Material Selection Process for Gas Turbine Blade, Disk and Shaft with equations

7/23/2019 Material Selection Process for Gas Turbine Blade, Disk and Shaft with equations

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Talha bin Yaqub

ID:200991826

Material Selection and Specification for Blade Di!c andShaft for the Turbine Sta"e of Static #a! Turbine

Talha Bin Yaqub

School of Mechanical $n"ineerin" %ni&er!it' of (eed! (eed! (S2 9)T %*


2/25

Table of +ontent!:

1. Introduction..............................................................................................................................3

2. Turbine Blade:.........................................................................................................................4

2.1 Performance Specification.....................................................................................................4

2.2 Possible Materials:.................................................................................................................7

2.1 Processing:.............................................................................................................................

2.1.1 !orging "#$it%ur& 1'():.................................................................................................

2.1.2 In$estment *asting "+alpa,-ian& 21):.........................................................................

3. Turbine /isc...........................................................................................................................11

3.1 Performance Specification...................................................................................................11

3.1.1 Possible Materials:........................................................................................................12

3.2 Process Specification...........................................................................................................14

4. Turbine S0aft.........................................................................................................................17

4.1 Performance Specification...................................................................................................17

4.1.1 Bending stiffness:.........................................................................................................1

4.1.2 Torsional Stiffness:.......................................................................................................1

4.1.3 Possible Materials:........................................................................................................2

4.2 Process Specification:..........................................................................................................2

. oining:..................................................................................................................................22

(. Specification and Sourcing....................................................................................................22

7. Inspection:..............................................................................................................................22

. ifetime..................................................................................................................................23


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(i!t of ,i"ure!:

,i"ure 1: Material Selection +hart -Yield Stren"th &! Den!it'................................................7

,i"ure 2: Material Selection +hart -Youn"/! Modulu! &! Den!it'...........................................7,i"ure : #raphical +opari!on of roce!!in" Technique! -Di!creet &! +apital +o!t........1

,i"ure 3: #raphical +opari!on of roce!!in" Technique! -Surface 4ou"hne!! &! +apital

+o!t...............................................................................................................................................11

,i"ure 5: #raphical +opari!on of roce!!in" Technique! -Di!creet &! 4elati&e +o!t

Inde.............................................................................................................................................11

,i"ure 6: Material Selection +hart -Yield Stren"th &! Den!it'..............................................13

,i"ure 7: +opari!on of Toolin" +o!t for riar' roce!!e!................................................1(

,i"ure 8: +opari!on of +apital +o!t for riar' roce!!e!................................................1(

,i"ure 9:+opari!on of 4elati&e +o!t Inde for riar' roce!!e!....................................17

,i"ure 10: +opari!on of Section Thicne!! 4an"e for riar' roce!!e! .........................17

,i"ure 11: Material Selection +hart -Shear Modulu! &! Den!it'. ..........................................2

,i"ure 12: Material Selection +hart -Youn"/! Modulu! &! Den!it'.......................................2

,i"ure 1: +opari!on of Ma!! 4an"e! of roce!!e!...............................................................22

,i"ure 13: +opari!on of 4elati&e +o!t Inde of roce!!e!...................................................23

(i!t of Table!:

Table 1: erforance Specification for Turbine Blade..............................................................

Table 2: roce!!in" Specification for Turbine Blade..................................................................'

Table : erforance Specification for Turbine Di!c..............................................................12

Table 3: roce!!in" Specification for Turbine Di!c...................................................................1

Table 5: erforance Specification for Turbine Shaft.............................................................1

Table 6: roce!!in" Specification for Turbine Shaft.................................................................21


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1 Introduction

# gas turbine is a tpe of internal combustion engine in 50ic0 air is used as 5or,ing fluid. T0e

gaseous energ of air is used to con$ert c0emical energ of fuel to mec0anical energ.

6utput s0aft po5er& 50ic0 is needed to dri$e t0e propeller& is pro$ided b t0e turbine section of

t0e engine. T0e compressor and all ot0er engine accessories are also dri$en b t0e po5er

pro$ided b t0is section. T0e gradual ad$ancement in t0e material science 0as made it possible to

manufacture gas turbine engines 5it0 0ig0 efficienc le$els and 0ig0 po5er ratings. It is t0e

capabilit of a material to 5it0stand 0ig0er temperature 50ic0 leads to t0e 0ig0er efficienc

5eig0t reduction can also be ac0ie$ed if material 0as 0ig0 ele$ated temperature strengt0 to

5eig0t ratio "Mu,tinutalapati& 211).

