Patent Application
20130285374
The present application claims the priority under 35 U.S.C. 119 of Japanese Application No. 2011-004969, filed Jan. 13, 2011, which is hereby incorporated herein by reference in its entirety.
The present invention relates to a connecting structure for pressure piping for permitting connection of the pressure piping on-site without requiring welding.
In Japanese Industrial Standards, the strength of couplings that should be used is defined for connected pressure piping. In particular, concerning the strength of couplings, the strength that the base material of the pressure piping connected to the coupling must have before failure in a tension test is defined. In addition, with respect to a connection by welding, the pressure piping is required to extend a leg length for all over the place in order to keep weld strength that the base material of the pressure piping before failure in the same way. Such welding work requires skill, and therefore, the number of persons able to perform the work is limited.
Different connecting means than welding includes adhesive and bolts. For example, patent literatures 1 and 2 disclose means for combining pipe and pipe by bolts. These technologies are to fix pipes for accommodating electric wires with the fastening force of bolts screwed on peripheral surface walls of the pipes in their radial direction. These pipes are to protect the inner electric wires, and the electric wires in themselves do not either have pressure or leak. Patent literature 3 discloses a technique for connecting poles with the bolts, wherein the poles are fixed with the fastening force of the bolts.
In connecting pressure piping for transmitting high pressure fluid without using welding, it is necessary to keep a high tensile strength to seal in the internal fluid. In the above-mentioned bolt-connecting, it is predicted that the connecting strength is improved by enhancing the material strength of the bolts, bolt diameter, and/or fastening pressure. However, a problem about an arrangement to improve the strength or a means to seal a fluid flowing through the pressure piping has not been solved. The present invention aims to provide a connecting structure for pressure piping using bolts as a connecting means.
The present invention is characterized by a connecting structure for connecting pressure piping to convey pressure fluid inside, including a cylindrical sleeve having a plurality of through holes at separate locations in a lengthwise direction, and with identical angular intervals in the circumferential direction and without overlapping in the circumferential direction, and a plurality of bolts to be inserted into the through holes of the sleeve. Non-through holes having screw threads are provided in the pressure piping at locations corresponding to the holes of the sleeve. When the pressure piping is inserted into the interior space of the sleeve, the non-through holes of the pipes open into the through holes of the sleeve, and the bolts are screwed into the communicating holes.
According to pipe couplings of the present invention, it is possible to connect the pressure piping with the bolts without using welding in furnishing the pressure piping in which the tensile strength is required.
The tensile strength of a connecting structure for connecting pressure piping with bolts will be examined. In the above-mentioned patent documents, pipes are connected by transformation of the outer circumferential walls of the pipes, which is caused by the pressing force of screwed bolts. On the other hand, in a pressure piping equipment, the tensile strength for the pressure piping is set forth in the Japanese Industrial Standards, and to obtain enough connecting force, the bolts are inserted into holes provided on the pressure piping in addition to the transformation of the outer circumferential walls.
Besides, although the breaking strength of the pressure piping itself decreases because the holes are provided on the pressure piping, an object of the present embodiment is to obtain a connecting strength that is greater than the yield load of the pressure piping.
Even when the bolts 4 are tightened, an inner wall of the sleeve 1 does not equally adhere on outer walls of the pressure pipes p1, p2. A reason is that the walls of the cylindrical sleeve 1 and the pipes p1, p2 one side of the connecting structure move away from each other when the walls of the cylindrical sleeve 1 in the pipes p1, p2 on the other side are closely adhered by tightening the bolts 4. Accordingly, in the case of the connecting structure like this sample, the tensile strength of the connecting structure depends not on the frictional force of the walls by tightening of the bolts 4, but wholly on the ability of the bolts to withstand the shearing force at a gap between the sleeve and the pressure pipes due to the tensile force imposed by the pipes on the connecting structure.
