FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention: REPAIR WELDING METHOD
2. Applicant(s)
NAME NATIONALITY ADDRESS
MITSUBISHI POWER, LTD. Japanese 3-1, Minatomirai 3-Chome, Nishiku,
Yokohama-shi, Kanagawa
2208401, Japan
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it
is to be performed.
1
TECHNICAL FIELD
[0001] The present disclosure relates to a repair welding method.
5 BACKGROUND
[0002] After a member having a welded portion is used, repair welding may
be performed for repair.
For example, in high-temperature pipes of boilers and turbines in thermal
power and nuclear power plants, chemical plants, etc., creep damage may occur in
10 the welded portion due to long-term use.
In such a case, instead of replacing the entire pipe in which the creep
damage has occurred, the portion where the creep damage has occurred is excised,
and the excised portion is subjected to repair welding (see Patent Document 1).
15 Citation List
Patent Literature
[0003] Patent Document 1: JPS60-008148B
SUMMARY
20 Problems to be Solved
[0004] In the repair welding method disclosed in Patent Document 1, stress
acting on the heat-affected zone is reduced by considering the extending direction
of the heat-affected zone generated by repair welding inside the main welded joint
deposited metal, that is, the weld metal of the existing welded portion.
25 A region where the heat-affected zone of the existing welded portion and the
heat-affected zone due to the repair welding overlap is affected by both heat when
2
the existing welded portion has been obtained and when the repair welding is
performed, so that this region is likely to be damaged due to the acting stress,
compared with a region affected by either one of heat when the existing weld has
been obtained or heat when the repair welding is performed. Therefore, it is
desired to reduce the region where the heat-5 affected zone of the existing welded
portion and the heat-affected zone due to the repair welding overlap as much as
possible. However, the repair welding method disclosed in Patent Document 1
does not mention the region where the heat-affected zone of the existing welded
portion and the heat-affected zone due to the repair welding overlap.
10 [0005] In view of the above, an object of at least one embodiment of the
present invention is to suppress the influence of the heat-affected zone due to
repair welding on the lifetime of the member.
Solution to the Problems
15 [0006] (1) A repair welding method according to at least one embodiment of
the present invention is a method for a member in which a first end and a second
end of a parent material are connected by welding, comprising: a step of removing
a portion including at least a part of a first heat-affected zone of an existing
welded portion of the member; and a step of performing repair welding after
20 removing the portion. In a cross-section including the parent material and the
existing welded portion, all intersection portions between the first heat-affected
zone of the existing welded portion and a second heat-affected zone due to the
repair welding have an intersection angle between the first heat-affected zone and
the second heat-affected zone of 70° to 110°.
25 [0007] In a cross-section including the parent material and the existing welded
portion, the intersection portion between the first heat-affected zone of the
3
existing welded portion and the second heat-affected zone due to the repair
welding is likely to be damaged by the acting stress as described above, so that it
is desired to reduce the intersection portion as much as possible. In a crosssection
including the parent material and the existing welded portion, since the
first heat-affected zone and the second heat-5 affected zone are formed with
constant widths along the interfaces with the respective weld metals, when the
intersection angles between the first heat-affected zone and the second heataffected
zone are 90°, the cross-sectional area of the intersection portion can be
minimized, and as the intersection angles are deviated from 90°, the cross10
sectional area of the intersection portion increases.
In this regard, with the above method (1), since the intersection angles
between the first heat-affected zone and the second heat-affected zone range from
70° to 110°, in a cross-section including the parent material and the existing
welded portion, it is possible to suppress the increase in cross-sectional area of the
15 intersection portion. As a result, it is possible to suppress the reduction in
lifetime of the member due to the repair welding.
[0008] (2) In some embodiments, in the above method (1), in a cross-section
including the parent material and the existing welded portion, the repair welding is
performed from the parent material on a first end side to the parent material on a
20 second end side, and a second distance is 1.1 to 2.0 times a first distance, where
the first distance is a distance on a surface of the parent material between the first
heat-affected zone formed in the parent material on the first end side and the first
heat-affected zone formed in the parent material on the second end side before
removing the portion including at least a part of the first heat-affected zone, and
25 the second distance is a distance on a surface of the parent material between the
second heat-affected zone formed in the parent material on the first end side and
4
the second heat-affected zone formed in the parent material on the second end side.
[0009] With the above method (2), since the second distance is 1.1 times or
more the first distance, it is possible to suppress the overlapping of the first heataffected
zone and the second heat-affected zone in the vicinity of the surface of
the parent material. Further, 5 with the above method (2), since the second
distance is 2.0 times or less the first distance, it is possible to suppress the range of
the repair welding.
[0010] (3) In some embodiments, in the above method (1) or (2), in a crosssection
including the parent material and the existing welded portion, the repair
10 welding is performed from the parent material on a first end side to the parent
material on a second end side, and a third distance is not greater than a fourth
distance, where the third distance is a distance between the intersection portion on
the first end side and the intersection portion on the second end side, and the
fourth distance is a distance between positions of the second heat-affected zone on
15 the first end side and the second end side at a depth 0.8 times a maximum value of
a depth from a surface of a weld metal of the repair welding to the second heataffected
zone.
[0011] With the above method (3), the depths of the intersection portion on
the first end side and the intersection portion on the second end side, i.e., the depth
20 of the weld metal of the repair welding from the surface can be set to 0.8 times or
more the maximum value of the depth from the surface of the weld metal of the
repair welding to the second heat-affected zone. Thus, in a cross-section
including the parent material and the existing welded portion, the positions in the
depth direction of the intersection portion on the first end side and the intersection
25 portion on the second end side can be brought closer to the deepest position in the
second heat-affected zone. Accordingly, the extending directions of the
5
intersection portion on the first end side and the intersection portion on the second
end side can be brought closer to a direction perpendicular to the depth direction.
