Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

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Failure Analysis Mechanical Seal Reliability 557 The purpose of a mechanical seal is to prevent, or at least limit, leakage. Normally, the leakage from a mechanical seal is so slight that it is difficult to measure. For example, a 2-inch seal containing water at 100 psig should leak less than 2 ml/hr. Current federal regulations require that the concentration of certain volatile organics be less than 10,000 ppm near the seal leakage point. In some areas, this limit is 1000 ppm. It is likely that none of these examples would show any visible leakage. Because most seals are wearing devices, they will fail, that is, leak excessively t at some point in time. The machinery engineer must therefore be prepared to learn from each seal failure and use that information to improve future designs and applications so that seal life is improved. In order to do this, detailed records of each failure should be maintained. Failure analysis is simply allowing the seal to tell why it did not perform as expected. This means acting the part of a detective. The following simple guidelines will make failure analysis easier and more consistent: • Know what a new seal looks like. » Know what a successfully applied seal looks like. » Examine the failed seal carefully. • Write down the differences between the new, successful, and failed seals. • Formulate a consistent explanation about the differences. Although manufacturers and mechanics are familiar with new seals, sometimes a machinery engineer may not see the unused item. He only sees the failures. Similarly, he may not see many successfully applied seals because they are not called to his attention. He is too busy looking at failures. On the other hand, some failure modes are so common that a mechanic may come to accept them as "normal wear." For failure analysis to be useM, all differences in the new and failed seal should be noted. These differences must be written down in a consistent format. The form shown as Table 21-1 is a good starting point and can be modified to suit particular needs. There is a great temptation to take mental notes and write them later. This temptation must be overcome, and written notes must be made while examining the seal. If these notes become soiled, they can be rewritten later. For many refineries and chemical plants, the statistics in Table 21-2 have been developed from analysis of many pump seal failures. Statistics show that most seals fail prematurely, that is, prior to wearing out. They also show that these early failures can be prevented by sim-
558 Centrifugal Pumps: Design and Application Table 21-1 Mechanical Seal Failure Analysis Checklist Machine Identification , Reason for Service Request Last. Known Failure , Summary of Analysis ; ; , ; Seal Identification Manufacturer Type Face Materials Gasket Materials Mounting Balance Ratio Liquid Temperature, F Seal RPM Operating Conditions Specific Gravity Sealed Pressure, psig Inspection of Seal Stationary Face (OK) Rotating Face (OK) Work out ( ) Worn out ( ) Grooved ( ) Grooved ( ) Heat checked ( ) Heat checked ( ) Warped ( ) Warped ( ) Corroded ( ) Corroded ( ) Gasket, Stationary Face (OK) Gasket, Rotating Face (OK) Hardened ( ) Hardened ( ) Chemical attack ( ) Chemical attack ( ) Broken/cut ( ) Broken/cut ( ) Gasket, Gland (OK) Gasket, Sleeve (OK) Hardened ( ) Hardened ( ) Chemical attack ( ) Chemical attack ( } Broken/cut ( ) Broken/cut ( ) Gland (OK) Drive Collar (OK) Corroded ( ) Corroded ( ) Bushing rubbed ( ) Tlirned on shaft ( ) Number of bolts Setscrews Antirotation Pins (OK) Sleeve/Shaft (OK) Fretted ( ) Fretted ( ) Corroded ( ) Corroded ( ) Flush Plan Springs/Bellows (OK) Location Broken ( ) Hole Size Corroded ( )
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CENTRIFIUGAL PUMPS Design & applica
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CENTRIFUGAL PUMPS Design & Applicat
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Contents Preface —..... —......
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ern Pumps, Mine Dewatering Pumps. W
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Stage Pumps. Single-Suction Single-
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Preface When Val and I decided to c
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CENTRIFUGAL PUMPS Design & applicat
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Part 1 Elements of Pump Design
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1 Introduction System Analysis for
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Introduction 5 Figure 1-2. The syst
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Introduction 7 mate responsibility
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Introduction 9 Figure 1-6. Maximum
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2 Specific Speed and Modeling Laws
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Specific Speed and Modeling Laws 13
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Figyre 2-7, New pump from model pum
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Impeller Design 29 Figure 3-1. Requ
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Impeller Design 31 Figure 3-4. Capa
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Impeller Design 33 Step 8: Estimate
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Impeller Design 35 Figure 3-7. Volu
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impeller Design 37 (2) 5 , as final
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Impeller Design 39 The vane develop
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Impeller Design 41 Figure 3-12. Are
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impeller Design 43 Figure 3-16. Inf
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4 General Pump Design It is not a d
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General Pump Design 4? Figure 4-1.
