IPE-TM-510-16 — Hydraulics | Engineering Library

1. Purpose

This procedure provides Inflection Point Engineering practice and guidelines for the hydraulic calculations and the generation of the process hydraulics reports

2. General

2.1 Hydraulic calculations are important:

Line Sizing
To determine pump and compressor head requirements
To determine control valve requirements
To ensure unit will operate at hydraulic conditions other than normal, for example
Startup and Shutdown
Plugged Reactor
Special Customer Requirements
To determine design pressure values for equipment
Also good for trouble shooting hydraulic problems on existing equipment and systems.

The hydraulics are not based on a unit specific plot plan but a typical plot plan layout. This is necessary because during the Schedule A design the final plot plan, piping lengths and layout are not yet known. Equivalent line lengths are not exact but determined from a combination of standard factors and specified nozzle elevations. The Contractor is responsible for verifying that the system hydraulics represented in the project specifications are adequate and must adjust them as necessary for the final plot layout, piping arrangement, and actual equipment purchased.

The Process Hydraulics can be used by the Contractor for their initial hydraulic estimates; however, they are not intended to take the place of the Contractor’s final hydraulics. Modification of the hydraulics to be consistent with the “as built” units and the final hydraulic check of equipment is the Contractor’s responsibility.

2.2 Review the following:

Process specific hydraulic guidelines

3. General Data Inputs

Normal Flow Scenario	Always 100%
Pressure Drop (piping and velocity related equipment)	Pressure drops for the Design and Alternate flow scenarios are based on the ratio of flow rates, densities and viscosities. For multiple process cases, the non-governing normal case pressure drop will be recalculated to reflect the pressure drop in relation to the governing case.
Elevation	If the P&ID indicates “Free Draining” downstream of the equipment, then elevate the equipment to have the material flow downward in the outlet pipe. If the P&ID indicates “Locate on platform as close to inlet nozzle as possible”, then make the equipment elevation the same as the inlet nozzle elevation with the pipe close coupled.

4. Vessels

Minimum Liquid Level	The distance from the point defined for elevation to the minimum liquid level, typically 0.5 ft. The 0.5 ft value is set based on most vertical vessels having the lower level connection 6” from the bottom tangent and the height of the vortex beaker in a horizontal vessel of 6”. Use 0.5 ft for horizontal vessels to be more conservative. If a vessel has a LLL greater than 6”, then enter the LLL value instead. This makes sure that any pumps on the vessel outlet do not take credit for any static heads that may not always be there. This approach applies when the liquid is being pumped or pressured from the vessel. For vertical liquid full vessels, use the tangent length.
Maximum Liquid Level	Receivers/Hor. Surge Drum = vessel diameter The vessel diameter (more conservative) rather than the max controlled level is used when calculating the pump shutoff pressure. Vertical Surge drums/Liquid Full vessels = tangent length Fractionators/Vertical Product Separator = level range plus distance from bottom tangent to bottom level nozzle (typically level range plus 6”).
Actual Elevation	From vessel drawing or P&ID Horizontal: This is the distance from grade to the bottom of the main shell (excluding any water boot). Vertical: The distance from grade to the bottom tangent of the vessel.
Section Max DP	Fractionators: The tray/packing pressure drop for each section Receivers, Separators, Surge Drums, KO Drums, Compressor Interstage, Suction Drums: 0 psi
Pressure Drop	Horizontal receivers: No frictional pressure drop Fractionators/Trayed Columns/Packed: The frictional pressure drop is constant for all cases. The fractionator pressure drop is primarily a function of tray loadings (which are relatively constant even if the reflux changes) and not proportional to changes in flow to the fractionator. This value should be consistent with the value shown on the 307 and 301 project specifications. Treaters/Reactors (including internals): The frictional pressure drop does vary with flow. Absorbers: The frictional pressure drop is constant for all cases. If the pressure drop is large, consider adjusting the pressure drop with flow.

