DESCRIPTION
TITLE OF INVENTION: HEAT TRANSFER TUBE FOR STEAM GENERATOR
AND METHOD FOR PRODUCING THE SAME
TECHNICAL FIELD
[0001]
The present invention relates to a heat transfer tube used for a steam generator
of nuclear power generation and thermal power generation plants and to a method for
producing the same. In more detail, the present invention relates to a heat transfer
tube for a steam generator, which can improve an inspection efficiency in the
inspection by an inner probe type eddy current test, and to a method for producing
the same.
[0002]
Here, unless otherwise described, the definition of a term in the preset
description is as follows.
"Heat transfer tube for steam generator": this term defines a heat transfer tube having
a small diameter and a longer-length used for a steam generator or the like in nuclear
power generation and thermal power generation plants. In particular, a heat transfer
tube for a steam generator for the nuclear power generation is also abbreviated as an
SG (steam generator) tube.
BACKGROUND ART
[0003]
An SG tube in an U-like form and used for a steam generator and a heat
exchanger such as a feed water heater, which are used in a nuclear power plant, is
produced by bending a heat transfer tube having a small diameter and a longer length
into the shape of a letter U. In this SO tube in an U-like form, an inspection for
detecting a flaw from the inner surface of the tube by an inner probe type eddy
current test is performed as a pre-service inspection after the tube is incorporated into
the heat exchanger and as an in-service after servicing for a predetermined period.
An inspection standard for the inner probe type eddy current flaw detection of the
tube is extremely strict because the safety ofthe nuclear power generation plant
needs to be secured.
[0004]
FIG. 1 is an example ofa chart showing the result of the eddy current flaw
detection of an inner surface of a tube. As shown in the drawing, in the chart are
shown a signal S from a standard notch specified by Inspection Standard and a signal
N having a constant cycle P. The signal N is referred to as base noises and is
caused by a minute dimensional variation generated along an axial direction of the
tube. The magnitude ofthe signal N needs to be made as small as possible so as to
prevent the signal N from being falsely determined as a signal due to a detected flaw
and to perform a quick flaw interrogation to thereby improve inspection efficiency.
In the following description, a ratio of the signal S caused by a standard notch to the
signal N is referred to as "an SIN ratio."
[0005]
For example, in the case where when the inner probe type eddy current test is
performed for the inspection ofthe inner surface oftube, an automatic flaw
interrogation is made on the basis of signals shown on the chart, when base noises
are high, that is, the SIN ratio is small, a signal exhibiting a small but deleterious
defect is hidden under base noises, which makes it difficult to distinguish the small
deleterious defect from the base noises.
[0006]
For this reason, when the eddy current flaw detection is performed, an
examiner visually observes the result of the eddy current flaw detection and when the
examiner finds a doubtful signal that might be generated at a specific portion, the
examiner again inspects the specific portion at a lower speed to thereby distinguish
the small deleterious defect from the base noises, which decreases inspection
efficiency. Since the base noises are caused by a minute dimensional variation
generated along a longitudinal direction of an SG tube, the reduction in the
dimensional variation along a longitudinal direction of the SG tube is important so as
to improve the inspection efficiency in the eddy current flaw detection.
[0007]
3
In general, the SG tube like this is produced by a production process including
the following steps of:
(I) finishing a tube into a predetennined size in a cold working process;
(2) removing the residual stress ofthe tube and homogenizing the microstructure of
the tube in a solid solution heat treatment process; and
(3) straightening bends and out-of-roundness ofthe tube that are generated by the
residual stress attributable to the solid solution heat treatment process, by use of a
roll straightening machine in a straightening process.
[0008]
In the cold working process, a cold rolling method (Pilger rolling) by a Pilger
mill using rolls and a mandrel or a drawing work using tools such as a die and a plug
is employed. In this drawing work, in order to reduce friction caused when the tool
is brought into contact with a tube as workpiece to thereby prevent seizing and
vibration/chattering from being caused, in general, a chemical treatment lubricating
coating is fonned on the inner surface and the outer surface ofthe tube to be drawn
to thereby apply a lubricating treatment to the inner surface and the outer surface of
the tube.
[0009]
However, since the SG tube has a small diameter and a longer length, the
fonnation of the chemical treatment lubricating coating requires a long time and a
large amount of man-hours and a chemical agent used for the fonnation of the
chemical treatment lubricating coating is comparatively expensive, which results in
increasing an operating cost. Further, since an Ni-based alloy is used for the SG
tube in many cases, the alloy is inhibitive for the chemical treatment lubricating
coating to be fonned on the surface ofthe alloy. Thus, in the case where the SG
tube made of the Ni-based alloy is produced, the operating cost required for fonning
the chemical treatment lubricating coating is further increased.
[0010]
Thus, in the drawing work for producing the SG tube made of the Ni-based
alloy, a high-pressure drawing (forcibly lubricating drawing) is used in many cases.
The high-pressure drawing is a kind of cold drawing in which a lubricating treatment
is perfonned by a direct oil lubrication. The high-pressure drawing can slabilize the
4-
-y
cold drawing and has a remarkable effect on the improvement of the quality of the
drawn tube.
[0011]
The drawing work ofthe tube by the high-pressure drawing is perfonned by
the following steps of:
(1) filling a high-pressure container, into which a tube as workpiece is inserted, with
a lubricating oil, and then pressurizing the lubricating oil by a pressure booster;
(2) fonning a lubricating oil film between the tube and tools, i.e., a die and a plug,
with the pressurized lubricating oil, the die being mounted in a leaktight manner onto
an open end ofthe high-pressure container, the plug being securely disposed at a
working position by the pressurized lubricating oil; and
(3) drawing the tube in a state where the inner surface and the outer surface of the
tube are forcibly lubricated by the fonned lubricating oil film to finish the tube into a
predetennined size by the tools.
[0012]
As for the drawing work by such a high-pressure drawing, there have been
proposed various methods. For example, there is proposed Patent Literature 1. In
Patent Literature 1 is proposed a method for producing a tube having a small
diameter and a longer length by the cold working using the high-pressure drawing,
that is, a method for drawing a metal tube in which at least the last cold working
including a wall thinning working is perfonned by a plug drawing using a highpressure
lubricating oil having a pressure of 500 kgf/ cm2 or more. In Patent
Literature 1, it is described that since at least the last cold working including the wall
thinning working is perfonned by the high-pressure drawing using the high-pressure
lubricating oil, the produced metal tube does not cause seizing and hence can reduce
a dimensional variation along an axial direction ofthe tube.
[0013]
In Patent Literature 1, it is described that according to a method for drawing a
metal tube, a dimensional variation along an axial direction of the produced metal
tube can be reduced and hence noises generated by the dimensional variation in the
metal tube can be prevented in the inner probe type eddy current flaw detection of
the inner surface of the tube and hence a defect on the inner surface of the tube can
-/-
be correctly detected on the basis of the output ofa flaw detection device. However,
a surface roughness RMAX (JIS 0601) ofthe inner surface of the tube, which is shown
by an example of Patent Literature 1, is 2.8 to 4.0 J..lm and an SIN ratio is 13 to 18.
These values are measured before the tube is straightened by a roll straightening
machine, but after straightening, it is presumed that the surface roughness and the
SIN ratio ofthe straightened metal tube should become smaller than these values.
