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  • Vibration Testing and Troubleshooting of Coke DrumsTroubleshooting of Coke Drums

    Mahmod Samman, Ph.D., P.E. Senior Associate

    Stress Engineering Services, Inc. mms@stress.com

    Coking.com Coke Drum Workshop Rio de Janeiro, Brazil

    August 2009

    1

  • OVERVIEWOVERVIEW

    • Vibrations BasicsVibrations Basics • Drum Dynamics

    Wh t i Aff t d• What is Affected • Potential Consequences • Case study

    2

  • VIBRATIONS BASICSVIBRATIONS BASICS  Response of a flexible structure to excitation

    (fluid flow pressure pulsations sloshing etc )(fluid flow, pressure pulsations, sloshing, etc..)  Components

    • Mass (inertia) • Spring stiffness (Force–Displacement) • Dashpot viscous damping (Force–Velocity)

     Basic characteristics: Basic characteristics: • Natural frequency (or frequencies) • Mode shapes

     Input – output • Force • Displacement

    3

    • Displacement

  • DRUM DYNAMICSDRUM DYNAMICS

    4

  • WHAT IS AFFECTEDWHAT IS AFFECTED

     Pipes and pipe supports  Base-plate bolts and grout  Non-structural (stairs, lights, guardrails,..)( , g , g , )  Machinery (elevator, pumps, ..)  Superstructure (concrete and steel)Superstructure (concrete and steel)  Foundation system (substructure and soil)

     Humans!

    5

  • POTENTIAL CONSEQUENCESPOTENTIAL CONSEQUENCES

    • Operator discomfort or fatigue• Operator discomfort or fatigue • Poor performance • A l ti f i d• Acceleration of corrosion damage • Interruption of operations during repairs

    ( / f )• Fatigue cracks (leaks/ fires) • Bodily injuries

    6

  • WHAT TO DO?WHAT TO DO?

    • Measure • Vibrations • Strain • Process variables• Process variables

    • Analyze • Stress / fatigueg • Human tolerance

    • Mitigate • Process • Structure

    7

  • CASE STUDY - 1 T d it• Two-drum unit

    • “Significant” vibrations in structure • Conflicting views on  When they vibrate the most  Which one vibrates more Which one vibrates more

    • Failures  Piping supportsp g pp  Anchor bolts  Base plate grout

    • I th it f ?• Is the unit safe? • Can the process be optimized to

    minimize vibrations? 8

    minimize vibrations?

  • DRUM DESIGN AND OPERATION 1996 API Coke Drum Survey, 2003

    16 f i di l i l ll f h id• 16 feet in diameter - relatively small for the mid 80’s

    • 76 f t i h i ht t t ll• 76 feet in height - average to tall • Slender drums

    V 1 ¼ C 1/2M i l• Very common 1 ¼ Cr -1/2Mo material • 17 hour fill cycle - average to relatively slow

    tioperation

    9

  • OBJECTIVES

    • Monitor vibrations in the drums, piping, and structure.

    • Obtain synchronized temperature and strain measurements.

    • Determine the timing and characteristics of maximum vibrations.

    • Determine severity of dynamic stresses and potential for fatigue damage in the structure.

    • Conduct sensitivity analysis of vibrations versus process variables.

    10

  • PROCEDURE • Installed 33 sensors and two data acquisition

    systems on the drums piping and structuresystems on the drums, piping, and structure. • Monitored the unit for a period of 20 days (14

    cycles)cycles) • Processed and analyzed the data in time and

    frequency domain.eque cy do a • Analyzed the correlation between key process

    variables with vibration, strain, and temperature , , p measurements.

    11

  • INSTRUMENTATION Vibration data acquisition system

    16 channel unit16 channel unit 16 seismic accelerometers @ 102 samples per second 2 strain gages (low-speed DC channels)2 strain gages (low speed DC channels)

    Temperature data acquisition system StrainDAQ unit 16 thermocouples 1 sample per two seconds

    Data collection was continuous without interruption during the entire monitoring period.

