Piping Terms Glossary
This list is intended to include most commonly used abbreviations and acronym found in Piping Engineering and Design work.
It has been compiled and prepared to aid both the newcomer and others with a convenient list for mutual use and understanding.
Abbreviation Definition with Description, Meaning or Source
A Absolute - (See ABS)
A Air – Used to define the commodity in a Line Number
A Analog signal - This is normally the indication of the existence of and type signal from some instrument in the plant back to the control room panel
A Inlet Nozzle - See Note #1
A Pipe Anchors – This is a fixed anchor restricting the pipe movement at a specific support from moving in any (horizontal of vertical) direction.
A/G Above Ground – The most common use for this abbreviation is on a P&ID to indicate that portion of a line that is to be or will be above ground.
ABS Absolute - Unit of measure. This term is normally used along with another qualifier as in Absolute Pressure.
AC Air Conditioner - Equipment designation
AC Air to Close – This is normally found on a P&ID at a control valve and indicates that the control valve is a “spring to open and therefore needs air to close.
AC Combustion -
ADAPT. Adaptive control mode -
AFC Approved For Construction – This is a status indicator for engineering documents such as Flow Diagrams, Specifications, Drawings, etc. This indication (note) is normally stamped on a document in red so that it is very visible. The “Approved” part of the note normally means that the Client has done the Approving.
AFD Approved For Design – This is also a status indicator. But in this case the document is normally an early schematic drawing such as a P&ID. The “Approval” is still by the Client.
AG Above Ground
AGA American Gas Association
AISC American Institute of Steel Construction
AISI American Iron and Steel Institute
ANSI American National Standards Institute
AO Air to Open - This is normally found on a P&ID at a control valve and indicates that the control valve is a “spring to close and therefore need air to open.
AP Plant Air – Used to define the commodity in a Line Number
API American Petroleum Institute
AS Air Supply – Used to define the commodity in a Line Number
AS Sprinkler system
ASA American Standard Association -
ASME American Society of Mechanical Engineers -
ASTM American Society for Testing and Materials -
AWS American Welding Society -
AWWA American Waterworks Association -
B Outlet Nozzle – See Note #1
BA Base Anchor – This is a type of support often used under piping low to grade or floor surface. It is rigidly connects the piping to the paving or floor surface.
BBE Beveled Both Ends – This is an end prep qualifier for piping fittings such as reducers and swedges.
BBL Barrel – This is most commonly used when discussing the plant capacity (100,000 Bpd) or the capacity of a tank. It normally refers to a “55 Gallon Barrel” but one should remember that a barrel actually holds only 42 US gallons.
BBP Bottom of base plate – The Base Plate in this case is the bottom ring plate of a vertical vessel support or the bottom plate of a saddle support of a piece of horizontal equipment.
BC Bolt Circle – This might be for a flange, a Vertical vessel support or for a Manhole.
BD Blow down - – Used to define the commodity in a Line Number
BF Blind / Blank Flange
BFW Boiler Feed Water – This is the cleaned, treated, preheated high pressure water that is pumped into a Boiler to make steam.
BG Base Guides – This is a type of support under low piping that is designed to allow the pipe to move back and forth in a specific direction.
BL Battery limit – This is the invisible boundary around specific portion of a process plant (i.e.: The Crude Unit Battery Limits)
BLE Beveled Large End - This is an end prep qualifier for piping fittings such as reducers and swedges.
BLVD Boulevard – As in a type of street
BVLD Beveled – This would normally refer to the end preparation for pipe and fittings.
BOF Bottom of Face of Flange – This would be used as a reference point clarification when used with an elevation (i.e.: BOF Elev. 109’ - 0”) for a flange on a vertical line.
BOM Bill of Material – This term can have two meanings. First there is the BOM that is included as a part of an individual document such as a piping isometric. The second is the summary of the material from all documents or isometrics.
BOP Bottom of Pipe – This refers to the bottom of a pipe when lying in the horizontal position.
BS British Standard
BSE Beveled Small End - This is an end prep qualifier for piping fittings such as reducers and swedges.
BTU British thermal unit - Unit of measure
BW Butt Weld or Butt Welded – Butt welding means that the end of the pipe, fitting and/or flange are beveled to a specific contour as defined by the Code (per different wall thicknesses) then welded together.
C Centigrade or Celsius - Unit of measure
C Clean Drain – This is a system qualifier that would appear on P&ID’s, Underground and other Drawings to designate the Clean Drain system.
