CASE STUDIES OF FAILED COMPONENTS

Introduction

• Most of the current day failures are due to mistakes of :

– Operator

– Manufacturer

– Designer or

– Inspector

• It will be evident when we go through some of the case studies

Objectives

• To demonstrate by examples through actual reports investigated in Metallurgical Lab

Case study of Broken journal of wagon no. SR 27807 TG(L)RB

investigated at KGPW

Background

• A goods T/No. D/DRG LPG got derailed while on run with w/no. SR-27807 on 5.12.96 due to cold breakage of journal

• ROH (wagon) at PWS(Phulwari Sharif)/ER/DNR

Test conducted

• Visual examination & fracture study

• Chemical test

• Mechanical test

• Micro-examination

Visual examination & fracture study

• The axle fractured transversely at a distance of 271 mm from one of the ends.

• The f/f showed fatigue (70%) originated from a weld spot (mainly)

Chemical & Mechanical tests

• Chemical test: – Carbon%....................................0.49

• Mechanical test: – Hardness(HB)………………………….179,183

(on the section away from fracture)

– Hardness(HB)…………………………..509,516

(on the surface close to weld spot)

• UTS(kgf/mm2)………………………….62.5 (calculated from average hardness value)

Micro-Examination

• Section-Longitudinal

• Observation:(etched)-

– martensite & bainite

(close to fracture)

– ferro- pearlitic structure(ASTM grain size 6&7)

(on the body away from the fracture)

Spec No. R-16/1995

Test parameter Specified

UTS (N/mm2) 550-650

Chemical composition:- C% Mn% Si% Cr% Ni% Mo% V% Cu% S% P%

0.45-55 1.12 Max 0.15-0.46 0.30 MAX 0.30 MAX 0.05 Max 0.05 Max 0.30 Max 0.03 Max 0.03 Max

Micro-exam:- Grain size Structure

Not coarser than 5 Normalised structure

Discussion

• VE indicated presence of weld spot at the origin of f/f

• Chemical composition, Hardness & UTS-OK as specified in IRS:R-16

• Micro structure-OK

Conclusion

• VE suggested that the axle had failed due to initiation of fatigue crack mainly from weld spot

• Sufficient heat might have generated due to drip of the weld pool on the axle surface forming martensite/ bainite which have acted as an origin of fatigue crack.

Case study of failed Helical spring of L/No.15506 WDP2 investigated

at M&C/RDSO

Background

• Date of fitment…………..20.02.2002

• Date of failure…………….02.04.2002

• Life spanned………………one month (approx)

Tests conducted

• VE & fracture study

• Chemical comp & Hardness test

• Metallographic exam

• Supplier: M/s G.B.Springs

VE & Fracture study

• The spring fractured from 2nd coil in fatigue manner (small fatigue zone covering a depth of about 11 mm)

• Noticed biting/rubbing (homing- 2nd coil rubbing with the 1st coil) marks on almost whole of the coils

• Observed a longitudinal surface crack adjacent to biting mark on the 2nd coil.

Showing Biting/rubbing marks

Showing small fatigue zone

Chemical & Hardness tests • Chemical composition:

C%...........................0.56

Mn%........................0.95

Si%...........................0.24

Cr%..........................1.15

Mo%........................0.18

V%............................0.10

• Hardness (BHN): On the surface………415, 429

At the core……………415, 429

Metallographic exam

• Macro-exam (deep etched in 1:1 HCl) – Revealed no abnormality

• Micro-exam: – Unetched (Inclusion rating on longitudinal

section): • Revealed 0.5 Thin (sulphide) & 0.5 Thin oxide

• Etched: (Transverse section): – Decarburisation- 0.08 mm

– Structure: fine tempered martensite

Discussion

• VE revealed small fatigue zone initiated from longitudinal surface crack present adjacent to biting/rubbing mark.

