Process Diagrams

Process Diagrams

Process diagrams are the most effective way of communicating information about a process. A process diagram consists of activities, events, and gateways, which a sequence flow puts in a flow sequence. Activities, events, and gateways are summarized under the term flow object.  A process diagram is the key to the development and management of an industrial production process. It is a diagram of the steps in a process and their sequence. It constitutes a simplified sketch which uses symbols to identify instruments and vessels and to describe the primary flow path through a unit.

Flow diagrams show the structure and function of the process plants and are part of the entire set of technical documents which are needed for planning, assembly, construction, management, commissioning, operation, maintenance, shutdown, and decommissioning of a plant. Flow diagrams are a means by which information is exchanged between parties involved in the construction, assembly, operation, and maintenance of such process plants. General rules and recommendations for preparation of flow diagrams are given in ISO 15519.

Process diagrams can be classified into three categories namely (i) block flow diagram (BFD), (ii) process flow diagram (PFD), and (iii) piping and instrumentation diagram (P&ID). Depending on the information needed, a distinction is made between BFD, PFD, and P&ID. Each particular type of flow diagram is to take the functional requirements into consideration. For example, in P&ID, the focus is more on the process than the piping.

BFDs can also be used to simplify and decompose process flow systems. Moreover, such diagrams are the simplest form of the industrial flow chart and are normally considered as the first step to complete a PFD. PFD and P&ID share some common points but they also have considerable differences. Both PFD and P&IDs contain a series of standard symbols for users to describe a process. P&IDs normally include more details than the PFDs, since the latter type primarily show the relationship between main equipments. Normally, a PFD includes process pipelines, major equipment items, and control valves etc. However, PFDs do not normally include pipeline grades, pipeline numbers, or secondary bypass lines etc. In practice, PFDs can be used for training of the new employees, while P&IDs is normally used by process personnel such as pipeline designers, electrical engineers, instrumentation engineers and other technical experts for their production development.

The graphical presentation is to conform to the rules set down in clause 5 of ISO 10628 which gives the drafting guidelines. Flow routes and flow directions are to be indicated by lines and arrows. All equipment, machinery, flow lines (e.g., pipelines, transport routes), and valves are to be represented as per ISO 10628-2 which describes in detail the graphical symbols.. The measuring, control, and regulating tasks are to be represented as per IEC 62424. Designation of objects in diagrams are to be performed using reference designation as per IEC 81346 series.

Block flow diagram

BFD is a drawing of the process used to simplify and understand the basic structure of the process. It is the simplest form of the flow diagrams used in the industry. Blocks in a BFD can represent anything from a single piece of equipment to an entire plant. For a complex process, BFDs can be used to break up a complicated system into more reasonable principal stages / sectors.

BFD is made for a process unit. It reflects (i) functional requirements of the unit, (ii) depicts the different processes carried out within the process unit and their sequence, and (iii) shows the inputs (feed) and outputs (products). BFD is used to explain the normal material flows throughout the entire plant. It is generalized to certain plant sectors or stages. The diagram helps orient operators to the products and important operation zones of a process facility.

BFD shows overall processing picture of a process complex. Flow of raw materials and products can be included on a BFD. BFD is a superficial view of the facility. Emphasis is not on details regarding blocks and focus is on flow of streams through process. Conventions used in BFD are (i) operations are shown by blocks, (ii) major flow lines are shown with arrows giving flow direction, (iii) flow goes from left to right whenever possible, (iv) light streams are toward top while the heavy streams are toward bottom, (v) critical information unique to the process is included (i.e., reaction stoichiometry, and conversion etc.), (vi) crossing of lines is avoided by showing horizontal lines continuous and  vertical lines broken, and (vii) simplified material balance (overall) is shown.

BFD provides an overall view of the process, normally on a single sheet of paper, with each major operating step represented by a block. BFD is mainly used for training people who are not familiar with the unit. It is also useful for conceptual safety studies since it provides a good overview of the process.

In the planning stage or early in design, a BFD is normally made by a process engineer. BFD shows the main processes as rectangles or circles with lines and arrows for the main flow paths. Major process streams are shown connecting the blocks. The flow of process streams is normally from left to right, with a gravity bias wherever possible, which means that liquids leave from the bottom of a block, gases from the top. A BFD can also show a few of the more important operating parameters, such as flow rates and temperature. Excluded from BFDs are single pieces of equipment and package numbers. Fig 1 shows an example of a simple BFD.

