1. A method of repairing a lining for plant equipment, in which a damaged inner surface of an existing lining is repaired with a new lining, the plant equipment having a manhole on a longitudinal end, the method comprising the steps of: preparing a plurality of corrosion-resistant rectangular plates serving as the new lining, the corrosion-resistant rectangular plate having a short side shorter than an inside diameter of the manhole and a long side longer than the inside diameter of the manhole; and placing the corrosion-resistant rectangular plate, which has the long side along a longitudinal direction of the plant equipment, into the plant equipment from the manhole, and disposing the corrosion-resistant rectangular plate, which has the long side along the longitudinal direction of the plant equipment, on the inner surface of the existing lining, wherein in the step of placing, the adjacent corrosion-resistant rectangular plates are joined to each other and the corrosion-resistant rectangular plate and the inner surface of the existing lining are joined to each other.

2. The method of repairing a lining for plant equipment as claimed in claim 1, wherein in the step of preparing, a plate serving as the new lining is divided into the corrosion-resistant rectangular plates, and each of the corrosion-resistant rectangular plates is shaped along the inner surface of the existing lining by curving the corrosion-resistant rectangular plate in a direction of bringing the two long sides of the corrosion-resistant rectangular plate close to each other.

3. The method of repairing a lining for plant equipment as claimed in one of claims 1 and 2, wherein the plant equipment is formed with the longitudinal direction extending in a vertical direction and the manhole formed on an upper end of the plant equipment, and the plant equipment includes a jig for positioning the short side at a lower end of the corrosion-resistant rectangular plate, the jig being installed on a part of the existing lining where the corrosion-resistant rectangular plate is disposed.

4. The method of repairing a lining for plant equipment as claimed in one of claims 1 and 2, wherein the adjacent corrosion-resistant rectangular plates are joined to each other by complete penetration welding in the step of placing, and the method further comprises, before the step of placing, a step of forming a through hole in each part of the existing lining where the corrosion-resistant rectangular plate is disposed, the through hole guiding a fluid leak from the new lining to outside of the plant equipment in order to detect the fluid leak.

FIELD OF THE INVENTION The present invention relates to a method of repairing a lining for plant equipment including an existing lining that is damaged by corrosion or the like.
BACKGROUND OF THE INVENTION Plant equipment including static apparatuses such as a pressure vessel and a heat exchanger in a plant, urea plant equipment for example, handles a high-pressure corrosive fluid and thus has a thick pressure-resistant shell and an existing corrosion-resistant lining provided on the inner surface of the pressure-resistant shell. The existing lining has corrosion resistance but may be thinned and damaged by a corrosive fluid over an extended period of use.
As the lining becomes thinner, the thickness of the existing lining may not satisfy the design criteria. For this reason, when the lining is thinned to a certain degree, proper maintenance is necessary for the plant equipment.
For the maintenance, for example, a repairing method is available in which the upper part of the plant equipment is cut, the thinned existing lining is removed from the inside of the plant equipment, and then the existing lining is replaced with another lining. This repairing method is, however, a large-

scale construction equivalent to a renovation of the plant equipment and thus is considerably expensive and time consuming. Moreover, this method causes a loss because the operation of the plant equipment needs to be stopped during the construction period. Therefore, in order to solve the problem, a method is proposed to attach a lining on the inner surface of a thinned existing lining without removing the existing lining (for example, Patent Literature 1)
PATENT LITERATURE [0005] Patent Literature 1: National Publication of International Patent Application No. 1998-505795
DISCLOSURE OF THE INVENTION [0006] In the method described in National Publication of International Patent Application No. 1998-505795, a new lining is hung into the plant equipment from a manhole formed on the upper end of the plant equipment (urea plant equipment). In National Publication of International Patent Application No. 1998-505795, the manhole has an inside diameter of 550 mm as described on page 19, whereas metal sheets formed by dividing the new lining have dimensions of 400 by 1500 mm as described on page 20. Thus, the metal sheet is hung with the long side (1500 mm) vertically extending from the

