R&D-PRC-SRC

Surface Conditioning & Interaction courseFocus areas: Rolls, Defects & Inspection

Champion: Sudhansu Pathak

Lecturer: Dr Henk Bolt & Dr Lene Hviid

March 2013 - Jamshedpur

2Surface Conditioning & Interaction course

Time schedule

1. Rolls

training

2. SIS

training

1. Rolls

training

2. SIS

training

1. Rolls

training

2. SIS

training

Two sessions

in plants

(choice)7th of March

15.00 to

16.00

LUNCH

11.30 to

12.45

BREAK

10.45 to

11.30

BREAK

9.00 to 10.30Thursday

Exercise

customer

defect

complaint

Lec. 8

A3 solving

method for

defects

Lec. 7

Inspection &

Coilgrading

Lec. 6

Surface

inspection

and control

Lec. 5

Quality

control

SDC

6th of March

16.15 to

17.15

BREAK

15.00 to

16.00

LUNCH

11.30 to

12.45

BREAK

10.45 to

11.30

BREAK

9.00 to 10.30Wednesday

Exercise

Rolls/lubric.

problem

Lec. 4

Lubrication

Lec. 3

Rolls failure

& Rolls

database

Lec. 2

Performance

of rolls &

surface

Lec. 1

Importance

of Rolls5th of March

16.15 to

17.15

BREAK

15.00 to

16.00

LUNCH

11.30 to

12.45

BREAK

10.45 to

11.30

BREAK

9.00 to 10.30Tuesday

3Take good care of Rolling Mill Rolls Quality & Condition

to ensure safe & smooth rolling

This lecture will highlight roll failure analyses, mechanisms and

prevention in development: TSG-wide roll defects & failures expert system

A focus on rolling mill rolls within Tata Steel

Rolling Failures & Roll Failure Prevention expert system development for rolls defects & failures

Lecture 3

5Topic No. 1: Safety

Safety in roll usage =

priority no. 1 !!! General risk of handling heavy items

Specific risk:

catastrophic roll spalling

-1200

-1000

-800

-600

-400

-200

0

200

400

0 50 100 150 200 250

Depth in radius (mm)

A

p

p

r

o

x

i

m

a

t

e

t

a

n

g

e

n

t

i

a

l

r

e

s

i

d

u

a

l

s

t

r

e

s

s

(

M

P

a

)

Typical stress distribution in

forged 5%Cr steel work roll

Forged rolls: very high internal stress levelsup to 1000 MPa

Large amount of energy stored in roll

Defect in roll:Sudden energy release can occur in violent way Inherent explosion risk

Also CPC-HSS rolls are high-stress rolls>500 MPa

6Risk analysis

Risk = (probability) * (effect)

Risk of personal injuries due to roll failures =

(probability of a roll failure) *

(probability of someone being struck) *

(effect of flying roll piece on person)

7Probability of a Roll Failure

Any defect origin could create an explosion risk:

defect origin

manufacturingflaw

rolling incidentinstantaneous damage

fatigue; undiscovered /insufficiently removed

damage fromprevious incident

Rollmakers:- Roll quality !- Trend:

quality versusrequirements

Roll users:- Rolling mill

process stability- Incoming HR strip

quality

Roll users:- adequate roll change,

redress, NDT scanroutines

NDT specialists:- NDT hardware

& expertise

8Instantaneous roll failures

moment & locationof a roll failure

instantaneousfailure in mill stand

during rolling

Immediate riskvery low

Catastrophic effect of rather heavy cold rolling process incident

on conventional forged 5%Cr steel work rolls

Strip derailment at full speed

Immediately followed by roll spalling in mill stand

9Probability of person being struck

by roll piece

moment & locationof a roll failure

instantaneousfailure in mill stand

during rolling

delayed failureafter mill incident

(minutes, hours, days)

unexpected failureoutside mill

Immediate riskvery low

Comprehensive mill &roll shop procedures

Rare butmost dangerous

- suspect rolls:quarantine

- covers- handling-

- Early defect detection& adequate removal

- Reduce explosive natureof roll spalling

- Stress relievemay be incomplete

- Knock-on damagingof other rolls in mill

10

Partially spalled rolls can still be

dangerous !