[0014]
On the other hand, an inclined roll type system in which a plurality of concave
globoidal drum typed rolls are combined is generally employed as the configuration
of a roll straightening machine used in a straightening process in producing an SG
tube. The inclined roll type straightening machine includes various configurations
in terms ofthe combination ofthe number of rolls, the alignment ofthe rolls (upper
and lower direction, left and right direction), and the arrangement ofthe rolls
(cross/opposite arrangement, zigzag arrangement). However, a roll straightening
machine having the rolls arranged in a crossing manner as being opposite to each
other is employed in a finishing process ofthe SG tube.
[0015]
FIG. 2 is an illustration depicting a roll alignment example of an inclined roll
type straightening machine. The roll straightening machine has a plurality of pairs
of straightening rolls Ra, Rb (these rolls are collectively referred to as "ROO) arranged
opposite to each other in a vertical direction in the state where rotating shafts cross
each other. In the roll alignment shown in the drawing, three pairs of straightening
rolls including entrance rolls RaI, RbI, center rolls Ra2, Rb2, and delivery rolls RaJ,
Rb3 are arranged opposite to each other and an auxiliary roll Rc is arranged at the
delivery side of the delivery rolls. A roll straightening machine having a roll
alignment like this is usually referred to as a (2-2-2-1) type straightening machine.
[0016]
A gap between opposite rolls and a cross angle of a pair of rolls Ra1, Rb1 can
be individually adjusted. Further, vertical positions of paired straightening rolls
Ral, RbI and next paired rolls Ra2, Rb2 can also be individually adjusted. Yet
further, a horizontal interval between paired straightening rolls RaI, RbI and next
paired rolls Ra2, Rb2, that is, a stand interval can also be individually adjusted.
[0017]
When bends ofthe tube are straightened, a cross angle eofthe rotating shafts
of the respective straightening rolls R to the tube to be straightened, that is, a roll
angle is adjusted in such a way that the surface of the tube 1 to be straightened is
along the surfaces ofthe straightening rolls. Further, the gap of opposite paired
straightening rolls Ral, Rb1 is set slightly smaller than the outside diameter of the
tube 1 to be straightened to thereby apply crushing to the tube 1 to be straightened
and the crush height ofthe straightening rolls Ra2, Rb2 arranged next to the
straightening rolls Ral, RbI is adjusted to thereby apply offsetting to the tube 1 to be
straightened, whereby the bends and out-of-roundness ofthe tube 1 to be
straightened can be straightened.
[0018]
As for the method for straightening a tube by a roll straightening machine,
there have been also proposed various methods. For example, there are proposed
Patent Literatures 2 and 3. In Patent Literature 2 is proposed a method for
straightening a tube by which an inspection of the tube can be performed at a high
SIN ratio in the inner probe type eddy current flaw detection ofthe inner surface of
the tube by the use of the straightening rolls in which at least an outside surface layer
of a roll body is formed of an elastic member having a hardness Hs of 50 to 100
measured by a spring hardness test (A type) specified by JIS K 6301.
[0019]
In an example in Patent Literature 2, a (2-2-2-1) type straightening machine is
used as a roll straightening machine and an offset amount is set at a large amount of
10 to 11 mm. Moreover, in the example of Patent Literature 2, a variation in the
outside size of a produced SO tube is shown and is 0.004 to 0.005 mm. However, a
level of stress developed on the outer surface of tube by the cold working and the
straightening is different from the case on an inner surface and hence a dimensional
variation on the outer surface along a longitudinal direction of the tube is also
different from the case on the inner surface. Thus, even if the tube is straightened
by the roll straightening machine described in Patent Literature 2, it is not clear
whether or not the dimensional variation along a longitudinal direction of the inner
-7-
surface of the tube can be deterred. Further, the SIN ratio of the SG tube shown in
embodiment examples of Patent Literature 2 is as low as 20 to 50.
[0020]
According to a method for straightening a tube described in Patent Literature
3, a tube is straightened by at least three pairs of straightening rolls, each pair ofrolls
being arranged opposite to each other, that are disposed on a delivery side by
applying offsetting to the tube, the offsetting being formed by three positions along a
tube axial centerline, each position being a crossing position of upper and lower
straightening rolls, wherein TJ specified by Formula (1) described below is set at 1.0
x 10-3 to 1.5 x 10-3.
TJ = (1 / R) x (d / 2) .... (1)
where given that d (mm) denotes an outside diameter of the tube, L (mm) denotes a
stand interval ofthe roll straightening machine and 8 (mm) denotes an offset amount,
R = (82 + L2) / 28 is satisfied.
[0021]
In Patent Literature 3, it is described that according to a method for
straightening a tube, TJ specified by Formula (1) described above satisfies a
predetermined range and hence it is possible to perform an inspection ofthe inner
surface of the produced tube by the inner probe type eddy current flaw detection at a
high SIN ratio. In an embodiment example of Patent Literature 3 is shown an SIN
ratio of an SG tube which is straightened by the use of a (2-2-2-1) type straightening
machine having three pairs of straightening rolls with an offset amount of 6 mm or
more applied thereto, and the value ofthe SIN ratio is 32 to 91. Further, in the
example of Patent Literature 3, a dimensional variation in the inner surface ofthe SG
tube is not addressed.
[0022]
When the SG tube is produced, bends and out-of-roundness are generated in
the tube by a residual stress caused in the solid solution heat treatment process, so
that the bends and out-of-roundness need to be straightened in the straightening
process performed thereafter. However, according to the conventional method for
straightening a tube described in Patent Literatures 2 or 3, when the bends and outof-
roundness of the tube are straightened by the (2-2-2-1) type straightening machine,
/-
it happens that the dimensional variation in the inner surface of the tube should
become noticeable and hence should decrease an SIN ratio in an inspection by the
eddy current flaw detection to reduce an inspection efficiency in some cases.
CITATION LIST
PATENT LITERATURE
[0023]
Patent Literature 1: Japanese Patent Application Publication No. 03-18419
Patent Literature 2: Japanese Patent Application Publication No. 2000-317521
Patent Literature 3: International Application Publication No. W02007/119817
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0024]
As described above, according to the conventional method for producing an
SO tube by a production process including a cold working process, a solid solution
heat treatment process, and a straightening process, the bends and out-of-roundness
of the tube generated in the solid solution heat treatment need to be straightened in
the straightening process performed after the solid solution heat treatment process.
However, according to the conventional method for producing an SO tube, when the
bending and the out-of-roundness of the tube are straightened, the dimensional
variation in the inner surface of the tube becomes noticeable and hence decreases an
SIN ratio in an inspection by an eddy current flaw detection to reduce an inspection
efficiency in some cases.
[0025]
The present invention has been made in view ofthis situation, and an object
of the present invention is to provide a heat transfer tube for a steam generator that
reduces a dimensional variation in the inner surface of the tube after a straightening
process and makes it possible to inspect the tube at a high SIN ratio to thereby
improve inspection efficiency, and a method for producing the same.
SOLUTION TO PROBLEM
[0026]
The present inventors studied an effect that the dimensional variation along a
longitudinal direction of the inner surface of the tube affects an SIN ratio in the
inspection of the inner surface of the tube and found that a certain dimensional
variation with a short cycle has a small effect on the SIN ratio.
[0027]
FIG. 3 is a graph showing one example of a roughness measurement chart in a
longitudinal direction on an inner surface of a tube produced by a production process
including a cold working process, a solid solution heat treatment process, and a
straightening process. The roughness chart shown in the figure is a surface
roughness of the inner surface of a tube produced and straightened in the example to
be described later, the surface roughness being measured by a surface roughness
measurement device (made by Tokyo Seimitsu Co., Ltd. Type: SURFCOM
1500SD3). When the surface roughness is measured, a contact probe made of
diamond and shaped like a cone having a diameter of4 ~m and a vertical angle 60°
was used as a detector.
