JP2014136246A - Repairing structure and repairing method of fillet weld zone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide repairing means capable of attaining the long-term life prolongation effect by inexpensive and short-term construction with respect to creep damage having occurred in a fillet weld zone.SOLUTION: A fillet weld zone w1 is formed by welding a nozzle stub 12 to a header 10 which is a hollow cylindrical member and in which hoop stress due to internal pressure is generated, the welding being performed in a direction in which the nozzle stub 12 intersects with the header 10. A surface of an area including existing weld metal Mof the fillet weld zone w1 where a creep damage d1 has occurred and an existing heat-affected zone Hformed on the periphery of the existing weld metal M, is counter-bored up to the depth including a creep damage occurrence area, a bottom surface 14 of a counter-bored part formed after being counter-bored is formed along the action direction of the hoop stress F and in the inclined direction to the axis of the header 10, and a counter-bored space (s) formed in the counter-bored part is filled with new repairing weld metal M.

Description

  The present invention relates to a repair structure and a repair method for repairing creep damage occurring in a fillet weld of a member exposed to a high temperature environment such as a boiler pipe.

  9-12Cr high Cr ferritic steel containing 9-12 wt% Cr is superior in strength, corrosion resistance and oxidation resistance to low alloy steel in the temperature range of 500-650 ° C, and is more thermally conductive than austenitic steel. It has the advantages of high degree and low thermal expansion coefficient. Therefore, it is widely used for steam piping and headers of boilers for thermal power generation. On the other hand, an important characteristic for a heat-resistant material exposed to high-temperature and high-pressure steam for a long time is the creep rupture strength. Creep rupture is a phenomenon in which deformation of a material proceeds even when the stress is lower than the tensile strength of the material when a constant stress is applied and left to stand under a certain temperature environment. That is, the generation of creep voids, the coarsening of crystal grains, and further creep damage such as cracks including microcracks may occur, eventually leading to fracture.

  A thick tube such as a header of a boiler is welded with fillet welds and gamma plugs for connecting a large number of small-diameter steam pipes. The gamma plug is a cylindrical short pipe into which a gamma ray source is inserted in order to inspect the pipe welded part at the time of plant construction, and is plugged after the plant construction. When a member made of high Cr ferritic steel is welded, the weld heat-affected zone causes a softening phenomenon and the strength is lower than that of the base material. For this reason, it has been found that creep rupture strength is greatly reduced compared to the base material due to the intensive accumulation of creep strain in the heat affected zone.

  4A shows a state in which the nozzle 102 is fillet welded to the header 100 at the welded portion w1, and FIG. 4B is an enlarged view of the welded portion w1. FIG. 5 (A) shows a state where the gamma plug 106 is fillet welded to the thick-walled pipe 104 at the welded portion w2, and FIG. 5 (B) is an enlarged view of the welded portion w2. When creep damage d1 or d2 occurs in these welds w1 or w2, the construction is carried out separately for emergency measures or permanent measures depending on the degree of creep damage.

  When repair work is performed as an emergency measure, the region where the creep damage d1 or d2 has occurred is removed, and repair welding is performed in which the countersink space is indicated as a welded portion w3 as shown in FIGS. 6A and 6B. I do. As a result, normal operation is maintained until the next periodic inspection. If many creep damages occur, take permanent measures. That is, the entire welded portions w1 and w2 are countersunk and the nozzle 102 is newly welded.

  Patent Document 1 discloses a repair method when creep damage occurs in a butt weld in a high-temperature pipe of a boiler. This repair method includes a welded portion and base materials on both sides of the welded portion, performs countersink from the surface of the base material to a depth including creep voids, and fills the countersink space with weld metal by repair welding. In this case, by forming the bottom surface of the countersink portion substantially parallel to the surface of the base material or welded portion, the direction of action of the hoop stress generated in the pipe and the direction of occurrence of creep damage are made substantially parallel. ing. This prevents hoop stress (tensile stress) from acting on the entire creep damage and suppresses the progress of creep damage.