5. Shell and Tube Exchangers

Elevation	Typically at grade, except thermosiphon reboilers. If the pipe from the shell and tube overhead condenser to the overhead receiver has a note on the P&ID saying “Free Draining”, then the elevation should be set 5 ft above the top of the receiver shell. For water cooled condensers, see Procedure IPE-TM-320-02 “Design of Fractionator Condensing Systems” Section 6.10.

6. Air Cooled Exchangers

Condenser Rundown	If yes, then the static head should be ignored for the Fractionator Overhead condenser mounted above the overhead receiver and an equalization line should be shown on the P&ID.
Elevation	Typically at 40 ft.

7. Pumps

Suction strainer pressure drop	The clean service strainer pressure drop is included in the calculation of the suction piping equivalent length. See Procedure IPE-TM-510-08 Piping Equivalent Length Guidelines.
Maximum Pump Suction Pressure	Vessel Set Press + Vessel Press Drop + Max LL + Vessel elevation – Pump CL (Use the highest average SG from all cases)

8. Control Valves

Elevation	Elevation: Typically at grade. Feeds to a column: In many cases, it is difficult to design around slug flow by increasing or decreasing the line size, assuming that we can even predict it with any degree of certainty. Consider placing the control valve at the level of the column inlet flange for flashing fluids. Use T-800-02, “Piping Pressure Drop” to determine the flow regime. This minimizes the velocity and slug flow and hammering in the column inlet line as the fluid rises up the line to the column inlet.
Control Valve in Pump Circuit	This is for the minimum pressure drop for the normal case. For multiple process cases, the minimum control valve drop is applied to the governing case for the pump. All other normal cases will have higher control valve pressure drops. The minimum pressure drop is the greater of the following: 25 psi (no lower than 24.5 psi) 50% of circuit friction drop (start to end of circuit, excluding static head and nonfloating CV pressure drop) 10% of pump head or 7% of pump head when differential head is greater than 1000 psi If Cvmax/Cvmin is greater than 8, then consult the process control coordinator (PCC) for standard and enhanced scope projects. If two control valves in parallel are required, P&IDs should indicate two.
Inlet Pressure	The design hydraulic pressure at the inlet of the (all liquid stream) valve should be at least 25 psi above the vapor pressure to ensure that the fluid remains all liquid at the valve inlet.

9. Flow Devices

Elevation	Typically at grade.
Pressure Drop	See IPE-TM-510-01 Permanent Pressure Loss for Primary Flow Elements.
Liquid Base Specific Gravity	Base SG = 141.5 / (131.5 + API) To convert from Base SG to Flowing SG, this can be done manually by using the graph in Crane Appendix A-7 titled “Specific Gravity-Temperature Relationship for Petroleum Oils”
Normal Flow on Meter, % of Meter Maximum	The default value is 80%.
(Transmitter Differential)	See table below This is based on the criteria that process P (psia)/meter range (in H2O) >1 for vapor streams.
Beta Ratio	If the beta ratio is outside the acceptable range: For new units, increase the line size to decrease beta ratio For revamps, increase the orifice meter range to decrease beta ratio For revamps, increase the % of meter max to decrease beta ratio

Flow Meter Type	Stream Phase	Process Press, psig	in H2O
Venturimeter	Any	Any	50
Fulltap (Pipetap) orificemeter or Flangetap orifice meter	Liquid	Any	100
Fulltap (Pipetap) orificemeter or Flangetap orifice meter	Vapor	10-35	25
Fulltap (Pipetap) orificemeter or Flangetap orifice meter	Vapor	>35	50
Fulltap (Pipetap) orificemeter or Flangetap orifice meter	Vapor	>85	100

10. Mixer

Elevation	Typically at grade.
Multiple	If there are multiple lines combining into one, Inflection Point Engineering does not know the order that the lines will be combined. Therefore, the flowsheet and hydraulics should just show one node even if the PFD and the P&ID show multiple mix points. If the intermediate lines need to be sized on the P&ID, list the line size after the mix point (based on total flow rate of all streams).

