BR112020009583B1 - METHOD FOR COATING A PIPE FIELD JOINT BETWEEN TWO JOINED PIPE LENGTHS - Google Patents

Abstract

The present invention relates to a method for coating a pipe field joint comprising the steps of (a) applying a layer of a coating material composition comprising (i) a propylene polymer and (ii) an ethylene copolymer substantially linear, a linear ethylene copolymer, or mixtures thereof, to the uncoated region of the field joint, preferably the coating is applied by injection molding.

Description

Field of invention

[001] The present invention relates to improvements in pipe coating and, in particular, to a method for coating pipe field joints and a coated pipe field joint.

Background of the invention

[002] Piping used in the oil and gas industry is generally formed by lengths of steel tubes welded together end to end when the tubing is laid. It is also common to manufacture a pipe rod onshore on a spool base and transport the prefabricated pipe offshore for laying, for example in a spool laying operation in which the pipe rods are welded together and stored in a compact form. of coil in a tubing container.

[003] To mitigate corrosion of the piping and, optionally, also to isolate the fluids that the piping carries in use, the pipe joints are pre-coated with protective coatings that, optionally, are also thermally insulating. Many variations in the structure and composition of the coating are possible to obtain the necessary protective or insulating properties. However, polypropylene (PP) is most commonly used to line the pipe joints from which pipelines are made. For example, a so-called three-layer PP coating (3LPP) can be used for corrosion protection, and a so-called five-layer PP coating (5LPP) can be used for additional thermal insulation. Additional layers are possible.

[004] A 3LPP coating typically comprises an epoxy primer applied to the clean outer surface of the steel pipe joint. As the primer cures, a second thin layer of PP is applied to bond with the primer, and then a third, thicker layer of extruded PP is applied over the second layer for mechanical protection. A 5LPP coating adds two additional layers, namely a fourth layer of modified PP for thermal insulation, e.g. glass synthetic PP (GSPP) or a foam, surrounded by a fifth layer of extruded PP for mechanical protection of the fourth layer insulating.

[005] A small length of the tube is left uncoated at each end of the tube joint to facilitate welding. The resulting “field joint” must be coated with a field joint coating to reduce corrosion and maintain whatever level of insulation is necessary for the purposes of the piping.

[006] Two common processes for coating field joints of pipelines formed from polypropylene-coated tubes are the Injection Molded Polypropylene (IMPP) and Injection Molded Polyurethane (IMPU) techniques.

[007] An IMPP coating is typically applied by first blast cleaning and then heating the tube using induction heating, for example. A layer of powdered fusion bonded epoxy (FBE) initiator is then applied to the heated pipe, along with a thin layer of polypropylene adhesive, which is added during the FBE curing time. Exposed bevels of factory-applied coating on the tube are then heated. The field joint is then completely surrounded by a heavy-duty, high-pressure mold that defines a cavity around the unlined ends of the tubes, which is subsequently filled with molten polypropylene. After the polypropylene cools and solidifies, the mold is removed, leaving the field joint liner in place.

[008] Since the polypropylene used for re-insulation has very similar mechanical and thermal properties to PP pipe coating, the pipe coating and field joint coating are sufficiently compatible to fuse at their mutual interface.

[009] On the other hand, an IMPU coating uses a chemically curable material instead of injecting polypropylene as a filler material into the IMPP field joint. Typically, the initial step in the IMPU technique is to apply a liquid polyurethane primer to the blast-cleaned exposed surface of the tube. Once the initiator is applied, a mold is positioned to enclose the field joint in a cavity and the chemically curable material is injected into the cavity defined by the mold. The filler material is typically a two-component urethane chemical. When the curing process is sufficiently advanced, the mold can be removed and the field joint coating can be left in place.

[010] An IMPU process is advantageous because this process depends on a curing time versus a cooling time that can result in a shorter coating cycle. Furthermore, the mold used in an IMPU operation does not need to withstand high pressures and can therefore be compact, lightweight and simple in design.

[011] However, existing insulated pipelines comprising field joints with one of the insulating materials mentioned above, whilst demonstrating a number of significant advantages, may still have certain limitations, for example cracking. For example, with PU coatings, the shrinkage caused during curing can cause internal stresses that can lead to cracks in the insulation. Cracks can also occur when insulation material and underlying steel equipment are heated and cooled. During heating, the inner surface of the insulation material (adjacent to the hot steel equipment) expands more than the outer surface of the insulation material (adjacent to the cold sea water). This differential expansion can also cause cracking. During cooling, the insulation material shrinks more and faster than the steel equipment, causing more cracks.

[012] New insulation materials that reduce internal stresses and cracks in molded insulation have been disclosed, for example, see US Application 2015/0074978; WO 2017/019679; and copending US provisional application number 62/381037. However, due to the chemically different nature of new field joint coatings and PP pipe coatings, the maximum bond strength that can be achieved between them and polypropylene with conventional adhesive layers and/or initiators is less than the maximum bond strength union that can be achieved between polypropylene/polypropylene or polyurethane/polypropylene. For this reason, there is a perceived risk that fractures may occur between the pipe and new non-PP field joint linings, which is undesirable as it allows water to penetrate the pipe lining, causing corrosion of the pipe.

[013] There is a need for an improved adhesive layer material and coating process to adequately bond conventional PP pipe coatings with non-PP field joint coatings.

