Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1996-12-11
2001-01-09
Szekely, Peter A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S209000, C523S212000, C523S218000, C524S492000, C524S493000, C526S320000
Reexamination Certificate
active
06172134
ABSTRACT:
This invention relates to a sealant composition and to a method of sealing, in particular, pipeline leaks using such a composition.
The leakage of gas from gas pipelines is a serious economic and, particularly, environmental problem. The gas leaks through pores in pipeline joints and/or corrosion defects. It is not economic to cure leakage by making an excavation at each joint and applying sealant externally but, despite much effort, not truly effective and economic method has been found of sealing pipelines internally.
Hitherto, anaerobic sealants have been used in an endeavor to seal leaks. Anaerobically curing compositions comprise an anaerobic monomer, which is an ethylenically unsaturated compound which polymerises in the absence of oxygen and in the presence of a polymerization initiator and a ferrous or other suitable metal. As well as the monomer and the initiator, anaerobic compositions normally contain an agent to prevent polymerization of the composition when in storage. Anaerobically curing compositions based on acrylate or methacrylate systems are well known for sealing porosity in metals (GB 1297103 and GB 1547801). GB 1297103 and GB 1547801 describe compositions containing a major part of a monofunctional methacrylate ester (e.g. lauryl or butyl (methacrylate) and a minor part of a polyfunctional methacrylate ester (e.g. triethylene glycol dimethacrylate). The sealant of GB 1297103 comprises a peroxide initiator and is stabilised by aeration. The sealant of GB 1547801 comprises an inhibitor (e.g. hydroquinone) as well as a catalyst.
The compositions described in the two British patents are used in the vacuum impregnation of porous articles. Such anaerobically curing compositions, which are stable in the presence of oxygen (air), penetrate into pores and cracks where they cure in anaerobic conditions to form polymeric material permanently blocking the pores and sealing the cracks. The concept has been more recently extended for sealing leaking flexible pipeline joints by the use of inflatable balloon or bladder devices (EP 0164907) and by direct spraying of leaking joints in gas mains (Anaerobic Spraying—a New South Eastern Development, British Gas. Jan. 11, 1990). According to the latter method, leaking joints in gas pipelines are treated by internally spraying anaerobic sealant from a single excavation while the pipeline is carrying gas.
Anaerobic spraying of gas pipelines realises considerable savings in excavation, reinstatement and time when a number of locations require treatment. It is possible to treat up to 140 m of main from a single excavation in a fraction of the time taken using conventional external sealing techniques. The method results in a reduction in measured leakage but still leaves residual leakage from a pipeline.
In anaerobic spraying the anaerobic composition is normally applied to the joint by low pressure “wash” spray which avoids formation of droplets in the gas stream. A large portion of the sprayed material, however, washes down the wall of the pipe and remains in liquid uncured state for a period of from minutes to hours depending on the nature and conditions of the pipe and gas flow. Therefore, conventional anaerobic spraying is not as effective as would be desirable in sealing leaks in the upper portion of pipelines.
A representative anaerobic pipeline sealant comprises ethylhexyl methacrylate as the monomer, cumene hydroperoxide as the polymerisation initiator and p-methoxyphenol as an inhibitor to prevent premature polymerisation. In addition, the sealant normally contains hydroxypropyl methacrylate or another hydroxy functional (meth)acrylate ester.
Such a sealant formulation corresponds to the base preparation referred to hereinafter.
The present invention provides an anaerobically curable composition comprising an anaerobically curable monomer, a curing initiator, and fine particulate filler. In one embodiment the particles are closed, gas-containing particles. The gas may be air. In another embodiment the particles have an average particles density of less than 1 g/cm
3
. Thus, the invention resides in an anaerobically curable preparation characterised by containing such fine particulate filler. The compositions will usually contain in addition an agent to prevent premature curing and/or a rheology modifier to render the composition pseudoplastic.
The invention includes an anaerobically curable composition, comprising:
i) an anaerobically curable monomer;
ii) a free radical catalyst;
iii) an agent to prevent premature curing;
iv) hollow inert particles preferable having one or more of the following properties:
an average true particle density of from about 0.02 to 0.6 g/cm
3
;
a cross sectional dimension of from about 5-200 &mgr;m;
a minimum % survival of 80 at a pressure of 500 psi (3.5 MPa) over ambient;
a minimum volume % which floats in water of 90%;
which hollow particles suitably do not promote premature curing of the composition and conveniently are in an amount of from 1-25% by weight of the composition; and
v) fumed silica coated with a trimethylsilane or a silicone oil, the coated, fumed silica preferably being in an amount of from 2-15% by weight of the total composition.
The inert particles are optionally glass particles or polymer microspheres or other particles having functionally equivalent properties to such glass or polymer particles. The coated fumed silica may be replaced by an alternative material which imparts substantially the same rheological properties and phase stability to the composition.
Also provided by the invention is a composition for use as a premix for making a catalysed anaerobic composition whose curing will be initiated upon being placed in an anaerobic environment, comprising an anaerobically curable base preparation and a fine particulate filler, the particles of which have an average density of less than 1 g/cm
3
, the composition being substantially free of active curing initiator. The composition may be free of any curing initiator or it may contain an inactive curing initiator e.g. one part of a two part initiator. An exemplary two part initiator is a hydroperoxide catalyst and a metal promoter.
The invention further provides a method of sealing a wall, usually a pipeline wall, to control or prevent leakage through the wall, comprising applying to the wall a composition of the invention.
Additional aspects and embodiments of the invention are stated in the claims.
In one aspect, the invention comprises an anaerobic composition comprising a base preparation and a low density filler. The composition preferably contains in additional a rheology modifier.
The Base Preparation
The base preparation may in principle be any anaerobically curable preparation compatible with the low density filler and any rheology modifier to form an anaerobically curable composition. Such preparations are well known to those skilled in the art.
The base preparation normally comprises an ester of acrylic acid or an &agr;-substituted acrylic acid, especially methacylic acid. A mixture of esters may of course be used.
The base preparation preferably contains a hydrocarbyl methacrylate and optionally a hydroxy functional methacrylate. Other monomers may optionally be included to modify the physical and/or chemical properties of the composition. Preferred hydrocarbyl methacrylates useful in the invention are of the formula:
where R is a hydrocarbon group optionally containing at least 8 and often at least 9 carbon atoms and optionally at least one ether linkage. R is preferably an aliphatic (e.g. alkyl), aromatic and cycloaliphatic group or comprises one of these groups substituted by another thereof, in either case optionally containing at least one ether linkage. Preferably, the hydrocarbon group does not contain more than 14 carbon atoms.
More preferred R groups are alkyl groups, especially 8C-14C alkyl groups, which may be straight chain or branched, such as nonyl, decyl, isodecyl, lauryl or myristyl for example.
A suitable hydroxyfunctional methacrylate is hydroxypropyl or hydroxyethyl methacrylate, or anot
British Gas plc
Holt William H.
Szekely Peter A.
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