Piping Isometrics

Roy A. Parisher , Robert A. Rhea , in Pipe Drafting and Design (Fourth Edition), 2022

Abstract

An extensive discussion of the need for, and development of, piping isometric drawings is provided. An explanation of how piping isometrics are created from plan and elevation views is explained. The use of a North Arrow in establishing pipe orientation and routing on the isometric is shown graphically. The fitting, flange, and valve drawing symbols unique to isometrics are depicted. The use of coordinate and elevation callouts to determine configuration dimensions of the routed pipe is explained. The visualization, representation, and dimensioning of single, multiangle, and rolling offsets are explained. Dimensional solutions of various pipe lengths using Pythagorean's theorem and various trigonometric formulas are presented. Pipe Stress is introduced.

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Piping Isometrics

Roy A. Parisher , Robert A. Rhea , in Pipe Drafting and Design (Third Edition), 2012

Isometric Orientation

Note in Figures 13.1 and 13.2 how the height, width, and depth dimensions of the L-shaped object in the orthographic views are oriented on the isometric view with A as a point of reference. By using a point of reference, proper orientation of the isometric can occur by transferring distance and direction from the orthographic view. Similarly, on piping isometrics, establishing a point of reference is imperative. Although the A can be seen in Figures 13.3 and 13.4, it is not an adequate point of reference. The complexity of piping configurations requires a more descriptive "point of reference" be used to establish orientation between the orthographic and isometric views. In the piping discipline a north arrow is used as a "point of reference." Accurate isometric layout is based on the correlation of the orientation of the north arrow on the Piping Arrangement drawing and the north arrow on the piping isometric. Figure 13.8 illustrates the representation of the north arrow on the arrangement drawing and the north arrow on the isometric.

Figure 13.8. Orthographic and isometric north arrows.

Knowing that the Piping Arrangement drawing is a plan, or top, view drawing, a pipe can be determined to be turning north, south, east, or west when oriented relative to the drawing's North Arrow. So, if a pipe that has been traveling north turns down and then east on the arrangement drawing, it should also be shown to travel north, turn down, and then east on the isometric drawing. Figure 13.9 illustrates the correlation between pipe components shown in a Plan View and those same items in an isometric view. As you may notice, items that can be difficult to visualize on the Plan View drawing become much more evident on the isometric.

Figure 13.9. Isometric orientation.

Most companies prefer to draw piping isometrics with the north arrow pointing up and to the right. An alternate position is to draw the North Arrow pointing up and to the left. This is done, however, only in exceptional cases to improve drawing clarity. Figure 13.10 uses the configuration from Figure 13.9 to demonstrate how drawing an isometric with the North Arrow pointing up and to the left will affect the isometric representation. The North Arrow rarely, if ever, points down.

Figure 13.10. Alternate isometric orientation.

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Engineering drawings

Maurice Stewart , in Surface Production Operations, 2016

5.1.2.7 Piping fabrication drawings or "isometrics" and "spools"

The two most common methods for producing piping designs for a process facility are making either plan and elevation drawings and constructing a scaled model. For fabricating welded piping, plans and elevations are sent directly to a subcontractor, usually a shop fabricator. Isometric views (ISOs) are commonly used in prefabricating parts of butt-welded piping systems. ISOs showing the piping to be prefabricated are sent to the shop fabricator.

The prefabricated parts of the piping system are called "spools." The piping group either produces ISOs showing the required spools or marks the piping to be plans and elevations, depending on whether or not a model is used.

Piping "isometric" and "spool" drawings shows a complete line from one piece of equipment to another. It gives all information necessary for fabrication and erection of piping. Today, ISOs are usually drawn using CAD. The various runs of pipe, fittings, and valves should be roughly in proportion for easy understanding. Items and information that are shown on an ISO include the following:

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North arrow (plant north).

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Dimensions and angles.

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Reference number of plan drawing from which an ISO is made, line number, direction of flow, insulation, and tracing.

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Equipment numbers and locations of equipment.

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Identify of all items by using common symbols and a description if necessary.

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If a flange is different from the specification for the connected pipe, then the details of the flanged nozzles on equipment to which piping has to be connected should be included.

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Size and type of every valve.

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Size, pressure rating, and instrument number of control valves.

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Number, location, and orientation for each instrument connection.

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Shop and field welds. Limits of shop and field fabrication.

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ISO sheet continuation numbers.

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Unions required for installation and maintenance purposes.

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On screwed and socket-welded assemblies, valve handwheel positions need not be shown.

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Materials of construction.

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Locations of vents, drains, and traps.

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Locations of supports, identified by pipe support number.