Fatigue path hidden by a bridge

surrounded longitudinally by two

cone shaped-spalls.

Large stresses still present

Fatigue path evident on the fracture

face after removal of the bridge.

Stresses relieved

11

Roll inspection

Hardness Testing (by rollmaker) Equotip (LD, LE) Vickers (HV)

Shore-C, Shore-D Rockwell-C

Manual NDT methods Visual Testing (VT)

Dye Penetrant Testing (DPT)

Magnetic Particle Testing (MPT)

Etch testing (3 - 20% nital)

Manual Ultrasound Testing (UT)

Acoustic Emission (AE)

NDT methods for automatic roll inspection systems Automated Eddy Current Testing (ET)

Automated Ultrasound Testing (UT)

Electro Magnetic Acoustic Testing (EMAT)

Dye Penetrant Testing

(DPT)

Nital-etched roll surfaceEvidence of bruising.

Note the presence of longitudinal

fire cracks within the bruise

Surface crack made

visible with MPT

12

Hardness testing

Check for:

Work hardening (particularly back-up rolls !) Softening

Hardness drop during roll life

Hardness heterogeneities Equotiphardness test being performed on a roll barrel

Small BUR barrel spalling

due to work hardening

13

Eddy Current Testing (ET) - Principle

Conductive material(e.g. roll)

Coil

Coil's

magnetic field

Eddy currents

Eddy current's

magnetic field

eddy current

disturbance:

sudden => crack

gradual => bruise

14

ET roll inspection

Advantages+ easy to automate

+ bruise detection

+ sensitive

Disadvantages- only surface defects

- no clear relation between ET signal and

defect size/defect harmfulness

tight cracks / electrical bridging cracks- magnetism interferes with ET signal

Cracks

Bruises

Since its introduction in

the 80-s, routine ET

inspection in roll shops

has greatly contributed

to the reduction of roll

spallings and increased

roll performance

15

Ultrasound Testing (UT) Principle

High frequency sound waves are introduced into a material and they are

reflected back from surfaces or flaws.

Reflected sound energy is displayed versus time, and inspector can

visualize a cross section of the specimen showing the depth of features

that reflect sound.

0 2 4 6 8 10

initial pulse

crack echo

back surface echo

Oscilloscope, or flaw detector screen

plate

crack

16

UT roll inspection

Advantages+ versatile

+ detects deep-seated defects

+ sensitive

+ defect sizing & depth (tof)

Wave types

- Straight beam waves: 0 longitudinal 0.5-1 MHz for deep / through roll inspection ~ 2 MHz for standard applications up to 10 MHz for sub-surface defect detection manual and automatic UT systems in roll shops

- Shear waves: 45/60/70 transversal (angle beam)

- Several types of surface acoustic waves (SAW): 90 Sensitive to (sub-)surface defects 5 mm depth Surface waves, longitudinal Rayleigh surface waves, transversal Creep surface waves, longitudinal Manual probes require skilled operators CM2 IJmuiden has 2 novel automated SAW+UT(0)+ECT combi systems

US2 depth

Disadvantages- coupling required

- complicated, and sensitive to dirt

- not sensitive for bruises

- defect orientation affects detectability

- dead zone

17

Topic No. 2: Incident resistance

Incident resistance in general very important Even without safety aspect

Strip breaks, pinches, strip derailments, also minor incidents

Mill incidents excess roll stock loss often >50% of total work roll consumption in tandem mills

scrap, salvaging, extra grinding

Roll shop effort Impact on daily mill operations (roll changes)

Tolerance for mill incidents

key requirement for tandem mill rolls

Ideal roll: not affected by any incident

2nd best solution: no effect of minor incident;

minimal redress after big incident

slow crack propagation

18

Hardness-vs-depth curve

in damaged work roll

6 mm on radius

3%Cr steel work roll no. 687390typical damage after medium-heavy strip break

thermal

cracking

strip scrap

adhering to roll

strip scrap

work roll

200 m

optical

micrograph

nital-etched

sample

19

Incident/thermal impact resistance:result of required grade & heat treatment

Forged 5%Cr steel rolls

650

700

750

800

850

900

100 150 200 250 300 350 400

Tempering temperature (C)