In t0e start it 5as 0ig0 temperature tensile strengt0 50ic0 ser$ed as prime re8uirement for t0e

materials de$elopment. ater on& stress rupture life and t0en creep properties became factors for

material de$elopment. T0e c0oice of material 5as based on its capabilities to 5it0stand 0ig0er

loads "Mu,tinutalapati& 211).

T0is re$ie5 gi$es an analsis on t0e ad$ancement of materials and processes t0at are in$ol$ed in

t0e production of $arious components of gas turbine engine.


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#lt0oug0 t0ere are se$eral components t0at -oin up to ma,e a gas turbine engine& emp0asis 0ere

0as been on t0ree main components i.e. blade di!c and !haft of turbine T0ese components are

critical to t0e performance of t0e gas turbine engine.

2 Turbine Blade:Turbine blades are core component for t0e gas turbine engine as t0e are responsible for

e9tracting t0e energ from 0ig0 temperature and 0ig0 pressure gasses "ura-arapu& et al.& 214).

;it0out turbine blades t0ere 5ill be no po5er at all 50ile a slig0test fault in t0e blades costs a

fortune to repair.

21 erforance Specification

/uring t0e operation& blades are sub-ected to significant gas bending and rotational stresses at

$er 0ig0 temperatures. T0e also 5it0stand se$er t0ermo mec0anical loading ccles during

normal start


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#nd 0=2b

T0e ob-ecti$e function is an e8uation for t0e mass t0at 5e appro9imate as

m=bhL

;0ile&

hStands for t0e lengt0 of blade&

Stands for t0e densit of material&

# Stands for t0e area of cross section&

Is a constant multiplier

>ig0 strengt0 of t0e turbine blades re8uires t0at:FL

2b2=y

Substituting $alue of b from t0is e8uation: m=hL

3 /2

21/2

1/2

?o5 for 0ig0 bending stiffness&S=

C1EI

L3 S

S* is the desired stifness,Eis Youngs modulus,*1is a constant that

depends on the distribution o load and I=bh

3

12is t0e second moment of t0e area of

t0e beam. T0us

h=( 12 S

C1bE )

1

3 L

Inserting t0is in e8uation gi$es e8uations for t0e performance metrics: t0e mass m2of t0e blade

m( 12S

C1b)

1

3 L( E13)Material indices for t0ese e8uations:


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M1=

1/2

@ M2=

E1/3

,i"ure 1: Material Selection +hart -Yield Stren"th &! Den!it'.

,i"ure 2: Material Selection +hart -Youn"/! Modulu! &! Den!it'.


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22 o!!ible Material!:

Airconia& ?ic,el *0romium #llos& ?ic,el based Super #llos& Tungsten *arbides

6ut of t0ese selected materials& I 0a$e c0osen ?ic,el based super allos using t0e information

gi$en in *Sedupac,. T0e reasons be0ind t0is selection are:

Airconia is a ceramic material and it is 0ig0l brittle. Secondl& its process


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*onsidering all t0e facts mentioned abo$e& I t0in, ?ic,el based Super allos are t0e best

materials for turbine blade applications. It 0as ma9imum ad$antages or merits to be used as

turbine blade.

21 roce!!in":#fter s0ortlisting t0e material to be used in turbine blades i.e.& nic,el based super allos& 5e need

to specif t0e processing routes b 50ic0 blades s0ould be manufactured using lo5est cost.

Important parameters to be considered are:

Table 2: roce!!in" Specification for Turbine Blade

,unction Turbine blade

b;ecti&e Minimi%e cost

+on!traint!