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Fluid Flow

A. Kayode Coker , in Fortran Programs for Chemical Process Design, Analysis, and Simulation, 1995

Problem 3-1

A piping isometric ( Figure 3-8) shows a 6-inch (Schedule 40) line with six 90°LR elbows and two flow-through tees. The actual length of pipe is 78 ft. The fluid flow is 75,000 lb/h and its physical properties are viscosity μ = 1.25 cP, density ρ = 64.30 lb/ft3, and pipe roughness ɛ = 0.00015 ft. Calculate the equivalent length of pipe fittings, total length of the pipe, velocity head, head loss, and the overall pressure drop.

Figure 3-8. Piping isometric layout.

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Procedures

Richard Beale , Paul Bowers , in The Planning Guide to Piping Design (Second Edition), 2018

3.7.4 Prerequisites and checking procedure

Before piping arrangement and isometric checking begins, the following documents should be complete. It is the responsibility of the checker to obtain and use the most current copy of the

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instrument list and data sheets;

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tie-in list (if applicable);

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specialty item list and data sheets;

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Piping Job Notes (PJN);

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piping classes;

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piping standards;

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IFC P&IDs;

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IFC LDT;

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90% model review comments;

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final stress isometrics;

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spring support data sheets;

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structural steel drawings issued for checking;

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equipment check files;

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recent clash check report run and cleared.

Prior to commencement of checking, the piping arrangements and isometrics should be put on an IDR. Any comments arising from the IDR should be reviewed by the checker and incorporated into the piping arrangements and isometrics during the backdrafting.

3.7.4.1 Piping arrangement drawing content check list (must be established on the drawing)

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Plant North arrow (up or to the left) in top left-hand corner of drawing

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Key plan in top right-hand corner of the drawing

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Title block:

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Drawing number

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Drawing title

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Project name and number

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Revision number

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Revision description and date

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Drawing scale

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Reference drawings

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Matchline coordinates and references to adjoining drawings

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Area limit coordinates

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Continuations to underground drawings

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Equipment tag numbers, coordinates, elevations, and nozzle tags (Note: These are already checked. Verify the information on the drawing)

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Flow arrows

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General notes

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Call-outs and notes for any temporary shipping supports or strapping, or for any part of a line that is shipped loose (pipe rack and equipment modules only)

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Critical dimensions

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Insulation breaks are 500   mm back from all termination points of butt welds to allow for later field welding (pipe rack and equipment modules only)

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Cloud "HOLDS" and create a holds list

3.7.4.2 Piping arrangement design content check list (checked in the model and verified on the drawing where applicable)

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Pipe and equipment support numbers, coordinates, and TOS elevations

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Modules are within the width, height, and length allowances for shipping requirements

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Line spacing. Check that line spacing also allows for expansion growth at changes of direction. Refer to Table 3.5

Table 3.5. Linear thermal expansion between 70°F/21°C and indicated temperature. (Inches per 100 feet or millimeters per 30.48   m)

Identify the pipe material and the design temperature (use the higher number for in-between temperatures), then apply the following formula to calculate the expansion:

length of pipe in feet 100 × exp . per 100 feet = exp . in inches

or

length of pipe in meters 100 × exp . per 30.48 meters = exp . in millimeters

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Correct call-outs for shoes, anchors, guides, etc., per the stress isometrics

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BOP elevations

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Centerline work point elevations and trimmed shoe and shim heights for sloped lines

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Call-outs for reducers/swages at equipment nozzles: concentric, eccentric (FOB, FOT) with sizes

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Adequate space provision to swing spades and remove blinds

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Adequate space provision for valve rising stems

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Left- or right-hand instruments correctly orientated, e.g., ball pattern control valves

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Personnel protection insulation limits

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Drop zones

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ID the TOS to underside of shoe spring heights, or underside of steel to centerline of pipe of hanger rods and hanger springs

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Sliding/fixed saddle locations

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Vendor package tag numbers and limits

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Module tag numbers and limits

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Datum point and plant coordinates of pipe rack and equipment modules

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Building tag numbers

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Line numbers

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Spec. breaks

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Tie-in numbers

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Instrument tag numbers

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Cable trays shown

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Utility station tag numbers

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Safety shower and eye wash station tag numbers

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Sample cooler tag numbers

3.7.4.3 Isometric drawing content check list (must be established on the drawing)

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Plant North arrow up and to the left (preferred in industry) or up and to the right per company standard.

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Title block:

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Drawing and sheet number

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Project name and number

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Revision number

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Revision description and date

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Line number

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Area number

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Model number reference

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P&ID reference

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NDE and PWHT requirements

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Painting, insulation, and tracing requirements

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Code, e.g., B31.3.

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Check the operating, design, and test conditions against the master stick file LDT. In theory, these will be correct because they are imported from the native spreadsheet, but do not assume this to be true. In reality the updating of the LDT native spreadsheet often trails behind the plotting of the isometrics for checking. (Note: When isometric production is out of sync with LDT updates, it is best to leave the conditions off of the isometrics and require that only the LDT be referred to as the governing document. This can be covered by a note on the isometrics and avoids manual edits and/or revising and re-issuing at a later date.)

