ML20235Q055

Investigation Rept FAL-00024, Emergency Diesel Generator Floating Busing Failure

ML20235Q055
Person / Time
Site:	North Anna
Issue date:	05/21/1987
From:	Shelton M VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML20235Q047	List: ML20235Q044 ML20235Q055 ML20235Q066
References
FAL-00024, FAL-24, NUDOCS 8710070477
Download: ML20235Q055 (12)

Text

,

ATTACIMENT 1 POW 18 PERFORMANCE SERVICES FAILURE ANALYSIS LABORATORY

1. REPORT TITLE: Emergency Diesel Generator Floating Bushing Failure

2. REPORT NUMBER: FAL-00024

3. DATE: May 21, 1987 ,

4. WORK AREA / STATION AND UNIT: North Anna Unit 1

5. WORK REQUESTED BY: M. R. Kansler, 5. M.-Kotowski

6. WORK PERFORMED BY: M. B. Shelton, E. M. Focht

7. COMPONENT /OR SYSTEM AND LOCATION: Number 12 Floating Bushing from the lH Emergency Diesel Generator. The Number 9 Floating Bushing (undamaged) was supplied for comparison.

8. STATEMENT OF PROBLEM: The Number 12 floating bushing showed two distinct but related damage mechanisms: wear of the bushing interior and exterior surfaces and plastic extrusion of the worn regions.

9. CONCLUSIONS REACHED BY FAILURE ANALYSIS LABORATORY:

The results of this investigation indicate that the bushing wear damage is due to insufficient lubrication, which in turn can occur from use of an inadequate lubricat-ing oil, excessive engine loads, or a combination of both.

The plastic extrusion is likely the result of increased stresses imparted on the bushing rather than a degradation in mechanical flow strength of the bushing material. A determination of the source of these stresses, whether from increased contact stresses from insufficient lubrication or 8710070477 870930 PDR ADOCK 05000338 G PDR

,y,

POW 18 from excessive engine loading, was beyond the scope of this 4

investigation.

10. . ANALYSIS'RESULTS:

Macroscopy

. Figure 1 is an exterior surface view of bushing #12 as received.. The lead flashing was wiped from the exterior and interior surfaces of the bushing over a.circumferential arc of slightly less than 180*, however, lead was still visible within the oil grooves. In areas where the lead flashing was removed, the surface had a burnished appearance with discoloration due to a heat tint film. Some visible removal of the lead flashing and a similar heat tint were present over portions of the remaining interior and exterior sur-faces of the bushing, however, the damage was not as severe.

In addition to the removal of the lead' flashing and the heat tint film, some base metal had been smeared into. the oil grooves as shown in Figure 2. Figure 3 is a macrophoto-graph of the less severely damaged interior surface of the bushing with the lead flashing still intact and only limited wear evident.

Dimensional Measurements:

Dimensional measurements were performed by station NDE services, and so were not repeated in detail in this analy-sis. Random measurements were made, however, to verify that plastic deformation had occurred on the damaged portion of the bushing. The bushing had been extruded, effectively reducing the bushing thickness and increasing the axial

POW 18 length in the damaged region by roughly 0.015" and 0.07",

respectively.

Electron Microscopy The damaged surfaces of the bushing were examined by scanning electron microscopy in order to determine the  !

damage mechanism. Figure 4 is an electron micrograph of the interior surface of a damaged area of the bushing which shows a large amount of adhesive wear (galling) with some evidence of abrasive wear (score marks).

Chemical Analysis Chemical analyses were performed on samples from undamaged and damaged regions of the Number 12 bushing and on a sample from the Number 9 bushing. Results are shown in Table 1.

The chemical analysis results indicate that the materi-al of both bushings meets the specified composition require-ments of SAE64 cast bronze.

Microscopy Several metallographic specimens were prepared of damaged and undamaged cross sections of the Number 12 bushing and of undamaged bushing Number 9. Variances in grain size were observed in bushing Number 12, apparently a result of the casting process (Figures 5 and 6). The variation did not ' appear to be a contributing factor to, or a result of, bushing damage.

Figure 7 is a photomicrograph of the Number 12 bushing j cross section at the damaged interior surface. The 1

L_____---------

if ,' :t POW 18 y microstructure is indicative of centrifugally

/, [4x cast high jf '

o lead-tin-bronze. The ' lead flashing is completely removed  ;

, from the bushing surface. No significant grain deformation was observed in the damaged region. A cross section of the undamaged portion 1'of bushing Number the 12 shows lead flashing still intact and a similar microstructure to that of the damaged area. The lead flashing is still visible on the bushing surface (Figure 8). Bushing Number 9 revealed a microstructure similar to bushing Number 12 (Figure 9).