Summary of the invention

[014] The present invention is a method of lining a pipe field joint between two joined lengths of pipe, each comprising a polypropylene pipe lining along part of its length and an uncoated end portion between where the polypropylene pipe coating terminates and the field joint, the method comprising the steps of (a) applying a layer of a coating material composition comprising (i) an ethylene polymer and (ii) an ethylene copolymer substantially (SLEP) and/or a linear ethylene copolymer (LEP) to an uncoated region of the field joint so that it overlaps and extends continuously between the polypropylene pipe liner of each of the two pipe lengths .

[015] In one embodiment of the method disclosed herein above, the propylene polymer is a block or random propylene copolymer.

[016] In one embodiment of the method disclosed herein above, the substantially linear ethylene polymer and/or linear ethylene polymer (ii) is characterized as having (a) a density of less than about 0.873 g/cm3 to 0.885 g/cm3 and/or (b) an I2 greater than 1 g/10 min to less than 5 g/10 min.

[017] In one embodiment of the method disclosed herein above, the SLEP and/or LEP is a copolymer of ethylene with one or more C3 to C20 alpha-olefins, preferably a copolymer of ethylene and propylene, ethylene and 1-butene, ethylene and 1-hexene, ethylene and 1-octene, or a terpolymer of ethylene, propylene and a diene comonomer.

[018] In one embodiment of the method disclosed here above, the SLEP and/or LEP is produced using a restricted geometry catalyst.

[019] In an embodiment of the method disclosed herein above, (i) the propylene polymer is present in the coating composition in an amount equal to or greater than 50 weight percent and equal to or less than 85 weight percent and (ii ) SLEP and/or LEP is present in the coating composition in an amount equal to or greater than 15 percent by weight and equal to or less than 50 percent by weight, with the weight percentage being based on the total weight of the coating composition. coating.

[020] In one embodiment of the method disclosed herein above, the coating material composition is applied by injection molding.

[021] In one embodiment, the present invention is a method for lining a pipe field joint between two joined lengths of pipe, each length comprising a polypropylene pipe liner along part of its length and an end portion not coated between where the polypropylene pipe liner terminates and the field joint, the method comprising the step of (a) fitting a split injection mold around the joined lengths of pipe so that it overlaps and extends between the polypropylene tube coating of each of the two tube lengths and (b) injection molding a coating material composition into the injection mold, the coating material composition comprising (i) a propylene polymer and (ii ) a substantially linear ethylene copolymer (SLEP), a linear ethylene copolymer (LEP) or mixtures thereof.

Brief description of the drawings

[022] FIG. 1 is a photograph of the ring shear sample.

[023] FIG. 2 is a schematic of the ring shear experiment used to determine residual stress.

[024] FIG. 3 is a schematic of the force-displacement curve in the ring shear experiment.

[025] FIG. 4 shows the locations on a tested ring shear sample that are analyzed for morphology.

[026] FIG. 5 is a phase image of Comparative Example A.

[027] FIG. 6 is a phase image of Example 1.

Detailed description of the invention

[028] One embodiment of the present invention is a method of coating a pipe field joint between two joined pipe lengths, with each extension being coated along part of its length, but not at the ends that are joined, with a pipe liner, any suitable factory liner, but preferably a 3LPP or 5LPP liner. Subsequent to welding the tubes together, the method comprises the steps of: i) applying a layer of a coating material composition to the uncoated region of the field joint (i.e., the uncoated ends of the tubes) so that it contact and extend between the pipe casing of each of the two lengths of pipe.

[029] In the method of the invention, the coating material composition is applied so as to overlap or cover at least part of the pipe coating on the uncovered end(s) of the joined pipes, to allow the Coating material compositions contact and form a barrier resistant to moisture and other contaminants.

[030] In one embodiment of the process of the present invention, the coating material composition is applied by injection molding. For example, a split injection mold may be fitted around the connected region of the field joint and the coating material composition is injected into the mold by conventional high pressure (i.e. IMPP) or low pressure injection molding techniques. (i.e. IMPU).

[031] In some embodiments, the coating material composition has a relatively low viscosity, which thereby reduces pressure during injection and allows the use of lightweight molds, compared to heavy duty high pressure molds associated with some IMPP coating techniques.

[032] In one embodiment of the process of the present invention, the field joint is cleaned before applying the first coating material composition. Cleaning methods include surface dust cleaning, surface sanding, surface dissolution cleaning, scraping and the like. Any suitable cleaning solution and/or procedure used to clean this tube may be used.

[033] The coating material composition suitable for the method of the present invention comprises, consists essentially of, or consists of (i) a propylene polymer and (ii) a substantially linear ethylene copolymer (SLEP) or an ethylene copolymer linear (LEP) or mixtures thereof, preferably the propylene polymer (i) and the substantially linear ethylene copolymer (SLEP), a linear ethylene copolymer (LEP) or mixtures thereof (ii) form cocontinuous phases.

[034] The first component (i) of the coating material composition is a propylene polymer. Suitable propylene polymers for use in this invention are well known in the literature and can be prepared by known techniques. Polypropylene can be in isotactic form, although other forms can be used (e.g., syndiotactic or atactic). The polypropylene used for the present invention is preferably a homopolymer of polypropylene or a copolymer, for example a random or block copolymer, of propylene and an alpha-olefin, preferably a C2 or C4 to C20 alpha-olefin. The alpha-olefin is present in the polypropylene of the present invention in an amount of not more than 20 mol percent, preferably not more than 15 percent, even more preferably not more than 10 percent and most preferably not more than 5 percent. in moles.

