reliability improvements on high speed reciprocating

Reliability improvements on high speed reciprocating compressors through bearing and process modifications

- Case Study

Jim Cencula GE O&GCarlo Mazzali GE O&G/ FLRVinh Do GE O&G/ HouRay Gallagher GE O&G/ HouGreg Bone Miba Bearings

291

Contents

• Brief overview to recip compressor bearing/ orbital needs

• Brief Issues history on EF bearing issues

• Discussion of Failure Modes and Root Cause Analysis (RCA)

• Use of Design for Reliability (DFR) process and corrective actions

• New EF bearing design options and testing

• Summary

292

Bearing analysis - Background

MOFT

POFP

SHAFT SHAFT

Bearing operating principle

The reciprocating motion of the shaft generates a variable lubrication film thickness: the pin changes its position both circumferentially and radially

The geometry of the bearing gives a pressure trend within its width

BEARING

LUBRICATION GAP

Fluid friction needed to minimize power losses and rapid wear → Hydrodynamic operation

Bearing performance

To avoid rapid bearing wear:• Adequate separation between moving

components (↑ MOFT)• Low stress level (↓ POFP)

Bearing design criteria

Wide bearing surface to ↓ POFP

↓ oil inlet T and ↑ cooling flux to ↑ oil viscosity and therefore ↑ MOFT

SAE40 Viscosity vs T

0

20

40

60

80

100

120

140

100 110 120 130 140 150 160 170 180 190 200 210 220

Oil Temperature [deg F]V

isc

os

ity

[c

st]

293

RCA Process – Key Parameters

Bearings• overloaded Babbitt• geometry out of cylinder/ parallel• improper clearance• oil delivery improper (flow/ temp)• contaminated lubricant

• anti-rotation tab deform• surface hardness mismatch• debris imbedded• poor fit / contact pressure

Crankshaft • overloaded journal• geometry out of cylinder/ parallel• oil delivery improper to bearing

Conn Rod • uneven /improper bearing housing • geometry out of tolerance/ assy fit• oil removal uneven or improper

Lubrication System • Packager– oil delivery (temp/ press variation)

294

The first major focus of this effort was to eliminate the early operation (infant mortality) issues by addressing the fundamental part/ unit quality issues.

• An extensive effort was made to work with the crankshaft, connecting rod, and bearing manufacturers to ensure the critical to quality component features were maintained (CS pin cylindricity, CS pin surface finish, bearing as-assembled roundness, tin-flashing consistency, etc.).

• The compressor team also focused on cleanliness processes and in-house inspections for increased confidence as well.

• At the same time, the high speed recip OEM had extensive P&ID reviewers with the packagers and were able to get lube oil supply temperatures and pressures to be delivered in a much more consistent way.

Within a late 2006 to early 2009 period, the two-year operational reliability increased from ~90% to 100% (that is, no new bearing failure for over 3 years of shipments now).

Approach

295

• Weibull analysis shows = 0.35.

• This indicates an Infant Mortality failure mechanism.

• The units produced since Mar-2007 demonstrate 14 times improvement in Reliability

Bearing Weibull AnalysisProbability - Weibull

before 3/19/2007: after 3/19/2007:

Service Hours

Unr

elia

bilit

y, F

(t)

10.0 1000000.0100.0 1000.0 10000.0 100000.00.1

0.5

1.0

5.0

10.0

50.0

90.0

99.0

0.1

Probability-WeibullCB@90% 2-Sided [T]

after 3/19/2007Weibull-1PMLE SRM MED FMF=0/S=123

Susp PointsProbability Line

before 3/19/2007Weibull-2PMLE SRM MED FMF=44/S=477

Data PointsSusp PointsProbability LineTop CB-IBottom CB-I

Grzegorz KubikWIA, EDC4/11/20082:54:06 PM

Before 3/19/2007 After 3/19/2007

No of Failures 44 0No of Suspensions 477 123Beta 0.35 0.35Eta 10,874,385 156,206,865MTTF 55,268,030 794,239,601B10 17,202 246,915

