tim akroyd, tim akroyd, concentration manager, mmg century - century pipeline refurbishment project
DESCRIPTION
Tim Akroyd, Concentration Manager, MMG Century and Chris Austin, Estimator, Nacap presented this at the 3rd Annual Slurry Pipeline Conference. The Conference focuses on the design, construction, operation and maintenance of mineral slurry pipelines. For more information, visit http://www.informa.com.au/slurrypipelineconferenceTRANSCRIPT
Century pipeline refurbishment
project
Tim Akroyd, MMG Century Mine
Chris Austin, Nacap Australia
November 2013
250 kilometres north/north west of Mt Isa
Mine site
• 1887 First silver, lead and zinc discovery in area.
• 1887-1960 Intermittent production from area.
• Late 1930s Start of modern exploration in the area.
• 1986 CRAE select the area and applied for EPM.
• 1990 Century discovery hole drilled on 4th April.
• 1990-1996 Resource definition drilling and feasibility.
• 1997 Century acquired by Pasminco – Native Title issues resolved.
• 2000 Century officially opened on 4th April.
• 2002 Officially reached full production on 31st August Awarded MINEX on 2nd September.
• 2009 MMG buys majority of OZ Minerals assets, including Century
Century’s history
Production data
• 24,000 tonnes of ore processed daily
• 900,000 tonnes of zinc concentrate
• 70,000 tonnes of lead concentrate
Pipeline summary
• 304Km from Lawn Hill (mine-site) to Karumba
• 300NB X70 grade steel pipe
• Pipewall varies in thickness from
• 8.4mm at Lawn Hill to
• 4.8mm at Karumba
• HDPE liner nominally 7.5mm thick
• 1.2Km flanged strings
• Buried to a minimal depth of 750mm
• Directional drilling under all major rivers
• Single pump station at Lawn Hill
• Instrumentation
• Pressure - start and end, plus 5 intermediate positions
• Flowrate - start and end, with differential leak detection alarms
• Density – start and end
• Pig launching and receival stations
• Impressed current cathodic protection system
Pipeline profile
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Pipeline Distance (km)
Lawn Hill (mine site) pump station
• 3 x Wirth Triplex Diaphragm Pump 8¾" x 14" • 1.13MW VSD Motors • Parallel arrangement • Discharge pressure – 20MPa (max)
Pipeline monitoring spools (original design)
Monitoring Spools • KP82
• KP85
• KP107
• KP138
• KP152
• KP156
• KP256
• KP265
• KP296
• Unlined approximately 8m in length • 2 x 50mm riser • 1 x pressure gauge on selected risers (5 spools) • Susceptible to external interference
Pipeline operations and maintenance
• Pipeline operates continually at approximately 270m3/hr – 300m3/hr
• Zinc and lead concentrates are pumped in batches separated by water.
• Zinc and lead batches are often in the pipeline at the same time
• In the event of an outage pipeline must restart within about 12 hours to minimise trail-out and mixing of zinc and lead concentrate
• Changes in friction losses along the length of pipeline are closely monitored – used to infer slurry deposition within the pipeline
• Pigging using soft foam or medium density pigs occurs as required
Pipeline operational advantages
Reduced life cycle cost compared to road transport
• For a similar operation to Century, over 20yrs, approximate Life Cycle Costs
• Pipeline $400M
• Road transport $650M
Lower operational risk profile
• High likelihood of vehicle accidents, with very serious consequences, particularly on public roads
Unaffected by surface weather conditions
• During wet season the roads to Century and Karumba are often cut for several weeks
Pipeline operational history
2003 - liner failed in D38 string (KP115 - KP116)
• String was bypassed while method of repair was determined
• Liner was removed and string returned to service
• 2 x unlined monitoring spools were installed at either end of the D38 string
• Subsequent clock face spot thickness testing showed minimal corrosion/erosion in monitoring spools
Pipeline operational history continued
2009 - D38 string failed, following a pipeline restart
• D38 string was replaced with a thick wall unlined pipe
• An inline reduced bore ball valve was inserted ahead of the failed string to assist repairs.
• The valve was left in the pipeline after repairs were completed
2011 - During programmed inspections of monitoring spools, near through wall failure was identified at KP296
• All unlined monitoring spools were thickness tested using phase array technology
• Any areas of spot corrosion were repaired using Kevlar/fibreglass wrap
2012 Refurbishment plan
• De-slurry pipeline via water pumping only
• Completely dewater pipeline using compressed air and medium and soft density foam pigs (due to valve restriction at KP115)
• Replace unlined D38 string with HDPE lined steel pipe
• Replace all monitoring spools with new
• Encase new monitoring spools in concrete access chambers
Project lead-in, minimising outage time
A number of mitigation measures were identified up-front to minimise the down-time for the refurbishment scope including:
• Fast-tracked contract with flexible commercial terms
• Fast-tracked camp supply to support pipeline project and reduce travel time to maximise driving safety and reduce fatigue (this became increasingly important when the shut-down was prolonged).