Therefore, when the first heat-affected zone in the intersection portion extends in
substantially the same direction as the depth direction, the intersection angle at the
intersection portion can be brought closer 5 to 90°, so that it is possible to suppress
the increase in cross-sectional area of the intersection portion.
[0012] (4) In some embodiments, in any one of the above methods (1) to (3),
in a cross-section including the parent material and the existing welded portion, an
intersection angle between an extending direction of the second heat-affected zone
10 formed in a weld metal of the existing welded portion due to the repair welding
and a thickness direction of the member is 70° to 110°.
[0013] The second heat-affected zone formed in the weld metal of the existing
welded portion due to the repair welding, i.e., the second heat-affected zone at the
weld metal of the existing welded portion is more likely to be damaged due to the
15 acting stress, than the weld metal of the existing welded portion not affected by
heat of the repair welding or the second heat-affected zone of the parent material.
Accordingly, if tensile stress acts on the member in a direction in which the first
end and the second end are away from each other, it is desired that the projection
area of the second heat-affected zone at the weld metal of the existing welded
20 portion when viewed from the acting direction of the tensile stress is as small as
possible.
In this regard, with the above method (4), in a cross-section including the
parent material and the existing welded portion, since the intersection angle
between the extending direction of the second heat-affected zone at the weld
25 metal of the existing welded portion and the thickness direction of the member is
70° to 110°, the extending direction of the second heat-affected zone at the weld
6
metal of the existing welded portion is close to the direction in which the tensile
stress acts, so that it is possible to reduce the projection area.
[0014] (5) In some embodiments, in any one of the above methods (1) to (4),
a weld toe of the repair welding is at the parent material.
[0015] With the a 5 bove method (5), compared with the case where the weld toe
of the repair welding is at the weld metal of the existing welded portion, it is
possible to reduce a region of the second heat-affected zone at the weld metal.
[0016] (6) In some embodiments, in the above method (1), in a cross-section
including the parent material and the existing welded portion, the repair welding is
10 performed from the parent material on a first end side to a weld metal of the
existing welded portion, and an intermediate position between a position of the
second heat-affected zone appearing on a surface of the parent material on the first
end side and a position of the second heat-affected zone appearing on a surface of
the weld metal of the existing welded portion is at the weld metal of the existing
15 welded portion before removing the portion including at least a part of the first
heat-affected zone.
[0017] With the above method (6), while suppressing the increase in crosssectional
area of the intersection portion, the removal amount in the step of
removing the portion including at least a part of the first heat-affected zone and
20 the volume of the weld metal by the repair welding can be reduced, and the
production cost for the repair welding can be reduced.
[0018] (7) In some embodiments, any one of the above methods (1) to (6)
further comprises: a step of measuring a shape of the first heat-affected zone prior
to the step of performing the repair welding; and a step of determining a removal
25 range to be removed in the step of removing the portion including at least a part of
the first heat-affected zone, based on the shape of the first heat-affected zone
7
measured in the step of measuring the shape of the first heat-affected zone.
[0019] With the above method (7), the portion including at least a part of the
first heat-affected zone can be removed such that the intersection angle between
the first heat-affected zone and the second heat-affected zone is 70° to 110°. As
a result, it is possible to suppress the 5 increase in cross-sectional area of the
intersection portion in a cross-section including the parent material and the
existing welded portion, and it is possible to suppress the reduction in lifetime of
the member due to the repair welding.
[0020] (8) In some embodiments, in the above method (7), the step of
10 measuring the shape of the first heat-affected zone includes measuring the shape
of the first heat-affected zone by ultrasonic flaw detection with a phased array
method, or measuring the shape of the first heat-affected zone by developing the
shape of the first heat-affected zone by etching.
[0021] With the above method (8), by measuring the shape of the first heat15
affected zone by ultrasonic flaw detection with the phased array method, the shape
of the first heat-affected zone can be measured non-destructively. Further, with
the above method (8), by making the shape of the first heat-affected zone appear
on the surface of the member by a simple method of etching, the shape of the first
heat-affected zone can be easily measured.
20 [0022] (9) In some embodiments, in any one of the above methods (1) to (8),
the parent material is high-strength ferritic heat-resistant steel.
[0023] The method (9) is suitable for repair welding of a member in which the
parent material is made of high-strength ferritic heat-resistant steel.
[0024] (10) In some embodiments, in any one of the above methods (1) to (9),
25 the member is a boiler tube.
[0025] The method (10) is suitable for repair welding of a boiler tube.
8
Advantageous Effects
[0026] According to at least one embodiment of the present invention, it is
possible to suppress the influence of the heat-affected zone of due to repair
5 welding on the lifetime of the member.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1 is a diagram showing a part of a pipe as an example of a
member to which the repair welding method according to some embodiments is
10 applied.
FIG. 2 is a diagram schematically showing a part of a cross-section of the
pipe including a parent material and an existing welded portion.
FIG. 3 is a flowchart showing the process of the repair welding method
according to some embodiments.
15 FIG. 4 is a diagram showing an example of a part of a cross-section of the
pipe including a parent material and an existing welded portion. Part (a) is a
diagram showing the macro-structure of the cross-section, and part (b) is a contour
diagram showing a result of ultrasonic flaw detection by the phased array method
on the cross-section.
20 FIG. 5 is a diagram showing an example of the surface of the pipe after
micro-etching.
FIG. 6 is a diagram schematically showing a part of a cross-section of the
pipe after removing a removal range in the removing step S30.
FIG. 7 is a diagram schematically showing a part of a cross-section of the
25 pipe after removing a removal range in the removing step S30.
FIG. 8 is a diagram schematically showing a part of a cross-section of the
9
pipe after removing a removal range in the removing step S30.
FIG. 9 is a diagram schematically showing a part of a cross-section of the
pipe after repair welding.
FIG. 10 is a diagram schematically showing a part of a cross-section of the
5 pipe after repair welding.
