Welding Hazards Barry McKay
Transcript of Welding Hazards Barry McKay
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Process used for identification andProcess used for identification andmanagement of hazards associated withmanagement of hazards associated withhot work in a hazardous zone.hot work in a hazardous zone.
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AustarCoal Mine
• Located approximately 10kms south west of Cessnock.• Mines the Greta seam of coal.
• Owned by Yancoal Australia Pty Ltd .
• Introduced the top coal caving technology to Australia in 2006
(LTCC).
• Seam gas content of the Greta Seam is 0.4m3 / tonne, of this 90%
CO2 and 10% CH4.Therefore very small amounts of methane
detected.
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Roof Shield Repair Area
PIT TOP
#2 SHAFT - Flooded
#3 and #4
VENT
SHAFTS
#1 SHAFT
Vent + 2nd Egress
PROPOSED
SHAFTS +
KITCHENER
FACILITY
CHPP
PROPOSED WORKINGS
OLD ABANDONED WORKINGS
MINING AREA
WHERE
REPAIRSOCCURRED
b1
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Slide 3
b1 bmckay, 3/11/2010
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Repair Background
Recently, an incident occurred on the longwall face, where damage was
caused to two of the 6 legged tailgate shields (Number 122 and 123). The
shield clevises were subjected to excessive tensile forces resulting in aductile failure when the shield canopy was raised to the roof in a localised
cavity.
Due to the unique operation of the shields, the middle two hydrauliccylinders (legs), were raised by the outer legs extending them into this
cavity. This caused severe damage to the shield canopy middle clevises.
A decision was made by Austar management to repair as soon aspossible. The ongoing operation of these shields and possibly the
adjacent shields, was definitely not sustainable. This was due to an
estimated 50% reduction in roof support density (estimated by OEM
Design Engineer) above any one shield that was not operating as it wasdesigned.
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Longwall Equipment
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Damaged Clevis of 123
Shield
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Top Cylinder Pin Locating
Bore
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Top of a Typical Shield Leg
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Methodology
Identif ication of Repair Options and Risk Assessment
A group of employees including mine workers, tradesmen,engineers, management, OEM representatives and a local
check inspector were involved in an options evaluation. A risk
assessment to determine the best options available to repair theshield, included the following -
1. Continue to operate the longwall with the damaged clevis
2. Remove the canopy and repair at the workshop3. Remove the entire shield and repair at the workshop
4. Replace the shield
5. Install a bolt on clevis
6. Weld the clevis
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Considerations
Adherence to and compliance with relevant guidelines, standards and
legislation were considered throughout the process, with particular
focus on:-
OHS Act 2000
CMHSR 2006
MDG 25 – removal or coverage of flammable materials. All loose coal removed inclusive of accumulations on the canopy.
AS1674.1 Safety in Welding & Allied Processes
Part 1: Fire Precautions AS1674.2 Classification of Welding Environment
Part 2: Category ‘C’ environment
AS1674.2 Safety in Welding & Allied Processes
Part 2: Electrical
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Considerations
Audit check lists were developed for MDG25 and were included in all
site Safe Work Procedures
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Repair Option Evaluation
Option Major Advantage Major Disadvantage
1/ Use hot work torepair the c levis
•Would result in thenormal shield operation• The quickest solution
•Required anexemption for hot workin the hazardous zone•Dust explosion
2/ Install a bolt onfork clevis
•Eliminated thewelding process fromhot work activities
•Hot work was stillrequired•As a result of drillingprocesses the OEM
identified that thestructural integrity ofthe shield canopywould result
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Repair Option Evaluation
Option Major Advantage Major Disadvantage
3/ Remove thedamagedcanopies andtransport to a
workshop
•A full repair would becompleted•Repairs undertaken ina normal environment
•No roof support whilethe canopy wasremoved•Hot work may be
required for lemniscatepin removal•Risks associated withthe removal of a 7tonne canopy
underground
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Repair Option Evaluation
Option Major Advantage Major Disadvantage
4/ Continue tooperated with thedamaged clevis
•No undergroundrepairs required
•Uncontrolled canopymovement duringoperation•Reduced support
density•Shield operationslower
5/ Remove the
shields forworkshop repairs
•No hot work required
underground
•No roof support the
beginning and end ofthis process
6/ Replace theshield with a similar
unit
•No hot work requiredunderground
• A very complexoperation
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Evaluation Outcome
• The group believed with the appropriate controls in place,
welding on the LW face had the lowest level of risk.
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Notification to I&I NSW
Notification of a High Risk Activity
CMH&S Reg 2006
Clause 49 High Risk Activities.
