Checklist for Piping Isometrics: P&ID, Layout, Drafting Related

Here is a checklist for Piping Isometrics

Sr. No. Check Points


1 Following items are checked with the P&ID (IFD or later issue):
  a)    Line number and pipe class.
  b)    Tag nos. of equipment, instruments, special items, actuated and manual valves (if applicable).
  c)    Flow direction (including flow direction of check valve)
  d)    Slope/no pocket/free draining requirement, if any.
  e)    Min/max distances, straight lengths, etc. as specified in P&ID.
  f)     Close/open position for spectacle blind or spacer & blind.
  g)    Removable spool requirement, if any.
  h)    Sequence of branch connections (as agreed with Process in case of any changes).
  i)     Piping spec break, if any (preferably be at flange joints/valves, each iso to contain only one spec).
  j)     Special feature of valves (e.g. LO, LC, etc.)
  k)    Insulation symbol for insulated lines.
  l)     Equipment nozzle/TP numbers and tie-in numbers.
  m)  Insulating gaskets are selected as shown in P&IDs
  n)    Specific requirements mentioned in applicable P&ID notes (if any) are complied


2 High point vents and low point drains are provided, as per project requirements, for lines that will be hydro-tested.
3 Drains are provided wherever liquid stagnation can occur in the lines e.g. downstream of a check valve.
4 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.
5 The platform/grade/building wall/dyke or bund wall/floor penetrations and limits of road crossings are properly shown wherever applicable.
6 The insulation limits are specified appropriately (esp. for personal protection)
7 The electrical tracing requirement and its limits are specified appropriately.
8 The wrapping and coating requirement and its limits are specified appropriately for u/g lines.
9 Minimum distance between welds is 50mm or five times the wall thickness whichever is greater, unless otherwise indicated in Project specifications.
10 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.
11 Full couplings are provided where applicable for small bore piping.
12 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).
13 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.
14 Lifting lugs are provided for removable spools wherever required as per project requirements.
15 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.
16 The valve stem orientation angle is indicated wherever the stem is not in the vertical and horizontal planes.
17 The piping interfaces with equipment/package nozzles/terminal points are checked (w.r.t. size, rating, flange face type and nozzle/TP nos.).
18 The straight length requirement for suction & discharge piping for compressors and certain pumps is as required by Vendor/project specs.
19 Straight lengths and branch configuration of upstream/downstream lines for anti-surge valves is as per Compressor Vendor’s recommendation.
20 The F/F dimensions of all valves, special items and in-line instrument items are as per approved vendor drawings.
21 The instrument connections are checked with Piping-Instrument interface drawings/Instrument hook-up drawings.
22 The rotameters are installed in vertical run with flow in upward direction.
23 The orifice tapping orientation is done considering liquid or gas flow as applicable and the BOM is as per the piping-instrument interface diagram.
24 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.
25 The line configuration for lines containing magnetic flowmeters or vortex type flowmeters is such that they are always flooded.
26 Line configuration allows easy removal of spectacle blinds/spacers & blinds and valves in case of RTJ flange joints.
27 Flanged spools are provided in the case of conical strainers to enable removal.
28 Orientation of valve handwheel / lever is checked in model for proper access and commented accordingly
29 Line routing is visually checked in model for general requirement like access to in line items, supporting, clearances, obstructions, consistency and aesthetic requirement, etc.
30 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.
31 Drip leg size and dimension is checked with Standard drawing for steam lines.
32 Requirement of Weep holes for atm vent lines is indicated.


33 The drawing border conforms to the Project specifications or Company standards, as applicable.
34 The isometric numbering is as per the approved project format and the line number matches with isometric number.
35 The correct isometric revision number is mentioned in the title block.
36 Pipe class printed at the bottom of the drawing matches with that in the line number.
37 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
38 Applicable reference documents (e.g. Line List, Isometric Index, Pipe Supports Spec, etc.) are mentioned.
39 Data such as inch-dia, etc. appear at the bottom of the isometric.
40 The “Cont. on …” description correctly appears at each end of the line isometric which is continued in another sheet.
41 The isometric print is readable (if required, the isometric should be split into more sheets).
42 Isometric number change is made preferably at a flange joint/valve (not at a weld joint).
43 Dimensions and elevations are adequately given. At least one elevation is mentioned and WP elevations for sloped lines are marked.
44 There are no HOLDs in the isometric (issue of any isometrics with HOLD requires approval by HOD/PEM).


The following documents are to be used for checking isometrics:

  1. Issued For Design (or later issue) P&IDs and Line Lists (and any Process DCNs issued thereafter)
  2. Approved Vendor drawings review of equipment & package mechanical drawings
  3. Issued For Design Instrument-Piping Interface drawings
  4. Approved vendor drawings of in-line instrument items including control valves, Pressure safety relief valve, motor operated valves and emergency shutdown valves
  5. Approved vendor drawings for manual valves and SP items.
  6. Approved Pipe Support specification and Piping Material specification
  7. Issued For Construction Civil and Structural drawings wherever applicable
  8. In case approved drawings are not available at the time of isometrics issue, it should be brought to the notice of the Lead engineer and the isometrics shall not be issued.

One comment

  1. Very Useful Information.

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