Sandvik Sanicro 38/4L7*
Composite tube
for Black Liquor Recover y and other boilers
Product and product history
UP
RT96
TA19
Composite tubes consist of an external layer of stainless steel,
metallurgically bonded to an internal load carrying layer of normal
boiler tube material. All composite tubes are subject to 100% ultrasonic
examination to check for inner and outer surface defects and to verify
the metallurgical bond.
Sandvik has been producing composite tubes since the early 1970s.
The biggest application is furnace walls in recovery boilers for the pulp
and paper industry. More than 1.5 million metres in 3R12/4L7 have
been supplied to more than 250 recovery boilers worldwide.
Sandvik Sanicro 38/4L7 for more severe conditions
Figure 1. First complete floor of Sanicro 38/4L7, installed in a recovery boiler,
delivered by Tampella Power to Mets-Rauma Mills, Finland in 1996.
By courtesy of Kvaerner Pulping, Finland
Grades
Outer component Sandvik Sanicro 38
Type UNS N08825, Mod. Alloy 825, W.-Nr. 2.4858
Chemical composition (nominal), %
C
max.
Si
max.
Mn
Cr
Ni
Mo
Cu
Ti
0.030
0.5
0.8
20
38.5
2.6
1.7
0.8
Type ASME SA-210 A1, EN P265GH, EN 1.0425, W.-Nr. 1.0405,
St 45.8.III, SS 1435.
Chemical composition (nominal), %
C
max.
Si
max.
Mn
P
max.
S
max.
0.18
0.3
0.7
0.030
0.030
Sandvik spec. 7-1-0009
ASME Code Section 1 and Section II
VD-TV Werkstoffblatt 541.03.2001
TV Wien Werkstoffblatt 140
Dimensions and tolerances
Stock standard sizes
Outside
diameter
Total minimum
wall thickness
Thickness
of stainless
component
mm
mm
inch
mm
inch
Minimum
thickness of
carbon steel
component
mm inch
5.08
6.53
6.58
.200
.257
.259
1.42
1.82
1.86
.056
.072
.073
3.66 .144
4.71 .185
4.72 .186
inch
50.8 2
63.5 2.5
76.2 3
Other dimensions can be supplied on request.
Inner component Sandvik 4L7
Specifications
Sandvik has developed a more resistant composite tube product,
Sandvik Sanicro 38/4L7*, mainly intended for the floors of recovery
boilers. This product has considerably improved corrosion resistance.
It is more resistant to SCC, has better fatigue strength and improved
structural stability. See pages 3 and 4.
Tolerances
Permissible variations in O.D. and wall thickness
Outside diameter
0.5%
Total wall thickness
+15/-0%
Thickness of stainless
0.40 mm (0.016 inch)
steel component
The thickness of the stainless steel component is checked by testing
the entire length of each tube.
Welding
Butt welding
Butt welding of composite tubes must be carried out in such a
manner that dilution of the components is kept under control.
The melting point of the bonding zone is lower than the melting
point of the stainless steel, and, if the bonding zone is exposed to
Austenitic filler
metal for top run
60
> 0.12"
(3 mm)
Sanicro 38
Sanicro 38
3
2
1
00.08"
(02 mm)
00.08"
(02 mm)
too much heat, a local melting may occur. Therefore, in order to obtain
the optimum corrosion resistance and mechanical properties of the
welded joints, the following edge preparation (fig. 2) and welding
sequences (fig. 3) are recommended. See table 1.
Load
carrier
Unalloyed filler metal
for root and filler runs
Load
carrier
7062
7061
Figure 3. Welding sequence.
Figure 2. Edge preparation.
Table 1. Filler metals and welding methods for butt welding.
