GB2279354A - Method of sealing leaks in underground gas mains and compositions for use therein - Google Patents

Abstract

A method and composition are described for the sealing of leaks in underground gas mains. The composition used is an accelerated anaerobic sealant containing a transition metal compound, e.g. copper naphthenate, as an accelerator. Other components include acrylate-type monomers, peroxide or hydroperoxide free-radical initiators, polymerisation inhibitors and chelating agents.

Description

METHOD OF SEALING LEAKS IN UNDERGROUND GAS MAINS AND COMPOSITIONS FOR USE THEREIN This invention relates to a method of sealing leaks in underground gas mains and sealant compositions for use therein. More particularly, the invention relates to a method and composition for sealing leaks in underground gas mains, particularly, but not exclusively, whilst the main is in the live condition, that is to say without interrupting the gas flow.

The sealing of leaks from underground gas mains is a major and increasing problem, especially in view of the increasing age of many underground gas mains. Leaks from gas mains arise from a number of different causes, for example, cracks and holes resulting from corrosion, fractures arising as the result of heavy traffic passing across the road or other surface under which the gas main is located, and leaking joints. Leaking joints are a particular problem arising from the fact that many gas mains were laid at a time when town gas, i.e. gas obtained by the gasification of coal, was the gas to be carried by the gas main. At that time the joints in the gas main were sealed with hemp, which was maintained in a moist condition by moisture contained in the town gas.With the advent of natural gas, which has a much lower moisture content, as the major fuel source in place of town gas, the hemp packing dries out and no longer provides an effective gas-tight seal in the joints between the adjacent lengths of gas main. Attempts to cure this particular problem have included feeding ethanediol, for example, into the gas main to keep the packing moist, and injecting liquid sealants into the packing either from the exterior of the main or from the interior. Even with more modern mechanical joints using a rubber gland, rather than hemp packing, leakage of gas from the joint can still be a problem, caused perhaps by a misaligned or damaged gland, or more usually simply through ageing and eventual cracking of the rubber. Again the sealing of those leaks can be a problem, as can be the sealing of any leak in an underground gas main, whatever the cause.

Excavation of an underground gas main in order to effect a repair or plugging of a leak, whilst obviously necessary in some cases, e.g.

a major fracture, or excavation of the main for the purposes of an external repair is costly and time consuming, and in some cases may actually be impossible, e.g. if the main passes under a building.

Various methods have been used or proposed for the internal repair of underground gas mains. Usually these comprise advancing a mechanical pig along the gas main until the pig reaches the leaking joint, or the crack or fracture or whatever, that pig carrying sealant applicator means actuable from a distance to apply a fluid sealant composition to the interior of the gas main at the site of the leak, and thereby to seal the crack or leaking joint or whatever is the cause of the leak.

Whilst that system is reasonably successful, problems do arise in the design of the mechanical pig owing to the need for the pig to be flexible enough to pass round bends in the gas main and small enough to be fed into the main at an appropriate access point, those access points often being of relatively small dimensions. Not only that, but the sealing operation is usually carried out with the main in the dead condition, i.e. with the gas flow turned off.

