Salient Points to check while reviewing Piping Isometric Drawings

Many a times you must be checking the isometric drawings prepared by juniors or other engineers/designers. In your tight schedule you have to ensure that the isometric drawings are released/ issued to clients with quality. There are many points which you must check for proper quality. The following article lists many of such points to help you in the activity.

Check list for isometrics:

  • Line numbers (nos.)
  • Line specs
  • Start point location
  • End point location
  • Branch connection
  • Piping spec break in proper location as per P&ID, if any (preferably be at flange joints/valves, each isometric (iso) to contain only one spec).
  • Valve accessibility
  • Support location
  • Insulation (for insulated line only)
  • Instrument connection
  • Flow arrow
  • High point vent, low point drain
  • Hydro test vent and drain
  • Equipment nozzle connection
  • Nozzle nos.
  • Equipment nos.
  • Coordinates and elevations
  • North direction
  • Bill of material
  • Valve tag nos.
Sample Piping Isometric
  • Instrument tag nos.
  • Continuation sheets or iso. nos.
  • Grid location and nos.
  • Tag nos. of special items (if applicable).
  • Slope/no pocket/free draining requirement, if any.
  • Minimum or Maximum distance, straight length requirements etc. as specified in P&ID.
  • Close/open position for spectacle blind or spacer & blind.
  • Removable spool pipe requirement, if any.
  • Sequence of branch connections (as agreed with Process in case of any changes).
  • Special feature of valves (e.g. LO, LC, etc.)
  • Insulation symbol for insulated lines.
  • Insulating gaskets are selected as shown in P&IDs
  • Specific requirements mentioned in applicable P&ID notes (if any) are complied

Required documents for isometrics checking:

  • piping and instrument diagram (P&ID)
  • piping layouts
  • sectional drawings
  • equipment drawings
  • nozzle orientations
  • piping specification
  • piping support standard
  • special items drawings
  • stress analysis report

Points to remembers in isometrics checking:

  • Pump suction is bigger than discharge line (Refer P&ID)
  • Eccentric reducer (flat side top) using for pump suction line this is using for avoid the air block in pump suction.
  • Pump suction line and compressor suction line keep always downward position, Avoid loops in pump suction.
  • The “Continuation on …” description correctly appears at each end of the line isometric which is continued in another sheet.
  • PSV outlet always rising position.
  • Check the valve accessibility for maintenance purpose. valve operating height min 250mm to 1200mm from floor level.
  • Lift check valve always horizontally using. swing check valve verticaly and horizontally using.
  • Isometric number change is made preferably at a flange joint/valve (not at a weld joint).
  • Control station operating height 500 mm to 750 mm from floor level.
  • Shoe not required for trunion. (insulated lines)
  • Headroom clearance minimum 2.2m from ground/floor level.
  • Drip leg required for steam line header.
  • Shoe required for insulated lines (steam ,chilled water,brine,steam condensate).
  • Nozzle orientations should be keep as per piping requirement.
  • Avoid the obstacles. keep a piping routing neat and clearly.
  • Control stations locates side of near the walls or columns
  • Give a support to control station both side of control valves.
  • Use a dike wall around the equipment for avoid the liquid to spread in the plant area. the volume of dike wall is 1.5 times more than total capacity of equipments.
  • Use weld neck flange for pressure piping.
  • The isometric numbering is as per the approved project format and the line number matches with isometric number.
  • Adequate pipe spool lengths are provided for wafer type butterfly and check valves to prevent the interference of the valve disc with adjacent piping items.
  • The platform/grade/building wall/dyke or bund wall/floor penetrations and limits of road crossings are properly shown wherever applicable.
  • The insulation limits are specified appropriately (esp. for heat conservation or personal protection)
  • The electrical tracing requirement and its limits are specified appropriately.
  • The wrapping and coating requirement and its limits are specified appropriately for u/g lines.
  • Minimum distance between welds is 50mm or five times the wall thickness whichever is greater, unless otherwise indicated in Project specifications.
  • Unions are provided in galvanized piping where threaded in-line items need to be removed for maintenance. Also, unions are provided at regular intervals (e.g. 24m) in straight pipe runs.
  • Full couplings are provided where applicable for small bore piping.
  • For piping below 2”, WN flanges are not directly welded to SW fittings. Also, PE pipes are not directly welded with swaged reducers (couplings are used in between).
  • Appropriate break-up flanges are provided in piping with internal lining and hot-dip galvanized piping (based on tub size). Spool configuration is made with one elbow or one tee only to ensure proper galvanizing.
  • Lifting lugs are provided for removable spools wherever required as per project requirements.
  • There is adequate clearance between pipe support and the adjacent piping component (e.g. flange, drain valve) to allow for flange bolt removal, valve operation, etc.
  • The valve stem orientation angle is indicated wherever the stem is not in the vertical and horizontal planes.
  • The piping interfaces with equipment/package nozzles/terminal points are checked (w.r.t. size, rating, flange face type and nozzle/TP nos.).
  • The straight length requirement for suction & discharge piping for compressors and certain pumps is as required by Vendor/project specs.
  • Straight lengths and branch configuration of upstream/downstream lines for anti-surge valves is as per Compressor Vendor’s recommendation.
  • The F/F dimensions of all valves, special items and in-line instrument items are as per approved vendor drawings.
  • The instrument connections are checked with Piping-Instrument interface drawings/Instrument hook-up drawings.
  • The rotameters are installed in vertical run with flow in upward direction.
  • The orifice tapping orientation is done considering liquid or gas flow as applicable and the BOM is as per the piping-instrument interface diagram.
  • The straight length requirement (u/s & d/s) has been provided for flow meters (e.g. flow orifices, flow nozzles, venture meters) and is as per Project standards/Vendor requirements.
  • The line configuration for lines containing magnetic flowmeters or vortex type flowmeters is such that they are always flooded.
  • Line configuration allows easy removal of spectacle blinds/spacers & blinds and valves in case of RTJ flange joints.
  • Flanged spools are provided in the case of conical strainers to enable removal.
  • Orientation of valve handwheel / lever is checked in model for proper access and commented accordingly
  • Line routing is visually checked in model for general requirement like access to in line items, supporting, clearances, obstructions, consistency and aesthetic requirement, etc.
  • Branches like drains, drip legs, etc. are located with sufficient clearance from the supports, steel or other obstructions so that they do not clash during expansion/contraction.
  • Drip leg size and dimension is checked with Standard drawing for steam lines.
  • Requirement of Weep holes for atm vent lines is indicated.
  • The drawing border conforms to the Project specifications or Company standards, as applicable.
  • The correct isometric revision number is mentioned in the title block.
  • Pipe class printed at the bottom of the drawing matches with that in the line number.
  • Line data (e.g. process parameters, P&ID no., PWHT & testing requirements, insulation & painting specs, etc.) match with the Line List, if given in the isometric
  • Applicable reference documents (e.g. Line List, Isometric Index, Pipe Supports Spec, etc.) are mentioned.
  • Data such as inch-dia, etc. appear at the bottom of the isometric.
  • The isometric print is readable (if required, the isometric should be split into more sheets).
  • Dimensions and elevations are adequately given. At least one elevation is mentioned and WP elevations for sloped lines are marked.
  • There are no HOLDs in the isometric (issue of any isometrics with HOLD requires approval by HOD/PEM).

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

2 thoughts on “Salient Points to check while reviewing Piping Isometric Drawings

  1. Major points
    1. Nozzle co-ordinates
    2.vessel clip orientation given to mech.
    3.orientation of gate valve on steam PSV outlet

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