Pumping corrosive fluids contain- ing abrasive solids is a chal- lenge. To face this challenge,
Sulzer has developed a specific heat
treatment procedure for steel that improves wear resistance, while leaving
corrosion resistance nearly unchanged.
There are several pumps that can
operate in corrosive and abrasive environments, such as chemical or metal
processes and wastewater treatment.
To ensure high reliability, research
and development in the fields of fluid
mechanics and materials technology,
as well as detailed knowledge of the
applications and operating conditions,
are essential, Sulzer said.
Hydroabrasive wear and corrosion
can significantly reduce the lifetime of
pump components. One possibility to
optimize operational life in such aggres-
sive surroundings is the use of specially
adapted hydraulics or seals. Further-
more, the selection of appropriate mate-
rials is the key to substantially extending
the service intervals of a pump.
Cast duplex stainless steels, as defined by ASTM International (the international standards organization formerly
known as American Society for Testing
and Materials), are the materials mainly
used today under corrosive and erosive
conditions. When sourcing from commercial foundries, pump manufacturers are required to use these standard
grades for their components.
Sulzer, meanwhile, operates its
own foundries in Karhula, Finland, and
in Jundiaí, Brazil, allowing the com-
pany to develop alloys and methods
for material treatment that commercial
foundries do not offer. The foundry in
Karhula supplies corrosion-resistant
steel and special cast-iron cast-
ings. Of the total annual production
of roughly 30,000 castings, almost
90% are made of corrosion-resistant
duplex and super duplex cast steel
grades, Sulzer said.
Making a standard material better
Even though duplex steel offers outstanding wear properties along with
its corrosion resistance, some demanding applications require an enhancement. Precipitation hardening
is a specific heat treatment that can
improve the characteristics of duplex
steel without the need for additional
This heat treatment strengthens
the material by allowing the controlled
release of constituents that form precipitated nanoscale and microscale
intermetallic clusters. However, it is
not applicable to all duplex grades and
bears the risk of impairing the corrosion resistance and the toughness of
the respective material. Sulzer has
examined several procedures for the
precipitation hardening of duplex steel
containing copper. By varying the
copper content and the parameters of
the heat treatment, Sulzer engineers
improved the wear resistance of the
material without undermining its corrosion properties and toughness.
Proprietary testing knowledge
Various process parameters, such
as heating rate, heating temperature,
dwell time and cooling rate, influence the size and the distribution of
the precipitates. The optimal control
of these two characteristics provides
the balance between the resulting
increase in strength and the loss of
ductility and toughness.
A Firm Stance
n Sulzer’s foundry in Karhula, Finland, manufactures castings for pumps,
mixers and agitators.
Sulzer develops heat treatment
procedure to strengthen pumps
BY THOMAS KRAENZLER AND RAIMO AROLA
Thomas Kraenzler is head of the materials group of Sulzer Pumps in Winterthur, Switzerland.
He can be reached at firstname.lastname@example.org. Raimo Arola is the material specialist of Sulzer Pumps Finland in Karhula, and can be reached at email@example.com.