To avoid those problems other methods have been devised for the internal sealing of live gas mains, i.e. without interrupting the flow of gas through the main. One such system comprises drawing a spray head through the live main to a position adjacent the crack or joint to be sealed, feeding a liquid anaerobic sealant to the spray head, usually from a reservoir of liquid sealant located above ground and connected to the spray head by one or more flexible feed lines, and operating the spray head to spray the liquid sealant onto the interior surface of the main. That system in turn presents a number of problems. It is not possible, for example, to locate the spray head in the gas main with any very great degree of accuracy, nor to direct the spray of sealant liquid very precisely at the crack or joint to be sealed.The tendency is therefore to apply the sealant over a considerable length of the internal surface of the gas main and extending on either side of the point to be sealed, but this brings other problems into play. One such problem, which arises particularly when trying to seal a leaking hemp-packed join, is that in order to penetrate the hemp packing, the sealant must be a relatively low viscosity liquid. This means that excess liquid sealant drains down off the walls of the main and collects as a pool or puddle of uncured liquid sealant in the bottom of the main. A similar situation arises when trying to seal rubber-packed joints, where the liquid sealant composition is used to penetrate the rubber seal, causing it to swell, and then to undergo cure in situ in the leaking joint, thus sealing the leak. Again any excess sealant will drain down and collect in the bottom of the main.Indeed, in almost any method of sealing an underground gas main by internal application of a liquid, anaerobic sealant will result in excess uncured sealant collecting in the bottom of the gas main and exposed to the flowing gas stream. As a result, uncured monomer tends to be entrained into the flowing gas stream and to be carried downstream where it may polymerise and form unwanted and disadvantageous polymeric deposits in downstream equipment, e.g. in flow control valves, and gas metering equipment located downstream of the leak, and resulting eventually in a malfunction of that equipment due to the build up of the deposits.

Liquid anaerobic sealant compositions currently used for such in situ internal sealing of leaks in underground gas mains, especially live gas mains, are typically Newtonian viscosity liquids having viscosities (at 250C) of the order of 5 mm2.s~l or less, and which cure in a relatively short period of time, e.g. 60 minutes or less to a relatively soft, flexible polymer having a torque strength, when fully cured, of the order of 10 Nm on a mild steel M8 nut and bolt. A Newtonian viscosity liquid having that order of viscosity, is important in that it promotes wicking of the sealant into the fracture or into the hemp packing, or absorption by the rubber in the case of joints comprising a rubber gland.

Prior art methods and apparatus for the sealing of leaks and joints in underground gas mains are described, inter alia, in GB-A2133497, GB-A-2140530, GB-A-2142703, GB-A-2159902, GB-A-2159906, GB-A2160289, GB-A-2174776 and GB-A-2199386.

The present invention seeks to provide a method and composition for the sealing of leaks in gas mains, especially live gas mains which avoids, or at least reduces, the formation of excess sealant deposits at unwanted downstream locations either in the gas main itself or in ancillary downstream equipment fed by the gas main.

In accordance with the present invention, the problem is solved by incorporating into the liquid anaerobic sealant composition used to seal the leaks in the gas main a relatively small amount of a transition metal-containing compound, preferably a copper-containing compound, to provide an anaerobic sealant composition of controlled cure rate. Surprisingly, it has been found that, whilst a small amount of a transition metal containing compound such as copper naphthenate, might be expected to cause too rapid a polymerisation of the composition, such that the sealant no longer penetrates, and therefore no longer effectively seals the leaking joint, this is not the case.

Surprisingly the wicking and sealing properties of the liquid sealant are not materially affected. Accordingly a sealant composition can now be provided for sealing leaks in underground gas mains which undergoes relatively rapid (1 to 4 days) bulk cure when in contact with a cast iron surface, e.g. when lying in puddles on the floor of the gas main, thereby to prevent the entrainment of unpolymerised monomer into the flowing gas stream, with consequential unwanted polymeric deposits downstream from the point of application, but which still is effective in penetrating and sealing the leak in the main.

In a first aspect, therefore, the present invention resides in a method of sealing leaks in a gas main, especially a live gas main, which comprises applying to the internal surface of the main, in the region of the leak, a liquid anaerobic sealant composition having the fluid flow properties of a Newtonian liquid and a viscosity, measured at 250C of 5mmz.s-l or less, said composition containing one or more anaerobically polymerisable acrylate and/or methacrylate monomers and an initiator system containing an organic peroxide or hydroperoxide free radical polymerisation initiator and a combination of one or more polymerisation inhibitors, metal chelating agents and/or polymerisation catalysts such that the composition remains stable in the presence of oxygen but undergoes spontaneous polymerisation when excluded from contact with oxygen, characterised in that there is added to the composition prior to application transition metal-containing compound soluble in the monomer, thereby to accelerate the bulk cure rate of the composition under non-anaerobic conditions.

