A sintered metal powder element is made by filling a mould or a tube with metal powder, compacting it, and heating it until the particles bond at their contact points. The result is not a screen and not a membrane. It is a rigid, isotropic porous solid in which the pore channels run in every direction through the wall. That single structural fact explains most of the behaviour: deep dirt-holding capacity, the ability to be cleaned and returned to service, and a rating that does not drift after pressure reversal.
This guide covers the four forms we supply, how to read a grade table, the alloy and temperature limits that decide a specification, and the cleaning methods that work and the ones that destroy an element.
The four element forms
Powder sintering produces a near-net shape, so the element is normally made in the form the housing needs rather than cut from a sheet. The four forms below cover the great majority of industrial service.
| Form | Typical dimensions | Wall thickness | Best suited to |
|---|---|---|---|
| Tube / candle | OD 10 – 180 mm, length 100 – 1500 mm | 1 – 5 mm | Liquid filtration in pressure housings, catalyst recovery, slurry polishing |
| Disc | Diameter 2 – 500 mm | 1 – 10 mm | Short flow paths, gas filtration, sparging plates, vacuum service |
| Plate / sheet | Up to 500 x 500 mm | 0.6 – 10 mm | Flat membrane support, fluidising beds, large face area at low headroom |
| Sparging head / aeration | Threaded or flanged standard sizes | 3 – 10 mm | Gas distribution into liquids, aeration, ozone and oxygen contactors |
The form does not change the pore structure, only the flow path. A tube gives the largest filtration area per unit of housing volume and is therefore the default choice when the dirt load is high; a disc gives the shortest path and the lowest pressure drop at high flow; a sparging head is specified for bubble size rather than for particle retention, which is why its rating is quoted in a different range from the filtration grades.
Reading a grade table
A powder element is ordered by nominal filtration rating, but the rating alone does not define the element. Pore size, permeability and wall thickness move together, and the compressive strength changes with the grade. The table below is the standard production range.
| Nominal rating (um) | Max. pore (um) | Air permeability (m3/h.m2.kPa) | Wall thickness (mm) | Compressive strength (MPa/cm2) |
|---|---|---|---|---|
| 0.5 | 4 | 3 | 0.6 – 10 | 3.0 |
| 1 | 6 | 5 | 0.6 – 10 | 3.0 |
| 2 | 10 | 15 | 0.6 – 10 | 3.0 |
| 5 | 15 | 40 | 0.6 – 10 | 2.5 |
| 10 | 30 | 120 | 0.6 – 10 | 2.5 |
| 20 | 60 | 250 | 0.6 – 10 | 2.5 |
| 30 | 100 | 500 | 0.6 – 10 | 2.5 |
| 50 | 160 | 800 | 0.6 – 10 | 2.5 |
Two practical consequences follow. First, a finer rating is always paid for in pressure drop: moving from 20 um to 1 um costs roughly fifty times the permeability at the same wall thickness. Second, the maximum pore is typically five to eight times the nominal rating, which is why a bubble point test is the only reliable way to confirm which grade actually arrived.
Alloy and temperature limits
Stainless steel covers most service, but the wall between a working element and a failed one is usually the alloy choice. Powder-sintered elements are available in the alloys below, and the useful temperature is lower in an oxidising atmosphere than in a reducing one.
| Alloy | Max. temperature, oxidising | Max. temperature, reducing | Chosen when |
|---|---|---|---|
| 316L stainless steel | 400 C | 480 C | General chemical, water, oil, food. The default answer |
| 304 stainless steel | 400 C | 480 C | Cost-sensitive duty without chlorides |
| 310 / 310S | 600 C | 700 C | High-temperature gas, furnace and flue duty |
| Titanium (Gr1 / Gr2) | 300 C | 350 C | Seawater, chlorides, oxidising acids, low density |
| Hastelloy C-276 / C-22 | 700 C | 800 C | Strong acids, mixed acid, wet chlorine |
| Monel 400 | 480 C | 550 C | Hydrofluoric acid, seawater, caustic |
| Bronze / copper | 200 C | 250 C | Sparging and aeration where copper is acceptable |
Temperature alone is not the limit. A 316L element rated to 480 C in a reducing atmosphere will oxidise far sooner in air at the same temperature, and a titanium element that is excellent in seawater suffers above about 300 C where its oxide layer becomes unstable. Quote the atmosphere with the temperature.
Where powder elements are used
- Refinery slurry-oil polishing. RFCC slurry-oil filtration to remove catalyst fines. Published pilot work on a fractionation-bottom slurry at 380 C reported ash falling from 2,000-3,000 ug/g to below 100 ug/g at above 95% removal over more than a month of continuous operation.
- Catalyst recovery. Recovering suspended fine catalyst and replacing centrifuges, with filtrate quality below 1 ppm suspended solids in reported installations.
- Gas distribution and sparging. Disc and head forms where pore uniformity sets bubble size, used in aeration, ozonation and gas-liquid contacting.
- High-temperature gas filtration. 310 or Inconel elements ahead of protection equipment in metallurgical and thermal process gas.
- Membrane support. A powder plate used as a support layer under a finer deposited membrane, where the support must be smooth, rigid and permeable.
Cleaning and regeneration
Because the medium is a single bonded metal structure with no binder, it can be cleaned repeatedly without media migration. The method has to suit both the alloy and the contaminant.
| Method | Removes | Watch out for |
|---|---|---|
| Reverse-flow backwash | Surface cake, loosely held solids | Rate of pressure recovery is the health indicator. A recovery point that drifts upward means the cycle, not the element, needs changing |
| Ultrasonic cleaning | Fine particles held in the pore channels | Use a compatible bath chemistry; verify with a bubble point test afterwards |
| Chemical cleaning (acid or caustic) | Scale, polymer, oxidised deposits | The cleaning agent must itself be compatible with the alloy |
| Pyrolytic / furnace burn-off | Carbonised organics | Temperature must stay below the alloy limit quoted above |
| Mechanical brushing or scraping | Soft heavy cake | Do not use on fine grades; it deforms the surface pore layer |
A 316L powder element in cleanable service typically goes through several regeneration cycles before the bubble point drifts beyond the acceptance band. That is the practical reason a sintered element usually wins on total cost of ownership against a disposable cartridge in a dirty, high-temperature duty – not the purchase price.
How to specify one
- Form and dimensions. Overall outer diameter, inner bore, length or wall thickness – or a drawing.
- Rating. State whether the figure is nominal or absolute. If the element protects a component, state the target cleanliness class as well.
- Alloy and atmosphere. Give the medium, its concentration and the normal and peak temperature, plus whether the atmosphere is oxidising or reducing.
- Pressure. Forward differential pressure, and the reverse differential if the element is backwashed. The collapse rating must cover the higher of the two.
- Connection. DOE, 222/226 bayonet, threaded, flanged, tie-rod or welded end caps, plus the seal compound.
Send those five items with a sketch and the rating, alloy and connection can be confirmed before any tooling or production commitment, and the drawing returned for approval.
Related pages
- Sintered stainless steel powder filters – specification table, variants and ordering
- Sintered metal fiber felt filters, the depth-media alternative at high viscosity
- 5-layer sintered wire mesh filters, for when a laminate rather than a powder structure fits the housing
- How to choose a micron rating