[0028]
As shown in FIG. 3, the roughness measurement chart along a longitudinal
direction ofthe inner surface ofthe produced tube exhibits wave undulation that has
a cycle of about 35 mm, with short-cycled variations as encircled by a double-dot
and dash line being superimposed. The variations of a short cycle hardly affect the
SIN ratio by the eddy current flaw detection, but the wave undulation having a long
cycle terribly affects the SIN ratio. Here, in order to measure the wave undulation
having a long cycle and exerting a big effect on the SIN ratio except the variations
having a short cycle, it is effective to increase the diameter of the contact probe of
the detector that is used at the time of measuring a dimensional variation along a
longitudinal direction of the inner surface of the tube. Further, the present inventors
found that in the wave undulation having a long cycle, the amplitude of variation in
the wave undulation, that is, an amount of dimensional variation exerts a big effect
on the SIN ratio.
[0029]
\'0
-yi-
FIG. 4 is a schematic illustration to depict an amount ofdimensional variation
along a longitudinal direction of the inner surface of a tube, which is specified by the
present invention. The illustration shows a roughness measurement chart along a
longitudinal direction of the inner surface ofthe tube, and a horizontal axis indicates
positions(mm) in a longitudinal direction ofthe tube and a vertical axis indicates a
height (Ilm). As for an amount ofdimensional variation along a longitudinal
direction ofthe inner surface ofthe tube, which is specified by the present invention,
the roughness measurement chart is obtained by use of a detector whose contact
probe has a radius of 0.8 mm to thereby find an amount of dimensional variation
along a longitudinal direction ofthe inner surface ofthe tube. As shown in FIG. 4,
a maximum value and a minimum value in a specific length of 50 mm taken from the
roughness chart are determined and a difference between the maximum value and the
minimum value is obtained as an amount of dimensional variation along a
longitudinal direction of the inner surface ofthe tube.
[0030]
As the result of an earnest study, the present inventors found that when an
amount of dimensional variation along a longitudinal direction of the inner surface of
the tube, which is shown in FIG. 4, is controlled to be 4 Ilm or less, an inspection of
inner surface of the tube by the eddy current flaw detection can be made with a high
SIN ratio to improve the inspection efficiency.
[0031]
Further, an amount of dimensional variation along a longitudinal direction of
the inner surface of the tube subjected to a straightening process correlates with an
amount of dimensional variation prior to the straightening process and, in general,
the amount of dimensional variation is increased by the straightening process. For
example, when Pilger rolling is used in a cold working process, a noticeable
dimensional variation is generated along a longitudinal direction ofthe inner surface
of the tube in the cold working process and the noticeable dimensional variation
remains also after the tube is straightened, which hence impairs the SIN ratio in the
eddy current flaw detection.
[0032]
t-y-
In the cold working process, when drawing work is used, the dimensional
variation generated along a longitudinal direction of the inner surface ofthe tube in
the cold working process can be reduced as compared with the case where Pilger
rolling is used. This is because since the drawing work is performed by use of a die
and a plug, the inner surface of the produced tube can be made smoother. Further,
when drawing work by a high-pressure drawing is used, the dimensional variation
generated along a longitudinal direction ofthe inner surface of the tube in the cold
working process can be further reduced. In this way, it was found that drawing
work using a high-pressure lubricating oil having a pressure of 40 MPa or more is
suitable for the cold working process.
[0033]
The operating conditions ofthe roll straightening machine such as an offset
amount, the number of pairs of straightening rolls (the number of stands), and a stand
interval have a large effect on an increase in an amount of dimensional variation of
the inner surface ofthe tube in the straightening process. For example, when the
number of pairs of straightening rolls of the roll straightening machine is small, an
amount of work per a pair of straightening rolls is increased and hence the tube is
subjected to be deflected heavily when the tube is straightened, whereby an amount
of dimensional variation of the tube after the straightening is markedly increased.
Hence, the present inventors found that when a (2-2-2-2-2) type straightening
machine having five pairs of straightening rolls is used, the amount of work per one
pair of straightening rolls can be decreased to prevent the amount of dimensional
variation along a longitudinal direction of the inner surface of the tube from being
increased by the straightening.
[0034]
The present invention was completed on the basis ofthe findings described
above and summaries of the present invention are a heat transfer tube for a steam
generator described in the following (1) to (4) and a method for producing a heat
transfer tube for a steam generator described in the following (5) and (6).
[0035]
(1) A heat transfer tube for a steam generator, wherein an amount of dimensional
variation in a specific length of 50 mm taken from a roughness measurement chart,
-}Zwhich
is obtained by measuring a surface roughness of an inner surface of the tube
along a longitudinal direction, is 4 J..lm or less and an amount of bend crookedness in
a portion of a length of 1000 mm from a tube end is 1mm or less.
[0036]
(2) The heat transfer tube for a steam generator according to (1) described above,
wherein the tube is produced by the steps of: cold drawing by use of a high-pressure
lubricating oil of40 MPa or more in pressure; solid solution heat treatment; and
straightening by a roll straightening machine.
[0037]
(3) The heat transfer tube for a steam generator according to (2) described above,
wherein the roll straightening machine uses at least five pairs of concave globoidal
drum type straightening rolls, each pair ofrolls being arranged opposite to each other
in a vertical direction and in a crossing manner where directions of rotating shafts
cross each other.
[0038]
(4) The heat transfer tube for a steam generator according to anyone of (1) to (3)
described above, wherein chemical composition of the tube consists of, in mass%, C:
0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or
less, Cr: 10.0 to 40.0%, Ni: 8.0 to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, AI:
0.5% or less, and N: 0.20% or less, the balance being Fe and impurities.
[0039]
(5) A method for producing a heat transfer tube for a steam generator, wherein when
a tube subjected to cold drawing by use of a high-pressure lubricating oil of 40 MPa
or more in pressure and to solid solution heat treatment is straightened by use of a
roll straightening machine in which at least five pairs of concave globoidal drum type
straightening rolls are provided, each pair of rolls being arranged opposite to each
other in a vertical direction and in a crossing manner where directions of rotating
shafts cross each other, and in which a stand interval is set at 300 mm or less, the
tube is subjected to offsetting that is formed by three points literally along a tube
axial centerline as being crossing positions of at least successive three pairs of upper
and lower straightening rolls of the roll straightening machine and that allows 11
I~
-y'-
expressed by Formula (1) described below to satisfy 0.9 x 10-3 or more and to ensure
an offset amount of 5 mm or less:
11 = I / R x (d / 2) .... (1)
where given that an outside diameter ofthe tube is d (mm) and a stand interval ofthe
roll straightening machine is L (mm) and an offset amount is 3 (mm), R =(32 + L2) /
23 is established.
[0040]
(6) The method for producing a heat transfer tube for a steam generator according to
(5) described above, wherein chemical composition ofthe tube consists of, in mass%,
C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030%
or less, Cr: 10.0 to 40.0%, Ni: 8.0 to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, AI:
0.5% or less, and N: 0.20% or less, the balance being Fe and impurities.
ADVANTAGEOUS EFFECTS OF INVENTION
[0041]
In the heat transfer tube for a steam generator according to the present
invention, an amount of dimensional variation along a longitudinal direction of the
inner surface of the tube is 4 Jlm or less, so that when the tube is produced, an
inspection of the tube by the eddy current flaw detection can be performed with a
high SIN ratio and hence the inspection efficiency can be improved.
