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Clad steel for seawater service
Desalination, 97 (1994) 121-129 Elsevier Science B.V., Amsterdam - Printed in The Netherlamb
121
Clad steel for seawater service T. Fukuda, T. Fukami, Y. Baba and K. Honma TheJapan
Steel Works, Ltd., 4Gatsu
Machi, Muroran, Hokkaido (Japan)
SUMMARY
The weldabilities, corrosion resistance and benefits of Ni insertion of Cu alloy and austenitic stainless clad steel for seawater service are described in this paper. The main points are summarized as follows: (1) Hot-rolled clad steel needs the nickel insertion of a bonding interface in order to achieve the integrally metallurgical bonding and satisfaction with service performance; (2) hot-rolled Cu-Ni alloy clad steel exhibits excellent weldabilities by the application of low impurity Cu alloy for cladding layer, low dilution welding method and nickel insertion in bonding interface; and (3) 90/10 Cu-Ni alloy cladding layer shows such good resistance to seawater corrosion and to marine organism deposition as expected for solid 90/10 Cu-Ni alloy.
INTRODUCTION
Cu alloy and austenitic stainless steel are used for such seawater services as desalting plant, heat exchanger and seawater piping due to their better service performance for seawater environments. Recently the steels cladded with these alloys have been increasingly applied to seawater services since the clad steel can realize better economy and higher strength in comparison with solid corrosion resisting alloy. The Japan Steel Words Ltd. (JSW) manufactures the clad steel plate and pipe by a hot-roll bonding process and has supplied them to seawater services. OOll-9164/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved. SSDIOOll-9164(94)00080-8
122
In this paper the characteristics and applicabilities of JSW’s clad steel to seawater service and the mechanical and corrosion test results of clad steel and the welds are described in conjunction with a detailed explanation of the effective nickel insertion in bonding interface.
TESTING PROCEDURE AND RESULTS
Application of electrolyzed nickel plating Electrolyzed nickel plating was applied to the surface of cladding alloy and/or backing steel plate to be bonded before roll bonding due to the following advantages and good characteristics of clad steel: (1) easier metallurgical bonding by hot rolling and higher bonding strength; (2) no formation of hard martensite structures in the bonding interface and higher resistance of the bonded zone to hydrogen embrittlement; (3) scarce migration of carbon and other elements between cladding alloy and backing carbon steel. As shown in Fig. 1, alloy and carbon steel sheets can be more easily bonded by a hot-rolling process, that is, a larger metallurgically bonded area is obtained at smaller rolling reduction when nickel plating is used. This is because of the soft material of nickel (better contact of cladding and backing layers during rolling) and the higher resistance of nickel to oxidation at high rolling temperatures. 90/10 Cu-Ni alloy rolled clad steel plates with and without nickel plating were subjected to the fillet welding and weld restraint tests. The GTAW method was used for each welding test, and the testing procedure and results are summarized in Table I. This table shows better weldability of nickel-plated clad steel plate. The nickel-plated clad steel can maintain the high bonding strength even if the thermal stress caused by welding is applied to bonding interface. When the nickel plating is not used, Fe in backing steel easily migrates to the 90/10 layer by diffusion during welding which leads to the precipitation of Fe along grain boundaries of 90/10 CuNi and results in poor hot ductility of 90/10 Cu-ni [ 11. In the case of practice of Ni plating, an intermediate Ni layer can prevent the bonding interface from Fe diffusion and mitigate the degradation of bonding properties caused by the welding operation.