Material: ?ic,el based super allo

S0ape: solid 3/& ?oncircular prismaticMass: /epends on t0e si%e of turbine

Surface roug0ness: #& $er smoot0

,ree ur 1968.:

!orging is a s0aping process in 50ic0 t0e material in a rectangular or a billet s0ape is ta,en and it

is t0en 0eated to a 0ig0 temperature "usuall austenitic range) and t0en it is pressed in t0e dies

,no5n as forging dies to ma,e t0e re8uired or desired s0ape. In some cases& cold forging is also

carried out in 50ic0 t0e pre0eating step is missing t0is is normall done on relati$el soft

metals. In ot0er 5ords& material is s8uee%ed b appling large plastic deformations. T0is process

is 5idel used to s0ape steel or allo parts. T0ere are t5o ,inds of forging dies used in industries:

1. 6pen die& in 50ic0 t0e component limit is muc0 0ig0er but t0e precision is less. Blan, is

forced bet5een t5o dies t0at are open and t0e material is e9posed to t0e en$ironment. T0e

lo5er die is immo$eable and t0e upper die comes and stri,es t0e blan, and s0apes it.2. *losed die forging is t0e one in 50ic0 t0e dies -oin toget0er and t0e materials is forced to

ta,e t0e internal s0apes of t0e dies. T0is is t0e most precise form of forging but t0e

component si%e is limited. *omple9 s0apes can be gi$en to t0e parts using closed die forging.


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212 In&e!tent +a!tin" -*alpa;ian 2001.:

In$estment casting also ,no5n as lost 5a9 casting is a $er old casting tec0ni8ue for comple9

parts 5it0 $er 0ig0 precision. # 5a9 pattern is made and it is t0en dipped is a slurr. T0e slurr

material stic,s to t0e pattern. T0is is t0en dried and sintered. #fter t0is& t0e 5a9 is melted b

appling little 0eat and is remo$ed. T0en onl ceramic mold is left be0ind. T0is mold is t0en

fired to gi$e it final compactness. #fter t0is t0e melt is poured into t0e mold. Simple s0apes can

be made easil 5it0out use of e9ternal forces in t0e melt but for ma,ing comple9 and intricate

parts& air pressure or $acuum is sometimes necessar for 0ig0 precision. T0is process is suitable

for ma,ing parts 5it0 materials 0a$ing a 0ig0 melting temperature as t0e refractor material of

mold is stable at $er 0ig0 temperatures. It can 5or, 5it0 bot0 large and small batc0 si%es as per

re8uirement. Tpicall used for -e5elr ma,ing and dental implants. Most ad$ance use is to cast

nic,el and cobalt based allos.

Bot0 of t0e processing tec0ni8ues 5ere anal%ed and grap0s 5ere plotted b considering $arious

parameters as s0o5n belo5

,i"ure : #raphical +opari!on of roce!!in" Technique! -Di!creet &! +apital +o!t.


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,i"ure 3: #raphical +opari!on of roce!!in" Technique! -Surface 4ou"hne!! &! +apital +o!t.

,i"ure 5: #raphical +opari!on of roce!!in" Technique! -Di!creet &! 4elati&e +o!t Inde.

It is clear from t0e grap0s t0at capital cost of in$estment casting is muc0 lo5er t0an t0e forging

processes in case of bot0 discrete parts and lo5 surface roug0ness products. ;0ile in case of

comparing relati$e cost inde9 5it0 discrete parts production& forging seems better but t0e


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difference is not $er 0ig0 t0us I 5ill prefer in$estment casting o$er forging for producing

turbine blades.

Turbine Di!c

# gas


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max=R

2

2

2

But t0is ma9 stress s0ould be less t0en t0e fracture stress.

so& combining abo$e t5o e8uations gi$e us:

U

m=f

2

*onstraints:

M=f

,i"ure 6: Material Selection +hart -Yield Stren"th &! Den!it'.


Boron carbide

#luminum nitride

?ic,el c0romium allos

?ic,el based super allos

Tungsten carbide


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Titanium #llos

*arbon Steels

*ast iron

6ut of all t0ese possible materials& I 0a$e c0osen nic,el based super allos for turbine disc. Some

of t0e reasons are e9plained belo5:

Boron carbide: Boron carbide alt0oug0 $er 0ard and 0ig0 temperature stable compound& and

lig0t but it cannot be used in t0e manufacturing of disc of turbine because it is $er e9pensi$e to

be prepared. T0e tooling cost is also $er 0ig0 as it can onl be surface finis0ed or surface

modified using diamond grinding "Mat,o$ic0& 1'77). Moreo$er& t0e toug0ness of boron carbide

is also less t0en nic,el super allos.

