Applies To
Product(s):	AutoPIPE
Version(s):	ALL;
Area:	Reporting
Date Logged & Current Version	Sept2020 12.04.00.13

Problem:

Why are spring or rigid hangers on vertical legs showing large reaction loads in the Hydrotest load set case compared to the Gravity (Gr) case?

Solution:

Recall how AutoPIPE performs a hydrotest analysis, from AutoPIPE Help:

Please note that the AutoPIPE Hydrotest option automatically converts all spring hangers into rigid supports to simulate the holding pin which is still in the spring hanger during the hydrotest.

Therefore, the vertical leg in the piping effectively becomes a restrained piping system between the hanger and an anchor or another vertical support above or below the current hanger support. Therefore the large reaction on the vertical leg support in the hydrotest load set is due to the combined effects of pressure extension, any hydrotest thermal effects (usually taken at ambient) and deadweight under hydrotest load set and fluid+pipe weight loads under the GR case. The pipe wants to expand due to pressure but is restrained by the locked spring hanger therefore generating a large pressure reaction.

As mentioned the Hydrotest includes rigorous pressure analysis which for high pressure systems causes significant pressure extension in the pipe e.g if remove the v-stop at A03N and run the hydrotest shows upward displacement of 0.005". i.e with the system pumped up with 4950 psi pressure.

With the v-stop at A03N it is assumed locked and generates this upward load = 27482lb trying to resist the pressure extension.

Note:

1. If it is considered that the hanger rod assembly is not rigid in compression (i.e. some slack which is not unreasonable) then it would better to use a separate model with GR, P1 (Pressure Analysis = Checked)and T1 as hydrotest loads, and enter upward gaps for the v-stops then run the analysis as Non-linear. This will allow the pipe to move up and not be restrained.

2. To include the axial stress due to the pressure analysis cases (P1 - P3) in the calculation of longitudinal pressure stress (may be significant for high pressure systems), under tools/code combinations/longitudinal pressure, option "Include rigorous pressure stress" = checked. By default this option is OFF.

13. Why are spring or rigid hangers on vertical legs showing large reaction loads in the Hydrotest l

Problem:

Solution:

See Also