PCE, Refractoriness, and Refractoriness-Under-Load Aren't Synonyms
One number says when the material softens on its own. Another says when it softens while holding a load. Furnaces are full of the second situation.
Three phrases get used as if they mean the same thing: refractoriness, PCE, and refractoriness under load. They are related, but they answer different questions, and picking a lining on the wrong one is a classic way to get a short campaign.
Three words, three questions
Refractoriness is the general, qualitative idea: the ability to take high temperature without softening or melting. It is the umbrella term, not a measurement.
PCE (pyrometric cone equivalent) is a specific lab test. A small cone made from the crushed material is heated next to a set of standard reference cones, and the PCE is the number of the standard cone that slumps at the same moment. It captures softening behaviour under nothing but the sample's own weight.
Refractoriness under load (RUL) heats a specimen under a constant compressive load, commonly around 0.2 MPa, and records the temperature at which it deforms by set amounts. Creep in compression is the more service-relevant cousin: hold at a fixed temperature under load for many hours and measure how much it subsides.
PCE: melting behaviour, no load
PCE is a purity and composition indicator. Two materials with the same aggregate but different impurity levels will show it here. It is a useful ceiling and a good way to compare grades on a shelf. It is not a temperature you can run a loaded lining at.
RUL and creep: melting behaviour, with load
Put weight on the same material at temperature and it starts to move long before it would slump in the PCE test, because the glassy bond phase flows under stress well below the melting point of the whole system. RUL and creep tell you where that starts and how fast it proceeds. For roofs, arches, and anything carrying its own weight over a span, creep data at the working load is the number that matters.
Why the gap, and how big it gets
The size of the gap between PCE and RUL is set by how much liquid phase forms at temperature. A fireclay brick can show a high PCE and an RUL several hundred degrees lower, because it has a lot of glassy bond. High-alumina and basic materials have far less liquid phase, so their RUL sits much closer to their PCE. Impurities widen the gap. Cleaner chemistry narrows it.
Where hot strength fits in
There is a fourth number worth keeping next to these: hot modulus of rupture (HMOR), the bending strength at a stated temperature. RUL and creep tell you when a loaded lining subsides. HMOR tells you whether a spanning member, an arch or a suspended roof block, can carry a bending load at temperature without cracking. A material can pass RUL comfortably and still be weak in hot bending if its bond phase has softened. For roofs and arches, read HMOR and creep together.
Speccing a lining by PCE is like hiring a weightlifter based on how tall they are. Design against the temperature and the load the zone will actually see, checked against RUL or creep data at that load, with margin.
What to actually design with
None of these three numbers include thermal shock, slag attack, abrasion, or atmosphere. They are about hot deformation only. Use PCE to compare and screen. Use RUL and creep to size the lining for load at temperature. Then check the other failure modes separately.
If you want help matching creep and RUL data to a loaded application, talk to us with the span, the load, and the working temperature.