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Isometric continuation references.

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Equipment tag numbers, coordinates, elevations, and nozzle tags (note: these are already checked. Verify the information on the drawing).

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Flow arrows.

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Isometrics without a piece of equipment in them, i.e., a nozzle, require a reference to a column centerline.

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Notes for base guides are correct, e.g., "ALLOW N-S or E-W MOVEMENT."

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Cloud "HOLDS" and create a holds list.

3.7.4.4 Isometric design content check list (checked in the model and verified on the drawing where applicable)

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Components in the BOM (note: do not check quantities).

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Correct piping class used.

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The correct calculated wall thickness is called out.

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Branch lines checked against the branch chart, and for vapor and liquid traps. It may seem unnecessary to check the branch fittings given that the choices available are predetermined and limited per the piping class database. However, I have seen reducers added to branch lines on P&ID's and designers who have followed this exactly, placing a straight tee and reducer when a reducing tee should have been used.

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Call-outs for shoes, anchors, guides, etc., are per the standards, and the locations and the piping configurations are per the latest stress isometrics.

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Pump suction piping checked for eccentric (FOT) reducers and 5–10 straight pipe diameters prior to the suction nozzle.

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Hydrostatic vents and drains have been provided at all high and low points, and are per standards and piping class, e.g., double block.

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Instrument connections are per standards and piping class, e.g., flanged thermowells versus threaded or socket welded.

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Piping configurations for inline instruments conform to the data sheets and standards, e.g., upstream and downstream requirements have been met.

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Orifice flanges are Class 300 minimum, and tap orientations are identified.

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Rotated valves' angles are possible, e.g., a valve with a flange pattern of eight bolts rotated to 45 degrees is possible. A valve with a flange pattern of 12 bolts rotated to 45 degrees is not.

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Check valves that are positioned in the direction of flow. Note that swing disk type check valves cannot be positioned in the vertical with the flow down.

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Out-of-spec items are identified (e.g., flanges at pumps).

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Spool sizes are within the shipping box size, Mark numbers are noted and field welds and field fit-up welds are logically located, e.g., field welds in the horizontal plane when possible, field fit-up welds between rotating equipment.

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Nonstandard bolt lengths on PSV inlets, wafer valves, and bleed rings.

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Shop material and field material split is correct in the BOM.

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Centerline elevations of control valve stations above grade and platforms are at the height required by the standards, i.e., adequate height to ensure drain valve clearance.

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Dimensional checking is to be limited to

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face-to-face dimensions of inline instruments;

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face-to-face dimensions of specialty items;

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clearance is adequate for the removal of control valve operators;

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clearance is adequate for the removal of equipment.

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Specialty items (SP) noted.

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Tie-in numbers noted.

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Platform, floor, and wall penetrations are shown.

A checking file is to be created. Initially this may be compiled by the designer and added to by the checker. This file must contain all of the drawings and information used or created for the check, and is to be stored for future record.

Backdrafting must be done in the models and the drawings regenerated. Never manually edit the automatically generated parts of any drawings using straight 2D CAD.

After the checks and backdrafting are completed the models are frozen, and prior to IFC a "Yellow Off" of the lines is conducted by the piping lead, or designate, on the master P&IDs. The piping arrangements and isometrics are followed and demarcations are noted to indicate the extent of the lines checked. This is one last quality check to ensure nothing slips through the cracks.

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The Discipline of Layout in Context

Seán Moran , in Process Plant Layout (Second Edition), 2017

2.5.12 Isometric Piping Drawings

At the detailed design stage, isometric piping drawings, or "isos," are produced for larger pipework, either by hand on "iso pads" or by CAD (Fig. 2.8).

Figure 2.8. Isometric pipeline drawing.

The purpose of the iso is to facilitate shop fabrication and/or site construction. They are also used for costing exercises and stress analysis, as they conveniently carry all the necessary information on a single drawing.

Producing isos by hand or 2D CAD is quite time-consuming. Most 3D CAD plant layout software packages can automatically produce isometric drawings from model databases, but it is still usually thought prudent for these to be checked by experienced pipers, and the setup time of such systems is not worthwhile on smaller plants. 2D CAD is still, therefore, the norm on smaller projects.

Isometric piping drawings are not scale drawings, so they are dimensioned. They are not realistic: pipes are shown as single lines, and symbols are used to represent pipe fittings, valves, pipe gradients, and welds. The lines, valves, etc. are tagged with the same codes used on the P&ID and GA. Process conditions such as temperature, pressure, and so on may also be marked on the iso.

It may well be that "clashes"—where more than one pipe or piece of equipment occupy the same space—are only identified at the stage of production of isos, so pipework design cannot be considered complete before isos are produced. Clash detection is a common functionality of 3D CAD and is carried out during design development.