123
o: VJ ilhout Ni-plating l
,t-,o_
:
Ni-plaling
o: Oxidization Ni-pbting
wilhoub
_-__-o;_-__-__
m: Oxidiration with
I
h
1
I
5
10
Rolling
reduction
2b
50
1
3
(%)
Fig. 1. Effect of nickel plating on.percentage of bonded area. (One pass rolling at 90°C under 4X 10e3 Torr pressure. TABLE I Testing procedure and result of 90/10 Cu-Ni alloy clad steel T-join1
fillcl
welding
Kcslrainl
crackInK
Lcrl SO/lOCu-Ni
Result of welding test Intermediate nickel plating
Restraint cracking test/ side bend (R=2.0)
T-joint fillet welds
Yes None
Good (no crack) Debond
Good (no crack) Debond
124
Nickel plating is not always effective for the’ manufacture of all hotrolled clad steel. For example, intermediate nickel layer gives the adverse effect on the bonding properties of Cu-Al alloy @luminum bronze) clad steel which has good erosion-corrosion resistance in seawater. When the intermediate nickel layer is inserted between Cu-Al and carbon steel, nickel and the aluminum migrated from the Cu-Al alloy by diffusion, form brittle inter-metallic compound of Ni-Al, which leads to low bonding strength and poor ductility of the bonding zone. To cope with this problem, a doublelayer plating of pure nickel and copper has been newly developed. Such double-layer plated Cu-Al alloy clad steel showed the satisfactory bonding strength and ductility at room and high temperatures [2]. This is for the reason that the Cu layer prevents the migration of Al to the nickel layer in addition to no oxidation of the Cu layer with the protection by the Ni-plated layer from air. When the intermediate nickel layer is not used for hot-rolled stainless clad steel, the generation of the hardened zone at bonding interface has been observed by us and other investigators [3,4]. This hardened zone has been found to consist of a high carbon martensitic structure. Such martensite is thought to be formed during cooling from the rolling temperatures through the retardation of ferrite transformation in the backing carbon steel
tud
Lc,
0
I
.
:
_25
1,
Am
f
K-
Fig. 2. Hydrogen-induced cracks observed in the bonding interface of Tp.316L without nickel plating.
clad steel
125
adjacent to the bonding interface enriched by Ni, Cr and MO and condensation of carbon in bonding zone. The hard martensite structure becomes troublesome when clad steel is used in such environmental conditions of hydrogen generation as cathodic protection in seawater and immersion in sour gas solution. Fig. 2 shows the typical hydrogen-induced cracks in the martensite phase of Tp.316L/A, 516 Gr.70 clad steel when the clad steel is immersed in H2S saturated solution (NACE solution [S]: 5% NaCl +OS% CHsCOOH solution) at 25°C. The cracks are seen to initiate at the voids and propagate into the martensite structure. On the other hand, no hydrogen-induced crack is observed when the nickel plating is applied to clad steel manufacturing. This is due to the avoidance of martensite formation and lower hardness of a bonding interface with a nickel layer. Weldability of hot-rolled clad steel
Under the appropriate precautions with respect to the welding conditions including welding materials, clad-steel plate may be easily butt welded or fillet welded as shown in Fig. 3. For butt welding the cladding side of 90/10 Cu-Ni alloy clad steel, iron pick-up from the backing steel shall be minimized to avoid the hazard of hot cracks and pitting corrosion problems of weld metals. Fig. 4 indicates the hot-cracking sensitivity of Fe-Ni-Cu alloy system. The increment of iron content in 90/10 Cu-Ni weld metal is found to enhance the hot-cracking sensitivity, In order to investigate the effect of iron pick-up on the corrosion resistance of weld metal, 90/10 Cu-Ni weld metal with various iron contents (various dilution ratios with steel) was prepared by butt welding of 90110 Cu-Ni clad steel and subjected to a corrosion test in seawater. The effects of iron pick-up in weld metal on the corrosion rate are shown in Fig. 5. The corrosion resistance deteriorates from the level for 9000 Cu-Ni alloy when the dilution ratio with steel exceeds 5 % . In order to compensate for the excess iron pick-up and mitigate the degradation of corrosion resistance in weld metal, an appropriate first barrier pass for the steel as pure nickel or Monel, or multi-layer welding with a deposition of 90/10 Cu-Ni alloy, is commonly used. 90/10 Cu-Ni alloy itself, however, sometimes indicates lower hot ductility during welding when the contents of such impure elements as Si
126 Fillet
welding
But1
welding AtLachaent of
Cladding alloy Backing steel
to cladding alloy
Fig. 3. Typical welding procedure for clad steel. Ni
40
20
Fe
Copper.
Fig. 4. Hot-cracking
60
80'
Cu
%
sensitivity of Fe-h-Ni
alloy system.
O/ DILUTION WITH STEEL 01.
