Selecting Steel Anchors for Monolithic Refractory Linings
by Greg Palmer, CPEng, PhD, Palmer Technologies Pty Ltd, Australia
Matthew Smillie, PhD, MPT Solutions Ltd, New Zealand

Abstract
The reliability of stainless steel refractory anchors in refractory lined process vessels is becoming more critical as companies chase greater efficiencies and safety. Therefore understanding the failure mechanism of stainless steel refractory anchors is the key to improved production efficiencies and better safety. The most common refractory anchor failure is at the interface between the hot face and insulation layer.

The poor performance of ceramic anchors has meant that stainless steel anchors are relied upon for maintaining the integrity of the refractory lining. Thus in high temperature environments, greater than 1000 °C, the selection of an appropriate anchor material is vitally important. Equally important is consideration of the load condition that is imposed on the anchor over the time in service.

In the design of static refractory structures the most common selection criteria is the published scaling temperature in an oxidization environment, i.e. the higher the operating temperature generally means a stainless steel with the highest scaling temperature is selected. However, there are other factors in the design phase that need to be considered, including creep rupture, oxidation and yielding.

It has been found that failure of refractory linings, i.e. steel anchors, is due to yielding or creep rupture of the steel at the interface zone. This is due to the combination of stress and high temperatures at that location. Given a high enough stress, the anchor material will yield in a short amount of time (e.g. minutes), or at lower stress levels, the anchor will deform and fracture due to creep mechanisms over a longer time (e.g. hundreds or thousands of hours).

The current approaches to anchor design and spacing which have been developed from experience and applied “rules of thumb” are inadequate and fundamentally incorrect. Setting anchor spacing as a multiple of lining thickness should not be used. This paper shows that designing anchor spacing and anchor material selection must be undertaken by accounting for process temperature, corrosion of steel, lining weight, creep rupture and thermal strain on the anchor steel. The appropriate anchor spacing and anchor thickness can then be determined.