manhole. However, as shown in FIG. 2 of National Publication of International Patent Application No. 1998-505795, the metal sheet is disposed with the horizontally extending long side on the existing lining. Thus, all the metal sheets need to be rotated 90° about the horizontal axis in the plant equipment, from the hanging position (vertical position) to the placement position on the existing lining (horizontal position). It takes a long time to rotate all the metal sheets in the small space of the plant equipment. Hence, the method described in National Publication of International Patent Application No. 1998-505795 does not sufficiently shorten the construction period.
[0007] An object of the present invention is to provide a method of repairing a lining for plant equipment so as to obtain a sufficiently short construction period.
[0008] In order to solve the problem, in a method of repairing a lining for plant equipment according to a first invention, the damaged inner surface of an existing lining is repaired with a new lining, the plant equipment having a manhole on the longitudinal end,
the method including the steps of:
preparing a plurality of corrosion-resistant rectangular plates serving as the new lining, the

corrosion-resistant rectangular plate having a short side shorter than the inside diameter of the manhole and a long side longer than the inside diameter of the manhole; and
placing the corrosion-resistant rectangular plate, which has the long side along the longitudinal direction of the plant equipment, into the plant equipment from the manhole, and disposing the corrosion-resistant rectangular plate, which has the long side along the longitudinal direction of the plant equipment, on the inner surface of the existing lining,
wherein in the placement in the step of placing, the adjacent corrosion-resistant rectangular plates are joined to each other and the corrosion-resistant rectangular plate and the inner surface of the existing lining are joined to each other.
[0009] In a method of repairing a lining for plant equipment according to a second invention, in the method of repairing a lining for plant equipment according to the first invention, in the preparation in the step of preparing, a plate serving as the new lining is divided into the corrosion-resistant rectangular plates, and each of the corrosion-resistant rectangular plates is shaped along the inner surface of the existing lining by curving the corrosion-resistant rectangular plate in a direction

of bringing the two long sides of the corrosion-resistant rectangular plate close to each other. [0010] In a method of repairing a lining for plant equipment according to a third invention, in the method of repairing a lining for plant equipment according to one of the first and second inventions, the plant equipment is formed with the longitudinal direction extending in the vertical direction and the manhole formed on the upper end of the plant equipment, and
the plant equipment includes a jig for positioning the short side at the lower end of the corrosion-resistant rectangular plate, the jig being installed on a part of the existing lining where the corrosion-resistant rectangular plate is disposed. [0011] Additionally, in a method of repairing a lining for plant equipment according to a fourth invention, in the method of repairing a lining for plant equipment according to one of the first and second inventions, the adjacent corrosion-resistant rectangular plates are joined to each other by complete penetration welding in the step of placing,
the method further including, before the step of placing, a step of forming a through hole in each part of the existing lining where the corrosion-resistant rectangular plate is disposed, the through hole guiding a fluid leak from the new lining to the

outside of the plant equipment in order to detect the fluid leak.
[0012] According to the method of repairing the lining for the plant equipment, the corrosion-resistant rectangular plate placed in the plant equipment is disposed on the inner surface of the existing lining and thus does not need to be rotated about the horizontal axis, achieving a sufficiently short construction period.
BRIEF DESCRIPTION OF THE DRAWINGS [0013] FIG. 1 is a partially cut cross-sectional view showing urea plant equipment in a method of repairing a lining for urea plant equipment according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view showing the interior of the urea plant equipment;
FIG. 3 is a plan view showing a corrosion-resistant plate serving as a new lining disposed in the urea plant equipment and corrosion-resistant rectangular plates formed by dividing the plate;
FIG. 4A is a front view showing that the corrosion-resistant rectangular plates are curved;
FIG. 4B is a perspective view for explaining a short side of the curved corrosion-resistant rectangular plate;

FIG. 5 is a side view showing that the corrosion-resistant rectangular plate is hung into the urea plant equipment from the manhole of the urea plant equipment;
FIG. 6 is a cross-sectional view showing that the corrosion-resistant rectangular plate is brought close to the existing lining of the urea plant equipment;
FIG. 7 is a cross-sectional view showing that the corrosion-resistant rectangular plate is positioned by a jig installed in the urea plant equipment;
FIG. 8 is a perspective cross-sectional view showing that the corrosion-resistant rectangular plates are joined by welding;
FIG. 9 is a perspective cross-sectional view showing the urea plant equipment before the new lining is disposed;
FIG. 10 is a development of the pressure-resistant shell and the existing lining of FIG. 9 developed in a plane; and
FIG. 11 is a development showing that lining-part through holes, lining-part communicating grooves, and the new lining are added to the development of FIG. 10.
DESCRIPTION OF THE EMBODIMENT

