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FAILURE ANALYSIS CASE STUDIES I1 A sourcebook of case studies selected from the pages of Engineering Failure Analysis 1997- 1999 An imprint of Elsevier Science... PREFACE It is now thre

FAIZURE ANAZYSIS

CASE SZZLDIESII

Pergamon

Failure Analysis

FAILURE ANALYSIS CASE STUDIES I1

A sourcebook of case studies selected from the pages of

Engineering Failure Analysis 1997- 1999

An imprint of Elsevier Science

ELSEVIER SCIENCE Ltd

The Boulevard, Langford Lane

Kidlington, Oxford OX5 1 GB, UK

0 2001 Elsevier Science Ltd All rights reserved

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First edition 2001

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PREFACE

It is now three years since Elsevier Science published the first book of Failure Analysis Case

Studies selected fiom volumes 1 , 2 and 3 of the journal Engineering Failure Analysis The book has proved to be a sought-after and widely used source of reference material to help people avoid

or analyse engineering failures, design and manufacture for greater safety and economy, and assess operating, maintenance and fitness-for-purpose procedures In the last three years,

Engineering Failure Analysis has continued to build on its early success as an essential medium for the publication of failure analysis cases studies and papers on the structure, properties and behaviour of engineering materials as applied to real problems in structures, components and design

Failure Analysis Case Studies I1 comprises 40 case studies describing the analysis of real

engineering failures which have been selected from volumes 4, 5 and 6 of Engineering Failure

Analysis The case studies have been arranged in sections according to the specific type of

failure mechanism involved The failure mechanisms covered are overload, creep, brittle fracture, fatigue, environmental attack, environmentally assisted cracking and bearing failures The book constitutes a reference set of real failure investigations which should be useful to professionals and students in most branches of engineering My sincere thanks go to the authors

of the case studies for finding the time to communicate their experiences to the wider world for the benefit of us all

Shear failure of a road-vehicle steering shaft

J.H Cleland and D.R.H Jones 1 1

Breakup of the firewall between the B and C modules of the Piper Alpha

platform - I Analysis by hand calculation

A.C Palmer 19

Failure of a flexible pipe with a concrete liner

M Talesnick and R Baker 3 1

Torsional failure of a wire rope mooring line during installation in deep water

C.R Chaplin 45

Creep failures

Type I11 creep cracking at main steam line welds

K.G Sedman, J.C Thornley and R.M Griffin 63

Creep failure of a spray drier

P Carter 73

Catastrophic failure of a polypropylene tank Part I: primary investigation

P.R Lewis and G.W Weidmann 79

Catastrophic failure of a polypropylene tank Part 11: comparison of the DVS 2205

code of practice and the design of the failed tank

G.W Weidmann and P.R Lewis 97

Brittle fracture

Investigation of the M V Kurdistan casualty

S.J Garwood 117

Investigation of failed actuator piston rods

T.F Riitti and E.J Wentzel 139

Premature failure of prestressed steel bars

A Valiente and M Elices 147

Premature fracture of a composite nylon radiator

P.R Lewis 157

P.A Withey 185 Low-cycle fatigue of titanium 6A1-4V surgical tools

H Velasquez, M Smith, J Foyos, F Fisher O.S Es-Said and G Sines 193 Failure analysis and experimental stress analysis of a threaded rotating shaft

R.B Tait 199

An investigation of the failure of low pressure steam turbine blades

N.K Mukhopadhyay, S Ghosh Chowdhury, G Das, I Chattoraj, S.K Das and

D.K Bhattacharya 211 Vibration-induced fatigue failure of an impulse line

K.R Al-Asmi and A.C Seibi 225 Malfunctions of a steam turbine mechanical control system

J.H Bulloch and A.G Callagy 235 Fatigue failure of hold-down bolts for a hydraulic cylinder gland

C Tao, N Xi, H Yan and Y Zhang 241 Analysis of a vehicle wheel shaft failure

J Vogwell 247

Fatigue failure analysis of a leg press exercise machine

P.J.Vernon and T.J Mackin 255 Failure analysis of rubber fuel pipes in aero-engines

G Fu 267

Environmental attack

Failure of austenitic stainless steel components used in nitrogen oxide plant

V.M.J Sharma, A.K Jha, P Ramesh Narayanan, S Arumugham and T.S Lakshmanan 277 Corrosion of central heating systems

D.R.H Jones 285 Crevice corrosion of 3 16L caused by chloride partition in water-butanone mixtures

J.H Cleland 301 Type I pitting of copper tubes from a water distribution system

P.J.L Fernandes 307 Corrosion of flexible waveguides

D Papatheodorou, M Smith and O.S Es-Said 3 13 Failure of automobile seat belts caused by polymer degradation

J.M Henshaw, V Wood and A.C Hall 317 Oxidation failure of radiant heater tubes

K.B Yoon and D.G Jeong 33 1

Environmentally assisted cracking

Sustained load crack growth leading to failure in aluminium gas cylinders in traffic

J.W.H Price, R.N Ibrahim and D Ischenko 345 Hydrogen-assisted stress-corrosion of prestressing wires in a motonvay viaduct

L Vehovar, V Kuhar and A Vehovar 357

ix

Failure analysis of camer chain pins

G.A Slabbert, J.J McEwan and R Paton 365

Unusual cases of weld-associated cracking experienced in a high temperature

catalyst reduction reactor

M.L Holland 373 Hydrogen cracking of ferritic stainless steel thermal storage tanks

