60 years of duplex stainless steel applications

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17
60 Years of Duplex Stainless Steel Applications
by
Jan Olsson and Mats Liljas,
Avesta Sheffield AB,
S-774 80 Avesta, Sweden
Introduction-
developments
1930-1960
Stainless steels were developed dur-
ing the first decades of this century
in Great Britain and Germany. The
earliest stainless steel types were
martensitic and ferritic iron-chromium
steels but quite soon austenitic iron-
chromium-nickel steels became the
largest group. This was mainly due to
the ease of production and fabrica-
tion, particularly welding, of this type
of steels. The minimum carbon levels
that could be reached with the exist-
ing furnaces and refining techniques
were about 0.08%. This made the
steels sensitive to grain boundary
carbide precipitation in heat treat-
ment operations and in welding. Thus
the heat affected zone after welding
could be sensitised to intergranular
corrosion attack.
In 1927 Bain and Griffiths (1) pre-
sented phase diagrams of the iron-
chrome-nickel system. They described
austenite-ferrite alloys with 22-30%
Cr and 1.2-9.7% Ni. No data were
given on properties in the article.
Avesta Ironworks developed two
ferritic-austenitic stainless steels in
1930 (2). The main object was to
reduce the problem with intergranular
corrosion attack in austenitic steels.
The compositions of the two alloys
are shown in Table 1. Grade 453E
was essentially alloyed with chro-
mium and nickel, while grade 453S
also had an addition of molybdenum
to achieve increased corrosion resist-
ance. The molybdenum addition was
compensated with a higher nickel
content to maintain the ferrite-aus-
tenite balance. These ferritic-austenitic
steels had essentially the same carbon
content as the austenitic grades, but
showed clearly improved resistance
to intergranular corrosion. They also
had equal or better resistance to
uniform corrosion than the austenitic
grades. The positive effect of a
duplex microstructure regarding the
resistance to intergranular corrosion
was described by Payson and
Harrison in 1932 (3) and by Lindh in
1933 (4).
The first ferritic-austenitic stainless
steels contained typically 60-70%
ferrite after quench annealing at
1000-1050°C. The duplex micro-
structure resulted in a much higher
strength than for the austenitic steels,
see Table 2. The duplex steels also
had good castability. Due to the com-
paratively high chromium content the
duplex steels had much improved
scaling resistance as compared to the
austenitics. Therefore, 453E was used
extensively for different high tempera-
ture applications already during the
1930's. The molybdenum-containing
grade 453S was used mainly in the
sulfite pulp industry as castings, bars
and plate. The interesting properties
of the ferritic-austenitic grades re-
sulted in substantial tonnages. Thus,
in 1932, the duplex grades amounted
to 6.5% of the total stainless steel
production which was 5500 metric
tonnes. The production of these
duplex grades was held fairly con-
stant in the following years. During
the second world war the shortage of
raw materials, especially nickel, made
the interest in duplex steels even
greater. Although the use of duplex
steels was fairly widespread, it was
not until 1947, that grade 453S was
included in the Swedish standard as
SIS 2324. Later, this steel also was
listed in USA as AISI 329. It is inter-
esting to note that this grade is still
produced by the company in a
slightly modified version with lower
Table 1.
Typical compositions of duplex steels.
UNS S Cmax. Cr Ni Mo N Oth.
(453E) 0.1 26 4 - -
32900 0.1 26 5 1.5 -
32404 0.08 21 5 2.7 - Cu
31200 0.03 25 5 1.5 0.15
31500 0.03 18.5 5 2.7 0.1 Si
32304 0.03 23 4 0.2 0.1
31803 0.03 22 5 3 0.17
32750 0.03 25 7 4 0.28
32760 0.03 25 7 3.7 0.25 W, Cu
Table 2.
Mechanical properties of ferritic austenitic stainless steels
1
)
Grade 453E Grade 453S
Wrought bar Casting Wrought bar Casting
Yield strength MPa 510 490 590 570
Tensile strength MPa 640 630 715 700
Elongation % 25 13 21 10
Contraction % 48 12 40 15
Hardness Brinell 220 200 240 210
1
) Translated from Avesta Jernverks Catalogue from 1932.

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carbon content and some nitrogen
added. The applications are mainly
forgings and bars for rotating com-
ponents.