In the preferred method of the invention the uncured sealant composition containing the accelerator component is applied to the internal surface of the main by spraying. Preferably this is achieved in known manner by drawing a spray head through the gas main to a point adjacent the leak to be sealed, the spray head being positioned on the axis of the gas main and being operable to spray the sealant composition to the internal surface of the gas main and being supplied with preformulated uncured but accelerated sealant under pressure from the surface. Whilst, as indicated, in the preferred method of the invention, the sealant is applied inside the gas main without interruption of the gas flow, i.e. to a live main, there is no reason why the flow should not be interrupted if desired, or indeed interrupted for other reasons.In other words, the sealant composition of this invention may be used to seal leaks in underground gas mains whether live or dead.

As an alternative to spraying, the sealant composition may alternatively be applied directly to the internal surface of the gas main in the region of the leaking joint, or whatever is the cause of the leak, by means of, for example, a rotary arm mounted on the pig and having a sealant applicator means, e.g. a brush or porous pad, located at its extremity and by means of which the sealant may be wiped onto the internal surface of the main by driving the arm in an arc about the pig, or by any other suitable application means.

As already indicated, the sealant compositions used in the method of this invention will contain one or more, anaerobically polymerisable acrylic or methacrylic monomers, that is to say a monomer or monomeric mixture which inherently has, or which has been so treated that it or compositions containing it have the property of undergoing spontaneous polymerisation in the absence of air or oxygen. Typical of such monomers are the monoacrylates disclosed in U.K. 1,151,196 viz compounds of the formula

where R1 is hydrogen, or methyl and R is the residue of an esterifying alcohol, and which residue contains at least one reactive centre capable of cross-linking and provided, for example, by a labile hydrogen atom e.g. as an -OH group, an alicyclic radial, a hetero atom of a heterocyclic ring, a cyano group, a halogen atom, or an alkylamino group.Typical amongst such monomers are hydroxyethyl acrylate, glycidyl acrylate and methacrylate, cyclohexyl acrylate and tetrahydrofurfuryl methacrylate.

Also suitable for use in this invention are liquid anaerobic sealant compositions comprising a polyfunctional acrylate as the anaerobically polymerisable monomer, typical such acrylates being represented by the formula:

where R and R1 are each H or CH3; R11 is H or OH; n is O or 1; and x and y are each positive integers, and specifically such monomers as diethyleneglycol diacrylate and tri- and tetra-ethyleneglycol dimethacrylate. Also suitable are anaerobically curable compositions comprising a urethane acrylate as the monomeric species.

Additionally, such sealant compositions may also contain a toughening agent, e.g. a low molecular weight elastomer comprising one or more reactive groups in a terminal or pendant position on an elastomeric backbone, e.g. one or more carboxy, vinyl, acrylate or sulphonyl chloride groups disclosed in GB-A-1,505,348, GB-A-1,550,778.

Preferred toughening agents are chlorosulphonated polyethylenes as sold under the registered trade mark Hypalon, and the carboxy and vinyl terminated butadiene polymers and copolymers sold under the registered trade mark Hycar.

The preferred anaerobically curable monomeric systems for use in the method of the present invention are those based on the esters of methacrylic acid especially the monoalkyl, monohydroxy alkyl and monoalkoxyalkyl methacrylates containing from 1 - 20 carbon atoms in the ester moiety, e.g. methyl, ethyl, n-propyl, 2-ethylhexyl, lauryl methacrylate etc., 2-hydroxypropylmethacrylate, tetrahydrofurfuryl methacrylate etc. Optionally such monomeric systems may contain small, e.g. up to 15X by weight of longer chain methacrylates or dimethacrylates such as polypropylene glycol monomethacrylate, triethyleneglycol dimethacrylate, etc. as is conventional in the art.

