ML20087L351

Emergency Diesel Generator Air Start Valve Capscrew Dimension & Stress Analysis, Prepared for Transamerica Delaval,Inc (Tdi) Diesel Generator Owners Group

ML20087L351
Person / Time
Site:	05000000, Shoreham
Issue date:	03/31/1984
From:	STONE & WEBSTER ENGINEERING CORP.
To:
Shared Package
ML20087L309	List: ML20087L351
References
NUDOCS 8403270157
Download: ML20087L351 (23)

Text

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March 1984 EMERGENCY DIESEL GENERATOR AIR START VALVE CAPSCREW DIMENSION AND STRESS ANALYSIS l'

Prepared for:

O TDI OWNERS GROUP 1

i Prepared by:

Stone & Webster Engineering Corporation 8403270157 840323 '

PDR ADOCK 05000322 S PDR

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EMERGENCY" DIESEL' GENERATOR f l .. . . . i i AIR START VALVE CAPSCREW DI!!ENSIONAL-ic -

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}' STRESS ANALYSIS -t 4 . ,

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MARCil, 1984  ;

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TABLE OF CONTENTS

!: Section- Title -

Page t ji ,

! 1: APPLICABILITY' 1 r

, .2 -EXECUTIVE

SUMMARY

2-OBJECTIVES- 3 3'-

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SUMMARY

OF SERVICE CONDITIONS 4 I

I 5 METHODS OF ANALYSIS S 5.1 Air Start-Valve Dimension Check 5.2 Determination of Applied Stresses

' 5.3 Determination of Endurance Limits

~6. -DISCUSSION OF RESULTS 10~

, 7- CONCLUSIOliS 12

, APPElIDIX A STRESS SUf1 MARY APPENDIX B DRAWING-FATIGUE DIAGRAMS 4

l- APPENDIX C TASK DESCRIPTION

., . APPENDIX D REFEREliCES t

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1 1 SECTION 1 Y

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[ APPLICABILITY ,

4 This report is applicable to the TDI nuclear standby servica diesel generators utilized at the Shoreham Nuclear Power Station.

Other TDI nuclear standby service diesel engines have essentially the same air start valve capscrew design, based on incorporation of the 10CFR Part 21 Report issued by TDI on the old design.

However, as part of the TDI Owners Group Design Review / Quality

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a Revalidation effort, each nuclear service standby diesel engine j air start valve will be reviewed to compare specified torque d values, gasket material, etc., with those for the airstart capscrews on the Shoreham engines.

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"i EXECUTIVE

SUMMARY

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An analysis was conducted for the-2-3/4" capscrews utilized t j in the TDI nuclear' standby service diesel generators in use at -

t Shoreham.

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j. - The purpose of this analysis is to evaluate the capscrew

. design based on the criteria referenced'in the component design

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- review task description, (see Appendix C). This analysis concluded that.the air start valve capscrews design is adequate l

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SECTION 3 OBJECTIVES 1 .

The objectives of this analysis are as follows: -

1. Perform a dimension check on the Air Start Valve Capscrews to determine if adequate clearance exicts within the cylinder head tapped hole.

2. Determine if the specified torque value ensures adequate capscrew preload. ,

3. Determine the total restart bolt stress.

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4. Evaluate TDI's recommended retorquing requirements.

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4 d The details of this analysis are provided in SWEC calculation number 11600.60-245'.1-M3 (Ref. 2).

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SECTION'4

SUMMARY

OF SERVICE CONDITIONS ,

The air start' valve assembly is secured to the cylinder head via two capscrews. These capscrews are installed with a l ^

specified torque,-which produces a tensile load in the capscrew ..

and subsequent clamping force'on the air start valve assenbly. -

This clamping force opposes the cyclic forces induced by the

cylinder pressures.

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Initially, a stress (Spy) is induced in the capscrew by  ;

-preload. In addition to this preload stress, a cyclic fatigue

streru is induced in the capscrews due to the cylinder firing

pressure force. ,

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SECTION 5 METHODS OF ANALYSIS 5.1 - Air Start. Valve-Dimension Check ,

To ensure proper assembly of components, the capscrew must not " bottom out" within the cylinder head. This will

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not occur providing'the minimum clearance available exceeds

' the maximum capscrew length. . The minimum capscrew clearance is determined _by taking dimensions of the various parts of the air start valve assembly penetrated by the Capscrew. As

- shown in Appendix B, Figure 1, the four items requiring measurement are the valve cap, valve housing, space between cylinder. head and valve housing, and-the cylinder head tapped hole. Thus by adding these four dimensions while ,

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considering the maximum tolerance in the direction to z

'I I- . pr' ovide minimum length, the minimum'capscrew clearance is

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determined.

