You have asked a very complex question. One that a forum like this may not be able to answer.
However I will offer the following:
Most engineering companies set some minimum analysis criteria on a project by project basis but there is always the exception for even "That" project.
Stress Analysis Criteria may include:
- High Temperature pipe
- Very large diameter pipe
- Very heavy wall pipe
- Very thin wall pipe
- Exotic Alloy Pipe
- Attachment to strain sensitive equipment (Pumps, Glass lined vessels, etc.)
- Extremely low temperature (Cryogenic) systems
- Any pipe installed in Arctic locations
- All other lines below the stated minimum temperature level on a job installed in a place like Oman or Kuwait


To develop an Estimate you need to know the Scope of the Work.
- You need to have a count of the total number of lines in the plant.
- You need to have a breakdown of these lines by categories such as Size, Material, Temperature, Service, Function, etc.
- You need to have a clear idea of which lines do not require Stress Analysis due to size and service
- You need to know the different kinds or levels of "Stress Analysis" there are and the approximate number of hours for each.


Flexibility Analysis might come in a number of forms and should consider many situations.
Forms:
- Simple, Visual Review = Estimate 3 to 5 hours per line
- Intermediate, Informal Calculations = Estimate 8 to 10 hours per line
- Complex, Formal Analysis for excessive stress caused by common factors (Temperature induced expansion, Dead/Live Loads) = Estimate 30 to 40 hours depending on complexity
- Special Analysis (i.e.: Analog studies for reciprocating compressors, seismic studies, Sea-Force studies for Offshore Platforms) Estimate 40 to 60 hours.

Estimated Stress hours include the time to develop any Specifications, Data Sheets and procurement documents for Stress related products such Spring Hangers, Expansion Joints or Struts. It also includes all supervision time, meeting time, any travel to vendors or job sites.