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General Pump Design 49 designed and
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Volute Design 51 Figure 5-1. Volute
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Volute Design 53 Figure 5-2. Radial
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Volute Design 55
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Volute Design 57 Figure 5-4. Effici
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Volute Design 59 Figure 5-5. Typica
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Volute Design 61 Figure 5-8. Univer
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Volute Design S3 Manufacturing Cons
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6 Design of Multi-Stage Casing Mult
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Design of Multi-Stage Casing 67 How
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Design of Multi-Stage Casing 69 Fig
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Design of Multi-Stage Casing 73 sec
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7 Double-Suction Pumps and Side-Suc
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Double-Suction Pumps 79 two. Experi
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Double-Suction Pumps 81 Figure 7-3.
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Double-Suction Pumps 83 LOCATION AR
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8 NPSH The expressions NPSHR and NP
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NPSH 87 Predicting NPSHR The other
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NPSH 89 Figure 8-4. Pressure loss b
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NPSH 91 SUCTION VELOCITY TRIANGLES
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NPSH 93 Figure 8-8. Performance cur
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NPSH 95 Figure 8-10. Leakage across
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NPSH 97 Figure 8-13. Plate inserts
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NPSH 99 Figure 8-17. Influence of p
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NPSH 101 Figure 8-19. Estimating K
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NPSH 103 Step 3: Determine KI* From
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Figure 8«22. Calculating NPSHA for
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NPSH 107 Figure 8-24. NPSHR cavitat
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NPSH 109 Notation KI Friction and a
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Part 2 Application
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9 by Erik B. Fiske BW/JP Internatio
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Vertical Pumps 115 Figure 9-2. Well
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Vertical Pumps 117 Figure 9-4. Subm
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Vertical Pumps 119 Figure 9-6. Inst
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Vertical Pumps 121 Figure 9-8. Barr
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Vertical Pumps 123 • Loading pump
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Vertical Pumps 125 Wet Pit Pumps Th
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Vertical Pumps 127 • Fresh water
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Vertical Pumps 129 Condensate and H
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Vertical Pumps 131 mally insulate w
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Vertical Pumps 133 Figure 9-15. Imp
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Vertical Pumps 135 checked for corr
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Vertical Pumps 137 crating paramete
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10 Pipeline Pipe line, Waterflood,
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Pipeline, Waterflood and CO 2 Pumps
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Pipeline, Waterfiood and CO 2 Pumps
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Figure 10-11. Performance change wi
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Figure 10-13. Seven-stage pump dest
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Pipeline, Waterflood and COa Pumps
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11 By Edward Gravelle Sundstrand Fl
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High Speed Pumps 175 History and De
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High Speed Pumps 177 Figure 11-2. (
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High Speed Pumps 179 some portion o
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High Speed Pumps 181 This is to say
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High Speed Pumps 183 This expressio
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High Speed Pumps 185 Figure 11-3. P
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High Speed Pumps 187 As an aside, p
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High Speed Pumps 189 Figure 11-5. I
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High Speed Pumps 191 Figure 11-7. I
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High Speed Pumps 193 Figure 11-9. R
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High Speed Pumps 195 Figure 11-10.
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High Speed Pumps 19? Figure 11-11.
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High Speed Pumps 199
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High Speed Pumps 201 Figure 11-13.
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High Speed Pumps 203 nal bearings a
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High Speed Pumps 205 Barske, U, M.,
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Double-Case Pumps 207 jected to ext
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Double-Case Pumps 209 Figure 12-3.
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Double-Case Pumps 213 ally by split
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Double-Case Pumps 215 The throttle
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Figure 12-11. pump for 4,000 psi In
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Double-Case Pumps 219 so that the t
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Doubte-Case Pumps 223 Volute Casing
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Double-Case Pumps 225 5. Survey of
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Slurry Pumps 227 An approximate com
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Slurry Pumps 229 Figure 13-2. Nomog
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Slurry Pumps 231 Table 13-2 Alloys
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Slurry Pumps 233 Figure 13-3. Class
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Figure 13-4, (A) (B) (C)
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Slurry Pumps 237 There is little to
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Figyre 13-7, (courtesy Pumps, Inc.)
