GB2114255A - Lining pipes - Google Patents

Abstract

A reformed underground pipe comprises an outworn underground pipe and a lining layer formed with use of the pipe as a frame and having strength to withstand an external pressure of at least about 0.1 kg/cm<2> G per meter of the depth of installation of the pipe underground. The lining layer for reforming the pipe is formed from a liquid resin composition eg an epoxy which is curable at ambient temperature and has a viscosity of 20,000 to 200,000 cps and a thixotropic index of at least 3. When the outworn pipe has a greatly bent portion, the resin composition is applied to the inner surface of the pipe with use of a pig comprising two members interconnected by a flexible linear member.

Description

SPECIFICATION Reformed underground pipes and method of forming same The present invention relates to reformed underground pipes for supplying gases, water, etc., a method of forming the same and a method of forming reformed pipes with use of a special moving body.

Outworn underground pipes are reformed usually by various methods, for example, by sealing off leaks or lining the pipe with a thin layer. These methods are measures for remedying small defects chiefly resulting from the corrosion of the inner surface of the pipe caused by the fluid through the pipe as when a small clearance occurs at pipe joints or pinhoies are formed in the pipe wall. Accordingly they are useful insofar as the pipe wall retains its substantial strength without entailing any problem, in other words, as far as the pipe wall remains as contemplated.

Such methods nevertheless fail to give reforming effect when external corrosion due to groundwater, underground stray current or the like develops to form a large hole in the pipe wall or wear away the pipe wall over a large area, When the external corrosion develops into a large hole or opening in the wall of a pipe reformed with a thin lining, the groundwater pressure and earth pressure act directliy on the thin lining, breaking the lining and permitting invasion of water and soil into the pipe to render the pipe no longer serviceable for the transport of fluid.

To cope with such serious external corrosion, it is known to insert a new pipe of polyethylene or like resin into the outworn pipe.

However, the insertion method has the following problems because a new pipe of predetermined dimensions is forced into the pipe from its one end (while being drawn in at the other end thereof when needed).

(1) Since every time a unit segment of new pipe having a relatively short length of about 10 m has been forced in, another unit segment is thermally joined to the segment, the method requires a very inefficient procedure.

(2) The new pipe, which is inserted into the outworn pipe from its one end, encounters exceedingly great resistance, so that the new pipe used has an outside diameter which is smaller than the inside diameter of the outworn pipe. This consider ablyireduces the effective sectional area of the pipe to result in a lower transport capacity.

(3) The method is not applicable as it is when the pipe has a bend or branch. The soil adjoining the bent or branched portion must be removed by excavation first, and the portion must be cut or separated and worked on separately. The procedure is in no way simple.

The present invention has been accomplished in view of the foregoing situation.

A first object of the present invention is to reform outworn underground pipes even with external corrosion which has developed therein seriously and to provide reformed pipes which are satisfactory in characteristics inclusive of transport capacity.

A second object of the invention is to provide a method of forming such reformed underground pipes efficiently.

A third object of the invention is to provide a method of forming such reformed underground pipes with use of a special body movable through pipes.

The reformed underground pipe according to a first feature of the invention is characterized in that the pipe comprises an outworn underground pipe and a lining layer formed by applying a liquid resin composition in the form of a tube of uniform or approximately uniform wall thickness to the inner surface of the outworn pipe serving as a frame and curing the resin composition, the lining layer having strength to withstand an external pressure of at least about 0.1 kg/cm2 G per meter of the depth at which the pipe is laid underground.

The chief external pressures acting on an underground pipe are earth pressure and groundwater pressure. Since a pipe which has been so worn out as to develop external corrosion is laid underground for a prolonged period of time, the soil adjoining the pipe has been consolidated usually to an equilib- rium, while the remaining pipe wall restrains the adjoining soil. Accordingly the earth pressure gives rise to almost no problem except at the portion of the pipe which is subjected directly to wheel load.

Thus the groundwater pressure is the main external pressure factor. This pressure is usually about 0.1 kg/cm2 G per meter of the depth.

In view of the above factor, the lining layer of the reformed underground pipe of this invention has strength capable of withstanding an external pressure of at least about 0.1 kg/cm2 G per meter of the depth at which the pipe is laid underground. While it is likely that the wall of the outworn pipe outside the lining layer will have a large hole or be worn away over a larger area due to external corrosion to subject the layer directly to the groundwater pressure, the layer has sufficient strength to withstand the pressure. Thus the lining layer provides a satisfactory seal for the fluid channel and sufficient strength.