Also as is conventional in the art, the anaerobically curable composition will contain an initiator system capable of initiating polymerisation of the composition when isolated from contact with oxygen, but which maintains the uncured composition in an unstable equilibrium condition whilst in contact with oxygen, that unstable equilibrium possibly, but not necessarily requiring oxygenation of the mixture as taught for example in GB-A-1,375,351. As the primary component, the initiator system will contain an organic peroxide or hydroperoxide as a free radical polymerisation initiator or activator, usually in admixture with one or more polymerisation catalysts, polymerisation inhibitors and/or chelating agents. Preferred initiators are organic hydroperoxides such as cumene hydroperoxide.

Suitable polymerisation catalysts for use in the initiator system include saccharin and/or N,N-dimethyl-p-toluidine, whilst suitable polymerisation inhibitors include the quinones and hydroquinones, e.g.

1,4-naphthaquinone. The preferred chelating agent is the tetra-sodium salt of ethylenediamine tetracetic acid, although many other suitable chelating agents are available in the art.

For a general discussion of anaerobically polymerisable compositions for use in this invention reference may be made to any of the following: GB-A-1,151,916, GB-A-1,347,068, GB-A-1,375,351, GB-A1,505,348, GB-A-1,550,778.

In accordance with the present invention, the anaerobically curable sealant composition is modified by incorporating therein prior to application to the interior wall of the gas main, and preferably by preformulation of the complete composition at the surface prior to passing the sealant composition under pressure to a spray head drawn through the gas main to a point adjacent the leak to be sealed, for example, a leaking joint, of polymerisation accelerator consisting of or containing a transition metal-containing compound soluble in the monomer.

Preferred are transition metal carboxylate salts especially those of long chain (C1O-Cl8) fatty acids or of naphthenic acid. Whilst any transition metal salt soluble in the monomer will act as an accelerator, e.g. zinc, chromium, nickel iron etc. preferred are the copper salts, especially copper naphthenate. Usually the amount of transition metal incorporated into the uncured liquid anaerobic sealant will be in the range 1.0 to 500 ppm, preferably 3 to 60 ppm, based on the total weight of the composition.

Surprisingly it has been found that small, controlled amounts of transition metal in the range stated enable anaerobic sealant compositions to be formulated with closely controlled anaerobic and non-anaerobic cure times, with minimum anaerobic cure times in excess of 20 minutes or more, thus enabling the sealant composition to penetrate well into the fracture or leaking joint before curing, but showing bulk cure times under non-aerobic conditions no longer than about 4- days, so that any excess sealant which drains from the internal surface of the gas main and collects in the bottom of the main cures before any significant amount of monomer is entrained by the gas flow.Nor are the cure times significantly affected by dust or dirt particles in the gas main or by moistening or conditioning agents such as monoethyleneglycol or diethyleneglycol conventionally injected periodically into gas mains to prevent hemp-packed joints from drying out and which consequently also tends to collect in puddles and pools along the length of the main.

The use of transition-metal accelerators in accordance with the present invention thus enables the formulation of anaerobic sealants, which when in contact with the cast iron gas main itself cure completely within about four days, or possibly less, whilst retaining sufficient fluidity for the uncured sealant to be supplied to the spray head under pressure, and then adequately to penetrate the cracks and joints to be sealed after spraying on to the gas main, e.g. by wicking into the hemp packing of hemp-packed joints in the gas main, or by simple capillary attraction into other cracks, before curing.

Additional control over the cure times can be effected by incorporating into the accelerator component one or more polymerisation inhibitors and/or chelating agents of the kinds already mentioned.

Whilst the invention has so far been described in terms of a method of sealing gas mains, the invention also extends to anaerobically curable sealant compositions for use therein, such compositions comprising an anaerobically polymerisable composition having the fluid flow characteristics of a Newtonian liquid and a viscosity at 250C of Smm.sec'l or less and containing one or more anaerobically polymerisable acrylate or methacrylate monomers in admixture with an initiator system comprising an organic peroxide or hydroperoxide free radical polymerisation initiator and a combination of one or more polymerisation catalysts, polymerisation inhibitors, chelating agents, characterised in that the composition also contains in admixture therein a polymerisation accelerator component consisting of or containing a transition metal-containing component soluble in the monomer, said composition having a bulk cure time under non-anaerobic conditions not less than 24 hours but not greater than 4 days.