First, concerning the sample of
Next, concerning the sample of
In a pulling test for this sample, the pressure pipes broke at a position along the circle on which bolt holes h1 are provided, at 78 KN. Therefore, it has been found that the pressure pipes of this case can withstand a tension bigger than the yield load. On the other hand, it is believed that the used pressure pipes made of STPG370 were stronger than the standardized strength of 370 N/mm2 to begin with as a reason why the tension was bigger than the tensile breaking load calculated from the cross-sectional area of the pressure pipes p1, p2 of the sample of
Furthermore, a sample of
In the case of this sample, the decrease in the cross-sectional area of the circles is 39 mm2, which is equivalent to the dimensions of one lost hole. It is anticipated that the tensile breaking load of the base material of the pressure pipes p1, p2 on the circles a1, a2, a3 and a4 becomes equal to or greater than 92 KN, because the decrease in cross-sectional area reduces the strength. This value exceeds the yield load of 62 KN. On the other hand, when the sleeve 1 and the bolts have greater strength than the pressure pipes p1, p2, it is anticipated that a posterior position a5 of each of the holes h2 of the pressure pipes p1, p2 breaks due to the tension. When a tension test for each sample in
A pressure pipes of STPT410, sch160, 20A was tested for the sample shown in
The tests reveal that the cross-sectional area of the pressure pipes lost by the bolts can be reduced and yet the strength can be maintained by raising the tensile breaking load per unit area of the bolt. Here, because the shearing strength is expected to be 60% of the tensile strength, the strength of the bolt is 1.67 times (1/0.6) the tensile strength of the pressure pipe to be used. Therefore, it is desirable to use a bolt with strength equal to this.
Furthermore, although a sample in which adhesive was applied between the pressure pipes and the sleeve of
Moreover, the material of the sleeve has a tensile strength that is the same as, or greater than, the connected pressure pipes. Otherwise, a sleeve having a cross-sectional area that provides it with a tensile breaking load bigger than the tensile breaking load of the pressure pipes is used.
Thus, when the pressure pipes were connected with bolts, it was found that a tensile breaking load equal to or greater than the yield strength of the pressure pipes was shown without a break at least on the circles a1 to a4 of the pressure pipes having their cross-sectional area reduced by the bolts, due to proper control of the tensile shearing load, and the number and dispositions of the bolts.
Specifically, the bolts are arranged on the different circles, and the number of bolts and the strength of a bolt unit area can be determined for the yield strength of the pressure pipes and g as follows.
F<(S−L)×N1=n×(r/2)2×π×N2×0.6 Expression 1
In Expression 1, N1 is the tensile breaking strength of a pressure pipe per unit area; N2 is the tensile breaking strength of a bolt per unit area; r is the diameter of a bolt; S is the cross-sectional area of a pipe; n is the number of bolts; F is the yield load of a pressure pipe; L is the cross-sectional area lost due to a bolt hole on the same circle; and 0.6 is a correction factor for the strength of a bolt due to shearing force.
When there is a plurality of bolt holes on the same circle, the cross-sectional area L becomes the total cross-sectional area lost due to the bolts. Further, the cross-sectional area L becomes the cross-sectional area of the circle that is most greatly lost in case the cross-sectional area to be lost differs among the circles. The bolt hole may be provided to one place on the same circle because the strength of the pressure pipe is lost when a plurality of bolt holes are present on the same circle. Accordingly, it is possible to avoid breaks on the circles a1 to a4 and fracture of the bolts themselves when the cross-sectional area of the pressure pipe is reduced.
The following construction is used as a connecting structure of pipes for conveying a pressure fluid inside.
The bolt holes do not penetrate the pressure pipes because inner fluid leaks outside through the bolt holes. In addition, sealing is performed at a position of an end face of the pressure pipes to limit the area with which the inner fluid comes in contact. Moreover, an O-ring is used, and a groove for the O-ring is provided, not on the end face of the pressure pipe but on an insert side, because the pressure pipe is often cut for length adjustment at a piping site, and it is difficult to notch the O-ring groove within the wall thickness of the pressure piping at the site. Hereinafter, concrete examples for connecting pressure pipes piping using a connection strength to be provided by a bolt will be explained with reference to the figures.
