Steam Relief

7/29/2019 Steam Relief

1/8

team Relief (Time History) Example

he following example demonstrates the procedure to analyze a typical steam relief model by automatically calculating the thrust loads and the resultingansient shock load on the safety valve piping system using the time history analysis.

roblem Definition

alculations

efinition of the Steam Relief Example in AutoPIPE

utoPIPE Steam Relief (Time History) Report

roblem Definition: Steam Relief

boiler steam system is shown below with a 8" saturated steam line connected to a 11.5' x 1.97" steam drum. A 4" safety relief valve (4" inlet / 6"utlet) with a 8" non-integral vent discharge line is mounted on the steam line. The pressure in the system starts to rise and the relief valve opens andmains open for one second before closing. The steam relief utility will be used to automatically generate time history point load cases (*. THL) and timestory loads (*.TIH) which will be then used to perform the time history analysis (stored in *.TIM files).

AutoPIPE Modeling Approaches


Pgina 1 de 8team Relief (Time History) Example

14/6/2013le://C:\Documents and Settings\XP\Configuraes locais\Temp\~hh9827.htm


2/8

alculations: Steam Relief

he following calculations/methods are used in determining Steam Relief values and properties:

etermine pressure and velocity at piping/vent interface point

alculate maximum operating pressure at the valve exit

alculate reaction force at piping/vent interface pointalculate the thrust at the cent exit discharge point (non-integral/open discharge system)






3/8

etermine pressure and velocity at piping/vent interface point.

here:

efer to the Steam Relief Analysis section of the appendix for steam quality factors)

Mass flow rate (17.26 lb/sec)

1 Pipe inside area at pipe/vent inlet interface point(28.89in)

2 Pipe inside area at vent inlet (50.03in)

3 Pipe inside area at vent exit (50.03in)

o Stagnation enthalpy at the valve inlet (1200 Btu/lbm)

Joule-Thompson coeff. (778.16 ft-lbf/Btu)

c Gravitational constant, 32.2 lbm-ft/lbf-sec^2

823 Btu/lbm

4.33

alculate maximum operating pressure at the valve exit

utoPIPE automatically calculates the value of f(L/D) (where the friction factor, f = 0.013) from the relief valve exit to the pipe/vent interface point.he ratio (P/P*) is then determined from Chart 1 of ASME B31.1 Appendix II. In this example we estimate f(L/D) as:

aximum operating pressure at the valve exit, P1a

D for 6" sch 40 pipe = 2(0.66-0.5)12 / 6.065 = 0.63

D for 6" sch 40 SR B/W Elbow = 20

(L/D) = 20.63

(L/D) = 0.268

rom chart 1, (k=1.1): (P/P*) = 1.43





4/8

alculate reaction force at piping/vent interface point

eaction Force, F1

1 =

a = 14.7 psia (i.e 1 atmosphere pressure for open discharge).

alculate the thrust at the vent exit discharge point (Non-integral / open discharge system)

utoPIPE automatically calculates the factor f(L/D) for the vent piping from the vent inlet to exit points. In this example we estimate(L/D)s:

D for 8" sch 40 pipe

Pressure at the vent p ipe exit, P3

Note: This exit pressure is below atmosphere and therefore P3 should be set to 14.7 psia.

Maximum operating pressure at the vent pipe inlet, P2

elocity at vent exit, V3 = V1 = 1570.5 ft/sec

om Chart 1, the ratio (V/V*) is determined for the value of

(L/D) = 0.1155 and specific heat ratio, k=1.1.

rom chart 1, (V/V*) = 0.80

5.91*12 / 7.981 = 8.89

f(L/D) = 0.1155

From chart 1, (P/P*) = 1.27

3

2






5/8

Velocity at vent inlet, V2

Check the blow-back conditio n for non-integral open vent systems

ence the above condition is satisfied and steam blow-back will not occur. We have chosen to resize the vent pipe and since the above inequality istisfied no further vent pipe sizing is necessary.

Calcul ate Loads on the Vent Pipe.

hrust force at vent pipe inlet, F2

hrust force at vent pipe exit, F3

he thrust force, F3 at the vent exit is along the direction, in this case along the vertical Y-axis.

2

2

3

xecuting Steam Relief Example (ap50sr1)

his section illustrates the steps required to define and perform a Steam Relief and Time History analysis in AutoPIPE. Follow the text and enter data intoe input boxes exactly as shown and described in each of the following steps. The steps shown are configured for AutoPIPE for Windows.

1. Open AutoPIPE, then select File/Open and load the Steam Relief fileAP50SR1. A working model of a saturated steam line connected to asteam drum is displayed as shown below.