T0e ma9imum ser$ice temperature of titanium allos is $er less appro9. * so t0e cannot be

used 0ere "eens& 23). Same is t0e case 5it0 carbon steels and cast irons. T0eir ma9imum

ser$ice temperature in around 4*.

#luminum ?itride: >ere again t0e problem of manufacturing limits its use as it is $er e9pensi$e

to be grinded using diamond. #lso t0e sintering temperature re8uired for aluminum nitride is

around 1'* 50ic0 is too 0ig0 and costl. T0ere is anot0er issue t0at aluminum nitride s0o5s

0drolsis issues in presence of 5ater. So moisture can affect its performance.

?ic,el based super allos "/a$is& 2)& nic,el c0romium allos& tungsten carbide 0a$e alreadbeen e9plained in t0e turbine blades section. 9cept t0ose general reasons of m selection& one

ot0er reason is t0at t0e ield strengt0 of nic,el super allos is t0e 0ig0est among all t0ese and its

densit is also lo5er t0en nic,el c0romium allos& tungsten carbide and tungsten allos. /ensit

of tungsten allos and tungsten carbides is also greater t0en super allos. So considering all t0e

manufacturing issues& general properties& densit and mec0anical properties so for me nic,el

based super allos seem to be t0e best c0oice for disc manufacturing material.


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2 roce!! Specification

Table 3: roce!!in" Specification for Turbine Di!c

,unction Turbine /isc


+on!traint!

Material: ?ic,el based super alloS0ape: solid 3/

Mass: 2


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,i"ure 7: +opari!on of Toolin" +o!t for riar' roce!!e!

,i"ure 8: +opari!on of +apital +o!t for riar' roce!!e!


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,i"ure 9:+opari!on of 4elati&e +o!t Inde for riar' roce!!e!

,i"ure 10: +opari!on of Section Thicne!! 4an"e for riar' roce!!e!

!rom t0e grap0s& it is clear t0at t0e forging relati$e cost inde9 is lo5 as compared to t0e 0ot

isotactic pressing tec0ni8ues but section t0ic,ness range and tooling cost is better in case of 0ot

isotactic pressing t0en t0at of forging. T0e capital cost is some0o5 comparable in bot0 of t0e


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cases. T0e c0oice is bit difficult but due to t0e abilit of 0ot isotactic pressing of ma,ing precise

and accurate parts 5it0 good surface finis0& I 5ill c0ose 0ot isotactic pressing. #s in forging

t0ere ma be some issues of surface o9idation and material softening at 0ig0 temperature

5or,ing. So& post forging treatments 5ill also cause a lot of mone addition to t0e process.

*onsidering all t0ese factors& 0ot isotactic processing seems to be t0e best c0oice for me.

3 Turbine Shaft

T0e transmission s0aft in a turbine is t0e first component to recei$e t0e po5er generated at t0e

turbine blade. T0e role of t0e s0aft in t0e 0dro,inetic turbine sstem is to transmit t0e tor8ue

generated at t0e turbine blades to t0e generator. T0e tor8ue and t0rust at t0e blades are t0e ma-or

e9ternal forces acting on t0e sstem and t0erefore are considered as t0e primar forces acting on

t0e s0aft. T0e t0rust does not lead to an bending moment because t0e 0ori%ontal component of

t0rust "acting parallel to t0e a9is of t0e s0aft) cancel eac0 ot0er due to t0e smmetr and

accounts to onl a normal force along t0e a9is of t0e s0aft. So t0e main forces acting on t0e s0aft

are t0e rotational forces.

31 erforance Specification

Table 5: erforance Specification for Turbine Shaft

,unction BeamFS0aft

b;ecti&e Minimi%ing mass for greater po5er to 5eig0t ratio

+on!traint!

