Patent Application
20090035459
This invention relates generally to pipeline protection and, more particularly, to the use of fiber-reinforced brittle matrix inorganic composites in such applications.
Metal pipes used in pipeline applications are typically coated with a layer of corrosion-resistant material, often a thin resinous layer, which serves as a barrier to penetration of water and other corrosives thereby protecting the base metal from corrosion damage. While in practice cathodic protection of the metal pipe may also be employed, this thin resinous layer is critically important to maintaining the integrity of the pipeline after installation.
During the transportation and installation process, both the pipe and the anti-corrosion layer are susceptible to mechanical damage, impact, and abrasion caused by falling rock and debris during backfilling operations. To prevent this potentially disastrous damage, a protective jacket is required to protect both the metal pipeline and thin resinous layer from impact or abrasion.
Current construction practice for protection of pipeline coatings provides for initial placement of the pipe into a bed of sand in a constructed trench. The pipeline segments are carefully laid into the trench and delicately covered with sand material over their entire length. The fine particle size of this sand prevents impact, penetration, and abrasion loads from rocks and other overburden that may cause damage to the thin resinous anti-corrosion layer. Once backfilled with sand to a level higher than the pipeline crown, local backfill materials are used to restore the site. Trucking of vast quantities of sand for embedment of pipelines is prohibitively costly and time consuming.
However, a major obstacle to providing an effective structural protective coating around the thin resinous anti-corrosion layer is the seemingly contradictory requirements of high impact, penetration, and abrasion resistance while providing sufficient flexibility to accommodate bending of the coated metal pipe up to a specified amount, typically 1.5° of permanent deflection per pipe diameter.
An example of such a coating that can be applied to a metal pipe for pipeline applications is described in U.S. Pat. Nos. 4,611,635 and 4,759,390. These cladding structures are dependent upon a stratified layering of brittle matrix material surrounding the coated pipe, covered with reinforcing mesh for tensile strength, toughness, impact resistance, and cracking control, and surrounded with additional brittle matrix material to protect the reinforcement and provide further impact resistance. A polymer outer wrapping is then added. This complex layered protective cladding is difficult to manufacture, as noted by U.S. Pat. Nos. 4,544,426 and 4,785,854.
Concrete-coated metal pipes have been used previously in primarily offshore applications where the weight of concrete coatings is needed to permanently submerge pipeline installations. Canadian Patent Nos. 959,744 and 1,076,343 specifically relate to this application. Due to the high rigidity of these claddings however, their application to terrestrial applications is limited with respect to accommodation of pipeline bending as it is constructed.
Inherent within providing pipeline protection against failure during initial construction, pipeline operators need routine maintenance and capacity for sensing accidental impacts or loadings and thereby monitoring of the pipeline systems for leaks or failures. For this reason, some sensing cables (either electrical cable or optical fiber cable or distributed optical fiber sensors) are laid or attached along the pipelines for realizing such monitoring functions. Installation of the cables along pipelines is difficult and highly time-consuming, and some additional protection measures to the cables are required during the construction period.
The present invention improves upon prior-art pipe protection methods by providing a cladding material, which is damage tolerant by design, without reliance upon the structural configuration of the cladding to accommodate limited bending of the pipe.
This is accomplished with an isotropic cladding material that can be applied or extruded in a continuous fashion without regard to specific structural configuration, layering, or stratification requirements. As pipe diameters become exceedingly large or small, existing pipe claddings that rely on structural geometry or stratification can be difficult to manufacture. However, in contrast to existing materials, the invention material may be applied without regard to pipe diameter. The material may be applied to any type of pipe to be protected, including metal pipelines, plastic/polymeric and glass/ceramic, with thicknesses in the range of 5 mm or less to 100 mm or more.
The invention is suitable for fabrication of concrete weight coating around pipe for off-shore applications. This can be done while eliminating structural mesh reinforcement through dispersed fiber reinforcement and reducing the product cost significantly by uniformly doping the reinforced fiber cladding with heavyweight fillers, such as metal powders, etc.
According to one aspect of the invention there is provided a pipe of any size diameter, which is then coated with an impact, and abrasion resistant cladding material that is isotropic and inherently damage tolerant by nature. The cladding material does not rely on stratified layers of reinforcing mesh embedded within concrete or other brittle cementitious matrices for impact resistance, fracture toughness, or crack width control.
In the preferred embodiments, the cladding material is based upon a fiber-reinforced matrix, cementitious in nature for certain applications, which demonstrates pseudo-strain-hardening behavior in uniaxial tension with random orientation of fibers within the composite to provide impact and abrasion resistance. This cladding material possesses which tensile ductility to allow bending of the coated pipe without causing large cracks or disintegration through cladding material fracturing.