[0042]
The method for producing a heat transfer tube for a steam generator according
to the present invention has marked effects described below.
(I) Since the cold drawing is applied to the tube by use ofthe high-pressure
lubricating oil of 40 MPa or more in pressure, an amount of dimensional variation
along a longitudinal direction of the inner surface of the tube after the cold drawing
and before the straightening can be reduced.
(2) The tube is straightened by use of the roll straightening machine having at least
five pairs of concave globoidal drum type straightening rolls and a stand interval of
300 mm or less with 11 set at 0.9 x 10-3 or more and with an offset amount set at 5
mm or less by at least three pairs of straightening rolls in a row. This can reduce an
14-
-y(
increase in the amount of dimensional variation along a longitudinal direction of the
inner surface of the tube by the straightening.
(3) The method for producing a heat transfer tube for·a steam generator in
accordance with the present invention, as described above in (1) and (2), can produce
a tube in which an amount of dimensional variation along a longitudinal direction of
the inner surface ofthe tube is 4 llm or less and in which an amount of bend
crookedness in a portion of a length of 1,000 mm from a tube end is 1 mm or less.
BRIEF DESCRIPTION OF DRAWINGS
[0043]
[FIG. 1] FIG. 1 is an example of a chart showing the result of an inner probe type
eddy current flaw detection of an inner surface of a tube.
[FIG. 2] FIG. 2 is an illustration depicting a roll alignment example of an inclined
roll type straightening machine.
[FIG. 3] FIG. 3 is a graph showing one example of a roughness measurement chart
along a longitudinal direction of an inner surface of a tube produced by a production
process including a cold working process, a solid solution heat treatment process,
and a straightening process.
[FIG. 4] FIG. 4 is a schematic illustration to depict an amount of dimensional
variation along a longitudinal direction of the inner surface of the tube, which is
discussed by the present invention.
DESCRIPTION OF EMBODIMENTS
[0044]
Hereinafter, a heat transfer tube for a steam generator and a method for
producing the same will be described.
[0045]
[Heat transfer tube for steam generator]
A heat transfer tube for a steam generator according to the present invention is
characterized in that an amount of dimensional variation in a specific length of 50
mm taken from a roughness measurement chart, which is obtained by measuring a
surface roughness of an inner surface ofthe tube along a longitudinal direction, is 4
-}l-
~m or less and that an amount of bend crookedness in a portion of a length of 1000
mm from a tube end is Imm or less.
[0046]
In the present invention, when the surface roughness ofthe inner surface of
the tube is measured along a longitudinal direction, a dimensional variation along a
longitudinal direction of the inner surface ofthe tube shall be measured by use ofa
detector having a contact probe of 0.8 mm in radius. As described above with
reference to FIG. 4, this is because short-cycled variations having a little effect on an
SIN ratio in an eddy current flaw detection are to be removed to thereby measure
wave undulation with a long cycle. Further, in the present invention, "an amount of
dimensional variation" means a difference between a maximum value and a
minimum value in a specific length of 50 mm taken from the measured roughness
chart.
[0047]
The dimensional variation along a longitudinal direction of the inner surface
of the tube is generated and increased by Pilger rolling and drawing work in a cold
working process or by straightening by a roll straightening machine in a
straightening process. The dimensional variation generated and increased as such is
known to have a cycle of 50 mm or less, so that an amount of dimensional variation
is determined from a specific length of 50 mm taken from the measured surface
roughness chart.
[0048]
When the amount of dimensional variation along a longitudinal direction of
the inner surface ofan SG tube is more than 4 ~m, the SIN ratio in the eddy current
flaw detection is decreased to thereby impair the inspection efficiency. When the
amount of dimensional variation along a longitudinal direction of the inner surface of
the SG tube is 4 ~m or less, an inspection by the eddy current flaw detection can be
performed with a high SIN ratio and hence the inspection efficiency can be improved.
[0049]
Further, in the case where an amount of bend crookedness in a portion of a
length of 1000 mm from a tube end, that is, in a range of 1000 mm from the tube end
is controlled to be I mm or less, in assembling tubes into a steam generator/heat
Ib
-;6-
exchanger, the interference of the tube with other parts attributable to such bend
crookedness of the tube can be inhibited and hence an assembling operation can be
readily performed.
[0050]
[Method for producing heat transfer tube for steam generator]
A method for producing a heat transfer tube for a steam generator according
to the present invention is characterized by the following: when a tube subjected to
cold drawing by use of a high-pressure lubricating oil of 40 MPa or more in pressure
and to solid solution heat treatment is straightened by use of a roll straightening
machine in which at least five pairs of concave globoidal drum type straightening
rolls are provided, each pair of rolls being arranged opposite to each other in a
vertical direction and in a crossing manner where directions of rotating shafts cross
each other, and in which a stand interval is set at 300 mm or less, the tube is
subjected to offsetting that is formed by three points literally along a tube axial
centerline as being crossing positions ofat least successive three pairs of upper and
lower straightening rolls of the roll straightening machine and that allows 11,
expressed by Formula (I) described below to satisfy 0.9 x 10-3 or more and to ensure
an offset amount of 5 mm or less
11 = 1 / R x (d / 2) .... (1)
where given that an outside diameter ofthe tube is d (mm), a stand interval of the roll
straightening machine is L (mm) and an offset amount is 8 (mm), R =(82 + L2
) /28
is established.
[0051 ]
When the tube is subjected to the drawing work by a high-pressure drawing
by e use of the high-pressure lubricating oil of40 MPa or more in pressure in the
cold working process, an amount of dimensional variation along a longitudinal
direction generated on the inner surface of the tube after the cold working (before
straightening) can be reduced as compared with the case where the tube is subjected
to Pilger rolling or drawing work under a lubrication treatment by a chemical
treatment lubricating coating.
[0052]
11-
-)1-
When the pressure of the lubricating oil used in the cold drawing by the highpressure
drawing is less than 40 MPa, a lubricating oil film having a sufficient
thickness is not fonned between tools and the tube and hence seizing and/or
vibration/chattering is caused, which hence increases the amount of dimensional
variation along a longitudinal direction generated on the inner surface ofthe tube.
For this reason, the pressure ofthe lubricating oil is set at 40 MPa or more. It is
preferable that the pressure ofthe lubricating oil is set at 50 MPa or more. Further,
it is preferable that the pressure ofthe lubricating oil is set at 150 MPa or less.
When the pressure ofthe lubricating oil is more than 150 MPa, there is a risk that
part ofthe lubricating oil is trapped in a portion on the inner surface ofthe tube to
fonn a recessed portion to thereby generate a defect referred to as an oil pit. The oil
pit generated on the inner surface of the tube develops dimensional variations of a
short cycle in a roughness measurement chart and hence has a small effect on the SIN
ratio in the inspection by the eddy current flaw detection, but causes the roughness
on the inner surface ofthe tube, referred to as an arithmetic average roughness, to be
deteriorated.
[0053]
Various conventional methods can be employed as a solid solution heat •
treatment, and when the solid solution heat treatment is perfonned, a heating
temperature and a retention time thereof for the tube can be adequately detennined
from the size and the chemical composition of the tube. The solid solution heat
treatment can be applied to the tube, for example, at a heating temperature of 1000 to
1300 °C and for a retention time of 5 to 15 min.
[0054]
In the straightening process, the tube is straightened by use of the roll
straightening machine which has at least five pairs of concave globoidal drum type
straightening rolls, each pair of rolls being arranged opposite to each other in a
vertical direction and in a crossing manner where directions of rotating shafts of
paired rolls cross each other, and which has the stand interval of 300 mm or less.