A connecting structure 100 related to a first example is illustrated in
The sleeve 1a is a linear cylindrical pipe, and the insert 2a is inserted in an inner circumferential face side of the linear cylindrical pipe.
The insert 2a has annular faces b1, b2 in a centerline c direction of the sleeve 1a, and annular ring grooves b11, b21 are provided in the annular faces b1, b2, respectively. An O-ring 3 is put in each of the ring grooves b11, b21. The bolts 4 are tightened on different circles spaced in the centerline c direction, with each bolt 4 shifted 90 degrees from an adjacent bolt 4, as is the case with the connecting structure in
Referring now to a point to connect two pressure pipes p1, p2 having the connecting structure 100.
Ends of the pressure pipes p1, p2 are pushed into the sleeve 1a to the insert 2a from both sides and pressed toward each other to compress the O-ring 3 of the insert 2a. The compressed pressure is equivalent to prestress in using the O-ring 3.
Under this condition, the pressure pipes p1, p2 are marked in accordance with the position of a necessary plurality of holes h1. Then, the pressure pipes p1, p2 are removed from the sleeve 1a, and holes h2 are provided in the marked position. The depth of the hole h2 is not beyond the wall thickness of the pressure pipes p1, p2. A screw thread is provided in the holes h2.
Next, the pressure pipes p1, p2 are pushed into the sleeve 1a across from one another at the insert 2a and pressed by a pressure equivalent to the prestress of the O-ring 3 to return each of the pressure pipes p1, p2 and the sleeve 1a to the relative positions that had previously, positions corresponding to the positions for which the hole h2 was marked. Thereafter, the bolts 4 through the holes h1 of the sleeve 1a are screwed into the holes 2a and tightened, respectively. If a screw thread is simultaneously made in the holes h1, h2 when the pressure is applied from both sides on the pressure pipes p1, p2, the screw hole h2 can be made without marking, and screw threading bolts can be tightened in the holes h1, h2.
In addition, if the ring grooves b11, b21 have a depth just adapted for putting appropriate sealing pressure on the O-ring 3, appropriate pressure is naturally put on the O-ring 3 by pushing the pressure pipe p1 or p2 into the sleeve 1a or 1b until the end face of the pressure pipe p1 or p2 contacts the annular face b1 or b2 of the insert 2a. If the depths of the ring grooves b11, b21 are decided in advance in this way, the locations of the holes h2 can be identified and processed without marking, because it is known beforehand where along the pressure pipes p1, p2 the holes h1 of the sleeve 1a or 1b are located when the pipes p1, p2 are pushed to their limits.
According to this, the pressure pipe p1 is connected to the pressure pipe p2 in the state that the appropriate prestress is imposed on the O-ring 3. An adhesive can be used for the face of either the outer circumference area of the pressure pipes p1, p2 or the inner circumferential face of the sleeve 1a before again pushing the pressure pipes p1, p2 into the sleeve 1a after forming the hole h2. By using the adhesive, the fluid tightness is improved. The O-rings 3 are positioned at the end faces of the pressure pipes p1, p2 because the insert 2a is restricted from moving in the pipe by an inner wall of the sleeve 1a. The areas of the perforated holes h2 of the pressure pipes p1, p2 are quenched by carburizing or induction quenching to increase the tensile strength for those areas, and to increase the tensile breaking load that was decreased by the forming of the perforated holes h2 in the pressure pipes p1, p2.
In the first example, the pressure pipes p1, p2 and the sleeve 1a are made with steel materials, but use other metal materials.
Inserts 2a are respectively inserted from both ends of the sleeve 1b with the O-rings 3, and each comes into contact with the neck portion 5. Even if all of the bolts 4 break, the sleeve 1b can be restricted from slipping on the pressure pipes p1, p2 and falling away from the contact portion because the neck portion 5 is provided.