[035] Examples of the C2 and C4 to C20 alpha-olefins to constitute the copolymer of propylene and alpha-olefin include ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadodecene, 4-methyl-1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, diethyl-1-butene, trimethyl- 1-butene, 3-methyl-1-pentene, ethyl-1-pentene, propyl-1-pentene, dimethyl-1-pentene, methylethyl-1-pentene, diethyl-1-hexene, trimethyl-1-pentene, 3- methyl-1-hexene, dimethyl-1-hexene, 3,5,5-trimethyl-1-hexene, methylethyl-1-heptene, trimethyl-1-heptene, dimethyloctene, ethyl-1-octene, methyl-1-nonene, vinylcyclopentene, vinylcyclohexene and vinylnorbornene, where the alkyl branch position is not specified, it is usually at the 3 or higher position of the alkene.

[036] In one embodiment of the present invention, a propylene homopolymer is the preferred polypropylene.

[037] In one embodiment of the method disclosed herein above, the propylene polymer is a block or random propylene copolymer.

[038] The polypropylene of the present invention can be prepared by various processes, for example, in a single stage or in multiple stages, by such polymerization method as paste polymerization, gas phase polymerization, bulk polymerization, solution polymerization or a combination thereof using a metallocene catalyst or a so-called Ziegler-Natta catalyst, which is generally one comprising a solid transition metal component comprising titanium. Particularly a catalyst consisting of a solid/transition metal component, a solid titanium trichloride composition containing as essential components titanium, magnesium and a halogen; as an organometallic component, an organoaluminum compound; and, if desired, an electron donor. Preferred electron donors are organic compounds containing a nitrogen atom, a phosphorus atom, a sulfur atom, a silicon atom or a boron atom and preferred are silicon compounds, ester compounds or ether compounds containing these. atoms.

[039] Polypropylene is generally made by catalytically reacting propylene in a polymerization reactor with appropriate molecular weight control agents. Nucleating agents can be added after the reaction is completed during a melt processing step, to promote crystal formation. The polymerization catalyst must have high activity and be capable of generating highly tactical polymer. The reactor system must be capable of removing the heat of polymerization from the reaction mass so that the reaction temperature and pressure can be adequately controlled.

[040] A good discussion of various polypropylene polymers is contained in Modern Plastics Encyclopedia/89, mid-October 1988 edition, Volume 65, Number 11, pages 86 to 92, the entire disclosure of which is incorporated herein by reference. The molecular weight of polypropylene for use in the present invention is conveniently indicated using a melt flow measurement, sometimes referred to as melt flow rate (MFR) or melt index (MI), in accordance with ASTM D 1238 at 2300C and an applied load of 2.16 kilograms (kg). The melt flow rate is inversely proportional to the molecular weight of the polymer. Thus, the higher the molecular weight, the lower the melt flow rate, although the relationship is not linear. The melt flow rate for the polypropylene useful herein is generally greater than about 0.1 g/10 min, preferably greater than about 0.5 g/10 min, more preferably greater than about 1 g/10 min, and even more preferably greater than about 10 g/10 min. The melt flow rate for the polypropylene useful here is generally less than about 200 g/10 min, preferably less than about 100 g/10 min, more preferably less than about 75 g/10 min and more preferably less than about about 50 g/10 min.

[041] The polypropylene polymer as component (i) can also be characterized by its crystalline structure.

[042] One method for characterizing crystallinity is by the pulse nuclear magnetic resonance (NMR) method of K. Fujimoto, T. Nishi and R. Kado, Polymer Journal Volume 3, 448-462 (1972), with the crystalline phase (I), intermediate phase (II) and amorphous phase (III) are determined. Generally, the weight ratio of crystalline phase (I)/intermediate phase (II) is greater than about 4, preferably greater than about 5, more preferably greater than about 8, and most preferably greater than about 10. The content of amorphous phase (III) is at least about 1, preferably at least about 2, more preferably at least about 5, even more preferably at least about 10, and most preferably at least about 15 per cent by weight. The content of the amorphous phase (III) is less than about 40, preferably less than about 30, more preferably less than about 25, even more preferably less than 20 and most preferably less than about 15 weight percent.

[043] Generally, in pulse NMR determinations, a pulse of energy is applied to a rotating polymer sample at high resolution in a specified temperature range in specific temperature ranges (temperature in degrees Kelvin, 0K). The resulting energy is monitored in the time domain (time scale in microseconds). The energy/time curve is a measure of the time required for the polymer to return from the excited energy state back to its base energy level. This is called the Free Induction Decay (FID) curve. The curve is then mathematically divided into a fast Gaussian equation (usually associated with crystallinity), a slow Gaussian equation, and an exponential equation. The last two equations are generally associated with the amorphous phase of polymers and an intermediate phase that is between the properties of crystallinity and amorphous, respectively. These equations are used to calculate coefficients that characterize the appropriate amplitude and time components of the FID curve. The coefficients are then placed in a matrix and undergo regression processes, such as partial least squares. The crystalline, amorphous, and intermediate phases are calculated and reported as weight percentages as a function of temperature, 0K.

