Chemical Engineering January 2017 - 34

ing the design process. This can be achieved
with isocorrosion curves, such as the one
shown in Figure 10, which are produced
using data from general corrosion testing
whereby a test sample is exposed at a certain
temperature and concentration. Figure
10 relates specifically to the cooler and condenser;
the shaded area represents roughly
the range of condensation of NOx in highpressure
processes.
The curves show that a high-chromium
austenitic stainless steel can be used at
higher concentrations and temperatures.
This can be attributed to the material's extremely
low carbon and impurity contents
compared to the other grades measured:
an austenitic stainless chromium-nickel
steel with a low carbon content; a lean duplex
(austenitic-ferritic) stainless steel; and a
super-duplex stainless-steel seamless pipe.
Closing thoughts
Dependable seals
start with DeWAL
Seals, gaskets and diaphragms can all leak, so DeWAL
Industries has developed a broad range of durable,
bondable PTFE and UHMW film and tape compositions
that create dependable seals despite abrasion, harsh
chemicals, high temperatures or irregular surfaces.
In phosphoric-acid heat exchangers, more
cost-effective performance is one reason
why high-chromium alloyed austenitic
stainless steels are proven
as a suitable replacement for traditional
graphite-reinforced tubing.
Another reason is mechanical integrity,
which can be attributed mainly
to the grade's high-chromium
alloy content.
For nitric acid service, use of highMore
than a dozen DeWAL PTFE and UHMW films and
tapes are designed specifically for gaskets, expansion
joints, valve seals and diaphragms.
chromium-alloyed austenitic stainless
steel is also recommended
when problems are identified with
standard steels of type 304L due
to condensation or evaporation of
nitric acid droplets. Grades developed
particularly for nitric acid service
can withstand the corrosion
problems that may vary from plant
to plant because of local service
conditions. High-chromium austenitic
grades are also expected to
increase the service life by several
times compared to standard 304L.
For critical phosphoric or nitric
acid service, it is vital to carefully
select the material that is best
equipped to withstand corrosion.
While the initial cost may be higher,
a later change to a more corrosionresistant
material will always be
more expensive. The additional
investment can also be recouped
by increased production times that
are enabled by more advanced
material grades.
■
Edited by Mary Page Bailey
Author
Let DeWAL engineering
help you with your most
difficult challenges.
Quality of Product...First
Narragansett, RI 02882
www.dewal.com * usa1@dewal.com
800-366-8356 * 001-401-789-9736
Daniel Gullberg is an engineer
at Sandvik Materials Technology
(SE-811 81, Sandviken, Sweden;
Email:
daniel.gullberg@sandvik.
com; Website: smt.sandvik.com)
specializing in steel grades used
in the fertilizer industry. Gullberg
graduated with an M.S. degree in
materials engineering from Uppsala
University in 2010. Since
Circle 25 on p. 62 or go to adlinks.chemengonline.com/66424-25
34
then, he has been focusing on corrosion issues, application
knowledge and product development, as well as
new grade development, at the R&D department of
Sandvik Materials Technology.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JANUARY 2017
http://smt.sandvik.com http://www.dewal.com http://adlinks.chemengonline.com/66424-25 http://WWW.CHEMENGONLINE.COM
Chemical Engineering January 2017

Table of Contents for the Digital Edition of Chemical Engineering January 2017
