Dears,
I am doing analysis of heater transfer line for hydro cracker project.
The line is high temperature (450 deg.C) high pressure (#2500-181 Kg per sq.cm) and is subjected to vibration (two phase line).
Considering above parameters, do I have to consider fatigue analysis.
Regards
Khalid

Khalid,

The base code B31.3 calls for a single analysis covering fatigue and shakedown ( i.e. prevention of ratchetting). However the high pressure piping chapter of this code( although not mentioned explicitely , the application of this chapter is typically for rating > 2500 Lbs)calls for a separate check for ratchetting and fatigue. The fatigue check has to be done as per ASME SEC VIII DIV 2 APPENDIX 5.Wheteher or not a rigorous faigue analysis is required is governed by AD-160 of the SEC VIII Code.

Regarding your particular case: Flow induced loading is typically stress or load controlled rather than displacement or strain controlled and the addressal of fatigue in both ASME SEC VIII and B31 codes is in the line of strain controlled fatigue. These codes do not expliciately discuss the checkings required for stress controlled fatigue.

Refer the document ASME -OM-S/G for guidelines pertaining to stress controlled fatigue.

For the transfer line ( I believe that you are referring the line from the column to the fired heater at nearly vacuum condition) gets Two Phase loadings and use of Sway Braces have been extremely successful ( in my experience) for these systems.

Regards

anindya ,
Thanx for the information.
the line which I am refering to is heater outlet line(20" SS-TP321) connected to reactor.
Thanx again for reply.

Khalid

Khalid,
Some additional points...
This particular line u r mentioning will be subjected to slug and u may have to calculate the slug force to c if it is significant to be included in the calc.
Also this line will have a startup and shutdown case for which u may have to get details from ur process group. Check if the fluid densities are different during start up!
And don't forget to check the small bore purging lines usually connected at the high point close to reactor. Sometimes springs are required in these lines as well!!!