Because the lining layerfor reforming is formed by applying a liquid resin composition to the inner surface of the outworn pipe to a required thickness and curing the composition, the layer results in only a small reduction in the effective cross sectional area and a minimized reduction in the transport capacity.

According to a second feature of the present invention, there is provided a method of forming a reformed underground pipe characterized by using a liquid resin composition which is curable at ambient temperature and has a viscosity of about 20,000 to 200,000 cps and a thixotropic index of at least about 3. The resin composition is applied in the form of a tube to the inner surface of an outworn underground pipe by the pushing action of a moving body and is cured to afford a lining layer having strength to withstand an external pressure of at least about 0.1 kg/cm2 G per meter of the depth at which the pipe is laid underground.

When less than 20,000 cps in viscosity, the resin composition sags to make it difficult to obtain a thick layer, whereas if the viscosity exceeds 200,000 cps, the composition is too resistant to the running body, presenting difficulty in lining the pipe. Further if the resin composition is less than 3 in thixotropic index, i.e. p21p20 wherein 2 is the viscosity thereof at a shearing speed of 2 r.p.m. and 20 is the viscosity at 20 r.p.m., the lining layer after the passage of the running body has too low a sol-to-gel transition velocity and therefore sags or deforms before curing, consequently failing to have a uniform thickness. Thermosetting resins, which become less viscous when heated, are not desirable to use for the lining composition.

Because the liquid resin composition used for the present method is adjusted to the properties stated above, the composition permits the running body to run smoothly for an efficient lining operation and will not sag or deform when applied in the form of a tubular layer, forming a lining layer reliably which is uniform in thickness as specified.

However, when conventional running bodies are caused to run through outworn pipes, the body is unable to run therethrough if the pipe has a bend or branch. The present invention also includes means for overcoming this problem. More specifically the present method employs a moving body A compris ing a plurality of members each of which is symmet rical with respect to a plane perpendicular to the direction of its movement and which are congruent or approximately congruent with one another and interconnected by a flexible linear member. A fluid pressure is applied to the back side of the moving body A as placed in the pipe to thereby move the body along the line of flow through the pipe and cause the body to line the pipe with the resin composition while pushing the composition forward by the body, whereby the above problem is avoided.

Other objects and advantages of the present invention will become apparent from the following description of embodiments given with reference to the accompanying drawings.

Fig. 1 is a sectional view showing a mode of method of forming a reformed pipe; Figs. 2A and 2B are sectional views for illustrating a problem heretofore encountered with existing pipes having a bend; Fig. 3 is a sectional view showing another mode of method of forming a reformed pipe; Figs. 4A and 4B are sectional views showing how a moving body runs through a T-shaped bend when the method of Fig. 3 is practiced; Fig. 5 is a sectional view similarly showing how the moving body runs through a different T-shaped bend; Figs. 6A to 6E are side elevations showing various moving bodies; and Fig. 7 is a sectional view showing a spherical moving body.

The liquid resin composition curable at ambient temperature is preferably of the moisture curable type or the two-component type containing a curing agent. Especially preferable is a liquid resin composition which is curable at ambient temperature and which has a viscosity of about 20,000 to 200,000 cps, more preferably about 30,000 cps, and a thixotropic index of at least about 3. An example of such composition is of the two-component type comprising an epoxy resin as the main component and a curing agent which are mixed together immediately before application. This composition forms a flexible resin layer.

The epoxy resin is prepared by the condensation polymerization of bisphenol A and epichlorohydrin as shown below.

bisphenol A epichlorohydrin

When an amine as the curing agent is added to epoxy resin (the main component), the following reactions are promoted for curing.

(1) Bonding reaction between epoxy groups by the amine.

(2) Bonding reaction of epoxy groups with an aliphatic or aromatic compound having hydroxyl.

(3) Cross-linking reaction of epoxy groups by the amine.

The resin composition forms a lining layer which is characterized in that it has shape retentivity and high stretchability and is to some extent adhesive to the inner surface of the pipe. The composition is therefore useful for fulfilling the objects of the invention.

The resin composition has further incorporated therein a thixotropic agent. Examples of useful thixotropic agents are organic agents such as low molecular-weight polyethylene and inorganic agents such as bentonite, silicon oxide and oxide and asbestos.

Preferably the lining layer has a thickness of about 11100 to 1110 of the diameter of outworn pipes. In practice, the thickness ranges from about 1 mm to 10 mm. For example, the thickness is about 2 mm for 2-inch pipes.