[044] However, a more preferable method for determining crystallinity in polypropylene polymer is by differential scanning calorimetry (DSC). A small sample (milligram size) of the propylene polymer is sealed in an aluminum DSC pan. The sample is placed in a DSC cell with a nitrogen purge of 25 centimeters per minute and cooled to about -100°C. A standard thermal history is established for the sample by heating up to 10°C per minute to 225°C. The sample is then cooled to about -100°C and reheated at 10°C per minute to 225°C. The observed heat of fusion (ΔHoobserved) for the second scan is recorded. The observed heat of fusion is related to the degree of crystallinity in weight percentage, based on the weight of the polypropylene sample by the following equation: where the heat of fusion for isotactic polypropylene (ΔHisotactic PP>, as reported in B. Wunderlich, Macromolecular Physics, Volume 3, Crystal Melting, Academic press, New Your, 1980, p 48, is 165 Joules per gram (J/g ) polymer.

[045] The degree of crystallinity for the high crystalline propylene polymer, as determined by DSC, is at least about 62 weight percent, preferably at least about 64 weight percent, more preferably at least about 66 percent by weight, even more preferably at least about 68 percent by weight and more preferably at least about 70 percent by weight, based on the weight of the high crystalline propylene polymer. The degree of crystallinity for the high crystalline propylene polymer, as determined by DSC, is less than or equal to about 100 weight percent, preferably less than or equal to about 90 weight percent, more preferably less than or equal to about of 80 weight percent, and more preferably less than or equal to about 70 weight percent, based on the weight of the high crystalline propylene polymer.

[046] part or all of the propylene polymer of the present invention can be modified by grafting. A preferred graft modification of polypropylene is obtained with any unsaturated organic compound containing, in addition to at least one ethylenic unsaturation (e.g., at least one double bond), at least one carbonyl group (-C=O) and which will graft onto a polypropylene as described above. Representative of unsaturated organic compounds that contain at least one carbonyl group are acids, anhydrous, carboxylic esters and their salts, both metallic and non-metallic. Preferably, the organic compound contains ethylenic unsaturation conjugated with a carbonyl group. Representative compounds include maleic, fumaric, acrylic, methacrylic, itaconic, crotonic, methyl crotonic and cinnamic acid and their anhydrous, ester and salt derivatives, if any. Maleic anhydrous is the preferred unsaturated organic compound that contains at least one ethylenic unsaturation and at least one carbonyl group.

[047] The unsaturated organic compound containing at least one carbonyl group can be grafted onto polypropylene by any known technique, such as those taught in USP 3,236,917 and USP 5,194,509. For example, the polymer is introduced into a two-roll mixer and mixed at a temperature of 60°C. The unsaturated organic compound is then added, together with a free radical initiator, such as, for example, benzoyl peroxide and the components are mixed at 30°C until grafting is complete. Alternatively, the reaction temperature is higher, for example, 210°C to 300°C and a free radical initiator is not used or is used at a reduced concentration. An alternative and preferred method of grafting is taught in USP 4,905,541, the disclosure of which is incorporated herein by reference, using a twin-screw devolatilization extruder as the mixing apparatus. The polypropylene and the unsaturated organic compound are mixed and reacted within the extruder at temperatures at which the reactors are melted and in the presence of a free radical initiator. Preferably, the unsaturated organic compound is injected into a zone held under pressure in the extruder.

[048] The unsaturated organic compound content of the grafted polypropylene is at least about 0.01 weight percent, preferably at least about 0.1 weight percent, more preferably at least about 0. 5 weight percent and, most preferably, at least about 1 weight percent based on the combined weight of the polypropylene and organic compound. The maximum amount of unsaturated organic compound content may vary for convenience, but typically it does not exceed about 10 weight percent, preferably it does not exceed about 5 weight percent, more preferably it does not exceed about 2 percent. by weight and, most preferably, it does not exceed about 1 percent by weight based on the combined weight of the polypropylene and the organic compound.

[049] Polypropylene or graft-modified polypropylene is employed in the propylene polymer blend compositions of the present invention in amounts sufficient to provide the desired processability and good balance of stiffness and toughness. If present, the graft-modified polypropylene may be employed in an amount equal to 100 percent by weight of the total weight of the polypropylene, preferably in an amount up to or equal to 50 percent by weight, more preferably up to or equal to 30 percent. by weight, even more preferably, up to or equal to 20 weight percent and, more preferably, up to or equal to 10 weight percent of the weight of the polypropylene.

[050] The propylene polymer (i) is present in the coating composition of the present invention in an amount sufficient to be a co-continuous phase with component (ii), the substantially linear ethylene copolymer or a linear ethylene copolymer, or mixtures thereof, preferably in an amount equal to or greater than 15 percent by weight, preferably equal to or greater than 30 percent by weight, more preferably equal to or greater than 40 percent by weight based on the total weight of the coating composition. The propylene polymer (i) is present in the coating composition of the present invention in an amount such that component (ii), the substantially linear ethylene copolymer or a linear ethylene copolymer, or mixtures thereof, is a cocontinuous phase, preferably equal to or less than 85 weight percent, preferably equal to or less than 70 weight percent, more preferably equal to or less than 60 weight percent based on the total weight of the coating composition.

