Sandvik® 3R12/4L7
Composite tubes for recovery boilers
and other boiler applications
A superior alternative
to carbon or low alloy
steels
Sandvik 3R12/4L7 composite tubes have been developed to cope
with the corrosive conditions around waterwalls in black liquor
recovery boilers (BLRB). They are also used in other corrosive
steam boiler applications, such as waterwalls, evaporators and
superheaters in biomass, municipal waste fired boilers and waste
Figure 1. Hot extrusion.
heat boilers in the metal smelting industries.
To date, Sandvik 3R12/4L7 composite tubes have been installed
Production route of composite tubes
in more than 300 recovery boilers around the world. With the first
commercial installation in 1972 still operating successfully, the long
service record demonstrates that their performance is excellent
and that composite tubes provide a superior alternative to carbon
or low alloy steels. Inner and outer component
From inspection of recovery boilers, the corrosion behaviour
of composite tubes is well documented. Laboratory investigations
after prolonged operation show no micro-structural changes, a
perfect bond between the stainless and carbon steel components
Extrusion billet
and only a few cases of corrosion.
The overall performance of Sandvik 3R12/4L7 composite tubes
installed in furnace walls indicates a general service life of well
over 30 years.
For more severe conditions
For more severe conditions two, more resistant outer compo-
Hot extrusion
nents alloys, Sanicro™ 38 and Sandvik Sanicro 67, are available.
Sanicro 38 is mainly intended for the floor in recovery boilers
and Sanicro 67 for air ports and floors. These products have con-
siderably improved resistance against stress corrosion cracking
(SCC), improved fatigue strength and structural stability.
For more information, see the respective product sheets for:
Extruded composite tube or composite hollow
Sanicro 38 and Sanicro 67.
For higher steam pressures
For higher steam pressures the almost 40% stronger inner compo-
nent, Sandvik 3Mo1 is recommended. For more information, see
page 2 and 4.
Cold pilgering
Non destructive testing
Figure 2. Sandvik composite tubes consist of two different
materials metallurgically bonded together through hot extrusion.
By selecting the correct alloy for the outside and inside compo-
nent, the corrosion resistance and the mechanical properties are
optimised and a tube that meets conflicting material requirements
inside and outside is obtained.
1
Grades
Outer component Inner component
Sandvik® 3R12, EN 1.4306, ASTM 304L Sandvik 4L7, EN 1.0425, P265GH, ASME SA 210 A1
Inner component
Sandvik 3Mo1, EN 1.5415,
16Mo3, (ASME SA 209 T1, lower Mo content)
Chemical compositions (nominal), %
Sandvik ® C max. Si Mn P max. S max. Cr Ni Mo
3R12 0.030 0.5 1.3 0.030 0.015 18.5 10 –
4L7 0.20 0.3 0.7 0.025 0.020 – – –
3Mo1 0.20 0.3 0.7 0.025 0.020 – – 0.3
Dimensions, standard sizes
Outside diameter Total minimum wall Thickness of stainless Minimum thickness
thickness component of component
mm inch mm inch mm inch mm inch
38 1 1/2 5.00 0.197 1.30 0.051 3.70 0.146
50.8 2 5.08 0.200 1.30 0.051 3.78 0.149
63.5 2 1/2 6.53 0.257 1.65 0.065 4.88 0.192
76.2 3 6.58 0.259 1.65 0.065 4.93 0.194
Permissible variations in straightness Tolerances
Out-of-straightness max 1.5 mm/1000 mm Permissible variations in O.D. and wall thickness
(0.06 inch/39.4 inch). Outside diameter 38 mm (1 1/2 inch) ± 0.2 mm (0.008 inch)
50.8 mm (2 inch) ± 0.25 mm (0.010 inch)
Specifications 63.5 mm (2 1/2 inch) ± 0.3 mm (0.012 inch)
Sandvik specification 7-1-0009 76.2 mm (3 inch) ± 0.38 mm (0.015 inch)
PED 97/23/EC Total wall thickness O.D. <50.8 mm (2 inch); +22%-0
EN 10216-2, EN 12952 Annex C O.D. ≥50.8 mm (2 inch); +15%-0
ASME Code Section I and Section II
Thickness of stainless steel component
VD-TÜV Werkstoffblatt 541 03.2001
+ 0.60 mm (0.024 inch) – 0.40 mm (0.016 inch )
The thickness of the stainless steel component is verified by Eddy
current testing of the entire length of each tube.