Under the condition involving an abnormal earth pressure due to wheel load, etc., the lining layer may be adapted to have an elongation of about 10 to 100%, preferably about 20%. The layer will then undergo elastic deformation to absorb and mitigate the abnormal earth pressure, so that the leakage of fluid resulting, for example, from the rupture of the layer is avoidable. In this case, it is desired to take a specified safety measure upon detecting a reduction in the rate of flow through the pipe due to the elastic deformation.

With reference to Fig. la amode of practicing the present method will be described. First, a running body 2 is placed into an outworn pipe 1 from one open end thereof, and a liquid resin composition a which is curable at ambient temperature is also placed into the pipe 1 in front of the body 2 with respect to the direction of its movement. Subse quently a fluid pressure is applied to the body 2 at the above-mentioned one end to cause the body to run through the pipe 1.

Although not shown, a wire or like cable is usable instead of the fluid pressure. The cable is inserted through the pipe 1, the resin composition a is placed into the pipe 1, the running body 2 is placed in as attached to the cable and the cable is pulled at the other open end of the pipe 1, whereby the body 2 is caused to run.

In either case, the pipe 1 is lined in the form of a tube with the composition a undergoing gel-to-sol transition by being pushed by the running body 2.

The tubular lining is cured at ambient temperature while conversely undergoing sol-to-gel transition by being allowed to stand after the passage of the running body 2, whereby a lining layer 11 is formed.

If the existing wornout pipe has bends as shown in Figs. 2A and 2B, the moving body stops at the bend and is unable to move further ahead. For example, when a body 02 is caused to move through a pipe 01 having an L-shaped bend 01R,the body moving forward will be impeded upon striking against the inner surface 01A of the bend ahead, if it is in the shape of a bullet as illustrated in Fig. 2A. In the case of a T-shaped bend 01 R which is closed with a plug as illustrated in Fig. 2B, a moving body 02 becomes no longer movable upon dashing into the plugged space 04 or upon striking against an inner portion of the pipe if not dashing in.A spherical body, on the other hand, will turn aside by rolling at the bend of Fig. 2A and move forward without remaining at the bend, but the spherical body similarly becomes impeded or is prevented from moving at a T-shaped bend such as the one shown in Fig. 2.

The method illustrated in Fig. 3 for performing work in the interior of pipes is provided to overcome the above problem. A pipe 1 is prepared with its opposite ends open for working. First, a moving body A is inserted into the pipe 1 at one open end.

The pneumatic pressure produced by a blower 5 and supplied via a pressure adjusting device 6 and a stop valve 7 is appled to the moving body A as a back pressure to cause the body A to move through the pipe 1 toward the other open end thereof. The moving body A comprises two members 2, 2' each of which is symmetrical with respect to a plane perpendicular to the direction of its movement and which are congruent or approximately congruent with each other. Figs. 6A to 6E show examples of such members 2, 2' which are spherical, regular hexagonal, elliptical, oval or irregular hexagonal.

(Although the illustrated moving body comprises two members, three or more members may consti tute such a moving body.) These members 2, 2' are interconnected by a flexible linear member 3, such as a string of fabric, wire or spring.

Through a bore 8 formed in the pipe 1 close to the above-mentioned one open end, a lining composi tion a of high viscosity is injected into the pipe 1 ahead of the moving body A thus constructed. The blower 5 is then operated to cause a pneumatic back pressure to move the body A along the inner surface of the pipe 1, whereby the pipe 1 is lined with the composition a in the form of a continuous tube.

The moving body A useful for the method of this invention passes through T-shaped plugged bends in the following manner. Of the two members 2, 2' moving forward in the front-to-rear relation shown in Fig. 4A, the preceding member 2 first enters a plugged space 4 and comes to a halt at or near the inlet of the space to close the space. Since the T-shaped bend is approximately L-shaped, the fol lowing member 2' consequently comes into contact with the preceding member 2 at a stop and moves forward into another pipe section as seen in Fig. 4B.

Subsequently the following member 2' precedes the member 2, pulling the member 2 at a stop through the linear member 3, with the result that the two members pass through the bend in a reversed front-to-rear relation indicated in phantom lines in Fig. 4B. Since the two members 2, 2' are congruent or approximately congruent with each other and are each symmetrical with respect to a plane perpen dicularto the direction of its movement, the reversed front-to-rear relation produces hardly any adverse effect on the subsequent movement of the body per se and work within the pipe.

Fig. 5 shows a T-shaped bend having an elongated space 4 closed with a plug. When the preceding one 2 of the two members 2, 2' enters the space 4, the air in the space 4 is compressed to give an increased pressure, consequently acting as an air damper, whereby the preceding member 2 is stopped without moving deep into the space 4. Accordingly the two members 2, 2' behave substantially in the same manner as above and pass through the bend with their front-to-rear realtion reversed without blocking.