[0014] A method of repairing a lining for plant equipment according to an embodiment of the present invention will be described below in accordance with the accompanying drawings.
[0015] Referring to FIG. 1, urea plant equipment will be described as an example of the plant equipment. [0016] As shown in FIG. 1, urea plant equipment 10 includes a vessel body 1 in which urea is manufactured, and a pedestal 9 supporting the vessel body 1 that the longitudinal direction of the vessel body 1 extends along the vertical direction. The vessel body 1 has a cylindrical body and upper and lower hemispherical parts that seal the body. On the upper end of the vessel body 1, a manhole 2 is formed that allows the passage of required workers and materials. The manhole 2 in FIG. 1 lies horizontally (perpendicularly to the longitudinal direction of the vessel body 1) and concentrically with respect to the vessel body 1. The orientation of the manhole 2 is not limited. For example, the manhole 2 may be inclined from the horizontal direction or may not be concentric with the vessel body 1. In any case, the manhole 2 is closed by a manhole cover, which is not shown, during an operation of the urea plant equipment 10.
[0017] The urea plant equipment 10 being operated contains a high-pressure corrosive fluid necessary

for the process of manufacturing urea. For this reason, the vessel body 1 needs to have pressure resistance and corrosion resistance and thus includes a thick pressure-resistant shell 3 made of carbon steel or low-alloy steel (alloy steel composed of several % of chrome, nickel, molybdenum, and the like) and a corrosion resistant existing lining 4 provided on the inner surface of the pressure-resistant shell 3. The existing lining 4 has corrosion resistance but may be internally (specifically, the inner surface) thinned and damaged by the corrosive fluid over an extended period of use. In addition to the thinning, the lining may be damaged in various ways due to aged deterioration or the like. To compensate for the damage, a new lining 5 needs to be placed on the inner surface of the existing lining 4. The main point of the present invention is a method of placing the new lining 5 on the damaged inner surface of the existing lining 4, that is, a method of repairing the lining for the urea plant equipment 10.
[0018] The method of repairing the lining for urea plant equipment 10 will be specifically described below as the main point of the present invention. Since damage on the inner surface of the existing lining 4 is mostly caused by thinning, thinning

damage will be discussed below for the sake of simplicity.
[0019] Typically, the height of the urea plant equipment 10 exceeds 10 m and thus as shown in FIG. 2, a temporary scaffold 11 for an operation of a worker W is assembled in the vessel body 1. The temporary scaffold 11 is assembled using, for example, a tray that is an existing internal part (a member for stirring gas, not shown). The worker W uses the temporary scaffold 11 to smooth the roughened inner surface of the existing lining 4, which is damaged by thinning, by grinding with a grinder G.
[0020] A corrosion-resistant plate serving as the new lining 5 is to cover the inner surface of the existing lining 4 and thus is too large to pass through the manhole 2. Hence, as shown in FIG. 3, the corrosion-resistant plate serving as the new lining 5 is divided into pieces (for example, 16 pieces in FIG. 3) by cutting in a preparing process such that the pieces can be hung into the vessel body 1 through the manhole 2. Hereinafter, the divided plates will be referred to as corrosion-resistant rectangular plates 6. The corrosion-resistant rectangular plate 6 has a short side 7 that is shorter than the inside diameter of the manhole 2, so that the corrosion-resistant rectangular plate 6 with a vertically extending long side 8 can be hung into