For ease of formulation of the transition metal-containing compound into the anaerobic sealant, the accelerator may first be formulated in a solvent such as diisodecylphthalate miscible with the anaerobic monomers (and which also acts as a plasticiser for the cured composition) or with a preliminary quantity of the monomer(s). That preliminary mix may also contain the additional inhibitors and chelating agents, if any.

The invention is illustrated by the following Examples.

Example 1 Copper-based Accelerator Composition A copper-based accelerator composition (Composition A) was prepared containing: WtX Diisodecylphthalate (DIDP) 92.49 5% solution of l,4-naphthaquinone in triethyleneglycol dimethacrylate 1.0 5% solution of the tetra-sodium salt of ethylenediaminetetraacetic acid in 50/50 v/v aqueous propanol-2 1.5 Copper naphthenate (6X copper) 5.0 Dye 0.01 Example 2 The above accelerator composition A was added in varying amount to a conventional anaerobic sealant formulation, Formulation C, as follows: C 2-ethyl hexyl methacrylate 47.37 % by weight 2-hydroxy propyl methacrylate 47.37 phenothiaz ine 0.05 oxalic acid 0.025 EDTA* 0.5 saccharin 0.1 methacrylic acid 3.93 dyes 0.155 cumene hydroperoxide 0.5 *EDTA: 5X solution of the tetrasodium salt of ethylenediamine tetracetic acid in 50:50 v/v aqueous propanol-2.

The bulk cure rates of the accelerated compositions were then investigated at different temperatures and with and without addition of an iron-containing catalyst to simulate cure rates on a cast iron surface. For this purpose an iron-containing polymerisation catalyst (Nuosyn; 9X iron) was added to the accelerated composition in the amounts indicated.

In a first test, high density polyethylene bottles were filled with 12g quantities of the accelerated compositions, with an without the iron-containing catalyst, (0.075g) and the gel time noted at different temperatures. The results obtained are as follows in Table A: Table A

Acceler- Temper- Fe/ No Amount of Final Copper Gel ator ature Fe Accelerator Concentration Time C ppm A 22 No Fe O 0 > 96h n n n 5Z 150 4.8h " " " 20% 600 3.lh 22 Fe O 0 72h n n n 5X 150 4h I n n 20X 600 2.lh n 9 No Fe O 0 > 96h 5% 150 32h 20% 600 26h 9 9 Fe O 0 > 96h " " " 5% 150 32-44h " " " 20% 600 28h Similar tests carried out in high density polyethylene vials containing 2.5g of accelerated sealant gave the following results, Table B Table B

Acceler- Temper- Fel No Amount of Final Copper Gel Time ator ature Fe Acceler- Concen C ator tration ppm A 4 No 2X 60 9 days " " " 5% 150 > 3 < 6 days 10% 300 > 3 < 6 days Fe 10% 300 > 3 < 6 days 22 22 No 2X 60 27h n n n 5X 150 > 9 < 23h n 10% 300 > 9 < 23h n Fe 10% 300 > 9 < 23h The above results clearly demonstrate that, in accorance with the objective of the present invention, the bulk cure rates of the anaerobic sealant under non-anaerobic conditions can be closely controlled by incorporating into the anaerobic composition an accelerator component containing a transition metal compound (Composition A).

Under anaerobic conditions, e.g. when applied to the thread of an M8 mild steel nut and bolt, Composition C, containing 5% by wt. of the accelerator Composition A (giving approximately ?ppm copper), cures to provide a fingertight bond between the nut and the bolt at room temperature in 20-30 minutes. The same composition shows a capillary rise of 12 mm or more in one minute in a capillary of 0.7 mm internal diameter. The wicking and anaerobic sealant properties are thus unaffected. The invention thus enables the design and formulation of anaerobic sealant compositions for use in the sealing of leaks in underground gas mains (or other underground pipes or mains for that matter) having closely controlled rates both under anaerobic and nonaerobic conditions.

