Abstract:
Provided are a connection structure for connecting corrugated synthetic resin pipes and a corrugated synthetic resin pipe used in the connection structure. The pipe is lightweight, low cost, and simply structured with a small number of components, having sufficient resistance to water and pressure, and excellent sealing performance without the use of robust material or requiring high precision, and capable of being easily connected and manufactured. A first corrugated synthetic resin pipe  1 A is provided at an end  10  with a cylindrical insert end  3  formed by adhering a synthetic resin layer  5  to the outer surface of the end  10  so as to fill at least corrugated recesses  2   a . A second corrugated synthetic resin pipe  1 B is provided at an end  11  with a socket  4  formed by adhering synthetic resin to the outer surface of the end  11  and cylindrically extending the resin outwardly in the axial direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a corrugated synthetic resin pipe including a pipe wall having a spirally corrugated shape, which is used, for example, as an underground drainage pipe or a sewage pipe, and also relates to a method for manufacturing the pipe. 
     2. Description of the Background Art 
     Conventionally, Hume concrete pipes have been used as underground drainage pipes and sewage pipes. In recent years, however, it has become popular to use corrugated synthetic resin pipes with a body having a substantially flat inner surface and an outer periphery having reinforcing projections spirally arranged thereon. The corrugated synthetic resin pipes are popular because they are as strong as and more durable, lighter in weight, and simpler in construction than Hume pipes. Two such corrugated synthetic resin pipes are connected to each other as follows. First, half joints each having a connecting flange are attached to the facing ends of the pipes with packing sheets set on the inner surfaces of the pipes. Next, the gaps between waterproof blocks and recesses are filled with caulking material. Then, the packing sheets are wound in a fully stretched condition around the pipes and fixed with a vinyl tape or the like. Finally, one half joint is put over the other, and then the flanges of the half joints are fixed to each other by bolts and nuts. 
     Such a connection structure, however, requires putting the upper and lower half joints, the packing sheets, the caulking material, and other parts together in the field in a specific procedure. This takes a lot of time and effort, thus decreasing the operating efficiency. It is also troublesome to manage the large number of component parts. Furthermore, it is a heavy burden for field workers to move two pipes to specific positions of the packing sheets after the packing sheets are laid on the inner surfaces of the half joints. In addition, the amount of the caulking material to be filled and the degree of stretching the packing sheets in the field vary between individuals, thus causing quality variations. 
     On the other hand, a new connection structure which makes the connection process easier and faster has been suggested (see, for example, Patent Document 1). In this connection structure, first, connecting flanges are welded to the facing ends of two corrugated synthetic resin pipes. Next, a packing is attached to a contact surface where the flanges are surface-contacted with each other, and finally, the flanges are fixed to each other by bolts and nuts. This connection structure provides higher workability and reliability than the conventional connection structure. 
     This connection structure, however, has the following problems. The connecting flanges, which are required to be connected using bolts and nuts, decrease operating efficiency. The pipe ends to which the flanges are welded can cause water leakage unless they are made watertight, and deformation of the flange surfaces can also cause water leakage. Avoiding the water leakage requires high quality in welding, and also in the strength, shape, and size of the flanges, which hinders cost reduction. Another problem is that the robust flanges, and the bolts and nuts to connect them inevitably increase the weight of the connected areas. Further another problem is that the connection between the flange surfaces via the packing limits the resistance to water and pressure of the flange surfaces, and requires evenly tightening bolts and nuts, which hinders improving operating efficiency. 
     Patent Document 1: Japanese Patent Unexamined Publication No. 2002-139178 
     SUMMARY OF THE INVENTION 
     In view of the above-described problems, the present invention has an object of providing a corrugated synthetic resin pipe which is lightweight, low cost, and simply structured with a small number of components, having sufficient resistance to water and pressure, and excellent sealing performance without the use of robust material or requiring high precision, and capable of being connected easily in the field. The present invention has another object of providing a method for manufacturing the corrugated synthetic resin pipe efficiently at low cost. 
     Through detailed studies for solving the problems, the inventors of the present invention have found the following facts and completed the present invention. In the connection of two corrugated synthetic resin pipes, a cylindrical insert end can be formed at an end of one pipe by filling the spiral recesses, which can cause fluid leakage, with a synthetic resin layer. A socket, which is inserted by the insert end, is formed at an end of the other pipe in such a manner as to project in the axial direction. The mere insertion of the insert end into the socket in the axial direction can complete the connection process with stable sealing performance. 
     The present invention is directed to provide a connection structure for connecting two corrugated synthetic resin pipes at facing ends thereof, the corrugated synthetic resin pipes each including a pipe wall having a spirally corrugated shape, the connection structure comprising: a cylindrical insert end at an end of a first corrugated synthetic resin pipe, the insert end being formed by adhering a synthetic resin layer to the outer surface of the end in such a manner as to fill at least corrugated recesses; and a socket at an end of a second corrugated synthetic resin pipe, the socket being formed by adhering synthetic resin to the outer surface of the end and cylindrically extending the synthetic resin outwardly in the axial direction, wherein the insert end of the first corrugated synthetic resin pipe is inserted into the socket of the second corrugated synthetic resin pipe so as to be connected to each other. 