Hardness Testing -

Macrohardness measurements were made of damaged and undamaged regions of the bushing. The results of these i

measurements show an increase in hardness in the damaged "

area. of the bushing versus the undamaged area. Hardness averages ranged from 50.1 Rb -(~89 Brinell) in the undamaged area to 64.7 Rb (~ 109 Brinell) in the damaged area. No significant variations in hardness were observed from the exterior to interior surface of the bushing. '

11. DISCUSSION:

Bushing damage appears to be the result of lubrication i film failure which results in adhesive and abrasive wear of the bushing and subsequent plastic extrusion. The visual appearance of the damage is similar to that which has been observed in some Navy diesel engine bushing i

failures. )

.l Research performed on the Navy bushing failures attributed '

the damage to the use of zine bearing lubricating oils l

1

__ ___ - _ . _ _ .]

?

POW 18 i

similar to types used nthe past in the North Anna diesel engines.

Smearing of the bushing metal into the axial oil grooves will result in further degradation of lubrication

, effectiveness. Inadequate lubrication will result in increased bushing metal temperatures due to friction heat.

-The increase in bushing hardness is indicative of strain hardening due to cold working. The presence of a temper film and apparent strain ha'rdening suggest that the bushing metal temperature was in the 400*F - 700'F tempera-ture range during operation with inadequate lubrication.

Only limited reduction in flow strength will occur in this temperature range versus normal lubricated temperatures of approximately 350*F (Figure 10). This indicates that the plastic extrusion of the bushing is likely the result of j increased stress rather than decreased flow strength.

{

Increased contact stresses will occur with insufficient lubrication. Insufficient lubrication may result from either an inadequate lubricating oil or excessive engine j loading, or a combination of both.

l f

//'/ , , LJ  !

M. B. Shelton investigating Engineer MBS/035: cit

3, POW 18 TABE 1 OEMICAL ANALYSIS OF FURTING BUSHING #9 and #12 Cu,% Sn,I Pb,% Ni,! Zn,I Number 12 Bushing 78.67 9.73 8.77 0.44 0.75

-(undamaged)-

Nubmer 12 Bushing 78.70 9.02 8.66 0.43 0.76 (damaged)

Nteber 9 Bushing 78.66 9.12 8.95 0.43 0.72

POW 18 r -- -

m -

e um . 4 FIGURE 1 EXTERIOR SURFAG VIEW OF BUSHING #12 AS-REGIVED, A TEMPER OXIDE FIIM IS VISIBLE ON THE BUSHIIC SURFAG.

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FIGURE 2 INTERIOR SURFAG VIEW OF BUSHING #12 SHORING BASE METAL SMEARED INIO OIL GROOVES, J

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FIGURE 3 L \ 2B .

INIERIOR SURFACE OF RELATIVELY UNDAMAGED SECTION OF BUSHING #12. THE LEAD FLASHING IS STIII INIACI.

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FIGURE 4 SCANNING ELECTRON MICR0 GRAPH SH0 JING ADHESIVE AND I ABRASIVE WEAR ON INITRIOR SURFACE OF BUSHING #12.

MAGNIFICATION - 68.8X.

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FIGURE 5 PHOIW ICROGRAPH OF BUSHING #12 CROSS SECTION SHOW-ING 1ARGE GRAIN SIRUCIURE. MAGNIFICATION - 12X.

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FIGURE 6 PHOIW ICROGRAPH OF BUSHING #12 CROSS SECTION SHORING FINE GRAIN STRUCIURE. MAGNIFICATION - 12X.

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FIGURE 7 PHOITMICROGRAPH OF BUSHING #12 CROSS SECTION AT MRGED WIERIOR SURFACE. MAGNIFICATION - 400X.

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Lead Flashing FIGURE 8 PHDIIMICROGRAPH OF B'JstING #12 CROSS SECTION AT UNDAMAGED INTERIOR SURTACE. MAGNIFICATION - 400X.

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POW 18

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FIGURE 9: PHOIN ICROGRAPH OF BUSHING #9 CROSS SECTION AT INIERIOR SURFACE. MAGNIFICATION - 400X. EIGANT

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Yield strength A . i 1 20 N O 5'4 e:t under load 15

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Q 'w + =

Q O.2% of fset J C i i_ i

-00 O +100 200 300 400 500 600 700 800 Testmg temperature, F

{ Data extrapolated above 450 F based on discussions with Mr. Carl Caffoglio of the Copper Development Association )

{

k FIGURE 10- YIELD STRENGTH VS. TEMPERATURE FOR SAE 64 i

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