Since the roll straightening machine which has at least five pairs of concave
globoidal drum type straightening rolls is used, the bends and the out-of-roundness of
the tube can be straightened while an amount of work per a pair of straightening rolls
I~
-yis
decreased as compared with a conventional (2-2-2-1) type straightening machine
which has three pairs of straightening rolls. In the case where the stand interval is
more than 300 mm, the bends of the tube cannot be straightened unless an offset
amount is increased, but increasing the offset amount so as to straighten the bends of
the tube should increase an amount of dimensional variation in the inner surface of
the tube after straightening.
[0055]
When the 11 expressed by Formula (I) described above is in the range of 0.9 x
10-3 or more, the out-of-roundness and the bends ofthe tube can be straightened.
On the other hand, if the 11 expressed by Formula (1) described above is less than 0.9
x 10-3
, the bends remain in the tube after being subjected to the straightening process,
thus resulting in a defective product.
[0056]
When the offset amount applied to the tube is 5 nun or less, an amount of
work per a pair of straightening rolls is decreased and hence the imposed deflection
ofthe tube is decreased at the time of straightening, which can hence suppress an
increase in an amount of dimensional variation along a longitudinal direction of the
inner surface of the tube by the straightening. When the offset amount applied to
the tube is more than 5 mm, the amount of dimensional variation along a longitudinal
direction ofthe inner surface ofthe tube by the straightening is noticeably increased.
[0057]
According to the method for producing a heat transfer tube for a steam
generator in accordance with the present invention, the cold drawing is performed to
the tube by use of the high-pressure lubricating oil of 40 MPa or more in pressure
and then the tube is straightened with offsetting in which the 11 expressed by Formula
(1) described above is in the range of 0.9 x 10-3 or more and in which an offset
amount is 5 mm or less. In the heat transfer tube for a steam generator produced as
such, an amount ofdimensional variation along a longitudinal direction of the inner
surface of the tube is 4 Jlm or less and the amount of bend crookedness in a portion
of a length of 1000 mm from a tube end is I mm or less, which hence makes it
possible to inspect the tube by the eddy current flaw detection with a high SIN ratio
and hence can improve the inspection efficiency.
[0058]
For example, in the case where the tube is straightened by use of a (2-2-2-2-2)
type straightening machine having five pairs of straightening rolls, at least successive
three pairs of straightening rolls in which II and the offset amount are set within
ranges specified by the present invention can be arranged either on an entrance side,
or in the intermediate region excluding foremost and rearmost pairs of rolls, or on a
delivery side.
[0059]
Further, a straightening roll cross angle and an amount of crushing that are
setup conditions of the roll straightening machine can be selected adequately from
the size and material grade of the tube to be straightened. It is preferable that in
each pair of straightening rolls, the roll cross angle is set in a range from 280 to 31 0
and the amount of crushing is set in a range from 1.5 mm to 3.0 mm.
[0060]
[Chemical composition of tube]
In the heat transfer tube for a steam generator according to the present
invention and in the method for prod~cing the same, it is preferable that the chemical
composition of the tube consists of, in mass%, C: 0.15% or less, Si: 1.00% or less,
Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0 to 40.0%, Ni: 8.0 to
80.0%: Ti 0.5% or less, Cu: 0.6% or less, AI: 0.5% or less, and N: 0.20% or less, the
balance being Fe and impurities.
[0061 ]
Here, the impurities mean constituents which are mixed in the tube from ores
and/or scraps when the tube is commercially produced and which are allowed in a
range not having an adverse effect on the present invention. The reasons of limiting
the contents ofthe respective elements are as follows. Here, in the following
description, "%" ofthe content of the element means "mass%".
[0062]
C: 0.15% or less
If a C content is more than 0.15%, it is likely that stress corrosion cracking
resistance can be deteriorated. Thus, when C is contained, it is preferable that the
content ofC is 0.15% or less, more preferably, 0.06% or less. Here, C has an effect
2..0
-;6-
of increasing the grain boundary strength of an alloy. In order to acquire this effect,
it is preferable that the content ofC is 0.01% or more.
[0063]
Si: 1.00% or less
Si is used as a deoxidizer at the time ofmelting and remains as impurities in
the alloy. At this time, it is preferable that the content ofSi is limited to 1.00% or
less. If the content of Si is more than 0.50%, the cleanliness of the alloy is lowered
in some cases. Thus, it is more preferable that the content of Si is limited to 0.50%
or less.
[0064]
Mn: 2.0% or less
Mn is an element that immobilizes S, an impurity element, as MnS to thereby
improve hot workability and that is effective as a deoxidizer. If the content ofMn
is more than 2.0%, the cleanliness of the alloy is lowered. Thus, it is preferable that
the content ofMn is 2.0% or less, more preferably, 1.0% or less. Further, in the
case of acquiring the effect of improving the hot workability by Mn, it is preferable
that the content ofMn is 0.1% or more.
[0065]
P: 0.030% or less
P is an element that remains as impurity in the alloy and if the content of P is
more than 0.030%, P has an adverse effect on a corrosion resistance in some cases.
Thus, it is preferable that the content ofP is limited to 0.030% or less.
[0066]
S: 0.030% or less
S is an element that remains as impurity in the alloy and when the content of
S is more than 0.030%, S has an adverse effect on the corrosion resistance in some
cases. Thus, it is preferable that the content of S is limited to 0.030% or less.
[0067]
Cr: 10.0 to 40.0%
Cr is an element necessary for keeping the corrosion resistance ofthe alloy
and hence it is preferable that the content of Cr is 10.0% or more. However,
containing Cr by more than 40.0% means that the content ofNi gets relatively
2/
-/
smaller and hence it is likely to lower the corrosion resistance and the hot
workability of the alloy. Thus, it is preferable that the content ofCr is 10.0 to
40.0%. In particular, if the content ofCr is 14.0 to 17.0%, the alloy exhibits
excellent corrosion resistance in the environment including chloride, and if the
content ofCr is 27.0 to 31.0%, the alloy is excellent in the corrosion resistance even
in the environment including pure water and alkali at high temperatures.
[0068]
Ni: 8.0 to 80.0%
Ni is an element necessary for securing the corrosion resistance ofthe alloy
and it is preferable that the content ofNi is 8.0% or more. On the other hand, since
Ni is expensive, it is enough that a minimum content ofNi as needed is contained
according to use and hence it is preferable that the content ofNi is 80.0% or less.
[0069]
Ii: 0.5% or less
If the content of Ti is more than 0.5%, it is likely that the cleanliness ofthe
alloy is deteriorated. Thus, it is preferable that the content of Ii is 0.5% or less and,
more preferably, 0.4% or less. However, from the viewpoint of improving
workability ofthe alloy and of inhibiting a grain growth at the time of welding, it is
preferable that the content ofTi is 0.1% or more.
[0070]
Cu: 0.6% or less
Cu is an element that remains as impurity in the alloy, and if the content ofCu
is more than 0.6%, the corrosion resistance of the alloy is lowered in some cases.
Thus, it is preferable that the content ofCu is limited to 0.6% or less.
[0071]
AI: 0.5% or less
Al is used as a deoxidizer at the time of steelmaking and remains as impurity
in the alloy. The remaining Al becomes oxide-based inclusions in the alloy and
lowers the cleanliness of the alloy. Hence, it is likely that Al has an adverse effect
on the corrosion resistance and the mechanical property of the alloy. Thus, it is
preferable that the content of Al is limited to 0.5% or less.
