JPS61144293A - Mending method of crack caused on pressure container shell - Google Patents

Abstract

PURPOSE:To carry out sure reinforcement based on dynamical ground by mending with welding by the reinforcing plate of the width and thickness according to the equation after welding and mending after gouging the cracked part. CONSTITUTION:The steel made reinforcing plate (practically said quality with the pressure contained shell) in the width and thickness as shown by the equation is reinforced with welding so as to bridge the center part on the crack mending part or the both end parts after mending with welding the cracked part with gouging. However, sigma: shell allowable stress, W: width of the reinforcing plate, B: thickness of reinforcing plate, Bo: shell plate thickness, E: shell Young's modulus, sigmaf: equivalent yield strength of shell (means value of yield strength and tensile strength), upsilon: shell poison ratio, JIC: estimated minimum elastoplastic fracture toughness values around both end parts of shell crack, a: length of shell crack.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a mechanically reliable and quick repair method for preventing further propagation of cracks occurring in the shell of a pressure vessel such as a blast furnace or hot blast furnace. [Prior art] When cracks occur in the shell of a pressure vessel such as a blast furnace or hot blast furnace, the gas inside the vessel does not just blow out to the outside, but if left untreated, the cracks will grow and cause a large problem. , it becomes impossible to maintain the strength required for the pressure vessel shell, resulting in a large-scale accident. Repairs must be made as soon as possible to prevent the crack from growing. Conventionally, repairs have been carried out using various methods as shown in FIGS. 2(a) to 2(f). First, Figure 2 (a) and (b)
In the method shown in Fig. 1, cracks 2 in the steel skin 1 are welded after gouging,
A reinforcing material 3 made of half a thin-walled pipe or a thin plate is welded with a dowel so as to cover the gagging welded part. Next, in the method shown in FIGS. 2(C) and 2(d), the crack 2 is welded after gouging, and the rib 4 is welded so as to overlap the gouged welded part to prevent the recurrence and propagation of the crack. Furthermore, in the method shown in FIGS. 2(e) and 2(f), after gouging the crack 2 as necessary, stop holes 5 are formed at both ends, and a circular steel plate is inserted into the stop hole 5 to fill the hole 5. This is a method to prevent cracks from developing by welding. [Problems to be Solved by the Invention] With each of the repair methods shown in Fig. 2 above, the crack may recur within a few days or months after repair, and another crack may occur along the extension line of the crack. There were many things. This is because, in the repair method shown in Figures 2(a) and (b), the thin-walled pipes and thin plates attached as reinforcing materials do not have sufficient binding force to suppress the opening of cracks, and the ribs 4 are welded. In the method shown in Fig. 2 (c) p (d), the rib 4 and the iron skin 1
Due to the three-dimensional thermal deformation of the sheath 1 caused by the insufficient strength of the fillet weld between the shib 4 and the shib 4, the shib 4 was often displaced and was not very effective in preventing the recurrence of cracks. Furthermore, the second
The method of providing stop holes shown in Figures (e) and (f) was effective in preventing the re-occurrence of cracks because it alleviated the stress concentration at the tip of the crack, but once a crack has occurred, reinforcement is required. Since no material was used, there was a problem in that the effect of inhibiting cracks was completely lost. In addition, each of the above repair methods has the disadvantage that it is difficult to repair the entire length of the crack when there is a three-dimensional obstruction due to the presence of a structure such as a pipe around the crack. . Needless to say, if a partial repair is unavoidable, the desired effect will not be achieved. Therefore, the present inventors have found that the effect of preventing the recurrence of cracks is excellent, and even if only partial repair is possible due to three-dimensional obstruction, the effect of alleviating stress concentration at the crack tip and suppressing crack opening can be sufficiently reduced. The present invention has been completed as a result of repeated efforts to develop a repair method that can perform these functions reliably and quickly. [Means for solving the problem] In order to solve the above problem, after gouging the crack and repairing it by welding, a steel reinforcing plate (with the pressure vessel shell) whose width and thickness are expressed by the inequality The gist of the present invention lies in reinforcing the center portion or both ends of the crack repair portion by welding the crack repair portion (substantially the same material) in a welding manner. However, W=W/a (plate width made dimensionless by crack length) B=B