V

i

c

k

e

r

s

h

a

r

d

n

e

s

s

incident

resistance

wear

resistance

Forged rolls in cold millsHigh barrel hardness requiredLow tempering temperature = key limiting factor for incident resistanceConventional forged roll grades: trade-off

0

0 time

t

e

m

p

e

r

a

t

u

r

e

HSS, semi-HSS, HiCr steel (HiCr iron):high-T austenitising

+ multiple temperings

Heat treatment for (enhanced) ICDP, (S)NG, (HiCr iron):

only double/triple tempering

~1000C

~550C

~500C

Incident

resistancewear resistance &

anti-roll mark properties

Cast rolls (e.g. in hot strip mills)Maximum achievable barrel hardness lowerRoll mark resistance and strip cleanliness less critical than in cold millsHigher alloying wear resistanceHigh tempering temperature thermal impact resistance

Other heat treatment key aspects: temperature homogeneity over roll barrel

T-t combinations adequate for

retained austenite transformation

residual stress decrease

Effect of poor heat treatment:

HiCr steel roll barrel surface with

non-uniform hardness showing

premature thermal degradation

20

Rail Failure analysis example: spalling of cold mill work

roll 687463 - roll history (1)

5-stand tandem batch cold mill CM21 IJmuiden, 29 April 2006

Tail pinch work roll 687-463 in stand #1 damaged.

Roll immediately changed and placed for 48 hours in quarantine (bomhok).

cracks

bruises

4 May 2006

First grinding pass, followed by first UT/ET scan

ET: Bruise and Crack indications detected.

UT: no subsurface (>2 mm depth) indications

21

Failure of work roll 687463: roll history (2)

4 May - 24 July 2006

Multiple grinding passes. Total stock

removal 1,61 mm (on )

Bruise & Crack signals now below

threshold roll released.

Max. Bruise value =0.53 V. i.e still quite

significant.

25 July 2006, 22:45 h: Work roll 687-463 inserted into stand #2 top side.

26 July 2006, 2:30 h:

After rolling 990 tonnes, work roll 687-463 suddenly spalls during strip acceleration.

Spalled roll piece disrupts the rolling process

strip break between stands #2 & #3.

havoc; all 10 work rolls damaged; also back-up rolls in stand #2. Mill down for 4 hours to clean up; all damaged rolls in quarantine (bomhok)

cracks

bruises

22

Failure of work roll 687463:

Inspection of spalled work roll (1)

9 August 2006

Inspection of spalled work roll

Fatigue pattern observed

(ribbon fatigue spall or cat tongue).

23

Ribbon fatigue spalling

Crack propagation direction is

opposite to the revolution direction

of the roll

6

54

3

21

24

Failure of work roll 687463:

Inspection of spalled work roll (2)

9 August 2006 (continued)

Initiation point localised:

crack.

Location coincides with old

bruise indication.

Fatigue path spirals about

1 times around the roll

Spalling was just a matter

of time.

25

Learnings from failure of work roll 687463:

Measures in roll shop

Incident = each operation, manoeuvre or

set of circumstances by which damage is

inflicted to the roll surface. E.g.: Pinches

Strip derailments Strip breaks

Unlucky crane manoeuvres

Any damage inflicted to a roll during a heavy rolling process incident has to be

removed completely before the roll can be released for production again.

Partial damage removal by grinding until ET indications are reduced (just) under

threshold is no option any more.