Fig 1 A simple block flow diagram

BFD depicts a process or process plant in simplified form by means of rectangular frames which are interconnected by flow lines. The rectangular frames can represent (i) processes, (ii) process steps, (iii) unit operations, (iv) process plants or groups of process plants, (v) plant sections, and (vi) equipment. The flow lines can represent streams of materials or energy flows.

The BFD contain at least the basic information consisting of (i) denomination of frames, (ii) denomination of in-going and out-going materials, and (iii) direction of main material flows between frames. Fig 2 shows block flow diagram with basic information.

Fig 2 Block flow diagram with basic information

The BFD diagram can also contain additional information such as (i) denomination of the main material flows between the frames, (ii) flow rates or quantities of in-going and out-going materials, (iii) flow rates or quantities of in-going and out-going energy or energy carriers, (iv) main material flows between the frames representing energy or energy carriers, and (v) characteristic operating conditions. Fig 3 shows block flow diagram with basic and additional information.

Fig 3 Block flow diagram with basic and additional information

Process flow diagram

A PFD is a type of flow-chart which demonstrates the relationships between major components of a plant unit. It is very frequently used in process engineering, though its concepts are sometimes applied to other processes as well. It is used to document a process, improve a process, or model a new process. Depending on its use and content, it can also be called a process flow chart, flow-sheet, schematic flow diagram, macro flow-chart, top-down flow-chart, system flow diagram, or system diagram.

PFD primarily defines (i) a schematic representation of the sequence of all relevant operations occurring during a process and includes information considered desirable for analysis, (ii) the process presenting events which occur to the material(s) to convert the feed-stock(s) to the specified products, and (iii) an operation occurring when an object (or material) is intentionally changed in any of its physical or chemical characteristics, is assembled or dis-assembled from another object or is arranged or prepared for another operation, transportation, inspection or storage.

PFD normally includes (i) plant design basis indicating feed-stock, product and main streams flow rates and operating conditions, (ii) identify the scope of the process, (iii) shows graphically the arrangement of major equipment, process lines, and main control loops, and (iv) shows needed utilities which are used continuously in the process.

PFD has multiple purposes which include (i) documenting a process for better understanding, quality control, and training of employees., (ii) standardizing a process for optimal efficiency and repeatability, (iii) studying a process for efficiency and improvement, hence helping to show unnecessary steps, and other inefficiencies, (iv) modelling a better process or creating a brand-new process, and (v) communicating and collaborate with diagrams which speak to different roles in the organization or outside of it. Diagramming is quick and easy.

PFD uses a series of symbols and notations to depict a process. The symbols vary in different places, and the diagrams can range from simple, hand drawn scrawls, or sticky notes to professional-looking diagrams with expandable detail, produced with software.

PFD has its roots in the 1920s. In 1921, industrial engineer and efficiency expert Frank Gilbreth, Sr. introduced the ‘flow process chart’ to the American Society of Mechanical Engineers (ASME). Over the next several decades, the concept spread throughout industrial engineering, manufacturing and even business, in the form of ‘business process diagram’, and information processing, in the form of ‘data flow diagram’ and other chart types.

A typical PFD for a single unit process include the elements consisting of (i) major equipment including names and identification numbers, e.g., compressors, mixers, vessels, pumps, boilers, heat exchangers and coolers, (ii) process piping which transport the product, normally fluids, between equipment pieces, (iii) process flow direction, (iv) control valves and process-critical valves, (v) major bypass and recirculation systems, (vi) operational data e.g., pressure, temperature, density, mass flow rate, and mass-energy balance, (vii) values which frequently include minimum, normal, and maximum, (viii) composition of fluids, (ix) process stream names, and (x) connections with other systems.

A PFD does not normally include detailed items such as (i) pipe classes and pipe line numbers, (ii) process control instruments, (iii) minor by-pass valves, (iv) isolation and shut-off valves, (v) maintenance vents and drains, (vi) relief valves and safety valves, and (vii) code class information.

PFD comprises but not limited to the items consisting of (i) all process lines, utilities, and operating conditions necessary for heat and material balance, (ii) type and utility flow lines which are used continuously within the battery limits, (iii) equipment diagrams to be arranged as per the process flow, designation, and equipment number, (iv) simplified control instrumentation pertaining to control valves and the likes involved in process flows, (v) major process analyzers, (vi) operating conditions around major equipment, (vii) heat duty for all heat transfer equipment, (viii) changing process conditions along individual process flow lines, such as flow rates, operating pressure, and temperature etc., (x) all alternate operating conditions, and (x) material balance table.

