Piping Stress Critical Linelist: Format and Use, Responsibilities and Method of Operation

1. Format and Use of Piping Critical Line List

   1. The Piping Critical Line List is normally an internal document.
   2. The Piping Critical Line List comprises of a lead sheet (s) and continuation sheet (s).
      1. Lead Sheet
         The lead sheet is used to summarise the definitions of critical lines applicable codes etc. and amended to reflect any specific requirements of the contract (See Appendix – I).
      2. Continuation Sheet
         At the initial stage of preparation, this sheet is used to record the line data, the reason (s) why the line is critical, and identify requirements for Stress Sketches (See Appendix – II).

         Essential Read: Procedure Defining the Basis For Piping Critical Line List

2. Responsibilities related to Piping Critical Line List

   1. Piping Group
      1. The Lead Piping Engineer along with Lead Stress Engineer is responsible for the following activities :
         1. Compiling the initial issue of the Piping Critical Line List.
         2. Ensuring that the Piping Critical Line List is periodically updated to reflect relevant changes resulting from the issue of P&ID change notes and subsequent amendments to the Line Designation List. Such changes may result in additions or deletions to the Critical Line List (See 5.2.6)
   2. Construction Group
      Based on the completed Critical Line List, Lead Engineer shall mark lines which are critical in Line Designation List under the column provided and issue it to site.

      Construction Engineers shall properly understand the implication of criticality of the lines listed in the line designation list and take proper care in erection and commissioning phase of these lines. The layout of different piping components as well as the piping supports have to be designed and after obtaining prior approval from proper authority from Piping / Stress groups.

3. Method of Operation

   1. General
      1. It is most important that the Critical Line List is as complete as possible on the first issue to advise all concerned of the key design problems.
      2. In the case of vendor engineered packages, reference shall be made to the appropriate contract instructions to determine exact involvement.
      3. The completed document shall be used as key information by the layout designers and by checkers of Piping General Arrangement Drawings, who will check against the information given on the list.
   2. Piping Critical Lines
      1. The Piping Critical Line List shall be produced as soon as possible after the Approved for Design issue of the P&ID’s, Line Designation List, and Piping Specifications are available.
      2. Stress sketches shall not be drawn or any formal pipe stress analysis be carried out until the Piping Critical Line List has been issued.
      3. The original document is retained by the Lead Piping Engineer and photocopy is issued to the Lead Stress Engineer for review and approval.
      4. A master copy of the Piping Critical Line List shall be held by the Piping Stress Engineer which shall be used as a working document and modified to suit changes resulting from the issue of P&ID change notes. At a suitable time, the Lead Piping Engineer will update the original after getting line additions and deletions highlighted, and reissue.
      5. Lines may be added to or deleted from the Critical Line List subsequent to the initial review for the following reasons:
         1. Additional Lines:
            All lines introduced subsequent to the Approved for Design issue of the documents mentioned in 5.2.1 are reviewed and added to the Critical Line List if they fall into any of the categories listed earlier.
         2. Deleted Lines:
            Any critical lines deleted form the Line Designation and P&ID List are deleted from the Critical Line List.
         3. Process Changes:
            All lines affected by alterations to the service conditions are reviewed again, and added to or deleted from the Critical Line List if the changed conditions warrant it. Attention is also paid to changes in the size and specification.
         4. Line affecting the flexibility of Critical Lines:
            Non-critical lines found to affect the flexibility of critical lines which have not been included during the initial review are subsequently added to the Critical Line List.
      6. As work progresses the Stress Engineer will update critical line list showing the progress of stress analysis. This document is meant for monitoring status and receipt / approval / revision of stress information.
      7. Non-Critical lines on which advice may be sought by the Piping Engineer are not normally entered on the Critical Line List but covered verbally, otherwise by a memorandum if a record is required. In some instances as a result of this consultation the Lead Piping Engineer will request that a line be added to the Critical Line List.
      8. Formal computer stress analysis need not be carried out for the lines, which are similar to some other lines in the same project or some other project. This decision of not doing formal calculation shall be taken by lead piping engineer and lead stress engineer.
      9. Stress group is generally responsible to carry out stress analysis for the lines connected to turbine, compressors, air fin coolers, lines with bellows, fired heaters reformer etc. since the equipment are critical in nature.

Appendix-I

NOTES:

1. IN CASE OF LINE CONNECTED TO ROTARY EQPT.,WRITE EQPT. TYPE, TAG NO. & OPERATING PHILOSOPHY (WORKING/STANDBY) IN REMARKS COLUMN.
2. IN CASE OF RELIEF CRITICAL LINE, WRITE OPEN DISCHARGE OR CLOSE IN THE REMARKS COLUMN.
3. IN CASE OF VIBRATION WRITE CAUSE OF VIBRATION IN REMARKS COLUMN.
4. LEGEND FOR METHOD OF ANALYSIS
   C: FOR COMP.ANALYSIS METHOD
   V: VISUAL CHEK METHOD
5. LEGEND FOR PHASE
   V: VAPOUR
   L: LIQUID
   M: MIXED

Appendix-II (click here to enlarge)