New roll shop practice implemented at CM2 IJmuiden

Damages: visual damages

invisible damages: ET bruise & crack indications; UT indications

5-stand sheet mill

catastrophic work roll failures per quarter

due to fatigue crack propagation

0

1

2

3

year

2004

year

2005

year

2006

Q1 -

2007

Q2 -

2007

Q3 -

2007

Q4 -

2007

Q1 -

2008

Q2 -

2008

Q3 -

2008

Q4 -

2008

Q1 -

2009

#

o

f

r

o

l

l

s

p

e

r

q

u

a

r

t

e

r

2009+

2010

mill crew error:

roll pair not

changed after

rolling incident

improved procedure

26

New roll redressing and release procedure at

implemented at CM2 IJmuiden by 2006-Q4

Yes

No

No

Yes

No

Yes

Extra

take off (m

axim

um 0.6 m

m)

Roll goes for normal grindingprocedure followed by a Lismar scan

Roll change reason given by mill

Is roll salvaging needed?

Positive release of the

roll for production

Roll goes for grinding/scanning

procedure followed by Lismar scan

Normal reason Incident reason

Yes

Roll goes for final grinding procedure to

meet the customer demands(roughness and crown)

Roll salvaging

UT1 > 35% or

UT2 > 35%

Bruise < 0,3 and

Crack < 0,2

Roll is destined

for circulation

Roll attended for

Roll manager

UT1 > 35% or

UT2 > 35%

Bruise > 0,8 or

Crack > 0,5

Bruise < 0,5 and

Crack < 0,3

Extra

take off (m

axim

um 1.5 m

m)

No

No

No

Yes

Yes

Yes

No

27

Roll failure causes overviewRoll failure analyses

Last 8 years: >100 individual industrial cases of roll failures/damage/defects at Tata Steel cold rolling mills in IJmuiden, South-Wales and India

In-depth analysis of certain selected cases

Reasons for catastrophic roll failures

A. Fatigue crack propagation (ribbon fatigue path or cat tongue) most common catastrophic work roll failure type origin = pre-existing defect (e.g. crack) at roll surface, from earlier mill incident,

propagating under rolling load

28

Roll failure analyses

Reasons for catastrophic roll failures in cold rolling mills

A. Fatigue crack propagation (ribbon fatigue path or cat tongue) most common catastrophic work roll failure type origin = pre-existing defect (e.g. crack) at roll surface, from earlier mill incident,

propagating under rolling load

B. Spalling due to instantaneous thermal and/or mechanical overload Origin = heavy mill incident (pinch, strip break, strip derailment, )

29

Roll failure analyses

Reasons for catastrophic roll failures in cold rolling mills

A. Fatigue crack propagation (ribbon fatigue path or cat tongue) most common catastrophic work roll failure type origin = pre-existing defect (e.g. crack) at roll surface, from earlier mill incident,

propagating under rolling load

B. Spalling due to instantaneous thermal and/or mechanical overload Origin = heavy mill incident (pinch, strip break, strip derailment, )

C. Roll manufacturing defects Frequent 30 years ago but nowadays rare E.g: deep-seated inclusions, hydrogen, too much (>10%) retained autenite Such incidents tend to be severe

Countermeasures

A. Main focus in failure prevention at mills/roll shopsB. Additional focus for development of incident-resistant roll gradesC. Strict QA at rollmaker; optionally routine Ultrasound inspection at roll shops

30

Scenarios leading to fatigue crack propagation (A)

A1. Roll damaged in mill incident roll not changed fatigue crack growth roll spalling in same rolling campaign

A2. Roll damaged in mill incident roll changed redressing in roll shop insufficient; remnant crack/bruise roll back to mill fatigue crack growth roll spalling

A3. Combination of A1+ A2Roll damaged in mill incident roll not changed fatigue crack growth but not up to spalling regular roll change redressing in roll shop insufficient; remnant crack/bruise roll back to mill fatigue crack growth roll spalling

31

Example of scenario A3

Case: crack in forged 3%Cr steel work roll 687365

remarkably low Eddy Current Testing (ECT) signal why ?

Finally intercepted by straight beam UltraSound Testing (UST) probe

installed by Lismar on grinding machine in parallel

with ECT

10 mm

Cross section of crack

25 m

Crack ragged, side-branched, discontinuous

electrical bridging

low ECT response

32

Roll failure analysis example: spalling of

work roll 687539

Incident description

5-stand tandem batch cold mill CM21 IJmuiden, 1 May 2006

18:05 hours: Heavy pinch of strip tail end in stand #1.

