Hot tapping a pipe line with a new branch line. The header pipe is running under operating conditions, while branch piping is operating at initial conditions.
What are the stresses in the system:
As of Dec 2021, AutoPIPE has only one initial condition, ambient, that is applied to the entire system, then the piping operating conditions are added with load cases P1T1, P2T2,... PnTn. Consider this scenario, while the header pipe is displacing from initial conditions to operating conditions, the header pipe is not restrained nor takes into consideration any affects of the new branch line . The header pipe is already at operating condition / displacement when hot tapped to add the new branch piping. Therefore, one would model the header pipe at the displaced state before adding the new branch piping. Next, raise the branch piping from initial conditions to operating conditions. Finally, add another scenario where both pipes (header and new branch) cools down to shut off states.
Suggested modeling approach:
Note: AutoPIPE has a number of limitations (ex. apply more than 1 ambient temp across the model, ignore piping affects for part of the model, etc..) to correctly model this scenario. Therefore, this is only a suggestion where the user is cautioned to run tests to be sure results appear to be logical / respectable.
1. Model the header pipe and apply all load cases as needed.
2. Analyze the system and review the results. Find the displacement of the header pipe under the operating condition.
Note: Ambient temperature should be the temperature that header pipe was installed at.
3. Create a new model that models the header pipe in the displaced shape.
4. Insert the new branch piping into model #2.
5. Under AutoPIPE load case 1 (T1P1), header pipe is at operating condition while branch piping is at ambient condition and no pressure.
6. Under AutoPIPE load case 2 (T2P2), both header pipe and branch piping are at operating condition.
7. Under AutoPIPE load case 3 (T3P3), both header pipe and branch piping have shutdown conditions applied to the piping.
a. Suggest, ambient temperature should be the temperature that header pipe was operating at.