FIG. 11 is a diagram schematically showing a part of a cross-section of the
pipe after repair welding.
DETAILED DESCRIPTION
10 [0028] Embodiments of the present invention will now be described in detail
with reference to the accompanying drawings. It is intended, however, that
unless particularly identified, dimensions, materials, shapes, relative positions,
and the like of components described in the embodiments shall be interpreted as
illustrative only and not intended to limit the scope of the present invention.
15 For instance, an expression of relative or absolute arrangement such as “in a
direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric”
and “coaxial” shall not be construed as indicating only the arrangement in a strict
literal sense, but also includes a state where the arrangement is relatively
displaced by a tolerance, or by an angle or a distance whereby it is possible to
20 achieve the same function.
For instance, an expression of an equal state such as “same” “equal” and
“uniform” shall not be construed as indicating only the state in which the feature
is strictly equal, but also includes a state in which there is a tolerance or a
difference that can still achieve the same function.
25 Further, for instance, an expression of a shape such as a rectangular shape or
a cylindrical shape shall not be construed as only the geometrically strict shape,
10
but also includes a shape with unevenness or chamfered corners within the range
in which the same effect can be achieved.
On the other hand, an expression such as “comprise”, “include”, “have”,
“contain” and “constitute” are not intended to be exclusive of other components.
[0029] FIG. 1 is a diagram showing a part 5 of a pipe as an example of a
member to which the repair welding method according to some embodiments is
applied.
The member (target) to which the repair welding method according to some
embodiments is applied is, for example, high-temperature pipes of boilers and
10 turbines in thermal power and nuclear power plants, chemical plants, etc. Such a
high-temperature pipe (pipe) 1 has multiple types of welds. For example, the
high-temperature pipe has a circumferential weld that connects pipes and a header
tube weld that connects header and branch pipes. Further, in the case where the
pipe 1 is produced from plate members, as shown in FIG. 1, the pipe has a
15 longitudinal weld 10 extending in the pipe axis direction for connecting ends of
the plates which are the parent material.
[0030] A material used for a long time in a high-temperature and highpressure
environment, such as the high-temperature pipe 1, may get a crack due to
creep damage at a welded portion, particular, at a heat-affected zone (HAZ). In
20 the following, an example where the crack occurs in the heat-affected zone of the
longitudinal weld 10 of the pipe 1 will be described. FIG. 2 is a diagram
schematically showing a part of a cross-section of the pipe 1 including a parent
material 2 and an existing welded portion 11. In other words, FIG. 2 is a
diagram schematically showing a part of a cross-section of the pipe 1 taken
25 perpendicular to the pipe axis direction (cross-section viewed from the pipe axis
direction). In FIG. 2 the right-left direction is the circumferential direction of the
11
pipe 1, the upper side is the radially outer side, and the lower side is the radially
inner side. In the following, the longitudinal weld 10 existing before repair
welding is referred to as an existing welded portion 11.
[0031] The existing welded portion 11 is a welded portion connecting a first
end 3 and a second end 4 5 of the parent material 2 of the pipe 1, and includes a
weld metal 5, and a heat-affected zone 6 generated in the parent material 2 by the
influence of heat during welding of the existing welded portion 11. In the pipe 1
shown in FIG. 2, a crack 7 occurs in the heat-affected zone 6 at a side of the first
end 3. Hoop stress acts mainly on the pipe 1 due to the pressure of a fluid
10 flowing inside the pipe 1. Accordingly, tensile stress mainly acts on the existing
welded portion 11 in the circumferential direction, that is, in the right-left
direction in FIG. 2.
[0032] For instance, in some embodiments, the pipe 1 is inspected at periodic
inspections of the plant. In the following, a case where the crack 7 in the pipe 1
15 is found by periodic inspections, and the pipe 1 is to be repaired by repair welding
will be described.
When the crack 7 is generated in the pipe 1, the pipe 1 can be repaired by
removing a partial region of the pipe 1 including the crack 7 and performing
repair welding on the removed portion. However, when the repair welding is
20 performed, a heat-affected zone affected by heat of the repair welding is formed in
the pipe 1. In the following, the heat-affected zone 6 generated in the parent
material 2 by the influence of heat during welding of the existing welded portion
11 is referred to as a first heat-affected zone 6. Further, the heat-affected zone
generated by the influence of heat during welding of a repair welded portion 21
25 (see FIGs. 9 to 11) is referred to as a second heat-affected zone 26 (see FIGs. 9 to
11).
12
[0033] For example, after removing a part of the pipe 1 including the existing
welded portion 11 as shown in FIGs. 6 to 8 described later, when the repair
welding is performed as shown in FIGs. 9 to 11 described later, a region where the
first heat-affected zone 6 and the second heat-affected zone 26 overlap is formed.
In the following, this overlapping region is referred 5 to as an overlapping heataffected
zone 36.
It is revealed that the overlapping heat-affected zone 36 is likely to be
damaged due to the acting stress, compared with a region, such as the first heataffected
zone 6 and the second heat-affected zone 26, affected by only heat when
10 the existing welded portion 11 has been obtained or when the repair welding is
performed. Therefore, if the overlapping heat-affected zone 36 is formed due to
the repair welding, it is desired to reduce the overlapping heat-affected zone 36 as
much as possible.
[0034] Then, in the repair welding method according to some embodiments,
15 the size of the overlapping heat-affected zone 36 is reduced as much as possible in
the following manner.
FIG. 3 is a flowchart showing the process of the repair welding method
according to some embodiments. The repair welding method according to some
embodiments includes a heat-affected zone shape measuring step S10, a removal
20 range determining step S20, a removing step S30, and a repair welding step S40.
The schematic flow of the repair welding method according to some
embodiments is as follows. In the repair welding method according to some
embodiments, the shape of the first heat-affected zone 6 is measured in the heataffected
zone shape measuring step S10, and a range to be removed from the pipe
25 1 is determined based on the measurement result in the removal range determining
step S20. Then, the removal range determined in the removal range determining
13
step S20 is removed in the removing step S30, and repair welding is performed on
the removed portion in the repair welding step S40. Details of each step will
now be described.
