Ceramic fabrics are woven or needled textiles made from refractory ceramic fibre. They appear wherever a hot surface must be insulated, protected or handled without losing strength: wrapping on steam and condensate lines, covers over valves and flanges, blankets on ladle transfer equipment, and the outer layer of modular furnace linings. Unlike mineral wool or glass fibre, they keep their integrity above 500 degrees Celsius and remain usable beyond 1000 degrees Celsius.
The attraction is not only thermal. A fabric layer can be removed and replaced without dismantling the host equipment, it tolerates vibration and thermal cycling better than rigid board, and it can be shaped on site with a knife. These properties decide whether a hot surface is protected by a permanent lining or by a serviceable maintenance system.
The same properties create the risks. A fabric is porous, so it should not be the only barrier between hot gas and personnel; it can shed fibres; and if it is cut badly or installed with gaps it loses much of its value.
Crystalline insulation, calcium silicate board and refractory brick are excellent where the insulation is permanent and the geometry simple. They are weak where the insulation must be opened repeatedly, on irregular surfaces such as flanges and branch connections, and where movement and vibration are present. Ceramic fabrics handle all three, provided the fastening system is designed with them from the start.
Selection starts with the metal temperature of the equipment and the maximum surface temperature the insulation may reach. The fabric designation must exceed both, with a sensible margin, and the rating must be confirmed against the supplier datasheet rather than assumed from the fibre name. The second step is to define the job: hold insulation in place, act as a removable cover, provide a flame barrier, or form part of a furnace lining.
| Service condition | Recommended fabric construction | Note for the installer |
|---|---|---|
| Pipe and vessel wrapping, 200 to 700 degrees Celsius | Woven cloth or tape of aluminosilicate or glass fibre yarn | Cloth for large areas, tape for elbows and flanges |
| Boiler and furnace penetrations, 700 to 1000 degrees Celsius | Ceramic cloth with stainless or nickel alloy wire reinforcement | Reinforcement holds shape under vibration |
| Removable jacket on valves and sight glasses | Needled felt or blanket with a woven outer cloth | Felt fills the gap, cloth carries the load |
| Flame barrier in ducts and openings | Ceramic cloth curtain, tiles or multi-layer blanket | Must be continuous, gaps remove the barrier effect |
For procurement and acceptance, ask for areal density in grams per square metre, thickness in millimetres, tensile strength in newtons per 50 millimetre strip in warp and weft, continuous use temperature, and the temperature at which the fabric retains half of its strength. Ask for the fibre chemistry and whether the material is pure, blended with a reinforcing fibre, or coated.
For piping, the usual sequence is a line insulation layer of ceramic fibre, board or spray applied refractory in the required thickness, wrapped in a layer of ceramic fabrics, and finished with a protective outer layer of aluminium sheet, stainless mesh or coated glass cloth. The fabric does two jobs there: it keeps the line insulation from falling away, and it gives the operator a surface that stays cool enough to work on even when the inner layer has aged.
On horizontal lines the wrap is applied as tape spiralled with a defined overlap, or as a pre-cut cloth jacket closed with stainless banding. On vertical lines and nozzles, panels are cut and secured with a laced or pinned joint so that the weight of the insulation is carried by supports. Where a line vibrates, the joints must be free to move, because a rigidly tensioned wrap cracks and sheds fibres.
A removable insulation jacket is a fabric system designed to be taken off and put back on without damage. It is the normal solution for valves, pumps, strainers and expansion joints, and for any item opened regularly. The jacket normally has three layers: a liner holding the insulation away from the hot part, an insulation layer of ceramic fibre board or blanket, and an outer layer of ceramic fabric or coated cloth that carries the load.
| Jacket component | Function | Selection point |
|---|---|---|
| Liner | Separates insulation from hot metal and prevents abrasion | Must follow a curved or irregular surface |
| Insulation layer | Sets heat loss and the achievable surface temperature | Thickness follows design temperature, not pipe diameter |
| Outer fabric | Gives strength, weather resistance and a safe surface | Use the grade matching the service temperature |
| Fastening and closure | Holds the jacket closed and allows repeated opening | Banding, toggle fasteners or lacing that will not shed |
The closure is the weak point of every removable jacket. A seam that is only overlapped opens after the first few heating cycles, because the inner layers expand while the cover contracts. Lapse the seams generously and secure them with a continuous stainless band on pipes, and with lacing on irregular shapes. Where a hot surface is visible from the floor, place the closure on the lower or far side.
Furnace linings built from castable or brick are difficult to repair once the hot face is damaged. Modular lining divides the hot face into panels that can be removed individually. In the textile version, ceramic fabrics are cut into blank panels, sometimes quilted with ceramic fibre batting, then coated with a refractory material or backed with a rigid board and a castable facing. The panel is fixed to the shell with studs, hooks or welded anchors and sealed with ceramic fibre rope.
The textile approach works because a panel can be shaped to the furnace contour, and because a damaged panel can be replaced in one shift instead of during a full cold repair. Its limitation is that the fabric has little resistance to slag or abrasion unless coated or faced, so the design needs a wear layer in high velocity zones.
Ceramic fabrics are cut with a sharp knife or with scissors, but they fray at the edge, and the fibre ends are the part most likely to become airborne. Mark the cut with a template or chalk line, cut on a clean hard surface, and support the fabric so it does not drag. Tearing is not acceptable for a load carrying layer: a torn edge is weaker and leaves a path for fibre loss.
Two risks have to be controlled. The first is fire: a ceramic fabric will not burn, but one used as a flame barrier, a curtain or a firestop element must be installed so that it works as a system, with the frame, fixings and adjacent materials taken into account. The second is airborne fibre. Fibres released by abrasion, by erosion of a coated surface or from an unprotected cut edge can be inhaled by people working nearby, and workplace limits for respirable refractory fibre apply in many jurisdictions.
Design measures reduce the second risk before installation begins. Sealed and coated surfaces release less than cut or torn edges, and film backed grades should be specified wherever the fabric is handled frequently. Handling is the third control: cut under local extraction where practical, wear protective clothing and a respirator, and clean with a vacuum rather than a brush, since dry sweeping puts the fibre back into the air.
A fabric installation is easy to inspect and document. During commissioning, record the fabric grade and batch used on each line, the number of layers, the measured surface temperature at normal load, and any visible gaps, cuts or damaged edges. In operation, a monthly walk-down checking exposed edges, loose seams, contamination and local hot spots usually catches problems before they cause a shutdown.
There is no universal figure, because the life depends on the number of opening cycles, the temperature, the atmosphere and the quality of the seam. A jacket opened once a month for inspection can last for years, while one handled every shift on a hot valve will normally need its fabric replaced earlier. Inspect the fabric at every opening and judge replacement on the condition of the fibre.
Not as a general rule. Fabric is a poor stand-alone insulator compared with ceramic fibre blanket, board or spray applied coating, because of its open weave and low thickness. Its normal role is to retain and protect the insulation and to provide a durable outer surface. Where it is used alone, the design must be checked for heat loss and surface temperature.
The usual causes are unprotected cut edges, abrasion from a moving part or from vibration, damage during removal and reinstallation of a jacket, and erosion of a coating applied too thinly. Repeated thermal cycling also weakens the binder that holds the yarn together. Routine inspection of cut edges, seams and coating condition removes most of these problems.
Small tears are repaired by cutting a patch slightly larger than the damaged area, binding the edges and fixing it with a wrap of the same fabric or with stainless banding. Damage near a hot flange or burner should be replaced rather than patched, because the heat concentration will destroy the patch quickly.
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