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5.2 iDetermination of Applied Stresses' In determining _the stresses applied to the air start valve capscrews,.the tensile-preload resulting'from the.

applied' torque is first--calculated lar the relation Fpy= W .2d -Eq. 1 (Reference 3) where T= applied torque, LB f-in

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d= r,ominal capscrew diameter, in Fpy= capscrew preload~,_LBf due to torque T

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.The resulting tensile load is taken to act uniformly over

. the' minimum cross sectional. area ( A (min) ) of the capscrew, located at.the~thiaads, so that the resulting preload stress is maximized.

Theftensile loa's d produced in the capscrews are converted to i ) alclamping(force _on the air st' art valve Assembly which serves to The-pressure loads are calculated resist-the pressure loadings.

by.mdisiplying a conservative, cylinder firing-pressure by the valve--face area.. 'This force is resolved into a single vector

, acting at.the geometr i c center of t h e va l ve.oppos i ng th e-pre l oad clamping forces.

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'The cyclic stress induced on the capscrews due to the alte'rnating load is given by:

S3 =,+ Fpb / _

(Reference 3)

-A(rinT Where Sg = alternating stress F pb = alternating load

= Fcp b Kb +Km )

and Kb = spring rate for the capscrew

-K -= spring rate for the section joined by the capscrews F = maximum resultant force due to cylinder pressure.

p As per Reference 3 & 5, the spring rates K b and K are

. - determined.by:

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(,J . Kb = Wd E (Reference 3)

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Kg=2TdE Where Dj < 3D h ( eference 3) 3 L

K 2 m2 = { _+ 'E (of-d ]+1I(m_j/yr s

DJ Dh ' + L" "

Dh L 5 100 , ,

Where Dh<D <3D h (Reference 5) 3 Where d a nominal capscrew dianeter, in D = capscrew head diameter, in h

D.= joint diameter, in 3- 2 E = nodulus of elasticity, lb /in f L = length of joined sections, in K g = spring rate for cylinder head, lbf /in.

Kb2 = spring rate for. valve cap and valve housing,

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Sin'ce a number of joint sizes occur, the individual spring

' rate must be calculated for each joint. The overall. spring rate

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, ' constant K ,is.then determined by adding the individual rates in '

,1 series as follows:

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K-'= 'l m-1 g 1 (Reference 3)

! K Km1 m2

.The spring rate for the copper gasket is relatively large

, ' compared to K,y and Km2 and thus has an insignificant effect on the overall spring constant-K m' l Once the preload stress (S p) y and the alternating stress

(+Sb) are determined, the total applied mean stress ~(St) 1" defined as:

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t =S py+ S.y V

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M-Q 5.3- Determination of Endurance Limits

-The endurance limit-(S ) f r the capscrew design is e

, determined _by:

S, = K a K b Kc d e f S

e (Reference 3) where S '= the~ endurance limit'of a rotating beam specinen K' = component surface factor HKb = component size factor K = reliability tactor Kd = temperature factor K* = modifying factor for stress concentration Kf = miscellaneous effects-factor

'The endurance limit of the two designs is compared,as well

-as the' total applied nean stress (St ) and the yield strength (Sy) 2 --

of the material in order.to determine the suitability of the z component design for the given service.

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('( j _ SECTION 6 DISCUSSION.OF RESULTS

- Per Reference j2, a dimension check indicates .that a 0.2 -inch minimum clearance exists within the cylinder tapped hole. As a result,'thecair start valve capscrew will-not " bottom out" upon

- torquing..

Per reference 5, fatigue failure in capscrews is avoided if the total applied mean. stress (St ) is below the yield point for the' component material and the endurance strength exceeds the cyclic. stress by an acceptable margin. ' Jus per Appendix A

. Table ~1, the total: applied-mean stress (St ) taken at the minimum cross sectional' areas A(min) is:37.5 ksi.

Per. Reference 4, the yield strength for the capscrew

' materiallis 92 ksi minimum. 'As a result, the criteria for a.