[0035] (Heat-affected zone shape measuring step S10)
The heat-affected zone 5 shape measuring step S10 is a step of measuring the
shape of the first heat-affected zone 6 prior to the repair welding step S40. In
order to reduce the size of the overlapping heat-affected zone 36 as much as
possible, it is necessary to consider the setting of the shape of a region to be
subjected to the repair welding. To this end, it is necessary to determine the
10 shape of the heat-affected zone 6 of the existing welded portion 11. Therefore,
in the repair welding method according to some embodiments, in the heat-affected
zone shape measuring step S10, the shape of the heat-affected zone 6 in the
vicinity of the crack 7 is measured.
[0036] Specifically, in the heat-affected zone shape measuring step S10, the
15 shape of the heat-affected zone 6 in the vicinity of the crack 7 is measured by, for
example, ultrasonic flaw detection with the phased array method. FIG. 4 is a
diagram showing an example of a part of a cross-section of the pipe 1 including
the parent material 2 and the existing welded portion 11. Part (a) of FIG. 4 is a
diagram showing the macro-structure of the cross-section, and part (b) of FIG. 4 is
20 a contour diagram showing a result of ultrasonic flaw detection by the phased
array method on the cross-section. For convenience of description, in parts (a)
and (b) of FIG. 4, the boundary between the first heat-affected zone 6 and the
parent material 2 or the weld metal 5 is shown by the dotted line. The two-dot
chain line 12 in part (b) of FIG. 4 is an imaginary line representing the shape of
25 the pipe 1.
[0037] As is seen from the contour diagram 13 shown in part (b) of FIG. 4,
14
the shape of the heat-affected zone 6 can be measured by ultrasonic flaw detection
with the phased array method. In the contour diagram 13, back surface echo 14
on the inner peripheral surface of the pipe 1 appears. Further, in the contour
diagram 13, noise 15 and wedge noise 16 in the weld metal 5 may also appear.
Therefore, it is necessary to identify the shape 5 of the first heat-affected zone 6 in
consideration of the appearance of the back surface echo 14 and the noises 15, 16.
In the case of inspecting the presence or absence of damage to the pipe 1 by
ultrasonic flaw detection with the phased array method in periodic inspections,
information on the shape of the heat-affected zone 6 in the vicinity of the crack 7
10 may be acquired based on the inspection result obtained by the inspections.
[0038] The shape of the heat-affected zone 6 in the vicinity of the crack 7 may
be measured by ultrasonic flaw detection with a method other than the phased
array method.
Thus, by measuring the shape of the first heat-affected zone 6 by ultrasonic
15 flaw detection with, for example, the phased array method, the shape of the first
heat-affected zone 6 can be measured non-destructively.
[0039] Alternatively, in the heat-affected zone shape measuring step S10, the
shape of the first heat-affected zone 6 may be measured by developing the shape
of the first heat-affected zone 6 by etching, for example. FIG. 5 is a diagram
20 showing an example of the surface of the pipe 1 after micro-etching. As is seen
from FIG. 5, for example by etching, the shape and position of the first heataffected
zone 6 on the outer peripheral surface of the pipe 1 can be measured.
The shape of the first heat-affected zone 6 inside the pipe 1 can be estimated
based on design information regarding the existing welded portion 11 such as the
25 groove shape.
By making the shape of the first heat-affected zone 6 appear on the surface
15
of the pipe 1 by a simple method of etching, the shape of the first heat-affected
zone 6 can be easily measured.
When the intersection angle between the first heat-affected zone 6 and the
second heat-affected zone 26 can be set to a desired angle as described later
without measuring the shape of the first heat-affected 5 zone 6, the heat-affected
zone shape measuring step S10 does not necessarily have to be performed.
[0040] (Removal range determining step S20)
The removal range determining step S20 is a step of determining the
removal range to be removed in the removing step S30, based on the shape of the
10 first heat-affected zone 6 measured in the heat-affected zone shape measuring step
S10.
For instance, as shown in FIG. 9, in a cross-section of the pipe 1 including
the parent material 2 and the existing welded portion 11, the first heat-affected
zone 6 is formed, along an interface with the weld metal 5, with a constant width
15 W1 from the interface to the parent material 2. Similarly, in a cross-section of
the pipe 1 including the parent material 2 and the existing welded portion 11, the
second heat-affected zone 26 is formed, along an interface with the weld metal 25
of the repair welding, with a constant width W2. Accordingly, in a cross-section
of the pipe 1 including the parent material 2 and the existing welded portion 11,
20 when the intersection angles θ1 to θ5 between the first heat-affected zone 6 and
the second heat-affected zone 26 are 90°, the cross-sectional area of the
intersection portion between the first heat-affected zone 6 and the second heataffected
zone 26, that is, the overlapping heat-affected zone 36 can be minimized.
Conversely, as the intersection angles θ1 to θ5 between the first heat-affected zone
25 6 and the second heat-affected zone 26 deviate from 90°, the cross-sectional area
of the overlapping heat-affected zone 36 increases.
16
[0041] Therefore, in the removal range determining step S20 according to
some embodiments, the removal range to be removed in the removing step S30 is
determined such that the intersection angles θ1 to θ5 between the first heataffected
zone 6 and the second heat-affected zone 26 range from 70° to 110° and
5 the crack 7 is removed.
Specifically, in the removal range determining step S20 according to some
embodiments, the removal range of the removing step S30 is determined such that
the intersection angles between the first heat-affected zone 6 and the second heataffected
zone 26 range from 70° to 110°, considering that the second heat-affected
10 zone 26 is formed with a constant width W2 inside the member constituting the
pipe 1 from a surface appearing after removing a part of the pipe 1 in the
removing step S30.