the vessel body 1 from the manhole 2. The long side
8 of the corrosion-resistant rectangular plate 6 is
as high as the new lining 5 (repair height), thereby
shortening circumferential welding 53 on the inner
surface of the existing lining 4. However, in
consideration of the limitation on the length of the
corrosion-resistant rectangular plate 6 being
transported, the long side 8 is actually a half or
one third of the height of the new lining 5 (repair
height). The long side 8 needs to be longer than at
least the inside diameter of the manhole 2. The
corrosion-resistant rectangular plate 6 is preferably
sized in consideration of existing internal parts
such as the tray. The corrosion-resistant
rectangular plate 6 for repair preferably has, in order to reduce the weight of the new lining 5, substantially the same thickness as a reduction in the thickness of the existing lining 4 in the thinning and the grinding. In order to set the thickness, thickness reductions by the thinning may be measured in advance over the surface (a range of repair) and then the mean value of the measured values may be set as the thickness reduction caused by thinning. If the measured values are locally biased, for example, if a part of the surface has a large value but another part of the surface has a small value, a mean value is calculated for each part

of the surface. The mean value for each part of the surface may be set as the thickness reduction caused by thinning. In this case, the corrosion-resistant rectangular plate 6 is varied in thickness among the parts of the surface such that the corrosion-resistant rectangular plate 6 in each part has substantially the same thickness as a reduction in the thickness of the existing lining 4 in the thinning (mean value) and the grinding. [0021] As shown in FIG. 4A, the corrosion-resistant rectangular plates 6 are curved along the inner surface of the existing lining 4. Specifically, the 16 corrosion-resistant rectangular plates 6 are joined in parallel into the circular (360°) new lining 5. Thus, the corrosion-resistant rectangular plate 6 is curved such that the short side 7 of the corrosion-resistant rectangular plate 6 is arc-shaped with a central angle of 22.5°, which is determined by dividing 360° by 16. In this way, the corrosion-resistant plate serving as the new lining 5 is divided into the corrosion-resistant rectangular plates 6 by cutting and then the corrosion-resistant rectangular plates 6 are curved along the inner surface of the existing lining 4. Thus, the corrosion-resistant rectangular plates 6 are more accurately shaped as necessary.

[0022] The corrosion-resistant rectangular plates 6 do not always need to be curved as shown in FIG. 4A. Thus, the concept of the corrosion-resistant rectangular plate 6 includes a curved plate (if curved) and a flat plate (if not curved). If the corrosion-resistant rectangular plate 6 is a curved plate, the short side 7 is a chord on the outer surface (curved surface) of the corrosion-resistant rectangular plate 6 in FIG. 4B, that is, a straight line corresponding to the short side 7 of a rectangle R formed by projecting the corrosion-resistant rectangular plate 6 in parallel with a plane P. In FIG. 4B, to enhance understanding of the short side 7 of the curved corrosion-resistant rectangular plate 6, the central angle of the corrosion-resistant rectangular plate 6 is larger than 22.5° indicated in FIG. 4A.
[0023] Thereafter, as shown in FIG. 5, the corrosion-resistant rectangular plates 6 in the step of placing are hung one by one into the vessel body 1 from the manhole 2 by a hoist 22 capable of traveling on a horizontal rail 21. The hoist 22 has a wire rope 23 capable of hoisting and lowering and a damage-free clamp 24 connected to the lower end of the wire rope 23, so that the corrosion-resistant rectangular plate 6 can be hung up and down. The damage-free clamp 24 holds the vicinity of the short side 7 of the

corrosion-resistant rectangular plate 6 and thus the long side 8 of the corrosion-resistant rectangular plate 6 hung from the hoist 22 extends along the vertical direction (the longitudinal direction of the urea plant equipment 10). The horizontal rail 21 extends immediately above the manhole 2 so as to hang the corrosion-resistant rectangular plate 6 into the vessel body 1 from the manhole 2, and extends so high that the lower end of the corrosion-resistant rectangular plate 6 hung from the hoist 22 can be lifted above the manhole 2.
[0024] Then, as shown in FIG. 6, the corrosion-
resistant rectangular plate 6 is gradually lowered in
the vessel body 1; meanwhile, the workers W manually
bring the corrosion-resistant rectangular plate 6
close to the smoothed inner surface of the existing
lining 4. Even if the corrosion-resistant
rectangular plate 6 being brought close to the existing lining 4 is slightly inclined, the long side 8 of the corrosion-resistant rectangular plate 6 is deemed to extend along the vertical direction as long as the corrosion-resistant rectangular plate 6 is welded to the existing lining 4 with the long side 8 extending along the vertical direction. In this configuration, a jig 41 for positioning the short side 7 at the lower end of the corrosion-resistant rectangular plate 6 is preferably installed in