For cases in which the piping material is non-corroding, such as plastic, organic, or other material, the anti-corrosion polymeric layer barrier may be eliminated and only the abrasion resistance, damage tolerant cladding be used to clad the pipe. The pipe may be metal pipe for use in pipeline applications, in which case a protective anti-corrosion layer barrier may be bonded to the external pipe surface. This coating may be a polymeric coating impermeable to water.
The protective cladding layer may be of any thickness, and of any density provided that the material is isotropic and inherently damage tolerant. However, thinner cladding configurations of lightweight material are preferred to facilitate shipping, construction, maintenance, and disposal of the pipeline sections, and to reduce material volume and cost. In some applications the cladding may be configured as heavyweight material to facilitate offshore applications. In this case, heavyweight fillers (i.e. non-reactive in nature) may be used to increase the density of the heavyweight, pseudo-strain-hardening, and fiber reinforced matrix. The material may be formulated for lightweight applications, with densities even below that of water (typically 1,000 kg/m3), while heavyweight versions of the cladding material range from 2200 kg/m3 (the density of common concrete) or less up to 4000 kg/m3 or more.
According to another aspect of the present invention, there is provided a structural configuration integrated within the impact-resistant cladding for protective housing of in-line leakage and failure monitoring technology. The present invention relies on optical sensing technology integrated into the pipe system for continuous or intermittent sensing of pipeline leakage or failure. According to the invention, a side path can be easily fabricated upon the top of the protective coating (or cladding) for housing the sensing cable along the pipe. With this pre-built side path along the pipeline, sensing cable can be installed quickly and protected effectively, and easily accessed later on for maintaining services.
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When cementitious in nature, fiber reinforced brittle matrix composites may be formed of a mixture of cementitious materials, inert fillers, reinforcing fibers, water, and processing chemical additives. The term “cementitious” includes conventional cements and mixtures thereof, and other building compositions that rely on hydraulic curing mechanisms. Examples of such materials include, but are not limited to, lime cement, Portland cement, refractory cement, slag cement, expansive cement, pozzolanic cements, industrial slags, industrial fly ash, mixtures of cements, etc. The term “inert fillers” includes, but is not limited to, natural sands, metal or other powders (for concrete weight coating), industrial wastes, processed aggregates, etc. The term “fibers” includes, but is not limited to, metallic fibers, polymeric fibers, inorganic fibers, and natural fibers, etc. any of which are used for structural reinforcement or fracture suppression within the brittle matrix. The term “processing chemical additives” includes, but is not limited to, stabilizing admixtures, derivatized celluloses, and superplasticizers.
A specific example of a useful composition for this fiber reinforced brittle matrix composite, expressed as a weight ratio, unless otherwise indicated, is as follows:
1Ordinary Portland Cement Type I (average particle diameter size = 11.7 ± 6.8 μm, LaFarge, Co.
2Silica Sand (average particle diameter = 110 ± 6.8 μm, U.S. Silica Corp.)
3Fly Ash (average particle diameter = 2.4 ± 1.6 μm, Boral Material Technologies, Inc.)
4High Range Water Reducer (Polycarboxylate-based superplasticizer, W.R. Grace Chemical Co.)
5Poly-vinyl-alcohol fibers (average length = 6-8 mm, average diameter = 39 μm ± 6 μm, Kuraray Company, Ltd.)
The anti-corrosion coated pipe is encased within a second layer of pseudo-strain-hardening composite 3 which is isotropic and inherently damage tolerant by nature, not requiring external or embedded reinforcement in the form of rebar, mesh, large strands, or continuous fabrics. The composite may have a thickness in the range of 5 mm or less to 50 mm or more in thickness to provide the necessary level of impact resistance and damage protection to both the metal pipe and anti-corrosion layer. The anti-impact cladding is not intended to be truly water-impermeable so as not to prohibit cathodic protection of the metal pipe.
Along the length of the pipe, a completely enclosed protective housing 4 is optionally integrated within the cladding structure to facilitate installation of optical-based sensing equipment to detect leakage or failure along the pipe structure. Referring to
The preferred embodiment, however, includes a pipe 1 of any size diameter with a two-layer protective coating of external anti-corrosion polymers 2 (in the case of corroding pipe material) and an impact and damage resistant cladding 4 composed of pseudo-strain-hardening composite material. Optical sensing technologies are integrated along the length of the pipe within a specifically constructed housing 4.
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