Control Valves and Valve Flow Testing

Transcription

1 Control Valves and Valve Flow Testing Webinar Tariq Boussouara Project Engineer Slide 1

2 Contents Slide 2

3 Control Valve Types and Characteristics Concepts and Definitions Control Valve Flow Testing Control Valve Wear CFD Modelling Slide 3

4 Control Valve Types and Characteristics Slide 4

5 Isolation Valves - Butterfly - Gate - Plug - Globe stop valve - Ball Non Return / Check Valves Process/Self activated - Flap Valve - Double flap (2x half moon) - Ball - Cone Slide 5

6 Pressure/Flow Control Valves Control Valves regulate or control the rate of flow of a fluid by varying the size of the flow passage Slide 6

7 Pressure/Flow Control Valves - Choke Valve - Cage-trim - Globe - Butterfly - Eccentric plug/disc - Ball - Needle Slide 7

8 FLOW CAPACITY Control Valve Characteristics VALVE TRAVEL Source: Slide 8

9 Control Valve Actuation Many shapes, sizes and types Manual operation, power actuated or process/self activated Can be a combination of all the above /redcms-p/node-8350/order-desc/sortfriendly_name/1,111003,29635.html Slide 9

10 Control Valve Selection FLOW RANGE ACTUATION TEMPERATURE MATERIALS PRESSURE ACCESSIBILITY CONTROL VALVE SELECTION FLUID PROPERTIES PIPING DIFFERENTIAL PRESSURE NOISE LIMITATIONS ALLOWABLE LEAKAGE FIRE RESISTANCE Slide 10

11 Concepts and Definitions Slide 11

12 Flow Coefficient Expresses the performance capability of a control valve Independent of valve size or type Slide 12

13 Choked Flow Vapour formation so large that the flowrate cannot increase by further increasing the differential pressure across the valve or restriction Slide 13

14 Cavitation and Flashing Slide 14

15 Cavitation and Flashing Cavitation Noise emission Vibration of valve Erosion due to collapsing bubbles and shockwaves Flashing Noise emission Vibration of entire pipeline due to imbalance between liquid/vapour phases Erosion liquid droplet impact Slide 15

16 F L - Fluid Recovery Factor Capability of the valve to transform kinetic energy of fluid in vena contracta in to pressure energy Slide 16

17 Valve Type Globe 0.9 Eccentric Plug Butterfly Ball F L Typical F L Values Slide 17

18 Cavitation Index σ = (P 1 P v ) (P 1 P 2 ) Slide 18

19 Acceleration or sound pressure level Increasing Cavitation Level Cavitation Index (σ) Choking Cavitation Damage σch (Equivalent to Flmax) Maximum Vibration Cavitation σmv Cavitation Regime IV Change of slope from III to IV Incipient Damage σid III Constant Cavitation σc Change of slope from II to III Incipient Cavitation σi II σ I Slide 19

20 σ 2 No cavitation 1.7 < σ <2.0 No cavitation control required 1.5 < σ < 1.7 Some cavitation control required 1.0 < σ < 1.5 Potential for severe cavitation σ 1 Flashing is occuring Typical globe valve example Slide 20

21 Valve Sizing Example Determine size of control valve (Cv) required to regulate water flow from a storage tank. 5-40m Max water level = 40m Min water level = 5m Water flow = 100 l/s Slide 21

22 Valve Sizing Example USGPM C v = Q 1 P 5-40m 100 l/s flow C v max = 1585 psi = 597 Cv range?? C v min = = 211 Cv range Slide 22

23 Valve Sizing Example Slide 23

24 Control Valve Flow Testing Slide 24

25 Why Flow Test Valves? Provides confidence Validates predicted performance data Highlights any issues with valve design Slide 25

26 Valve Flow Testing Standards (Cv and F L testing) ISA75.02, Control Valve Capacity Test Procedures IEC :2015 Industrial-process control valves Part 2-3: Flow Capacity Test Procedures Slide 26

27 Slide 27

28 Test Considerations Upstream/downstream pipework Pressure tapping dimensions Stem Calibration Differential pressure measurement Reference flowrate measurement Slide 28

29 Flow Coefficient Testing Cv recorded at three differential pressures Any large percentage deviation in Cv values from the average can indicate the presence of cavitation Slide 29

30 Valve Flow Coefficient- Cv (US) Stem Position- Steps Slide 30

31 Valve Flow Coefficient Cv (Us) Valve Travel Position % Slide 31

32 F L Testing Data point taken with high inlet pressure, and low differential pressure Data point taken with outlet pressure in facility reduced to a minimum Data points plotted in between both conditions Slide 32

33 Fl Value Q2 Data Fl Data F LA Flow Differential Pressure -(bar) Slide 33

34 F LA Limit Point at which cavitation is just starting to make itself evident hydrodynamically Lies between constant cavitation sigma level and choking cavitation condition Slide 34

35 Increasing Cavitation Level Cavitation Index (σ) Choking Cavitation Damage σch (Equivalent to Flmax) Maximum Vibration Cavitation σmv Cavitation Regime IV Change of slope from III to IV Incipient Damage σid III Constant Cavitation σc Change of slope from II to III Incipient Cavitation σi II σ I Slide 35

36 Control Valve Wear Slide 36

37 Control Valve Wear CORROSIVE WEAR CORRISION- EROSION ABRASIVE WEAR CONTROL VALVE WEAR JET IMPINGEMENT CAVITATION EROSION PARTICULATE WEAR Slide 37

38 Corrosive Wear Generally the most common cause of wear in valves Can increase surface roughness May reduce valve Cv Slide 38

39 Abrasive Wear Sand or particles get in between surfaces Gate valve sliding surfaces Ball valve rotating surfaces Slide 39

40 Abrasive Wear Slide 40

41 Particulate Wear Erosive wear due to solid particles Impinge surfaces at high velocity wear = f (velocity) 2.6 Slide 41

42 Particulate Wear Slide 42

43 Wear on a choke plug Choke Valve plug Slide 43

44 Cavitation Erosion Vapour formation in valve As pressure recovers, vapour bubbles implode Collapse of bubbles can remove material Slide 44

45 Reducing the effects of valve wear Velocity reduction Material selection Multi stage valve trim CFD and physical testing to predict and manage erosion Slide 45

46 CFD Testing Slide 46

47 CFD Testing FLOW Define Geometry Mesh Solution Slide 47

48 CFD Testing Slide 48

49 CFD Testing Gate Valve Slide 49

50 Combining CFD and Physical Erosion Testing Slide 50

51 Erosion in a choke valve cage Slide 51

52 Summary Key concepts and definitions Flow testing of control valves Control valve wear mechanisms CFD modelling Slide 52

53 Thanks for listening Questions? Slide 53