/Bo (plate width made dimensionless by iron skin plate thickness) J = J
xoπE/4a(1-1')t((dimensionalized J integral)?
= σ/σf (non-dimensional allowable stress) where σ: steel shell allowable stress, W: reinforcing plate width B: reinforcing plate thickness, Bo: steel shell thickness E: steel shell Young's modulus. σf: Equivalent yield strength of steel shell (average value of yield strength and tensile strength) C: Poisson's ratio of steel shell. Jzo: Expected minimum elastic-plastic fracture toughness value near both ends of a steel shell crack. a: Steel skin crack length. are shown respectively. In addition, there is a method in which a disk-shaped test piece is taken from the tip of a crack in the steel shell by core boring, etc., and the elastic-plastic fracture toughness value (Jxo) obtained from the test piece is used to determine the thickness 19 width of the reinforcing steel plate. You may use it. [Operation] When a crack 2 as shown in Fig. 1 (a) and (b) K occurs in the pressure vessel shell, the tip of the crack is core-bored and a disk-shaped test piece 6 is taken and subjected to elastic-plastic fracture. A toughness test is performed to determine the fracture toughness value (JIO). However, if the fracture toughness value (JIO) has already been measured around the crack,
Alternatively, if the fracture toughness value (JXO) can be predicted by another method, the step of collecting and testing the disc-shaped test piece can be omitted. Then, the cracked portion is gouged and welded, and a steel plate having the same shape as the sample specimen is inserted into the core-bored hole 5 and repaired by welding. However, the cooling plate and the cooling section pipe attached to the pressure vessel may become an obstacle to the work of arranging the reinforcing plate 7. Therefore, taking this into consideration, the method of arranging the reinforcing plate 7 is shown in Fig. 1 (C).
Partial arrangement as shown in (d), specifically the method of providing at both ends of the crack (Case 1) or Fig. 1(e). (f) Method of installing in the center of the crack as shown in K (starting step 2)
Choose one. The dimensions of the reinforcing plate are (Case 1)
For each of (Case 2) and (Case 2), the above inequality (Formula A)
The basis for setting the inequality (Formula A) is as follows. “Introduction to Linear Fracture Science, Baifu # (1976) J and rDug
daletDes,,J,Mech,Phys,5ol
According to fdst8 (1960,) SpiooJ, a general solution for determining the opening amount of the crack tip with respect to the magnitude of applied stress is given for a completely elastic-plastic body containing a crack. This is a model that makes it possible to treat the behavior of a fully layered body in terms of elastic fracture mechanics by applying a cohesive force (σf) that closes the crack to the dusty region generated at the tip of the crack. . In the method of the present invention, we interpret not only this bonding force but also the stress reduction in the reinforced part caused by welding the reinforcing plate as another bonding force. Apply as is. That is, for the reinforcement conditions of (K71) and (K72), the load stress σ (σ/1ry) on the crack tip opening displacement line
can be expressed by the following equation. CB-1 formula) However, in the above formula, R and δ1 are defined by the following formula. (Equation B-2) (Equation B-3) Equation CB-1) The first term on the right side is the elastic group when no plastic region occurs, and the second term is the amount of closure due to the bonding force generated in the wi-like region. , the third term is the amount of closure due to the reinforcing plate. If there is no reinforcing plate, the eighth term is zero and equal to Dugdale's model μ. It is known that the relationship between the crack tip opening displacement δ and the J integral, which is the energy μ at the crack tip, is as follows: If the value Jxot- specific to the skin material is exceeded, the crack will propagate without further stress being applied. Therefore, the limit condition under which cracks do not propagate is expressed by the following equation. δ≦Jxo/σf (Formula D) By substituting (Formula B-1) to the left side of (Formula D), the steel skin material (Ix
o and σf), reinforcement plate dimensions (B and W) and allowable stress σ
It is possible to derive the relationship between Figure 3 shows a graph in which limit conditions are set using (D formula) for the case of B = 1, where the thickness of the pressure vessel iron is the same as the thickness of the reinforcing plate, for various allowable stresses using the above formula. Shown below. The east line shows (Case 1) t-, and the dashed line shows (K72)
It shows. t, the dimensionless allowable stress is 0.5 (σ=0
．． FIG. 4 is a graph showing the limit conditions for various dimensionless plate thicknesses 'i' in case 5). In this case, the solid line is

