A copper concentrate pipeline descending from a mine at 1,500 m elevation or higher carries serious static head. If the lower end plugs, or an accidental shutdown leaves one section holding the full head of two or more sections above it, pressure in that section can exceed the design limit of the pipe. Rupture discs are installed in mining slurry pipelines to prevent this overpressure case. It is a non-reclosing relief device with no moving parts, applied in an difficult / challenging area.
Why a concentrate pipeline is a severe pressure relief application
Long-distance slurry pipelines move concentrate, tailings or mineral diluted in water at high pressure from the mine down to the plant or port. The medium punishes everything in the line. In the copper concentrate case examined below, calcium carbonate dosed to hold the pH during transfer deposited as heavy internal scale along the pipeline, reducing the internal bore. Copper settling in the bottom of the steel pipe during downtime set up galvanic action, every unscheduled shutdown and restart added wear in the pipe bottom and the slack-flow areas, and aerobic and anaerobic bacteria in the slurry drove treatment costs up while the plant water discharge sat under environmental scrutiny.
The standard design response to static head is to section the pipeline with valve stations. Block valves are opened in sequence from the lowest point to the highest, and shut down in sequence from the highest point first, which limits the static head any one section sees. That sequencing also allows the pipe wall thickness to be telescoped down the line, saving considerable cost in steel. What the sequencing cannot remove is the abnormal case: the lower end plugged, or an accidental shutdown that traps the full static head of two or more sections against a closed valve.
A reclosing relief valve is a poor match for that case. Concentrate slurry abrades seats and fouls the moving parts a relief valve depends on, so the valve you need to lift may not lift, and a valve that lifts may not reseat. A rupture disc presents no moving parts to the process. It holds a bubble-tight seal in normal operation and bursts within a certified tolerance of its marked burst pressure when the overpressure case arrives, giving instantaneous, full-opening relief.
A worked example: a high-altitude copper concentrate pipeline
One high-altitude copper operation runs concentrate down 167 km of 9-5/8 inch (244 mm) outside diameter ERW steel pipeline, designed to operate at pressures as high as 255 barg (3,700 psig). Three valve stations section the line, each fitted with three block valves: an isolation valve, a seal valve and a wear valve. On the upstream side of each station, a rupture disc with a set point up to 276 barg (4,000 psig) is installed ahead of the isolating valve, protecting that pipeline section from the combined static head of two or more sections.
The valve stations are remote, so each disc is paired with a burst disc indicator that signals the operator the moment a disc has burst to relieve an overpressure condition. The control room knows immediately, without a trip to an unmanned station, and the section can be isolated and the disc replaced on plan rather than discovered after the event.
The relief design paid for itself beyond the overpressure case. Slurry sitting in the line during long downtime had driven the galvanic corrosion and wear problems described above. Fewer unscheduled shutdowns reduced both, delivered an operating cost saving, and left the outfall water suitable for reuse elsewhere on site.
Common questions to ask when selecting relief devices in mining
Why use a rupture disc instead of a relief valve on a slurry line?
Severe service. Slurry solids abrade the seat and foul the internals a reclosing valve depends on to lift and reseat. A rupture disc has no moving parts in the process stream and maintains a bubble-tight seal until it bursts. Where a relief valve is still required by the relief philosophy, a disc can be installed in series upstream to isolate the valve from the slurry.
How is a burst detected at a remote valve station?
With a burst disc indicator installed with the disc. When the disc bursts, the indicator alarms to the control room, so a relief event at an unmanned station is known immediately and the response is planned rather than reactive.
What determines the disc specification?
Set pressure, media, temperature and line size are the starting points, together with the operating ratio: how close normal operating pressure runs to the marked burst pressure. Pipelines that cycle or pulse in normal operation favour reverse-acting designs, which tolerate high operating ratios and pressure cycling better than forward-acting discs.
What standard governs selection and installation in Australia?
Rupture discs are selected and installed in accordance with AS 1358. The disc, holder and any indicator are specified together against the relief case, not as interchangeable parts.
Measurement Solutions supplies the Continental Disc Corporation range in Australia. The range spans burst pressures from below 1 barg to 276 barg (4,000 psig), line sizes to 900 mm (DN900) and maximum recommended operating ratios up to 95 per cent of the marked burst pressure, with reverse-acting, forward-acting, non-fragmenting and sanitary designs available together with burst disc indicators and holders. The ASME Section VIII UD stamp and CE marking under the Pressure Equipment Directive are available when specified.
Our application engineers support the selection from specification through commissioning: sizing the disc to the relief case, checking the operating ratio against the pipeline pressure profile, and specifying the holder and indicator for the installation. Send the set pressure, media, temperature and line size for a recommendation and quotation.
Measurement Solutions Pty Ltd, A Bestech Company, has supported Australian process industries since 1985 and is now integrated into Bestech Australia, with nationwide sales and application engineering support. Write to us for more information or call +61 2 9894 4300 to speak with an application engineer.