Reference is made to a combination procedure for two pressure pipes p1, p2 according to the connecting structure 101. The insert 2a is inserted from the sleeve 1b, and then, the two pressure pipes p1, p2 are pushed into the sleeve 1b from both sides, and then, a pressing force is imposed on the pressure pipes p1, p2. The pressing force is equivalent to the prestress that the O-ring 3 mounted on the insert 2a has in a use state.
Under this state, as in the case of the first example, the pressure pipes p1, p2 are marked at positions corresponding to the positions of the holes h1, and thereafter, each of the pressure pipes p1, p2 is pulled out of the sleeve 1b, the holes h2 are formed, and the screw thread is formed.
The inserts 2a are respectively inserted from opposite ends of the sleeve 1b, and the end portions of the pressure pipes p1, p2 are pushed therein and tightened by screwing with bolts 4 while a pressing force corresponding to the prestress of the O-ring 3 is applied. In addition, an adhesive can be used between the pressure pipes p1, p2 and the sleeve 1a together with the bolts.
Just as in the earlier example, if the depth of the ring grooves b11, b21 of the insert 2a is made to such a depth that the O-ring 3 is fit for the ring grooves b11, b 21 when appropriate sealing pressure is applied thereon, the positions of the holes h2 can be specified and processed without marking.
According to this example, when each of the inserts 2b is pushed toward the neck portion 5, the sleeve 1c and the pressure pipes p1, p2 become concentrically positioned by the conical male taper face.
EXAMPLE 4 is explained with reference to
The sleeve portion 1d and the flange portion 6 form a flange coupling 8 as a unified part. The flange portion 6 has an inner hole 6a concentric with a hollow inside the sleeve portion 1d as a fluid channel, besides having an annular face 6b perpendicular to the centerline c between the inner hole 6a and the sleeve portion 1d. Multiple bolt holes 6c are formed in an outer circumference portion of the flange portion 6 to insert bolts for connecting the flange portion 6 to a like flange coupling. The insert 2a is inserted into the inner circumferential face of the sleeve portion 1d. Here, multiple holes h1 pass through the sleeve portion 1d.
The order for connecting the pressure pipe p1 according to the connecting structure 103 is the same as the order for connecting a pressure pipe at one side in EXAMPLE 2. The pressure pipe p1 may be connected to the sleeve portion 1d by using the annular face 6b, just as the pipe p1 is connected to the sleeve portion 1b by using one of the sides of the neck portion 5 in EXAMPLE 2 (
The thus connected pressure pipe p1 with the flange portion 6 for example, bolts inserted into the bolt holes 6c and nuts, and packing screwed on the bolts.
A connecting structure of EXAMPLE 5 may be so constructed that a female taper face having a diameter that decreases in a direction toward the annular face 6b is formed on the inner circumferential face of the sleeve portion 1d of EXAMPLE 4 and the insert 2b of EXAMPLE 3. In this case, it is easy to locate the insert 2a, as i the t is in EXAMPLE 3.
EXAMPLE 6 is explained with reference to
This structure is comparable to the neck portion 5 in EXAMPLE 2 with respect to the sealing function of the insert 2a. In this example, it is not easy to install the O-rings 3 in the ring-grooves b11, b21 formed in the inner part of the sleeve le, but the number of parts can be reduced because the insert 2a is not used.
The connecting structure 103 referred to EXAMPLE 4 can be transformed to a connecting structure 105 as shown in
Accordingly, even if there are radial gaps g1, g2 between the inner circumferential face of the sleeve if and the inserted pressure pipes p1, p2, they are automatically made concentric by the guiding of the male and female tapering faces.