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fatigue. resistant design, namely S # b is satisfied.

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As shown in Appendix A, Table _1, the capscrew design utilizes an endurance stress of 9.0 ksi with a cyclic stress of

+1.6 ksi (see Appendix B, Figure 3) and therefore, satisfies the

' second criteria for~a fatigue resistant design. The presence of-the^p'eload-.

r serves to' reduce the range of stress cycling and

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subsequent fatigue effects on the capscrews. As a result, the specified torque ~which provides the preload is acceptable.

During start up of the engine, a stress'is imposed on the capscrewssdue to starting air pressure within the air start valve assembly. This stress 11s insignificant compared to the greater alternating stress induced by cylinder firing pressures.

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. LDuring engine' operation,'the' valve. assembly copper-gasket is subjected to elevated temperatures. -As-a-result, of the-

, 4 . temperature rise and preload, creep occurs within the gasket whichiwill decrease the totalicapscrew preload. To compensate, the': existing diesel engine maintenance procedures require

~ ; retorquing at specified1 intervals until no change is detected.

- Atithis time'the gasketDis fully ~ compressed at its operating l:temperaturcLwith the requiredLpreload. ,Hence, capscrew preload 1

is maintained.during thelfull range'of engine operation.-

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CONCLUSIONS il  !

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Reference:

2 provided a dimensional and fatigue analysis for th'e air. start. valve'capscrews. Based on this analysis, the

- capscrew is. adequately designed for the intended service.

The restart bolt stress has an insignificant effect on the

'.  ;; capscrews. .In addition, any possible loss of preload due to -

. creep' of- the sof t copper gasket is . recovered through the existing i retorque_-procedure, p

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APPENDIX A - STRESS

SUMMARY

TABLE 1: STRESS SUMf1ARY 4

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SPL SB SE ST KSI KSI KSI KSI 35.9 t1,6 90 37.5 i O SPL- PRELOAD STRESS S B - ALTERNATING STRESS S E - ENDURANCE LIMIT S T - TOTAL APPLIED MEAN STRESS i

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$I APPENDIX ~B - DRAWINGS - FATIGUE DIAGRAMS d-g .

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APPENDIX C >

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TASK DESCRIPTION J

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i COMPONENT DESIGN REVIEW TASM DESCRIPTION i f

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Classification A l AIR START VALVE CAPSCREWS Completion 3/1/84

, ,, . . PART NO.03-359 9.

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PRIMARY FUNCTION:

The air start valve capscrews provida clamping force to l..* hold air start valves in place on cylinder heads.

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FUNCTIONAL ATTRIBUTES:

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2. The air start valve capscrews must have sufficient strength to

withstand the necessary preload a r.d reaction air loadir.g without yieldir.g and resultang in loss of clamping force on the air start f fj valves.

SpECIFIED STANDARDS: None i~

f ARi4_UATICN:

1. v'er 2 f y adequacy of r.ew capscrew length to prevt -

s botteming out of the capscrew during insta11aticc.

Review to include maximum tolerar.ce of capscrew ler.gth coupled with cylir. der head minimum hole depth. '

2. Evaluate adecuacy of soecified toraue value.

2. Perform worst case ar.alysis of react ion air loadang i r. capscrews.

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l j j 4. Det erm i r.e the total restart bolt stress.

I 5 Evaluate the TDI recommended retorquang recutremerits J;

a't er operat :en due to use of copper gaskets. ,

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l REVIE*' TD AN A'_YSES

Review .ozd and deflect ion analyses

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INFC C'<AT I ON RET'! PED:

1. Capscrews ar.d washer materials and dimensions E. Cylinder head drawings

. 3. Specsfied torque value and lubrication reautremer.ts L

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APPENDIX.D - REFERENCES

• - Reference'1:- TDI Drawing 03-359 Air' Start Valve, s Assembly

[' . '-Reference 2: - SWEC Calculation 11600.'60-245.1-M3 1-

. Reference 3: Mechanical Engineering Design,

.J.E. Shigley, 3rd edition Reference'.4: ASM Metals Handbook, Vol. I, 9th Edition, Pg. 274.

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s Reference 5: Simple Diagrams Aid in Analyzing Forces in Bolted Joints, Assembly Engineering,

' G. Meyer 1972 i.

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