ISATRANSACTIONS®

ISA Transactions 41~2002! 389–394

Editorial viewpoint

A P&ID standard: What, why, how?Frederick A. Meier*

412 Colony Woods Dr., Chapel Hill, NC 27517, USA

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Introduction

This paper is written for all who develop anuse P&IDs. It will aid in solving the long existingand continuing problem of confusing informatioon P&IDs. Some of this confusion can be eplained because there is no agreement on whaformation should be included on a P&ID or evewhat the P&ID letters stand for. The P is somtimes ‘‘piping’’ and sometimes ‘‘process.’’ The I issometimes ‘‘instrument’’ and sometimes ‘‘instrumentation.’’ The D is sometimes ‘‘drawing’’ andsometimes ‘‘diagram.’’ P&IDs are also calle‘‘flow diagrams,’’ often preceded by ‘‘engineering’’ or ‘‘controls’’ or other descriptors. For sim-plicity, we will call the document a P&ID. There ino universal standard for the developmentP&IDs. ISA-5.1 is an excellent flexible documeto define instrument symbolism. In this paperhave used ANSI/ISA-5.1 1984 as my definitivreference, although I am aware that the documis under review and revision. P&IDs in many locations have been developed over the yearsmany different developers. Revisions to refleprocess improvements and additions may habeen documented by many different individuasome using symbolism and format that differ frothe original and from each other. Therefore tsymbolism and the format are not consistent athe P&IDs are subject to misunderstandings.solve this problem, I suggest that every organi

*E-mail address: famjp@aol.com

0019-0578/2002/$ - see front matter © 2002 ISA—The Instru

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tion that develops and/or uses P&IDs produtheir unique standard. The standard would inclua typical P&ID or P&IDs plus legend sheets tdefine all types of relevant process information.should include not only the basic symbolism finstrument and control, but also typical sketchwith explanations of repetitive complex advancontrol schemes and other information importaor unique to that location. It should be the basfor all P&ID work done at that location. In thispaper, for simplification, we will call this set odocuments the ‘‘standard.’’ The following pagedevelop the concept of the ‘‘standard’’ and posome of the questions that the ‘‘standard’’ can aswer.

The acronym P&ID is widely understood tmean the principal document used to definedetails of how a process works and how it is cotrolled. The ISA Dictionary definition for P&IDtells what they do, ‘‘show the interconnection oprocess equipment and the instrumentation usecontrol the process. In the process industry a stdard set of symbols is used to prepare drawingsprocesses. The instrument symbols used in thdrawings are generally based on ISA-S5.1.’’1 Inthis paper the ISA standard will be referred toISA-5.1.

1ISA-S5.1 refers to ISA Standard ANSI/ISA-5.1-198Instrumentation Symbols and Identification.

mentation, Systems, and Automation Society.

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390 Frederick A. Meier / ISA Transactions 41 (2002) 389–394

P&ID development

Although the P&ID is the overall document defining the process, the first document developfor a process is often the PFD, the ‘‘process flodiagram’’ or ‘‘drawing.’’ Most would agree that aa minimum the PFD shows a material balance amajor equipment and process flows, pressures,temperatures. Some PFD’s show much moretail, sometimes including major instrumentatioand some PFDs show significant details of tcontrol schemes. Once a PFD is available, P&development commences. P&IDs develop in steThe key personnel, perhaps piping, process,project specialists, lay out a first try showing vesels, equipment, and major piping. Since it oftrequires additional space, the instrumentationadded next, followed by the contributions of thspecialists in electrical, equipment, mechanicvessel, and other disciplines. The developmenprocess is an iterative one with a P&ID developiin several steps to a finished document complwith all necessary detail, and eventually the P&will be issued for construction.

It is important throughout the life of a P&ID thaeveryone works with the same information. Thefore everyone needs the same revision ofP&ID and that revision must reflect all current information. This is true not only during engineerindesign and construction but equally true after tplant is in operation. There must be a central cotrol of P&IDs, which will have responsibility torevise, reissue, and distribute P&IDs as necessthroughout their life. This control group or persomust have enough experience to judge when aissue should be made, enough knowledge to knthat the revision is consistent with the standaand enough authority to make the decision stiOf course, all proposed changes must be analyzreviewed, and approved by specialists before geral reissue.

