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S+C Competence

Alloys for Midrex® Reformers

Centralloy® 60 HT D

Third change, a new concept in tube metallurgy

Since 2004, Schmidt + Clemens has introduced the first DR reformer tubes manufactured with this completely new concept of tube metallurgy. The new alloy Centralloy® 60 HT D aims to increase the operational temperature of the DR reformer box, improving plant productivity and overall plant capacity.

The superior creep resistance of Centralloy® 60 HT D is evident when the operational temperature is raised to new limits. This nickel base alloy has been specially design to withstand the mechanical requirements at extremely high temperatures with the best performance in operation.

Enhanced reliability, longer service life

Centralloy® 60 HT D has been designed for the operation of the reformer tubes up to a maximum firebox temperature of 1185ºC thus, resulting in a significant increase in plant productivity. This is based in a completely new metallurgy with superior oxidation and mechanical properties.

In former times, the chromium oxide scale layer would protect the alloy only up to 1150º C. At higher temperatures, Cr2O3 would evaporate from the tube surface leaving the alloy unprotected against corrosion processes.

Centralloy® 60 HT D is part of a new generation of Schmidt + Clemens alloys named HT Family (High Temperature Family), in which the usual Cr-Si protective layer is enhanced by the addition of Al. These new Ni-Cr-Al alloys, would generate Cr and Al oxide scales, and would provide high temperature corrosion resistance at box temperatures higher than 1200ºC

Based on a Nickel-Chromium matrix, Centralloy® 60 HT D bears five of the most powerful oxide formers, including Aluminium.

Schmidt + Clemens has been able to reproduce successfully the operational conditions of a Midrex® DR Reformer on a small Pilot Plant. A top furnace box temperature of 1200ºC was reached for a period of 6 months. During this operational period, normal operational conditions and related issues were tested. Furnace and TMT temperatures, as well as tube elongations and air flow were recorded.

Two reformer tubes with different alloy configurations were tested at 1200ºC. One tube was operated with the usual alloy configuration that Schmidt + Clemens has been supplying worldwide. The other tube was manufactured using the new alloy configuration Schmidt + Clemens developed for higher temperature operation. This tube configuration uses the alloy Centralloy® 60 HT D, which introduces the Al protective oxide layer, allowing the tube to withstand temperatures in excess of 1200ºC, always maintaining its protective Al2O3 layer.

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