[0042] For example, in the removal range determining step S20 according to
an embodiment, as shown in FIG. 6, not only a part of the heat-affected zone 6 on
15 the first end 3 side with the crack 7, but also a part of the heat-affected zone 6 on
the second end 4 side without the crack 7 is determined as the removal range 40.
FIG. 6 is a diagram schematically showing a part of a cross-section including the
parent material 2 and the existing welded portion 11 of the pipe 1 after removing
the removal range 40 in the removing step S30.
20 In the embodiment shown in FIG. 6, the bottom surface of the removal
range 40, i.e., the surface 41 extending in the circumferential direction (right-left
direction in figure) of the surface appearing after removing the removal range 40
may be plane as schematically shown in FIG. 6, or may be curved about the axis
of the pipe 1 such that the depth of the removal range 40 increases toward the
25 circumferentially central side as compared with the plane case, although it is not
illustrated.
17
[0043] Further, in the embodiment shown in FIG. 6, the side surfaces of the
removal range 40, i.e., the surface 42 on the first end 3 side and the surface 42 on
the second end 4 side extending in the thickness direction of the parent material 2
(upper-lower direction in figure) of the surface appearing after removing the
removal range 40 may extend from the outer peripheral 5 surface 1a of the pipe 1 in
substantially the same direction as the thickness direction of the parent material 2,
and the extending directions may be set such that the removal range 40 becomes
narrower toward the radially inner side of the pipe 1, as schematically shown in
FIG. 6.
10 When the extending directions of the surface 42 on the first end 3 side and
the surface 42 on the second end 4 side are close to the thickness direction of the
parent material 2 (radial direction of pipe 1), the removal range 40 can be
narrowed, that is, the range for the repair welding can be narrowed, and the
production cost required for the removal and the repair welding can be reduced.
15 [0044] For example, in the removal range determining step S20 according to
another embodiment, as shown in FIG. 7, a part of the heat-affected zone 6 on the
first end 3 side with the crack 7 is determined as the removal range 40. FIG. 7 is
a diagram schematically showing a part of a cross-section including the parent
material 2 and the existing welded portion 11 of the pipe 1 after removing the
20 removal range 40 in the removing step S30.
In the embodiment shown in FIG. 7, the surface 41 may be plane as
schematically shown in FIG. 7, as with the embodiment shown in FIG. 6, or may
be curved about the axis of the pipe 1 although not illustrated.
[0045] Further, in the embodiment shown in FIG. 7, the surface 42 on the first
25 end 3 side and the surface 42 formed on the weld metal 5 may extend from the
outer peripheral surface 1a of the pipe 1 in substantially the same direction as the
18
thickness direction of the parent material 2, and the extending directions may be
set such that the removal range 40 becomes narrower toward the radially inner
side of the pipe 1, as schematically shown in FIG. 7, as with the embodiment
shown in FIG. 6.
[0046] For example, in the removal 5 range determining step S20 according to
still another embodiment, as shown in FIG. 8, not only a part of the heat-affected
zone 6 on the first end 3 side with the crack 7, but also a part of the heat-affected
zone 6 on the second end 4 side without the crack 7 is determined as the removal
range 40. FIG. 8 is a diagram schematically showing a part of a cross-section
10 including the parent material 2 and the existing welded portion 11 of the pipe 1
after removing the removal range 40 in the removing step S30.
In the embodiment shown in FIG. 8, the surface 41 includes a first surface
41 inclined so as to be close to a direction perpendicular to the extending direction
of the heat-affected zone 6 on the first end 3 side, and a second surface 41b
15 inclined so as to be close to a direction perpendicular to the extending direction of
the heat-affected zone 6 on the second end 4 side. In other words, in the
embodiment shown in FIG. 8, the extending direction of the first surface 41a and
the extending direction of the second surface 41b are individually set in
accordance with the heat-affected zone 6 on the first end 3 side and the heat20
affected zone 6 on the second end 4 side with having slightly different extending
directions.
[0047] Further, in the embodiment shown in FIG. 8, the surface 42 on the first
end 3 side and the surface 42 on the second end 4 side may extend from the outer
peripheral surface 1a of the pipe 1 in substantially the same direction as the
25 thickness direction of the parent material 2, and the extending directions may be
set such that the removal range 40 becomes narrower toward the radially inner
19
side of the pipe 1, as schematically shown in FIG. 8, as with the embodiment
shown in FIG. 6.
[0048] Thus, since the repair welding method according to some
embodiments includes the heat-affected zone shape measuring step S10 and the
removal range determining step S20, the 5 removal range 40 can be set such that the
inclination angle between the first heat-affected zone 6 and the second heataffected
zone 26 is 70° to 110° and removed. As a result, it is possible to
suppress the increase in cross-sectional area of the overlapping heat-affected zone
36 in a cross-section including the parent material 2 and the existing welded
10 portion 11, and it is possible to suppress the reduction in lifetime of the pipe 1 due
to the repair welding.
[0049] (Removing step S30)
The removing step S30 is a step of removing a portion including at least a
part of the first heat-affected zone 6 of the existing welded portion 11.
15 In the removing step S30, the removal range 40 determined in the removal
range determining step S20 is removed with a grinding tool such as a grinder.
The pipe 1 after removing the removal range 40 in the removing step S30 has a
cross-sectional shape as shown in FIGs. 6 to 8 as described above.
[0050] (Repair welding step S40)
20 The repair welding step S40 is a step of performing repair welding after
removing the removal range 40.
In the repair welding step S40 according to an embodiment, the repair
welding is performed as shown in FIG. 9. FIG. 9 is a diagram schematically
showing a part of a cross-section of the pipe 1 including the parent material 2 and
25 the existing welded portion 11 and shows the case where the repair welding is
performed after removing the removal range 40 shown in FIG. 6 in the removing
20
step S30 according to an embodiment.