Cutting or welding in a hazardous zone underground required the following:
– Risk Assessments.
– Consultation and meetings with all stakeholders including DII
representatives.
– Review of the Austar Cutting and Welding Management Plan.
– Guidance Note GNC-009 requirements to be adhered too.
– A summary of risks identified and controls to be implemented.
– A drawing displaying the location where the hot work was to be
undertaken and the associated equipment required for the task.
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Exemption
• Austar Coal Mine applied for an exemption under
CMHSR2006 clause 19 (1) (c). Specifically this was for the use
of non Gazetted electrical equipment in the hazardous zone.
• The exemption was time limited therefore Austar could not
allow for any major delay during the repair process. A detailed
time line was developed which included contingencies.
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Major Hazards and Issues
Identified for Hot Work Issue Consequence
• Hot material Damages hydraulic hoses whichcould lead to high pressure fluid
being released
Electrical equipment damaged
• Welding in a wet / damp
environment
Personnel receive electric shock
during welding
• Non explosion proof equipment Gas Ignition
• Ineffective welding Another clevis failure
• Dust Explosion
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Further Details
• The Mig welder powered from a 1000 to 415 volt transformer. Theprimary welding machine was a MIG Kempi Master 5001.
• The 415 volt outlets of this transformer provided earth leakageprotection. This was achieved by using 10mA earth leakage circuitbreakers.
• This transformer was powered via a 50mm squared cable from thelongwall substation.
• A spotter was positioned at an emergency stop while ever weldingoccurred. This emergency stop tripped the 1000 to 415 volttransformer.
• Existing tailgate methane detectors were configured to trip thewelding transformer and the shield electrics if 0.25% was detected.
• A spotter was positioned at emergency oxygen acetylene shut offvalves when this equipment was being used.
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1 2 4
T/G
GOAF
9ct
A3 Block
Retreat Direction
5m
0.9
LnL
0.9
LnL
PROPSETTERS & BRATTICE
TIGHT ROOF TO FLOOR
AIR
FLOW
AIR
FLOW
EXISTING
QUIKSEAL
PARTIALLY
REMOVEDFOR
VENTILATION
PERMANENT GOAF
STREAM SAMPLE POINT
TUBE BUNDLE POINT No 5
X
X
X
XWELDING POINTS
WING TO BE ADJUSTED FOR
VENTILATION REGULATION
BRATTICE WINGS
HAND HELD GAS
MONITORING DEVICE SET
TO ALARM AT 0.25%
ADJACENT TO WELDING
SITE
WELDING POD
OXY ACETYLENE BOTTLES
XWELDING
SITE
415v TO
1000v
TRANSFORMER
TX
0.9LnL
0.9LnL
0.9LnL
DCBMINIMUM 3m APART
MIG GAS
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Instruction
• 16 site specific Safe Work Procedures were developed. Theseprocedures ranged from the preparation of the site right through tothe recommissioning of the shields.
• Safe work procedures were formatted in a way that allowedindividuals to sign off as each step was completed.
Prop Settersx 2 off
CST DRIVE
Link n lockpacking
#124
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Special Preparation
• The Boilermakers and equipment needed to meet Austar andOEM competency requirements. A trial welding programme usingthese people and equipment was undertaken in the OEM’sworkshop.
• Welding equipment and compliance to MDG25 & AS 1674.2.
• Non Destructive Testing personnel competence – Australian
Institute for Non Destructive Testing.• Site preparation had to be audited prior to hot work commencing.
This was undertaken by the MME, MEE & MME.
• I&I instructed the Austar MME, MEE & MME or their nominateddelegates to audit the site every 24 hours.
• I&I randomly audited the welding site during the project.
• Continuous monitoring of the atmosphere was undertaken by a
mine official.
A li ti fth
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Application of the
Hierarchy of ControlsDuring the hot work repairs
• The OEM designed and supplied a shear pin to be installed onthe bottom leg clevis. This was rated at 33.6 tonnes and wasdesigned to fail, prior to any structural damage occurring.
During the subsequent longwall relocation• The capabilities of the top clevis were increased during the
longwall relocation. This still incorporated the shear pin.
Longer Term
• Continued mechanical and structural improvements with the sixlegged shields.
• Replace the six legged shields with four legged types
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Summary of Shield Repairs
• All personnel involved contributed positively and professionally.
• The repairs were completed as per plans and without an incident.
• A failure of one welding machine occurred during the repair
process.
• No extra ordinary hazards or conditions were encountered during
the entire repair process.