Standardization

To understand a book, it must be written inlanguage we know, in which words have specimeanings. It must be printed in a format wiwhich we are familiar. A book written in JapaneKanji read from right to left may be beautiful aninteresting to look at and readable if you kno

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Japanese, but if you are not familiar with the laguage, it is totally incomprehensible. So it is wiP&IDs. If we understand the language and the fmat, the book is readable. The language of P&Iis the symbolism and the format is how the symbolism is presented. The language of the instment and control portion is based on ISA-5.1,as ISA defines ‘‘The standard offers the foundatifor that common language.’’2 However, there areseveral major problems that develop:• First, ISA-5.1 is a very flexible standard. Foexample, it uses every letter of the alphabetdefine process variables, or as the standard smeasured or initiating variables. There are seveletters—C, D, G, M , N, andO—which are user’schoice, andX as unclassified to be selected by tP&ID developer to define any variable not listedirectly and used as the first letter of an instrumeidentifier. This gives ISA-5.1 flexibility but makeexact standardization impossible. For example,identify a conductivity analyzer, one locatiomight use the user’s choice letterC for conductiv-ity and another might use the standard letterA foranalysis, with a conductivity modifier showabove the identifying bubble. Still another locatiomight useC for capacitance. Without referencethe ‘‘standard,’’ this use of letters will cause misunderstanding and confusion. To be understothese letters must be defined somewhere andcourse their definitions will vary from plant toplant; therefore the ‘‘standard’’ is the logical placfor definitions of this type.• Second, ISA-5.1 is a consensus standard,quote ‘‘Its weakness is generally that of not beinspecific enough to satisfy the special requiremeof particular interest groups.’’3

Engineering contractors, user engineerigroups, and other P&ID developers develop sof symbols. Since they are based on a flexibstandard, as technology changes they have adency to change. One developer’s set does notways agree with another’s. Additionally, an engneering contractor might work repetitively withparticular client, or perhaps specialize in a particlar branch of the process industry, and their P&IDwill reflect this and will not be universally understood.

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391Frederick A. Meier / ISA Transactions 41 (2002) 389–394

My career has included many years in the devopment and use of P&IDs as an instrument enneer, chief instrument engineer, and engineermanager. For the last ten years, I have been aninstructor, teaching documentation of control sytem projects and have had hundreds of studentclasses I have taught. Many of my studentsvery young, very bright engineers and techniciawho have been assigned the job of reworking thplant P&IDs to a single standard because theisting P&IDs are confusing operations, and matenance personnel. It is indeed fortunate that thare young and bright because, I predict, theworking will be a time consuming and very difficult undertaking.• Third, if P&IDs are not consistent within a location, the task of updating the P&IDs may becomonerous or even impossible. One student mtioned 15 to 20 sets of P&IDs developed by macontractors over a 20 to 30 year period. None wdeveloped to a plant standard.

Arthur Little, Inc., after developing Process Haard Management~PSM! plans for petroleum re-fineries saw the seriousness of the probleminconsistent and out of date P&IDs and mastatements such as:

‘‘The cost of updating P&IDs for the PSM analysis could double the cost.’’4

‘‘The most universal deficiency is keepinP&IDs up to date.’’4

• Fourth, the P&ID will have many uses during iexistence. For example, an engineering contracmight use the P&ID to develop an early estimaof project cost. The estimators may need detaearly in the project for control valves, includinsize, body type, materials of construction, typeactuator, presence of positioners and hand jacand the extent, size, and type of block and bypvalves and drains. Therefore all of this informatiois included on the P&ID. Since it would cost momoney and man hours to remove it, the informtion stays on the P&ID, even though it is modetailed than required. Since this information wadded early, it would require revision as thproject proceeds. All of the accurate informatiowill be available later on the valve specificationand other project documents. This informati

4ISA Training Course FG 15. Revision 2.1 Slide 34.

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may make the P&ID appear crowded. Plant opetors might rather see a generic valve symbol. Fexample, the bow tie combined with the sprinand diaphragm actuator might be used as the sbol for all control valves. Additionally, plant operations might want control valve blocks and bpass valves identified with tags on P&IDsfacilitate their operator training and instructionTo the P&ID developer this adds needless clutand complexity to the P&ID.

P&IDs are developed for the design and costruction of a plant. They may be used for thpurpose for three or more years. After this periplant operations may use the document as longthe plant is in operation, perhaps 10 to 30 yeaThe standard should therefore reflect requiremefor information useful during operations, trainingmaintenance, HAZOPS, safety reviews, and otuses.• Fifth, ISA-5.1 is dedicated to the languageP&IDs. It does not address in any detail the formof P&IDs. Consequently, the formats vary with industry segments and contractors. A P&ID forwater treating plant might be difficult or even impossible for a refinery specialist to understand.

