Designing And Failure Of Monolithic Refractory Structures – Part 2
Refractory lining design has posed significant engineering challenges but the understanding of failure mechanisms is enabling improvements in refractory lining life.
Previous research, Part 1, has shown that failure of refractory linings due to creep rupture of the steel anchor at or near the interface zone is the major failure mechanism. This is due to load induced stress (<10MPa) at high temperatures. However, the thermal strain loads on steel anchors occurs at low strain rates, έ s-1, which is about 10-7s-1 depending on the heating rate. Research has shown that the yield stress of a stainless steel is much lower than the published yield stress (which is at a much higher strain rate) and will be < approximately 50MPa. However, once the refractory stops expanding the strain has reached its maximum value and will start to decrease due to creep at temperature. This creep is a relaxation process and occurs very quickly typically less than 30 minutes at temperatures >550C. This means once a refractory system is at steady state the anchor stress will not be maintained and start to decrease due to creep. If the design of the refractory structure is not properly considered the refractory anchors can fail in a short amount of time (e.g. hours).
The current approach to anchor design and spacing which have been developed from experience and applied “rules of thumb” are considered inadequate and incorrect. We discussed the analysis of failed refractory structures and numerical analysis used to predict anchor stress. Our research has shown that non-linear numerical analysis techniques are best used to design refractory structures.