Acoustic Resonance in Main Steam Line Side Branches

Size: px

Start display at page:

Download "Acoustic Resonance in Main Steam Line Side Branches"

Ada Byrd
5 years ago
Views:

Conzen, Fauske & Associates, LLC (FAI) 16W070 83 rd Street Burr Ridge,

1 Acoustic Resonance in Main Steam Line Side Branches Nuclear Science and Technology Symposium (NST2016) Helsinki, Finland November 2-3, 2016 Jens Conzen, Fauske & Associates, LLC (FAI) 16W rd Street Burr Ridge, Illinois (877) Fauske1 or (630) Fax: (630)

2 Overview Overview Introduction Acoustic resonance What is a side branch/drip leg? What are the main mechanisms? Why are we talking about acoustic resonance? Two brief industry examples that caused loss in production It happens all the time! How do the physics work and how can one screen for it? Vortex shedding Column resonance Helmholtz resonance Screening by review, walkdown and testing Example of a recent project with successful resolution 1150 MWe Generating Station 2

condensate collection or system drainage A stand pipe for a valve

3 Acoustic Resonance Side Branch What qualifies as a side branch? A side branch is pipe attachment to the process line such as: A drip leg for condensate collection or system drainage A stand pipe for a valve (sampling/instrument line or safety valve) A dead ended branch (e.g. system in standby) Drip leg 3

A vortex shed occurs at the leading edge of the side branch. 3. The vortex frequency is constant. 4.

4 Acoustic Resonance Column Resonance Observations: 1. The direction of the flow is from the left to the right. 2. A vortex shed occurs at the leading edge of the side branch. 3. The vortex frequency is constant. 4. The side branch is excited harmonically at its quarter wave frequency (like an organ pipe) 5. Pressure waves travel both up and downstream as long c > U f Valve closed = Dead ended side branch 4

5 Acoustic Resonance Helmholtz Resonance Same phenomenon as blowing across a bottle opening Observations: 1. Similar to column resonance 2. Side branch has a neck and a resonating cavity 5

This led to equipment failures and fatigue cracking of the dryers.

6 Industry Example Quad Cities (Column Resonance) The implementation of an Extended Power Up-rate resulted in significant increases in steam line vibration as well as acoustic loading of the steam dryers. This led to equipment failures and fatigue cracking of the dryers. Vortex shedding coupled column resonance in the relief and safety valve stub pipes were the principal sources of large magnitude acoustic loads in the main steam system. 6

7 Industry Example OKG The implementation of an Extended Power Up-rate resulted in significant increases in steam line vibration. The vibration levels were sufficiently high to prohibit full power production. The power level needed to be kept roughly 20% below full for a prolonged time period. The power uprate program also included a plant modernization, which resulted in the replacement of the main steam isolation valves. Vortex shedding coupled with Helmholtz resonance in the new valves were the principal sources of the vibrations in the main steam system. 7

Engineering Physics Description of Physical Phenomena: U = Flow Velocity Vortex shedding is defined as: = ( 0.25) turbulent boundary layer, St = 0.33, n = 1, 2, 3, = laminar boundary layer, St = 0.

8 Engineering Physics Description of Physical Phenomena: U = Flow Velocity Vortex shedding is defined as: = ( 0.25) turbulent boundary layer, St = 0.33, n = 1, 2, 3, = laminar boundary layer, St = 0.52, n = 1, 2, 3, D = Throat Diameter The Strouhal number (St) is a dimensionless number that is related to vortex shedding. The higher the velocity the higher the frequency. The smaller the diameter of the side branch the higher the frequency. 8

9 Engineering Physics Description of Physical Phenomena: Column resonance is defined as: = 4 n = 1, 3, 5, (odd numbers) L = length of the dead ended side branch c = speed of sound (ca. 485 m/s for BWR main steam system) L The longer the side branch the lower the frequency. 9

10 Engineering Physics Description of Physical Phenomena: A Helmholtz resonance is defined as: L = 2 V A = cross sectional area of neck L = length of the neck V = static volume of the cavity c = speed of sound (ca. 485 m/s for BWR) Larger opening provides a higher frequency since gas can rush in and out faster. Larger volume provides lower frequency since more gas must move. Longer neck provides lower frequency due to increased friction. 10

11 Screening by Review Desktop Screening (Example) Screening of isometric piping drawings by applying previously defined equations. Requires good documentation Use computational tools such as MathCad If vibrations are already present use a stencil or ruler to walk down the drawings to check for critical lengths an openings 11

air and Mach number scaling to check for elevated

12 Screening by Testing or Measurement Pre-Power Uprate Testing Subscale testing (typically 1/8 th scale) with air and Mach number scaling to check for elevated acoustic vibration potential in side branches and safety relief valves. 12