JP 2011-194458 A

  When the creep damage occurrence area is removed by the above-mentioned emergency measures and repair welding is performed in the countersink space, a heat-affected zone by repair welding is formed in the existing weld metal. From recent test results, it has been confirmed that the creep rupture strength of the heat-affected zone formed in the weld metal is significantly reduced. Therefore, this emergency measure cannot be expected to prolong life. In addition, the above-mentioned permanent countermeasures require a great deal of cost and construction period, and the power plant stop period is long, so it cannot be easily adopted.

  Further, the repair method disclosed in Patent Document 1 is applied to butt welding, and the repair method disclosed in Patent Document 1 is applied as it is to repair of creep damage occurring in the fillet weld. I can't.

FIG. 7A shows a case where the nozzle 102 is fillet welded in the perpendicular direction to the outer peripheral surface of the header 100. Figure 7 (B) is a sectional view of the weld portions w1 which is fillet welded, the heat affected zone H _0, which is formed around the existing weld metal M _0, shows the case where the creep damage d1 occurs.
In FIG. 7B, the distribution of the hoop stress F acting on the fillet weld is indicated by a two-dot chain line. The hoop stress F (tensile stress) works in a direction inclined with respect to the axial direction (arrow a direction) of the header 100. The hoop stress F is higher in the vicinity of the outer surface than the inner surface of the header 100 due to the internal pressure generated inside the header 100 and the shape of the fillet weld. In particular, it has been found that creep damage is likely to occur in the region B because stress concentration of the hoop stress F occurs in the surrounding portion B.

A conventional repair method in this case will be described with reference to FIG. In FIG. 8A, first, a region where the creep damage d has occurred is removed by scrambling.
Next, as shown in FIG. 8 (B), it performs the repair weld to fill the new weld metal M ₁ in counterbored space s after repeated seat. In this case, a new heat affected zone H ₁ is formed around the new weld metal M ₁ , but this new heat affected zone H ₁ is also formed inside the existing weld metal M ₀ .

As described above, from the recent test results, it is being confirmed that the creep rupture strength of the new heat-affected zone H ₁ formed inside the existing weld metal M ₀ is the lowest. Thus, the new heat-affected zone H ₁ formed inside the existing weld metal M ₀ is distributed in a direction close to a right angle to the direction of action of the hoop stress F. Therefore, the hoop stress F (tensile stress) acts on the entire creep damage occurrence region, and the creep damage d propagates as a crack.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to realize a repair means that can achieve a long-life extension effect with low cost and short-term construction against creep damage occurring in a fillet weld.

  The fillet weld repair structure according to the present invention is formed by welding a second member to be welded to a first member to be welded which is a hollow cylindrical member and generates hoop stress due to internal pressure. This is applied when creep damage occurs in the welded fillet. The “hollow tubular member” is, for example, a thick pipe such as a steam pipe or a header where high-temperature steam flows in a boiler facility. Further, “creep damage” means generation of creep voids, coarsening of crystal grains, or cracks including microcracks that are generated by further progress.

  In order to achieve the above object, the repair structure of the present invention is such that the surface of the region including the existing weld metal of the fillet weld where the creep damage has occurred and the existing heat affected zone formed around the existing weld metal is creeped. The bottom surface of the countersunk portion that is countersunk to a depth that includes the damage occurrence area and that is formed after the countersink is a direction that is inclined with respect to the axis of the first welded member and that is along the direction of action of the hoop stress. In this case, a new repair weld metal is filled in the countersink space formed in the countersink portion.