6/8

2. Select Load/Steam Reliefto display the Steam Relief dialog . Select C02 as the "Valve exit point," then specify an open discharge (O) in the"[O]pen /[C]losed Discharge" field. Input C04in the "Pipe/Vent Interface point" field, then input D00 and D01 in the vent "Inlet" and "Outlet"fields, respectively. Next, set the "Vent discharge direction" to Global Y, and enable the "Size Vent" option. The "Manifold Pressure" field isdisabled because it is only applicable for closed discharge systems. Input 1200 in the "Enthalpy" field. Input 2 in the "Quality" field for saturatedsteam (refer to the Determine pressure and velocity at interface point discussion in the appendix for more information). Input 1.1 in the"Sp. Heat Ratio" field for saturated steam (refer to Table G-2 in the appendix). Input 17.26 in the "Mass Flow Rate" field.

Under the following "Time-sec" fields, enter 0 for the "Start" and 0.1 for the "Rise" and "Fall." Input 1.0 in the "Open" field. Finally, enable the"Generate report" option. AutoPIPE automatically creates a Force-Time history file (C04.TIH) and a time history point load file (C02.THL) forsteam relief case C02.

3. Select Load/Time History Location to display the Time History Location dialogs for Steam Relief case C02. Although these dialogs can bemodified, editing is not necessary using the Steam Relief analysis. Press Cancel.

The following ASCII file, C02.THL, is created. Although not necessary for the steam relief analysis, it may be edited using a text editor.

AP50SR11C04 C04 1. 000 0. 000 - 1. 000 0. 000 0. 00000

4. Select Load/Time History Profile to display theTime History load dialog . A force-time history file can be displayed or modified. Thefollowing is the force-time history called C04 (i.e. pipe/vent interface point C04 of Steam Relief case C02). Press Cancel.

The following ASCII file, C04.TIH, is created with Time (1st column) in seconds and Force (2nd column) in lbf. (Refer to the discussion onPerforming a Linear Static Analysis for additional information). The 4 refers to 4 lines of data, and 5 refers to force units.




7/8

For ce vs ti me hi st or y f or st eam r el i ef event - C024 50. 00000 0. 0000. 10000 1064. 5351. 10000 1064. 5351. 20000 0. 000

Steam Relief Step 4 Notes

5. Select Tools/Model Options/Editto display theEdit Model Options dialog. To accurately capture the higher and intermediate naturalfrequency modes (applicable for impulse loading such as Steam Relief), the mass discretization algorithm should be invoked. This is achievedby enteringA (for automatic) in the "Mass points per span" field and entering a cutoff frequency at least equal to the Modal analysis cutoff

frequency (e.g. 150Hz).

6. Select Load/Dynamic Analysis/Modal Tab to display the Modal Analysis dialog . Enter 100in the "Maximum number of modes" field (notethat this number may have to be increased if the cutoff frequency is not reached). Enter a "Cutoff frequency" of150Hz (note that for larger

piping systems, higher modes may be present). Use the defaults ofNONEin the "Pressure stiffening case" field, and enable the "Include

contents" option. Press OK. Note: A dialog will appear asking, "Do you want to analyze the model?" Press the Yes button, and Modal should beenabled while all others are disabled. Press the OK button.

The modal analysis must always be run before a Time History analysis.

7. Select Load/Dynamic Analysis/Time History Tab to display the Time History dialog in which the number of load cases is specified. The firsttime this dialog is displayed, case no. 1 is already populated for one time history case (M1) to be analyzed (press the New button for additionalcases M2 and M3). Press OK.

8. Select Load/Dynamic Analysis/Time History Tab. The Time History analysis dialog is displayed. Verify case no. 1 settings. The "GroundMotion" field is disabled. Select File1 = C02 from the "Filenames" selection list. Next enter 1.2 in the "Duration" field. Note that the "AnalysisSteps" and "Output Steps" fields contain a value of "Automatic" (meaning that AutoPIPE calculates a time step = 1/10 of the shortest period at

the highest mode). The output step should normally be set equal to the analysis step to ensure the highest response is reported. Only theanalysis "Time Steps" affect the accuracy of the results. The "Number of Time Steps" is automatically shown as 1634 (i.e. Duration = Numberof analysis time steps analysis time step; hence time step = 0.737ms). Enter 2 for the "Damping Ratio (%)". Press OK. Note: A dialog willappear asking "Do you want to analyze the model?" Press the Yes button. The "Modal" and "Time History" options should be enabled, while allother options are disabled. Press the OK button.

Steam Relief Step 9 Notes

9. Select Result/Displacement . When the Deflected Shape dialog appears, specify M1 as the load combination. The following displacementprofile for the Steam Relief event C02 is displayed.

10. Make C04 the active point, then press F3 to display the results.




8/8

11. Select Quit to return to the Main Menu.

12. Select Tools/Model Input Listing and turn on only the loads summary sub-report.

13. Select Result/Output Report , then enable the Displacement, Restraint, Model listing, Result summary,Analysis summary, and Steam reliefoptions and press OK.

his concludes the modeling of the Steam Relief example. The result file you have just created should match the results shown below.

Click here to view the AutoPIPE Steam Relief (Time History) Report.


Steam Relief

Documents

Transcript of Steam Relief