Rapid NDT Replaces Destructive Refractory Testing

The Challenge

Final inspection of conventional shaped refractories typically involves random destructive testing—crushing samples for strength, sectioning for density. The disadvantages: product destruction, delayed results, labor expense, and statistically insignificant sampling. Only high-quality, high-priced refractories justified NDT costs; conventional products remained tested the destructive way.

Barriers included ASTM compliance requirements, time-consuming correlation development, and difficult interpretation of NDT readings. J.H. France Refractories needed practical methods to extend NDT to production-scale conventional refractories.

The Solution

Mathematical models correlate dynamic modulus of elasticity (Ed) to properties traditionally measured destructively. For 70% alumina brick (229 × 114 × 63 mm), regression analysis on 50 bricks established strong correlations: porosity decreases linearly with Ed (r = 0.893), bulk density increases with Ed (r = 0.871), and modulus of rupture shows the tightest relationship (r = 0.935). A single Ed measurement thus predicts all three critical properties with high confidence.

These equations are valid across most brick shapes. For shapes showing consistent offset, shape factors Fn = (100 - DEV)/100 adjust the calculations. Example: #2 wedges (229 × 114 × 76 mm) showed -4.4% deviation in porosity, yielding shape factor F = 1.044.

Results

One set of empirical equations per mix composition enables NDT-based final inspection for entire product lines. The method produces more meaningful statistical information about structural integrity, strength, density, porosity, and crack location than small-sample destructive testing ever could.

Equations remain valid for specific brands and manufacturing processes. Raw material selection and firing conditions affect regression coefficients, so correlations must be developed per brand—but once established, they enable accurate, cost-effective assurance of final properties.