Pass
Welding
method
Filler metal options
specification
Max. heat input 1)
kJ/mm (kJ/in)
Max. interpass
temp. C (F)
Carbon Steel
(No. 1 2)
Stainless Steel
(No. 3)
TIG/MIG
MMA
TIG/MIG
TIG/MIG
MMA 3)
MMA 3)
Matching filler AWS A5.18: ER 70 S-6
Matching filler AWS A5.1E 7018
Sandvik 27.31.4.LCu AWS A5.9 ER 383
Sandvik Sanicro 60 AWS A5.14 ER NiCrMo-3 2)
Sandvik 27.31.4.LCuR AWS A5.4 E 383-16
Sandvik Sanicro 60 AWS SFA5.11 E NiCrMo-3 2)
2.5 (63)
2.5 (63)
1 (25)
1 (25)
1 (25)
1 (25)
150
100
150
100
(300)
(212)
(300)
(212)
1)
A higher heat input may be applied for the root- and filler runs, if the stainless peel off is increased.
Sanicro 60 for waste incineration boilers.
3) MMA is recommended for manual welding to ensure low penetration and maintenance of the carbon steel cross section of the butt weld.
2)
Panel welding
Two types of panel are normally fabricated: either tangential panels,
tubes joined directly by a weld, or finned panels, with tubes linked by
fins (see figs. 4 and 5).
In both cases, shop welding must be carried out with a machine
specially designed for the purpose. The weld should not penetrate
the stainless steel layer of the composite tube, as this may result in
hot cracking or the formation of brittle weld structures. Furthermore,
excessive dilution of the fully austenitic stainless steel filler metal, during
fin welding (carbon steel fin), may also lead to hot cracking or a brittle
weld structure.
MIG (GMAW/131) or SAW (12) are suitable methods for fabrication
of finned panels. The choice of filler metal depends upon the fin material
used. A basic flux should be used in SAW (12). In general, dilution
should be minimised, in order to avoid hot cracking or brittle weld
metal structures. The impurity level in carbon steel fin materials should
be considered, in order to minimise susceptibility to hot cracking.
Thick fins should be bevelled, in order to minimise the amount of fin
material in the weld (see fig. 4).
6857
50
a
t d5/32"
(d4 mm)
t >5/32"
(>4 mm)
a = 0.0390.059"
(11.5 mm)
Figure 4. Edge preparation of fins.
2
Figure 5 . Welded finned panel.
Improved corrosion resistance
Physical properties
Density
g/cm3
lb/in3
4L7
Sanicro 38
7.9
8.1
0.28
0.30
The outer component, Sandvik Sanicro 38, is alloyed with 38% nickel,
compared to 10.5% for 3R12 (TP 304L/W.-Nr. 1.4306).
Fig. 6 shows isocorrosion in H2SO4 for Sandvik Sanicro 38 and
AISI 316L.
Temperature,C (F)
110
(230)
Thermal expansion/conductivity
The composite tube values below have been calculated on a typical size,
dimension 63.5 x 6.53 mm min. (2.5 x 0.257" min).
3R12 = 1.65 (.065") ave
4L7 = 4.88 (.192") min
Sanicro 38 = 1.82 (.072") ave
4L7
= 4.71 (.185") min
Total = 6.53 (.257") min
Total
= 6.53 (.257") min
Thermal expansion, mean values in temperature ranges (x10-6)
Per C
Temperature, C
4L7
30 100
30 200
30 300
30 400
30 500
12.3
12.8
13.5
14.0
14.3
3R12
16.5
17.2
17.7
18.0
18.4
San 38
14.2
14.6
14.9
15.1
15.3
3R12/
4L7
San 38/
4L7
13.4
13.9
14.6
15.0
15.3
12.8
13.3
13.9
14.3
14.6
6860b
90
(195)
Sanicro 38
70
(160)
50
(120)
AISI
316L
30
(85)
AISI
316L
20
40
60
100
80
H2SO4, weight-%
Figure 6. Isocorrosion diagram for Sandvik Sanicro 38 and AISI 316L (in sulphuric acid). The curves represent a corrosion rate of 0.1 mm/year (4 mpy).
The higher nickel content gives Sandvik Sanicro 38 a substantially
higher resistance to sodium hydroxide induced corrosion, see
fig. 7. Sandvik Sanicro 38 is more resistant to stress corrosion cracking
induced chiefly by the presence of chlorides, see fig. 8.