     It is preferable to provide a seal member between the insert end and the socket. 
     It is preferable that the insert end is provided on its outer surface with an annular groove for accommodating the seal member. 
     It is preferable that, among the socket and the insert end, at least the socket contains reinforcing fiber in a synthetic resin portion thereof. 
     It is preferable that the reinforcing fiber contained in the synthetic resin portion is either embedded in the form of a woven cloth, a nonwoven cloth, or a resin molding, or added as chips. 
     It is preferable that the reinforcing fiber is made of glass fiber. 
     It is preferable that the socket includes a pipe material having a larger diameter than the second corrugated synthetic resin pipe, the pipe material being connected to the end of the second corrugated synthetic resin pipe in such a manner as to project coaxially from the outer surface of the end outwardly in the axial direction, and the pipe material having a synthetic resin layer adhered at least on the inner surface thereof. 
     It is preferable that the pipe material and the end of the second corrugated synthetic resin pipe are integrated together with the synthetic resin layer disposed therebetween. 
     The present invention is also directed to provide a corrugated synthetic resin pipe used in the above-described connection structure, the corrugated synthetic resin pipe comprising: a pipe wall having a spirally corrugated shape; a cylindrical insert end at one end, the insert end being formed by adhering a synthetic resin layer to the outer surface of the one end in such a manner as to fill at least corrugated recesses; and a socket at the other end, the socket being formed by adhering synthetic resin to the outer surface of the other end and cylindrically extending the synthetic resin outwardly in the axial direction. 
     It is preferable that the insert end at the one end is provided on its outer surface with an annular groove for accommodating the seal member. It is preferable that, among the socket and the insert end, at least the socket contains reinforcing fiber in a synthetic resin portion thereof. It is particularly preferable that the reinforcing fiber contained in the synthetic resin portion is either embedded in the form of a woven cloth, a nonwoven cloth, or a resin molding, or added as chips. It is preferable that the reinforcing fiber is made of glass fiber. It is preferable that the socket includes a pipe material having a larger diameter than the corrugated synthetic resin pipe, the pipe material being connected to the end of the corrugated synthetic resin pipe in such a manner as to project coaxially from the outer surface of the end outwardly in the axial direction, and the pipe material having a synthetic resin layer adhered at least on the inner surface thereof. It is preferable that the pipe material and the other end are integrated together with the synthetic resin layer disposed therebetween. 
     It is also preferable that the socket includes a pipe material having a larger diameter than the corrugated synthetic resin pipe and projecting coaxially from the outer surface of the other end outwardly in the axial direction, and that the synthetic resin material for the synthetic resin layer is injected into at least the gaps between the pipe material and the corrugated synthetic resin pipe. 
     It is preferable that the pipe material has a pipe wall formed in a spirally corrugated shape similar to the pipe wall of the corrugated synthetic resin pipe. 
     The present invention is also directed to provide a method for manufacturing the above-described corrugated synthetic resin pipe, the method comprising: forming the pipe wall of the corrugated synthetic resin pipe; forming the pipe material having a larger diameter than the corrugated synthetic resin pipe on the other end of the corrugated synthetic resin pipe thus formed, the pipe material being formed coaxially with the corrugated synthetic resin pipe with support of a guide member from the radial outside; sealing the pipe material thus formed at inner and outer ends in the axial direction using sealing chucks; and injecting the synthetic resin material for forming the synthetic resin layer into the gaps between the pipe material thus sealed and the corrugated synthetic resin pipe. 
     In the manufacturing method, it is preferable that at least one of the sealing chucks has an inlet for injecting the synthetic resin material. 
     In the manufacturing method, it is preferable that during formation of the pipe material, continuously fed steel is deformation-processed to have an M-shaped cross section and then spirally discharged, and at the same time, an outer wound tape is continuously spirally discharged so as to be adhered to the outer surface of the steel and integrated in the axial direction, thereby providing the pipe material. 
     According to the present invention, the pipe connection process is performed only by inserting an insert end into a socket in the axial direction. The cylindrical insert end is formed by adhering a synthetic resin layer to the outer surface of an end of one pipe. The socket is formed by adhering synthetic resin to the outer surface of an end of another pipe and cylindrically extending the resin outwardly in the axial direction. This connection structure eliminates the need to evenly tighten bolts and nuts, unlike the conventional structure using connecting flanges, thereby significantly improving operating efficiency. In this mating structure between the socket and the insert end, the socket encases the insert end without the use of robust material or requiring high precision, thereby providing sufficient resistance to water and pressure, and excellent sealing performance. This allows the pipes to be lighter in weight and lower cost and to be connected more easily than the conventional pipes which require fixing the connecting flanges water-tightly and precisely. 
     The insert end is provided on its outer surface with an annular groove for accommodating the seal member. This simplifies the connection of the pipes with the seal member accommodated in the annular groove, thereby improving workability. 
     Among the socket and insert end, at least the socket contains reinforcing fiber in a synthetic resin portion thereof. This decreases the weight and cost, and increases the strength of the synthetic resin socket, thereby providing a connection structure having higher resistance to water and pressure as compared with the socket having a large-diameter pipe material, which will be described later. 