The previous paragraphs define some oftypes of problems that will be addressed whenP&ID developer and user each have a ‘‘standarand can sit at the same table and resolve diffences. The agreement will probably be a compmise, as most good agreements are. To the P&developer anything that is different or specialthe project adds cost, confusion, misunderstaing, and prolongs schedule. The developer wouof course, want to be compensated for the coand have the complexity reflected in the scheduTo the user, having a set of P&IDs requiring sinificant retraining and explanation before plapersonnel can use them effectively is alsoadded cost and will affect the training cost anschedule. Consequently, agreement shouldreached early when there is still sufficient leatime to cover these extra costs and possible schule extensions. Without agreement on a standamisunderstandings can occur, and misunderstaings cause unsafe conditions and accidents. Thare no universal standards that address the forto be used in developing P&IDs. The format ushas been developed over the years and thereguidelines that serve as an incompletede factostandard. Some of these are:

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392 Frederick A. Meier / ISA Transactions 41 (2002) 389–394

• The process flows from the left of the P&IDto the right.

• P&IDs are developed as ‘‘C’’ size(22334 in.) but must be legible when reduceto ‘‘B’’ size (11317 in.) for ease of use inthe office and in the field.

• P&IDs should show sufficient informationto define the process without crowding thP&ID. One to three pieces of equipmewith auxiliaries is sufficient for oneP&ID:

• To reduce clutter use typical sketches or dtails.

• When piping gets complex, use auxilliarP&IDs.

• Use notes to add understanding and clari• Show relative elevations of equipment b

do not include specific elevation.

Questions

How much information should be shown onP&ID? Since the P&ID may have different usethis question is a difficult one to answer. The folowing questions relate to instrumentation:

1. What type of instrument numbering systeshould be used?

a. Major equipment basedb. Serialc. Paralleld. Specification based

2. How should the fail position of controvalves be shown?

a. Arrows and barsb. Letters, FC, FI, FL, FOc. Shading part of the symbold. Not at all

3. Should the following items be shown?

a. Convertersb. Air suppliesc. Positionersd. Power supplies

4. Should all control valves be tagged?In some of the sketches in ISA-5.1, contrvalves do not have tag numbers and therefsome do not show control valve tags oP&IDs.

5. How closely should ISA-5.1 be followed?Since it is a consensus standard, it is nolegal document and many have revised itserve their use. For example, ISA-5.1 is veclear that a control valve in an instrumeloop will be designated by two letters. Thfirst letter defines the process variable in tloop and the second, a ‘‘V.’’ The valve inflow loop FIC-2 would therefore be designated FV-2. Even so, some use a three-ledesignation FCV-2.

P&IDs certainly show piping and major equipment. There is agreement that piping mustidentified by some sort of sequential number, bhow much more information should be includedThe following are questions relating topiping:

1. How should piping be identified?

a. By sequential numberb. By specification numberc. By pressure and temperature ratingd. By process fluide. By a combination of some or all of these

2. How should piping climatization be shown

a. By symbols onlyb. By word descriptionc. Not shown on P&ID, but included else

where

Major equipment needs to be identified, bthere is a wide variation in the information showon the P&ID.

1. How much information about the equipmeshould be shown?

a. Capacityb. Design flow, presure, temperaturec. Driver horsepowerd. Identifying lettere. Identifying numberf. Identifying tagg. Material of constructionh. Size

2. What identifying letters should be used? Tlist below is a typical set of letters. There amany other sets, each different:

C - Columns and towersD - Drums and vesselsE - Heat exchangers and coolers

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393Frederick A. Meier / ISA Transactions 41 (2002) 389–394

F - Furnaces and heatersK - Compressors and blowersP - Electric motorsT - TurbinesV - Those not included above

3. How should equipment climatization be show

a. By symbols onlyb. By word descriptionc. Not shown on P&ID, but included else

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Significant standards

There are many standards, both industry aspecialized, containing references to P&IDs thmay be helpful during P&ID development.

ANSI/ISA-5.1-1984 Instrumentation Symband Identification.This is the most widely usedstandard for symbols used to define measuremand control schemes. The ISA-5.1 diagrams shsymbols for the measurement and control portof the P&ID.