[051] The second component (ii) of the coating material composition is a substantially linear ethylene copolymer (SLEP) or a linear ethylene copolymer (LEP), or mixtures thereof. As used herein, the term “S/LEP” refers to substantially linear ethylene copolymers, linear ethylene copolymers or mixtures thereof. S/LEP copolymers are made using catalysts of a restricted geometry, such as metallocene catalysts. S/LEP copolymers are not made by conventional polyethylene copolymer processes, such as Ziegler Natta catalyst polymerization (HDPE) or free radical polymerization (LDPE and LLDPE).

[052] Substantially linear ethylene polymers and linear ethylene polymers are known. Substantially linear ethylene polymers and their method of preparation are described in more detail in USP 5,272,236 and USP 5,278,272. Linear ethylene polymers and their method of preparation are disclosed in detail in USP 3,645,992; USP 4,937,299; USP 4,701,432; USP 4,937,301; USP 4,935,397; USP 5,055,438; EP 129,368; EP 260,999; and WO 90/07526.

[053] Suitable S/LEP copolymers comprise two or more C2 to C20 alpha-olefins, preferably ethylene, and one or more C3 to C20 alpha-olefins, more preferably one or more C4 to C20 alpha-olefins in polymerized form, having a Tg of less than 25°C, preferably less than 0°C, more preferably less than -25°C. Examples of the types of copolymers from which the present S/LEP is selected include copolymers of alpha-olefins, such as ethylene and copolymers of 1-butene, ethylene and 1-hexene or 1-hexene or ethylene and 1-octene and terpolymers of ethylene, propylene and a diene comonomer such as hexadiene or ethylidene-norbornene, the most preferred being ethylene and propylene.

[054] As used herein, “a linear ethylene copolymer” means a copolymer of ethylene and one or more alpha-olefin comonomers having a linear (i.e., non-cross-linked) backbone, no long-chain branching, a narrow molecular weight distribution and a narrow composition distribution. Furthermore, as used herein, "a substantially linear ethylene-ethylene copolymer" means a copolymer of one or more C2 to C20 alpha-olefins, preferably, copolymers of ethylene and one or more C3 to C20 alpha-olefins having a linear backbone, a specific and limited amount of long chain branching, a narrow molecular weight distribution, and, for alpha-olefin copolymers, a narrow composition distribution.

[055] Short-chain branches of a linear copolymer arise from the resulting pendant alkyl group upon polymerization of intentionally added C3 to C20 alpha-olefin comonomers. Narrow compositional distribution is also sometimes called short-chain homogeneous branching. The narrow composition distribution and homogeneous short-chain branching refer to the fact that the alpha-olefin comonomer is randomly distributed within a given ethylene copolymer and an alpha-olefin comonomer and virtually all copolymer molecules have the same ethylene to comonomer ratio. The limitation of the composition distribution is indicated by the value of the Composition Distribution Branch Index (CDBI) or sometimes called the Short Chain Branch Distribution Index. CDBI is defined as the weight percentage of polymer molecules that have a comonomer content within 50 percent of the median total molar comonomer content. The CDBI is easily calculated, for example, by employing elution fractionation with increasing temperature, as described in Wild, Journal of Polymer Science, Polymer Physics Edition, Volume 20, page 441 (1982) or USP 4,798,081. The CDBI for the substantially linear ethylene-ethylene copolymers and the linear ethylene copolymers in the present invention is greater than about 30%, preferably greater than about 50%, and most preferably greater than about 90%.

[056] Long-chain branches in substantially linear ethylene polymers are polymer branches that are not short-chain branches. Typically, long-chain branches are formed by the in situ generation of an oligomeric alpha-olefin through beta-hydride elimination in a growing polymer chain. The resulting species is a relatively high molecular weight vinyl-terminated hydrocarbon that, upon polymerization, produces a large pendant alkyl group. Long chain branching can be further defined as hydrocarbon branches for a polymer backbone that has a chain length greater than n minus 2 (“n-2”) carbons, where n is the number of carbons of the largest comonomer of alpha-olefin intentionally added to the reactor. Preferred long-chain branches in homopolymers of ethylene or copolymers of ethylene and one or more C3 to C20 alpha-olefin comonomers have at least 20 carbons up to, more preferably, the number of carbons in the main chain of the polymer from which the branch is pendent . Long chain branching can be distinguished using 13C nuclear magnetic resonance spectroscopy alone, or with gel permeation laser chromatography light scattering (GPC-LALS) or a similar analytical technique. Substantially linear ethylene polymers contain at least 0.01 long chain branches/1,000 carbons and, preferably, 0.05 long chain branches/1,000 carbons. In general, substantially linear ethylene polymers contain less than or equal to 3 long chain branches/1,000 carbons and, preferably, are less than or equal to 1 long chain branches/1,000 carbons.

[057] As used herein, copolymer means a polymer of two or more intentionally added comonomers, for example, as can be prepared by polymerization of ethylene with at least one other comonomer from C3 to C20. Preferred linear ethylene polymers can be prepared in a similar manner, using, for example, metallocene or vanadium-based catalyst under conditions that do not allow polymerization of monomers other than those intentionally added to the reactor. Preferred substantially linear ethylene polymers are prepared using metallocene-based catalysts. Other basic characteristics of substantially linear ethylene polymers or linear ethylene polymers include a low residue content (i.e., a low concentration in the catalyst used to prepare the polymer), unreacted comonomers, and low molecular weight oligomers produced during the course of polymerization. ) and a controlled molecular architecture that provides good processability, although the molecular weight distribution is narrow relative to conventional olefin polymers.