     The reinforcing fiber contained in the synthetic resin portion is embedded in the form of a woven cloth, a nonwoven cloth, or a resin molding. This increases the strength of the projecting socket. The reinforcing fiber contained in the synthetic resin portion is added as chips. This increases the strength of the entire socket, and resistance to water and pressure. 
     The socket includes a pipe material having a larger diameter than the second corrugated synthetic resin pipe, the pipe material being connected to the end of the second corrugated synthetic resin pipe in such a manner as to project coaxially from the outer surface of the end outwardly in the axial direction, and the pipe material having a synthetic resin layer adhered at least on the inner surface thereof. This increases the strength of the socket, thereby providing the connection structure having higher resistance to water and pressure. 
     The pipe material and the end of the second corrugated synthetic resin pipe are integrated together with the synthetic resin layer disposed therebetween. This increases the strength of the socket, and prevents displacement between the pipe material and the pipe end in the axial direction, thereby improving sealing performance. 
     The socket includes a pipe material having a large diameter and projecting coaxially with the corrugated synthetic resin pipe, and the synthetic resin material is injected into the gaps between the pipe material and the corrugated synthetic resin pipe. This increases the strength of the socket, thereby providing the connection structure having higher resistance to water and pressure. 
     The pipe material has a pipe wall formed in a spirally corrugated shape similar to the pipe wall of the corrugated synthetic resin pipe. This increases the strength of the pipe material. The synthetic resin layer can be adhered to entirely coat the outer surface of the pipe material, but can alternatively be adhered in such a manner that the pipe material is partially exposed. This can reduce the weight and material cost. In addition, the pipe wall of the pipe material has the same appearance as the pipe wall of the corrugated synthetic resin pipe, thereby improving unity between the joint and the entire pipe, and hence, their appearance. 
     According to the method for manufacturing the corrugated synthetic resin pipe of the present invention, the pipe material as a component of the socket is formed immediately after the formation of the pipe wall of the corrugated synthetic resin pipe, and the synthetic resin material is injected into the gaps between the pipe material sealed using the sealing chucks and the corrugated synthetic resin pipe. This allows the corrugated synthetic resin pipe and the socket to be formed integrally at the same time, thereby improving production efficiency and decreasing cost. 
     At least one of the sealing chucks has an inlet for injecting the synthetic resin material. This facilitates the injecting of the synthetic resin material. 
     During formation of the pipe material, continuously fed steel is deformation-processed to have an M-shaped cross section and then spirally discharged, and at the same time, an outer wound tape is continuously spirally discharged so as to be adhered to the outer surface of the steel and integrated in the axial direction, thereby providing the pipe material. This continuous integral molding provides the high-strength pipe material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall view of a joint structure according to a first embodiment of the present invention. 
         FIG. 2  is a longitudinal sectional view of the essential part of the joint structure according to the first embodiment. 
         FIG. 3A  is a longitudinal sectional view of the essential part of a pipe wall, and  FIG. 3B  is a longitudinal sectional view of a modified example of the pipe wall according to the first embodiment. 
         FIG. 4  is a longitudinal sectional view of a modified example of a socket according to the first embodiment. 
         FIG. 5  is an overall view of a joint structure according to a second embodiment of the present invention. 
         FIG. 6  is a longitudinal sectional view of the essential part of the joint structure according to the second embodiment. 
         FIG. 7  is a longitudinal sectional view of the essential part of a joint structure according to a third embodiment of the present invention. 
         FIG. 8  is a longitudinal sectional view of a modified example of an insert end according to the third embodiment. 
         FIG. 9  is a longitudinal sectional view of a modified example formed by adding reinforcing fiber chips according to the third embodiment. 
         FIG. 10  is a longitudinal sectional view of a modified example which is formed by adding reinforcing fiber in the form of a woven cloth, a nonwoven cloth, or a resin molding to the modified example of  FIG. 9 . 
         FIG. 11  is an overall view showing a state in which corrugated synthetic resin pipes according to a fourth embodiment of the present invention are connected to each other. 
         FIG. 12  is an overall view of the corrugated synthetic resin pipe according to the fourth embodiment. 
         FIG. 13  is an enlarged longitudinal sectional view of the connected area of the corrugated synthetic resin pipes according to the fourth embodiment. 
         FIG. 14  is an explanatory drawing showing a method for manufacturing the corrugated synthetic resin pipe according to the fourth embodiment. 
         FIG. 15  is an enlarged longitudinal sectional view of another example of the pipe material as a component of the socket according to the fourth embodiment. 
         FIG. 16  is a flowchart showing the manufacturing procedure of the corrugated synthetic resin pipe. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described in detail as follows based on the attached drawings. 
       FIG. 1  is an explanatory drawing showing a connection structure S for connecting corrugated synthetic, resin pipes  1 A and  1 B of the present invention.  FIGS. 1 to 4  show a first embodiment,  FIGS. 5 and 6  show a second embodiment,  FIGS. 7 and 8  show a third embodiment, and  FIGS. 11 to 16  show a fourth embodiment of the present invention. The drawings include corrugated synthetic resin pipes  1 A,  1 B, and  1 C, a pipe wall  2 , an insert end  3 , and a socket  4 . 
