The model is complete and satisfies the requirements of B31.3. We can now evaluate the pump nozzles to ensure that the nozzle connections satisfy the requirements of API 610 for the pump. A total of 12 API-610 evaluations must be made in order to find the worst case scenario. These scenarios are shown below:
Pump A – All pumps on Pump A – Pump A idle Pump A - Pump B idle Pump A - Pump C idle Pump B – All pumps on Pump B - Pump A idle Pump B - Pump B idle Pump B - Pump C idle Pump C – All pumps on Pump C - Pump A idle Pump C - Pump B idle Pump C - Pump C idle
Access the API-610 module from the CAESAR II main window and create a new file for the first iteration – Pump A with all pumps activated.
Move to the Input Data tab to specify the data for the pump. Note the API coordinate system is different from the CAESAR II coordinate system, hence API My aligns with CAESAR II Mz. We are also only concerned with the Discharge nozzle; as such we do not need to enter any data into the Suction Nozzle tab or fields.
We wish to evaluate the discharge nozzle. This is pump A, so the nozzle is node 10. Fill in the correct data for Node 10.
Now we need to specify the loads on the discharge nozzle. As before, these loads can be imported from the analysis just done.
Select Load Case 3 – Operating case for all pumps active.
The results show that Pump A is OK for this condition. However, to determine the worst case, we must perform the other eleven evaluations.
After completing all twelve iterations, you should notice that one of the iterations fails. This is Pump C with Leg B Idle.
From these results, it can be seen that the local Y moment is failing, and is 262% of the allowable. As mentioned previously, the API-610 coordinate system is different to the CAESAR II local coordinate system. The local MY translates to the MZ in CAESAR II.
Return to the piping static output and review the results. View the restraint summary for all the Operating cases.
The MZ for Pump C in case 5 is the highest of any MZ moments – confirming the findings of the API 610 analysis.
View the 3D plot and view the deflected shape for Operating case with Pump B idle.
The datum for the thermal expansion is the line stop at node 80. The expansion at the leg for pump C is the greatest, and so is causing the higher moment at this point. Similar to the exercise SUPT01, if we can adjust the datum for thermal expansion, we should be able to reduce the amount of expansion which is causing the moment on Pump C.
This can be done by moving the line stop from node 80 to node 110.
Remove the Z restraint at node 80 and add a new Z restraint at node 110, then re-run the analysis. Notice now that the restraint summary shows that Pump C has a much lower MZ now. The loads have been more evenly distributed (Pumps A and B have slightly greater loads, but these pumps were OK anyway).
Select the Discharge nozzle tab. The loads on this pump have changed, so we will have to import these new loads.
Use the Refresh Loads from Current Job button to bring in the new loads and re-run the analysis.
Tutor
This exercise will develop various sequences of “run – evaluate – modify” workflow to determine the acceptability of the system. Each of the evaluations of the system will develop another aspect of CAESAR II.
Once the system is acceptable, we will generate a custom report and stress isometrics.
System parameters
Pipe: 8” diameter, standard wall, ASTM A-53 Gr. B Analysis temperature: 315°C
Analysis pressure: 2 bar Corrosion allowance: 0.8 mm Insulation: 75 mm CaSi Fluid: 0.8SG
Pipe Specification: 150 pound class components Design Code: B31.3
Node 10 is connected to a Pump and node 110 is connected to a vessel Nozzle. Their details are as follows:
Pump Details:
10 inch end suction, 8 inch top discharge Suction is -380 mm in X from pump centre
Discharge is 500 mm above and 300 mm in Z from pump centre Piping load on suction nozzle given as: (4450,-3550,-5340) N and
(-4070,-3390,2170) N-m Nozzle Details:
Fixed end is preceded by a long weld neck flange in the -Z direction: OD=247.65, wt=22.225, length=300 mm, weight=458 N and a standard, 8 inch weld neck flange and gasket
Model the system as shown in the isometric. When modelling the bypass loop, the Close Loop command can be used if required to connect node 150 to 60. Change the node numbers to 150 and 60 and click the close loop button. CAESAR II will add in an element of the required length
automatically.
Boundary Conditions
We now need to specify the boundary conditions for the analysis. The piping is connected to a pump and a vessel at the termination points, so we can apply the effects of these to the relevant nodes. Pump Connection – Node 10
The discharge is 500mm above (Y) and 300mm in Z from pump centre We have two options for the approach here.
1. Calculate the thermal growth of discharge nozzle from pump base point. Alpha= 0.003832 mm/mm Displacements therefore: X = 0 Y = 500 x 0.003832 = 1.916 mm Z = 300 x 0.003832 = 1.1496 mm No rotational displacements
2. Add a construction element between the nozzle node (10) and the pump base with appropriate material and temperature.
For this exercise, specify the displacement set for node 10 as above.
Vessel Connection – Node 110
As before we have the same two approaches; provide the thermal growth of the nozzle, or model the vessel. The thermal growth of the vessel is
X = 0 Y = 8.43 Z = -2.87 RX = 0 RY = 0 RZ = 0
Support Riser
We wish to unload the pump discharge nozzle as much as possible, and also support the thermal growth of the riser. To do this we will locate a spring hanger near the elbow (node 70).