Fig. 5. Effect of iron pick-up on corrosion resistance of 90/10 Cu-Ni alloy weld in seawater
127 --+I---+
Material A Material B Material C
-
/d [s lo_
.z 74 z E- o---co-_40 0
_
-A--
-/I,_&=-
I
/ , / I ‘/
/ 1 1
8
---
I
0
I
2 3 Applied strain
I
4 (X)
oI
5
6
Fig. 6. Effec.t of impurity content in 90/10 Cu-Ni on the weld cracking at intermediate temperature.
and Zn increase. Therefore, the control of impurities content in the 90/10 Cu-Ni cladding layer is important for better weldabilities of clad steel. To check the effect of the impurity level on weld cracking, a trans-varestraint test was performed using 90/10 Cu-Ni clad steel with three different impurity levels. The several bending tensile strains were applied to the cladding side while the cladding side was being fused with a TIG welding arc. After bending strained, the length of cracks in the heat affected zone was measured. Fig. 6 summarizes the results of the tests. Larger amounts of impurities cause higher sensitivity to cracking in the intermediate temperature range of approximately 500-65O”C. From this point of view, the impurity content is strictly controlled for JSW’s 9000 Cu-Ni cladding alloy. Corrosion resistance to seawater 90/10 Cu-Ni cladding alloy was subjected to a corrosion test for 1 year in natural seawater which flowed at 0.3 m/s in pipe. The corrosion test results are tabulated in Table II in comparison with other corrosion resisting alloys. The 90110 Cu-Ni alloy indicates the low corrosion rate of 213 km/y, although it has a slightly higher corrosion rate than titanium or super stainless steel. Among such industrial corrosion resisting materials, 90110 Cu-Ni demonstrates excellent resistance to marine organic deposits. Tar-epoxy coated steel, which is commonly used in power generating plants for the transportation of seawater, shows especially remarkable organic deposits.
128
TABLE II Resistances to seawater corrosion and marine organic deposits of corrosion resisting materials Material
Corrosion rate in seawater (pm/y)
Number of marine organic deposits on the material surface of 100 cm2
90/10 Cu-Ni alloy 70/30 Cu-Ni alloy cu-Al alloy Titanium Super stainless Tar-epoxy coated
2.24 4.75 2.28 0.044 0.015
16 61 89 285 256 597
-
13.6 20.0 25.0 0.133 0.097
-
steel pipe Test duration: 1 year; flow speed of seawater: 0.3 m/s.
TABLE III Corrosion test results of 90110 Cu-Ni cladding alloy in seawater Material
Rotating corrosion testa in natural seawater bm/y)
Loop testb in artificial seawater (pm/y)
Solid 90110 Cu-Ni alloy
89 - 104
73 - 86
Cladding layer
97-
78 - 90
Butt welds of cladding layer (weld metal: Monel 90110 Cu-Ni/one pass)
81 - 81
-
Butt welds of cladding layer (weld metal: 90/10 Cu-Ni/one pass)
-
92 - 94
104
“At 54°C for 6 d; flow speed: 2.0-2.7 m/s. bAt 25°C for 30 d; flow sped: 2.0-3.0 m/s.
129
Another corrosion test indicates some corrosion damage on the Cu alloy similar to crevice corrosion. This is confirmed by potentiokinetic analysis not to be crevice corrosion, which is often observed for stainless steel, but for differential aeration corrosion generated in crevice spaces. This corrosion was found to be mitigated for Cu alloy when the space of the crevice is larger than approximately 3.0 mm or the flow speed of seawater is more than 0.3 m/s. Table III shows the corrosion rate in seawater of 90/10 Cu-Ni cladding alloy and its welds. 90/10 Cu-Ni cladding alloy including welds exhibits such good corrosion resistance as expected for solid 90/10 Cu-Ni alloy. The welds made by a one-pass direct deposition of 90110 Cu-Ni also indicate good corrosion resistance. It is for this reason that a very low dilution welding practice was adopted so as to suppress excessive iron pickup from the backing steel.
CONCLUSIONS
It is concluded that hot-rolled clad steel with intermediate nickel insertion is thought to be the best choice as material for seawater services from both economic and reliability viewpoints.
ACKNOWLEDGEMENTS
Part of this research has been performed under the sponsorship of the Advanced Nuclear Equipment Research Institute contracting with the Agency of Natural Resources and Energy, Japanese Ministry of International Trade and Industry.
REFERENCES 1 2 3 4 5
J.P. Chubb et al., I. Metals, 3 (1978) 20. R. Honma, T. Fukuda and Y. Baby, Investigative Report, Maintenance free of nuclear power plants/Development of hot-rolled clad steel pipe for seawater piping, 1987. Y. Komizo and K. Ogawa, Paper presented at the 116th Research Committee of Welding and Metallurgy, WM-09-89, 1989. T. Kushida and T. Kudo, Iron and Steel, 75 (1989) 1508. NACE, TM-Ol-77.