     As shown in  FIGS. 1 and 2 , the connection structure S for connecting corrugated synthetic resin pipes of the present invention allows two corrugated synthetic resin pipes  1 A and  1 B each including the pipe wall  2  having a spirally corrugated shape to be connected to each other at their ends. In the present embodiment, the corrugated synthetic resin pipes  1 A and  1 B have the same structure: each pipe has an insert end  3  at one end  10  (left end in  FIG. 1 ), and a socket  4  at the other end  11  (right end in  FIG. 1 ). The connection structure of the present invention, however, is not limited to this example but the facing ends of the pipes include the insert end  3  and the socket  4  while the other ends do not include the insert end and the socket  4 . 
     First, a first embodiment will be described based on  FIGS. 1 to 4 . 
     The corrugated synthetic resin pipes  1 A and  1 B include the spirally corrugated pipe wall  2 , and are provided at the one end  10  (left end in  FIG. 1 ) with the cylindrical insert end  3 , and at the other end  11  (right end in  FIG. 1 ) with the socket  4  as shown in  FIG. 2 . The insert end  3  is formed by adhering a synthetic resin layer to the outer surface of the one end  10  in such a manner as to fill corrugated recesses  2   a . The socket  4  is formed by adhering synthetic resin to the outer surface of the other end  11  and cylindrically extending the resin outwardly in the axial direction (rightward in  FIGS. 1 and 2 ). 
     As shown in  FIG. 3A , the pipe wall  2  of each pipe has a series of waves with peaks and valleys of substantially triangular, substantially arc-shaped, or trapezoidal, and the portions including the valleys between the peaks form recesses  2   a . In the present embodiment, the pipe wall  2  includes a body  20  made of synthetic resin. The body  20  has a substantially flat inner surface and an outer periphery having reinforcing projections  21  spirally arranged thereon. The reinforcing projections  21  are made of a resin molding (for example, coated steel) containing steel  22  and are substantially triangular or substantially arc-shaped. The body  20  and the reinforcing projections  21  forming the peaks can be efficiently integrated with each other as follows. The partial molding of the body  20  is melt extruded and spirally wound around the axis of rotation so as to be sequentially welded. At the same time, the reinforcing projections  21  are spirally fed onto the partial molding. 
     The reinforcing projections  21  forming the peaks may not contain the steel  22  and may be formed of only a resin layer. The shape of the peaks and valleys is not particularly limited; it may be substantially V-shaped, substantially rectangular U-shaped, substantially circular, substantially oval, substantially square, polygonal, irregular, or other shaped. The body  20  is extended from the valleys to the inner periphery side of the peaks so as to make the pipe inner surface flat in the present embodiment. Alternatively, however, the body  20  may be omitted and the reinforcing projections  21  may be connected to each other so that the inner surface of each pipe is also spirally corrugated with peaks and valleys. 
     It is also preferable to provide a concave depression  23  at the top of each peak as shown in  FIG. 3B . The concave depressions  23  disperse the pressure (for example, earth pressure) applied on the peaks, thereby improving not only the strength and rigidity of the peaks, but also the pressure resistance of the entire pipe wall  2 . The presence of the concave depressions  23  often causes fluid leakage in the conventional pipe connection structure; however, the connection structure of the present invention causes no leakage regardless of the presence of the concave depressions  23 . The example of  FIG. 3B  further includes an outer surface layer  24  adhered along the outer surface of the substantially M-shaped reinforcing projections  21  made of coated steel. 
     Examples of the synthetic resin material used for the peaks and valleys of the pipe wall  2 , more specifically, for the body  20 , the reinforcing projections  21 , and the outer surface layer  24  include polyolefin such as polyethylene and polypropylene, vinyl chloride, synthetic rubber, and flexible resin. 
     As shown in  FIG. 2 , the insert end  3  at the one end  10  of each of the corrugated synthetic resin pipes  1 A and  1 B is formed by adhering a synthetic resin layer  5  to the outer surface of the one end  10  in such a manner as to fill at least the corrugated recesses  2   a . Thus, the insert end  3  is cylindrically shaped having a substantially flat outer surface in the axial direction so as to be close contact with the inner circumference surface of the socket  4 , which will be described later. The synthetic resin layer  5  is formed by enclosing the one end  10  with a forming die, injecting synthetic resin material thereinto, and curing the resin. In the present invention, however, the synthetic resin layer  5  can be separately molded, attached to the end  10 , and integrally thermally fused thereto, or can be adhered by other methods. 
     The insert end  3  can alternatively have a small diameter than the pipe wall  2 . To achieve this structure, the one end  10  is press-deformed in the diameter-reducing direction to crush the reinforcing projections  21  in such a manner that the recesses  2   a  have a predetermined depth, and then the synthetic resin layer  5  is adhered thereon. This also allows a reduction in the size of the socket  4  at the other end  11 , and hence, the size of the entire connected area including the insert end  3  and the socket  4 . 