Corrosion rate, mm/year
Per F
Temperature, F
86 200
86 400
86 600
86 800
86 1000
4L7
6.8
7.1
7.5
7.8
8.0
3R12
9.1
9.6
9.8
10.1
10.2
San 38
7.9
8.1
8.3
8.4
8.5
3R12/
4L7
7.4
7.7
8.1
8.4
7.6
San 38/
4L7
7.1
7.4
7.8
8.0
8.2
0.25
(10)
= Alloys with 1721% Cr
= Alloys with 2628% Cr
0.20
(8)
0.15
(6)
0.10
(4)
0.05
(2)
Thermal conductivity
10
W/m C
Temperature, C
4L7
20
100
300
500
46
48
46
42
3R12
15
16
20
23
San 38
11
12
16
19
3R12/
4L7
San 38/
4L7
31
33
35
35
25
27
31
32
20
30
40
50
60
70
% Ni
Figure 7. Corrosion rate of FeCrNi-alloys as a function of Ni content in 28%
NaOH plus 8% NaCl at 99C (210F).
Btu/ft h F
Temperature, F
4L7
3R12
San 38
3R12/
4L7
San 38/
4L7
68
200
600
900
26.5
27.5
26.5
24.5
8.5
9.5
12
13
6.5
7
9.5
11
18
19
20.5
20.5
14.5
15.5
18
18.5
Figure 8. Results of stress corrosion tests in 40% CaCl2 at 100C (212F),
pH = 6.5.
3
Thermal fatigue test
Sandvik Sanicro 38 has higher resistance against thermal fatigue than
3R12 and, therefore, resists larger thermal fluctuations than 3R12 (see
fig. 9).
Arguments for composite tubes versus normal
stainless tubing
Environment: outside flue gas
inside water or steam
1. Composite tubes have lower thermal expansion
2. Composite tubes have higher thermal conductivity, better
heat transfer properties, see table 3
3. Composite tubes eliminate risk of SCC, pitting and crevice
corrosion at the water side
4. Joint welding of composite tubes relies on carbon to carbon welds
5. Composite tubes eliminate low alloyed/high alloyed joints
6. Composite tubes are easier to bend.
In summary
Figure 9. Maximum temperatures where the samples survived 1000 thermal
cycles from room temperature.
Bending
Composite tubes can be bent by the same methods as those used for
single-component tubes.
Cold bending is recommended for radii down to 2.5 x D. For narrower
radii, hot bending is recommended. Temperatures, holding and
quenching times are the same as for carbon steel tubing.
The mechanical, welding and bending properties of a composite tube
are based on a conventional, well tested, low alloyed steel.
Composite tubes give security based on long experience from low
alloyed steels, with the added bonus of substantially improved corrosion
resistance.
Deliveries of Sandvik Sanicro 38/4L7
In total > 30 000 metres have been delivered, of which
> 20 000 metres have been installed in recovery boiler floors
The first installation was made in 1991
The first complete floor installation was made in 1996.
Ask for our reference list.
Heat treatment
Sandvik Materials Technology has a quality assurance system
approved by internationally recognised bodies and holds an
ASME Quality System Certificate as a Materials Organisation.
Approval to ISO 9001 is also held, as well as product approvals
from LRQA, JIS and other organisations.
Recommendations are for guidance only, and the suitability of a material for a
specific application can be confirmed only when we know the actual service
conditions. Continuous development may necessitate changes in technical data
without notice.
Sandvik and Sanicro are trademarks owned by Sandvik AB.
* Swedish patent publication No. 9102410-9, USA patent 5.324.595, patent
pending in other countries, for Sandvik 38/4L7.
SANDVIK MATERIALS TECHNOLOGY, TUBE DIVISION, COMPOSITE TUBES, SE-811 81 SANDVIKEN, SWEDEN, PHONE +46 26-26 30 00 FAX +46 26-25 27 70
www.smt.sandvik.com
S-12126-ENG, Jan 2003, Cancels June 1996. Printed in Sweden. Sandvikens Tryckeri AB
Stress relieving of composite tubes, after cold bending or welding, can
be carried out without any loss of strength or corrosion resistance.
Stress relieving at 650C (1200F) for 30 min. is recommended.