A sleeve 1h and a flange portion 9 form a unified part. The flange portion 9 has an inner hole 9a as a fluid channel. The flange coupling 11 differs from the flange coupling 8 of EXAMPLE 4 in that the flange portion 6 and the sleeve portion 1d are continuously connected without a perpendicular annular face 6b (
In
The bolt 4 connecting the pressure pipes p1, p2 to the sleeve bears shear force at the contact surface between the sleeve and the pressure pipe.
In addition, the connecting structure may be constructed so that an insert can be connected to the sleeve with bolts. In
In this structure, when removing the pressure pipe p2, all bolts 4 are removed, and the end of the pressure pipe p2 is exposed by sliding the sleeve 1a to the left. Therefore, the pressure pipe p2 can be removed without changing the positional relationship of the pressure pipe p1 installed in the spot.
During a connecting structure assembly of the, the pressure pipe p2 is put through the loose coupling 13 as shown in
The prestress on the sealing material of the inserts 2a, 2e can be determined by adjusting the screwed length. The present invention can be applied to the case in which the sleeve portions ld, 12c of the flange portions disclosed in the embodiments of
If the insert 2a has the ring grooves b11, b21 with a depth to fit the O-ring when proper sealing pressure is applied thereto, proper pressure comes to be spontaneously added on the O-ring by screwing the pressure pipe p1 or the pressure pipe p2 into the sleeve 1a or the sleeve 1b until the end face thereof contacts the annular faces b1, b2 of the insert 2a.
In EXAMPLE 8 shown in
The insert 2f is a form of ring; its inner circumferential surface 20 has a diameter that is the same as the internal circumferential surface of the pressure pipes p1; and its outer circumferential surface 21 has a diameter slightly smaller than the outer circumferential surface of the sleeve 1a. There are step-shaped grooves 23 in a concentric circle form in the outer circumferential surface 21 of the insert 2f at the right and left end faces 22 thereof. The step-shaped groove 23 has an annular face 24 parallel to the radial direction and a ring face 25 parallel to the centerline.
Besides, in the insert 2f, if the ring face 25 has a width such that the O-ring 3 just achieves the height of the end face 22 when proper sealing pressure is added on the O-ring 3, the proper pressure is spontaneously added to the O-ring 3 by pushing the pressure pipe p1 or the pressure pipe p2 into the sleeve 1a or the sleeve 1b until its end face hits the end face 22.
The insert 2f has non-through holes 26 that are used to fix to the sleeve 1a. The sleeve 1a has holes 5 passing from the outer circumferential surface to the inner circumferential surface. The holes 5 are connected to the holes 26 of the insert 2f with the bolts 4.
When fixing the insert 2f to the sleeve 1a with the bolts 4, the inner circumferential surfaces of the annular face 24, the ring face 25 and the sleeve 1a form the bottom face and both side faces of the groove for the O-ring 3, respectively.
A thick O-ring is superior in stabilizing seal characteristics, because it has a small compression set compressibility is constant. According to the present example, it is possible to use the thick O-ring. In addition, the bolts 4c were used, because the pressure pipes p1, p2 have no screw threads in the holes. However, the holes h2 may have screw threads, and in that case, the bolts 4 are used.
Furthermore, in the insert 2f, if the ring face 25 has a width such that the O-ring just achieves in the width of the ring face when the proper seal pressure is imposed on the O-ring 3, the proper pressure is spontaneously imposed on the O-ring 3 by pushing the pressure pipe p1 or p2 into the sleeve 1a or 1b until its end face hits the end face 22.
In making the ring face 25 of the insert 2g to have such a width that the O-ring 3 fits in completely with proper seal pressure, the proper pressure is spontaneously imposed on the O-ring 3 by pushing the pressure pipe p1 or p2 into the sleeve 1a or 1b until its end face engages the end face 22 of the insert 2g. Since screw threads are not formed in the holes 2 of the pressure pipes p1, p2, the bolts 4c are used. However, the holes h2 may have screw threads. In that case, the bolts 4 are used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-004969 | Jan 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/074116 | 10/20/2011 | WO | 00 | 7/10/2013 |
