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The pulp
and paper industry has successfully used duplex stainless
steels more than 35 years and a lot of service experience
has become available. Applications include the preparation
of the chips, chemical pulping, bleaching, chemi-thermomechanical
pulping, liquor tanks, paper machines and the recovery and
steam plants. The use of duplex stainless steels can often
be justified on cost since wall thickness reduction of 50%
on carbon steel and 35% on clad steel can be achieved. The
development of the second generation duplex stainless steels
has opened a wide range of applications, including batch and
continuous pulp digesters, oxygen delignifcation units and
pulp bleaching systems. In the digester application, soon
to be the largest application of duplex stainless steel in
this industry, 2205 duplex stainless steel is replacing steel
construction for both safety and operational conditions.
Increased
usage of duplex materials in manufacturing of pulping equipment
Authors:
Alpo Tuomi, (VP Marketing, Valmet Chemical Pulping Oy, Finland)
Allan Löfstrand, (Managing Director, Sunds Defibrator Pty
Ltd., South Africa) Mikko Harju, (Welding Engineer, Metso
Corporation, Pori Works, Finland), originally presented at
Duplex America 2000, Houston, USA, Manuscript number P2061
Abstract
Today
almost all pressure vessels used in the pulp and paper industry
are manufactured of duplex materials, mainly digesters used
for the cooking of chips in alkali conditions, as well as
reactors in the oxygen delignification and bleaching processes,
which work both in alkali and acid process conditions. Furthermore,
duplex material is increasingly used also in the fabrication
of non-pressurised vessels, as well as main process equipment.
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