10 coils left in campaign, operator chose to continue without roll change. Inspection of strip at stand #5 exit showed no marks

18:27 hours: with 3 metres left in the 4th coil after the pinch, the top roll no.

687539 exploded.

Top roll 687539: Many fire cracks

multiple fatigue paths underneath

Bottom roll 687540: Fire cracks up to 6 mm depth

no fatigue paths Increase in stand #1 roll

force during pinch

High local pressure & friction

33

Spalling of work roll 687539: images and

learnings

recovered strip from pinch

Spalled roll piece

Learnings:

strip inspection for roll mark defects is not

sufficient rolls must be changed in each case of (suspected) damage

Time between defect origin and spalling by

fatigue crack propagation can be very short (4

coils in this case)

Difficult to predict how fast (bottom roll had

similar cracks but no propagation observed yet

34

Roll defect analysis example: Cracks on

CM11 work rolls 556288 and 556292

12 January 2008, 4-stand batch tandem mill for tinplate CM11, stand #3

Work rolls 556292 (top) and 556288 (bottom), grade = forged 4%Cr-Mo steel, were

removed from CM11 stand #3, because imprints had been discovered on the strip.

Directly after pulling the roll pair, an area (30x30 mm) with several cracks, responsible for

the imprints on the strip, was indeed readily discovered on the surface of bottom work roll

566288.

35

Cracks on CM11 work rolls 556288 and 556292

Visual inspection of partner roll 566292 no cracks noticed

manual UST: presence of cracks also on roll 556292, but cracks smaller than on roll 556288 surface

Roll 556292: cracks ~4 mm deep

Roll 556288: cracks 3-6 mm deep, except one 14 mm deep crack starting to bend

early stage of crack propgation

36

Cracks on CM11 work rolls 556288 and

556292 roll shop history review

Critical review of roll grinding and Eddy Current Testing History Conclusion: rolls were sent to mill in defect-free condition

ECT after cracks were found Strong coincident Crack/Bruise indications in roll 556288, weaker but clear coincident

Crack/Bruise indications

cracks

bruises

cracks

bruises

37

Cracks on CM11 work rolls 556288 and 556292

mill campaign review

Review of last mill campaign: Only 3 coils rolled before roll pair was pulled

Anomaly: fast stop during rolling of 1st coil

Deceleration of stand #4 in 2.0 seconds,

stands #1, #2, #3 in 1.2 seconds

asynchronous slip friction overheating of stand #3 work roll surface Mill operator happy that strip break was

avoided during fast stop rolling continued

In hindsight fast stop generated roll surface overheating (bruising) crack initiation

Learnings: Damaging effect of this particular fast stop on the work rolls has been understimated.

Anticipate that a fast stop from run speed may generate significant damage to the work

rolls, even if a strip break has been avoided

Cracks in roll had 556292 had not caused marked on strips (in contrast to cracks on roll

556292) Inspection of the strip surface for roll marks is pertinently insufficient to intercept all work rolls that

contain one or more cracks.

2.0 seconds

stand #4 roll speedstands

#1 #2 #3 roll speeds

38

Lismars Prototype NDT system with novel

sensors tested in roll shop at Tata IJmuiden

Prototype system with a.o. novel automated UT-SAW sensors Better defect detection capability

After successful trial: 2 grinding machines equipped with SAW

systems in combination with ECT + normal beam UST

UT-SAW now integrated in standard roll shop operations !!!

Example case: two small cracks in forged 3%Cr steel work roll

Automated routine NDT of rolls in roll shops: added value of complementing Eddy Current Testing with Ultrasound Testing straight beam & novel surface wave UST system

39

Examples of successful interception of defect

roll by means of Ultrasound Testing

Forged work roll 687 341: multiple UST indications

1 campaign after rehardening at supplier

Cause: manufacturing problem (heat treatment) only becoming manifest after mill load

Forged back-up roll 187 209 Cluster of UST indications due to inclusions

Cause: manufacturing problem (ingot casting) only becoming detectable halfway roll life

40

Roll Failure Case Analysis approach

Roll Failure/Defect Case Analysis Elements

A. Check Roll/Roll Shop history data roll shop cause? In particular Eddy Current Scans and Ultrasound Testing data Review data from previous mill/roll shop cycles: previous roll change reasons, extra

redressing required on lathe or grinder, successive ECT/UST C-Scans

B. Check Mill process data mill cause? High time-resolution mill proces data recorded just before & during roll failure Rolling forces (total+differential), torque/power, tensions, speeds, screw positions, Any abnormalities recorded earlier in same campaign? Check roll cooling system data: (mal)functioning? On specification?