>ig0 Torsional StiffnessDPa>ig0 Bending StiffnessD2MPa>ig0 corrosion resistance

>ig0 temperature stabilit. T='


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311 Bendin" !tiffne!!:

SB=EI

L3

but 0ere &

I=A

2

12Putting it in stiffness e8uation and eliminating # gi$es&

m= 12SB 1F2F3

E1/2 J

312 Tor!ional Stiffne!!:

ST=A

2

G

7L

putting in m to eliminate # gi$e:

m=[7ST

L3 ] 1F23F2

(G )1/2 J


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T0e constraints are: M1=E

1 /2

&M2=

G1 /2

,i"ure 11: Material Selection +hart -Shear Modulu! &! Den!it'.


21/25

,i"ure 12: Material Selection +hart -Youn"/! Modulu! &! Den!it'.


o5 allo steel

o5 carbon steel

Tungsten carbide

Stainless steel

?ic,el based super allos

?odular cast iron

;* and nic,el based super allo 0as been re-ected due to t0eir $er 0ig0 cost and $er 0ig0

densit. Moreo$er t0e processing is also $er difficult for t0ese materials. *ast iron is too soft

and it ma bend easil. o5 carbon steel degrades at 0ig0 temperatures and also t0e lo5

0ardness of lo5 carbon steel ma,es it unsuitable for t0is -ob. o5 allo steel is a good option as

it 0as a comparable densit and strengt0 $alues. It can 5it0 stand t0e loads and pressure.

Stainless steel is also a good option but it is brittle in nature and its formabilit is 2 50ile

formabilit of lo5 allo steel is 3. #lso t0e fracture strengt0 of lo5 allo steel is greater t0an all

of t0ese s0ortlisted materials. *onsidering t0e ease of fabrication& densit& strengt0 and cost I 5ill

c0oose lo5 allo steel for turbine s0aft.


22/25

32 roce!! Specification:

Table 6: roce!!in" Specification for Turbine Shaft

,unction S0aft


+on!traint!

Material: lo5 allo steelS0ape: solid 3/

Mass: ,g"min)

Tolerance .1


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,i"ure 1: +opari!on of Ma!! 4an"e! of roce!!e!

,i"ure 13: +opari!on of 4elati&e +o!t Inde of roce!!e!


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5 )oinin":

To -oin blades 5it0 disc& material is t0e same for t0ese i.e nic,el based super allos& t0e -oint is

ta,en as tie -oint and t0e forces acting on t0e blades are ta,en as bending forces. ?o5 t0e best

-oining met0od found using *Sedupac, is laser 5elding.

oining of blades and disc reference: "Singer @ #r%t& 1'()

6 Specification and Sourcin"

>asteallo K: "International& 1''7)

Inconel 73: "Inc.& n.d.)

dupac,: "*S& 21)

7 In!pection:6$er0auling of t0e gas turbine engines must be carried out 5it0 a gap of 1 to 3 ears. Besides

t0is t0ere must be a setup of regular inspections. !or t0ese parts of t0e gas turbine& I 5ould go for

t0e ?/T inspection met0ods. In t0is& Lltrasonic can be used for s0aft and also /PT testing can

be carried out to inspect t0e blades and disc. Besides t0is& radiograp0 is a $er good tec0ni8ue

to inspect t0e component 5it0 0ig0 accurac. eal time monitoring of rotar e8uipment during

ser$ice can be done. ;0ile t0e mac0ine or sstem is in ser$ice& t0e de$ice is broug0t near t0e

e8uipment and it automaticall monitors t0e condition of t0e components. It 0as a built in

stroboscope& camera and laser prometer. It detects t0e crac, automaticall and generates t0e

results.

8 (ifetie

4eference!

1. #$it%ur& B.& 1'(. METAL FORMING.. PROCESSES AND ANALYSIS. ?; N6+:

M*#;I& I?*.& ?; N6+.

2. Bo0idar& S. +.& /e5angan& . @ +aurase& +.& 213. #d$anced Materials used for different

components of as Turbine. International Journal of Sientifi Re!earh an" Mana#e$ent%

pp. 1


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. ura-arapu& ?.& ao& G. ?. B. @ +umar& I. ?.& 214. Selection of a Suitable Material and

!ailure In$estigation on a Turbine Blade of Marine as Turbine ngine using e$erse

ngineering and !# Tec0ni8ues. International Journal of u,an" e,Ser-ie% Siene an"

Tehnolo#+% 7"()& pp. 2'7

Documents

Material Selection Process for Gas Turbine Blade, Disk and Shaft with equations