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Process plant design deliverables

Seán Moran , in An Applied Guide to Process and Plant Design (Second Edition), 2019

Isometric piping drawings

At the detailed design stage, piping isometrics are produced for larger pipework, either by hand on "iso pads" or by computer-aided design (CAD) ( Fig. 3.9).

Figure 3.9. Isometric pipeline drawing.

Isometric piping drawings are not scale drawings; they are dimensioned drawings. They are not realistic, pipes are shown as single lines, and symbols are used to represent pipe fittings, valves, pipe gradients, welds, etc. Lines, valves, etc. are tagged with the same codes used on the P&ID and GA. Process conditions like temperature, pressure, and so on may also be put on the iso.

It may well be that "clashes," where more than one pipe or piece of equipment occupy the same space, are only identified at the stage of production of isos, so design cannot be considered complete before isos are produced.

The purpose of the iso is to facilitate shop fabrication and/or site construction. They are also used for costing exercises and stress analysis, as they conveniently carry all the necessary information on a single drawing.

Producing isos by hand is quite time-consuming. There are some CAD systems now which can automatically produce isometric drawings from the GA drawings. It is claimed that these reduce drafting errors and inconsistencies, spot clashes earlier, facilitate links to other software such as costing programs, and save time. Hand drafting is, however, still the norm in many industries. The choice of approach is partly affected by the size of a project: for a large project with many isos there is justification for such a CAD system to save cost and time to produce (and in future revise) these iso drawings.

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Commissioning Phase One – Prepare

Martin Killcross EngTech TIChemE , in Chemical and Process Plant Commissioning Handbook, 2012

Isometric Drawing to P&ID Sanity Check

It is not uncommon post the production of the piping isometric drawings for the drawings to not fully comply and match the configuration of pipeline items and equipment as set out on the P&ID. A check therefore should be made of each isometric to its corresponding location on the P&IDs to ensure consistency. All differences must be resolved with the process engineering and piping group, with the isometric and/or P&ID being updated accordingly. This early documentation check will help resolve potential punchlist issues later in the construction phase when plant gets installed and is not consistent with the layout on the P&ID, which is always the document the commissioning group will use as their template for how the process must be constructed.

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Safety in Design

Ian Sutton , in Plant Design and Operations (Second Edition), 2017

Isometric Drawings

An isometric drawing provides a three-dimensional layout of the equipment and piping. Usually, piping isometrics are drawn on preprinted paper, with lines of equilateral triangles form of 60°. Isometric drawings are particularly important during the construction phase of a project. They are not to scale and so dimensions have to be shown. In practice most 3D isometrics are now created on a Computer-Assisted Design program. Images of piping systems and their corresponding isometric symbols are provided by Wermac (2016). As with P&IDs there are many examples (such as What Is Piping, 2016) of isometric drawings of process facilities on the Internet.

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Plant Piping Systems

Alireza Bahadori PhD, CEng, MIChemE, CPEng, MIEAust, RPEQ , in Oil and Gas Pipelines and Piping Systems, 2017

10.2 Fabrication

All materials included in the finished piping systems should be undamaged and fully in accordance with the piping material indicated on the isometric/piping plan drawing. Substitutions, including heavier or thicker materials, are not permitted without written approval of the engineer.

All weld numbers and welder's identification number should be painted close to the weld to enable traceability of each weld and each welder.

To allow easy and quick reference during handling and storage, the executor should maintain the color coding on piping.

The executor should provide identification marks on leftover pipe length whenever marked-up pipe lengths have been fabricated/erected.

All protective coverings of piping for shipment and shipping containers should be of sturdy construction to withstand normal shipping abuse.

Piping should be stored in a relatively clean, dry or well-drained area on elevated dunnage and protected against contact with salts or salty water.

On all lines DN 80 (NPS 3) and over, pipe clamps should be used to maintain alignment when welding pipes together, both in the executor's pipe fabrication shop and on site of over-ground piping.

All piping should be fabricated in strict accordance with isometric spool drawings. If spool drawings are not furnished, piping should be fabricated to the dimensions shown on the piping arrangement drawings.

All "FW" located by dimension should be held to dimensions noted. Additional field welds, other than those indicated on the spool drawings, which may be required to suit handling, may be added by the executor.

The executor should be responsible for working to the dimensions shown on the drawings. However, executor should bear in mind that there may be variations between the dimensions shown in the drawings and those actually occurring at site due to minor variations in the location of equipment, inserts, etc. The executor should take care of these variations.

Isometrics, if supplied, may have the field welds marked on them. However, it is the responsibility of the executor to provide adequate number of "FW."

Wherever errors/omissions occur in the drawings and bills of material, it should be the executor's responsibility to notify the engineer prior to fabrication or erection.

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