Introduction of Piping Drafting Basics
Piping drafting basics stands out as one in which the draftsman has great opportunities to express his knowledge of the uses of pipe and the best methods of representation. This needs piping drafting basics, which covers in this blog.
Requires basic drafting knowledge of machine drafting, architectural drafting, map drafting.
Consumes the major portion of the total design drafting manhours for process plants.
Inputs are required from various departments.
Drawings generated by piping department contains information pertaining to different departments. Hence all piping designers to know about piping drafting basics.
Piping Symbols
Every symbol has a definite meaning as has every line.
Single line symbols used in small-scale drawings and also used when the speed of execution is important.
Double line method in which double lines are drawn and spaced to represent the scaled nominal outside diameter of the pipe
Flanges are drawn to scale and face to face dimensions of flanged valves represent the actual scaled dimensions of the valve
Single line representation is used up to 300NB. Pipelines above 300NB are represented by double line method
Dimensions should be accurate enough
Dimensions for the double line method are marked to the centre line of the pipe.
AUTOCAD software is used for drafting
Methods of Representing Piping Systems
A piping system drawing may be represented by the following three methods
- Orthographic projection
- Developed – view method
- Pictorial representation
- Oblique Drawing
- Isometric Drawing
- Axonometric Drawing
Procedure for Drafting
The drawing sheet sizes shall be any of the following.
A1 – 840 x 594 mm
A2 – 594 x 420 mm
A3 – 420 x 297 mm
A4 – 297 x 210 mm
As far as possible drawings shall be made in the computer using AUTOCAD.
Plan and elevation shall be in first angle projection. This means that the elevation is shown above the plan.
All other details shall be in first or third angle projection. Drawings shall made in metric units only.
Drawings shall be drawn to standard scales.
Extended dimension lines with arrows shall be used for dimensioning
Piping Drawings
Piping Draftsman must be able to draw a piping system
He should understand the operating principles
Analyze the complicated piping arrangements
Turn a diagram into a working system
The piping drawings generated in FEDO for a project are,
- Plot Plans
- Planning Drawings
- Key Plans
- Pipe support Key Plans
- Isometrics
Plot Plans
There are three types of plot plans. They are listed below.
- Overall Plot Plan
- Area Plot Plan
- Unit Plot Plan
These drawings serve as reference for the following details
Battery limits of the plants
Location of all major equipment including structures and roads.
Construction of civil foundation at site.
Master document for various engineering departments for detailed engineering activities.
Overall Plot Plans
An overall plot plan is prepared for a large plant consisting of many process units, offices, etc. Each block is identified and divided by roads.
Area Plot Plan
When the scale of the overall plot plan is 1:1000 and more, the area plot plan is drawn to indicate the following for every designated plant area. Individual sections and storage General Pipe Bridge Details
Unit Plot Plan
When the scale of the overall plot plan is 1:1000 and more, the unit plot plan is drawn to a scale of 1 -250 or smaller
Presentation of Plot Plan Drawings
Presentation of the drawing shall conform to the following points/ clauses.
Plant north shall be indicated prominently on the plot plan at the right hand top corner.
Scale of the drawing selected so that smallest equipment in the plant will have a min dimensions 5 mm x 5 mm in the drawing.
Pumps & blowers shall be represented showing base plate dimensions.
Plant buildings shall be represented by outside dimensions to scale
All roads and access ways inside battery limits
Maintenance spaces, drop areas, tube pull out areas etc.
Piping Planning Drawings
Process plant drawings describe the arrangement of piping and may be drawn as plans and elevations.
The following are the data required to complete a planning drawing.
- Overall plot plan, Area / Unit plot plan(s)
- P& I Diagram
- Process Equipment specifications and Equipment drawings.
- Line schedule
- Piping specification, ETC.
The finished drawing shall include all line sizes and line numbers identical with those shown on the P&ID.
All valves and instruments shall be shown.
Presentation of Planning Drawings
Planning drawing scales shall be 3:100
Nozzle Orientation charts shall be drawn on the right hand side of the sheet
Plant North direction at the top-right corner.
Battery limit / match line shall be indicated with co-ordinates on all four sides, accompanied by the COD number.
All the nozzles shall be oriented in the planning drawing even if there is no connection to it.
Building & pipe bridge columns shall be marked with centre lines.
Indicate the load to be taken by the pipe supports which has to be designed by civil department.
Piping shall be drawn with standard symbol representation. Symbols shall be drawn to scale.
Layout of piping shall be drawn as per the P&ID and piping specification.
Give primary importance to accessibility to operation, maintenance and necessary clearances.
Provide necessary facilities for supporting the lines and the other piping materials.
Minimize the number of fittings and length of pipes for a good piping layout.
Avoid over crowding as well as wide spreading of pipelines which will create supporting problems.
As far as possible laying of pipe lines on the ground/ floor level shall be avoided.
For overhead lines a minimum headroom clearance of 2.2 meters to be provided.
Open and condensate drains shall be connected to the rain water drainage system.
When tapping are to be taken from a header, it shall be from the bottom side for liquids and from the topside for steam / gas lines.
Provide operating platforms with cat-ladders for valves located over pipe bridges.
Underground lines shall be shown in dotted lines. If the lines are in trenches, the trench dimensions also to be indicated in the planning drawings.
Pump suction and discharge lines shall be arranged such that it can be supported properly with no load applied on the nozzles.
Key plan
Key plans are the piping layouts, which are sent to site for erection work.
There are two types of Key Plans.
Piping Key Plan
This is the actual piping routing drawing and is generated from the relevant planning drawing by deleting certain additional information. This is basically the piping planning drawings without the details required by internal departments for their design
Pipe support Key Plan
This is essentially a key plan drawing in which all pipes supports with their identification details are also indicated.
Presentation of Key Plans
The following details are deleted in the planning drawings
The planning drawing signing table
All notes to other departments
Highlighted piping details including any isometric representations
Details in the revision table
Presentation of Pipe Support Key Plans
A reproducible copy of the key plan prepared is used for PS Key Plan.
All pipe support locations with identification as indicated in the marked-up copy of the planning drawing is transferred to this drawing
Isometric Drawings
Isometric drawings of pipe lines are prepared to further detail the pipe line.
The following data are required to prepare an isometric drawing.
- Line schedule
- Piping Key Plan/ Planning Drawings
- Piping specification
- Process & Instruments Diagram
- Dimensions of valve, flanges, fittings etc.
Presentation of Isometric Drawings
It is compulsory to follow the piping symbols not only in shape but also in dimension.
Standard A3 size isometric sheets shall be used for an isometric drawing.
The material take off for each line is to be entered in the space provided for it.
B.O.M. for each line to be entered in that isometric itself.
Listing of each item shall be in the ascending order of size.
Only Trunnion supports to be marked in the isometric
The construction issue of isometrics to site shall be only after Technical Audit and incorporation of any audit comments.