Sweden was not the only country
to produce duplex stainless steels in
the 1930's. A Finnish foundry has
been reported as having produced
duplex castings around 1930 (5). The
J. Holtzer steel works in France were
granted a patent in 1936 of ferritic
austenitic alloys containing 16-23%
chromium, 1.5-6.5% nickel, up to 3%
molybdenum and tungsten and up to
2.5% copper (6). From this patent,
Uranus 50* (UNS S32404), one
pioneer duplex alloy, was developed.
Many duplex grades have been
developed since the 1930's to meet
specific service conditions and to
solve different metallurgical problems.
All developments in different countries
cannot be covered in this paper. The
intention of the paper is to describe
parts of the European duplex stainless
steel development and to review
applications over more than 60 years
in different segments.
Developments
1960-1990
As the refining techniques in the
electric arc furnace were improved, it
was possible to gradually lower the
carbon contents in stainless steels.
This was of course also done with the
duplex grades. In the 1940's it was
observed that austenitic stainless
steels showed a certain sensitivity to
stress corrosion cracking (SCO. It
was also found that ferrite additions
reduced this sensitivity (71. The high
resistance to SCC of duplex stainless
steels was described by Colombier
and Hochmann (8). One of the first
new duplex stainless steels with low
carbon content and designed for
SCC resistance, was 3RE60** (UNS
S31500). This grade had a lower
chromium content but more molyb-
denum and silicon than the first
duplex alloys, see Table 1. The silicon
was added to further improve the
resistance to SCC. This grade was
used extensively in components where
* Trade name of Creusot Loire Industrie.
** Trade name of AB Sandvik Steel.
SCC had been a problem with type
304 or 316 austenitic steels. Nitrogen
was not deliberately added to this
steel. However, nitrogen alloying
was practiced later for hot working
reasons.
Although the first duplex stainless
steels proved to have a better resist-
ance to intergranular corrosion than
the austenitic grades, welding with
low arc energies could result in a fully
ferritic high temperature heat affected
zone. This was partly due to the high
ferrite level in the earliest grades. As
the solubility of carbon in the ferrite is
low, grain boundary carbide forma-
tion could occur even in low carbon
grades (<0.03% C). This could result
in intergranular corrosion and re-
duced ductility in the weldments.
The development of a 22% chro-
mium duplex stainless steel in the
1970's was to some extent focused
on the above sensitivity to inter-
granular corrosion of the heat af-
fected zone. Compared to the earlier
duplex steels this alloy had a high
molybdenum content and also a
nitrogen addition. In the patent
application it was claimed that the
new steel was resistant to inter-
granular corrosion after welding as
determined by the Strauss or Huey
test (9). This was the result of the high
alloy content including nitrogen.
However, the proposed composition
range, particularly that of nitrogen,
was very wide allowing for high
levels of ferrite in heat affected zone.
Also, the national standards for the
22% chromium duplex steel had the
same wide ranges. Thus, weldments
with high risks for fully ferritic HAZ
with both intergranular and intra-
granular precipitation of carbides
and nitrides, could be produced
within the specification. This could
cause problems with both hydrogen
embrittlement and pitting corrosion.
More stringent composition ranges
and especially a higher nitrogen level
were shown to be the best solution
and modern grades contain normally
0.15-0.20% N. The 22% Cr duplex
steel (S31803) proved to have much
higher mechanical strength and
better corrosion resistance than types
316L and 317L, and sometimes even
N08904. This duplex steel therefore
made up a low cost alternative for
many applications and could to-day
be considered as the duplex work-
horse. S31803 is produced world-
wide.
An increasing demand of 22% Cr
duplex stainless steel products devel-
oped during the 1980's, particularly
for the offshore industry. Much atten-
tion was paid to welding technique
and welding metallurgy and the
effect on properties. A great number
of research projects in this area were
accomplished and resulted in a
deeper knowledge for both pro-
ducers and users of duplex stainless
steels.
The role of nitrogen in controlling
the microstructure of weld thermal
cycles was first described in the
1980's (10). Thermodynamic data-
base programmes were used to
determine phase development during
heat treatment and weld thermal
cycling (11). This enabled producers
to select a balanced composition for
optimum microstructure in parent
material, weld metal and heat af-
fected zone. Nitrogen was shown to
play an important role in controlling
kinetics of the critical solid state
phase transformation under para-
equilibrium conditions. Nitrogen also
proved to improve the resistance to
pitting corrosion in a similar manner
to austenitic alloys.