[0072]
N: 0.20% or less
N may not be added to the alloy but the alloy intended by the present
invention typically contains about 0.01% ofN as impurity. However, ifN is
positively added to the alloy, N can increase the strength of the alloy without
impairing the corrosion resistance. However, when the content ofN is more than
0.20%, the corrosion resistance is lowered. Thus, it is preferable that the upper
limit of the content ofN is 0.20%.
[0073]
In the heat transfer tube for a steam generator according to the present
invention and in the method for producing the same, it is preferable that aNi-based
alloy having chemical composition consisting of C: 0.15% or less, Si: 1.00% or less,
Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0 to 40.0%, Fe: 15.0%
or less, Ti: 0.5% or less, Cu: 0.6% or less, AI: 0.5% or less, the balance being Ni and
impurities because the Ni-based alloy is more excellent in the corrosion resistance.
[0074]
The typical Ni-based alloy having the above-mentioned chemical composition
and preferably used for the tube will include two kinds of alloys described below.
[0075]
(a) Ni-based alloy consisting ofC: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less,
P: 0.030% or less, S: 0.030% or less, Cr: 14.0 to 17.0%, Fe: 6.0 to 10.0%, Ti: 0.5%
or less, Cu: 0.6% or less, AI: 0.5% or less, the balance being Ni and impurities.
[0076]
(b) Ni-based alloy consisting of C: 0.06% or less, Si: 1.00% or less, Mn: 2.0% or less,
P: 0.030% or less, S: 0.030% or less, Cr: 27.0 to 31.0%, Fe: 7.0 to 11.0%, Ti: 0.5%
or less, Cu: 0.6% or less, AI: 0.5% or less, the balance being Ni and impurities.
[0077]
The alloy (a) described above contains 14.0 to 17.0% ofCr and about 75% of
Ni, so that the alloy (a) is excellent in the corrosion resistance in the environment
including the chloride. In this alloy, it is preferable that the content of Fe is 6.0 to
10.0% from the viewpoint of the balance of the content ofNi and the content of Cr.
[0078]
23
-Jlf-
The alloy (b) described above contains 27.0 to 31.0% ofCr and about 60% of
Ni, so that the alloy (b) is excellent in the corrosion resistance not only in the
environment including chloride but also in the environment including pure water and
alkali at high temperatures. Also in this alloy, it is preferable that the content of Fe
is 7.0 to 11.0% from the viewpoint ofthe balance of the content ofNi and the content
of Cr.
EXAMPLES
[0079]
Tests for verifying effects ofthe heat transfer tube for a steam generator
according to the present invention and the method for producing the same were
conducted.
[0080]
[Test procedure]
A tube was acquired by a cold working process of finishing the tube into a
predetermined size, a solid solution heat treatment process, and a straightening
process using a roll straightening machine for straightening bends and the out-ofroundness
of the tube. In the cold working process, the tube was finished into a
predetermined size by Pilger rolling or drawing work (high-pressure drawing) using
a high-pressure lubricating oil of 120 MPa in pressure. In the straightening process,
a (2-2-2-1) type straightening machine having three pairs of straightening rolls or a
(2-2-2-2-2) type straightening machine having five pairs of straightening rolls was
used.
[0081]
Test conditions are as follows.
Chemical composition of tube:
Material grade: Ni-based alloy specified by ASME S8-163 UNS N06690
Ni-based alloy consisting of, in mass%, C: 0.021%, Si: 0.33%, Mn: 0.27%, P:
0.013%, S: 0.0002%, Cr: 29.4%, Fe: 9.8%, Ti: 0.25%, Cu: 0.03%, and AI: 0.11%,
the balance being Ni and impurities.
Solid solution heat treatment was performed at 11OO°C for three minutes.
[0082]
-y(-
Tube A and Tube B ofNi-based alloys, which had the chemical composition
shown in the above test conditions and were different from each other in size, were
tested. The Tube A had an outside diameter of 19.14 mm, a thickness of 1.125 mm,
and a length of 10,000 mm (10 m). The Tube B had an outside diameter of 17.57
mm, a thickness of 1.05 mm, and a length of 10,000 mm (10 m).
[0083]
In Table I and Table 2, shown are test number, test category, tube tested,
finishing method in cold working process, an amount ofdimensional variation along
a longitudinal direction'ofinner surface oftube after cold working process and
before straightening, straightening conditions, and test results. As for the
straightening conditions, the number of pairs of straightening rolls of the roll
straightening machine, the stand interval, the offset amount set for successive three
pairs of straightening rolls, and the value of TJ calculated by Formula (I) described
above are shown in Table I and Table 2. Here, in the tests using the (2-2-2-2-2)
type straightening machine having five pairs of straightening rolls, the value of TJ and
the offset amount shown in Table I and Table 2 are set for successive three pairs of
straightening rolls which were arranged in the intermediate region excluding
foremost and rearmost pairs ofrolls.
[0084]
[Table 1]
-/
Table 1
~
N
()'
Before straightening Straightening conditions Test results (after straightening)
Amount of dimensional Amount ofdimensional
Test
Category
Tube variation in Number of Offset variation in longitudinal
No. tested Cold working longitudinal direction pairs of rolls Stand
amount '1 Remaining direction of inner SIN ratio Overall
process of inner surface of tube (pair)
interval(mm)
(mm) (x 10-3
) bends
surface oftube (~m)
evaluation
(~m)
I Comparative example A 7.5 3 380 4 0.53 x 7.5 12 x
2 Comparative example A 6.5 3 380 5 0.66 x 6.5 15 x
3 Comparative example A Pilger rolling 8.0 3 380 6 0.80 x 8.5 8 x
4 Comparative example A 7.5 3 380 9 1.19 0 8.5 9 x
5 Comparative example A 6.5 3 380 10 1.32 0 8.0 11 x
6 Comparative example A 1.0 3 380 4 0.53 x 2.0 88 x
7 Comparative example A 1.0 3 380 5 0.66 x 3.0 78 x
8 Comparative example A
Higdhra-pwreinsgsure 1.0 3 380 6 0.80 x 3.5 75 x
9 Comparative example A 1.0 3 380 9 1.19 0 6.5 25 x
10 Comparative example A 1.0 3 380 10 1.32 0 7.0 21 x
II Comparative example A 7.5 5 270 2 0.53 x 7.5 15 x
12 Comparative example A 6.5 5 270 3 0.79 x 6.5 13 x
13 Comparative example A
Pilger rolling
8.0 5 270 4 1.05 0 8.0 10 x
14 Comparative example A 7.5 5 270 5 1.31 0 8.5 7 x
15 Comparative example A 1.0 5 270 2 0.53 x 1.5 95 x
16 Comparative example A 1.0 5 270 3 0.79 x 1.5 98 x
17 Inventive example A 1.0 5 270 4 1.05 0 2.5 75 0
18 Inventive example B
High-pressure 1.0 5 270 4 0.96 0 2.0 81 0
drawing
19 Inventive example A 1.0 5 270 5 1.31 0 2.5 65 0
20 Inventive example B 1.0 5 270 5 1.20 0 2.0 79 0
21 Comparative example A 1.0 5 270 6 1.57 0 5.0 34 x
[0085]
[Table 2]
-)ff-
Table 2
~.~
N
-{i
Before straightening Straightening conditions Test results (after straightening)
Amount of dimensional Amount of dimensional
Test
Category
Tube variation in Number of Offset variation in longitudinal
No. tested Cold working
longitudinal direction pairs of rolls
Stand interval
amount Tl Remaining
direction of inner surface SIN ratio
Overall
process of inner surface of tube (pair)
(mm)
(mm) (x 10'3) bends
oftube (~m)
evaluation
(~m)
22 Comparative example A 7.5 5 240 2 0.66 x 7.5 18 x
23 Comparative example A 6.5 5 240 3 1.00 0 6.5 12 x
24 Comparative example A
Pilger rolling
8.0 5 240 4 1.33 0 8.5 7 x
25 Comparative example A 7.5 5 240 5 1.66 0 8.5 8 x
26 Comparative example A 1.0 5 240 2 0.66 x I.5 88 x
27 Inventive example A 1.0 5 240 3 1.00 0 2.5 85 0
28 Inventive example A 1.0 5 240 4 1.33 0 2.5 76 0
29 Inventive example B
High-pressure 1.0 5 240 4 1.22 0 2.0 77 0
30 Inventive example
drawing
A 1.0 5 240 5 1.66 0 3.0 58 0
31 Inventive example B 1.0 5 240 5 1.52 0 2.5 64 0
32 Comparative example A 1.0 5 240 6 1.99 0 5.5 25 x
-J'f-
[0086]
[Evaluation criterion]
In each test, an amount of dimensional variation in the inner surface of the
tube subjected to the cold working was measured before and after the tube was
subjected to the straightening. Further, an SIN ratio of the tube subjected to the
straightening was measured by the eddy current flaw detection and remaining bends
of the tube was evaluated. Still further, an overall evaluation ofthe tube was made
on the basis ofthe results of remaining bends, the amount of dimensional variation
along a longitudinal direction of the inner surface of the tube subjected to the
straightening, and the SIN ratio.
