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Tube Products International October 2012
The case story
One of Turkey’s largest steel producers wanted to
reduce its energy consumption in one of its annealing
furnaces in the rolling mill section. It also wanted
to maintain and prolong the service life of furnace
recuperators and simultaneously increase steel
production. To make this possible, the recuperators,
essential for recovering outgoing heat from the
furnaces, had to be able to run at higher temperatures.
The maintenance department of the steel mill was, in
2002, in contact with engineers from Sandvik Materials
Technology regarding a solution for their problems.
Technical presentations and discussions were initiated
and the problems and the service parameters were presented
(see Table 1).
The main problem of the tubes was the relatively short lifetime,
caused mainly by oxidation. The existing tube material was a
common, low-alloyed carbon steel, St358, with a lifetime of
2-3 years. One cause was the fuel used in the furnace: 50 per
cent coal and 50 per cent fuel oils.
Another problem and cause for the short lifetime was the
relatively short distance between the furnace exhaust and
the recuperator; this led to very high temperature of the flue
gases entering the recuperator, which in turn attacked the
recuperator tubes more aggressively. The third distinctive
problem the customer faced was regional electrical cut-offs,
which left hot air trapped in the pipes, sometimes for long
periods, causing a faster oxidation of the tubes.
The challenge was to find a steel grade suitable for these
higher temperatures in this corrosive environment, keep the
high efficiency and prolong the lifetime of the recuperator
tubes. After consulting with engineers at Sandvik R&D
together with the customer’s maintenance manager, material
grade Sandvik 253 MA
[3]
was specified as the best solution.
Conclusion and summary
The Sandvik 253 MA tubes were installed in 2003, and were
still in use as of 2011. The new tubes have so far showed a
three times longer lifetime, running without any problems, and
the last inspection was made at the beginning of 2011.
This means that the customer has not only saved initial
tube cost for three complete bundles of recuperator tubes
of the old material, but also saved cost for maintenance,
replacement and tubing cost, standstill cost and loss of
production cost.
On top of this, the new tubes showed a higher efficiency
in production, and a higher resistance to the temperatures,
which resulted in higher preheating temperature of the
combustion air. This resulted in major fuel and cost savings
for the company. The forecast from the customer was to
save approximately €400,000 per year in energy cost for
four furnaces in its two rolling mills. In addition, the company
saved time-consuming processes of documentation and
bureaucratic paperwork for quotation and order processing.
References
[1]
[2]
[3]
Johan Wallin is the global technical marketing specialist
responsible for high temperature products at Sandvik Materials
Technology. He has been responsible for the technical
marketing for Sandvik’s special segments products in the
Middle East and North Africa for the last four years. He is in
close contact with end-users regarding corrosion-resistant,
high-temperature alloys for different applications.
Tommy Sand is a research and development engineer at
Sandvik Materials Technology. He conducts research and
development activities related to stainless steel for high-
temperature corrosion applications at the Sandvik R&D centre
in Sweden.
Sandvik Materials Technology
– Sweden
Figure 2
:
Typical corrosion caused by nitridation/oxidation at high temperatures