In the development of super duplex
stainless steels in the 1980's, thermo-
dynamic data were used. For
example, in UNS S32750, balance
and composition of ferrite and
austenite were optimised to achieve
best properties including pitting
corrosion resistance (12). Two super
duplex stainless steels are listed in
Table 1. A high alloy content resulted
in both superior corrosion resistance
and mechanical strength as com-
pared to the 22% Cr duplex steel.
Thus, the super duplex steels provided
a competitive alternative to the super
austenitic steels such as the 6% Mo
steels for service in aggressive en-
vironments. One such area was the
offshore industry, where super duplex
stainless steels were selected for high
pressure and sea water systems.
Development in the 1980's also
resulted in some lower alloy duplex
stainless steels. One example is
S32304 with the composition listed in

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Table 1. This Cr-Ni steel has a better
corrosion resistance than 304L and is
comparable to that of type 316L. The
obvious advantage, a reduced wall
thickness due to the higher strength,
has been used in several applications
that will be described in more detail
below.
The development over a span of
60 years has resulted in a family of
duplex stainless steels that provide a
very interesting combination of prop-
erties. Simultaneously product devel-
opment has also resulted in a wide
range of necessary product forms
covering most of the items required
for designing and fabricating equip-
ment, machinery components, pipe
lines etc. in duplex stainless steels.
Applications
Pulp & Paper Industry. The pulp and
paper industry, particularly the sulfite
industry, was probably the first pro-
cess industry to use duplex stainless
steels. There were examples of appli-
cations as early as the 1930's. The
Mo-free grade 453E was used in kies
kilns and in vessels for molten lead
due to its high strength at moderately
elevated temperatures. The Mo-con-
taining grade 453S was used in
various armatures and fittings for the
sulfite digesters. One example is 350
mm cast valves made in late 1930's
as shown in Figure 1. Most duplex
applications were castings or for-
gings but several components were
also made of welded plate. One
example is the Brobeck cooler, shown
in Figure 2, which was delivered in
1932.
S31500 was originally developed
to combat SCC in the pulp & paper
industry. The grade has been used
since 1970 with long service life as
tubes or sheets in preheaters to kraft
and sulfite digesters where 304 and
316 type austenitic steels failed by
SCC after only a couple of months.
The duplex alloys generally have
a superior corrosion fatigue strength
when compared with austenitic
alloys. This property has been used
for highly loaded rolls, such as suc-
tion rolls in paper machines. Centri-
fugally cast shells in duplex alloys
have been produced for this applica-
tion since the 1970's by various
foundries. In 1973, shells made from
plate in grade S31500, were intro-
duced (13). The lean composition
made it possible to use controlled air
cooling in the final heat treatment.
This resulted in low residual stresses
and high margins to fatigue failures.
More than a hundred shells, the
largest over 10 meters long and with
100 mm wall thickness, have been
used with good results. A typical
suction roll is shown in Figure 3 (page
20). Shells are also made in grade
S31803 if more aggressive paper
machine environments are foreseen.
In recent years, the suction roll ma-
terial has been given an improved
machinability to reduce manufactur-
ing costs and increase performance
(14). A similar application, where the
high resistance to corrosion fatigue is
employed, is washing presses, also in
the paper mill. Several presses with
perforated screen plates have been
manufactured in grades S31500 and
S31803.
Sulfite batch digesters have been
built mainly with austenitic stainless
steels since the early days of stainless
steel. Due to high pressures, heavy
wall sizes have been necessary. To
reduce costs, the austenitic steels
have been coldstreched or used as
clad plate. An apparent advantage is
to use a duplex stainless steel such as
S31803. The high strength in com-
bination with a better corrosion resist-
ance makes duplex steels outperform
standard austenitic materials of the
types 316L and 317L.
Figure 1.
Cast valve bodies made of 453S (AISI
329) for sulfite digesters.
Figure 2.
A Brobeck cooler fabricated of 453S for a
sulfite plant.

4. acomNo. 2-96
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For kraft digesters carbon steel is
the current construction material. A
considerable thickness allowance
must be made for corrosion. By using
a duplex stainless steel, no corrosion
allowance is needed and the wall
can be reduced by at least 50%.
Grade S31803 has been selected for
several batch kraft digesters in the
1980's (15).
