PIPING DRAWINGS BASICS

There are two types of views used in the piping drawings:

Orthographic- Plans and Elevations

Pictorial - Isometric Views

Piping layout is developed in both plan view and elevation view

and section details are added for clarity wherever necessary.

These drawings are called the General Arrangement of Piping.

In complex piping system, especially within the unit/plant building

where orthographic views do not illustrate the details of design,

pictorial view in isometric presentation is drawn for clarity.

HOW TO START THE PIPING GA?

•Obtain the drawings numbers and fill in the title block, with the

drawing number and title at the bottom right hand corner of the

sheet.

•Place the north arrow at the top left/right hand corner of the

sheet to indicate plant north.

•Do not plan drawing in the area above the title block of

drawing, as this is allotted for general notes, number and title of

reference drawings, brief description of changes during revision

and the bill of materials wherever applicable.

•Process equipment and piping have priority on the Piping GA.

•The piping drawings are started after fixing positions of the

equipments.

•Equipment layout is reproduced on the Piping GA to its scale

and drawn on the reverse side in case of manual drafting.

•In case of CAD separate layer is used. The major primary

beams and secondary beams are also shown if area covered is

indoor.

•Pertinent background details which govern piping routing,

such as floor drains, HVAC ducting, electrical and instrument

cable trays, etc. are also drawn in faint on the reverse.

•Utility stations are also established so that most convenient

utility header routing can be carried out.

Order of importance/preference of pipe lines in a piping

GA

Alloy steel/special material of construction.

Large bore piping

High temp/high pr. Piping

Lined piping

C. S. Process Piping

Utility piping

DEVELOPMENT OF PIPING GENERAL

ARRANGEMENT DRAWING

The piping drawings should be developed in such a way

that

all the process requirements are met with.

It is not always possible for the piping drawing to follow

exactly the logical arrangement of the P & IDs. Sometimes

lines must be routed with different junction sequence and

line numbers and subsequently the list may be changed.

•Performance and economics have to be considered in

parallel while deciding the routing.

Piping is represented by single lines up to a size of 150NB

and double lines for sizes 200NB and above. This is to save

the time of drafting and to avoid confusion.

In single line representation only the center line of the

pipeline is drawn using solid line and in double line

representation the actual size to scale is drawn with center

line marked in chain-dotted lines

Line numbers are shown against each line exactly in the

same way as represented in the P&I diagrams.

The change in specification should be shown in line with

P&I diagram. This change is usually indicated

immediately to the downstream of the valve, flange or

equipment.

Valves should be drawn to scale with identification

number from the P&ID marked thereon.

Draw valve hand wheels to scale with stem fully

extended.

If it is lever operated, then the movement of handle

position should be marked.

If a valve is chain operated, note the distance of the chain

from the operating floor.

Show location of each instrument connection with

encircled instrument number taken from P&ID.

Similar arrangement shall be shown as typical detail or

covered in a separate company standard as Instrument

Hook-up drawings.

Draw plan view of each floor of the plant and these views

should indicate how the layout will look like between

floors as seen from top.

Each line should be identified by line number and should

also show the insulation, tracing requirements, etc.

Lines, if required, shall be broken to show the required

details of hidden lines without drawing other views.

Do not draw details that can be covered by a note.

Draw plan to a larger scale for any part needing more

details and identify it as “Detail ‘A’”, etc.

Draw part isometrics sketches or part elevations to clarify

complex piping or piping hidden in the plan view.

•Full sections through the plant may be avoided if

isometric drawings are drawn for the lines. Part sections

where required shall be shown to clear the hidden details in

plan.

Sections in the plan views are identified by numbers say

1-1, 2-2, etc. and details by alphabets, e.g. “Detail ‘A’”.

Isometric drawing should also include the following

information:

Dimensions and angles.

Reference number of P & IDs, GA Drawings, line

numbers, direction of flow, insulation and tracing.

Equipment location and equipment identification.

Give nozzle identification on the connected equipment.

Give the details of flange on the equipment if the

specification is different from the connecting piping.

Size and type of every valve/ Direction of operation.

Size and number of control valve.

Location, orientation and number of each equipment.

Field weld - preferred in all directions to take care of site

variations. Can also be covered with a general note.

Location of high point vents and low point drains.

Covered with a standard arrangement note.