  According to the present invention, the surface of the existing weld metal and the existing heat-affected zone where creep damage is likely to occur and the area near the surface are replaced with the newly filled weld metal, so that the same life-prolonging effect as that of the newly-installed weld can be obtained. . Moreover, the new heat affected zone formed inside the existing weld metal is formed along the bottom surface of the countersunk portion. Therefore, since the distribution of the new heat affected zone is formed along the direction of action of the hoop stress, no large tensile stress acts on the entire new heat affected zone. Therefore, even if creep damage occurs in the new heat-affected zone, the progress of creep damage is slow, and a long-lived effect can be achieved.

  In the repair structure of the present invention, when the first welded member and the second welded member are made of 9-12Cr high Cr ferritic steel containing 9 wt% or more and 12 wt% or less of Cr, The long-term life-prolonging effect that is the purpose can be achieved significantly. As mentioned above, 9-12Cr high Cr ferritic steel is excellent in strength, corrosion resistance / oxidation resistance, high thermal conductivity, and low thermal expansion coefficient in the temperature range of high-temperature steam generated in boilers for thermal power generation. It is widely used for steam piping and headers of boilers for thermal power generation.

On the other hand, when welding a base material made of high Cr ferritic steel, a weld metal of the same type as the base material is usually used. The 9~12Cr based high Cr ferritic steel as a weld metal, if to repair the fillet weld creep damage occurs, as described above, is formed inside an existing heat affected zone H ₀ or existing weld metal M ₀ new HAZ H creep rupture strength ₁ there was a problem that significantly decreases. On the other hand, the life extension effect after construction can be improved by applying the method of the present invention.

  Further, the fillet weld repair method according to the present invention provides the surface of the region including the existing weld metal of the fillet weld and the existing heat affected zone formed around the existing weld metal in order to achieve the above object. The countersinks to the depth including the creep damage occurrence area, and the bottom surface of the countersink formed after the countersink is inclined with respect to the axis of the first welded member, and the direction of action of the hoop stress. And a repair welding process in which a new repair weld metal is filled in the countersink space formed in the countersink portion.

  As a result, the existing weld metal and the surface of the existing heat-affected zone where the creep damage is likely to occur and the area in the vicinity of the surface are replaced with the newly filled weld metal. In addition, the new heat-affected zone formed inside the existing weld metal is formed along the bottom surface of the countersink, and the distribution of the new heat-affected zone is formed along the direction of the hoop stress. Large tensile stress does not act on the entire portion. Therefore, even if creep damage occurs in the new heat-affected zone, the progress of creep damage is slow, and a long-lived effect can be achieved.

  In the method of the present invention, the method further includes a map creation step of creating a hoop stress map in advance showing a relationship between the depth from the surface of the existing weld metal and the existing heat affected zone and the hoop stress distributed according to the depth, The countersink step may include a countersink depth determination step of estimating a depth at which creep damage has occurred from the hoop stress map and determining a countersink depth based on the estimated depth. As a result, the depth of creep damage can be set without detecting the depth of creep damage by a conventional method one by one, and repair work is facilitated. Therefore, since the period of repair work can be greatly shortened, the stop period of the power plant and the like can be significantly shortened.

  ADVANTAGE OF THE INVENTION According to this invention, the life extension period after repair of the fillet weld part which received the creep damage can be extended significantly. This facilitates maintenance management of the fillet welded portion, shortens the stop period of the device having the fillet welded portion of the device, and improves the operation efficiency.