     The synthetic resin material used for the synthetic resin layer  5  can be either foamed or non-foamed. For example, it is possible to use olefin resin such as polyethylene resin and polypropylene resin. Examples of the foamed synthetic resin include polystyrene foam, polyethylene foam, rigid polyurethane foam, flexible polyurethane foam, rigid vinyl chloride foam, urea-formaldehyde foam, phenolic foam, acrylic foam, and cellulose acetate foam. The synthetic resin layer  5  is adhered in such a manner that the peaks at the end  10  are completely embedded in the present embodiment. Alternatively, the peaks may be partially exposed to a degree to maintain a substantially flat surface, or in the contrary, the synthetic resin layer  5  can be adhered thick enough to make the outer surface outside the tops of the peaks. 
     As shown in  FIG. 2 , the socket  4  includes a pipe material  7  having a larger diameter than the corrugated synthetic resin pipe  1 B. The pipe material  7  is connected to the other end  11  using a fixing screw  9  in such a manner as to project coaxially from the outer surface of the other end  11  outwardly in the axial direction. There is also provided a synthetic resin layer  8 , which is adhered to fill the gaps between the pipe material  7  and the corrugated synthetic resin pipe  1 B in such a manner that the pipe material  7  is embedded completely. The inner circumference surface of the cylindrical portion of the pipe material  7  projecting outwardly in the axial direction is substantially flat in the axial direction so as to function as an abutment surface  40  along which the insert end  3  is inserted. The fixing screw  9  is used to fix the positions of the pipe material  7  and the other end  11  until the synthetic resin layer  8  is adhered. The fixing screw  9  is preferably fixed in the peaks without penetrating the pipe wall  2 , but can be omitted by instead using another member for temporary fixation. 
     In the same manner as the insert end  3 , the socket  4  is formed by enclosing the other end  11  and the pipe material  7  with a forming die, injecting synthetic resin material thereinto, and curing the resin. Alternatively, however, the synthetic resin layer  8  including the pipe material  7  can be separately molded, attached to the end  11 , and integrally thermally fused thereto, or can be adhered by other methods. The synthetic resin layer  8  can be made of the same synthetic resin material as used in the insert end  3 . 
     Similar to the corrugated synthetic resin pipes  1 A and  1 B, the pipe material  7  is composed of a pipe portion having a series of waves with peaks and valleys to significantly increase the strength of the socket  4 . The peaks and valleys are substantially triangular, substantially arc-shaped, or trapezoidal. The pipe portion used for the pipe material  7  has the same wave structure as the corrugated synthetic resin pipes  1 A and  1 B in the present embodiment; however, the present invention is not limited to this structure. For example, the pipe material  7  having corrugation peaks with the concave depressions  23  at their tops as shown in  FIG. 3B  can be used for the corrugated synthetic resin pipe  1 B having the pipe wall  2  of  FIG. 3A . Conversely, the pipe material  7  having corrugation peaks with no concave depressions at their tops as shown in  FIG. 3A  can be used for the corrugated synthetic resin pipe  1 B having the pipe wall  2  of  FIG. 3B . It is also possible to use a pipe material  7 A, which is composed of a straight pipe portion as shown in  FIG. 4 . In the example of  FIG. 4 , the inner circumference surface of the straight pipe portion is provided with engaging protrusions  70 , which are engaged with the corrugation peaks of the pipe wall  2  so as to function as retainers, thereby improving the strength of the socket  4 . 
     The pipe materials  7  ( 7 A) are mainly used to maintain the strength of the cylindrically portion of the socket  4  that projects outwardly so as to receive the insert end  3 . However, it is possible to omit the insert member such as the pipe material  7  and to form the socket  4  having only the synthetic resin layer  8  by selecting its size and material that can maintain the strength of the cylindrically portion. The pipe materials  7  ( 7 A) and the outer peripheral surface of the pipe wall  2  are firmly integrated together with the synthetic resin layer  8  disposed therebetween. The synthetic resin layer  8  as a component of the socket  4  may be reinforced by embedding a reinforcing material such as reinforced fiber or net therein if necessary. 
     Both the insert end  3  and the socket  4  are formed substantially flat in the axial direction in the present embodiment; however, the present invention is not limited to such shape. For example, the insert end  3  may be tapered toward the open end, and the socket  4  may have an inner circumference surface which is tapered substantially at the same angle and substantially parallel to the insert end  3 . As another example, either the outer diameter of the insert end or the inner diameter of the socket may be curved in the axial direction. 
     Between the insert end  3  and the socket  4 , there is provided an O-ring  6  as a seal member as shown in  FIG. 2 . More specifically, the insert end  3  is provided on its outer surface with an annular groove  50  for accommodating the O-ring  6 , so that the pipes can be connected to each other with the O-ring  6  in the annular groove  50 . The annular groove  50  in which the O-ring  6  is accommodated is formed as a notch at the tip edge of the insert end  3  in the present embodiment, but may alternatively be formed at the proximal edge opposite to the insert end  3 , at a position between the tip edge and the proximal edge, or on the socket  4  side. The shape and structure of the seal member such as the O-ring  6  is not limited as long as sealing is ensured between the insert end  3  and the socket  4 . Thus, seal members of various shapes and structures can be applied at a proper position. Instead of separately providing the O-ring  6 , an annular protrusion as a seal member can be formed integrally with the insert end  3  or the socket  4 . 
     A second embodiment will be described as follows based on  FIGS. 5 and 6 . 