Figure 3. Metallurgical bond in Transducer
a compositetube of Sanicro™ (line-focused) Oscilloscope picture
28/4L7(UNS N08028/SA210-A1). Rejection level
The stainless layer is at the top of Water (the second echo)
the figure.
s
es n
o
Ca inl
rb
Sta
Reference standard FBH
Figure 4. Schematic diagram of metallurgical bond inspection
(Immersion-technique).
.
Figure 5. Fabricated lower furnace wall including air and smelt spout
openings, by courtesy Andritz, Finland.
Figure 6. Welded membrane panel.
2
Welding
Butt welding see Figure 6. Earlier boilers were also built with a tangential panel
In order to achieve a weld with optimum corrosion resistance and design i.e. with tubes joined directly by a weld. In both cases, shop
mechanical properties, butt welding of composite tubes should welding must be carried out with a machine specially designed for
be carried out in such a way that dilution of the components is the purpose.
controlled. The weld should not penetrate the stainless steel layer of
The preferred welding method is MMA (SMAW/111) with the composite tube, as this could lead to the formation of a
covered electrodes. TIG (GTAW/141) and MIG (GMAW/131) are brittle structure in the load-carrying carbon steel component.
also acceptable methods. Furthermore, excessive dilution of the stainless steel filler metal
Edge preparation, welding methods and filler metals should be during fin welding with a carbon steel fin can also result in a brittle
chosen, so that the desired corrosion and mechanical properties structure. Suitable welding processes and filler metals are shown
are obtained. in the table.
Before welding the carbon steel component, the stainless steel
layer should be removed by machining close to the joint, in order Membrane wall panels
to minimize dilution, see Figure 7a. The carbon steel component Welding should be performed from both sides of the panel. In
is welded with an unalloyed filler metal, Figure 7b. The stainless order to avoid embrittlement and subsequent cracking, dilution
component should be welded with an over-alloyed austenitic filler should be limited to an extent that can be tolerated by the filler
metal, see table. metal. In addition, thick carbon steel fins should be bevelled in
A composite tube butt weld correctly performed will be free order to minimize dilution, see Figure 8.
from embrittlement and resistant to stress corrosion cracking
(SCC) from the water side. Tangential wall panels
Welding is performed in a single pass from the inside of the panel
Panel welding (furnace side) in the natural joint formed between the tubes, see
Two types of furnace wall panel are normally fabricated – the Figure 9.
most common are membrane panels with tubes linked by fins,
Weld & Pass Welding Filler metals Correspond to Max. heat input
methods kJ/mm (kJ/inch)
Butt weld root & filler run 3) MMA Matching Depending on load
TIG/MIG Matching carrier used 1) 2)
Butt weld top run 3) MMA Sandvik® 23.12.2.LR AWS A5.4 E309LMo-17
TIG/MIG Sandvik 24.12.LHF AWS A5.9 ER309L
Stainless fin membrane panel MIG/SAW 4)
Sandvik 19.9.LSi AWS A5.9 ER308LSi
Carbon fin membrane panel MIG/SAW 4) Sandvik 29.9 AWS A5.9 ER312
Tangential panel MIG Sandvik 19.9.LSi AWS A5.9 ER308LSi
1)
Higher heat input may be applied for the root and filler runs if the stainless peel off is increased.
2)
Contact Sandvik for advice.
3)
MMA is recommended for manual welding to ensure low penetration and to maintain mechanical strength.
4)
Sandvik 15W is suitable for SAW.
Austenitic
Austenitic filler metal
stainless steel
Unalloyed Unalloyed filler metal
steel
Figure 7a. Edge preparation. Figure 7b. Welding sequence.