advance at the position of the short side 7. As shown in FIG. 7, the jig 41 is configured such that an annular angle steel 42 is divided into multiple arc-shaped members joined with bolts 43 with each other, thereby adjusting a circumference. The short side 7 at the lower end of the corrosion-resistant rectangular plate 6 is placed on the jig 41, and then the workers W push the corrosion-resistant rectangular plate 6 to a position where the outer surface of the corrosion-resistant rectangular plate 6 comes into contact with the inner surface of the existing lining 4. When the corrosion-resistant rectangular plate 6 reaches a predetermined position, the corrosion-resistant rectangular plate 6 is temporarily fixed to the inner surface of the existing lining 4 by tack welding. In the tack welding, the corrosion-resistant rectangular plate 6 may be held with a pole or the like (not shown) so as to be stably welded.
[0025] After the temporary fixation of the predetermined number of corrosion-resistant rectangular plates 6 on the inner surface of the existing lining 4 by the tack welding, main welding is performed as shown in FIG. 8. The main welding includes circumferential welding 53 along the short side 7 of the corrosion-resistant rectangular plate 6 and longitudinal welding 54 along the long side 8 of

the corrosion-resistant rectangular plate 6. The circumferential welding 53 joins the corrosion-resistant rectangular plates 6 longitudinally adjacent to each other, whereas the longitudinal welding 54 joins the corrosion-resistant rectangular plates 6 circumferentially adjacent to each other. In the main welding, the long side 8 of the corrosion-resistant rectangular plate 6 extends in the vertical direction, so that the circumferential welding 53 is shorter and the longitudinal welding 54 is longer as compared with National Publication of International Patent Application No. 1998-505795 in which the long side 8 extends in the horizontal direction. Generally, to the welding worker W, the circumferential welding 53 is more dangerous and difficult and the longitudinal welding 54 is less dangerous and difficult. This is because in the circumferential welding 53, the worker W who walks in the circumferential direction to circumferentially change a welding position may meet accidents, e.g., an injury or a drop in the event of a misstep on the temporary scaffold 11, and the worker W moves his/her arm over a wide range of welding. In contrast, in the longitudinal welding 54, the worker W does not change a standing position to vertically change a welding position. Thus, the worker W hardly makes a misstep on the temporary scaffold 11 and only needs

to bend and stretch his/her knees with an arm substantially fixed during welding. In the main welding, the circumferential welding 53 and the longitudinal welding 54 is complete penetration and thus weld metal between the long sides 8 and weld metal between the short sides 7 reach the inner surface of the existing lining 4. Hence, all the corrosion-resistant rectangular plates 6 are firmly joined to the inner surface of the existing lining 4, and the outer surface of one of the corrosion-resistant rectangular plates 6 and the outer surface of the adjacent corrosion-resistant rectangular plate 6 are spatially isolated from each other by the weld metal.
[0026] In the urea plant equipment 10, if an internal corrosive fluid leaks from the existing lining 4 into the pressure-resistant shell 3, the pressure-resistant shell 3 serving as a reinforcing member of the vessel body 1 may be corroded. For early detection of such a phenomenon, the urea plant equipment 10 includes a detection mechanism that detects the leakage of a corrosive fluid guided outside the pressure-resistant shell 3 from the existing lining 4. Referring to FIGS. 9 to 11, the detection mechanism (particularly a passage that guides a corrosive-fluid leak outside the pressure-

resistant shell 3) not illustrated in FIGS. 1 to 8 will be described below.
[0027] FIG. 9 is a perspective view showing a vertical half of the body part of the vessel body 1. FIG. 9 shows the vessel body 1 before the new lining 5 is installed, that is, the vessel body 1 including the pressure-resistant shell 3 and the existing lining 4. In FIG. 9, broken lines on the inner surface of the existing lining 4 are drawn to be lines for the longitudinal welding 54 of the corrosion-resistant rectangular plates 6 to be installed. As shown in FIG. 9, the pressure-resistant shell 3 and the existing lining 4 are actually circular in shape. For simplicity, the pressure-resistant shell 3 and the existing lining 4 will be discussed below with reference to FIG. 10, a development of the pressure-resistant shell 3 and the existing lining 4 developed in a plane.
[0028] As shown in FIG. 10, the pressure-resistant shell 3 has through holes 37 (hereinafter, will be referred to as pressure-resistant-part through holes 37) that are circumferentially and longitudinally formed at predetermined intervals so as to externally guide a corrosive fluid leaking from the existing lining 4. Moreover, on the inner surface of the pressure-resistant shell 3, communicating grooves 38 (hereinafter, will be referred to as pressure-