The items which are not normally shown on PFD, except in special cases are (i) minor process lines which are not normally used in normal operation and minor equipment, such as block valves, and safety / relief valves etc., (ii) elevation of equipment, (iii) all spare equipments, (iv) heat transfer equipments, pumps, and compressors etc., operated in parallel or in series are shown as one unit. (v) piping information such as size, orifice plates, strainers, and classification into hot or cold insulated of jacket piping, (vi) instrumentation not related to automatic control, (vii) instrumentation of trip system, (since it cannot be decided at the PFD preparation stage), (viii) drivers of rotating machinery except where they are important for control line of the process conditions, and (ix) any dimensional information on equipment, such as internal diameter, height, length, and volume, with internals of equipment are shown only if needed for a clear understanding of the working of the equipment.

PFD is not drafted to scale. However, its size is to be compatible with that of equipment drawings. As a rule, PFD is drawn from the left to the right as per the process flows. The main process flow is accentuated by heavy lines. Process utility lines is shown only where they enter or leave the main equipment. Pipe lines are not identified by numbers. Valves, vents, drains, by-passes, sample connections, automatic or manual control systems, instrumentation, electrical systems, etc. are omitted from the schemes. The direction of the flow is indicated for each line.

As a rule, process lines, utility lines, and loop lines for instrument are to be drawn as (i) main process line, (ii) secondary process lines and utility line, and (iii) lines showing all electrical, computer, and instrument signals.

PFD depicts a process or a process plant by means of graphical symbols which are inter-connected by lines. PFD contains at least the basic information consisting of (i) kind of apparatus and machinery, except drives, needed for the process, (ii) designations for equipment and machinery, except drives, (iii) route and direction of the in-going and out-going material and energy flows, (iv) denomination and flow rates or quantities of in-going and out-going materials, (v) denomination of energy types and / or energy carriers, and (vi) characteristic operating conditions. Fig 4 shows process flow diagram with basic information. In the diagram alternative designations for devices and equipment with back-up redundancy can be assigned using suffix letters (e.g., P1 A/B).

Fig 4 Process flow diagram with basic information

A utility flow diagram (UFD) is a special type of PFD. It is a schematic representation of the energy utility systems within a process plant, showing all lines and other graphic means needed for the representation of transport, distribution, and collection of forms of energy. In a UFD, process equipment can be represented by boxes with inscriptions and with utility connections. The graphical symbols represent equipment and the lines represent flows of mass, energy, or energy carriers. Fig 5 shows process flow diagram as utility flow diagram.

Fig 5 Process flow diagram as utility flow diagram

PFD can also contain the additional information consisting of (i) denomination and flow rates or quantities of materials between the process steps, (ii) flow rates or quantities of energy and / or energy carriers, (iii) essential valves and their arrangement in the process, (iv) functional demands for process measuring and control devices at important points, (v) supplementary operating conditions, (vi) characteristic data of equipment and machinery (except drives), given in separate lists if necessary, (vii) characteristic data of drives, given in separate lists if necessary, and (viii) elevation of platforms and approximate relative vertical position of equipment. Fig 6 shows process flow diagram with basic and additional information.

Fig 6 Process flow diagram with basic and additional information.

The most common PFD symbols in use today come from the standardization organizations such as ISO (International Organization for Standardization, ISO 10628 – Flow Diagrams for Process Plants, General Rules), and ANSI (American National Standards Institute). However, several organizations use their own symbols, which are frequently similar but vary as they become more detailed.

PFDs are frequently given to electrical and controls engineers for the purpose of creating P&IDs. PFDs are frequently used as the background in CAD for creating the P&IDs. Control and communication details are added to the PFD backgrounds to make P&IDs.

PFD shows all process engineering information. Typical conventions used in PFD are (i) all major equipment are represented and are uniquely numbered, (ii) all process flow streams are shown and are uniquely numbered, with description of thermo-dynamic conditions and composition (frequently in an accompanying table), (iii) all utility streams supplied to major process equipment are shown, (iv) basic control loops, showing control strategy during normal operation, (v) topology of the process showing the connectivity of all the streams and the equipment is shown, (vi) number streams are shown left to right when possible, (vii) crossing of lines is avoided by showing horizontal lines continuous and  vertical lines broken, and (viii) frequently the basic control loops (those involving maintaining material balance and reactor controls) are included on the PFD and instrumentation and other control loops are not shown.