[058] Although substantially linear ethylene polymers or linear ethylene polymers used in the practice of this invention include substantially linear ethylene homopolymers or linear ethylene homopolymers, preferably, substantially linear ethylene polymers or linear ethylene polymers comprise between about 50 to about 95 weight percent ethylene and about 5 to about 50 and, preferably, about 10 to about 25 weight percent of at least one alpha-olefin comonomer. The comonomer content in substantially linear ethylene polymers or linear ethylene polymers is generally calculated based on the amount added to the reactor and as can be measured using infrared spectroscopy in accordance with ASTM D-2238, Method B. Typically , substantially linear ethylene polymers or linear ethylene polymers are copolymers of ethylene and one or more C3 to C20 alpha-olefins, preferably, copolymers of ethylene and one or more C3 to C10 alpha-olefin comonomers, and more preferably, copolymers of ethylene and one or more comonomers selected from the group consisting of propylene, 1-butene, 1-hexene, 4-methyl-1-pentane and 1-octene. Most preferably, the copolymers are copolymers of ethylene and 1-octene.

[059] The density of these substantially linear ethylene polymers or linear ethylene polymers is equal to or greater than about 0.850 grams per cubic centimeter (g/cm3), preferably equal to or greater than about 0.860 g/cm3, and more preferably equal to or greater than about 0.873 g/cm3. Generally, the density of these substantially linear ethylene copolymers or linear ethylene polymers is less than or equal to about 0.93 g/cm3, preferably less than or equal to about 0.900 g/cm3, and more preferably equal to or less which is about 0.885 g/cm3. The melt flow ratio for substantially linear ethylene polymers, measured as I10/I2, is greater than or equal to about 5.63, is preferably about 6.5 to about 15, and is most preferably about 7. to about 10. I2 is measured in accordance with ASTM Projection D 1238, using conditions of 190 °C and 2.16 kilograms (kg) of mass. I10 is measured in accordance with ASTM Projection D 1238, using conditions of 190 °C and 10.0 kg mass.

[060] The Mw/Mn for substantially linear ethylene copolymers is the weight average molecular weight (Mw) divided by the number average molecular weight (Mn). Mw and Mn are measured by gel permeation chromatography (GPC). For substantially linear ethylene copolymers, the I10/I2 ratio indicates the degree of long-chain branching, that is, the higher the I10/I2 ratio, the more long-chain branching there is in the copolymer. In preferred substantially linear ethylene copolymers, Mw/Mn refers to I10/I2 by the equation: Mw/Mn < (I10/I2) - 4.63. Generally, Mw/Mn for substantially linear ethylene-ethylene copolymers is at least about 1.5, and preferably at least about 2.0, and is less than or equal to about 3.5, more preferably, less than or equal to about 3.0. In a more preferred embodiment, substantially linear ethylene copolymers are also characterized by a single DSC melting peak.

[061] The preferred melt index I2 for these substantially linear ethylene copolymers or linear ethylene copolymers is about 0.01 g/10 min to about 100 g/10 min, more preferably, about 0.1 g /10 min to about 10 g/10 min and, even more preferably, about 1 g/10 min to about 5 g/10 min.

[062] The preferred Mw for these substantially linear ethylene copolymers or linear ethylene copolymers is equal to or less than about 180,000, preferably, equal to or less than about 160,000, more preferably, equal to or less than about 140,000 and, with maximum preference, equal to or less than about 120,000. The preferred Mw for such substantially linear ethylene copolymers or linear ethylene copolymers is equal to or greater than about 40,000, preferably, equal to or greater than about 50,000, more preferably, equal to or greater than about 60,000, even more preferably, equal to or greater than about 70,000 and, most preferably, equal to or greater than about 80,000.

[063] In one embodiment, the S/LEP used in the process of the present invention can be modified by grafting. A preferential graft modification of S/LEP is obtained with any unsaturated organic compound that contains, in addition to at least one ethylenic unsaturation (e.g., at least one double bond), at least one carbonyl group (-C=O) and will be grafted to an S/LEP, as described above. Representative of unsaturated organic compounds that contain at least one carbonyl group are acids, anhydrous, carboxylic esters and their salts, both metallic and non-metallic. Preferably, the organic compound contains ethylenic unsaturation conjugated with a carbonyl group. Representative compounds include maleic, fumaric, acrylic, methacrylic, itaconic, crotonic, methyl crotonic and cinnamic acid and their anhydrous, ester and salt derivatives, if any. Maleic anhydrous is the preferred unsaturated organic compound that contains at least one ethylenic unsaturation and at least one carbonyl group.

[064] The unsaturated organic compound content of the grafted S/LEP is at least about 0.01 weight percent, preferably at least about 0.1 weight percent, more preferably at least about of 0.5 weight percent and, most preferably, at least about 1 weight percent based on the weight combination of the S/LEP and organic compound. The maximum amount of unsaturated organic compound content may vary for convenience, but normally does not exceed about 10% by weight, preferably does not exceed about 5% by weight, more preferably does not exceed about 2% by weight, and with Most preferably, it does not exceed about 1 weight percent based on the combined weight of the S/LEP and the organic compound.