C Condensate – Used to define the commodity in a Line Number
C Condensate Nozzle - See Note #1
C Cradles – The term Cradle, when used on piping drawings normally refers to a curved section of metal plate (approx 120 degrees) and about 24” (610mm) long. This metal (normally steel) is fitted on the underside of an insulated line (outside the insulation) at each pipe support so that the weight of the line at the support does not crush the insulation.
C Patchboard or matrix board connection -
CC Corrosion Coupon – This is a piece of metal that is welded to a holder of some type and placed inside the process fluid. From time to time the thickness of this is removed and measured to determine the amount of corrosion taking place in the system itself.
C-C Centre to Centre – Refers to the type of dimension (i.e.: Center to Center of two pipes)
CDO Certified Dimension Outline – This refers to a vendor drawing such as an Exchanger, a Pump or any other purchased equipment which has been reviewed by your company, your requirements for modifications have accepted and incorporated by the Vendor and they have signed (Certified) that they will build and deliver what is shown on “this” drawing.
CENT Centigrade - Unit of measure
CFM Cubic Feet per Minute
CHU Centigrade Heat Unit
CI Cast Iron -
cL Centerline – The centerline is the primary locating reference point used for the location of all objects such as Pipes Tanks, Vessels, Pumps, Structural Pipe Supports, Structures, Roads, etc. in Process Plant engineering and design.
CM Centimeter -
CO Chain Operated – This will apply to an operating valve that could not be located with-in reach and has been fitted with a device that used a chain from below to open or close.
CO Clean Out – This is commonly used on underground drawings to indicate the location of clean-out points for buried systems.
COP Critical Operating Parameters -
Cr Chromium – A metal found in some alloy pipe
CrMO Chrome Moly – A material often used in process plants for higher pressure and temperature services.
CS Carbon Steel – The most common material currently used in process plants such as Refineries and Power Plants.
CS Cold Spring – This is an indication that action has been taken to reduce the effect of stress by an expanding line due to the operating temperature. Example: A long line will expand 6” (152 mm) at normal operation conditions. That 6” (152mm) of growth will result in excessive stress on some point of the system. You determine that you need to reduce the excessive stress. To do this you calculate what the “true” dimension for the long run should be but you call for the shop (or the Field) to remove one half the expected growth, in this case 3” (76mm) from the “true” dimension. This is called “Cold Spring” or “Cold Springing” the line.
CSC Car Seal Closed – This is normally a designation that appears at a valve symbol on a P&ID (placed there by the Process Engineer) to indicate that this valve is to be fitted with a locking device of some sort to prevent inadvertent or unauthorized opening. This designation shall be placed on all subsequent piping drawings showing that valve and the piping material control group may be required to purchase the device.
CSO Car Seal Open – Same as CSC but indicated that the valve is to be in the Open position.
CTR Center – As in the center of a circle
CV Control Valve – The term “Control Valve” is commonly used for a wide range of actuator operated valves. The type of valve body is most often a Globe type but can also be a Ball, Butterfly, Pinch or other type. The actuator can be Pneumatic, Solenoid, Electric Motor or other type.
CWP Construction Work Package – A Construction Work Package is the identification of and all the paperwork including drawings, material lists, Specifications and contracts defining a segment of work for an EPCM process plant project. (Example: Underground Piping CWP, Aboveground Piping CWP, Insulation CWP, Electrical CWP, etc.)
CWR Cooling Water Return – Used to define the commodity in a Line Number
CYR Cycle Water Return – Used to define the commodity in a Line Number
CYS Cycle Water Supply – Used to define the commodity in a Line Number
D Derivative control mode – Commonly used with instrumentation
D Digital signal – Commonly used with instrumentation
D Drain – Used to define the commodity in a Line Number
D Drain or Draw off Connection - See Note #1
DBM Design Basics Memoranda
DCS Distributed Control System – Commonly used with instrumentation
DEG Degree - Unit of measure
DIA Diameter -
DIFF Difference, used in math meaning to Subtract
DIN Deutsche Industry Norm [German Standard]
DIR Direct-acting -
DO Drawing Office -
dP Delta P, Pressure differential
DRG Drawing [Not Preferred] see DWG
DS Dummy Support – A Dummy Support is a stub of pipe 3’ to 7’ long (1 meter to 2 meters long) that is attached to an elbow where a line leaves the pipe way short of the next support. The stub will extent to reach the next structural pipe support and provide support for the line.
DW Drywall -
DWG Drawing – The most commonly used and the more proper abbreviation for the term “Drawing”
E East - As in a direction. Often used with Coordinate method of defining location or position of in item of equipment.