Piping and instrument diagram

P&ID is sometimes called process and instrument diagram. It is more technical, describing mechanical details for piping designers, electrical engineers, instrument engineers, and other technical experts who need this detail more than they need process details. P&IDs take the conceptual aspects of a PFD and add detail about the equipment, process sequence, process and utility piping, bypass lines, instruments, valves, vents, drains and other items.

P&IDs are the drawings showing piping and communications as schematic (unscaled) lines and control features as symbols. P&IDs show the functional relationship of piping, instrumentation, equipment, and controllers. They are normally a part of the instrumentation drawings in a project drawing set. P&IDs are normally made by process engineers, controls engineers, and electrical engineers. The main purpose of a P&ID is to indicate if the equipments are automatically controlled, and if so, how they are inter-locked with instruments. P&IDs convey the inter-connectivity of automated equipments.

P&ID is based on the PFD and depicts the technical realization of a process by means of graphical symbols representing equipment and piping, together with graphical symbols for process measurement and control functions. All equipment, valves, and fittings are represented as per ISO 10628-2. The process measuring and control tasks are represented as per IEC 62424. Auxiliary systems can be represented by rectangular frames with references to separate flow diagrams.

The P&ID contains at least the basic information consisting of (i) function and type of equipment and machinery, including drives, conveyors, and installed back-up / reserve equipment, (ii) designation of apparatus and machinery, including drives, (iii) characteristic data of equipment and machinery, given in separate lists, if necessary, (iv) indication of nominal sizes, pressure ratings, material, and type of piping, e.g., by stating the pipeline number, piping class, or designations, (v) details of equipment, machinery, piping, valves, and fittings e.g., pipe reducers given in separate list if necessary, (vi) symbols for  process measurement, and control functions including letter codes for process variables, control functions, and  designation of the process, measurement, and control function, and (vii) characteristic data of drives, given in separate lists if necessary. Fig 7 shows piping and instrumentation diagram with basic information.

Fig 7 Piping and instrumentation diagram with basic information

As an alternative to the pump designation (pump aggregate), one of the two designations as shown in the bottom right corner of Fig 7 can be assigned to the pump and the associated motor. This identification method is particularly suitable for aggregates which have more than one motor.

P&ID can also contain additional information such as (i) denomination and flow rates or quantities of energy or energy carriers, (ii) route and direction of flow of energy or energy carriers, (iii) type of essential devices for process measuring and control, (iv) essential construction materials for equipment and machinery, (v) elevation of platforms and approximate relative vertical position of equipment, (vi) designations of valves and fittings, and (vii) denomination of equipment.

P&IDs are made during the project phase and are helpful (i) during design, in coordination of instrumentation, controls, and wiring details between process engineers, controls engineers, and electrical engineers, in helping to create detailed control descriptions and control loops, and in developing HAZOP (hazard and operability) studies, (ii) during procurement, in specifying instrumentation and controls details needed for getting quotation, and providing control details needed for estimating programming costs, (iii) during construction, in specifying details needed for purchasing and installing instruments, electrical devices, and controls components, in providing details needed for the programming of controllers, in helping to confirm that communication wires have been terminated correctly, in helping to record field changes easily on as-built drawings, and in utilizing during start-up and training of employees to understand the function of the system or process, (iv) during operation, as-built P&IDs provide control details needed for making decisions during operation, P&ID format is easy to understand compared to programming code or written descriptions, operators can read the P&IDs and understand options for operations, helpful for a JHA (job hazard analysis), and helps when preparing for system modifications as part of  MOC (management of change).

Typical steps to create a P&ID consist of (i) creation of BFD, (ii) creation of PFD, (iii) writing of high-level control descriptions, (iv) creating of draft P&IDs using PFDs as backgrounds, (v) drawing areas at the top of P&IDs for controllers, MCCs (motor control centres), and / or SCADA (supervisory control and data acquisition), (v) adding symbols and labels to P&IDs for control features, (vi) drawing wiring on P&IDs to connect electrical devices with controllers, MCCs, and / or SCADA, (viii) completing detailed control descriptions, (ix) defining control loops, typically in a table format, (ix) ensuring that the identification numbers on P&IDs are matched with control descriptions and control loops, and (x) performing quality review and making corrections.