C. Check failed roll itself indications for manufacturing defect or mill-induced defect or mechanical damage or .?

visually

ultrasound inspection; other manual NDT methods

if relevant: local hardness measurements (portable Equoptip HLE or HLD)

If relevant: ambulant microscopy or sampling for chemical and microscopic analysis It is only sensible to take samples if the relevant sampling location is known

D.Check other involved rolls when applicable circumstantial evidence & effects (Partner) work roll, Back-up roll/IMR

E. Check strip(s) for defects/marks when applicable time & nature of origin Strip rolled during failure/defect recognition as well as previous strips

41

Example roll failure analysis:

Spalling of work roll 556254 in

stand #2 of Cold Mill 11

Strip break in previous campaign,

followed by grinding off 0.24 mm

Eddy Current Scans OK

No sign of roll shop cause

Mill process data Process data from last campaign,

recorded at high time-resolution, have

been checked thoroughly

No process irregularities have occurred that could have induced a roll spalling

Roll examination

Roll shop data

42

Manual Ultrasound Testing results

(normal beam + Surface Wave)

Large number of internal irregularities all along the roll length and circumference were found.

The defects are deep seated, from ~50 mm depth to the roll centre

Several deep-seated defects are already visible with a 2 MHz probe, if the applied ultrasound

measuring sensitivity is sufficiently large (i.e. 100% intensity of the 2nd back wall echo). This

indicates that the largest defects are at least 1.5 mm in size.

The number of ultrasound reflections increases considerably when applying a 6 MHz probe,

which implies that there is also a large fraction of defects in the size range between 0.5 and

1.5 mm.

These detected deep-seated defects are obviously roll manufacturing defects. They could be

either inclusions (e.g. slag) or gas bubbles (e.g. hydrogen). The ultrasonic-method alone can

not identify the specific nature of these inhomogeneities.

In the exposed zone of the fracture, it is evident that a concentrically fractured area was

developed from internally in the roll, as part of it was exposed when spalled. The green arrows

indicate the direction of the centre of that fracture. The area with the large green arrows is the

deepest part of the exposed part of the spalling, at about 50 mm below the original roll surface.

The area in the vicinity of the fracture was also analysed with ultrasound and it is found that

the crack only covers an equivalent circle, meaning that there is no unidirectional fatigue path

along the circumference (cat tongue), but rather an oval-shaped fish eye. The fracture of this

roll was most likely originated from one of the larger imperfections in the roll material.

43

Conclusions work roll spalling case of roll 556254

Roll 556254 spalled because of internal defects in the roll material.

With ultrasound testing it was detected that the roll has numerous deep-

seated internal imperfections, most probably either inclusions or gas

bubbles.

A significant amount of the defects is quite large (1.5 mm or more), while a

major portion of the defects has a size in the range of 0.5 to 1.5 mm.

This roll shop used only automated ECT. With additional UST the spalling

could have been prevented

Textbook example:

roll spalling due to a

deep-seated defect

In development:

Global Expert System

Rolling Mill Roll Defects and Failures

Why - How - What

Charter

Example pages

45

1.WhyRobust and safe rolling

processes and roll handling

operations require failure-free

rolling mill rolls and adequate

detection of and

responsiveness to any roll damages and roll defects.

2. HowA global web-based platform is created for TSG-wide knowledge

sharing and development concerning rolling mill roll defects and roll

failures. In this expert system, relevant data, characteristics, root

causes and countermeasures of actual cases of roll failures/defects

from any TSG (flat) rolling mill are centrally and collected and stored

in a systematic way.