The high strength of a duplex grade
can also be utilized in non-pressur-
ized vessels, one example being pulp
storage towers. Calculations have
shown that it is possible to save both
weight and money, close to 40% and
10% respectively, if such tanks are
made of S32304 instead of lined mild
steel (15). One such an installation
was reported by Ward, a 5000 m3
tank for New Zealand Forest Products
(16).
One of the most aggressive en-
vironments in the pulp & paper indus-
try is the acid bleach stage. Filter
washers for the chlorine and chlorine
dioxide stages are traditionally fabri-
cated in high alloy austenitics or
superaustenitics. For a Swedish pulp
mill the entire chlorine dioxide filter
washer was built in S31803. The
performance after more than six years
of service has been fully satisfactory.
Chemical Process Industry. The
chemical process industry was,
together with the pulp and paper
industry, one of the very first to use
both the strength and the resistance
to intergranular corrosion of the
duplex stainless steels. Caulille in
Belgium placed an order as early as
1933 for an autoclave for the produc-
tion of gun powder, see Figure 4. The
grade used was 453S. The selection
of material was obviously a success
since a second unit was supplied in
1936, maybe a consequence of the
rearmament by the European military
forces at this time. The process used
was probably for the production of
nitrocellulose, i.e. the material was
exposed to a mixture of nitric acid,
oleum and cellulose.
The resistance to SCC has also
been utilized by using more modern
duplex grades. One such installation
took place in 1972 at a Swedish
pharmaceutical industry when two
distillation columns made of S31500
Figure 3.
Paper machine suction roll shell made of S31500.
Figure 4.
Autoclave made of AISI 329 for the
production of gun powder, delivered in
August 1933.
Figure 5.
Distillation columns made of S31500 for
a Swedish pharmaceutical industry.
Figure 6.
Stripping vessels for vinyl chloride monomer made of AISI 329.

5. acomNo. 2-96
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were erected, see Figure 5. The en-
vironment contained 5000 ppm of
chlorides at 100°C.
Another installation where the ma-
terial's selection was based upon the
risk of SCC is shown in Figure 6. In
the production of Poly Vinyl Chloride,
PVC, whether by the emulsion poly-
merization or the suspension poly-
merization method, unreacted Vinyl
Chloride Monomer (VCM) needs to
be reclaimed and the PVC-slurry
purified from the monomers. In the
recovery stage VCM is recovered by
simple flashing and stripping. How-
ever, in the stripping vessel, condi-
tions exist that may cause stress cor-
rosion cracking in austenitic stainless
steels of the type 304L or 316L. In the
mid 1970's, duplex stainless steel was
supplied for such vessels. For this
particular process the operating
temperature is about 85°C, pH value
3-3.5 and the water phase has an
average chloride content of 60 ppm,
occasionally up to 150 ppm.
The fabricated vessels were made
from 5, 6, 12 and 14 mm thick plates
and welding methods were SMAW
and SAW. The units went on stream
in 1976 and have performed satis-
factorily since then.
Similar installations with S31803
and S32550 have been reported in
1991 (15, 16). However, both grades
suffered some SCC which might be
explained by the higher service
temperatures reported for the latter
cases, 105°C.
Duplex grades are doubtles s more
resistant to SCC than conventional
austenitic grades but SCC has also
been reported when S31803 has
been exposed to seawater of 100°C
(19). A highly alloyed austenitic grade
like S31254 is better in that respect.
The modern duplex grades, S31803
especially, have also been used
extensively for solving uniform cor-
rosion problems. Table 3 shows the
maximum chloride contents that 316L
and S31803 can tolerate when ex-
posed to a wet process phosphoric
acid (WPA) at three different levels of
inhibitors, i.e. of ferric and aluminium
oxides. The consequence of this su-
perior corrosion resistance was that
Boliden Kemi specified S31803 when
installing an additional WPA storage
tank in 1988. A secondary effect of
Table 3.
Chloride content (ppm) giving a corrosion rate of 0.1 mm/year for some diffe-
rent steel grades when exposed in WPA* with different inhibitor levels at 50°C.
