant. P&IDs are commonly used by oil refineries, chemical plants, water treatment plants, food, power plants, oil & gas, engineering service companies, etc. P&ID is a medium used to communicate engineering information easily with others. Figures 1.1(a) and (b) show a process plant and a P&ID, respectively. From Figure 1.1(a), it can be seen that a processing plant has several processing units. Each process plant is different from the others. Each processing unit consists of multiple P&IDs. A processing unit can be easily understood by a set of P&IDs.

Figure 1.1: (a) A schematic of a process plant; (b) a schematic of a P&ID.

P&IDs are created by engineers who design a manufacturing process plant. The operating companies or the project or plant owners provide a contract to the engineering company. Typically, engineering companies develop or modify P&IDs based on the type of project, such as either grassroots or revamp. Oftentimes the technology licensor provides the P&IDs as a part of their basic engineering design package. Regardless of where the P&IDs are developed, the following key discipline engineers contribute mainly to developing the P&IDs:

• Chemical engineer

• Mechanical engineer

• Piping Design engineer

• Instrumentation engineer

• Plant operating engineer

There are several names for P&IDs practiced by many organizations and industrial plants. Some of the commonly used names are:

• Engineering Flow diagrams (EFDs)

• Engineering Line Diagrams (ELDs)

• Mechanical Flow Diagrams (MFDs)

• Utility Flow Diagrams (UFDs)

P&IDs are used by field technicians, plant operators, contractors, and engineers to understand the process. The plant operators or engineers use them for training new hires or trainees. Field technicians and plant operators use P&IDs for planning routine, maintenance, and shutdown tasks. Typical shutdown activities involve preparing a section of the process equipment or a process plant for pressure or leak test. Different activities involved in the maintenance tasks can be tracked using P&IDs. All routine or breakdown maintenance work permits are accompanied by highlighted P&IDs of the system being worked on, to show the scope of work. Engineers in engineering companies use P&IDs for revamp projects to debottleneck the existing plant and perform engineering studies. Engineers in operating companies use P&IDs to define the preliminary scope and make changes as per process requirements. P&IDs are also helpful in training new operators or technicians. New operators are usually given rigorous training inside a classroom before exposing them to the actual process plant and equipment.

1.2 Importance of P&IDs

Several functions are affected by the design and development of P&IDs. Some of these functions are control philosophy, equipment design, 3D model reviews, safety equipment requirements, etc. P&ID is used as a communication tool that helps in connecting with other disciplines. Figure 1.2 shows a schematic of communication involved in the development of P&IDs. A chemical engineer uses P&IDs to ask an equipment size-related question to a mechanical engineer, or a piping designer could ask about a free draining requirement of a piping from a chemical engineer.

Figure 1.2: Communication involved in the development of P&IDs.

Piping designers use P&IDs to develop 3D piping models. P&IDs show essential elements such as piping sizes, equipment connections, isolation valves, drain valves, etc., much needed to develop 3D models. Piping designers also look for any special notes on P&IDs regarding a piping arrangement or equipment, e.g., designing a free draining of a pipe or locating a piece of equipment at 25 ft. above grade level. Such important notes help develop the 3D models. Also, piping designers use P&IDs for determining material takeoff (MTO). MTO is the list of items such as piping size, length, number of gate valves, piping specification, etc. MTO is further used in cost estimation of the project. Piping designers use P&IDs to develop a line list. A line list document consists of all the engineering details for a pipe, such as operating and design temperature, operating and design pressure, pipe thickness, insulation type, etc. Also, once 3D models are reviewed and approved by a customer representative, the P&IDs are issued for construction. The piping designer uses P&IDs to develop piping isometric drawings. The piping contractors further use the isometric drawings of the piping for fabrication and installations.

Chemical engineers use P&IDs as a basis for a hazard and operability study (HAZOP). The chemical engineer marks a set of P&IDs for different sections of the process plant, and the HAZOP team, which usually consists of a plant operator, plant chemical engineer, chemical design engineer, HAZOP facilitator, and control system engineer, goes through different nodes and identifies hazards. Based on the identified hazards, appropriate design solutions are recommended and agreed upon by the team. These design solutions are further adopted either in the operating plant or in the ongoing and developing project.

P&IDs are helpful in planning hydrotesting and commissioning tasks of a processing plant. Different sections of the processing plant are divided into several sections based on the phase of the process fluid (gas or liquid phase). A section in the liquid phase is hydrotested using water, and a section in the gas phase is tested using high-pressure nitrogen. A processing plant is divided into several sections based on the steps involved in the commissioning process, such as water batching, start-up utilities, etc. Plant operators and engineers prepare a set of P&IDs for each section and divide responsibility for effectiveness. Figures 1.3 and 1.4 show the hydrotesting and commissioning steps in a schematic format.

Figure 1.3: An example of a hydrotesting loop.

Figure 1.4: Steps involved in the commissioning of a processing unit.

P&ID helps instrumentation and electrical engineers develop engineering diagrams and logic narratives. P&IDs serve as a basis for developing a control loop programming and dynamic control system interface. P&IDs serve as a basis for preparing operating guidelines for the manufacturing plant and can be used for analyzing a safety incident.

The P&ID and the scope marked are developed through all the engineering phases. P&IDs are mainly used by chemical engineers in the engineering industry from initial scope through detail design development of the process plant. Adding a new scope on P&IDs involves showing a scope cloud around equipment, piping, and instrumentation. An example is shown in Figure 1.5.

Figure 1.5: An example of scope mark-up on a P&ID.

As mentioned, there are several uses of P&IDs and many engineers and technicians use them in different scenarios. Figure 1.6 summarizes the importance of P&IDs in the industry.

Figure 1.6: Importance of P&IDs.

P&ID consists of many design details such as equipment, line, specialty items, isolation valves, trips, alarms, and design notes, which are very significant to those who are studying the plant operations either for training or for a possible revamp project. One can find an equipment type and the design details of the equipment on the P&IDs.

There are several types of process pieces of equipment. The P&ID user can get an idea based on the type of equipment. Figure 1.7 shows a typical type of pump. The centrifugal pump is higher in capacity but lower in discharge pressure. On the...