E Voltage signal - Commonly used with instrumentation or Electrical
ECN Engineering Change Notice – This is a part of the system used to control and track costs within a “Lump-Sum” contract. All changes, whether they are Client originated of the result of late design development is identified, given a “DCN” number, written up, reviewed through the project approval process. If the DCN is accepted then the change is made and the cost is added to (or deducted from) the contract.
ECN Engineering Charge Number – (Same as DCN)
EDS Engineering Design Specifications
E-E End to End – Used to clarify a dimension.
EFW Electric-Fusion-Welded – Refers to one of the ways that “rolled and welded” pipe is made.
EL Elbow – (Not Preferred)
EL Elevation -
ELB Elbowlet – (Not Preferred)
ELL Elbow – (Preferred)
EOL Elbow-let – A special shaped piping fitting that allows for a branch attachment onto an elbow and provides built-in reinforcement for the attachment point.
EOP End of Pipe – A term used as a part of the dimensional designation when locating the end of a piece of pipe such as a vent to atmosphere.
EA Engineer/Architectural - This can mean a type of company or a type of project. An AE company or project only does some engineering and then only produces conceptual drawings. They cannot and do not produce detailed engineering drawings or bills of materials because they do not purchase any equipment required to for detailed design.
EPC Engineering, Procurement & Construction - This can mean a type of company or a type of project. An EPC Company or Project means a full service capability of Engineering, Procurement and Construction of the complete process plant.
EPC&C Engineering, Procurement, Construction and Commissioning - Indicates type of company or project that is done by one contractor that includes Engineering, Design, Procurement, Construction and Commissioning (also see LSTK)
EPCM Engineering, Procurement & Construction Management - This can mean a type of company or a type of project. An EPCM Company or Project means a full service capability of Engineering, Procurement and the construction portion of the project is executed by Sub-Contractors under the Management of the EPCM Contractor.
ERW Electric-Resistance-Welded - Refers to one of the ways that “rolled and welded” pipe is made.
ES Electric Supply –
ESS Emergency Shutdown System –
ESV Emergency Shutdown Valve – This is used to identify certain valves that are manually or motor operated that shall be closed in case of a fire, explosion or Terrorist attack.
ET Electrically Traced – This indicates a pipe line (or piece of equipment) that shall be provided with heat tracing via electric resistance cable.
ETA Estimated Time (of) Arrival – Term used in procurement to indicate when an item will arrive at a destination.
F Fahrenheit - Unit of measure relating to temperature
F Feed Nozzle - See Note #1
(F) Furnished – Indicated that the object or item is supplied with something else.
F&D Faced and Drilled – Means that the indicated surface has been machined smooth and drilled to accept some other object.
(F&P) Furnished & Piped – Similar to “Furnished” but is further clarified to indicate that the required piping is also included as “Furnished”.
FAB Fabrication – Can be a noun or a verb. A Fabrication can mean a piping spool that is a “Fabrication”. Or it can be used to say the pipe spool is in “Fabrication”.
FAHR Fahrenheit - Unit of measure
FBW Furnace-Butt-Welded - Refers to one of the ways that “rolled and welded” pipe is made.
FC Fail Closed – This means that in case of power failure of loss of instrument air the valve (or other object) will default to a closed and safe position.
FCN Field Charge Number – A system for numeric indexing, identification and control of changes originating from the field.
FD Flex-Disc Valve – Normally relates to a type of Gate valve that has a special design for the disc that is intended to insure a tight closure.
FD&SF Faced, Drilled and Spot-Faced -
FE Flanged End – Meaning that an object has flanged connections.
FEED Front End Engineering & Design - The FEED part of a project would be characterized as the first twenty percent (20%) to thirty percent (30%) of the engineering of a project. The FEED Contractor may have been awarded all or a part of the project. They are now working with the Client (and Licensors if applicable) to prepare the front end requirements for the project. The heaviest work load during this FEED part will be in the Process Engineering group. However, there are some Piping activities that start at this time (Also see Pre-FEED)
FF Face to Face – As in Face-to-Face dimension
FF Flange Face [dimensioning] -
FF Flat Face (d)
FF Full Face [of gasket]
FFW Final Fit Weld - Refers to a piping weld that is to be made in the field (Point of installation) as opposed to being made in a pipe fabrication shop. This weld can only be pipe-to-pipe or pipe-to-fitting. The pipe component is to be fabricated long with (6” to 9”) of extra length for final field fit-up. This weld (for this line) is to be made only after all other Field Welds” have been completed.
FG Fuel Gas - Used to define the commodity in a Line Number
FI Fail Indeterminate - This means that in case of power failure of loss of instrument air the valve (or other object) will default in place or current position.