121
Clad steel for seawater service T. Fukuda, T. Fukami, Y. Baba and K. Honma TheJapan
Steel Works, Ltd., 4Gatsu
Machi, Muroran, Hokkaido (Japan)
SUMMARY
The weldabilities, corrosion resistance and benefits of Ni insertion of Cu alloy and austenitic stainless clad steel for seawater service are described in this paper. The main points are summarized as follows: (1) Hot-rolled clad steel needs the nickel insertion of a bonding interface in order to achieve the integrally metallurgical bonding and satisfaction with service performance; (2) hot-rolled Cu-Ni alloy clad steel exhibits excellent weldabilities by the application of low impurity Cu alloy for cladding layer, low dilution welding method and nickel insertion in bonding interface; and (3) 90/10 Cu-Ni alloy cladding layer shows such good resistance to seawater corrosion and to marine organism deposition as expected for solid 90/10 Cu-Ni alloy.
INTRODUCTION
Cu alloy and austenitic stainless steel are used for such seawater services as desalting plant, heat exchanger and seawater piping due to their better service performance for seawater environments. Recently the steels cladded with these alloys have been increasingly applied to seawater services since the clad steel can realize better economy and higher strength in comparison with solid corrosion resisting alloy. The Japan Steel Words Ltd. (JSW) manufactures the clad steel plate and pipe by a hot-roll bonding process and has supplied them to seawater services. OOll-9164/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved. SSDIOOll-9164(94)00080-8
122
In this paper the characteristics and applicabilities of JSW’s clad steel to seawater service and the mechanical and corrosion test results of clad steel and the welds are described in conjunction with a detailed explanation of the effective nickel insertion in bonding interface.
TESTING PROCEDURE AND RESULTS
Application of electrolyzed nickel plating Electrolyzed nickel plating was applied to the surface of cladding alloy and/or backing steel plate to be bonded before roll bonding due to the following advantages and good characteristics of clad steel: (1) easier metallurgical bonding by hot rolling and higher bonding strength; (2) no formation of hard martensite structures in the bonding interface and higher resistance of the bonded zone to hydrogen embrittlement; (3) scarce migration of carbon and other elements between cladding alloy and backing carbon steel. As shown in Fig. 1, alloy and carbon steel sheets can be more easily bonded by a hot-rolling process, that is, a larger metallurgically bonded area is obtained at smaller rolling reduction when nickel plating is used. This is because of the soft material of nickel (better contact of cladding and backing layers during rolling) and the higher resistance of nickel to oxidation at high rolling temperatures. 90/10 Cu-Ni alloy rolled clad steel plates with and without nickel plating were subjected to the fillet welding and weld restraint tests. The GTAW method was used for each welding test, and the testing procedure and results are summarized in Table I. This table shows better weldability of nickel-plated clad steel plate. The nickel-plated clad steel can maintain the high bonding strength even if the thermal stress caused by welding is applied to bonding interface. When the nickel plating is not used, Fe in backing steel easily migrates to the 90/10 layer by diffusion during welding which leads to the precipitation of Fe along grain boundaries of 90/10 CuNi and results in poor hot ductility of 90/10 Cu-ni [ 11. In the case of practice of Ni plating, an intermediate Ni layer can prevent the bonding interface from Fe diffusion and mitigate the degradation of bonding properties caused by the welding operation.