[0087]
The amount of dimensional variation is a difference between a maximum
value and a minimum value in a specific length of 50 m taken from a roughness
measurement chart, which was obtained by measuring the surface roughness of the
inner surface of the tube by use ofa surface roughness measurement devicee (made
by Tokyo Seimitsu Co., Ltd. Type: SURFCOM 1500SD3). When the surface
roughness was measured, a detector having a contact probe of 0.8 mm in radius was
used.
[0088]
The SIN ratio was determined in the following manner: the inner surface of
the tube was inspected by use ofthe eddy current flaw detection under conditions of
a frequency of 600 kHz and a type of detecting local differential by using a drilled
through-hole having a diameter of 0.66 mm cl> as a standard notch; to thereby obtain
values of SIN ratio where the total length oftube is subdivided into one-foot -length
portions and an individual value of SIN ratio is determined for each portion: and
among obtained values of SIN ratio, a minimum value was regarded as the SIN ratio
of the tube.
[0089]
As for remaining bends, particularly, the bend crookedness near an end of the
tube (hereinafter also referred to as "nose bend") was observed as the bend of the
tube subjected to the straightening. The meanings of signs in the column of
[Remaining bends] in Table 1 and Table 2 are as follows:
~..
-tt-
0: the amount of bend crookedness in a portion of a length of 1000 rnm from a tube
end was 1 rnm or less and hence the bends of the tube are considered as being
sufficiently straightened, and
x: the amount of bend crookedness was more than 1 mm for the portion as above and
hence the bends of the tube are considered as being insufficiently straightened.
[0090]
The meanings of signs in the column of [Overall evaluation] in Table 1 and
Table 2 are as follows:
0: the evaluation ofremaining bends ofthe tube subjected to the straightening was
good (0), the amount of dimensional variation along a longitudinal direction of the
inner surface of the tube was 4 ~ or less, and the SIN ratio was 50 or more.
x: anyone ofthe following conditions was not satisfied: that is, (Condition 1) the
evaluation of remaining bends ofthe tube subjected to the straightening was good
(0); (Condition 2) the amount of dimensional variation along a longitudinal
direction ofthe inner surface of the tube was 4 Jlm or less; and (Condition 3) the SIN
ratio was 50 or more.
[0091 ]
[Test results]
As shown in Table 1 and Table 2, in all of Test Nos. 1 to 5, 11 to 14, and 22
to 25, which are comparative examples, Pilger rolling was employed as the cold
working process and the amount of dimensional variation along a longitudinal
direction of the inner surface of the tube not yet subjected to the straightening was 4
Jlm or more. For this reason, in all of Test Nos. 1 to 5, 11 to 14, and 22 to 25,
irrespective ofthe straightening conditions including the number of pairs of
straightening rolls and the stand interval of the straightening machine, the offset
amount, and the value of 11, the amount of dimensional variation along a longitudinal
direction of the inner surface of the tube subjected to the straightening was more than
4 Jlm in any ofthe tests and hence the overall evaluations were all x.
[0092]
In Test Nos. 6 to 10 of comparative examples, the tube was subjected to the
cold drawing by the high-pressure drawing using the lubricating oil of 40 MPa or
more in pressure, and a (2-2-2-1) type straightening machine having three pairs of
-;Astraightening
rolls and having a stand interval set at 380 mm was used. In all of
Test Nos. 6 to 10, the amount of dimensional variation along a longitudinal direction
of the inner surface ofthe tube before straightening was 1.0 Jlm.
[0093]
Ofthese tests, in Test Nos. 9 and 10, the offset amount was set at 9 or 10 mm
and II was set at 1.19 x 10.3 or 1.32 x 10-3
, whereby the amount of working per each
pair of straightening rolls was increased as compared with the conditions specified
by the present invention. As a result, remaining bends ofthe tube subjected to the
straightening became 0 but the amount ofdimensional variation along a longitudinal
direction ofthe inner surface ofthe tube increased and became more than 4 Jlm, so
that the overall evaluation became x. Further, in Test Nos 6 to 8, the offset amount
was set at 4 to 6 mm and II was set at 0.53 x 10-3 to 0.80 x 10-3
, whereby the amount
of working per each pair of straightening rolls was decreased. As a result, the
amount of dimensional variation along a longitudinal direction of the inner surface of
the tube subjected to the straightening became 4 Jlm or less but remaining bends of
the tube subjected to the straightening became x, so that the overall evaluation
became x.
[0094]
In Test Nos. 15, 16, and 21, which are comparative examples, the tube was
subjected to the cold drawing by the high-pressure drawing using the lubricating oil
of 40 MPa or more in pressure and a (2-2-2-2-2) type straightening machine having
five pairs of straightening rolls and having a stand interval set at 270 mm was used.
In all of Test Nos. 15, 16, and 21, the amount of dimensional variation along a
longitudinal direction of the inner surface ofthe tube before straightening was 1.0
Jlm.
[0095]
Ofthese tests, in Test Nos. 15 and 16, the offset amount was set at 2 or 3 mm,
which is within the range specified by the present invention, but II was set at 0.53 x
10.3 or 0.79 x 10.3
, which is outside the range specified by the present invention. In
these cases, the amount of dimensional variation along a longitudinal direction of the
inner surface of the tube subjected to the straightening became 4 Jlm or less in both
cases but the remaining bends evaluation became x, so that the overall evaluation
•
-j6-
became x. Further, in Test No 21,11 was set at 1.57 x 10-3
, which is within the
range specified by the present invention, but the offset amount was set at 6 mm,
which is outside the range specified by the present invention. In this case, the
remaining bend evaluation ofthe tube subjected to the straightening became 0 but
the amount of dimensional variation along a longitudinal direction ofthe inner
surface ofthe tube became more than 4 J.1m, so that the overall evaluation became x.