(A) is sectional drawing which shows the countersink process of a fillet weld part, (B) is sectional drawing which similarly shows a repair welding process in one embodiment of the repair method of this invention. It is sectional drawing which shows typically the hoop stress distribution which generate | occur | produces in a fillet weld part in the said embodiment. It is a diagram which shows the remaining life of the fillet weld part after the repair by the said embodiment. (A) is a perspective view which shows the nozzle weld part of thick-walled piping, (B) is a partially expanded view of the said nozzle weld part. (A) is a perspective view which shows the gamma plug weld part provided in thick-walled piping, (B) is a partially expanded view of the said gamma plug weld part. The repair method of the conventional fillet weld part is shown, (A) shows the repair method of a nozzle weld part, (B) is a perspective view which shows the repair method of a gamma plug weld part. (A) is a perspective view which shows the creep damage which generate | occur | produced in the nozzle stub welding part, (B) is sectional drawing which follows the AA line in (A). (A) is sectional drawing which shows the countersink processing of a fillet weld part, (B) is sectional drawing which similarly shows a repair welding process in connection with the conventional repair method.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a state after the start of repair work according to this embodiment, and FIG. 2 shows a state before the start of repair work according to this embodiment. A header 10 having a hollow cylindrical cross section and a nozzle 12 having a smaller diameter than that of the header 10 and also having a hollow cylindrical cross section are joined by a weld w. The header 10 and the nozzle 12 are made of 9-12Cr high Cr ferritic steel containing 9-12% by weight of Cr. The axis of the nozzle 12 is arranged substantially perpendicular to the axis of the header 10, and the fillet welded by the welded portion w <b> 1 with the end face of the nozzle 12 implanted in the header 10.

This embodiment, as shown in FIG. 2, for example, the same position as the creep damage d1 shown in FIG. 7 (B), i.e., the existing heat-affected zone H creep damage d1 is present around the existing weld metal M _{0 The} case where the error occurs at ₀ is assumed. Hereinafter, the repair work according to the present embodiment will be described with reference to FIG.

First, as shown in FIG. 1, the spot facing machining the entire area of the existing weld metal M ₀ and existing heat-affected zone H _0. The countersink depth needs to be a depth at which the creep damage d1 generation region can be countersunk. It can also be determined by detecting the depth of the generated creep damage d1 using a conventional detection method such as a replica method, ultrasonic flaw detection or gamma ray irradiation method. However, these detection methods can cope with a small number of creep damages d1, but a long time is required when the number of creep damages d1 is large. Therefore, in the present embodiment, the countersink depth is determined using a method described below.

  In the configuration of the header 10 and the nozzle 12 shown in FIG. 1, the hoop stress F in the tensile direction generated in the welded portion w <b> 1 is relative to the axial direction (arrow a direction) of the header 10 as shown in FIG. 2. Occurs in an inclined direction. Therefore, the distribution of the hoop stress F generated in the header 10 in the depth direction from the surface of the welded portion w1 is measured in advance. Then, based on the measured value, this hoop stress distribution is mapped. FIG. 2 shows a map showing the state before the repair work according to the present embodiment is performed and the hoop stress distribution. The horizontal axis of the hoop stress map is the depth D from the surface of the welded portion w1, and the vertical axis is the hoop stress F.

As can be seen from FIG. 2, the region where the high hoop stress F is generated is concentrated near the surface of the welded portion w1. The present inventors have found that the value of the hoop stress F generated in the header 10 and the occurrence of creep damage d are substantially correlated. Therefore, by setting a threshold D ₀ of hoop stress F probability of creep damage d1 is generated is reduced, creep damage d1 is estimated to have occurred between the surface of the weld portions w1 to a threshold D _0.

Thus, determining the threshold D ₀ the depth of the bottom surface of the counterbore processed. Thus based on the determined counterbore depth D ₀ performing spot facing machining. Counterbore region, a range including the existing weld metal M ₀ and existing heat-affected zone H ₀ of the weld w1. For example, the countersink depth is 1 to 3 mm, and the countersink width is 10 to 20 mm. The bottom surface 14 formed by countersinking is formed in a direction substantially parallel to the direction of action of the hoop stress F.

Next, as shown in FIG. 1 (B), is filled with a repair weld metal M ₁ melted in counterbore space s solidified. This completes the repair work.

According to the present embodiment, the existing weld metal M ₀ and the surface of the existing heat-affected zone H ₀ of the weld portions w1 are repeated seat over the entire surface, a new weld metal M ₁ is filled in the counterbore space s. Therefore, since the surface of the creep damage is prone weld portions w1 is replaced with the new weld metal M ₁ over the entire surface, the life evaluation of creep damage is the same as new weld.