11. Splitter

Elevation	Typically at grade.
Multiple	If there is a single line splitting into multiple lines, Inflection Point Engineering does not know the order that the lines will be split. Therefore, the flowsheet and hydraulics should just show one node even if the PFD and the P&ID show multiple points. If the intermediate lines need to be sized on the P&ID, list the line size before the split point (based on total flow rate of all streams).

12. Pipes

Line Size	In general, the minimum line size for process lines is 1”. See Procedure IPE-TM-810-02 “Pipe Size Selection” Section 4.
Wall Thickness	The defaults are: 2” and smaller Sch. 80 3” to 10” Sch. 40 12” and larger 3/8” wall = 0.375”
Roughness	The pipe roughness has a default value of 0.00015 ft. This is the roughness shown on a Moody diagram for smooth commercial pipe. The roughness factor enters into the pressure drop calculation.
Static Head Calculation Method	Use a correlation of Lockhart and Martinelli to calculate an effective specific gravity. This effective specific gravity is higher than that obtained by dividing the total flowing pounds by the total flowing volume. Two-phase downflow static head is always ignored. Two-phase upflow: A liquid holdup method from Baker (1958) experimental data is used. See method in
Condenser Rundown	If yes, then the static head should be ignored for the Fractionator Overhead condenser mounted above the overhead receiver and an equalization line should be shown on the P&ID.

13. Miscellaneous

Filter	Set the pressure drops as: Normal/Design/Alternate flow scenarios Dirty /Dirty /Clean

14. Limits

Elevation	Typically at grade.

15. Circuits

Design case	We run hydraulics at 110% of normal to account for typical fluctuations in the plant. A real plant will not run constantly at the so-called Steady State conditions of the Process Simulation.
Pumped Circuit	If a pump has multiple destinations, then include the pump in all circuits not just the circuit governing the pump head.

16. Controlled Pressure

PIC	Assume that the PIC is located on the vessel (even though it is shown on the piping in the P&ID) when the PIC is associated with controlling the pressure of the vessel.

17. Revamps

17.1 Use the typical flow scenario factors of 100/110/60 (or 50) as if the unit is new. The customer expects the unit will operate at revamp capacity. Use the typical flow scenario factors to ensure that the unit has flexibility to be controlled at that capacity.

17.2 In a pumped circuit, the control valve normal pressure drop must be greater than 10 psi. Otherwise increase the impeller size or replace the pump. If the control valve design flow scenario pressure drop is less than 10 psi, then discuss this issue at the Hydraulics Review Meeting.

17.3 After the Hydraulics Review Meeting, change the design flow scenario factor for the entire project to 100 so that this case is not included in the EDI or the I-file.

17.4 If Inflection Point Engineering is giving a guarantee on the revamp flow rates:

a. Show the normal and design flow scenarios in the EDI.

b. Ensure that the control valve design pressure drop is greater than 10 psi.

c. Check that the control valve in the pumped circuit satisfies the needs for 50% of the circuit frictional pressure drop. If most of the circuit pressure drop is static head rather than frictional, then the control valve typically can tolerate a lower pressure drop.

Appendix A

The liquid holdup density is calculated as follows:

1. Calculate the pressure drop (psi/100’) in the piping based only on the flow of liquid.

2. Calculate the pressure drop (psi/100’) in the piping based only on the flow of vapor.

3. Interpolate from the following chart to calculate the liquid volume portion based on the square root ratio of liquid-only pressure drop to vapor-only pressure drop.

4. The average composite liquid holdup density is (where ρ=lb/ft³):

(DPL/DPV)½	Liquid Volume %
0.0058	1.0
0.01	1.55
0.02	2.65
0.04	4.65
0.1	9.4
0.2	15.8
0.4	24.4
0.7	33.0
1.0	38.5
2.0	52.0
4.0	66.0
7.0	78.0
10.0	87.0
15.5	100.0