〔Example〕

A method for repairing cracks in a pressure vessel (with a steel shell thickness of 30 m) using the method of the present invention will be explained with reference to FIG. If a crack with a total length of 2a (5000 mm) occurs in the steel skin at the base of the pipe, after gouging the crack and repair welding, I would like to use the reinforcing plate 7 to reinforce the crack. Since the pipe is located in the center of the crack, it is not possible to weld the reinforcing plate T over its entire length, so the method of the present invention was used to determine the required dimensions of the reinforcing plate. The elastic-plastic fracture toughness (JIO) of the steel shell was measured from the core boring material separately collected near the crack 2, and it was 7.5 mm/rin, and the Young* (E) was 21000011 m'', equivalent yield strength. (
σf) was 8Q KtJwx" and Poisson's ratio was 0.8. Based on the above values, the dimensionless J-integral (J) was 0.6G according to the calculation of the present invention, which is the same thickness as the container shell. If a steel plate with a thickness of B = 1) is used as a reinforcing plate,
Allowable stress (σ) is 1/2 of equivalent yield strength (/=0.5)
In this pressure vessel, the plate width 9 of the reinforcing plate 7 is (A
Equation) is jD (128. Therefore, the width (2W) of the reinforcing plate in this example is determined to be 0.28 x 500 (m) = 140 (a) since the crack area is 500 m. This means that the repair can be carried out by welding two steel plates with a thickness of 30 mm and a width of 70 mm as shown in Figure 5 at both ends of the crack.The repair was carried out based on this determined value. As a result, no re-occurrence or growth of cracks was observed even after one year had passed since the repair, proving that the method of the present invention is effective. [Effects of the Invention] By determining the dimensions,
It has become possible to apply <at* reinforcement metal on mechanical grounds to repair cracks that occur in the steel skin of a pressure vessel. In particular, even in areas where cooling plates and cooling pipes are placed on the surface of the steel shell and there are three-dimensional restrictions on welding the reinforcing plate, it is possible to quickly determine the dimensions of the reinforcing plate according to the structure. After crack repair, cracks are less likely to reoccur or grow.

[Brief explanation of drawings]

FIGS. 1(a) to (f) are explanatory diagrams showing typical embodiments using the method of the present invention, FIGS. 2(a) to (f) are explanatory diagrams showing a conventional crack repair method, and FIG. , 4 is a graph showing the relationship between line J integral and reinforcing plate dimensions, and FIG. 5 is a schematic diagram showing an example of repair using the method of the present invention.

Claims (2)

[Claims] (1) After gouging and welding the cracks that have occurred in the pressure vessel shell, a steel reinforcing plate whose width and thickness are expressed by the following inequality and which is made of substantially the same material as the steel shell is used as the gouge. A method for repairing cracks that have occurred in a pressure vessel shell, which comprises repairing by welding the repaired part so as to straddle the center or both ends of the repaired part. 1≧■≧3■−■/(2.1■■/3) ■=W/a (plate width made dimensionless by crack length)■=B/B
o (plate width made dimensionless by steel plate thickness)■=J_I_OπE
/4a(1-ν^2)σf (dimensionalless J integral) ■=σ/
σf (non-dimensional allowable stress) where σ: steel shell allowable stress, W: reinforcing plate width B: reinforcing plate thickness, Bo: steel shell thickness E: steel shell Young's modulus σf: steel shell equivalent yield strength (Average value of yield strength and tensile strength)
, ν: Steel skin Poisson's ratio, J_I_O: Expected minimum elastic-plastic fracture toughness value near both ends of the steel skin crack a: Steel skin crack length, (2) In claim 1, the steel material around the crack that has occurred in the pressure vessel shell is sampled and tested, the elastic-plastic fracture toughness value (J_I_O) is determined, and the width and thickness of the reinforcing plate are determined. Determine how to repair cracks in the pressure vessel shell.