In the present embodiment, the new weld HAZ H ₁ new around the metal M ₁ is formed, Shin'netsu affected zone H ₁ is formed into an existing weld metal M ₀ and existing heat-affected zone H _0. However, the area of the new heat-affected zone H ₁ formed in the existing heat-affected zone H ₀ is very small, and creep damage occurs and the probability is extremely small. Further, the new heat affected zone H ₁ formed inside the existing weld metal M ₀ is formed along the bottom surface 14 of the countersunk portion. Therefore, the distribution of the new heat affected zone H ₁ inside the existing weld metal M ₀ is formed along the direction of action of the hoop stress F. Thus, no longer the entire tensile stress in the new HAZ H ₁ acts greatly, even creep damage in New HAZ H ₁ occurs, the progress of creep damage is slow and can achieve survival benefit of long-term .

  Also, since the depth of creep damage d1 from the surface of the welded portion w1 is determined based on the hoop stress map created in advance, the repair work can be shortened and the stoppage period of the power plant etc. can be shortened it can.

FIG. 3 shows the remaining life of the welded portion w1 formed in the header by the conventional repair method and the repaired life of the welded portion w1 formed in the header by the repair method of the present embodiment. From FIG. 3, it can be seen that the repair method according to the present embodiment can achieve the life extension effect of twice or more.
The present embodiment is creep damage to the existing heat affected zone H ₀ d1 is an example of a case of occurrence, even when the creep damage d1 occurs in existing weld metal M _0, the present invention can be applied.

  ADVANTAGE OF THE INVENTION According to this invention, the repair means which can achieve a long-term life-prolonging effect by low-cost and short-term construction with respect to the creep damage which generate | occur | produced in the fillet weld part is realizable.

10,100 header 12,102 nozzle 14 bottom surface 104 thick pipe 106 gamma plug D ₀ threshold F hoop stress H ₀ existing heat affected zone H ₁ new heat affected zone M ₀ existing heat affected zone M ₁ new weld metal d1, d2 Creep damage s Countersink space w1, w2, w3 Welded part

Claims (4)

A fillet weld formed by welding in a direction in which the second welded member intersects the first welded member that is a hollow cylindrical member and generates hoop stress due to internal pressure,
The surface of the area including the existing weld metal of the fillet weld where the creep damage has occurred and the existing heat affected zone formed around the existing weld metal is countersunk to a depth including the creep damage generation area, The bottom surface of the counterbore formed later is formed in a direction inclined with respect to the axis of the first welded member and along the direction of action of the hoop stress,
A repair structure for fillet welds, wherein a new weld metal for repair is filled in a countersink space formed in the countersink.   The first welded member, the second welded member, the existing weld metal, and the new repair weld metal are made of 9-12Cr high Cr ferritic steel. Item 2. A fillet weld repair structure according to Item 1. Repair of fillet welds that are hollow cylindrical members that are welded in the direction in which the second welded member intersects the first welded member that generates hoop stress due to internal pressure, and where creep damage has occurred In the method
The surface of the region including the existing weld metal of the fillet weld and the existing heat-affected zone formed around the existing weld metal is countersunk to a depth including the creep damage generation region and is formed after the countersink. A countersink step formed in a direction in which the bottom surface of the countersink portion is inclined with respect to the axis of the first welded member and along the direction of action of the hoop stress;
A repair method for a fillet weld, comprising a repair welding step of filling a new repair weld metal in a countersink space formed in the countersink. A map creating step of creating a hoop stress map in advance showing a relationship between a depth from the surface of the existing weld metal and the existing heat affected zone and a hoop stress distributed according to the depth from the surface;
The countersink step includes a countersink depth determination step of estimating a depth at which the creep damage has occurred from the hoop stress map and determining a countersink depth based on the estimated depth. The method for repairing a fillet weld according to claim 3.

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