Piping Stress Man hour estimation (Detailed engineering) process for a specific Project

Estimating the project man hour is a very critical activity and should be done very accurately. Any mistake in this action may result in huge loss to any organization. If more man hours are quoted then the project may not be awarded to the organization and if less man hour is quoted then the design company may incur cost in the long run. So one should make a competitive man hour estimate considering all activities. Piping stress analysis is a very important activity in piping design and separate man hour must be claimed from client for this. Normally on an average piping stress analysis related activities require roughly 8-12% of total piping man hour. The man hour estimation is done either during the project bidding activity or during initial phase of any project. So hardly any firm data is available while man hour estimation is done. So sufficient cushion need to be added for rework activity. The following write up will try to provide a guideline for piping stress man hour estimation process for any project.Broadly there are three practices which are followed in established EPC organizations. They are:

  1. Estimating Man hour based on Stress Packages: Normal practice is to estimate the number of stress packages from available P&ID, then multiply the same by some constant value (decided based on experience). Few organisation divide stress packages in three groups, highly critical, moderately critical and lower critical. Lets for example if for a project 250 stress packages are estimated out of which 20 are highly critical, 100 are moderately critical and rest 130 are lower critical then manhour estimates will be =1.2 X (20×50+100×40+130×30)=10680 considering 50 man hour for a highly critical package, 40 man hour for a moderately critical stress package and 30 man hour for lower critical stress package. The total value is increased by 20% as data is not firm.
  2. Estimating man hour based on Stress Critical Lines: In this method the total number of stress critical lines are estimated from existing P&ID. Then that value is multiplied by a factor (Normally 12 to 18 depending on experience of existing organization). As for example is the project mentioned above contains 4 stress critical lines (you have to calculate critical lines from P&ID) on an average the total number of stress critical lines are 250×4=1000. So total man hour estimated would be approximately 1000×12=12000.
  3. Estimating man hour based on Critical equipment: This method is somewhat similar to the method mentioned in point no 1. In this method total number of equipments are calculated from P&ID. All equipments are then categorized in three groups-Highly critical (Turbines, Compressors, High temperature Reactors, Furnaces etc), Moderately critical (Air Fin Cooler, Pumps, High temperature Columns and Heat exchangers etc) and Lower Critical (Low temperature Columns, Heat exchangers etc). Then the number of equipments are multiplied by same predecided (based on experience) factors to get the total man hour.

In any of the above situation the following input documents are required at a minimum:

  • P&ID (If not available then man hour estimation can be done based on preliminary P&ID or FEED P&ID)
  • Line List if available
  • Equipment list if available

However in my opinion, one should look into the exact scope of working (activity wise) by the stress department. Then one should consider reasonable man hour (which normally takes based on experience) for each activity. And finally add all the man hours of each activity together to get the final man hour. This way one could get the actual man hour close to actual. The first step will be to list out all the activities in stress scope. As for example from initial start of any project broadly following stress activities has to be considered:

1. Study of Project Specifications and bid documents
2. Work Instruction and Specification preparation from bid documents if required
3. Rack Loading (Three or Four Stages)
4. Stress System definition from P&ID
5. Master Critical Line list preparation (Will be updated 3 to 4 times during project tenure)
6. Preliminary stress analysis before receipt of vendor equipment data (without proper documentation)
7. Final stress analysis after receipt of vendor equipment data (With proper documentation)
8. Spring datasheet and Spring Index preparation
9. Special support design
10. Datasheet preparation for miscellaneous items like expansion joint, sway brace, strut etc
11. Trunnion calculation
12. Review of Stress systems
13. Vendor communication
14. Interdepartmental communication with Civil, Mechanical and Process department
15. TBE of Spring and Special items
16. Job close out report preparation
17. Support Checking of critical lines
18. Support checking of Non critical line
19. Isometric review and issue
20. Other miscellaneous activities which are not listed above

After listing all such activities one need to decide actual time factors for each activity based on experience and then finally combine all those to get the final man hour. Request you to share your views or any other methods which will add value to the above article.

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.

4 thoughts on “Piping Stress Man hour estimation (Detailed engineering) process for a specific Project

  1. Excellent site. A lot of useful information here. I鈥檓 sending it to a few friends ans additionally sharing in delicious. And naturally, thank you for your effort!

  2. I think the adminn of this website is actually worrking hard in favor of his site, because here every
    material is quality based data.

  3. On Stress Packages how to discriminate  the threes highly critical, moderately critical and lower critical. Is there any tabulation for it. Besides, What does it mean of the Package?

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