REFRACTORY ANCHOR INSTALLATION BASICS

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.

THERMAL EXPANSION

Steel expands more than ceramic/castables/refractories and this must be taken into account. Usually anchors are

wrapped with something to leave an expansion gap and often a plastic cap is placed on the top of the anchors.

SHELL GEOMETRY

A dome structure is self-supporting and needs no anchors. The interior of a pipe needs less anchors than a flat wall.

ANCHOR SPACING

To a great extent, anchor spacing depends on the type of anchor alloy 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.

The quality of anchors required varies according to the particular application and the centre to centre anchor

measurement. The table as shown below gives the quantity of anchors required per square meter for various

anchor spacings.

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. In order to achieve the best result, especially

if studs are rectangular in base cross section, the long dimension should be welded at an angle to the vertical

position.

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, clipon 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.

WELDING

3CR12 has great weldability and can be readily welded using conventional techniques of austenitic stainless

steels. A great benefit is that it can be welded to other ferrous metals, as well as mild and stainless steels, quite

satisfactorily. The recommended filler wire is grade AWS 309L.

THIN LININGS

Thin linings for abrasion resistance or insulation use sheet anchorage. Hexmetal is an excellent system for 20mm

to 35mm thick linings. Thinner linings can be anchored by tacking expanded metal onto the shell.