The expert system is integrated and maintained within the TSG Hot

Rolling and Cold Rolling Process Improvement Teams (PITs) for

empowerment of the roll users by the roll users.

Global Expert System:

Rolling Mill Roll Defects and Failures

3. WhatUser-friendly web application containing:

Photos, roll data and mill data per roll

failure/defect

Breakdown of roll failure/damage modes

Breakdown of roll defect types

Breakdown per roll type/mill type

Breakdown of root causes

Description of prevention methods

This will be the backbone of the Expert

system to click-through site from

known symptoms to possible causes

and solutions

Discussion board

Links to relevant literature, functional and

technical documents

System controlled by roll users (one expert

per location/mill) modular and modifiable

normal beam UT scan

46

Global knowledge sharing and development, regarding rolling mill roll defects and failures.

Centrally collect and store data concerning rolling mill roll defects and roll failures

Ensure open reliable and unambiguous data; Clear descriptions with example photos of roll

defect/failure modes, root causes and

countermeasures Controlled process/data approved by roll users

Objectives Deliverables

All roll types for flat rolling mills: hot strip mills, cold rolling mills, temper mills; work rolls, back-up rolls, intermediate rolls.

Opportunity to include in the future: rolls for long products rolling

Scope

Data Collection - identify and gather updateable

database of roll defect and failure information Data Collation - categorize defect and failures in

appropriate groupings

Roll-out via PIT platforms Introduction at surface day 2012?

Key activities Action TimelineRequirements gathering

Development of web-based tool

Testing

Deployment

Inform customers/users

Charter

Global Expert System: Rolling Mill Roll Defects and Failures

User-friendly web application containing:

Photos, roll data and mill data per roll failure/defect

Breakdown of roll failure/damage modes and roll

defect types Breakdown per roll type/mill type

Breakdown of root causes Description of prevention methods

Expert system click-through site from known symptoms to possible causes and solutions

Discussion board

Links to relevent literature Links to relevant functional and technical documents

Benefits

Cross-border learning and sharing

Roll handling synergy Less roll failures/damages

Faster & adequate response to incidents

High quality input - input must be complete -Always up to date data set

System controlled by roll user modular and modifiable

Data is centrally stored in a controlled ( and back-upped) environment

Improved safety

Higher process stability/less downtime Less emotional burden for operators

Available manpower (R&D and GIS) (site

development

Absorption by PIT groups (future) Each plant will have a nominated local expert to

maintain and develop site content (future)

Critical Success Factors

Charter Global Expert System: Roll Defects & Failures

Share

Learn

Identify

Global

Expert

System

Ensure robust and safe rolling processes and roll handling operations by failure-free rolling mill rolls and by adequate

detection of and responsiveness to any roll damages and roll defects:

47

1. Roll Breakages1.1. Roll barrel breakage

Description:

A roll barrel breakage constitutes the catastrophic failure of a roll in which the roll

fractures into 2 or more pieces through the complete roll barrel diameter

Causes:

1.1.a - Porosity (references.)

1.1.b - Poor roll core (references..)

1.1.c - Too thick shell (references.)

1.1.d - Centre bore defects (references.)

1.1 e Roll cooling failure (references.)

Countermeasures:

Most roll breakages are caused by manufacturing flaws; however, roll breakages are

also generally a consequence of a smaller defect which has either gone un-noticed or

not been correctly removed. Therefore, correct and timely non-destructive testing (NDT)

of the rolls will not prevent the defect from occurring, but will, in most instances, prevent

a suspicious roll from entering service.

48

1.1. Roll barrel breakage 1.1.a Porosity

Porosity is characterised by hole defects that can appear on the surface, or subsurface of a roll. The holes can be circular or irregular in outline and with or without a shiny interior. They are randomly dispersed on the roll barrel of chill cast rolls. A prime example of this defect type was found in 4.5%Cr cast steel back-up rolls (RS 154449)

This particular defect type is considered a manufacturing flaw and is predominantly found in cast rolls

RefS. 154449 DSP-IJBR3223 static cast BUR 4.5%Cr double poured barrel breakage internal porosity supplier no.1