FIV Fire Isolation Valve – (See ESV)
FL Fail Locked – (See FI)
FLGD Flanged End
FMU Fitting Make Up – This means that two or more commonly manufactured piping fittings or flanges are welded together without any pipe between the items.
FO Fail Open - This means that in case of power failure of loss of instrument air the valve (or other object) will default to an open and safe position.
FOB Flat on Bottom – A term most commonly used with eccentric reducers and other non-concentric objects.
FOB Free on Board – A legal term commonly used in contracts and or procurement
FOB Freight on Board - A legal term commonly used in contracts and or procurement
FOT Flat on Top - A term most commonly used with eccentric reducers or other non-concentric objects.
FP Full Port Valve – This term often used with Ball Valves means that the “Port” or opening in the ball is the same size as the adjoining pipe inside diameter.
FPT Female Pipe Thread
FRP [Glass] Fiber Reinforced Pipe
FS Base Supports – Indicates a type of secondary support that is normally used under one side of a Control Valve Manifold.
FS Far Side
FS Field Supports – Indicates any of a number of secondary type pipe supports.
FS Forged Steel -
FTG Fitting – This is a universal term that applies to many trades and trade material (piping, electrical, etc.). For piping it includes elbows, TEEs and O-Lets.
FV Full Vacuum
FW Field Weld – Refers to a weld (normally in piping) that is to be made in the field (Point of installation) as opposed to being made in a pipe fabrication shop. This weld can be pipe-to-pipe, pipe-to-fitting or fitting-to-fitting. The pipe and fitting components on both sides of this weld are dimensionally correct and no trimming is to be done without the approval of the Design Office.
FW Fire Water - Used to define the commodity in a Line Number
G Gas – Used to define the commodity in a Line Number
G Glycol – Used to define the commodity in a Line Number
G Gram - Unit of measure
G Level Gauge or Gauge Glass -
G Pipe Guides -
GAL Gallon - Unit of measure
GALV Galvanized – Rust resistant plating added to metal objects
GO Gear Operated – Used in conjunction with a valve description.
GPH Gallon per Hour - Unit of measure
GPM Gallon per Minute - Unit of measure
GR Grade – Is commonly used for both Paved or Unpaved surfaces of a process plant
GS Gas Supply – Used to define the commodity in a Line Number
GT Glycol Traced – Commonly used to define a type of heat tracing
GV Gauge Valve – A valve used for isolation with various types of instruments
H Hand hole - See Note #1
H Horizontal – A direction or physical attitude
H Hot condensate drain - See Note #1
H Hour – Commonly used with Instruments or units of measure
H Hydraulic signal - Used to define the commodity in a Line Number
H. PT. High Point – (see HP)
HDR Header – May be used when defining a main supply pipe for a utility, example: HP Steam Header. Or it can be used to define a physical feature associated with a piping configuration, example: The Weld-O-Let was used to add a branch to the Header.
HEX Hexagonal – A shape with six sides
Hg Mercury - Used to define the commodity in a Line Number
HH Hand hole - See Note #1
HOA Hand / Off / Auto – Common electrical terminology for Pump controls
HP High Point – Used to define the reference for the highest point of the concrete paving or other service material. (Also see HPP)
HP High Pressure -
HP Horse Power -
HPC High Pressure Condensate – Used to define the commodity in a Line Number
HPP High Point of (finished) Pavement – (See HP)
HPS High Pressure Steam – Used to define the commodity in a Line Number
HPT Hose-Pipe Thread -
HR Hanger Rods – A device that is intended to provide support from above for an object such as a pipe
HR Hour - Unit of measure
HS Hose Station – (See US)
HS Hydraulic Supply – Used to define the commodity in a Line Number
HTR Heater – Relates to a type of equipment found on a project
HVAC Heating Ventilation and Air Conditioning – Can indicate the Profession, the Equipment or the Work.
I Current (electrical) signal
I Inorganic waste – Used to define the commodity in a Line Number
IA Instrument Air – Used to define the commodity in a Line Number
IAS Instrument Air Supply – Used to define the commodity in a Line Number
ID Inside Diameter – common usage terminology
ID Internal Diameter – not common usage terminology
IE Invert Elevation – (See Inv. El.)
IFA Issued For Approval – This is an indication of “Status” for an engineering or design document issued as a part of a Process Plant Project. This normally means issued to the Client for the required Approval.
IFB Issued For Bid - This is an indication of “Status” for an engineering or design document issued as a part of a Process Plant Project. This normally means a document that is intended for a Contractor or Sub-Contractor to use to prepare his (her) bid.