• Presence of biting marks indicates that the spring was excessively loaded. Due to such load a localized surface crack was produced which led to formation of fatigue & ultimate fracture of spring

• Chemical composition, Hardness, Macro-exam & Micro-exam as per spec no.WD-01-HLS-94(Rev.1)……………OK

Spec. IS:3195/95 Gr 51CrMoV Test parameter Specified

Hardness (BHN) 415-460 (as perspec no.WD01-HLS-94(Rev.1)

Chemical composition:- C% Mn% Si% Cr% Mo% V% S% P%

(as per IS:3195/95 Gr 51 CrMoV) 0.48-0.58 0.70-1.10 0.15-0.40 0.9-1.2 0.15-0.25 0.07-0.12 0.035 Max 0.035 Max

Decarburisation, mm 1.9 max (0.5% of nominal dia)

Micro structure TM

Inclusion rating: on longitudinal section

Inclusion Rating Sulphide

Thin Thick Oxide Thin Thick

Found 0.5 - 0.5 -

Specified as per spec no. WD-01-HLS-94(Rev.1)

2.0 max 2.0 max 2.0 max 2.0 max

Conclusion

• The spring had failed due to fatigue initiated from localized surface crack formed due to excessive load on spring, which is evident from sign of homing of coil.

Case study of Failed Wheel Disc of L/No. 23995 WAG-5H investigated

at RDSO

Background

• Fitted on 12.02.1999 • Failed in service on 21.12.2001 • Last checked on 28.12.2000 • Expected service life 3 years(approx) • Condemning criteria 1016 mm

Tests conducted

• VE & fracture study & Wear Measurement • Chemical test • Mechanical test • Metallographic Examination

VE & fracture study • The wheel fractured by

fatigue • A ‘V’ shape 11.9 mm

deep punch mark (against 10.0 mm Max. specified) on front rim side

• Slight corrugation on the tread surface (more towards brake application area)

• Wheel tread worn out up to 30 mm depth

Photograph showing the cracked pieces with deep punch marks on front rim side and fracture ends shown by arrow head.

Photograph showing the slight corrugation, more towards brake application area

Photograph showing the fatigue fracture initiated from deep punch mark.

Photograph showing the close view of the fatigue zone.

Chemical test

• Chemical Comp: C%...................................0.65

Mn%...................................0.76

Cr%..................................0.10

Ni%..................................0.08

Mo%..................................0.01

Cu%................................0.073

V%.................................0.007

S%.................................0.025

P%.................................0.022

Mechanical tests

• Hardness(HB): – 6mm below existing tread surface...302,293

– 7mm below existing tread surface covering HAZ……………………………………………….248, 255

– 17mm below existing tread surface..285

• Tensile test: – UTS(N/mm2)………………………………….997.70

– Elongation%.......................................13.39

• Impact Energy in J(v-notch Charpy test)-7.0

Metallographic Examination

• Macro-exam: – Revealed HAZ

• Micro-exam(one piece from std location & other containing punch mark ) – Std location:-

• Unetched: (Inclusion rating):2.0 Thin (sulphide) & 1.5 Thin (oxide)

• Etched: Fine pearlite & ferrite at places with ASTM grain size 4&5

– Containing punch mark: Decarburisation around punch mark

– Fine pearlite with dispersed specks of ferrite with ASTM grain size 6-7 at HAZ

Spec. IRS-R-34/99 Test parameter Specified

UTS (N/mm2) E% Hardness (BHN) up to depth of 30 mm from tread surface

980 min 8.0 Min 300-341

Chemical composition:- C% Mn% Si% Cr% Ni% Mo% V% Cu% S% P%

0.57-0.67 0.60-0.85 0.15 Min 0.25 Max 0.25 Max 0.06 Max 0.05 Max 0.28 Max 0.03 Max 0.03 Max

Micro – exam:- Grain size Structure

Not coarser than 5 Normalised structure

Discussion

• VE revealed that wheel had broken due to fatigue initiated from deep punch mark on front rim side which had acted as high stress raiser for initiation of crack

• Chemical comp, physical properties & inclusion rating-OK

• Macro-exam revealed HAZ (11.3mm depth) [no HAZ away]caused due to brake binding, resulted heat generation in the rim region. The abnormal rise in temp may cause reversal of stress

• Decarburisation around the p/mark had aggravated the initiation of fatigue

Conclusion

• The failure is attributed to the presence of deep p/mark associated with decarburisation around it. Reversal of stress might have caused due to rise in temp input by brake binding as evidenced by change of micro-structure up to a certain depth in tread.

