Tutorial on Refrigeration Piping using CAEPIPE

Analysis of Refrigeration Piping as per ASME B31.5 Code:

The snap shot below shows the sample layout of a refrigeration piping system. The system experiences two (2) different temperatures during its operation (from -50 deg. F to 200 deg. F) with installation temperature as 70 deg. F. Being refrigeration piping, the analysis code is selected as ASME B31.5 for this system.

Step 1:

Select the Analysis code as ASME B31.5 through Layout Window > Options > Analysis as shown below.

Step 2:

As the piping layout involves two (2) operating temperatures, “Number of Thermal Loads” needs to be set as “2”. This can be done through Layout Window > Analysis > Temperature as shown below. In addition, the installation temperature (same as “Reference temperature”) can be input as shown below.

Note:

As per para. 519.4.5(a) of ASME B31.5 (2022), bending and torsional stresses shall be computed using the as-installed modulus of elasticity, i.e., E_c at installation temperature (same as “Reference temperature”). Hence, "Use modulus at reference temperature" is set as "default" and is disabled for user to modify.

Step 3:

Enter the Operating temperatures of the piping layout through “Layout Window > Misc > Loads” as shown below.

Note:

Design Temperature entered will be used to determine the allowable stress for material, which is in turn used to compute the Allowable Pressure as per the piping code selected (B31.5 in this case).

The Allowable Pressure so computed as per the piping code selected is then compared against the Design Pressure entered above and reported in the Code Compliance results.

In addition, starting CAEPIPE Version 10.20, a new load case called “Design (W+PD+TD)” is added. When this load case is selected for Analysis, CAEPIPE will compute and show results for Displacements, Element Forces & Moments, Support Loads and Support Load Summary. This load case is NOT included in Stress Calculations, Rotating Equipment Qualifications and Flange Equivalent Pressure Calculations, as many of the piping and equipment codes do not require the qualification to be carried out at Design condition.

Step 4:

Select the material properties corresponding to “A53 Grade A” through “Layout Window > Misc > Materials > File > Library…”.

From the dialog box shown, select the Material library as B315-2022 from the folder “Material_Library” available inside the CAEPIPE installation folder. Once selected, highlight the material as shown above and press the button “OK”.

Step 5:

Define the section properties through “Layout Window > Misc > Sections”.

Step 6:

Generate the piping layout as shown below.

Step 7:

After creating the stress model, turn ON load cases through “Layout Window > Loads > Load cases as follows: Expansion (T1) {which is the same as the range (T1 – Tref)}, Expansion (T2) {which is the same as the range (T2 – Tref)}, and Expansion (T1 – T2) [= (T1 – Tref) - (T2 – Tref)].

After analysis, Expansion Stress (SE) value given at any node in Results Window > Sorted stresses and Results Window > Code compliance is the highest thermal stress range at that node among the three thermal ranges (T1 – Tref), (T2 – Tref) and (T1 – T2). 

Step 8:

Save the model and perform analysis through Layout window > File > Analyze.

In order to understand the loads and load combinations used for analysis, review the CAEPIPE results file for Sorted Stress, Code Compliance, Displacements, 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).

As stated above, Sorted Stresses in CAEPIPE lists the maximum of Expansion stresses for all thermal range cases at each node. On the other hand, for Sustained case, it always uses the maximum pressure among the input pressures (P1 and P2 in this case) while computing Sustained Stress at each node.

Operating Stress for Impact Test can be seen by selecting the option “Show Operating Stress for Impact Test” through Mouse Right click.

Similarly, Code Compliance report lists the Stresses element-wise following the same procedure as done for Sorted Stresses.

From the Displacement results for Expansion (T1) and Expansion (T1-T2), it is observed that the Displacements are +ve in Global Y direction confirming that the piping is shrinking due to temperature decrease for both expansion cases.

Similarly, from the Displacement results for Expansion (T2), it is observed that the Displacements are -ve in Global Y direction confirming that the piping is expanding downward due to temperature increase.

Element Forces & Moments (local forces and moments on each element for Expansion (T2) load case) are shown below.

Element Forces & Moments (global forces and moments on each element for Expansion (T2) load case) are shown below.

Support Loads on all supports by the piping for Operating Load case 1 are shown below.

Support Load Summary (listing loads on a particular support by the piping) for all relevant load cases and load combinations) is shown below.