    12

  • Sensor Layout

    13

  • Example Quench Transient TEMPERATURE

    Quench

    TIMETIME

    ACCELERATION

    14

  • Integrated Displacement Data

    0.4

    0.5 Drum B - West Dir. (in) Drum B - North Dir. (in) Drum B - Down Dir. (in)

    0 1

    0.2

    0.3

    N T

    (IN )

    Drum B Down Dir. (in)

    -0.1

    0

    0.1

    PL A

    C EM

    EN

    -0.3

    -0.2D IS

    P

    Large Transient Displacement

    -0.5

    -0.4

    11035 11037 11039 11041 11043 11045 11047 11049 11051 11053 11055

    g p

    15

    TIME FROM START OF CYCLE 9 (SEC)

  • Vibration Versus Flow Rate 0.12 250

    DRUM B PIPE DRUM A PIPE DRUM A

    0.08

    0.1

    es R

    M S 200

    (G PM

    )

    DRUM A DRUM B STRUCTURE DRUM B ONLINE

    0.06

    on in

    In ch

    e

    100

    150

    um V

    al ue

    s

    0 02

    0.04

    Vi br

    at io

    50

    100

    M ax

    im u

    0

    0.02

    1 3 5 7 9 11 13 0

    16

    1 3 5 7 9 11 13 Cycle

  • Strain Gauge DataStrain Gauge Data

    Low dynamic strains

    17

  • CASE-1 SUMMARY • Drum vibration magnitude was maximum during the

    quench part of the cycle in the East-West direction. • The two drums vibrated in a comparable manner both

    from magnitude and frequency standpoints. • The maximum recorded peak displacements were 0 58The maximum recorded peak displacements were 0.58,

    0.35, and 0.23 inches for the drums, the piping, and the structure, respectively.

    • Measured dynamic strains in the structure were below• Measured dynamic strains in the structure were below the fatigue-inducing levels

    • The correlation between vibration levels and recorded bli h dprocess parameters was established

    18

  • CASE STUDY -2

    • Four-drum unit. • Blow-down line. • Cracks and leaks. • Angled-tee joint.Angled tee joint. • Thermal cycles. • 3D loads3D loads. • Vibrations. • Why?• Why? • How to fix it?

    19

  • ACTION PLAN 1. Instrumentation

    ACTION PLAN

     Strain gages  Thermocouples

    2 E t ti f l di diti2. Extraction of loading conditions 3. Finite element analysis 4 F ti A t4. Fatigue Assessment

    20

  • INSTRUMENTATION

    Intrinsically Safe Instrumentation System

    21

  • FIELD MONITORING

    22

  • TEMPERATURE MEASUREMENTS

    23

  • THERMAL GRADIENTS Every forth cycle

    24

  • CLOSEUP

    25

  • PAD THERMAL GRADIENTS

    26

  • Extracted load cases Five thermal profiles during the coking cycle

    27

  • Thermal Load CaseThermal Load Case

    28

  • Von Mises Stress in the pipep p

    outside inside

    29

  • Von Mises Stress inside the padVon Mises Stress inside the pad

    outside inside

    30

  • Fatigue AssessmentFatigue Assessment

    • Maximum thermal stress range is 92 ksiMaximum thermal stress range is 92 ksi.

    • Alternate stress is 49.8 ksi.

    • Correction for E at 4000F

    • Fatigue life is 4,441 cycles.

    31

  • CASE-2 SUMMARYCASE-2 SUMMARY • Vibrations and pressure are not the main problem.

    • The failure is caused by severe thermal transients that generate 92 ksi stress range in the pipe at the locationgenerate 92 ksi stress range in the pipe at the location of cracks.

    R d i i i i d i• Recommendations to minimize stresses and increase fatigue life:

    • Redesigned integral fitting.

    • Fatigue-resistant welds.

    32

    g

  • Q ti ?Questions?

    Mahmod Samman, Ph.D., P.E. Stress Engineering Services, Inc.

    281-955-2900281-955-2900 mms@stress.com

    33

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