Remedial measure

• B/Binding to be totally avoided

• P/mark on the hub only

• UST to prevent failures from internal flaws

Case study of failed Crank Shaft of Loco No.14049 of Ernaculam Diesel

Shed

Background

• Mfr…….M/s CSR/Ziyang

• Date of mfg……..7/2006

• Date of fitment…26.9.2006

• Date of failure…28.5.2009

• Spec: DLW spec no.31PD5203(Gr42CrMo)

Tests conducted

• VE & fracture study

• Chemical comp & Hardness test

• Metallographic exam

VE & Fracture study • 90% fatigue initiated

from sharp edge of key way slot at wheel seat portion

• Observed dents, metal deformation & scoring marks on cyl surface of gear seat journal adjacent to the collar.

Key way

Photograph showing counter fracture faces of Crank shaft .

Photograph showing dent

mark , metal deformation

and scoring mark on g/seat

journal

Nucleus Of fatigue

Initiation

of fatigue

Chemical comp & Hardness test

• Chemical comp:

– C%0.44, Mn%0.88, Si%0.30, Cr%0.99, Mo%0.20, V%0.0008

– Specified:C%0.38-0.45; Mn%0.5-0.8; Si%0.17-0.37; Cr%0.9-1.2;Mo%0.15-0.25;V%--

• Hardness:

– On hardened layer: Rc-46,47 (sp- Rc..44-50)

– At parent metal (sec): BHN-244,245(sp..241-302)

Metallographic test • Macro-exam: Depth of

induction hardening-3.4-9.0 mm

• Micro-exam-

– Inclusion rating:

• 1.0 thin(sulphide); 1.0 oxide (thin)

– Structure:

• TM on hardened layer & resolved & unresolved pearlite as genl structure

Induction

Harden

Layer

3.40 mm

9.00mmm

Photo macrograph showing induction hardened layer of crank shaft

Photo micrograph showing

mainly resolved &unresolved

pearlite in the matrix of ferrite.

Discussion • VE indicated sharp edge of key way slot at

wheel seat portion

• CC & Hardness—OK

• Metal deformation & scoring mark on the wheel seat journal shows that there was relative motion between split gear and journal meaning the interference between the two matting surfaces were lost and the key fitted in the key way would have also damaged.

Discussion • Relative motion between split gear & wheel seat

journal produced sudden forces resulting in initiation of fatigue from the sharp edge of key way.

• Presence of non uniform case depth on the main bearing journal varying from 3.4 mm to 9.00 mm showed the possibility of building up of non uniform residual compressive stresses, release of which, during service would have resulted distortion in the crankshaft.

• Distortion would have resulted in unusual vibration in the crankshaft and consequential fatigue initiation from the stress raiser (key way & seat of gear seat journal).

Conclusion

• The failure of crankshaft in fatigue manner covering 90% fatigue initiated from key way may be attributable to relative motion between split gear and wheel seat journal.

05 Case studies of knuckles investigated at LLH(W)

Particulars

Case No.