S Konosu and T Nakaniwa 383

Hydrogen embrittlement failure of hot dip galvanised high tensile wires

N.K Mukhopadhyay, G Sridhar, N Parida, S Tarafder and V.R Ranganath 393

Bearing failures

Contact fatigue in rolling-element bearings

P.J.L Fernandes 409

An air crash due to fatigue failure of a ball bearing

I Salam, A Tauqir, A U1 Haq and A.Q Khan 415

Failure analysis of a condensate pump shaft

A.M Lancha, M Serrano and D Gdmez Briceiio 425

Author Index 443

4

Fig 1 Damaged silos: view of the site

k l i - I , , / , i , ( , , , ,

Fig 2 Bolted joints of the sheets used for the silo In the lower part, a reinforcement nng was attached

occurred by rupture of the boltholes of the vessel in circumferential and longitudinal directions (Fig 4)

After the search had been carried out, specimens were taken, as detailed in Table 1

After the accident, the silo was still full up to the seventh ring (counted from the bottom), as can

be seen from Fig 5

(IV) level after bursting

!

I

Fig 4 Longitudinal bolted joint, presumably at location of start of rupture

Table 1 Specimens and samples taken

6

Fig 5 Top view of failed silo, showing remaining filling level

2.2 Tests for traces of an explosion

Specimens F were subjected to laboratory tests to detect possible traces of heat influence by fire

or explosion No such traces could be found Thus, one can conclude that failure was not caused

by the explosion of methane or any other gas produced in the silo by fermentation

2.3 Tensile tests

The sheet metal was tested using specimens BR, CR, BP and CP, as shown in Fig 6 and

Table 2

Fig 6 Specimens for mechanical tests

Table 2 Results of tensile tests on sheet material from silo Yield Tensile Reduction Elongation Uniform strength strength of area (5 diameters) elongation Specimen Orientation ( N ~ I I - ~ ) ( N ~ I I - ~ ) (”/) (”/I (”/)

BR I to joint 288 341 18 4 4 5 25

CR I to joint 261 316 I1 47.5 24

BP 11 to joint 300 345 IS 43 24

1) 278 313 70 46.3 29

Fig 7 Behaviour of bolted joints in tension tests

Specimens B 1, B.2, C 1 and C.2 were tested for the strength of the bolted joints From Fig 7, it can be seen that they started to yield between loads of 15 and 25 kN, and that the deformation before fracture was in most cases more than 25 mm

2.4 Determination of the density of the slurry

density of 1.05 kgl-I

3.1 Determination of$lling level from records of the user

After the accident, the user of the silo supplied notes of deliveries, from which the theoretical

This height corresponds to filling up to the upper edge of ring 7 (counted from the top)

filling level at the time of the accident could be calculated (Table 3)

3.2 Stress analysis of boltedjoint

material, with Rpo.2 = 283 MPa and R, = 330 MPa This gives for shear:

The average values for yield and ultimate strength are provided by the tensile tests on the sheet

Density according to tests, maximum 1.05 kgl-'

Base area of silo (inside) 27.98m2 Theoretical level 13.9m

8

3.3 Assessment of the theoretical bursting pressure

This also corresponds to the mean value of the forces calculated from Eqns (3) and (4)

In the test, the lower bound for the strength of the bolted joint was measured as FFractuIe = 22 kN

22 x 103

T= - 204Nmm-’

108 The burst pressure can be calculated from this, using the diameter of the silo (6m), as

2 x 204

The corresponding level over the ruptured ring is

This is equivalent to the height of 4.7 rings of the silo, and would mean that the level of the slurry was approximately in the middle of the third ring (counted from the top)

3.4 Spurting distance

From the visual inspection at the site of the accident, the approximate spurting distance of the slurry of 30m is known Since this was not a simple parabolical throw, but the jet was dispersed further after hitting the ground, the process can only be calculated approximately The intention of such an assessment is, of course, to determine the filling height of the silo

The horizontal velocity of the jet is given by u = q S H , and from the distance the jet travelled one obtains

9

= Dd2(HL - Ah) ’

Thus, the height of the liquid above the leak is

d* = S/D is the portion of the distance that the jet travels after hitting the ground, cp is the factor

of constriction of the jet (normally cp I I), and the other symbols are explained by Fig 8 If different

9

levels HL for the first leak and different ratios of sloshing (d* = 6 / D ) are assumed, it can be seen

from Fig 9 that the silo must have been filled to the top, and the liquid must have sloshed relatively

far after hitting the ground to have produced the observed pattern on the site

4 CONCLUSIONS

Thc visual inspection at the site of the accident showed the typical picture of failure by

the overpressure, were not found A pressure above atmospheric pressure can also be excluded because the necessary safety devices were installed and operative

According to the manufacturer of the silo, it was permissible to fill the silo with liquid up to the seventh ring (counted from the bottom), i.e ca 10 m high

The assessment of the filling height from the observed spurting distance also points to a filling level practically at the top of the silo

The design, manufacture and assembly of the silo can be judged as proper, suitable and according to normal engineering practice

Tests on the material also indicate a higher level than the seventh ring (counted from the bottom) This is supported by the observed deformations in the failed bolted joint of the silo

An additional argument against the statement of the user related to the filling level is the fact that the silo was still filled to the middle of the tenth ring (counted from the top), although the whole neighbourhood was covered with slurry from the silo

Based on these findings it can be said that failure of this silo was caused by filling it to too high a level with liquid instead of forage

It cannot be completely excluded that a mix-up in the way of counting the rings has contributed

to the failure Whereas one would normally count the rings starting from bottom, as for buildings, the manufacturer of the silo counts the rings starting from top, because the silo is

erected that way, assembling first the top, then putting rings under the top ring until the intended height of the silo is reached

Acknowledgemenf-The calculations were performed by R Primas, Section Materials and Structural MechdnicsiJoining Technology of EMPA