[0096]
In Test Nos. 26 and 32, which are comparative examples, the tube was
subjected to the cold drawing by the high-pressure drawing using the lubricating oil
of40 MPa or more in pressure and the (2-2-2-2-2) type straightening machine having
five pairs of straightening rolls and having a stand interval set at 240 rnm was used.
In both of Test Nos. 26, and 32, the amount of dimensional variation along a
longitudinal direction of the inner surface ofthe tube before straightening was 1.0
J.1m.
[0097]
Ofthese tests, in Test No. 26, the offset amount was set at 2 mm, which is
within the range specified by the present invention, but 11 was set at 0.66 x 10-3
,
which is outside the range specified by the present invention. In this case, the
amount of dimensional variation along a longitudinal direction of the inner surface of
the tube subjected to the straightening became 4 J.1m or less but the remaining bend
evaluation became x, so that the overall evaluation became x. Further, in Test No
32, 11 was set at 1.99 x 10-3
, which is within the range specified by the present
invention but the offset amount was set at 6 mm, which is outside the range specified
by the present invention. In this case, the remaining bend evaluation of the tube
subjected to the straightening became 0 but the amount of dimensional variation
along a longitudinal direction of the inner surface ofthe tube became more than 4
J.1m, so that the overall evaluation became x.
[0098]
On the other hand, in Test Nos. 17 to 20 and 27 to 31, which are inventive
examples ofthe present invention, the tube was subjected to the cold drawing by the
high-pressure drawing using the lubricating oil of 40 MPa or more in pressure. The
(2-2-2-2-2) type straightening machine having five pairs of straightening rolls and
~I
-;(-
having a stand interval set at 300 mm or less was used. The tube was straightened
with II set at 0.9 x 10-3 or more and with the offset amount set at 5 mm or less. As a
result, all ofevaluations including the remaining bends of the tube subjected to the
straightening, the amount of dimensional variation along a longitudinal direction of
the inner surface of the tube, and the SIN ratio became good, so that the overall
evaluation became O.
[0099]
From these tests, the following facts could be verified: when the tube
subjected to the cold drawing by the high-pressure drawing using the lubricating oil
of 40 MPa or more in pressure and to the solid solution heat treatment was
straightened by the roll straightening machine having at least five pairs of
straightening rolls and having a stand interval set at 300 mm or less with the value of
II set at 0.9 x 10-3 or more and with the offset amount set at 5 mm or less, the bends
of the tube could be straightened and the amount of dimensional variation along a
longitudinal direction ofthe inner surface of the tube subjected to the straightening
could be controlled to 4 /lm or less and the tube having an excellent SIN ratio could
be produced. Thus, it was made clear that according to the method for producing a
heat transfer tube for a steam generator according to the present invention, a heat
transfer tube for a steam generator according to the present invention, in which the
amount of dimensional variation along a longitudinal direction of the inner surface of
the tube is 4 J..1m or less, can be produced.
INDUSTRIAL APPLICABILITY
[0100]
In a heat transfer tube for a steam generator according to the present invention,
the amount of dimensional variation along a longitudinal direction of the inner
surface of the tube is 4 J..1m or less, so that when the tube is produced, an inspection
using an eddy current flaw detection can be conducted at a high SIN ratio and hence
the inspection efficiency can be improved.
[0101 ]
The method for producing a heat transfer tube for a steam generator according
to the present invention has the following remarkable effects.
-yi-
(1) The tube is subjected to cold drawing by use ofthe high-pressure lubricating oil
of 40 MPa or more in pressure, so that an amount of dimensional variation along a
longitudinal direction of the inner surface ofthe tube after the cold drawing and
before straightening can be reduced.
(2) The tube is straightened by using the roll straightening machine in which at least
five pairs of concave globoidal drum type straightening rolls are disposed and a stand
interval is set at 300 mm or less, and by applying offsetting, which is formed by at
least successive three pairs of straightening rolls ofthe roll straightening machine
and has Tl set at 0.9 x 10.3 or more and has the offset amount set at 5 mm or less, to
the tube. This can reduce an increase ofthe amount of dimensional variation along
a longitudinal direction ofthe inner surface of the tube attributable to the
straightening.
(3) The method for producing a heat transfer tube for a steam generator according to
the present invention, from the effects (l) and (2) described above, can produce the
tube in which the amount of dimensional variation along a longitudinal direction of
the inner surface of the tube is 4 J.1m or less and in which the amount of bend
crookedness in a portion of a length of 1000 mm from a tube end is 1mm or less.
[0102]
Therefore, the heat transfer tube for a steam generator according to the present
invention and the tube produced by the method for producing the same can secure an
excellent quality accuracy and hence can guarantee quality at high reliability.
REFERENCE SIGNS LIST
[0103]
1: tube to be straightened
R, Ra, and Rb: straightening roll

We claim:
1. A heat transfer tube for a steam generator, characterized in that an amount of
dimensional variation in a specific length of 50 mm taken from a roughness
measurement chart, which is obtained by measuring a surface roughness of an inner
surface ofthe tube along a longitudinal direction, is 4 fllll or less and an amount of
bend crookedness in a portion a length of 1000 mm from a tube end is Imm or less.
2. The heat transfer tube for a steam generator according to claim 1,
characterized in that the tube is produced by the steps of: cold drawing by use of a
high-pressure lubricating oil of 40 MPa or more in pressure; solid solution heat
treatment; and straightening by a roll straightening machine.
3. The heat transfer tube for a steam generator according to claim 2,
characterized in that the roll straightening machine is a roll straightening machine
using at least five pairs of concave globoidal drum type straightening rolls, each pair
of rolls being arranged opposite to each other in a vertical direction and in a crossing
manner where directions ofrotating shafts cross each other.
4. The heat transfer tube for a steam generator according to anyone ofclaims 1
to 3, characterized in that a chemical composition ofthe tube consists of, in mass%,
C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030%
or less, Cr: 10.0 to 40.0%, Ni: 8.0 to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, AI:
0.5% or less, and N: 0.20% or less, the balance being Fe and impurities.
5. A method for producing a heat transfer tube for a steam generator,
characterized in that when a tube subjected to cold drawing by use of a high-pressure
lubricating oil of40 MPa or more in pressure and to solid solution heat treatment is
straightened by use of a roll straightening machine in which at least five pairs of
concave globoidal drum type straightening rolls are provided, each pair of rolls being
arranged opposite to each other in a vertical direction and in a crossing manner
where directions of rotating shafts cross each other, and in which a stand interval is
set at 300 mm or less, the tube is subjected to offsetting that is fonned by three points
literally along a tube axial centerline as being crossing positions of at least successive
three pairs ofupper and lower straightening rolls of the roll straightening machine
and that allows 11 expressed by Formula (1) described below to satisfy 0.9 x 10-3 or
more and to ensure an offset amount of 5 mm or less:
11 = 1 / R x (d / 2) .... (1)
where given that an outside diameter ofthe tube is d (mm) and a stand interval ofthe
roll straightening machine is L (mm) and an offset amount is 8 (mm), R = (82 + L2) /
28 is established.
6. The method for producing a heat transfer tube for a steam generator according
to claim 5, characterized in that a chemical composition ofthe tube consists of, in
mass%, C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S:
0.030% or less, Cr: 10.0 to 40.0%, Ni: 8.0 to 80.0%, Ti: 0.5% or less, Cu: 0.6% or
less, AI: 0.5% or less, and N: 0.20% or less, the balance being Fe and impurities.