[065] The S/LEP copolymer (ii) is present in the coating composition of the present invention in an amount sufficient to be a co-continuous phase with the propylene polymer (i), preferably equal to or greater than 15 percent by weight, preferably equal to or greater than 20 weight percent, more preferably equal to or greater than 30 weight percent based on the total weight of the coating composition. The S/LEP copolymer (ii) is present in the coating composition of the present invention in an amount that allows the propylene polymer (i) to be a cocontinuous phase, preferably equal to or less than 85 weight percent, preferably equal to or less than 70 weight percent, more preferably equal to or less than 60 weight percent based on the total weight of the coating composition.

[066] Optionally, the coating material composition may further comprise a filler (iii). Examples of suitable fillers are calcium carbonate, talc, clay, mica, wollastonite, hollow glass beads, titanium oxide, silica, carbon black, fiberglass, potassium titanate and the like. Preferred fillers are talc, wollastonite, clay, single layers of a cation exchange layered silicate material or mixtures thereof. Talcs, wollastonites and clays are generally known fillers for various polymer resins. See, for example, USP 5,091,461 and 3,424,703; EP 639,613 A1; and EP 391,413, where these materials and their suitability as fillers for polymeric resins are generally described.

[067] If present, the filler is used in an amount equal to or greater than 1 percent, preferably equal to or greater than 2 percent, more preferably equal to or greater than 5 percent, even more preferably equal to or greater than 7.5 percent and more preferably equal to or greater than 10 percent based on the total weight of the coating material composition. If present, the filler is employed in an amount equal to or less than 60 percent, preferably equal to or less than 50 percent, more preferably equal to or less than 40 percent, even more preferably equal to or less than 20 percent, and most preferably equal to or less than 15 percent based on the total weight of the coating material composition.

[068] In one embodiment, the method of the present invention is a method for lining a pipe field joint between two joined lengths of pipe, each length comprising a polypropylene pipe coating along part of its length and a portion of uncoated end between where the polypropylene pipe liner terminates and the field joint, the method comprising the step of (a) fitting a split injection mold around the joined lengths of pipe so that it overlaps and extends between the polypropylene pipe liner of each of the two lengths of pipe and (b) injection molding a liner material composition into the injection mold, wherein the liner material composition comprises (i) a propylene polymer and (ii) a substantially linear ethylene copolymer (SLEP), a linear ethylene copolymer (LEP) or mixtures thereof.

Examples

[069] The following components are used in Examples 1 and Comparative Example A:

[070] “PP-1” is an injection moldable impact modified polypropylene commonly used for steel pipe coating applications having good low temperature impact resistance and a melt flow rate of 0.3 g/10 min (230°C/2.16kg).

[071] “ENGAGETM 8842” available from The Dow Chemical Company is a metallocene-catalyzed ultra-low density ethylene-octene copolymer (0.857 g/cm3.) with a melt index of 1 g/10min (190°C/2. 16kg).

[072] Comparative Example A is PP-1.

[073] Example 1 is a 70:30 melt mixture of PP-1: ENGAGE 8842.

Fusion Composition.

[074] For Example 1, PP-1: ENGAGE 8842 is dry mixed in a plastic bag. Air is introduced into the bag to blow it into a ball shape. The opening of the bag is sealed tightly to prevent air from escaping. The bag is shaken by hand multiple times to obtain a well-blended mixture of resins and additives. The blended mixture is then gravity fed through a feeder to a hopper which is fed to the barrel of a Micro-18 twin screw extruder. Feeding starts at about 2.2 lbs/hour and is then increased to 4 lbs/hour later as the torque and pressure in the extruder becomes more stable. The pellets flew from the hopper down through the feed neck, which dispensed them into a double rotation screw at a speed of 200rpm, operating inside a horizontal cylinder. The pellets passed through the cylinder on the screws while being heated. The extruder barrel had controlled heating zones that are preheated to 140, 160, 180, 190, 200 and 200 °C, running from the feed section to the die. When the resin has reached the end of the screw length, it is thoroughly mixed and pushed through a screen and then through the extruder die. The hot polymer exits the matrix in the form of a bead and is then cooled by blowing air from fans. The product is achieved by pulling the cord through a crusher and then cut into pellets at a speed of 3.8rpm.

Ring Shear Sample Preparation.

[075] A round tube made of low carbon steel was cut to a length of 10.16 cm (4 inches) using a band saw. The outer diameter of the tube is 5.08 cm (2 inches) and the wall thickness was 0.10 cm (0.04 inch). 10.16 cm (4 inch) segments are then blasted using a silica-based media to remove all oil, rust, debris, etc. of the tube surface. The 10.16 cm (4 inch) segments are rinsed with acetone and dried using nitrogen. This metal tube is fixed concentrically to a 6 inch (15.24 cm) diameter metal pan with high temperature sticky tape. The space between the metal tube and the metal pan is filled with extruded polymer exiting the die of a Micro-18 extruder. Once filled to the top level of the metal pan, the polymer is allowed to cool over time, FIG. 1.

[076] The following tests are performed in Comparative Example A and Example 1 and the results are reported in Table 1:

Residual voltage measurement.