123
o: VJ ilhout Ni-plating l
,t-,o_
:
Ni-plaling
o: Oxidization Ni-pbting
wilhoub
_-__-o;_-__-__
m: Oxidiration with
I
h
1
I
5
10
Rolling
reduction
2b
50
1
3
(%)
Fig. 1. Effect of nickel plating on.percentage of bonded area. (One pass rolling at 90°C under 4X 10e3 Torr pressure. TABLE I Testing procedure and result of 90/10 Cu-Ni alloy clad steel T-join1
fillcl
welding
Kcslrainl
crackInK
Lcrl SO/lOCu-Ni
Result of welding test Intermediate nickel plating
Restraint cracking test/ side bend (R=2.0)
T-joint fillet welds
Yes None
Good (no crack) Debond
Good (no crack) Debond
124
Nickel plating is not always effective for the’ manufacture of all hotrolled clad steel. For example, intermediate nickel layer gives the adverse effect on the bonding properties of Cu-Al alloy @luminum bronze) clad steel which has good erosion-corrosion resistance in seawater. When the intermediate nickel layer is inserted between Cu-Al and carbon steel, nickel and the aluminum migrated from the Cu-Al alloy by diffusion, form brittle inter-metallic compound of Ni-Al, which leads to low bonding strength and poor ductility of the bonding zone. To cope with this problem, a doublelayer plating of pure nickel and copper has been newly developed. Such double-layer plated Cu-Al alloy clad steel showed the satisfactory bonding strength and ductility at room and high temperatures [2]. This is for the reason that the Cu layer prevents the migration of Al to the nickel layer in addition to no oxidation of the Cu layer with the protection by the Ni-plated layer from air. When the intermediate nickel layer is not used for hot-rolled stainless clad steel, the generation of the hardened zone at bonding interface has been observed by us and other investigators [3,4]. This hardened zone has been found to consist of a high carbon martensitic structure. Such martensite is thought to be formed during cooling from the rolling temperatures through the retardation of ferrite transformation in the backing carbon steel
tud
Lc,
0
I
.
:
_25
1,
Am
f
K-
Fig. 2. Hydrogen-induced cracks observed in the bonding interface of Tp.316L without nickel plating.
clad steel
125
adjacent to the bonding interface enriched by Ni, Cr and MO and condensation of carbon in bonding zone. The hard martensite structure becomes troublesome when clad steel is used in such environmental conditions of hydrogen generation as cathodic protection in seawater and immersion in sour gas solution. Fig. 2 shows the typical hydrogen-induced cracks in the martensite phase of Tp.316L/A, 516 Gr.70 clad steel when the clad steel is immersed in H2S saturated solution (NACE solution [S]: 5% NaCl +OS% CHsCOOH solution) at 25°C. The cracks are seen to initiate at the voids and propagate into the martensite structure. On the other hand, no hydrogen-induced crack is observed when the nickel plating is applied to clad steel manufacturing. This is due to the avoidance of martensite formation and lower hardness of a bonding interface with a nickel layer. Weldability of hot-rolled clad steel
Under the appropriate precautions with respect to the welding conditions including welding materials, clad-steel plate may be easily butt welded or fillet welded as shown in Fig. 3. For butt welding the cladding side of 90/10 Cu-Ni alloy clad steel, iron pick-up from the backing steel shall be minimized to avoid the hazard of hot cracks and pitting corrosion problems of weld metals. Fig. 4 indicates the hot-cracking sensitivity of Fe-Ni-Cu alloy system. The increment of iron content in 90/10 Cu-Ni weld metal is found to enhance the hot-cracking sensitivity, In order to investigate the effect of iron pick-up on the corrosion resistance of weld metal, 90/10 Cu-Ni weld metal with various iron contents (various dilution ratios with steel) was prepared by butt welding of 90110 Cu-Ni clad steel and subjected to a corrosion test in seawater. The effects of iron pick-up in weld metal on the corrosion rate are shown in Fig. 5. The corrosion resistance deteriorates from the level for 9000 Cu-Ni alloy when the dilution ratio with steel exceeds 5 % . In order to compensate for the excess iron pick-up and mitigate the degradation of corrosion resistance in weld metal, an appropriate first barrier pass for the steel as pure nickel or Monel, or multi-layer welding with a deposition of 90/10 Cu-Ni alloy, is commonly used. 90/10 Cu-Ni alloy itself, however, sometimes indicates lower hot ductility during welding when the contents of such impure elements as Si
126 Fillet
welding
But1
welding AtLachaent of
Cladding alloy Backing steel
to cladding alloy
Fig. 3. Typical welding procedure for clad steel. Ni
40
20
Fe
Copper.
Fig. 4. Hot-cracking
60
80'
Cu
%
sensitivity of Fe-h-Ni
alloy system.
O/ DILUTION WITH STEEL 01.