• The dedicated local camp accommodation also maximised available working time during execution of the works
Project lead-in, minimising outage time
Further mitigation measures included:
• Additional material procurement (eg – twice the required qty of HDPE pipe) + back-up spools (if required)
• 3D Laser Survey of monitoring spools to ensure precise fabrication (and therefore fit-up)
• Early engagement of local plant suppliers/sub-contractors to ensure sufficient resource pooling during the shut-down scope
• Early identification of shut-down teams required for pipeline scope and early engagement of the same
New D38 string construction
• DN300 (12”) pipeline welding
New D38 string construction – HDPE liner pull-back
New D38 string construction – HDPE liner insertion
Dewatering challenges
• Soft foam and medium density pigs used due to reduced bore ball valve
• Air bypassed pigs creating numerous hydraulic locks in pipeline
• Pigs were removed from Lawn Hill (the start) of the pipeline three days after launch
Dewatering challenges Pipeline profile with potential water retention zones
How dewatering was achieved
• Safe depressurisation of pipeline via open ends and intermittent venting from small (less than 1”) bleed valves on monitoring spool blinds – day and night operations
• Use of tanker trucks to remove water from upstream sections of the pipeline, water brought back to mine site at Lawn Hill
• Hot taps installed on under-side of monitoring spools adjacent to pipeline low-points to assist with dewatering effort
Dewatering into tankers at KP82
Bi-di pig launched downstream of KP115 valve
• Bi-direction pig launched from KP138 to dewater pipeline through to Karumba
• Original foam pig dewatering duration was 5 days of 24-hour dewatering followed by 6 days to perform spool change-outs and D38 installation.
• Actual dewatering duration was 30 days including staged pipeline release to enable spool change-out and D38 pipe-string tie-in
• Further delays mitigated by:
• Twice daily management meetings to track dewatering operations and maximise opportunities and synergies to mitigate delays to pipeline re-commissioning
Minimising downtime
• Further delays mitigated by:
• Early engagement of water tankers to remote areas of pipeline to assist with dewatering
• Fast-tracked hot tapping service (including fittings)
• Availability of specialist pipeline Contractor services, including provision of coded welders, pre-fabricated and pre-tested pig traps
• Rolling pipeline roster to ensure continuous resourcing during shut-down up to and including re-commissioning
Minimising downtime
Monitoring spool replacement underway
Installation of new D38 string
Installed (new) D38 string
The result
• D38 string replaced with lined pipe and buried
• All monitoring spools replaced
• Concrete access chambers installed
• Routine wall thickness inspection program of all monitoring spools
Don’t get bitten!
• Flanged joints about every 1-2 kilometres introduce potential leak points
• Matching of flange/HDPE ends and correct use of gaskets when new technologies replace old
• Lined pipe removes ability to hot tap (without detriment to the liner) in case of (pressure) air-lock issues during testing, commissioning, operational error, dewatering works or on re-start after shut-down. Consider high point vent and low-point drain locations during design stage
Challenges of HDPE lined pipe
Further challenges of HDPE lined pipe
• Leak detection methods between HDPE liner and inner wall of steel pipe need to be considered at design stage, including monitoring regime
• Unknown impact of rigid-style pigging through HDPE liner
• Lack of experience and available operational data/history from the industry
• Constructability and maintenance (eg – very limited resources for HDPE pull-back available within Australia)
Results of 2012 refurbishment:
• Pipeline is now in a better than as-designed condition
• New D38 string means that pipeline is now fully lined (end to end), except for dedicated monitoring spools.
• Reduced risk of external interference
• Improved access to allow for complete monitoring of corrosion of unlined monitoring spools and faster response in the unlikely event of an incident
• Removal of KP115 in-line valve allows future use of bi-directional pigs for cleaning/batching/dewatering operations as required
Project benefits
Lessons for industry
• Pipelines have excellent operational advantages, including lower operational risk profiles and reduced life cycle costs, but can be challenging to operate
• The minerals processing industry lacks specialist “in-house” knowledge
• Collaboration with specialist contractors (design, construction, operation, maintenance as required) enables the best outcomes