In the repair welding step S40 according to another embodiment, the repair
welding is performed as shown in FIG. 10. FIG. 10 is a diagram schematically
showing a part of a cross-section of the pipe 1 including the parent material 2 and
the existing welded portion 11 and shows 5 the case where the repair welding is
performed after removing the removal range 40 shown in FIG. 7 in the removing
step S30 according to another embodiment.
In the repair welding step S40 according to still another embodiment, the
repair welding is performed as shown in FIG. 11. FIG. 11 is a diagram
10 schematically showing a part of a cross-section of the pipe 1 including the parent
material 2 and the existing welded portion 11 and shows the case where the repair
welding is performed after removing the removal range 40 shown in FIG. 8 in the
removing step S30 according to still another embodiment.
For convenience of description, in FIGs. 9 to 11, the position where the first
15 heat-affected zone 6 of the existing welded portion 11 was present is represented
by the two-dot chain line.
[0051] The pipe 1 after the repair welding in the repair welding step S40
according to some embodiments has the following features. In other words, the
removal range 40 is determined in the removal range determining step S20 such
20 that the pipe 1 after the repair welding has the following features.
[0052] In some embodiments shown in FIGs. 9 to 11, in a cross-section
including the parent material 2 and the existing welded portion 11, all intersection
portions (overlapping heat-affected zones 36) between the first heat-affected zone
6 of the existing welded portion 11 and the second heat-affected zone 26 due to
25 the repair welding have an intersection angle between the first heat-affected zone
6 and the second heat-affected zone 26 of 70° to 110°.
21
[0053] In a cross-section including the parent material 2 and the existing
welded portion 11, the intersection portion (overlapping heat-affected zone 36)
between the first heat-affected zone 6 of the existing welded portion 11 and the
second heat-affected zone 26 of the repair welded portion 21 is likely to be
damaged due to the acting stress as described above, 5 so that it is desired to reduce
the overlapping heat-affected zone 36 as much as possible.
Further, as described above, in a cross-section including the parent material
2 and the existing welded portion 11, since the first heat-affected zone 6 and the
second heat-affected zone 26 are formed with constant widths W1, W1 along the
10 interfaces with the weld metals 5, 25, respectively, when the intersection angles θ1
to θ5 between the first heat-affected zone 6 and the second heat-affected zone 26
are 90°, the cross-sectional area of the overlapping heat-affected zone 36 can be
minimized, and as the intersection angles θ1 to θ5 are deviated from 90°, the
cross-sectional area of the overlapping heat-affected zone 36 increases.
15 In this regard, in some embodiments shown in FIGs. 9 to 11, since the
intersection angles θ1 to θ5 between the first heat-affected zone 6 and the second
heat-affected zone 26 range from 70° to 110°, in a cross-section including the
parent material 2 and the existing welded portion 11, it is possible to suppress the
increase in cross-sectional area of the overlapping heat-affected zone 36. As a
20 result, it is possible to suppress the reduction in lifetime of the pipe 1 due to the
repair welding.
[0054] In the embodiments shown in FIGs. 9 and 11, in a cross-section
including the parent material 2 and the existing welded portion 11, the repair
welding is performed from the parent material 2 on the first end 3 side to the
25 parent material 2 on the second end 4 side.
Further, a second distance d2 is 1.1 to 2.0 times a first distance d1, where the
22
first distance d2 is a distance on the surface of the parent material 2 between the
first heat-affected zone 6 formed in the parent material 2 on the first end 3 side
and the first heat-affected zone 6 formed in the parent material 2 on the second
end 4 side before removing the removal range 40, and the second distance d2 is a
distance on the surface of the parent material 2 5 between the second heat-affected
zone 26 formed in the parent material 2 on the first end 3 side and the second
heat-affected zone 26 formed in the parent material 2 on the second end 4 side.
When the second distance d2 is 1.1 times or more the first distance d1, it is
possible to suppress the overlapping of the first heat-affected zone 6 and the
10 second heat-affected zone 26 in the vicinity of the surface of the parent material 2.
Further, when the second distance d2 is 2.0 times or less the first distance d1, it is
possible to suppress the range of the repair welding.
[0055] In the embodiment shown in FIG. 9, in a cross-section including the
parent material 2 and the existing welded portion 11, the repair welding is
15 performed from the parent material 2 on the first end 3 side to the parent material
2 on the second end 4 side.
Further, a third distance d3 is not greater than a fourth distance d4, where the
third distance d3 is a distance between the overlapping heat-affected zone 36 on
the first end 3 side and the overlapping heat-affected zone 36 on the second end 4
20 side, and the fourth distance d4 is a distance between a position P1 of the second
heat-affected zone 26 on the first end 3 side at a depth 0.8 times the maximum
value hmax of the depth h from the surface of the weld metal 25 to the second
heat-affected zone 26 and a position P2 on the second end 4 side at a depth 0.8
times the maximum value hmax.
25 [0056] Thus, the depths H of the overlapping heat-affected zone 36 on the
first end 3 side and the overlapping heat-affected zone 36 on the second end 4 side
23
can be set to 0.8 times or more the maximum value hmax of the depth h from the
surface of the weld metal of the repair welding to the second heat-affected zone
26. Thus, in a cross-section including the parent material 2 and the existing
welded portion 11, the positions in the depth direction of the overlapping heataffected
zone 36 on the first end 3 side and 5 the overlapping heat-affected zone 36
on the second end 4 side can be brought closer to the deepest position in the
second heat-affected zone 26. Accordingly, the extending directions of the
overlapping heat-affected zone 36 on the first end 3 side and the overlapping heataffected
zone 36 on the second end 4 side can be brought closer to a direction
10 perpendicular to the depth direction. Therefore, when the first heat-affected zone
6 in the overlapping heat-affected zone 36 extends in substantially the same
direction as the depth direction, the intersection angles θ1, θ2 at the overlapping
heat-affected zones 36 can be brought closer to 90°, so that it is possible to
suppress the increase in cross-sectional area of the overlapping heat-affected zone
15 36.
