Dr Greg Palmer

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Research / Refractory Anchors, Refractory Linings

Designing and Failure of Monolithic Refractory Structures – Part 1

Introduction

The design of static refractory structures has traditionally been based on empirical or trial and error methods and has evolved over the years. Design methodology has been based on heat transfer analysis for material selection and the most common selection criteria are the published scaling temperatures of the anchor steel in an oxidization environment and a 1D heat transfer analysis to determine the interface and shell temperature under perfect conditions [1, 2]. The problem witha 1D heat transfer analysis has been discussed previously [2] and does not take into consideration the anchors temperature profile. It has been shown that the temperature of the anchor is critical in refractory lining design and design life.

Refractory lining design has posed significant engineering challenges but the understanding of failure mechanisms is enabling improvements in refractory lining life.

Previous research [5] has shown that failure of refractory linings is primarily due to creep rupture of the steel anchor at or near the interface zone. This is due to the stress induced by the thermal load, which is generally a low stress (<10MPa) at high temperatures. Given a high enough stress,the anchor material will fail in a short duration (e.g. minutes) but at relatively lower stress levels, the anchor will deform and fracture due to creep mechanisms over time (e.g. hundreds or thousands of hours).

The current approach to anchor design and spacing which has been developed from experienceand applied “rule of thumb” is considered inadequate and fundamentally incorrect. This paper discusses the engineering principles that need to be considered when determining anchor spacing and selecting anchor material. Our research has shown that anchor design needs to consider maximum process temperature, corrosion of steel when encased in concrete, lining weight, the placement of the anchor relative to the panel centroid, creep rupture stress at the maximum temperature and thermal strain on the anchor steel. This can be done by non-linear numerical analysis.

The reliability of stainless steel refractory anchors in refractory lined process vessels is the key to efficiency and safety. Therefore understanding the failure mechanism of stainless steel refractory anchors is critical to improve production efficiencies and safety. With advances in technology it is possible to design refractory structures with greater reliability and the trial and error approach can be replaced with finite element analysis (FEA) more effectively and economically.

It is possible to provide guidelines which can form the basis of international standards for the design of refractory structures. It is also clear that the use of 1D perfect heat transfer and anchor metal selection based on scaling temperature is totally inadequate for design purposes.