A pipe support has to do two things at once: carry the weight of the pipe and its contents without deforming, and let the pipe move as it heats up and cools down without dragging the whole system with it. A bronze sliding plate with graphite plugs is one way to satisfy both. The bronze matrix takes the bearing pressure; the graphite plugs release a solid film so the sliding interface stays at a low, predictable friction coefficient for years without regreasing. This page covers the load and temperature envelope, how to size a plate from the thermal movement, which alloys are used, how the plate compares with PTFE and greased steel, and the installation details that decide whether it actually works.

What the plate has to do

Movement comes first, because it sets the size of the plate. Carbon steel expands at roughly 12 × 10⁻⁶ per °C (6.7 × 10⁻⁶ per °F), so a 30 m (98 ft) run of pipe taken from ambient to 200 °C (360 °F) above ambient grows by about 72 mm (2.8 in). That movement has to happen somewhere, and if the support resists it the load is transferred into the pipe wall, the welds, the nozzles and the connected equipment.

The horizontal force transferred is simply the vertical load multiplied by the friction coefficient of the sliding interface:

• Vertical load on the support: 40 kN (9,000 lbf)
• Graphite-plugged bronze plate at μ = 0.12: friction force ≈ 4.8 kN (1,080 lbf)
• PTFE pad at μ = 0.06: ≈ 2.4 kN (540 lbf)
• Steel on steel, dry and corroded at μ = 0.40: ≈ 16 kN (3,600 lbf)

That last line is the failure case these plates exist to prevent. A seized support roughly triples the load the anchor and the equipment nozzle have to carry, which is how pipe shoe failures and pump nozzle cracks start. Keeping μ low and stable over the life of the plant matters more than achieving the lowest possible value on day one.

Performance envelope

Plates quoted at the hardness and tensile figures above are normally supplied in C86300 or a high-tensile aluminium brass. Softer leaded tin bronze plates are common at moderate loads; the two are not interchangeable, so state the load on the enquiry rather than just the dimensions.

Alloy selection

Bronze-graphite against the usual alternatives

PTFE is not a bad material; it is a low-load one. Where the bearing pressure is modest and the temperature is low, a polymer pad costs less and slides well. The problems start when a polymer pad is used under a heavy, hot, large-diameter line, where creep and temperature combine — the pad thins, the pipe drops, and the alignment is lost. A comparison against hardened steel is set out in GCr15 slide plate versus bronze wear plate. Similar sliding duties in boilers and furnaces are covered under bronze slide plate in boiler expansion plates and oil-free slide plate for furnace expansion plates.

Sizing and fitting

Most problems with sliding plates are geometry and installation problems, not material problems. The points below are the ones that come up in practice:

• Plate length. Allow for shoe length plus the full calculated travel plus a margin of 25–50 mm (1–2 in) at each end. A plate sized only for the static footprint will run off its counterface at full expansion.
• Preset the shoe. Install the pipe shoe offset from the plate centre by roughly half the expected travel, in the direction opposite to expansion, so the plate stays within its travel range across the full temperature cycle.
• Mating surface. Use a clean, flat steel counterface finished to about Ra 0.8–1.6 µm (32–63 µin). A rough counterface abrades the graphite film; a mirror finish gives the film nothing to hold onto.
• Flatness and contact. The plate must sit flat. Grout under a bolted plate or weld continuously on a welded one; a plate bridging a gap will bend and load unevenly.
• Plug side faces the movement. Fit the plate with the graphite plugs against the sliding counterface, not against the fixed structure.
• Welding. Keep plug rows clear of the weld zone, or specify bolted fixing with counter-sunk holes. Heat from welding damages the plugs and the surrounding matrix.
• Dissimilar metals. Where the plate is in contact with stainless steel or aluminium in a wet or coastal environment, add an insulating shim or coating. Copper alloys sit in a different position in the galvanic series and will corrode the less noble metal.
• Clearances. Leave room for the plate to shed debris and for inspection at turnaround. Enclosed, unvented supports collect dust that works into the interface.
• Inspection. At each shutdown, check plug protrusion, plate flatness, corrosion and bolt torque. A plate that has worn to the plug backing is due for replacement, not for regreasing — see bronze liners and wear plates for the replacement route.

Plug diameter, spacing and depth are sized from the contact area and the expected travel per cycle; the method is the same one used for plugged bushings and is set out in calculating plug size for graphite-plugged bronze bearings.

When a bronze sliding plate is not the right choice

• Low load and low temperature. A small, cool line on a light support does not need 100 N/mm² of capacity. A PTFE or UHMWPE pad is cheaper and slides well at low pressure.
• Fixed and anchor points. A plate that never moves never forms a graphite transfer film. Anchor and guide points need restraint, not a sliding surface.
• Movement in one direction only, once. Similarly, a support that shifts a few millimetres during commissioning and then stays put gains nothing from the graphite.
• Graphite dust is not acceptable. In some clean, food or electrical environments the shed graphite is a contaminant. Use a polymer-faced plate and accept the lower load capacity.
• Fast sliding. These plates are designed for slow thermal movement. Where the interface sees higher velocity, check the PV figure — 3.3 N/mm²·m/s is the usual ceiling, and it is reached sooner than most people expect.
• Below −40 °C (−40 °F). Standard builds stop there. Cryogenic service needs a specific lubricant pairing and supporting test data.
• Strongly acidic or sulfidic atmospheres. Copper alloys are not the right family; consider a lined or coated steel assembly.

Frequently asked questions

Why not just use PTFE instead of a bronze sliding plate?

PTFE slides well at low friction but creeps under sustained load and loses capacity as temperature rises. Where the bearing pressure stays under roughly 15–30 N/mm² and the temperature under about 260 °C (500 °F), it is a reasonable, cheaper option. On heavy-wall, hot, large-diameter lines the creep and the heat take the pad out of specification, which is when bronze-graphite earns its cost.

How much movement should I allow for?

Calculate it from the coefficient of expansion rather than guessing. Carbon steel at about 12 × 10⁻⁶ per °C (6.7 × 10⁻⁶ per °F) gives roughly 1.2 mm per metre per 100 °C of rise. Multiply by the distance to the nearest anchor, then add a margin of 25–50 mm (1–2 in) at each end of the plate and preset the shoe to about half the travel.

Which alloy should be specified?

C93200 covers most moderate-load pipe supports and conforms well to less-than-perfect counterfaces. Where the specification calls for about 210 HB minimum and 750 N/mm² tensile, the plate is normally C86300 or a high-tensile aluminium brass. For high temperature, coastal or chemically aggressive sites, C95400 or an aluminium iron bronze is the safer call. Related heavy-duty examples are shown under custom bronze plate bridge bearings and bronze plates for offshore cantilever skidding.

Can the plates be welded in place?

Yes, but keep the weld away from the plug rows, because the heat damages both the graphite and the surrounding matrix. Where the design allows, bolted fixing with counter-sunk holes is simpler and makes future replacement straightforward. If welding is the only option, say so on the drawing and we will leave a clear margin around the plug pattern.

How long do they last?

Life is governed by total sliding distance and bearing pressure rather than by time. A support that moves a few millimetres with each thermal cycle accumulates little travel, and plates commonly outlast the pipe insulation around them. Inspection at each turnaround is the practical way to decide replacement: check plug protrusion, plate flatness, corrosion and fixings.