In this case, it is desirable that the length of the linear member 3 be slightly larger than the distance L of entry of the preceding member 2 into the space 4.

It is especially preferable that the moving body have the structure shown in Fig. 7 on an enlarged scale. The two members 2, 2' of the moving body shown are made of an elastic material. The flexible linear member 3 has such a length that the face-to face distance between the two members is about 1/2 of the diameter of the pipe to be worked on. It is suitable to use a natural or synthetic rubber, espe cially foam rubber, as the elastic material, because when the two members made of such material are subjected to a back pressure of about 1 to 1.2 kg/cm2 G and to the pressure of air confined between the members, these members are stretched radially of the pipe and brought into intimate contact with the inner surface f the pipe.Another reason is that such members run smoothly and are unlikely to locally reduce the thickness of the lining layer beneath the members under gravity. It is preferable to use a stainless steel wire rope as a linear member 3 which has suitable flexibility and strength. Advantageously the rope has a diameter of 1.6 mm for use with 2-to 3-inch pipes or about 1 mm for 1 - to 1 :inch pipes. If the face-to-face distance between the two members is exceedingly larger than 1/2 of the diameter of the pipe to be worked on, e.g. equal to the diameter, or is extremely smaller than the diameter, the members will not turn smoothly at L-shaped orT-shaped bends.We have found that the best result can be achieved when the flexible linear member has the above-mentioned length (i.e. face-to-face distance) and suitable bending rigidity.

Fig. 7 further shows plates 9 for anchoring the linear member 3 in the members 2, 2' and retainers 10 for holding the ends of the member 3 inserted through holes in the plates 9. These plates, ends and retainers are all embedded in the foamed Neoprene rubber of the members 2, 2'.

When practiced for an existing pipe having a leak of unnegligible size, the method described above will entail the objection that the lining composition flowing through the leak to the adjoining soil during lining will be blown out immediately after the passage of the moving body by the body running fluid pressure. The objection can be overcome by maintaining the interior of the pipe 1 at a pressure higher than the pressure for running the body A for lining for a predetermined period of time before lining. The lining composition a then fully flows into the adjoining soil through the leak to consolidate the soil. More specifically this can be done by filling the pipe 1 with the lining composition and maintaining the interior at an increased pressure for a period of time, or by inserting a pair of front and rear moving bodies A, A into one end of the pipe 1 with the lining composition a held therebetween and moving the bodies A, A to the location where the bodies are positioned on the opposite sides of the leak, with the other end of the pipe 1 closed.

Claims (8)

1. A reformed underground pipe characterized in that the pipe comprises an outworn underground pipe (1) and a lining layer (11 ) formed by applying a liquid resin composition (a) in the form of a tube of uniform or approximately uniform wall thickness to the inner surface of the outworn pipe (1 ) serving as a frame and curing the resin composition (a), the lining layer (11 ) having strength to withstand an external pressure of at least about 0.1 kg/cm2 G per meter of the depth at which the pipe is laid underground.

2. A pipe as defined in claim 1 wherein the resin composition (a) is cured to give the lining layer (11) an elongation of about 10 to 100%.

3. A method of forming a reformed underground pipe characterized in that a liquid resin composition (a) curable at ambient temperature and having a viscosity of about 20,000 to 200,000 cps and a thixotropic index of at least about 3 is applied in the form of a tube to the inner surface of an outworn underground pipe (1) by the pushing action of a moving body (2,A) and is cured to form a lining layer (11) having strength to withstand an external pressure of at least about 0.1 kg/cm2 G per meter of the depth at which the pipe is laid underground.

4. A method as defined in claim 3 wherein the pipe (1) is lined with the resin composition (a) to a thickness of about 1/100 to 1/10 of the diameter of the pipe (1).

5. A method as defined in claim 3 or 4 wherein a fluid pressure is applied to the back side of the moving body (A) as placed in the pipe (1) to thereby move the body along the line of flow through the pipe and cause the body to apply the resin composition (a) to the inner surface of the pipe (1), the moving body comprising a plurality of members (2), (2') each symmetrical with respect to a plane perpendicular to the direction of its movement and congruent or approximately congruent with one another, the members being interconnected by a flexible linear member (3).

6. Amethod as defined in claim 5 wherein the moving body A comprises spherical members.

7. A method as defined in claim 5 or 6 wherein the moving body members are made of an elastic material.

8. A method as defined in claim 7 wherein the moving body members are made of foam rubber.