13 Screening by Testing or Measurement Component Testing Subscale testing of components (typically 1/5 th scale) such as valves is possible to replicate undesirable conditions, to experiment with improving design changes, and to validate them. 13

14 Recent Project 1150 MWe Generating Station (GS) GS was experiencing noticeable and audible vibrations on the main steam system piping. Noisy and strong vibration were reported in particular near the main steam valves. The valves also exhibited more than normal wear and required regular maintenance. A vibration assessment was performed that consisted of an analytical approach (desktop screening) as well as vibration measurements (testing) during power operation. 14

15 Recent Project Desktop Review Results Based on the desktop review it was found that acoustic column resonance could occur at the main steam valves (M1, M2), their up- and downstream drain pipes (U1, U2, D1, D2), as well as the riser pipes (R1, R2). GS has two loops on the steam side. 1 stands for line 11 and 2 stands for line 12. The following schematic illustrates the measurement locations. 15

Recent Project Field Testing Performed a walk by of the complete steam line piping before the vibration measurements took place. Noticed an audible tone near the main steam valves.

16 Recent Project Field Testing Performed a walk by of the complete steam line piping before the vibration measurements took place. Noticed an audible tone near the main steam valves. The microphone indicated 387Hz, which was a possible frequency (within scatter) according to the desktop screening for the 3 locations and also in agreement with preliminary measurements made by GS. 16

17 Recent Project Field Testing Observations The time domain signal appears clear and harmonic. May be an indicator for acoustic resonance. The strongest magnitude of vibration was measured in location D1. The peak value exceeds the maximum allowable value. Since D1 is in close proximity to the main steam valve, it must be assumed that the valve is experiencing a strong oscillatory force. That would justify the increased maintenance. Amplitudes of vibration were generally less at reduced power operation. The frequency of vibration did not change during the reduced power (reduced flow velocity) operation which may be indication acoustic resonance. GS provided documentation that during plant condition single line operation the flow velocity is about 30% higher. The vibration is not audible at this condition. Indication for passing trough resonance. 17

Recent Project Field Testing Observations D1 is a drip leg downstream of the main steam valve. It is a vertical DN150 pipe with a DN50 horizontal bypass to a dump tank for condensate removal.

18 Recent Project Field Testing Observations D1 is a drip leg downstream of the main steam valve. It is a vertical DN150 pipe with a DN50 horizontal bypass to a dump tank for condensate removal. It was possible to activate the bypass during power operation. This would add disturbance to quarter wave inside the drip leg and the vibration measurement should be affected. This test would demonstrate if D1 is the source of the vibration. Levels at D1 Bypass D1 18

19 Recent Project The Test Vibration levels dramatically dropped after bypass opening. The opportunity to test for the root cause on the operating plant rarely exists. The insights from this test are invaluable. Bypass open 19

Recent Project Conclusions The test data in combination with the analytical assessment indicate that D1 is undergoing a second mode acoustic column resonance.

20 Recent Project Conclusions The test data in combination with the analytical assessment indicate that D1 is undergoing a second mode acoustic column resonance. All drain stubs (D1, D2, U1 and U2) are of identical designs, i.e. DN150 and 1.2m long. It is expected that all drain pipes are producing an acoustic standing wave due to similarities in geometry and flow velocity. However, D1 is experiencing the strongest resonance. The flow is accelerated in the venturi style valve so that the velocity may be slightly higher at D1 (compared to U1) and provides a better excitation. The flow velocity at D2 and U2 is slightly lower due to higher line losses. 20

21 Recent Project Resolution Operations: Single line operation during part load production to increase flow velocity. Hardware modifications: 3 options below (1) was installed to increase throat diameter and lower shedding frequency Excitation source was successfully decoupled and vibrations lowered to acceptable levels 21

22 Thank you for listening. Time for questions!

To prepare for this lab, you should read the following sections of the text: Sections 3.4, 11.3, and 12.1 OVERVIEW

To prepare for this lab, you should read the following sections of the text: Sections 3.4, 11.3, and 12.1 OVERVIEW Section: Monday / Tuesday (circle one) Name: Partners: Total: /35 PHYSICS 107 LAB #4: WIND INSTRUMENTS: WAVES IN AIR Equipment: Thermometer, function generator, two banana plug wires, resonance tube with