[077] Reducing the residual stress in the field joint material is one of the main requirements for developing new materials for the field joint. An extraction experiment is conducted with ring shear samples described herein above on an Instron 5581 mechanical test frame at a displacement rate of 0.127 cm (0.05 inch)/min, to push the metal tube out of the polymer. The initial peak is high and then has a plateau that indicates frictional sliding of the polymer against the metal tube. A schematic of the load-displacement curve as well as the free-body diagram of the extraction experiment is shown in FIG. 2 and FIG. 3, respectively.

[078] From the plateau region of the force-displacement curve, the load is averaged over a range of 10 mm of displacement. After completing the ring shear experiment, the samples are weighed and the volume calculated. Since the pan area is the same, the height of the polymer in each sample is calculated. This height is necessary to calculate the overall residual stress. In the friction sliding region, the tangential force is essentially the force measured by the ring shear test. The coefficient of friction (μ) was measured in an ASTM characterization laboratory and an average value of 0.58 is considered for all samples. This is one of the assumptions in the calculation that the COF does not change significantly between samples due to the addition of elastomers. The residual stress can be estimated as where P is the measured pull-out force and A is the surface area of the polymer in contact with the steel tube. 3 samples are prepared for Comparative Example A and Example 1 and an average value is reported. Table 1

Morphology Analysis.

[079] After testing the ring shear sample, a 1 cm by 1.5 cm by 0.4 cm piece is cut from the raw sample to reveal a view of the center of the thickness, FIG. 4. Two locations are analyzed, one close to the metal tube and one close to the periphery of the sample. The objective of analyzing these two locations is to verify whether the boundary conditions have any effect during the crystallization process that could impact the morphology. A block face is established using a razor blade and then cryogenically polished to produce a planed surface. A Leica UC7/FCS ultramicrotome, equipped with diamond knives, was operated at -140 °C. A Brüker Dimension ICON atomic force microscope (AFM) is operated in drift mode for phase detection. A NanoScope V controller operates with NanoScope v8.15 operating software. Tips used for all scans: Mikro Masch #16 NSC without Al backcoat. Tips have a resonant frequency of about 170 kHz and a force constant of about 40 N/m. Image post-processing and analysis is done using Image Analysis SPIP v6.5.2 and shown in Comparative Example A, FIG. 5 and Example 1, FIG. 6.

Claims (7)

1. Method for lining a pipe field joint between two joined lengths of pipe, each length comprising a polypropylene pipe liner along part of its length and an uncoated end portion between where the polypropylene pipe liner terminates and field jointing, the method comprising the step of: (a) applying a layer of a coating composition to the uncoated region of the field joint so that it overlaps and extends continuously between the coating of polypropylene tube of each of the two tube lengths; wherein the coating material composition comprises: (i) a propylene polymer; and (ii) a substantially linear ethylene copolymer (SLEP), a linear ethylene copolymer (LEP) or mixtures thereof, the propylene polymer being and the substantially linear ethylene copolymer (SLEP), a linear ethylene copolymer ( LEP) or mixtures thereof form cocontinuous phases, with SLEP and/or LEP being a copolymer of ethylene with one or more C3 to C20 alpha olefins, and with SLEP and/or LEP being defined as having: (a) a density greater than 0.873 g/cm3 to 0.885 g/cm3; and/or (b) an I2 greater than 1 g/10 min to less than 5 g/10 min, where I2 is measured in accordance with ASTM D 1238 using the conditions of 190 °C and 2.16 kg mass . 2. Method according to claim 1, characterized in that the propylene polymer is a block or random copolymer of propylene. 3. Method according to claim 1, characterized in that the SLEP and/or LEP is a copolymer of ethylene and propylene, ethylene and 1-butene, ethylene and 1-hexene, ethylene and 1-octene, or a terpolymer of ethylene, propylene and a diene comonomer. 4. Method according to claim 1, characterized in that the SLEP and/or LEP is produced using a restricted geometry catalyst. 5. Method according to claim 1, characterized in that: (i) the propylene polymer is present in the coating composition in an amount equal to or greater than 50 percent by weight and equal to or less than 85 percent by weight. Weight; and (ii) the SLPE and/or LEP is present in the coating composition in an amount equal to or greater than 15 percent by weight and equal to or less than 50 percent by weight, with the weight percentages being based on the total weight of the coating composition. 6. Method according to claim 1, characterized in that the coating material composition is applied by injection molding. 7. Method for lining a pipe field joint between two joined lengths of pipe, each length comprising a polypropylene pipe liner along part of its length and an uncoated end portion between where the polypropylene pipe liner terminates and field jointing, the method comprising the step of: (a) fitting a split injection mold around the joined lengths of pipe so that it overlaps and extends between the polypropylene pipe liner of each of the two tube lengths; and (b) injection molding a coating material composition into the injection mold, wherein the coating material composition comprises: (i) a propylene polymer; and (ii) a substantially linear ethylene copolymer (SLEP), a linear ethylene copolymer (LEP), or mixtures thereof, wherein the SLEP and/or LEP is a copolymer of ethylene with one or more C3 to C20 alpha olefins , and where SLEP and/or LEP is defined as having: (a) a density greater than 0.873 g/cm3 to 0.885 g/cm3; and/or (b) an I2 greater than 1 g/10 min to less than 5 g/10 min, where I2 is measured in accordance with ASTM D 1238 using the conditions of 190 °C and 2.16 kg mass .