welding hazards barry mckay

8/18/2019 Welding Hazards Barry McKay

1/25

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.


2/25

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.


3/25

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


4/25

Slide 3

b1 bmckay, 3/11/2010


5/25

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.


6/25

Longwall Equipment


7/25

Damaged Clevis of 123

Shield


8/25

Top Cylinder Pin Locating

Bore


9/25

Top of a Typical Shield Leg


10/25

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


11/25

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


12/25

Considerations

Audit check lists were developed for MDG25 and were included in all

site Safe Work Procedures


13/25

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


14/25



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


15/25



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


16/25

Evaluation Outcome

• The group believed with the appropriate controls in place,

welding on the LW face had the lowest level of risk.


17/25

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.


18/25

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.


19/25

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


20/25

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.


21/25

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


22/25

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


23/25

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


24/25

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


25/25

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.

welding hazards barry mckay

Documents