IFC Issued For Construction - This is an indication of “Status” for an engineering or design document issued as a part of a Process Plant Project. This normally means that the data shown on the document is complete and approved for fabrication and or construction.
IFD Issued For Design
IFH Issued For Hazop
IFI Issued For Information / Issued for Implementation
IFR Issued For Review
IMP Imperial – This normally applies to units of measure such as feet and inches or opposite of metric.
INS Insulation – Applies to the non-metallic coverings applied to piping systems or equipment for the conservation or retention of heat or cold.
INST Instrumentation -
Inv. El. Invert Elevation – This is the bottom point of the inside diameter of a Drain system pipe. It is the point used to set and insure the correct slope of the pipe for drainage.
IPS Iron Pipe Size -
IRI Industrial Risk Insurers -
IS Inside Screw [of valve stem] – Refers to a type of Valve design.
IS&Y Inside Screw and Yoke - Refers to a type of Valve design.
ISBL Inside Battery Limits (or Onsite) – Refers to any single or collection of inter-related and inter-connected process units that performs an integrated process function. Typically any Onsite Unit could be made to function independently of another Onsite Unit.
ISO Isometric drawing - In piping this term refers to a semi-3 dimensional drawing representation of a pipe line or part of a pipe line. The Isometric should contain ALL the graphics, dimensions, identification and technical data necessary to purchase material, fabricate, test and install the displayed piping.
J Pump out Nozzle - See Note #1
K Carbonate – Used to define the commodity in a Line Number
K Kilo, times one thousand, x 1000
KG Kilo Gram
L Level Instrument Nozzle - See Note #1
L Liquid – Used as a qualifier for Process (and other) information. Example: HLL = High Liquid Level)
**LL Liquid Level (** Denotes suffix (es), for high, low, high high, low low, etc.) i.e. LLLL - Low Low Liquid Level
L.PT. Low Point – Often used in defining the other critical elevation point (see HP) for paving.
LA Level Alarm – Defines a type of instrument
LB, Lb Pound weight - Unit of measure
LC Level Controller - Defines a type of instrument
LC Lock Closed - Commonly used with valves that must remain closed unless special authority is granted otherwise.
LG Level Gauge - Defines a type of instrument
LI Level Indicator - Defines a type of instrument
LIC Level Indicating Controller - Defines a type of instrument
LO Lock Open – Commonly used with valves that must remain open unless special authority is granted otherwise.
LOL Low Oxygen Level
LP Low Point - (See L.PT.)
LP Low Pressure – Commonly used to define a condition or quality of a commodity. Example: LP Alarm)
LPC Low Pressure Condensate - Used to define the commodity in a Line Number
LPS Low Pressure Steam - Used to define the commodity in a Line Number
LR Long Radius [Of Elbow] – LR is equal to 1.5 times the nominal diameter
LS Level Switch - Defines a type of instrument
LSTK Lump Sum Turn Key – Indicates the type of company or a project that is done by one contractor that includes Engineering, Design, Procurement, Construction and Commissioning (also see EPC&C)
LT Level Transmitter - Defines a type of instrument
LT Light-wall [Of Pipe] -
M Manhole - See Note #1
M Mega, times one million, x 1 000 000 - Unit of measure
M Meter - Unit of measure
M Motor actuator
M Motorized – Used to indicate that a Valve is “Motorized (Has a motor operator).
MAWP Maximum Allowable Working Pressure – Most often used with vessels or piping systems
MAX Maximum control mode
MCC Motor Control Center – Defines a building with a collection of electrical equipment
MI Malleable Iron
MIN Minimum control mode
MIN Minute [Of time]
Mo Molybdenum – An element found in pipe steel.
MOS Maintenance Override Switch
MP Medium Pressure
MPC Medium Pressure Condensate - Used to define the commodity in a Line Number
MPS Medium Pressure Steam - Used to define the commodity in a Line Number
MPT Male Pipe Thread
MS Mild Steel
MSF Mill Scale Free – Means that the pipe (or other item) has been or must be wire brushed or sand blasted.
MSS Manufacturers' Standardization Society – Applies to the Valve and Fittings Industry
MT Magnetic Particle Inspection – (See NDE)
MTO Material Take Off – Describes both the act of doing the task and the product of the task.
MW Manway - See Note #1
N Nitrogen – Used to define the commodity in a Line Number
N North – This can be True North, Plant North, Platform North or Magnetic North.
N North - As in a direction. Often used with Coordinate method of defining location or position of in item of equipment.
N Reboiler Connection - See Note #1
NC Normally Closed – This is used to designate the normal setting of a valve.