It is common for a legend drawing to be included with a drawing set to define the symbols, abbreviations, line types, shading, etc., utilized on the PFDs and P&IDs. Sometimes there are common legend drawings and sometimes there are separate legend drawings for PFDs and P&IDs.

P&ID is a complex representation of the different units found in a plant. It is used by people in a variety of skills. The primary users of the document after plant start-up are process operators, as well as instrument and electrical, mechanical, safety, and engineering personnel. In order to read a P&ID, the operator needs an understanding of the equipment, instrumentation, and technology. The next step in using a P&ID is the memorization of the process symbol list of the plant. This information can be found on the process legend. Process and instrument drawings have a variety of elements, including flow diagrams, equipment locations, elevation plans, electrical layouts, loop diagrams, title blocks and legends, and foundation drawings. The entire P&ID provides a three-dimensional look at the different operating units in the plant.

The process legend provides the information needed to interpret and read the P&ID. Process legends are found at the front of the P&ID. The legend includes information about piping, instrument and equipment symbols, abbreviations, unit name, drawing number, and revision number. Several organizations use their own symbols in unit drawings. Unique and unusual equipment also need a modified symbols file.

P&ID includes a graphic representation of the equipment, piping, and instrumentation. Modern process control can be clearly inserted into the diagram to provide a process operator with a complete picture of electronic and instrument systems. Process operators can look at their process and see how the engineering department has automated the unit. Pressure, temperature, flow, and level control loops are all included on the unit P&ID.

Process operators use P&IDs in identifying all of the equipment, instruments, and piping found in their units. New operators use these drawings during their initial training period. Knowing and recognizing these symbols is important for a new operator. The processing industry has assigned a symbol for each type of valve, pump, compressor, steam turbine, heat exchanger, cooling tower, basic instrumentation, reactor, distillation column, furnace, and boiler. There are symbols for representing major and minor process lines, and pneumatic, hydraulic, or electric lines, and there is a wide variety of electrical symbols.

Drafting guidelines

A1 size (504 mm x 841 mm) as defined in ISO 5457 is preferably used as drawing sheets for drawing process diagrams. Considering the different copying techniques (reduction) available, long sizes and sizes larger than A1 are to be avoided. The basic title block for drawings and lists (with additional fields) as shown in ISO 7200 are used.

In the layout of flow diagrams, graphical symbols for equipment and machinery can be enlarged in order to give a clear representation of internals and connections. Devices to be expected at the upper-most level of the plant are to be shown at the top of the drawing and those expected to be located at the lowest level are to be shown at the bottom of the drawing. The graphical symbols for process-related measuring and control functions for equipment, machinery, and piping, as well as those representing piping and valves, are to be shown in the logical position corresponding to their functions. Fig 8 shows some of the graphical symbols used in process diagrams.

Fig 8 Some of the graphical symbols used in process diagrams

As regards connecting lines, line widths are related to the grid module (as per ISO 81714-1) for flow diagrams with M = 2.5 mm. For getting a clear representation, different line widths are to be used. Lines representing main flows or main piping are to be highlighted. The line widths as specified in ISO 128 (all parts) which are used are (i) 1 mm (0.4 M) for main flow lines, (ii) 0.5 mm (0.2 M) for graphical symbols representing equipment and machinery, except valves and fittings and piping accessories, rectangular frames representing unit operations, process equipment etc., subsidiary flow lines, and energy carrier lines and auxiliary system lines, and (iii) 0.25 mm (0.1 M) for graphical symbols representing valves and fittings and piping accessories, symbols representing process measuring and control functions, control and data transmission lines, reference lines, and other auxiliary lines. Line widths less than 0.25 mm (0.1 M) are not used.

The minimum space between parallel lines is at least twice the width of the widest line, but at least equal to 1 mm. Space between flow lines is higher than 10 mm.

As regards flow direction, the main flow direction is normally to be drawn from left to right and from top to bottom. In-going and out-going flows of a diagram, also flows coming from of continuous on other diagrams are to be identified with arrows as shown in Fig 8. For reversible flows arrows as per Fig 8 are to be used.

If a diagram consists of several sheets, it is desired that the lines representing in-coming and out-going flows and piping are drawn in such a manner that these lines continue at the same level when the individual sheets are placed next to one another horizontally and are aligned vertically. When a connection line continues to another diagram, the end is to be mutually referenced. The reference is to consist of a designation (Fig 8).