296

Weibull InterpretationBeta B10* Life (hrs)

Before improved Cleanliness .35 17,638After improved cleaning .38 26,683After New Bearing fit/ tab .27 141,168After New Factory Inspection .37 1,691,771

*B10 is the prediction of non-failure of this mode for 90% or more

B10 says ‘design life’ fall-out is very low; Beta supports failure occurs early in life

So what about beyond infancy?Detail: Crow AMSAA for 2006-ship Units…for units operating >5000 hrs, < 0.1% chance of failure in “design life” period (w/ 90% confidence)

1.00E-4

1.00

1.00E-3

0.01

0.10

1.00 100000.0010.00 100.00 1000.00 10000.00

ReliaSoft's RGA 6 PRO - RGA.ReliaSoft.com

Instantaneous Failure Intensity vs Time

Time

Inst

ant.

Fa

ilure

Int

ensi

ty

4/7/2008 05:50GEKasia Osowska

Crow-AMSAA (NHPP2006MLE

CB[C] 90%2-Sided-B [T2]

Beta=0.3268, Lambda=0.5493

… what else can cause infant failures?

297

Oil Cooling Flux (gallons/min)

0.0

0.5

1.0

1.5

2.0

2.5

HSRC 180F HSRC 160F HSRC 150F

Bearing analysis – HSRC oil cooling effect

= HSRC with upgraded oil cooling system (“plus” option, oil temp @ 150F)

= HSRC with upgraded oil cooling system (oil temp @ 160F)

= HSRC with actual cooling system (oil temp @ 180F)

Oil delivery system robustness is key impact to managing good bearing parameters… poor oil control impacts other factors (when MOFT is low)

MOFT [μm]

0.0

0.5

1.0

1.5

2.0

2.5


POFP [psi]

0

5000

10000

15000

20000

25000

30000

35000

40000


298

321

0.0010

0.0005

0.0000

Atlas (1) Lincoln (2) Ellwood (3)

All

Ven

dors

CS Parallel MainsCS Parallel MainsUSL=0.0010USL=0.0010

321

0.0010

0.0005

0.0000


All

Ven

dors



1 2 3

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014


All

Ven

dors

CS Parallel CranksCS Parallel Cranks

USL=0.0005USL=0.0005

1 2 3

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014


All

Ven

dors

CS Parallel CranksCS Parallel Cranks

USL=0.0005USL=0.0005

vendor vendor vendor

Bearing fit to Journals A Key …cylindricity/ parallelism

• Crankshaft geometry out of cylinder/ parallel … key manufacturing CTQ with suppliers

• Main CS journals ‘good’• Crank journals – vendor variation

‘devil is in the details’

• Also, bearing fit into Conn Rod in the final assembled condition a key to good journal

• Conn Rod cap torque level and machining are key

• Bearing ‘crush’ and deflection key

299

“DEF” Crankshaft/Bearing Rolling Failure Rate

• The last Crank end bearing failure occurred in units produced in Nov 2007.

• No failures since 3 years of shipment.

300

Time, (Hours)

Unre

liabi

lity,

F(t)

1.E-2 1000001.E-1 1 10 100 1000 100001.E-1

5.E-1

1

5

10

50

90

99

1.E-1

0.5

0.6

0.7

0.8

0.9

1.0

1.2

1.4

1.6

2.0

3.0

4.0

6.0

1/30/06 11/01/06 3/19/07 8/17/07

Cleanliness Improvement I

Bearings Improvement

Inspection Level Changed

Cleanliness & Test Load Improvement II

6/30/08

CS/ CR/ Brg re-certified process

1/30/06 11/01/06 3/19/07 8/17/07

Cleanliness Improvement I

Bearings Improvement

Inspection Level Changed

Cleanliness & Test Load Improvement II

6/30/08

CS/ CR/ Brg re-certified process

Test Inspection

Original

Bearings chng

Cleanliness I

Cleanliness II

DEF Crankshaft/ Bearing-only Weibull• Measurable Brg/ CS Reliability step

improvement from ‘05-’08 …. at three years (30 Khrs) : improved from >10% Failure Rate to < 0.5%

• No bearing failures on units shipped since November 2007… although some customers still limit bearings to ~ 2 years

Bearings /shaft Recertified

301

Bearing Design CalculationsHydrodynamic (HD) calculations have been preformed on a wide variety of

compressor connecting rod bearings.