[0057] In the embodiment shown in FIG. 9, in a cross-section including the
parent material 2 and the existing welded portion 11, the intersection angle θ6
between the extending direction of the second heat-affected zone 26 formed in the
weld metal 5 of the existing welded portion 11 due to the repair welding and the
20 thickness direction of the pipe 1 is 70° to 110°.
[0058] The second heat-affected zone 26 at the weld metal 5 of the existing
welded portion 11 is more likely to be damaged due to the acting stress, than the
weld metal 5 of the existing welded portion 11 not affected by heat of the repair
welding or the second heat-affected zone 26 of the parent material 2.
25 Accordingly, if tensile stress acts on the pipe 1 in the circumferential direction, i.e.,
in the direction in which the first end 3 and the second end 4 are away from each
24
other, it is desired that the projection area of the second heat-affected zone 26 at
the weld metal 5 of the existing welded portion 11 when viewed from the acting
direction of the tensile stress is as small as possible.
In this regard, in the embodiment shown in FIG. 9, since the intersection
angle θ6 between the extending direction of the 5 second heat-affected zone 26 at
the weld metal 5 of the existing welded portion 11 and the thickness direction of
the pipe 1 is 70° to 110°, the extending direction of the second heat-affected zone
26 at the weld metal 5 of the existing welded portion 11 is close to the direction in
which the tensile stress acts, so that it is possible to reduce the projection area.
10 [0059] In the embodiments shown in FIGs. 9 and 11, the weld toe 23 of the
repair welding is at the parent material 2. In the embodiment shown in FIG. 10,
the weld toe 23 of the repair welding on the first end 3 side is at the parent
material 2.
Thus, compared with the case where the weld toe 23 of the repair welding is
15 at the weld metal 5 of the existing welded portion 11, it is possible to reduce a
region of the second heat-affected zone 26 at the weld metal 5.
[0060] In the embodiment shown in FIG. 10, in a cross-section including the
parent material 2 and the existing welded portion 11, the repair welding is
performed from the parent material 2 on the first end 3 side to the weld metal 5 of
20 the existing welded portion 11.
Further, an intermediate position C1 between the position P3 of the second
heat-affected zone 26 appearing on the surface of the parent material 2 on the first
end 3 side and the position P4 of the second heat-affected zone 26 appearing on
the surface of the weld metal 5 of the existing welded portion 11 is at the weld
25 metal 5 of the existing welded portion 11 before removing the removal range 40.
Thus, while suppressing the increase in cross-sectional area of the
25
overlapping heat-affected zone 36, the removal amount in the removing step S30
and the volume of the weld metal 25 by the repair welding can be reduced, and the
production cost for the repair welding can be reduced.
[0061] In the embodiment shown in FIG. 11, in a cross-section including the
parent material 2 and the existing welded portion 5 11, the repair welding is
performed from the parent material 2 on the first end 3 side to the parent material
2 on the second end 4 side. Further, in the embodiment shown in FIG. 11, the
first heat-affected zone 6 on the first end 3 side is inclined with respect to the
radial direction of the pipe 1, at least in the intersection portion (overlapping heat10
affected zone 36) with the second heat-affected zone 26, so as to approach the
second end 4 as the distance from the outer peripheral surface 1a of the pipe 1
increases. In the embodiment shown in FIG. 11, the first heat-affected zone 6 on
the second end 4 side is inclined with respect to the radial direction of the pipe 1,
at least in the intersection portion (overlapping heat-affected zone 36) with the
15 second heat-affected zone 26, so as to approach the first end 3 as the distance
from the outer peripheral surface 1a of the pipe 1 increases.
Further, in the embodiment shown in FIG. 11, the second heat-affected zone
26 is formed such that, at least in the intersection portion (overlapping heataffected
zone 36) with the first heat-affected zone 6 on the first end 3 side, the
20 depth from the outer peripheral surface 1a of the pipe 1 decreases from the first
end 3 side to the second end 4 side. Further, in the embodiment shown in FIG.
11, the second heat-affected zone 26 is formed such that, at least in the
intersection portion (overlapping heat-affected zone 36) with the first heataffected
zone 6 on the second end 4 side, the depth from the outer peripheral
25 surface 1a of the pipe 1 decreases from the second end 4 side to the first end 3
side.
26
As a result, the intersection angles θ4, θ5 at the overlapping heat-affected
zones 36 can be brought closer to 90°, so that it is possible to suppress the
increase in cross-sectional area of the overlapping heat-affected zone 36.
[0062] The repair welding method according to the above-described
embodiments is suitable for repair 5 welding of the pipe 1 having the longitudinal
weld 10 of the pipe 1.
The repair welding method according to the above-described embodiments
is suitable for repair welding of high-temperature pipes of boilers and turbines in
thermal power and nuclear power plants, chemical plants, for example. Such
10 high-temperature pipes are important pipes that are used for a long time in a hightemperature
environment, so if breakage occurs, it is expected to have a
significant effect on the operation of the plant. Further, such high-temperature
pipes are required to be usable for a long time since plant inspections and repairs
are generally performed at a limited time such as periodic inspections. Further,
15 such high-temperature pipes may take a long time to obtain from the viewpoint of
material, thickness, and the like. Therefore, for example, if the crack 7 of the
pipe 1 can be repaired by the repair welding method according to the abovedescribed
embodiments within a limited period such as periodic inspections, the
great economic effect can be achieved.
20 [0063] In the above description, the material of the pipe 1 is not particularly
mentioned, but the repair welding method according to some embodiments is
suitable for repair welding of a member made of high-strength ferritic heatresistant
steel in which a decrease in strength at the overlapping heat-affected
zone 36 tends to be a problem.