resistant-part communicating grooves 38) that communicate the pressure-resistant-part through holes 37 adjacent to each other in the circumferential and longitudinal directions. Thus, a corrosive fluid having leaked from the existing lining 4 is guided from the pressure-resistant-part through holes 37 to the outside of the pressure-resistant shell 3 after passing through the pressure-resistant-part communicating grooves 38 or being directly guided into the pressure-resistant-part through holes 37. The corrosive fluid guided outside the pressure-resistant shell 3 is detected by a detector (not shown). The detection mechanism is not limited to a mechanism for detecting the leakage of a corrosive fluid guided outside the pressure-resistant shell 3 from the existing lining 4. The mechanism may detect leakage in the pressure-resistant shell 3. In this case, the detector (not shown) is configured as a detection mechanism that is installed in the pressure-resistant shell 3 and identifies a detected result outside the pressure-resistant shell 3. [0029] As shown in FIG. 11, the new lining 5 is disposed on the inner surface of the existing lining 4 in the present invention. As described above, the outer surfaces of the adjacent corrosion-resistant rectangular plates 6 (a clearance from the existing lining 4) are spatially isolated from each other by

the weld metal. Thus, a corrosive fluid leaking from the corrosion-resistant rectangular plates 6 may be left on the outer surfaces of the corrosion-resistant rectangular plates 6. In order to prevent the problem, the inner surface of the existing lining 4 is ground with the grinder G, and then through holes 47 (hereinafter, will be referred to as lining-part through holes 47) shown in FIG. 11 are formed in each part to be provided with the corrosion-resistant rectangular plate 6 on the existing lining 4. The two or more lining-part through holes 47 (for example, the two lining-part through holes 47 are vertically provided in FIG. 11) are preferably formed in each part to be provided with the corrosion-resistant rectangular plate 6 on the existing lining 4. In this case, a communicating groove 48 (hereinafter, will be referred to as a lining-part communicating groove 48) that communicates the lining-part through holes 47 is also formed. The lining-part through holes 47 are preferably formed at the positions of the pressure-resistant-part communicating grooves 38 or may be formed at the positions around the pressure-resistant-part communicating grooves 38. Thus, a corrosive fluid having leaked from the corrosion-resistant rectangular plates 6 is guided from the pressure-resistant-part through holes 37 to the outside of the pressure-resistant shell 3 through

the pressure-resistant-part communicating grooves 38 without being left on the outer surfaces of the corrosion-resistant rectangular plates 6 after passing through the lining-part communicating grooves 48 or being directly guided into the lining-part through holes 47.
[0030] In this way, according to the method of repairing the lining for the urea plant equipment 10, the corrosion-resistant rectangular plates 6 placed in the vessel body 1 are disposed on the inner surface of the existing lining 4 and thus do not need to be rotated about the horizontal axis, achieving a sufficiently short construction period.
[0031] In this way, the corrosion-resistant plate serving as the new lining 5 is divided into the corrosion-resistant rectangular plates 6 by cutting and then the corrosion-resistant rectangular plates 6 are curved along the inner surface of the existing lining 4. Thus, the corrosion-resistant rectangular plates 6 are more accurately shaped as necessary. This facilitates the placement of the corrosion-resistant rectangular plates 6 on the inner surface of the existing lining 4, thereby more sufficiently shortening the construction period.
[0032] Moreover, the short side 7 at the lower end of the corrosion-resistant rectangular plate 6 is positioned by the jig 41. This facilitates the