Inhibitor, % S31803 AISI 317LN AISI 316LN
Fe2O3 Al2A3 (S31753) (S31653)
0.9 0.6 >1000 200 >100
1.5 0.6 >1000 450 >400
1.5 1.1 >1000 600 400
* 53% P2O5, 5% H2SO4, 1.5% HF, 0.4% CaO, 0.2% SiO2, 0.7% MgO.
this material selection was that the
weight could be reduced by some
30% due to the higher strength of the
duplex grade (20), and the cost was
reduced by 7000 US dollars. The
plant in question was later bought
by a competitor and then closed but
the tank made of S31803 was still
reported to be in good condition.
Good performance of S31803 not
only in storage tanks but also in filter
pans has been reported by Audouard
et al (21).
Other chemical process industry
applications have been reported at
previous duplex stainless steel con-
ferences in The Hague and Beaune, a
few examples being
- pressure vessels made of type AISI
329L for a styrene plant (22)
- maleic anhydride cooler (17)
- flash drum heater in an amine plant
(17)
- reactor coil in an EDA plant (17)
- urea plant absorber cooler (17)
- benzoic acid reboiler (17)
The conclusion must be that duplex
stainless steel, mainly S31803 but
also S32304, in many cases can be
cost effective alternatives to standard
austenitic grades like AISI 304L, 316L
and 317L and sometimes also to
highly alloyed grades like N08904.
Food and Beverages. The resistance
to SCC and high strength are also of
concern in a number of operations
within the processing and handling of
food and beverages. Hot, chloride
containing solutions are common
within this industry.
One very early installation of a
modern duplex grade took place in
1973 when SCC-cracked 316 syrup
tanks in a Swedish sugar plant were
replaced by S31500 tanks. Unfor-
tunately S31500 was not fully
developed at that time, there being
an unfavourable balance between
ferrite and austenite forming elements.
This resulted in an almost fully ferritic
heat affected zone after welding;
carbides were precipitated and
intergranular corrosion occurred.
The syrup contained approximately
10 000 ppm of chlorides, had a pH
of 5, and the service temperature was
80°C.
The replacement was made by a
modernized version of S31500. An
increase of the nitrogen and nickel
contents towards the upper limits of
the specification ensured the neces-
sary amount of austenite in the heat
affected zone. The replacement tanks
were installed in 1974 and no prob-
lems have been reported since then.
Another application where SCC
was considered as a major concern is
driers for spent grains in breweries
and whisky distilleries. The spent
grains can contain close to 10 000
ppm of chlorides and the pH is as
low as 3.5. The wall temperature of
the drier is 170°C and the risk of SCC
is, at least at a first glance, obvious.
Some ten rotating driers made of
duplex stainless steel, mainly S31500,
were installed in the mid 1970's.
However, later experiences have
shown that the moisture content of the
spent grains is not high enough to
form a liquid film on the steel surface,
which is a prerequisite for corrosion.
The consequence was that the
manufacturer of these driers later on
changed material to a conventional
austenitic grade of type AISI 304 in
order to reduce the costs.
Hot water is of course handled in
hot water tanks and also calorifiers.
Temperatures approaching 100°C

6. acomNo. 2-96
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with some 100 ppm of chlorides imply
an obvious risk for SCC in standard
austenitic grades of type AISI 304.
The first duplex hot water tank in-
stalled was for an Australian brewery
in 1974 and the material, S31500,
suffered the same problem as the
syrup tanks described above. Leak-
age was detected after only 14 days
of service.
However, this problem was over-
come by a modification of the
chemical composition and since then
a number of duplex hot water and
hot liquor tanks have been installed.
The first grade to be used was
S31500 in 1974, then followed by
S31803 in the early 1980's and the
latest being S32304 in 1991, see
Figure 7.
The duplex grades represent a cost
effective alternative to the standard
austenitic grades for handling hot
water within brewereis, dairies etc.
The cheapest alternative should be
S32304, while S31803 should be
considered at the highest chloride
levels, i.e. at least at 500 ppm and
above.
Transportation. An early attempt to
utilize the high strength and the good
resistance to fatigue of S31500 was
made in 1978. A Swedish manufac-
turer of road tankers for milk used this
grade for the support beams upon
which the tank is attached to the
chassis via a carbon steel plate, steel
springs and rubber gaskets. Since
these road tankers are used for
collecting milk from farms they are
exposed to high dynamic loads due
to poor condition of some country
side roads. Some forty tank con-
tainers were equipped with this type
of duplex stainless steel beams but it
never became a success.