     In the present embodiment, the synthetic resin layer  8  is adhered in such a manner that the pipe material  7  as a component of the socket  4  is partially exposed. The pipe material  7  is embedded in the synthetic resin layer  8  only on the tip side, which requires strength and on the proximal side, which is important in terms of the integration between the pipe material  7  and the pipe wall  2 , and is exposed at the remaining portion. Exposing the pipe material  7  in this manner can reduce the weight and material cost. When the pipe material  7  has the same outer structure as the pipe wall  2  as in the present embodiment, the exposed portion of the socket  4  has the same appearance as the pipe wall  2 , thereby improving unity between the joint and the entire pipe, and hence, their appearance. Other configurations and modified examples are the same as those of the first embodiment described above. Therefore the same components are denoted by the same reference numerals, and thus a detailed description thereof will be omitted. 
     A third embodiment will be described as follows based on  FIGS. 7 and 8 . 
     In the present embodiment, instead of the pipe material  7 , the socket  4  contains reinforcing fiber  7 B in its synthetic resin portion (synthetic resin layer  8 ). The reinforcing fiber  7 B is embedded in the form of a woven cloth, a nonwoven cloth, or a resin molding in the present embodiment. This structure significantly reduces the weight and cost, while maintaining the strength, as compared with the example using the pipe material  7 . The reinforcing projections  21  of each pipe have the concave depressions  23  at the tops of the peaks as shown in  FIG. 3B  in the present embodiment. Needless to say, however, the concave depressions  23  can be applied to various corrugated synthetic resin pipes in the same manner as in the first embodiment. 
     The reinforcing fiber is preferably glass fiber. When the socket  4  is formed of synthetic resin, the woven cloth, nonwoven cloth or resin molding used as the reinforcing fiber  7 B can be set in a forming die so as to embed and mold the socket  4 . Alternatively, the socket  4  can be molded in two batches: one for inner side and the other for the outer side. When the first molding of the inner side is over, the woven cloth, nonwoven cloth, or resin molding as the reinforcing fiber  7 B is adhered to the outer surface, and then, the second molding is applied thereon so as to achieve embedding and molding. 
     The woven cloth, nonwoven cloth or resin molding as the reinforcing fiber  7 B can be applied around nearly the entire perimeter of the socket  4 . Alternatively, one or more woven cloths, nonwoven cloths or resin moldings can be applied to only a part of the perimeter. The resin molding can be formed in a sheet-like or cylindrical form. In term of adhesion, the resin used for the resin molding is preferably the same as the resin used for synthetic resin layer  8  which is a component of the socket  4 . It is also possible that the woven cloth, nonwoven cloth, or resin molding as the reinforcing fiber  7 B can be pasted on the outer surface of the socket  4 . 
       FIG. 8  shows an example in which the reinforcing fiber  7 B is contained not only in the synthetic resin layer  8  of the socket  4  but also in the synthetic resin layer  5  of the insert end  3 . Similar to the socket  4 , the woven cloth, nonwoven cloth, or resin molding used as the reinforcing fiber  7 B can be set in a forming die so as to embed and mold the insert end  3 . It goes without saying that the insert end  3  can contain the reinforcing fiber  7 B as in the present embodiment, and the socket  4  can be provided with the pipe material  7  of the first embodiment instead of the reinforcing fiber  7 B, or can be added with no reinforcing member. The socket  4  or the insert end  3  contains the reinforcing fiber  7 B in the form of a woven cloth, nonwoven cloth, or resin molding in the present embodiment. It is also preferable, as shown in  FIG. 9 , to add reinforcing fiber chips  7 C (short cut fiber) to the synthetic resin used for the insert end  3  and the socket  4  in such a manner as to be contained in the entire synthetic resin portion, thereby improving the strength of the entire insert end  3  or the entire socket  4 . It is also preferable, as shown in  FIG. 10 , to combine the reinforcing fiber chips  7 C with the reinforcing fiber  7 B in the form of the woven cloth, nonwoven cloth, or resin molding so as to further improve the strength. Other configurations and modified examples (including the position of the O-ring) are the same as those of the first embodiment described above. Therefore, the same components are denoted by the same reference numerals, and thus a detailed description thereof will be omitted. 
     A fourth embodiment will be described as follows based on  FIGS. 11 to 16 . 
     The corrugated synthetic resin pipe  1 C of the present embodiment includes the spirally corrugated pipe wall  2 , and are provided at one end (left end in  FIGS. 11 and 12 ) with the cylindrical insert end  3 , and at the other end  102   a  (right end in  FIGS. 11 and 12 ) with the socket  4  as shown in  FIGS. 11 and 12 . The insert end  3  is formed by adhering the synthetic resin layer  5  to the outer surface of the one end in such a manner as to fill at least the corrugated recesses. The socket  4  is formed by adhering the synthetic resin layer  8  to the outer surface of the other end and cylindrically extending the resin outwardly in the axial direction. When a plurality of corrugated synthetic resin pipes  1 C are connected to each other, the insert end  3  of a first corrugated synthetic resin pipe  1 C (right side in  FIGS. 11 and 12 ) is inserted into the socket  4  of a second corrugated synthetic resin pipe  1 C (left side in  FIGS. 11 and 12 ). In the present invention, the socket  4  includes the pipe material  7  having a larger diameter than the corrugated synthetic resin pipe  1 C and projecting coaxially from the outer surface of the other end  102   a  outwardly in the axial direction as shown in the longitudinal sectional view of  FIG. 13 . The synthetic resin material for the synthetic resin layer  8  is injected into at least the gaps between the pipe material  7  and the corrugated synthetic resin pipe  1 C. 
