Piping Analysis with Multiple Thermal Loads using CAEPIPE 3D+
Introduction
In the world of industrial piping, managing thermal loads is a critical aspect of ensuring the safety and reliability of piping systems. These systems often operate under a range of conditions where temperatures change due to process requirements, environmental factors, and operational cycles such as start-up, shutdown, and steady-state operation. Each of these scenarios imposes unique thermal stresses on the piping network, directly influencing its performance and longevity. Additionally, different sections of the piping may experience different temperatures during operation, leading to differential thermal expansion within the layout. Failing to account for these variations can result in issues such as thermal fatigue, material degradation, misalignment, or even catastrophic failures.
As an example, in a hot water distribution system in an industrial plant, multiple pumps are connected to a common header, each drawing hot water from different tanks. The system also includes a spare pump that remains idle during normal operation and is activated only if one of the primary pumps shuts down or becomes non-operational. As a result, the thermal load on the system varies depending on which pumps are operating. This causes different sections of the piping layout to experience different temperatures for different operating cases. Such variations create a more complex thermal load scenario, requiring a detailed analysis to accurately assess the impact of these multiple temperatures on the piping system.
This is where multiple thermal load analysis becomes indispensable. By incorporating various temperature scenarios into a unified model, engineers can design piping systems that remain safe, reliable, and code-compliant under all anticipated conditions. Advanced tools like CAEPIPE (built into CAEPIPE 3D+) allow engineers to account for these complex interactions, ensuring that the piping system can withstand the combined effects of thermal expansion, pressure, and other operational loads effectively.
Multiple Thermal Analysis in CAEPIPE
In CAEPIPE, users can choose up to 10 temperatures for analysis. These temperatures result in (10 +10C2 = 10 + 45) 55 combinations of expansion cases to evaluate. These cases include T1, T2, ...., T10, (T1-T2), (T1-T3), ...., (T1-T10), (T2-T3), (T2-T4), ...(T2-T10), (T3 -T4) .... (T9-T10).
Understanding Thermal Load cases in CAEPIPE:
Expansion Cases in CAEPIPE:
For the operating (W+P1+T1) case, CAEPIPE considers the weight, the pressure P1 corresponding to T1 and the expansion from Tref to T1.
The Reference Temperature is “the ambient temperature at which the pipe is to be/was initially installed”.? In other words, when the whole piping system is at Reference Temperature, the piping system is “stress free” and the involved pipe supports are “loads free” (excluding stresses and loads due to self-weight), as long as there are NO cold springs introduced during the installation of the system.? There is no need to input Reference Pressure, as at installation the pressure is zero.
The following are the Steps for performing Analysis with Multiple Thermal loads in CAEPIPE:
Below are the snapshots of a sample problem implementing multiple thermal loadings in CAEPIPE 3D+, which includes stand-alone CAEPIPE.
The below stress system illustrates the layout of four pipelines connected to five centrifugal pumps at one end (with one being a spare) and four tanks at the other end. Among the five pumps, Pump 2 serves as the spare and operates only when one of the other four pumps fails. Therefore, at any given time, four pumps are operational, with one on standby. To represent these scenarios, the following thermal load cases are required (see the attached model).
The above cases can be modelled in CAEPIPE as shown in below snapshots. For further details on the analyses and the associated model files, please visit us at "sstusa.com" (Click Here).
Layout and Graphics Window
Analysis Options, Materials and Pipe Sections
The above cases can be defined in CAEPIPE by defining the “Number of Thermal loads” as 10 through Layout window > Options > Analysis > Temperature. The snapshots for sections and pipe materials are also shown below.
Load Definition
Define the Pressures and Temperatures for different operating cases described above through CAEPIPE Layout window > Misc > Loads. Description corresponding to Loads C1 through CHL is given in the table below for clarity.
Assign the Loads C1 through CHL to different portions of stress system as required while creating the stress layout. After modeling the stress system, one can review the loads assigned to different portions using the Highlight feature through “Loads List window”.
Load Combinations
Select the load cases and load combinations required for analysis
Sample Results
You can review the CAEPIPE results file for Support Loads (loads acting on the supports by the piping for each load case), Element Forces & Moments (local/global forces and moments on each element for each load case) and Support Load Summary (listing support loads at a particular support for all relevant load cases and load combinations).
The Sorted Stresses in CAEPIPE lists the maximum of Expansion stresses for all thermal range cases at each node as well as the maximum of Sustained + Occasional stresses for all Occasional cases at each node. On the other hand, for the Sustained case, it always uses the maximum pressure among the input pressures (P1 through P10) while computing Sustained Stress at each node.
References:
[1]. SST Systems, Inc., CAEPIPE User’s Manual. Retrieved from CAEPIPE Users Manual
[2]. SST Systems, Inc., CAEPIPE Technical Reference Manual. Retrieved from CAEPIPE Technical Reference Manual