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Flgyr« 13-8, with (courtesy Goulds
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Slurry Pumps 243 ing the pump speed
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Slurry Pumps 245 Where there exists
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Hydraulic Power Recovery Turbines 2
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Figure 14-14. Internally adjustable
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14-22, Flow of hydraulic recovery a
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15 by Frederic W. Buse Ingersolf-Ra
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Chemical Pumps Metallic and Nonmeta
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Driver Chemical Pumps Metallic and
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Part3 Mechanical Design
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16 Shaft Design and Axial Thrust Sh
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Shaft Design and Axial Thrust 335 S
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Shaft Design and Axial Thrust 337 W
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Shaft Design and Axial Thrust 339 T
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Shaft Design and Axial Thrust 341 b
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Shaft Design and Axial Thrust 343 K
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Double-Suction Single-Stage Pumps S
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Shaft Design and Axial Thrust 347 F
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D (with subscript) P D P s T T (wit
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Mechanical Seals 355 Figure 17-1. M
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Mechanical Seats 357 Figure 17-2B.
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Mechanical Seals 359 Figure 17-2D.
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Mechanical Seals 361 Figure 17-4. H
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Mechanical Seals 363 Pressure-Veloc
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Mechanical Seals 365 The temperatur
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Mechanical Seals 367 Figure 17-7. B
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Mechanical Seals 369 Figure 17-9. P
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Mechanical Seals 371 where C 3 = 53
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Mechanical Seals 373 Classification
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Mechanical Seals 375 Double seals m
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Mechanical Seals 377 less than 100,
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Mechanical Seals 379 Figure 17-19.
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Mechanical Seals 381 Table 17-4 Tem
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Mechanical Seats 385 steam, is to p
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Mechanical Seats 38? rather than a
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Mechanical Seals 389 Mechanical Sea
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Mechanical Seals 391 seal to work i
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Mechanical Seals 395 The measured l
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Mechanical Seals 39? Figure 17-34.
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Mechanical Seals 401 This design is
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Mechanical Seals 403 alignment, par
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Mechanical Seats 419 Figure 17-58.
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Vibration and Noise in Pumps 421 Re
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Vibration and Noise in Pumps 423 me
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Vibration and Noise in Pumps 425 in
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Vibration and Noise in Pumps 427 pr
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Vibration and Noise in Pumps 429 ot
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Vibration and Noise in Pumps 431 Fi
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Vibration and Noise in Pumps 433 fi
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Vibration and Noise in Pumps 435 pr
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Vibration and Noise in Pumps 437 up
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Vibration and Noise in Pumps 441 na
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Vibration and Noise in Pumps 443 A
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Vibration and Noise in Pumps 453 Re
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Vibration and Noise in Pumps 457 Ac
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Vibration and Noise in Pumps 461 As
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Vibration and Noise in Pumps 463 ci
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Vibration and Noise in Pumps 467 sp
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Vibration and Noise in Pumps 469 Be
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Vibration and Noise in Pumps 475 Vi
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Vibration and Noise in Pumps 489 pe
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Vibration and Noise in Pumps 491 th
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Vibration and Noise in Pumps 4S3 fo
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Part 4 Extending Pump Life
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19 by Malcolm G. Murray, Jr. Murray
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Alignment 499 Figure 19-2. Pump dam
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Alignment 501 The best designs fail
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Table 19-1 Vertical Alignment Movem
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Table 19-2 Continued Horizontal Ali
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Page 528 and 529: Table 19-3 Continued Primary Alignm
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Page 532 and 533: Table 19*4 Continued Methods of Cal
Page 534 and 535: Alignment 510 parallelism/perpendic
Page 536 and 537: Alignment 521 Table 19-5 continued
Page 538 and 539: Alignment 523 3. Essinger, J. N., B
Page 540 and 541: Rolling Element Bearings and Lubric
Page 544 and 545: Roiling Element Bearings and Lubric
Page 560 and 561: Roiling Element Bearings and Lubric
Page 574 and 575: Table 21-2 Causes of Seal Failures
Page 576 and 577: Mechanical Seal Reliability 561 ^mi
Page 578 and 579: Mechanical Seal Reliability 563 Sea
Page 580 and 581: Mechanical Seal Reliability 565 run
Page 582 and 583: Reliability Mechanical Seal Reliabi
Page 584 and 585: Index A thermal growth, 519-522 ver
Page 586 and 587: Critical speed analysis. See also V
Page 588 and 589: Index 573 inlet angle, 37 classific
Page 590 and 591: Index 575 Shaft design, 333-343 ind
Page 592: double, 52-54 velocity ratio, 50-51
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Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

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