     As shown in  FIG. 13 , the pipe wall  2  has a series of waves with peaks and valleys of substantially triangular, substantially arc-shaped, or trapezoidal, the portions including the valleys between the peaks form recesses. In the present embodiment, the body  20  of synthetic resin has a substantially flat inner surface and an outer periphery having reinforcing projections  21  spirally arranged thereon. The reinforcing projections  21  are made of a resin molding (for example, coated steel) containing steel  22  and are substantially triangular or substantially arc-shaped. The reinforcing projections  21  may not contain the steel  22  and may be formed of only a resin layer. The shape of the peaks and valleys is not particularly limited; it may be substantially V-shaped, substantially rectangular U-shaped, substantially circular, substantially oval, substantially square, polygonal, irregular, or other shaped. The body  20  is extended from the valleys to the inner periphery side of the peaks so as to make the pipe inner surface flat in the present embodiment. Alternatively, however, the body  20  may be omitted and the reinforcing projections  21  may be connected to each other so that the inner surface of each pipe is also spirally corrugated with peaks and valleys. It is also preferable to provide the concave depression  23  at the top of each peak of the steel  22 . The concave depressions  23  disperse the pressure (for example, earth pressure) applied on the peaks, thereby improving not only the strength and rigidity of the peaks, but also the pressure resistance of the entire pipe wall  2 . The present embodiment further includes the outer surface layer  24  adhered along the outer surface of the steel  22 . Examples of the synthetic resin material used for the peaks and valleys of the pipe wall  2 , more specifically, for the body  20  and the outer surface layer  24  include polyolefin such as polyethylene and polypropylene, vinyl chloride, synthetic rubber, and flexible resin. 
     As shown in  FIGS. 12 and 13 , the insert end  3  at the one end is formed by adhering the synthetic resin layer  5  to the outer surface of the one end in such a manner as to fill at least the corrugated recesses. Thus, the insert end  3  is cylindrically shaped having a substantially flat outer surface in the axial direction so as to be close contact with the inner circumference surface of the socket  4  of the other end. The synthetic resin layer  5  as a component of the insert end  3  is formed by enclosing the one end with a forming die, injecting synthetic resin material thereinto, and curing the resin in the present embodiment. However, the synthetic resin layer  5  can be adhered by other methods. The synthetic resin material used for the synthetic resin layer  5  can be either foamed or non-foamed. For example, it is possible to use olefin resin such as polyethylene resin and polypropylene resin. Examples of the foamed synthetic resin include polystyrene foam, polyethylene foam, rigid polyurethane foam, flexible polyurethane foam, rigid vinyl chloride foam, urea-formaldehyde foam, phenolic foam, acrylic foam, and cellulose acetate foam. 
     The socket  4  at the other end includes the pipe material  7  having a larger diameter than the corrugated synthetic resin pipe  1 C and projecting coaxially from the outer surface of the other end  102   a  outwardly in the axial direction as shown in the longitudinal sectional view of  FIG. 13 . The synthetic resin material for the synthetic resin layer  8  is injected into at least the gaps between the pipe material  7  and the corrugated synthetic resin pipe  1 C. The inner circumference surface of the cylindrical portion of the pipe material  7  projecting outwardly in the axial direction is substantially flat in the axial direction so as to function as the abutment surface  40  along which the insert end  3  is inserted. The synthetic resin layer  8  of the socket  4  can be made of the same synthetic resin material as used in the insert end  3 . 
     Both the insert end  3  and the socket  4  are formed substantially flat in the axial direction in the present embodiment; however, the present invention is not limited to such shape. For example, the insert end  3  may be tapered toward the open end, and the socket  4  may have an inner circumference surface which is tapered substantially at the same angle and substantially parallel to the insert end  3 . As another example, either the outer diameter of the insert end or the inner diameter of the socket may be curved in the axial direction. It is also preferable that the abutment surface  40  of the socket  4  is reverse-tapered toward the opening outside from inside so as to gradually reduce the diameter, thereby making the O-ring  6  of the insert end  3  watertight and airtight. The socket  4  is provided at its opening with a stepped taper  42 , which prevents the O-ring  6  from being hooked by the opening and falling off when the insert end  3  is inserted. 
     Similar to the corrugated synthetic resin pipe  1 C, the pipe material  7  in the socket  4  is composed of a pipe portion having a series of waves with peaks and valleys of substantially triangular, substantially arc-shaped, or trapezoidal. The pipe material  7  significantly improves the strength of the socket  4 . The present embodiment includes a pipe material (without the body  20  on the inner periphery side) having the same wave structure as the corrugated synthetic resin pipe  1 C and a pipe wall  71  formed in a spirally corrugated shape. The same components are denoted by the same reference numerals, and thus a detailed description thereof will be omitted. However, the present invention is not limited to this type of the pipe material. A preferable modified example of the pipe material  7  has the body  20  on the inner periphery side as shown in  FIG. 15 . The pipe material  7  and the outer peripheral surface of the pipe wall  2  are firmly integrated together by the synthetic resin layer  8  disposed therebetween. 
