Chemical Engineering July 2022 - 34

TABLE 3. PHYSICAL PROPERTIES
Steel grade
Density, kg/
dm3
S32654
S31254
N08031
Alloy 625
N06022
N10276
N06059
8.0
8.0
8.1
8.5
8.7
8.9
8.6
Thermal
conductivity
at 20°C,
W/m.K
11
14
11.7
9.8
9.4
10.6
10.4
only small additions of nickel and
molybdenum. Adding nickel and reducing
the carbon content can improve
their rather poor weldability.
Martensitics are magnetic and hardenable.
The corrosion resistance of
these steels is generally lower than
the other stainless-steel families
and they are used mainly when high
hardness is a key requirement.
Ranking stainless steels
The PRE number is used to rank different
stainless steels regarding their
resistance to pitting corrosion, taking
into account the effect of the most
important alloying elements. PRE is
calculated by the following formula:
PRE = %Cr + 3.3 × %Mo + 16 × %N
(1)
The higher the PRE, the higher the
resistance to pitting.
Comparing S32654 to other alloys
For very demanding corrosion resistance,
stainless-steel
S32654
features
alloying elements that are
very important for resistance to localized
corrosion, such as Cr, Mo
and especially nitrogen (N). This
gives the grade resistance to pitting
and crevice corrosion that will
always outperform Alloy 625. Also,
S32654 is stronger than standard
austenitic stainless steels and nickel
alloys, while having the formability of
a conventional austenitic grade.
Cost. In terms of pricing, S32654 sits
between 316L, regarded as the starting
point for high-performance stainless
steels, and Alloy 625. Using 316L
as the baseline, as shown in Table 1,
S32654 is clearly considerably less
expensive than Alloy 625 while offer34
Electrical
resistivity
at
20°C, Ohms.
mm2/m
0.78
0.85
1.03
1.25
1.14
1.25
1.26
Modulus of
elasticity at
20°C, GPa
190
195
198
209
206
208
210
Coefficient
of thermal
expansion,
10-6/K
15
16.5
14.3
12.5
12.4
11.7
11.9
ing comparable performance.
A key benefit of S32654 is that it
offers better price stability than Alloy
625. This is because it has a lower
percentage composition of nickel
and molybdenum that are particularly
subject to variations in commodity
pricing (see Table 2).
Density. As
seen in Table
3,
S32654 has a lower density than
Alloy 625 - 8.0 compared with
8.5 kg/dm3. Although that difference
may appear small, it could be
crucial to the project costing. For
example, the lower density might
result in a typical reduction of
6% in tonnage when buying large
amounts of material, such as for a
long pipeline. Both stainless steel
and nickel alloys are purchased
by the ton, so the potential weight
saving translates directly
into cost savings.
Furthermore, the lower
density of S32654 also
makes the whole system
lighter. This could
enable easier handling
and installation, which
might be especially important
for subsea and
offshore structures.
Mechanical properties.
The
Steel grade
S32654
S31254
N08031
Alloy 625
N06022
N10276
N06059
mechanical properties
of some typical
corrosion-resistant alloys
are shown in Table 4,
namely the proof stress
(Rp), tensile strength
(Rm) and elongation
(A50). The conclusion is
that S32654 is stronger
than Alloy 625, enabling
components to be manufactured
using thinner
gauges, saving on both
Steel grade
S32654
S31254
Alloy 625
N06022
N10276
weight and cost.
Fabrication. An important indication
of a material with good drawing
properties is its " r-value " , otherwise
known as the plastic strain ratio.
The higher the r-value, the better.
Furthermore, measuring the r-value
in different tensile directions shows
how a sheet material will withstand
thinning during forming.
Figure 2 confirms that S32654
has excellent
r-values
in
different
directions, and much better than
316L. That makes it ideally suited for
pressed components such as sheets
for PHEs. The material also has similar
deformation hardening rates to
other austenitic grades.
S32654 is also suitable for hot
working. To maintain its mechanical
properties, it should be quenched
at a temperature of between 1,100
to 1,200°C to remove intermetallic
phases formed during the hot
working operation. For welding,
S32654 has good weldability in
common processes.
In common with all austenitic
stainless steels, S32654 workhardens
quickly. This, together
with
its
high toughness, means
that it can be perceived as challenging
from a machining perspective
in operations such as turning,
milling and drilling. However, with
TABLE 4. MECHANICAL PROPERTIES
Rp0.2
Rm
≥ 430
≥ 300
≥ 276
≥ 330
≥ 310
≥ 283
≥ 310
≥ 750
≥ 650
≥ 650
≥ 730
≥ 690
≥ 690
≥ 690
TABLE 5. CPT AND CCT TESTING
ASTM G48 E and F1
CPT, °C
> BP3
65
90
> 100
> BP
CCT, °C
60
35
25
60
50
A50
≥ 40
≥ 40
≥ 40
≥ 35
≥ 45
≥ 40
≥ 45
Green death2
CPT, °C
90
60
75
-
100
1. ASTM G48: 6% FeCl3 + 1% HCl; 24 h
2. Green Death: 11.4% H2SO4 + 1.2% HCl + 1% FeCl3 + 1% CuCl2;
24 h
3. BP = boiling point
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JULY 2022
http://WWW.CHEMENGONLINE.COM
Chemical Engineering July 2022

Table of Contents for the Digital Edition of Chemical Engineering July 2022