The following general guidelines have been established based on these calculations and actual performance:

• MOFT greater than 2.0 µm (≈ .00008”)• MOFP less than 3000 bar (≈ 43000 PSI)

Market Study of Crankshaft Diameter and MOFT at 85ºC

0

0.5

1

1.5

2

2.5

3

3.5

100 120 140 160 180 200 220 240

Crankshaft Diameter (mm)

MO

FT (m

icro

n)

. FS

Market Study of Crankshaft Diameter and MOFP at 85ºC

200

220

240

260

280

300

320

340

360

380

400

100 120 140 160 180 200 220 240

Crankshaft Diameter (mm)

MO

FP (M

Pa)

.FS

302

Bearing Materials• Steel Backed Leaded Bronze Tri-metal bearings are the default material choice for

compressor rod bearings. Given that MOFT range from roughly 2.0-3.0 and MOFP averages around 3000 bar on the rod bearings.

• Bi-metal Aluminum lined bearings are sometimes used. However, these are mainly for sour gas (H2S) applications that will destroy the leaded bronze bearings.

• The main bearings see much less loading than the rods (only about 25-30%).

HD Calculation range for Compressors

303

Improved oil feed - NP vs. current style

• leverages experience from other GE recip products• Double oil feed / bearing• Removed circumferential groove at high load• increased pin width• improved manufacturing local geometry at crank wallcurrent New - NP

304

Proposed Changes – NP Style Bearing Comparison of Standard Bearing vs. NP Style HD Plots.

Standard Crank Drilling will pass through these high press zones.

Note: ~2x reduction in POFP (on axis)

305

Instrumentation

6.25*

9.5

1

3

2

4

14.5

14.5*

* Includes Block I & II upgrades

Skid Package

• Engine Power / Torque

• Crankshaft Angle, RPM

• Gas Mass Flow Rate

• Suction, Interstage & Discharge Press

• Frame Vibrations

Lubrication System

• Oil Sump Temp

• Oil Cooler Oil Inlet & Outlet Temp

• Oil Cooler Coolant Inlet & Outlet Temp

• Main Saddle Oil Temp, Press, Flow Rate

• Main Bearing Temp, Orbits

Throw 1

• ConRod Rifle Hole Oil Press, Temp, Flow Rate

Throw 1 vs. 3

• Crank Pin Bearing Temp, Orbit

• Wrist Pin Oil Press, Orbit

• Bushing Temp

• Crosshead Vibration

• Rod Strain

• Cylinder Head & Crank End Press

• VVCP Backside Press

• VVCP Rod Load

Throw 2 & 4

• Cylinder Head & Crank End Press

DEF Block Change TestScope of design change

• Widen crankpin to big-end bearing contact surface to enhance the lubrication behaviour and achieve a higher degree of reliability

Crankgear components to be modified

• Crankshaft

• Crank pin bearing

• Connecting rod

306

Summary

OEM/ Field issues have been resolved for high bearing reliability (99.5+% reliable) for 2+ yrs. operation; the

– Key RC manufacturer improvements (CS, cleanliness, and bearing re-certifications; test process improved)…. ‘the devil’s in the details!’

– Packager > oil viscosity/ temperature

These and other Lessons Learned have been fed back to OEM and formally incorporated into Design Specification, vendor qualifications and Mfg work instructions

For further end user variation and confidence-– New Babbitt (Synthec) bearing option for increased

margins– New NP-style dual feed for significant margin

improvement to new units

307

reliability improvements on high speed reciprocating

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