NDE Non-Destructive Examination – This refers to a grouping of 5 methods used to indicate the quality of a weld on vessels or piping. These are VT, RT, MT, PT, and UT (See: http://www.ndt.net/article/0698/hayes/hayes.htm)
NEMA National Electrical Manufacturers' Association
NFPA National Fire Protection Association
NG Natural Gas – Used to define the commodity in a Line Number
NIC Not in Contact
NIPP Swaged Nipple
NLL Normal Liquid Level
NNF Normally No Flow
NO Normally Open
NPS Nominal Pipe Size
NPSC Straight pipe thread in pipe couplings
NPSF Dryseal straight pipe thread (lubricant optional)
NPSH Net positive suction head
NPSH Net Positive Suction Head
NPSH Straight pipe thread for hose couplings and nipples
NPSI Dryseal internal straight pipe thread
NPSL Straight pipe thread for locknut and locknut pipe thread
NPSM Straight pipe threads for mechanical joints
NPT National Pipe Thread
NPT Taper Pipe Thread
NPTF Dryseal taper pipe thread (lubricant optional)
NRS Near Side
NS Nitrogen Supply – Used to define the commodity in a Line Number
NV Needle Valve
O Electromagnetic or sonic signal
O Oil – Used to define the commodity in a Line Number
O Organic Waste Drain
OD Outside Diameter
Offsite (See OSBL)
OG Oxygen – Used to define the commodity in a Line Number
Onsite (See ISBL)
OP Operating Valve
OPT Optimizing control mode
OS Outside Screw [Valve stem]
OS&Y Outside Screw and Yoke [Valve stem]
OSBL Outside Battery Limits (Offsite) -- In a process plant (Refinery, Chemical, Petrochemical, Power, etc.), any supporting facility that is not a direct part of the primary or secondary process reaction train or utility block.
OSHA Operation Safety and Health Act (USA)
OVHD Overhead – This is used to define a specific piece of equipment (i.e.: OVHD Condenser) a specific nozzle on a vessel (i.e.: OVHD Nozzle) of the product in the line (i.e.: Crude OVHD)
OWD Oily Water Drain – Used to define the commodity in a Line Number
OX Oxide - A chemical element
P All process lines
P Pneumatic signal
P Pressure Connection - See Note #1
P Proportional control mode
P Purge or flushing device
P&ID Piping and Instrument Diagram – The primary document produced by the Process Engineer to define in detail what is required for any process plant.
PA Plant Air Supply – Used to define the commodity in a Line Number
PBE Plain Both Ends [Swage, etc.]
PC Pressure Controller
PC Pumped Condensate – Used to define the commodity in a Line Number
PCV Pressure Control Valve
PE Plain End [Pipe, etc.]
PFD Process Flow Diagram – Indicated a preliminary schematic drawing produced by the Process Engineer to define the simplified process concept. It is the precursor to the P&ID.
PFI Pipe Fabrication Institute
PG Pilot Gas – Used to define the commodity in a Line Number
PI Pressure Indicator – A direct reading gage or indicator.
PIV Post Indicator Valve – Common type valve used for shut-off of underground water lines to a fire hydrant or fire Monitor.
PLC Programmable Logic Controller
PO Pump Out – Used to define the commodity in a Line Number
POE Plain One End [Nipple, etc.]
POS Point of Support
PR Pressure Regulator
Pre-FEED A Pre-FEED project is one where someone is conceptually defining a proposed new project. Many Clients will perform the Pre-FEED part of a project with their own staff. Clients may also obtain the services of an engineering company to develop the Pre-FEED project package. The objective of contracting out the Pre-FEED package is three-fold. First, the Client may need the expertise of the engineering company to objectively look at the project goals and determine if it feasible. Second, the Client wants a package that they can issue to other selected Contractors for bidding purposes. Third, the Client will want the Pre-FEED Contractor to prepare a realistic estimate of total-installed-cost (TIC) for their internal requisition for funding and to evaluate the other bids. (Also see FEED)
PRV Pressure Reducing Valve – This is a valve functional description not a specific valve manufacturer of specific valve type.
PRV Pressure Relief Valve – This is a valve functional description not a specific valve manufacturer of specific valve type. Lots of companies make valves that are designed to open when the pressure inside a vessel or system goes above a specific set pressure. (Also see PSV)
PS Pipe Support – This is a general term and can mean any type of primary or secondary devices used to hold up pipe.
PS Pre-Spring – This is the technique of adding a small amount to the dimension of an actual length of pipe required to reach from point “A” to point “B”. This practice is to compensate fro systems in cryogenic service where the pipe would shrink due to the negative coefficient of expansion.
