Confronting corrosion issues

Jon Burke, marketing manager for Eutectic, looks at particularly high levels of corrosion that can occur in high temperature applications and offers various protection solutions

Damage caused by wear costs money – in terms of down-time and lost throughput, replacement parts, repair and maintenance. Wear is a prominent phenomenon in all major industries and usually leads to high costs. Corrosion is a complex form of wear to understand and really a science on its own.

Almost all corrosion is the result of some form of chemical attack or oxidation. In the case of steel, the rust that forms is iron oxide, which is a powder when dry and can easily be removed from the surface of the part. Corrosion is a surface attack, so if the surface can be protected, corrosion can be stopped or reduced. Very thin surface coatings such as paints and galvanised layers can be used – this makes thermal spray and non-metallic materials ideal for these applications.
There are several factors that cause, or accelerate the rate of, corrosive wear of metal parts:

  • existence of surface porosity or irregularities. Part of the reason for this is the increased surface area exposed to concentrated chemical attack (pitting or crevice corrosion),
  • presence of external or internal stresses (stress or fatigue corrosion),
  • proximity of two dissimilar metals (galvanic corrosion),
  • elevated temperatures (exfoliation),
  • high humidity in the environment (aqueous corrosion),
  • presence of active chemicals or reagents in the atmosphere or in the medium in which the part operates (intergranular corrosion). The causes of corrosive wear in individual cases are often not clear and significant studies are needed to understand the mechanisms in place and select the appropriate solution.

    In many industries that operate at higher than ambient temperatures, for example smelting, refining, hot forging, casting, power generation and cement production, particularly high levels of corrosion can be experienced. These are known as ‘high-load, high-wear’ applications.

    Waste incinerator

    In a waste disposal incinerator are 40 stepped rows, each containing 60 high-alloyed cast steel grate bars – these slide over each other and push the burnt waste forwards. Air is blown onto the two holes in the grate bars at a temperature of 120°C. Worn zones are located in two places – the pressure side of the grate bars and the two air holes. Worn grate bars are expensive to replace. Having previously used preventive maintenance to try and extend the life, the incinerator operator would disassemble and assemble the grate bars, incurring high down-time costs.

    The solution to truly enhancing the performance life was to preheat the surface across the width of the complete pressure side to at least 250°C, to prevent any cracking. One extra weld was then applied around the air blowholes. The whole grate was placed immediately in vermiculite, the sliding surfaces were flattened with a right-angled grinder, and the bar was finally heat-treated again to relieve further stresses. This procedure used Eutectic MAG wire 45513 and a TotalArc 2 digitally pre-programmed welding machine for faster, de-skilled operations. It extended the working life from one year to more than 700 days and saved the customer around £45,000pa.

    Furnace cooling ring

    The housing, composed of two steel plates in a ring, is cooled down by water and used to isolate the rotating furnace, in which the industrial waste of the feed chute is being burned. This housing is subject to corrosion caused by the combustion gases containing aggressive vapours derived from chlorine and sulphur. The solution to this problem was to protect the surfaces of the two steel plates constituting the internal and external housings, by means of a wire EnDOtec DO*80, one on the interior and one on the exterior.

    The tensions due to the surfacing have not caused any significant deformations after cutting the connecting welds. The steel plates have then been fitted to the final dimensions of the housing. The previous solution was to protect using surfaced steel plates resulting in cracks, which are incompatible with the corrosion-resistance. The hard cobalt alloy layer gives a sufficient resistance to corrosion (as well as abrasion) and has not caused any cracks during the final shaping. The performance life of the equipment was extended by 100% and the customer estimated annual savings to be £24,000.

    Waste & Recycling

    Eutectic offers a new Waste & Recycling Programme for the UK market, which covers all the forms of wear – including corrosion. This innovative programme shows the cost savings and improvements in plant equipment possible through the firm’s wear protection solutions, which reduce repair and maintenance occurrences, while extending working life.

    Eutectic’s business is in helping clients reduce maintenance costs, enhance plant performance and increase working capacity through less down-time. We cover every facet of waste and recycling, from incineration and automobile/tyre recycling to general waste, sewage and glass recycling to name but a few. Also included is data from TeroLink, our world-leading application database containing over 6,000
    successful cost-saving applications. This unique programme takes the application experience of our 800-plus technicians, engineers and business managers around the world and harnesses it in a single database – easy to search, cross-reference and full of detailed descriptions with high-quality images and documented cost savings approved by our customers

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