Cracks occurred in the welds be-
tween the stainless beams and the
carbon steel plate. This was ascribed
to notches in poor quality welds. The
manufacturer went back to austenitic
stainless steel beams, type 304 ma-
terial, and the cracking problem was
solved if the construction was made
heavier.
Another installation, a successful
one, of duplex stainless steel in a
road tanker was presented at the
Beaune conference (18). In that case
Figure7.
Hot water tank and calorifier made of
S32304 for an Austrian brewery.
the lower thermal expansion of a
duplex grade, compared to an
austenitic, resulted in less buckling of
the tanks during transportation of hot
cargoes. However, the high strength
of a duplex grade can normally not
be utilized for road tankers due to
existing design rules. It is only in
cases of high pressures, i.e. pressures
of 10.5 bar and above, where the
strength enables wall thickness
reductions and cost savings (18).
Perhaps the biggest single field of
application, after offshore, for duplex
stainless steel is chemical tankers.
Despite the large number of cargoes
transported, corrosion hazards are
linked to mainly three situations (23).
1. Uniform corrosion in connection
with WPA with too a high content
of impurities in form of chlorides
and fluorides. The superior cor-
rosion resistance of S31803 in
comparison with AISI 316L and
317L has already been described
above.
2. Uniform corrosion in dilute sul-
phuric acid contaminated with
chlorides. This is occasionally a
consequence of inadequate
rinsing after cleaning of the tanks
with seawater after a sulphuric
acid transport. Also under such
conditions S31803 is superior to
316L/317L.
3. Pitting either under the sludge
when seawater has been used for
the washing after a WPA cargo or
during the transportation of chlor-
inated hydrocarbons. S31803 is
far superior to 316L and 317L
against pitting corrosion.
Another advantage of the duplex
grades is their higher mechanical
strength. The consequence of that is
that thinner plates can be used when
building the ships, resulting in
reduced weight and reduced fuel
costs (or higher dead weights).
The first ship built with tanks made
of S31803 was launched in 1987 and
today (September 1993) more than
30 marine chemical tankers are in
service.
Experience with S31803 has been
very satisfying, in fabrication, i.e.
reported by the shipyards, and in
service performance.
Offshore Industry. The high strength
and good corrosion resistance of
duplex stainless steels have been
employed for down hole tubulars in
corrosive wells since the early 1970's.
Duplex stainless steels were also used
quite early in many applications in oil
refineries to solve problems with stress
corrosion cracking. In the offshore
industry a large demand for these
steels arose when the need for cor-
rosion resistant, high strength gather-
ing pipelines between wells and the
coast became apparent. The product
to be transported was gas containing
CO2 and traces of H2S. The first pipe-
lines of this kind were installed off the
Dutch coast in the late 1970's. The
pipelines were produced in seamless
pipe of grade S31803. Later, several
thousands of tonnes of seamless or
welded pipe in this grade were
installed. Initially, much work was
done in welding research to develop
suitable methods with high deposition
rates for field welding of the pipes.
In the late 1980's super duplex
stainless steels were also introduced
to the offshore industry. In fact, the
offshore industry was the first main
application area for this type of steel.
The main target was to use the steel
in high pressure process systems. The
higher strength was an obvious
advantage over the austenitic stain-
less steels. On certain occasions
super duplex steels were also in-
stalled in sea water systems due to
competitive price over 6% Mo super
austenitic steels.
Another interesting duplex applica-
tion for subsea service is a new type
of umbilical where a bundle of small

7. acomNo. 2-96
23
diameter hydraulic tubing in UNS
S32750 is surrounded by a larger
diameter pipe of the same grade. This
choice of material eliminates the risk
of collapse and the need for armour-
ing. Several umbilicals are now being
installed in the North Sea.
Construction. The duplex grades can
of course be utilized in applications
where their high strength is the prime
reason for the use. Typically there are
requirements for resistance to atmos-
pheric corrosion, which of course can
be demanding, and a higher strength
material enables weight savings and
direct or indirect also cost savings.
One such example is the use of
mainly S32304 and to a lesser extent
also S31803, for offshore blast walls.
The function of these walls is to resist
the pressure from a gas explosion
thereby guiding the blast wave into a
predetermined direction causing as
little harm as possible. Calculations
by different engineering companies
have indicated that duplex grades
should be far superior to austenitic
grades of type 316. That has also
been confirmed by full scale explo-
sion tests (24). Typical weight savings
are in the range of 30-35% which
means that the installed amount of
some 2000 tonnes of duplex stainless
steel corresponds to reduced topside
weights in the range of 1000 tonnes
for eight North Sea platforms in total.