S/No. at LLH(W)

W/No. Dt of failure

POH IOH/ROH

R/Dt

1. S/183/11 w/no.BVZISWR86150907383 30.3.11 TEXMA 16/4/09

BIA/12/11/10

NA

2. S/180/11 w/no.CR-BCNMI/L-151610 01.4.11 KTTW-07/03/07

NJP 09/09/10

03/2013

3. S/211/11 w/no.SE-175741(BOXN/Ld 19.4.11 RVPS-30/12/08

VSPS-22/7/10

08/13

4. S/289/11 w/no.WR BCN/L 311104/ 25889

30.5.11 JUDH-27/1/11

NA 03/17

5. S/316/11 w/no. BOBYN 700809/ 00354

07.6.11 BESCO 27.03.09

NA NA

Photographs of failed knuckle

Blow Hole & Shrinkage cavity

S/No.316-11

Darkened (oxidized) area indicating presence of old crack

S/No.289-11

S/No.211-11

Non-Metallic/Slag inclusions

Shrinkage Cavity

S/No.183-11 S/No.180-11

Non-uniform wall thickness

VE

Case N0.

Location of fracture

Nature of fracture

Other observations Id. mark

1. 96 mm from the tail end

Tr & crystalline

Shrinkage cavities/porosities (25% of fractured area)

HTE, S, 1501

2. 120 mm from the tail end

Tr & crystalline

Core shift-noticed Wall thickness-not uniform (it was20 mm at one face & 30mm at other face

HTE, RIL, 3 05

3. 180 mm from tail end

Tr & crystalline

Non-metallic/ slag inclusion( 5% of fractured area)

HTE, RIL D 435, 308

4. 50 mm from the nose end

Tr & crystalline

Oxidised area on the f/f indicating presence of old crack

RANGA, 511 THE

5. 50 mm from the nose end

Tr & crystalline

Shrinkage cavities/blow holes (60% of fractured area)

HTE, Rest not clear

Tests

Case No.

Chemical composition(%) Hardness (BHN)

Micro exam

C Mn Si Cr Ni Mo

1. 0.30 1.50 0.50 Nil Nil Nil 227 TM

2. 0.28 0.90 0.40 Nil Nil Nil 337 TM

3. 0.30 1.00 0.50 0.50 0.60 0.20 357 TM

4. 0.30 1.00 0.50 0.50 0.60 0.20 357 TM

5. 0.31 1.05 0.52 0.55 0.55 0.22 268 TM

Specified

0.28-0.33

0.80-1.10

0.40-0.60

0.50-0.80

0.50- 0.80

0.15- 0.25

261 – 291 TM

Discussion

Case No.

VE Chemical composition Hardness Micro exam

1. Presence of casting defects reduced the load bearing capacity & acted as points of stress concentration zone

Does not conform to latest spec no.48-BD-02, Gr.E amendt no.2 of Jan-2007

Lower than specified

Satisfactory

2. --Do-- --Do-- Higher than specified

Satisfactory

3. --Do-- Conforms --Do-- Satisfactory

4. Presence of old crack Conforms --Do-- Satisfactory

5. Presence of casting defects reduced the load bearing capacity & acted as points of stress concentration zone

Conforms Satisfactory Satisfactory

Conclusion

Case no.

Conclusion

1. The failure is considered under impact loading accentuated by lower hardness & presence of casting defects

2. The failure is considered under impact loading accentuated by higher hardness & presence of casting defects

3. The failure is considered under impact loading accentuated by higher hardness & presence of casting defects

4. Presence of old crack acted as prime cause of failure & higher hardness as a contributory factor

5. Presence of casting defects (60% of total fractured area) gave rise to weak zone & caused failure in service

Remedial measure Case No. Remedial measure

1. i)HT to be carefully monitored to achieve stipulated hardness ii)Appropriate steps to be taken to prevent casting defects

2. i)HT to be carefully monitored to achieve stipulated hardness ii)Appropriate steps to be taken to prevent casting defects

3. i)HT to be carefully monitored to achieve stipulated hardness ii)Appropriate steps to be taken to prevent casting defects by adopting (a)proper metal pouring technique (b) thorough oxdn (c)effective skimming

4. HT to be carefully monitored to achieve stipulated hardness & also preventing development of any crack during manufacturing stage

5. Proper solidification process should be adopted & moulds should be properly dried to avoid formation of blow holes/ shrinkage cavities.

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