Claims (18)

CLAIMS:

1. A method of sealing leaks in underground gas mains, which comprises applying to the internal surface of the main, in the region of the leak, a liquid anaerobic sealant composition having the fluid flow properties of a Newtonian liquid and a viscosity, measured at 250C of 5mm2.s~l or less, said composition containing one or more anaerobically polymerisable acrylate and/or methacrylate monomers and an initiator system containing an organic peroxide or hydroperoxide free radical polymerisation initiator and a combination of one or more polymerisation inhibitors, metal chelating agents and/or polymerisation catalysts such that the composition remains stable in the presence of oxygen but undergoes spontaneous polymerisation when excluded from contact with oxygen, that sealant serving to penetrate the leak prior to curing therein to effect the sealing of that leak, characterised in that there is added to the liquid anaerobic sealant composition prior to application a transition metal-containing compound soluble in the monomer thereby to accelerate the bulk cure rate of the composition under non-anaerobic conditions.

2. A method according to claim 1, characterised in that the said accelerator is a carboxylate salt of a transition metal.

3. A method according to claim 1 or 2, characterised in that the said transition metal is copper.

4. A method according to claims 2 or 3, characterised in that the said accelerator is copper naphthenate.

5. A method according to claims 1 to 4, characterised in that the transition metal compound is added to the anaerobic sealant composition in an amount sufficient to provide a transition metal concentration in the final composition in the range 1.0 to 500 ppm.

6. A method according to claim 5, characterised in that said transition metal concentration is in the range 3.0 to 60 ppm.

7. A method according to any one of claims 1 to 6, characterised in that the transition metal-containing polymerisation accelerator is added to the sealant composition in admixture with additional polymerisation inhibitor and/or chelating agent.

8. A method according to claim 7, characterised in that the transition metal-containing polymerisation accelerator and said additional inhibitor and/or chelating agent together provide an anaerobic sealant composition having a bulk cure rate under nonanaerobic conditions and in the presence of iron of not less than 24 hours and not greater than four days.

9. A method according to any one of claims 1 to 8, wherein the uncured sealant composition is applied to the internal wall of the main by spraying.

10. A method according to claim 9, wherein the uncured sealant composition is formulated at the surface and fed under pressure to a spray head drawn through the gas main to a position adjacent the leak to be sealed.

11. A method according to any one of claims 1 to 10, as applied to the sealing of a live gas main.

12. An anaerobically polymerisable composition having the fluid flow characteristics of a Newtonian liquid and a viscosity at 250C of 5mm. sec-l or less and containing one or more anaerobically polymerisable acrylate or methacrylate monomers in admixture with an initiator system comprising an organic peroxide or hydroperoxide free radical polymerisation initiator and a combination of one or more polymerisation catalysts, polymerisation inhibitors, chelating agents, characterised in that the composition also contains in admixture therein a polymerisation accelerator component consisting of or containing a transition metal-containing component soluble in the monomer, said composition having a bulk cure time under non-anaerobic conditions in the presence of iron not less than 24 hours and not greater than 4 days.

13. A composition according to claim 12, wherein the anaerobically polymerisable monomer(s) is or are methacrylate esters.

14. A composition according to claim 12 or 13, wherein the transition metal containing component is or contains a transition metal salt of a carboxylic acid.

15. A composition according to claim 14, wherein said salt is a copper salt.

16. A composition according to claim 15, wherein said salt is copper naphthenate.

17. A composition according to any one of claims 12 to 16 which contains from 1.00 to 500 ppm of said transition metal.

18. A composition according to claim 17, which contains from 3.0 to 60 ppm of said transition metal.