Two other examples can be found
on the Canary Islands where the
harsh climate (harsh to metallic
materials rather than human beings),
has caused severe corrosion on
different zinc coated mild steel com-
ponents.
For the refurbishment of the seafront
promenade of three beaches, Mas-
palomas. Inglés and San Augustin, it
was decided to install stainless steel
hand rails. Although 316 was dis-
cussed initially the final decision was
for S31803. In total 3400 m of tubes
and 5 tonnes of sheet were installed
for 1150 m of hand rails, see Figure 8.
The main reason for selecting S31803
was the superior pitting resistance.
Another similar application, is lamp
posts made of S31803. Lamp posts
made of zinc coated mild steel
suffered corrosion caused by high
humidity, high chloride content in the
air, and urinating dogs (and maybe
tourists). A standard austenitic grade,
AISI 316, was used for the first re-
placement of some 2000 lamp posts
but later on also S31803 has been
utilized (20). The higher strength of
S31803 enables a weight reduction
of 20% (from 75 to 60 kg per post)
which roughly balances the higher
price per kg. The extra benefit is of
course the better resistance to chlor-
ide induced corrosion, with conse-
quently less staining.
Conclusions
• Duplex stainless steel has been an
established material within a
number of industries for many years.
• Fabricators of duplex stainless steel
components have progressed a
long way up the learning curve.
Most welding and other metal-
lurgical problems have been
solved.
• The corrosion resistance of the
duplex grades makes them suitable
in a number of harsh environments.
• The high strength of the duplex
grades enables both weight and
cost savings when they are used as
corrosion resistant construction
materials.
Figure 8.
Handrails made of S31803 along the
promenade of beach Maspalomas of
Canary Islands.
References
1. E. C. Bain, W. E. Griffiths, Trans AIME, 75
(1927), p. 166.
2. C. Ericsson, Bergsmannen, (1988), p. 25 (in
Swedish).
3. P. Payson, N. J. Harrison, Trans AIME, 100,
(1932), p. 306.
4. G. Lindh, Jernkontorets Annaler, (1933),
p. 530 (in Swedish).
5. Private communication.
6. French Patent No. 803.361, (1936).
7. H. Benneck, Korrosion u Metallschutz, 20
(1944):4, p. 133.
8. L. Colombier, J. Hochmann, « Aciers
inoxydables, Aciers réfractaires », Dunod,
Paris, (1955).
9. German Patent Application No. 2 255 673,
(1972).
10.H. Miyuki et al. Duplex Stainless Steels,
St Louis, ASM. (1982), p. 95.
11. S Hertzman et al, DSS'86, The Hague
(1986). p. 257.
12. Swedish Patent Application No. 8504131-7,
(1985).
13. M. Liljas et al. Pulp & Paper Industry.
Corrosion Problems, NACE, (1974), p. 88.
14. J-O. Andersson et al. Application of
Stainless Steels '92, Stockholm (1992),
p. 379.
15. J. Nordström, B. Rung, J. Olsson. Tappi
Engineering Conference, Orlando (1993).
16. I. Ward, DSS'91, Beaune (1991) p. 1085.
17. D. J. A. Fruytier, ibid p. 497.
18. J. G. A. Aerts and M.J.G. Notlen, ibid
p. 1141.
19. I. Ovstetun, 9th Int. Conference on
Materials and Corrosion Offshore, Norway
(1993).
20. H.L. Groth, Ml. Erbing, J. Olsson, DSS'91,
Beaune (1991) p. 1257.
21. J. P. Audouard, P. Soulignac, ibid p. 1121.
22. J. Olsson, S. Nordin, DSS'86, The Hague
(1986) p. 219.
23. B. Leffler, DSS'91, Beaune (1991) p. 567.
24. Ml. Erbing, H.L Groth, Structural Design
Against Accidental Loads, London (1992)
p. 4.1.1.
This paper was first presented at the
NACE Corrosion '94 conference in
Baltimore, Maryland, 1994. Reprinted with
kind permission of NACE (National
Association of Corrosion Engineers,
Houston, Texas), the original copyright
holder.

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