PS Process Sewer - Used to define the commodity or service in a Line Number
PSI Pound per Square Inch – Defines a unit of measure related to pressure.
PSIA Pound per Square Inch Absolute - Defines a unit of measure related to pressure.
PSIG Pound per Square Inch Gage - Defines a unit of measure related to pressure.
PSV Pressure Safety Valve – (also see PRV)
PT Pressure Tap – Sometimes used to define the future purpose of a valved and plugged connection.
PT (Liquid) Penetrate Inspection – (See NDE)
PU Pick-Ups – Used to define a type of secondary pipe support. This method (short length of Angle Iron and “U” Bolts) uses a larger size pipe to provide support for a smaller pipe line.
Pup A “Pup” piece is a short length of pipe required between two fittings, a fitting and a flange or between two flanges to make-up a required dimensional distance.
PW Potable Water – Used to define the commodity in a Line Number
PWHT Post Weld Heat Treated – This is the action of applying heat to piping to relieve stress built up in the material due to the welding during fabrication.
R Automatic-reset control mode – Used in the electrical and controls systems.
R Radius -
R Reflux Nozzle - See Note #1
R Reset - Used in the electrical and controls systems.
R Reset of fail-locked device - Used in the electrical and controls systems.
R Resistance (signal) - Used in the electrical and controls systems.
R/L Random Length – Often used in the purchase of pipe. Single Random Length = 20 feet (+/-) 7meters (+/-). Double Random Length = 40 feet (+/-) 14 meters (+/-)
RED Reducer – Used in Concentric Reducer (Conc Red) or Eccentric Reducer (Ecc Red)
RED Reducing -
REF Reference -
REQ Requisition – Term used in Procurement activities or the actual document.
REQ Required -
REV Reverse-acting -
RF Raised Face – A type of flange face.
RFI Request for Information - Term used in Procurement activities or the actual document.
RFP Request for Purchase - Term used in Procurement activities or the actual document.
RFQ Request for Quote - Term used in Procurement activities or the actual document.
RJ Ring Joint – (see RJT) -
RPM Revolutions per Minute -
RS Rising Stem [Of valve] -
RT Reducing Tee -
RT Radiographic Inspection – (See NDE)
RTD Resistance (-type) temperature detector -
RTJ Ring Type Joint – A type of flange facing/gasket
RW Raw Water – Used to define the commodity in a Line Number
S Pipe Shoes – A device used under Hot Insulated pipes to raise the pipe up off the primary pipe support level thus protects the insulation.
S Solenoid actuator -
S South - As in a direction. Often used with Coordinate method of defining location or position of in item of equipment.
S Steam or Sample Connection - See Note #1
S Storm Water Drain – Used to define the commodity in a Line Number
S.G. Specific Gravity -
SAE Society of Automotive Engineers -
SC Sample Connection -
SC Steam Condensate – Used to define the commodity in a Line Number
SCH Schedule [Of pipe] – Relates to the wall thickness of pipe
SCRD Screwed – Method of joining some types of pipe, fittings and valves.
SCV Sample Point Valve -
SCV/T Sample Point Valve with Thief -
SD Shut Down -
SECT Section – A “View” in mechanical drafting (similar to Elevation used in Architectural drafting)
SF Spot-Faced – The machining-off the back side of an object (i.e.: a flange) to provide a true flat surface for the bolt head or nut.
Si Silicon -
SKT Socket - Method of joining some types of pipe, fittings and valves.
SMLS Seamless – A type of pipe
SO Slip-On – A type of flange
SO Steam Out – See Note #1
SOL Sock-o-let – A device used to make an integral reinforced branch for socket-weld (size) pipe
SP Sample Point -
SP Set Point -
SP Standard Practice [MSS term] -
SP Steam Pressure -
Spec Specification – A narrative description for the requirements of almost anything
Spool In piping a "Spool" is a contiguous fabricated part if an isometric or a pipe line.
Example: a spool can be small such as a flange, an elbow and another flange. Or it can be large such as a contiguous fabricated configuration not to exceed the designated shipping size set for the project.