placement of the corrosion-resistant rectangular plates 6 on the inner surface of the existing lining 4, thereby more sufficiently shortening the construction period.
[0033] Furthermore, the circumferential welding 53 is shortened so as to reduce the risk and burden of welding for the workers W performing welding. This can more sufficiently shorten the construction period. [0034] The corrosion-resistant rectangular plates 6 are joined to each other by complete penetration welding and thus all the corrosion-resistant rectangular plates 6 are firmly joined to the inner surface of the existing lining 4. The lining-part through holes 47 allow the detection of a corrosive fluid without leaving the corrosive fluid on the outer surfaces of the corrosion-resistant rectangular plates 6, thereby improving the reliability of the urea plant equipment 10.
[0035] In the mentioned embodiment, the length of the urea plant equipment 10 extends in the vertical direction. The length may be inclined or extended in the horizontal direction. If the length of the urea plant equipment 10 extends in the horizontal direction, the corrosion-resistant rectangular plate 6 is placed from the manhole 2 with the long side 8 extending in the horizontal direction and then is

disposed on the inner surface of the existing lining 4.
[0036] In the mentioned embodiment, the corrosion-resistant rectangular plate 6 is hung from the manhole 2 into the urea plant equipment 10 by the hoist 22. The hoist 22 may be replaced with any device.
[0037] Furthermore, in the mentioned embodiment, the main welding is joining between the adjacent corrosion-resistant rectangular plates 6 and joining between the corrosion-resistant rectangular plate 6 and the inner surface of the existing lining 4. The main welding may be any kind of joining.
[0038] Additionally, in the mentioned embodiment, the urea plant equipment 10 was described as an example of plant equipment. Any kind of plant equipment may be used as long as the existing lining 4 is provided as a repair part. Specific examples of plant equipment include ammonia plant equipment and refinery equipment.
[0039] In the mentioned embodiment, the pressure-resistant shell 3 is illustrated as a single layer for simplicity. The pressure-resistant shell 3 may have multiple layers.
[0040] The foregoing embodiment is merely exemplary and is not restrictive in all the aspects. The scope of the present invention is not indicated by the

foregoing description but the claims. The scope of the present invention is intended to include meanings equivalent to the claims and all changes in the scope. From among the configurations described in the embodiment, the configurations other than that described as a first invention in "Disclosure of the Invention" are optional and thus can be deleted and changed as appropriate.

I/We Claim:
1. A method of repairing a lining for plant
equipment, in which a damaged inner surface of an
existing lining is repaired with a new lining, the
plant equipment having a manhole on a longitudinal
end,
the method comprising the steps of:
preparing a plurality of corrosion-resistant rectangular plates serving as the new lining, the corrosion-resistant rectangular plate having a short side shorter than an inside diameter of the manhole and a long side longer than the inside diameter of the manhole; and
placing the corrosion-resistant rectangular plate, which has the long side along a longitudinal direction of the plant equipment, into the plant equipment from the manhole, and disposing the corrosion-resistant rectangular plate, which has the long side along the longitudinal direction of the plant equipment, on the inner surface of the existing lining,
wherein in the step of placing, the adjacent corrosion-resistant rectangular plates are joined to each other and the corrosion-resistant rectangular plate and the inner surface of the existing lining are joined to each other.

2. The method of repairing a lining for plant equipment as claimed in claim 1, wherein in the step of preparing, a plate serving as the new lining is divided into the corrosion-resistant rectangular plates, and each of the corrosion-resistant rectangular plates is shaped along the inner surface of the existing lining by curving the corrosion-resistant rectangular plate in a direction of bringing the two long sides of the corrosion-resistant rectangular plate close to each other.
3. The method of repairing a lining for plant equipment as claimed in one of claims 1 and 2, wherein the plant equipment is formed with the longitudinal direction extending in a vertical direction and the manhole formed on an upper end of the plant equipment, and
the plant equipment includes a jig for positioning the short side at a lower end of the corrosion-resistant rectangular plate, the jig being installed on a part of the existing lining where the corrosion-resistant rectangular plate is disposed.
4. The method of repairing a lining for plant
equipment as claimed in one of claims 1 and 2,
wherein the adjacent corrosion-resistant rectangular

plates are joined to each other by complete penetration welding in the step of placing, and
the method further comprises, before the step of placing, a step of forming a through hole in each part of the existing lining where the corrosion-resistant rectangular plate is disposed, the through hole guiding a fluid leak from the new lining to outside of the plant equipment in order to detect the fluid leak.