Arrows are incorporated in the lines to indicate the direction of the flows within the flow diagram. In order to facilitate understanding, arrows can be used at the inlets to equipment and machinery (except for pumps) and upstream of pipe branches as shown in Fig 8. Arrow heads for indication of flow are as per ISO 14617-2.

When pipes are represented by the same line width cross, but are not connected to each other, the line depicting the vertical pipe is interrupted as shown in Fig 8. When pipes are represented by different line widths cross, but are not connected to each other, the line depicting the thinner pipe is interrupted (Fig 8). A pipeline junction (tee) is represented as shown in Fig 8. Junctions of pipelines in close proximity are represented as shown in Fig 8.

Auxiliary system lines are shown by dashed lines with an indication of the flow direction and reference to the type of energy carrier and, if possible, the drawing number.

As regards type of lettering, type B vertical lettering as per ISO 3098-2 is desired. Legends and designations in flow diagrams are always to be written in upper-case characters. The only exceptions to this rule are chemical formulae (e.g., NaCl), abbreviations referring to technical regulations and legislation (e.g., BImSchG), and other cases where there is a danger of confusion if only upper-case characters are used.

The height of letters is (i) 5 mm for designations of equipment and machinery, and (ii) 2.5 mm for other lettering. Reference designations of equipment are located so that the relationship is unambiguous, but is normally not printed inside the relevant graphic symbol. Further details (e.g., designation, nominal capacity, pressure, and material) can either be placed below the reference designations or shown in separate tables.

Designations of flow lines or piping are written above and parallel to horizontal lines and to the left of and parallel to vertical lines. If the beginning and end of flow lines or piping are not immediately recognizable, corresponding elements are indicated by identical identification letters.

Reference designation of valves and fittings are normally written next to the corresponding graphic symbol and parallel to the flow direction. In case of the process measurement and control systems, the designation is as per IEC 62424.

Flow rates and / or quantities, operating conditions, and thermo-physical properties are entered either in rectangular frames or in a separate table. The frames are connected to the reference points by means of reference lines and are arranged parallel to and above horizontal lines and to the left or right of vertical lines, respectively. If the data are shown in tabular form, serial numbers corresponding to the data list are written in the frames. SI (The International System of Units), normally known as the metric system) units as per ISO 80000-1 are used.

When drafting P&IDs, the following aspects are to be taken into account with regard to scales, elevation levels, and piping.

As a rule, P&I flow diagrams are not drawn to scale. However, in order to show the relative sizes of main equipment and devices, such as vessels, columns, heat exchangers, etc., these are depicted in the same scale relationship, wherever possible.

Vessels and equipment are drawn or depicted large enough so that all needed piping connections can be clearly shown.

Elevation levels (heights) are only depicted if this is necessary to improve understanding of the diagram or of technical aspects.

Pipelines are not bound to elevation levels.

The indication limits of materials, supplier, or battery limits are as per Fig 8. The information can be placed in-side or out-side the symbol.

The graphical symbols are grouped in ISO 10628 -2:2012 as per the functional and / or design features. These groups are (i) vessels and tanks, (ii) columns with internals, (iii) heat exchangers, (iv) steam generators, furnaces, and re-cooling device, (v) cooling tower, (vi) filters, liquid filters, and gas filters, (vii) screening devices, sieves, and rakes, (viii) separators, (ix) centrifuges, (x) drier, (xi) crushing / grinding machines, (xii) mixers / kneaders, (xiii) shaping machines – processing in vertical direction, (xiv) shaping machines – processing in horizontal direction, (xv) liquid pumps, (xvi) compressors, and vacuum pumps, (xvii) blowers, and fans, (xviii) lifting, conveying, and transport equipment, (xix) proportioners, feeders, and distribution facilities, (xx) engines, (xxi) valves, (xxii) check valves, (xxiii) valves and fittings with safety function, (xxiv) fittings, (xxv) graphical symbols for piping, (xxvi) apparatus elements, (xxvii) internals, (xxviii) agitators, and stirrers, and (xxix) internal characteristics and built-in-components.

Rules for modification of proportions and orientation of graphical symbols are given in ISO 81714 and IEC 81714. If a graphical symbol is not accessible in ISO 10628-2, then ISO 14617 is to be consulted for the needed graphical symbol. If the needed graphical symbol is not available in ISO 14617, then the symbol is to be created by combining ISO 14617 symbols of basic nature with symbols given supplementary information as per the rules given in ISO 14617, ISO 81714 and IEC 81714.

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