Maximizing Refractory Service Life

Thermal cycling, thermal shock, mechanical impact or vibration can all cause cracking, which in turn can lead to premature failure and substantial cost penalties.   Achieving maximum refractory service life at a minimum cost is therefore a key element in the efficient operation of these processes, and in enabling companies to maximize their competitive edge.

The addition of Ribtec's Rapidly Solidified (RS) steel fibers to castable, gunning and moldable refractories inhibits crack formation (Figure 1) and transforms the conventional refractory from a brittle material to a tough and tenacious composite (Figure 2) exhibiting dramatic improvements in service life.

Figure 1	Figure 2

Ribtec is the refractory industry's No. 1 supplier of stainless steel fiber and is dedicated to product development and customer service.

The Best Choice for Casting and Gunning

Ribtec's direct spun stainless fibers are fully annealed and therefore are more pliable and ductile.  This is of particular benefit during the mixing cycle and when the refractory composite is installed.

These pliable fibers are not only more user friendly than the stiff "needle-like" cut fibers, but also have better flow characteristics. Dispersion is further aided by the optimum Aspect Ratio design guaranteeing rapid fiber separation during the mixing phase.

The ability to install fiber reinforced refractory mixes by gunning is an important consideration in today's modern refractory industry. 

Melt extracted fibers are specified as a mandatory requirement by most international petrochemical companies where fiber containing mixes are routinely gunned inside large processing vessels and ductwork. 

During gunning, annealed RS fibers readily pass through the equipment with minimal additional wear.

Cold drawn wire fibers can cause real problems.  The "stiff, inflexible" fibers often bridge the ports and orifices in the gunning machine, with resulting blockages leading to expensive delays and wasted materials.

50% Less Rebound

RS fiber also has a major influence on the cost of the sprayed linings.  On impact with a sprayed surface, the majority of ductile fibers contained within a mix stay in place, whereas a high proportion of the stiff drawn wire fibers rebound, resulting in a very expensive waste material.  Rebound loss of RS fibers is typically 50% less than that of drawn wire fibers.

Cement Kiln - Chain Section, South Africa

Perfect Refractory-Fiber Bond

The rough cast surface texture and irregular profile of Ribtec RS guarantees "mechanical interlock" with the refractory matrix (Figure 3).  The unique "kidney shaped cross-section" (Figure 4) provides a higher specific surface area for bonding than round or flat fibers, and is free of surface lubricants which are often present on chopped wire and slit sheet fiber and which prevents bonding.

Figure 3	Figure 4
Irregular surface contour of Ribtec RS fiber	High specific surface area of Ribtec RS fiber

Superior Resistance to High Temperature Corrosion

Ribtec RS stainless steel fibers are spun directly from the melt using the company's advanced Melt Extraction (ME) and Melt Overflow (MO) processes.  Rapid cooling of the fiber during manufacture (equivalent to 50,000°C per second) "freezes" the metallurgical structure, capturing it in an optimum state to resist high temperature corrosion - a state which is impossible for conventionally cast steel to match.

The RS processing maximizes the effective distribution of the primary nickel and/or chromium alloying elements throughout the fiber while simultaneously minimizing grain size.  When coupled with Ribtec's skill of blending non-standard levels of performance-enhancing key trace elements to the melt, a unique range of dedicated refractory fiber alloys have been produced which provide outstanding oxidation resistance and unmatched performance at elevated temperature (Figure 5).

Fiber Alloy

As Ribtec produces its own high quality steels, we have developed a range of alloys to cope with the full diversity of service temperatures, operating conditions, combustion gases, etc.  When coupled with the benefits of RS processing, Ribtec's alloys provide outstanding high temperature durability and substantially outperform other so called "equivalent" fiber types on the market with similar Cr and Ni additions.

Fiber Size

Our 3/4 or 1 inch long fiber is a popular choice for addition to preblended dry refractory castables and gunning mixes.  For on-site mixing and for precast shapes our 1-3/8 inch fiber is a preferred choice imparting even greater performance benefits for the same cost (Figure 6).  For special applications other lengths and diameters are also available.

Figure 5	Figure 6

Fiber Costs Up to 50% Lower than Comparable Products

Cost savings are the main reason for adding stainless steel fibers.  In all areas of high thermal and mechanical shock, fibers will at least double refractory life.

Ribtec's low cost/high performance RS fibers provide the quickest payback.  Our quality product costs substantially less because we produce our molten steel and spun fiber on-line in one fully integrated manufacturing plant.  Ribtec is able to keep fiber manufacturing costs to a minimum, which is reflected in the very competitive prices Ribtec charges.

Fiber Addition Rates

It is essential to include sufficient fiber in the mix to prevent the microcracks which develop under thermal stress from propagating into visible cracks which lead to premature refractory failure.  International experience has proven that the most cost-effective fiber addition for enhanced serviceability, irrespective of fiber type used, is 1% by volume.  (This is equivalent to 3-4% by weight for most non-insulating refractory mixes.)

In an endeavor to trim initial costs, a few refractory suppliers have been tempted to use fiber contents as low as 2% by weight.  This is contrary to the current trend towards the use of higher fiber dosage levels (up to 6% by weight) to maximize service life (see Figure 2).  Manufacturers of expensive drawn stainless wire fibers often promote 2% fiber addition in an effort to present their product as "competitive".  This approach is in reality a false economy, since the associated reduced service life of the composite makes the low fiber containing refractories work out significantly more costly over their shorter service life.

Attempts to support the argument for "low fiber addition" by simple laboratory tests of strength and toughness are misleading and do not reflect "real life conditions".

Ribtec - Unrivalled Service

Ribtec understands refractory users need immediate product availability to minimize delays in repairs and downtime costs.  Ribtec's range of products are therefore available from stock for prompt delivery worldwide.  Supported by its international network of local distributors built up over 20 years, Ribtec has developed an unrivalled reputation for service and delivery.  Ribtec's distributors are available to offer expert advice on how to get the best results from fibers in refractories.

• Tailor made, low cost stainless steel alloyed fibers to meet all applications. 
• Specialized packaging designed to minimize handling costs and to meet specific customer requirements. 
• Unrivalled in-depth knowledge of steel fiber technology and economic refractory fiber applications. 

Put simply, no other manufacturer can match Ribtec's service.

Ash hopper wall power station (USA) - fiber reinforced refractory on the left lasted 3 times longer.	Mobil Oil Company Ltd. - Coryton Refinery.  UK FCCU Turnaround 1996.   Ribtec fibers used in Regenerator, Third Stage Separator, Flue Gas Line and Transfer Lines refractories.	Steel refining by injection lance - refractory reinforced with Ribtec stainless steel fibers.