25 The high-strength ferritic heat-resistant steel may be, for example, an
equivalent material to grade 91 steel (KA-SCMV28, KA-STPA28, KA-SFVAF28,
27
KA-STBA28), an equivalent material to grade 92 steel (KA-STPA29, KASFVAF29,
KA-STBA29), an equivalent material to KA grade 122 steel (KASUS410J3,
KA-SUS410J3TP, KA-SUSF410J3, KA-SUS410J3TB, KASUS410J3DTB),
or an equivalent material to grade 23 steel (KA-STPA24J1, KA-
5 SFVAF22AJ1, KA-STBA24J1, KA-SCMV4J1).
The material of the pipe 1 is not limited to the high-strength ferritic steel,
but may be low alloy steel or stainless steel. The low alloy steel may be, for
example, an equivalent material to STBA12, an equivalent material to STBA13,
an equivalent material to STPA20, an equivalent material to KA-STPA21, an
10 equivalent material to STPA22, an equivalent material to STPA23, or an
equivalent material to STPA24. The stainless steel may be, for example, an
equivalent material to SUS304TP, an equivalent material to SUS304LTP, an
equivalent material to SUS304HTP, an equivalent material to KA-SUS304J1HTB,
an equivalent material to SUS321TP, an equivalent material to SUS321HTP, an
15 equivalent material to SUS316HTP, an equivalent material to SUS347HTP, or an
equivalent material to KA-SUS310J1TB.
[0064] The present invention is not limited to the embodiments described
above, but includes modifications to the embodiments described above, and
embodiments composed of combinations of those embodiments.
20 For example, in the above-described embodiments, the repair method for the
longitudinal weld 10 of the pipe 1 has been described as an example, but the
present invention is not limited thereto. The repair welding method according to
the above-described embodiments may be applied to repair welding of other welds
such as a circumferential weld connecting pipes or a header tube weld connecting
25 header and branch pipes. Further, the repair welding method according to the
above-described embodiments may be applied to repair welding of welds of
28
members other than pipes such as plates.
Reference Signs List
[0065]
5 1 High-temperature pipe (Pipe)
2 Parent material
3 First end
4 Second end
5, 25 Weld metal
10 6 (Heat-affected zone) First heat-affected zone
7 Crack
10 Longitudinal weld
11 Existing welded portion
21 Repair welded portion
15 23 Weld toe
26 Heat-affected zone (Second heat-affected zone)
36 Intersection portion (Overlapping heat-affected zone)
29
I/We Claim:
1. A repair welding method for a member in which a first end and a second end
of a parent material are connected by welding, comprising:
a step of removing a portion including at least a part of 5 a first heat-affected
zone of an existing welded portion of the member; and
a step of performing repair welding after removing the portion,
wherein, in a cross-section including the parent material and the existing
welded portion, all intersection portions between the first heat-affected zone of the
10 existing welded portion and a second heat-affected zone due to the repair welding
have an intersection angle between the first heat-affected zone and the second
heat-affected zone of 70° to 110°.
2. The repair welding method according to claim 1,
15 wherein, in a cross-section including the parent material and the existing
welded portion, the repair welding is performed from the parent material on a first
end side to the parent material on a second end side, and
wherein a second distance is 1.1 to 2.0 times a first distance, where the first
distance is a distance on a surface of the parent material between the first heat20
affected zone formed in the parent material on the first end side and the first heataffected
zone formed in the parent material on the second end side before
removing the portion including at least a part of the first heat-affected zone, and
the second distance is a distance on a surface of the parent material between the
second heat-affected zone formed in the parent material on the first end side and
25 the second heat-affected zone formed in the parent material on the second end side.
30
3. The repair welding method according to claim 1 or 2,
wherein, in a cross-section including the parent material and the existing
welded portion, the repair welding is performed from the parent material on a first
end side to the parent material on a second end side, and
wherein a third distance is not greater than a 5 fourth distance, where the third
distance is a distance between the intersection portion on the first end side and the
intersection portion on the second end side, and the fourth distance is a distance
between positions of the second heat-affected zone on the first end side and the
second end side at a depth 0.8 times a maximum value of a depth from a surface
10 of a weld metal of the repair welding to the second heat-affected zone.
4. The repair welding method according to any one of claims 1 to 3,
wherein, in a cross-section including the parent material and the existing
welded portion, an intersection angle between an extending direction of the
15 second heat-affected zone formed in a weld metal of the existing welded portion
due to the repair welding and a thickness direction of the member is 70° to 110°.
5. The repair welding method according to any one of claims 1 to 4,
wherein a weld toe of the repair welding is at the parent material.
20
6. The repair welding method according to claim 1,
wherein, in a cross-section including the parent material and the existing
welded portion, the repair welding is performed from the parent material on a first
end side to a weld metal of the existing welded portion, and
25 wherein an intermediate position between a position of the second heataffected
zone appearing on a surface of the parent material on the first end side
31
and a position of the second heat-affected zone appearing on a surface of the weld
metal of the existing welded portion is at the weld metal of the existing welded
portion before removing the portion including at least a part of the first heataffected
zone.
5
7. The repair welding method according to any one of claims 1 to 6, further
comprising:
a step of measuring a shape of the first heat-affected zone prior to the step of
performing the repair welding; and
a step of determining a removal range to be 10 removed in the step of removing
the portion including at least a part of the first heat-affected zone, based on the
shape of the first heat-affected zone measured in the step of measuring the shape
of the first heat-affected zone.
15 8. The repair welding method according to claim 7,
wherein the step of measuring the shape of the first heat-affected zone
includes measuring the shape of the first heat-affected zone by ultrasonic flaw
detection with a phased array method, or measuring the shape of the first heataffected
zone by developing the shape of the first heat-affected zone by etching.
20
9. The repair welding method according to any one of claims 1 to 8,
wherein the parent material is high-strength ferritic heat-resistant steel.
10. The repair welding method according to any one of claims 1 to 9,
25 wherein the member is a boiler tube.
32