Bill of Material.

Requirements of stress relieving, seal welding, pickling,

coating, etc.

A spool is an assembly of fittings, flanges and pipes that

may be prefabricated. It does not include bolts, gaskets,

valves or instruments. A spool sheet is an orthographic

drawing of a spool drawn either from piping GA or from

an iso sheet. Each spool sheet shows only one type of

spool and,

•Instructs welder to fabricate the spool

•Lists the cut lengths of pipe, fittings and flanges etc.

needed to make the spool

•Gives material of construction and any special treatment

of finished piping

•Indicates how many spools of the same type are required

Sufficient dimensions to be given for positioning

equipment and for erecting piping.

Duplicating dimensions in different views should be

avoided, as this may lead to errors if changes are made.

Reserve horizontal dimensions for the plan view.

If single pipe is to be positioned or a pipe connected to

nozzle is to be indicated, then show the centre line

elevation and mark as C .

If several pipes are sharing a common support, show

elevation of Bottom of Pipes and mark as BOP EL. This

is more applicable to non-insulated lines.

In case of several pipes on a pipe rack, show the

“Top of Support” elevation and mark as TOS

EL.

In case of buried pipelines in trench, show

elevation of bottom of pipes.

In case of drains and sewers, the Invert Elevation

of the inside of the pipe is marked as IE.

Centre lines of the equipment and pipelines shall be

located with reference to the building column centre lines or

the co-ordinates which can be considered as a reference

base.

The distance between the lines shall be dimensioned centre

line to centre line.

•The horizontal nozzles on the equipment shall be located

from centre to flange face in plan. For vertical nozzles show

Face of Flange elevation (FOF).

For valves, instruments and non-standard equipments,

show the dimensions from flange face to flange face.

Flanged valves are located with dimension to flange faces. Nonflanged

valves are dimensioned to their centres or stems.

For flanged joints show a small gap between dimension lines to

indicate gasket. Flanged joints can also be shown without

gasket but

cover the same with a general note and include gasket thickness

in the valve or equipment dimensions.

For Finished Floor (FF) the elevation shall be the high point of

the floor.

For foundation the Top of Grout (TOG) elevation is shown.

Show dimensions outside the drawn view - do not cut

pictures.

Draw dimension line unbroken with fine line. Write

dimension just above the horizontal line. For vertical lines

write sideways.

The dimension lines can be terminated with arrow heads or

oblique dashes.

If series of dimension is to be shown, string them together.

Show overall dimension of the string of dimensions. Avoid

one of the break-up dimensions to omit repetition and error

during changes.

Do not omit significant dimension other than fitting make

up.

For field run piping, give only those dimensions which are

necessary to route piping clear of equipments and other

obstructions. Locate only those items which are important

to

the process.

Underline out of scale dimensions or mark as NTS.

Do not terminate dimensions at screwed or welded joints

Checking shall be done only on the print or the

check plot of the drawings and by coloured

pencils/pens.

Corrected areas and dimensions are marked yellow.

Areas and dimensions which are to be deleted are

marked green.

Areas to be corrected/incorporated on the drawing

are marked in red.

The new print after correction is “back checked” for

incorporation.

Points to be checked on the piping drawing includes:

Title of the drawing.

Title of the drawing.

Orientation - North arrow against plot plan.

Inclusion of graphic scale (if drawings is to be reduced).

Co-ordinates of equipments against equipment layout.

Equipment numbers and their appearance on the piping

drawing.

Correct identification on all lines in all views.

Line specification changes.

Reference drawing numbers and files.

Correctness of all dimensions.

Whether representation is correctly made in line with

the standard symbols or not.

Location and identification of all instruments.

Requirements of upstream/downstream straight lengths.

Insulation requirements as per P&IDs.

Piping arrangement against P&ID requirements such as

gravity flow, seals, etc.

Possible interference

Floor and wall openings.

Correctness of scale in case of General Arrangement

Drawings

Whether all stress analysis requirements are met or not

Adequacy of clearance from civil structures, electrical

apparatus and instrument consoles.

Accessibility of operation and maintenance space and

provision of drop out and handling areas.

Foundation drawings and vendor equipment requirements

Details and section identification match.

“Matchline” provision and accuracy.

Presence of signatures and dates.

Accuracy of BOM in Isometrics.