     The synthetic resin layer  8  is adhered in such a manner that the pipe material  7  is partially exposed. The pipe material  7  is embedded in the synthetic resin layer  8  only on the tip side, which requires strength and on the proximal side, which is important in terms of the integration between the pipe material  7  and the pipe wall  2 , and is exposed at the remaining portion. Exposing the pipe material  7  in this manner can reduce the weight and material cost. When the pipe material  7  has the same outer structure as the pipe wall  2  as in the present embodiment, the exposed portion of the socket  4  has the same appearance as the pipe wall  2 , thereby improving unity between the joint and the entire pipe, and hence, their appearance. 
     Between the insert end  3  and the socket  4 , there is provided the O-ring  6  as a seal member as shown in  FIG. 13 . More specifically, the insert end  3  is provided on its outer surface with the annular groove  50  for accommodating the O-ring  6 , so that the pipes can be connected to each other with the O-ring  6  in the annular groove  50 . The annular groove  50  in which the O-ring  6  is accommodated is formed as a notch at the tip edge of the insert end  3  in the present embodiment, but may alternatively be formed at the proximal edge opposite to the insert end  3 , at a position between the tip edge and the proximal edge, or on the socket  4  side. The shape and structure of the seal member such as the O-ring  6  is not limited as long as sealing is ensured between the insert end  3  and the socket  4 . Thus, seal members of various shapes and structures can be applied at a proper position. Instead of separately providing the O-ring  6 , an annular protrusion as a seal member can be formed integrally with the insert end  3  or the socket  4 . It is possible to coat the outer surface of the pipe  1 C including the insert end  3  and the socket  4  at both ends with a coating agent for improving resistance to water, weather, and chemicals. 
     A method for manufacturing the corrugated synthetic resin pipe  1 C will be described as follows based on  FIGS. 14 and 16 . 
     The manufacturing procedure of the corrugated synthetic resin pipe  1 C includes Steps S 1  to S 4  as shown in  FIG. 16 . In Step S 1 , the pipe wall  2  of the corrugated synthetic resin pipe  1 C is formed. In Step S 2 , the pipe material  7  having a larger diameter than the corrugated synthetic resin pipe  1 C is formed coaxially therewith on the other end  102   a  of the corrugated synthetic resin pipe  1 C formed in Step  1 . In Step S 3 , the pipe material  7  thus formed is sealed at the inner and outer ends in the axial direction using sealing chucks  60  and  61 , respectively. In Step S 4 , synthetic resin material for forming the synthetic resin layer  8  is injected into the gaps between the pipe material  7  sealed using the sealing chucks and the pipe wall  2  of the pipe  1 C. 
     The formation of the pipe wall  2  in Step S 1  can be performed in the same manner as in the conventional method. The steel  22  continuously fed is deformation-processed to have an M-shaped cross section using processing rollers  92  and then discharged spirally. At the same time as this, an outer wound tape (outer surface layer  24 ) and an inner wound tape (body  20 ) are continuously discharged spirally from mouth rings  81  and  82 , respectively so as to be adhered to the outer and inner surfaces, respectively, of the steel  22 . As a result, the steel  22 , the outer surface layer  24  and the body  20  are integrated in the axial direction to form the pipe wall  2 . In the present embodiment, the formation of the pipe material  7  at the end of the pipe wall  2  is not performed after the pipe wall  2  is completed, but is performed in Step S 2  immediately after the pipe wall  2  is formed in Step S 1  so as to efficiently form the socket  4 . 
     Similar to the formation of the pipe wall  2 , in the formation of the pipe material  7  in Step S 2 , the steel  22  continuously fed is deformation-processed to have an M-shaped cross section using processing rollers  93 , and then discharged spirally. At the same time as this, an outer wound tape (outer surface layer  24 ) is continuously discharged spirally from a mouth ring  83  so as to be adhered to the outer surface of the steel  22 . In this case, no inner wound tape is used. As a result, the steel  22  and the outer surface layer  24  are integrated in the axial direction to form the pipe material  7 . The pipe material  7  thus formed is supported from the radial outside by a plurality of guide rollers  91  functioning as guides so as to be supported coaxially with the pipe wall  2 . 
     In Step S 3 , the sealing chucks  60  and  61  are attached to both ends of the pipe material  7  formed coaxially with the pipe wall  2  so as to seal the space between the pipe material  7  and the pipe wall  2 . The sealed space is formed by setting an unillustrated mold for the abutment surface  40  of the socket  4  on the inner circumference surface of the pipe material  7  projecting outer than the pipe wall  2 . 
     In Step S 4 , the sealed space is filled with the synthetic resin material for the synthetic resin layer  8 . The synthetic resin material is injected through an inlet  62  which is communicated with the sealing chuck  60  in the axial direction in the present embodiment, but can be injected differently. For example, the sealing chuck  61  or the mold for the abutment surface  40  may have an inlet. 
     It goes without saying that the present invention is not limited to the embodiments thus described, and various modifications could be made within the scope of the present invention.