Figure 8. Edge preparation of fins. Figure 9. Welded tangential panel.
3
Bending Delivery condition
Composite tubes can be bent by the same methods as those Composite tubes are normally delivered in the cold finished and
used for single component tubes, see Figure 10. The bond zone solution annealed condition, which means that, in addition to close
between the two materials does not reduce the formability of tolerances, the tubes have smooth and clean surfaces. This facili-
the tube. The bendability is therefore equivalent to that of the tates both visual inspection and non-destructive examination.
least ductile component. Cold bending can be carried out with a
minimum bending radii of 1.5 x D. Hot bending is recommended Fabrication and welding
for smaller radii. Further technical data on fabrication, welding etc. is available on
request.
For higher steam pressures
For higher steam pressures Sandvik offers the almost 40% strong-
er inner component Sandvik 3Mo1, EN 1.5415, EN 16Mo3.
Creep and hot tensile strength in MPa
▲
170
150
130
110
Figure 10. Bent Sandvik® 3R12/4L7 composite tube. The bond zone is
fully intact. 90
70
Heat treament 50
Stress relieving of composite tubes after cold bending or welding 30
▲
can be undertaken without any loss of strength or corrosion resist- 350 380 410 440 470 500
Temp °C
ance. Stress relieving should be performed at 650°C (1200°F) for
30 minutes 3Mo1, EN 1.5415, 16Mo3 4L7, EN 1.0425, P265GH
Sandvik 3Mo1, EN 1.5415, EN 16Mo3 (Mo 0.25-0.35%), approved
Inspection according to European standard. ASME SA 209 T1=16Mo5, EN
Experience shows that composite tube boilers require less 1.5423 (Mo 0.44-0.65%) is approved for US standard (ASME) but
inspection than carbon steel tube boilers, in spite of the fact that not for Europe.
composite tubes often handle a more corrosive environment, i.e.
higher tube temperature and more aggressive melts, combined Figure 11 shows hot tensile and 100.000 h creep test values for
with higher chloride and potassium contents. Composite tube EN 16Mo3 and P265GH, data from EN 10216-2:2002+A2:2007
units normally shut down only once a year for inspection and table 5 and Annex A.
maintenance of the boiler.
Sandvik Group Environment, health and safety
The Sandvik Group is a global high technology enterprise with 50,000 employees in Environmental awareness, health and safety are integral parts of our business and are
130 countries. Sandvik’s operations are concentrated on five business areas in which the at the forefront of all activities within our operation. We hold ISO 14001 and OHSAS
group holds leading global positions in selected niches: Sandvik Mining, Sandvik Machining 18001 approvals.
Solutions, Sandvik Materials Technology, Sandvik Construction and Sandvik Venture.
Disclaimer
Sandvik Materials Technology Recommendations are for guidance only, and the suitability of a material for a specific
Sandvik Materials Technology is a world-leading developer and manufacturer of products application can be confirmed only when we know the actual service conditions.
in advanced stainless steels and special alloys for the most demanding environments, as Continuous development may necessitate changes in technical data without notice.
well as products and systems for industrial heating. This printed matter is only valid for Sandvik material. Other material, covering the same
international specifications, does not necessarily comply with the mechanical and
Quality management corrosion properties presented in this printed matter.
Sandvik Materials Technology has quality management systems approved by internationally
recognized organizations. We hold, for example, the ASME Quality Systems Certificate Trademark
S-1219-PS-ENG. 06.2012. Printed in Sweden.
as a materials organization, approval to ISO 9001, ISO/TS 16949, ISO 17025 and PED Sandvik and Sanicro are trademarks owned by Sandvik Intellectual Property AB.
97/23/EC. We also have product and/or shop approvals from bodies such as TÜV, JIS,
DNV and Lloyd’s Register.
Sandvik Materials Technolog y
SE-811 81 Sandviken, Sweden, Phone +46 26 26 39 99, Fax +46 26 26 02 20
4 www.smt.sandvik.com