Place a Carpenter & Paterson hanger at node 70
Support Horizontal Runs
The suggested maximum support spacing for 8” water filled pipe is 5.8m for horizontal straight runs. 75% of that spacing for horizontal spans including changes in direction would therefore be 4.35m. This will support the pipe weight and so account for the SUS case. Since we will check these
SUStained stresses (and since the fluid weight is less than water-filled) we can exceed the suggested spacing.
Locate a restraint on each horizontal 8” run using the Break function. 70-80 add node 75, located 1200mm before node 80
80-90 add node 85, located 3000mm after node 80 Add the following restraints:
Node 75
1x (double acting) Y restraint, with a friction coefficient of 0.3 1x guide with a gap of 8mm, again with friction
Node 85
The model is now complete. Error Check the model and run the Recommended load cases.
Immediately it can be seen that there is an issue with the EXP case. Check the stresses for both the EXP and SUS cases.
The SUS case is OK
The EXP case however is an issue:
The only issue is at node 30, where the stress is 130% of the allowable.
Node 30 is the Tee connecting the bypass.
One of the easiest fixes for an overstressed component is to replace it with a stronger component. Component strength is indicated by the stress intensification factor (SIF). Here, the stub-in branches are overstressed. Their in-plane SIF is 3.96 and their out-plane SIF is 4.95. Adding a pad to these tees will strengthen them. Check the effect of adding a pad by using the Tee SIF Scratchpad. Change the unreinforced tee to a reinforced tee with a 9mm pad. Using the Recalculate button will show that the SIFs have been reduced to 2.04 and 2.38 for in-plane and out-plane respectively.
Accept these changes and apply to node 30. Re-run the analysis and review the results.
The expansion case is now ~75% rather than 130%.
The SUS case is still 14%. Hanger Sizing
Look at the operating load and installed load on the pump discharge nozzle (node 10). Typically, with a spring hanger above the pump, the pump will see a positive (up) load in the cold state and a negative (down) load in the hot state. Here, the piping pushes down on the pump in both states. This spring is undersized. Why? The calculated load carried by the spring is based on the overall distribution of weight between all vertical supports. The interaction of the pump nozzle (anchor), the spring and the other Y supports has very little load “assigned” to the hanger location. More weight is carried by the pump rather than the spring hanger.
Deadweight that is resting on the pump must now be transferred to the hanger. The easy way to do this is to remove the load-carrying capability of the pump in the initial weight analysis when the hanger load is first calculated. To do this, CAESAR II allows the restraint to be “freed” – effectively removing this node from the hanger sizing calculation, so the load is distributed amongst the remaining support locations.
Return to the input and on the hanger; free the restraint at node 10 in the Y axis:
Now reanalyse the system. Review the results again.
The EXPansion stress results are unaffected by this hanger change. The maximum SUS stress ratio is also still around 14%.
Review the hanger table with text.
A Carpenter & Paterson DV70 has been selected again, but the hot load has increased to 7000N and the installed load has increased to 8000N.
Review the restraint summary report to view the pump load (node 10).
The resized spring now pulls up on the pump in the cold position and unloads as the system heats up. (The riser growth drops the load supplied by the spring.) This spring is much better than in the first iteration; however it could be improved even more. The hanger data input provides for the specification of the hanger operating (hot) load:
Pump Load
Review the restraint summary report for the OPE and SUS (installed) cases. The loads shown for the pump are a little high in some directions – MX is almost 30000N. However no indication is given that these loads are excessive.
American Petroleum Institute Standard 610 (API 610) sets maximum nozzle loads for pedestal supported pumps. CAESAR II provides this calculation. Run this analysis with the pump data provided above and using the discharge loads from this analysis. Since both suction and discharge nozzles are evaluated together, the Table 4 limits in API 610 can be doubled (see API 610 Annex F).
API 610 Analysis
Access the API 610 module from the Analysis menu on the main window.
Create a new file and input the pump data.
The pump centreline can be seen to be in along the X axis, therefore the angle between X axis and pump Centreline is 0°. The angle between the Z axis and the pump centreline is 90°. The direction cosines are therefore
X Cosine = cos 0 = 1 Z Cosine = cos 90 = 0
The Base point node number can be any arbitrary node number. This node number does not have to appear in any of the piping model, but is used by API 610 as a point of reference about which to sum moments.
The suction Nozzle is not defined in the piping model as we are given the loads so can input these. We also know that this is a 10” End type suction nozzle.
The discharge nozzle is in our piping model, and is node 10. This is an 8” Top type suction nozzle. As mentioned, since both suction and discharge nozzles are evaluated together, the Table 4 limits in API 610 can be doubled.
The suction nozzle loads and location have already been given: Suction is -380 mm in X from pump centre.
Piping load on suction nozzle given as: (4450,-3550,-5340) N and (-4070,-3390,2170) N-m
The pump discharge nozzle is located 500 mm above (Y) and 300 mm in Z from pump centre.
The loads on the discharge nozzle can be imported from the piping model. This will be the OPE case.
Now analyse the pump.
The suction nozzle passes OK. But the discharge nozzle fails.
The load in the local Y direction (global Z) is excessive as are all three moment terms. The worst component is the local My (global Mz) which is almost 10 times the Table 4 limit.