Fig. 5. Effect of iron pick-up on corrosion resistance of 90/10 Cu-Ni alloy weld in seawater
127 --+I---+
Material A Material B Material C
-
/d [s lo_
.z 74 z E- o---co-_40 0
_
-A--
-/I,_&=-
I
/ , / I ‘/
/ 1 1
8
---
I
0
I
2 3 Applied strain
I
4 (X)
oI
5
6
Fig. 6. Effec.t of impurity content in 90/10 Cu-Ni on the weld cracking at intermediate temperature.
and Zn increase. Therefore, the control of impurities content in the 90/10 Cu-Ni cladding layer is important for better weldabilities of clad steel. To check the effect of the impurity level on weld cracking, a trans-varestraint test was performed using 90/10 Cu-Ni clad steel with three different impurity levels. The several bending tensile strains were applied to the cladding side while the cladding side was being fused with a TIG welding arc. After bending strained, the length of cracks in the heat affected zone was measured. Fig. 6 summarizes the results of the tests. Larger amounts of impurities cause higher sensitivity to cracking in the intermediate temperature range of approximately 500-65O”C. From this point of view, the impurity content is strictly controlled for JSW’s 9000 Cu-Ni cladding alloy. Corrosion resistance to seawater 90/10 Cu-Ni cladding alloy was subjected to a corrosion test for 1 year in natural seawater which flowed at 0.3 m/s in pipe. The corrosion test results are tabulated in Table II in comparison with other corrosion resisting alloys. The 90110 Cu-Ni alloy indicates the low corrosion rate of 213 km/y, although it has a slightly higher corrosion rate than titanium or super stainless steel. Among such industrial corrosion resisting materials, 90110 Cu-Ni demonstrates excellent resistance to marine organic deposits. Tar-epoxy coated steel, which is commonly used in power generating plants for the transportation of seawater, shows especially remarkable organic deposits.
128
TABLE II Resistances to seawater corrosion and marine organic deposits of corrosion resisting materials Material
Corrosion rate in seawater (pm/y)
Number of marine organic deposits on the material surface of 100 cm2
90/10 Cu-Ni alloy 70/30 Cu-Ni alloy cu-Al alloy Titanium Super stainless Tar-epoxy coated
2.24 4.75 2.28 0.044 0.015
16 61 89 285 256 597
-
13.6 20.0 25.0 0.133 0.097
-
steel pipe Test duration: 1 year; flow speed of seawater: 0.3 m/s.
TABLE III Corrosion test results of 90110 Cu-Ni cladding alloy in seawater Material
Rotating corrosion testa in natural seawater bm/y)
Loop testb in artificial seawater (pm/y)
Solid 90110 Cu-Ni alloy
89 - 104
73 - 86
Cladding layer
97-
78 - 90
Butt welds of cladding layer (weld metal: Monel 90110 Cu-Ni/one pass)
81 - 81
-
Butt welds of cladding layer (weld metal: 90/10 Cu-Ni/one pass)
-
92 - 94
104
“At 54°C for 6 d; flow speed: 2.0-2.7 m/s. bAt 25°C for 30 d; flow sped: 2.0-3.0 m/s.
129
Another corrosion test indicates some corrosion damage on the Cu alloy similar to crevice corrosion. This is confirmed by potentiokinetic analysis not to be crevice corrosion, which is often observed for stainless steel, but for differential aeration corrosion generated in crevice spaces. This corrosion was found to be mitigated for Cu alloy when the space of the crevice is larger than approximately 3.0 mm or the flow speed of seawater is more than 0.3 m/s. Table III shows the corrosion rate in seawater of 90/10 Cu-Ni cladding alloy and its welds. 90/10 Cu-Ni cladding alloy including welds exhibits such good corrosion resistance as expected for solid 90/10 Cu-Ni alloy. The welds made by a one-pass direct deposition of 90110 Cu-Ni also indicate good corrosion resistance. It is for this reason that a very low dilution welding practice was adopted so as to suppress excessive iron pickup from the backing steel.
CONCLUSIONS
It is concluded that hot-rolled clad steel with intermediate nickel insertion is thought to be the best choice as material for seawater services from both economic and reliability viewpoints.
ACKNOWLEDGEMENTS
Part of this research has been performed under the sponsorship of the Advanced Nuclear Equipment Research Institute contracting with the Agency of Natural Resources and Energy, Japanese Ministry of International Trade and Industry.
REFERENCES 1 2 3 4 5
J.P. Chubb et al., I. Metals, 3 (1978) 20. R. Honma, T. Fukuda and Y. Baby, Investigative Report, Maintenance free of nuclear power plants/Development of hot-rolled clad steel pipe for seawater piping, 1987. Y. Komizo and K. Ogawa, Paper presented at the 116th Research Committee of Welding and Metallurgy, WM-09-89, 1989. T. Kushida and T. Kudo, Iron and Steel, 75 (1989) 1508. NACE, TM-Ol-77.