SQ Square -
SQ.RT Square Root -
SR Short Radius [Of Elbow] -
SS Sanitary Sewer – Used to define the commodity in a Line Number
SS Spring Supports -
SS Stainless Steel -
SS Steam Supply – Used to define the commodity in a Line Number
SSO Intermittent hot process drain – Used to define the commodity in a Line Number
SST Stainless Steel -
SSV Soft Seat Valve -
ST Steam Traced -
ST Steam Tracing -
ST Steam Trap -
ST Support Trunnions -
STD Standard -
STM Steam – Used to define the commodity in a Line Number
STR Straight -
STS Storm Sewer – Used to define the commodity in a Line Number
SW Socket Welding -
SWG Swage -
SWG Swaged Nipple -
SWP Standard Working Pressure -
SWP Steam Working Pressure -
T Temperature -
T Temperature Connection - See Note #1
T Threaded -
T Trap -
T&C Threaded and Coupled [Pipe] – Pipe purchased from the supplier with both ends threaded and a coupling installed on one end (only) of each length.
T/F.F Tangent to Face of Flange -
T/T Tangent to Tangent – Used define the distance of the straight side of a vessel.
TB Traced Valve Body – Term used where Heat Tracing is used for process lines or equipment.
TBB Traced Body & Bonnet - Term used where Heat Tracing is used for process lines or equipment.
TBE Thread Both Ends - Used with Swedge Nipples
TC Temperature Controller -
TC Test Connection -
TE Threaded End -
TEF Teflon -
TEMA Tubular Exchanger Manufacturers' Association -
TGT Tangent -
TI Temperature Indicator – Indicates a direct reading gage or indicator.
TL Tangent Line – Indicates the point on a cylindrical vessel where the straight side intersects the curvature of the knuckle radius of the head.
TLE Thread Large End – Used with Swedge Nipples
TOC Top of Concrete -
TOE Threaded One End [Nipple or Swege] -
TOL Thread-o-let - A device used to make an integral reinforced branch for Threaded (size) pipe
TOP Top of Pipe -
TOS Top of Steel -
TOS Top of Support -
TPI Threads per Inch -
TS Twin Seal – A type of Gate Valve.
TSE Thread Small End - Used with Swedge Nipples
TSE Threaded Small End - Used with Swedge Nipples
TYP. Typical -
U/G Underground – A type of drawing or a buried piping system
UA Utility Air – Used to define the commodity in a Line Number
UDD Utility Distribution Diagram – A Plot Plan oriented drawing showing the main distribution headers with all the branches in the proper sequence.
UFD Utility Flow Diagram – Similar to a (process) P&ID but used for the drawing use to define the generation of a plant utility service (Steam, Plant Air, Cooling Water, etc.).
UG Underground – (See U/G)
UNC Unified Coarse [Bolt thread] -
UNF Unified Fine [Bolt thread] -
UNO Unless Noted Otherwise -
UNS Unified Selected [Bolt thread] -
UON Unless Otherwise Noted -
US Utility Station – A collection of multiple services (Steam, Plant Air, Plant Water, Nitrogen, etc.) arranged in locations at grade or on platforms for use by maintenance and clean-up.
UT Ultrasonic Inspection – (See NDE)
V Valve -
V Vanadium – An element found in some piping materials
V Vapor Outlet or Vent Connection - See Note #1
V Vent – Used to define the commodity in a Line Number
V Vertical -
VB Vortex Breaker – A device fabricated and installed inside a vessel as a part of the pump suction nozzle to prevent the formation of a Vortex.
Vert Vertical –
VT Visual Inspection – (See NDE)
W Relief Valve Nozzle - See Note #1
W Water – Used to define the commodity in a Line Number
W West – As in the direction. Often used with Coordinate method of defining location or position of in item of equipment.
W/ With -
WC Water Column – A piping configuration that allows for the attachment of multiple level and pressure instruments on a Tank or Vessel.
WE Welded End – Often used with a valve to indicate the type of end connections.
WGT Weight -
WLD Weld(ed) -
WN Welding Neck – Indicated the type of Flange
WOG Water, Oil and Gas -
WOL Weld-o-let – A self reinforced branch fitting for butt weld continuation
WP Working Point – Used on drawings with sloping pipe lines to indicate the point where key information is given (Locating coordinates and elevations).
WP Working Pressure -
WS Water Supply – Used to define the commodity in a Line Number
WT Weight -
x Multiply -
X Unclassified actuator – Used with instruments
XH Extra-Heavy – Refers to the Wall Schedule of pipe
XS Extra-Strong – (See XH)
XXH Double Extra Heavy - Refers to the Wall Schedule of pipe
XXS Double-Extra-Strong – (See XXH)
#1 This Abbreviation is intended to indicate the specific purpose or function for a nozzle on a vessel. However, the use of this specific letter for this specific purpose or function is not universal throughout the engineering community.
About the Author
Anton Dooley is a Piper with over 25 years experience covering process plant engineering, design & training. He is the founder of pipingdesigners.com