This pump suction line cycles between 42C cold and 165C when a pump is running. The temperature changes will cause thermal expansion that are expected to create stresses in the pipe and loads on the pump inlet flanges. The pump manufacturer has rated the inlet flanges to API 610 limits. The piping system must be designed to keep the loads below the specified limits.
Allowable Loads and Setup
Run 1 – Fails
Caesar runs the four load cases – “OPE 1”, “OPE 2”, “OP 3” and “SUS”. The pipe stresses are acceptable for this run and all other runs in this article. The loads on the pump inlet flanges are of interest, and in this case fail for Pump B.
The initial design creates inlet nozzle loads that exceed the pumps limits. A redesign is required.
Run 2 – Fails
Run 1 shows that the loads are acceptable for Pump A and fail for Pump B. It is logical to move the inlet location on the header to increase the flexibility of the inlet line on Pump B at the expense of Pump A.
This redesign fails. Now both pumps are overloaded.
Run 3 – Acceptable
Another solution is tried. The inlet line is returned to the center of the header and elbows are added to the pump inlets to increase flexibility.
Adding the elbows as shown in Fig-6 has increased the flexibility enough to lower the inlet loads to the allowable range for both pumps. This design is acceptable.
Run 4 – Acceptable
Although Run 3 has acceptable results, it increases the material cost by adding elbows and fabrication costs by adding welds. Another alternative is tried.
This alternative also is acceptable, although it increases the fabrication cost by adding small diameter pipe welds. It has lower fabrication cost than Figure 6.
Pipe stress provides 2 acceptable design alternatives. The best design for the application can be used.
Pipe Stress Analysis at PVEng
We offer pipe stress analysis services.
- Caesar II thermal, flexibility and dynamic pipe stress analysis
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