ISA-5.3-1983 Graphic Symbols for DistributeControl/Shared Display Instrumentation Logand Computer Systems. This standard was deveoped to supplement ISA-5.1 as computer, logand distributed control became popular. It clarifithe symbols for these technologies. It containsfew sketches to aid in development, but no reguidance in helping to develop a standard P&ID

SAMA Standard PMC 22.1—Functional Diagramming of Instrument and Control System.SAMA, The Scientific Apparatus Makers Assocition, no longer supports the document, howeveris still in use in some industries. It details the funtions of the control system showing, for exampthe modes of control in a controller—the propotional ~gain!, integral ~reset!, and derivative~rate!—which are rarely, if ever, included oP&IDs.

PMC 22.1 states that P&IDs are needed. ‘‘clarify the type of diagram with which this standard is concerned, it is assumed that in designincomplex measuring, control or computational sytem the following types of diagrams will be required:

a. functional diagramsb. detailed schematic diagrams

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Diagrams.’’5

The standard goes no further in defining an ISProcess & Instrumentation Diagram.

ASME: American Society of Mechanical Engneers. There are several ASME standards whicontain bits and pieces of information that migbe helpful in developing P&ID standards including:

ANSI Y14.15a Interconnection DiagramsASA Y32.11 Graphical Symbols for Proces

Flow DiagramsASA Z32.2.3~Re-designated ANSI/ASME

Y32.2.3! Graphical Symbols for Pipe, FittingsValves and Piping.

IEEE: The Institute of Electrical and ElectroniEngineers. IEEE has published the followingstandards which include the symbols for electricdrawings. but a few might be useful on P&IDs.

IEEE Std 315-Graphic Symbols for Electricaand Electronic Diagrams.

This standard is also recognized as ANY32.2 and CSA Z99

ANSI/IEEE Std 315A-Supplement to St315.

There are other industry groups that addreP&IDs in their publications:

1. OSHA: The Occupational Safety and HeaAdministration issued its Process SafeManagement Standard in 1992. The docment, 29 CFR 1910.119 Process SafeManagement of Highly Hazardous Chemcals, paragraph~d! Process Safety Information requires that all installations handlincertain hazardous materials will havP&IDs, but does not define them furtheOSHA standards are law in the United Statand therefore must be followed.

2. PIP: The Process Industry Practices groupcoalition of process industry owners anengineering/construction contractors is dveloping recommended practices for all aeas of the engineering-procuremenconstruction process, including P&IDs anthe field of instrumentation. PIP’s address

5SAMA Standard PMC 22.1-1981.

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394 Frederick A. Meier / ISA Transactions 41 (2002) 389–394

3208 Red River, Austin, Texas 78705-265and their phone is~512! 473-2968.

3. API: The American Petroleum Institute, iAPI Recommended Practice 750 Managment of Process Hazards mentions P&IDsfollows: ‘‘The mechanical design information should include the materials of construction, piping and instrument diagram@process and instrument diagram~P&IDs!#.’’ 6 They go no further in describing P&IDs.

4. ISA has formed a Standards SubcommitSP5.7—‘‘Development and Use of ProceFlow Diagrams and Piping and InstrumeDiagrams’’—to develop a standard for usin industry.

Conclusions

The preceding information will not magicallcreate a standard, but it is a start. The developmand maintenance of the standard will not be eaand will be time consuming. Once a standarddeveloped there is one further step that shouldconsidered very carefully. That is what should

6API Recommended Practice 750.

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done about the pre-standard P&IDs? To achieoverall consistency, it would be necessary but veexpensive to rework all the old P&IDs and to edcate all those using them.

There is help in this paper but there will also bunanswered questions. In my opinion all the timand effort is worth the results. When design, matenance, and operations engineers, specialists,technicians have to speak many different P&languages because different people develotheir P&IDs, it is costly, confusing, and dangeous.

Frederick A. Meier’s careerspans 50 years of experiencas a control systems engineechief engineer, and as an engneering manager in the oil,chemical, and engineering industries in the United StatesAlgeria, Canada, Germany, Japan, and the United KingdomHe has held professional engineer licenses in New York,New Jersey, California, Al-berta, Manitoba, andSaskatchewan. Fred has a U.S

Army Electrical Degree, a Mechanical Engineering Degree~StevensInstitute of Technology!, and an MBA~Rutgers University!. Since hisfirst retirement he served as an ISA staff engineer, since his secretirement, as an ISA instructor and consultant.