Since the development of monolithic refractory products, metal anchoring systems have been widely utilized in supporting the monolithic materials around the insulated vessels.
The proper design, material selection and installation of refractory anchors is of paramount importance in order to avoid premature failure of the refractory linings. Such failures would be highly costly, both in terms of lost production and the direct costs linked to correctional maintenance activities. This article briefly reviews some of the important considerations for refractory anchor system design and installation.
ANCHOR DEPTH
Many specifications call for refractory anchors to be 66% to 75% of the lining depth. In general practice, however, the anchor should extend no closer than 25mm of the lining surface.
ANCHOR SPACING
To a great extent, anchor spacing depends on the type of material used, the operating conditions and the physical characteristics of the unit to be lined. Spacing from 75mm on centres to 300 or 400mm is quite common. Some specifications call for spacing the anchor on centres three times the lining thickness. General guidelines for the spacing of anchors are as follows:
The more severe the operating conditions, such as cyclic temperatures, physical abuse, abrasion and vibration, the closer the anchors should be spaced.
The lower the physical stress imposed on the lining by the physical characteristics of the unit to be lined, the wider the anchor spacing.
ANCHOR PATTERNS
Diamond, square and satggered anchor patterns have been widely and successfully used. The most important fact is that an irregular pattern is achieved by opposing individual anchors. This increases the overall holding power of the anchor pattern, it also helps prevent cracks from extending dangerously far in any one direction or from linking together in regular networks to cause weakened areas.
ANCHOR ATTACHMENT
The fixing point of a metal anchor is one of the areas of the anchoring system subject to the greatest load. In refractory installation, anchors are attached to the shell in different ways, in addition to welded connections, screw-in, bolt-on, clip-on and plug-in connections are used. The choice of the type of attachment depends on the type of anchor, the alloy, the installation situation and the amount of anchors to be attached. The more common attachment methods are hand welding and stud welding. Hand welding is slower, more costly and requires skilled welders and welding electrodes. Stud welding is much faster, cheaper and only requires semi-skilled welders and no welding electrode is required.