AU2017365730A1

AU2017365730A1 - PVDF coated pipe for oil or gas applications

Info

Publication number: AU2017365730A1
Application number: AU2017365730A
Authority: AU
Inventors: Ronald J. Dunn; Catherine Lam; Dennis Wong
Original assignee: Shawcor Ltd
Current assignee: Shawcor Ltd
Priority date: 2016-11-24
Filing date: 2017-11-22
Publication date: 2019-06-13
Also published as: MX2019006046A; WO2018094519A1

Abstract

A three layer PVDF coating system is provided for oil or gas pipe. The system comprises a steel pipe, an epoxy layer, for example, made from a high temperature liquid epoxy or a FBE, preferably a high temperature FBE, which provides excellent adhesion to the steel pipe and anti-corrosion protection, a maleic anhydride modified PVDF tie layer which provides excellent bonding to both FBE and PVDF topcoat, and substantially blocks water and oxygen degradation of the FBE by forming a protective, bonded, coating overtop of the FBE, and a PVDF layer which provides a further excellent water and oxygen barrier, as well as excellent mechanical protection. Also provided is a method of manufacturing a pipe having said coating system.

Description

[0001] This application claims priority based on United States Patent Application No. 62/426,295 entitled PVDF COATED PIPE FOR OIL OR GAS APPLICATIONS filed November 24, 2016, which is herein incorporated by reference.

TECHNICAL FIELD [0002] The present disclosure relates to a PVDF coated pipe for oil or gas applications.

BACKGROUND OF THE INVENTION [0003] Steel pipes or tubing conduit, for example, steel pipes used for transportation of oil or gas, must be protectively coated against corrosion. This is especially important for oil or gas steel pipes which are intended for underground installation. This corrosion coating must also be impact and temperature resistant. The extent of corrosion and temperature resistance, and mechanical protection required often depends on the environment in which the pipe is intended, including the acidity, rockiness, and moisture content of the soil in underground installations. The temperature resistance required also depends on the temperature of the external environment, the temperature of the fluid being transported in the pipe, and the insulative properties of the pipe and its coatings.

[0004] Typically, steel pipe used for oil or gas transportation is coated, on the outside, to provide such corrosion resistance and mechanical protection. Such coating must also have temperature resistance, as noted. Such steel pipe may also be coated on the inside, to protect the internal steel wall of the pipe from corrosive elements found within the fluid being transported.

[0005] One such steel pipe known in the art is a three layer polyethylene system (3LPE), a multilayer coating composed of three

- 1 WO 2018/094519

PCT/CA2017/051395 functional components: a fusion bonded epoxy (FBE), followed by a copolymer adhesive, and an outer layer of polyethylene (PE). Primarily, the FBE layer provides excellent adhesion to steel, and corrosion resistance, while the outer layer of PE provides mechanical protection and impact resistance both during transportation and installation, and provides inground protection against shear forces, chemicals, and abrasive soil conditions. The copolymer adhesive layer, also known as a tie layer, provides compatibility between the FBE layer and the polyethylene layer, so that they can nicely bond.

[0006] Typically, such 3LPE pipe is manufactured utilizing a process including a preheating of the steel pipe, followed by a blast cleaning to generate anchor profile to increase the steel surface area for bonding; and grinding if needed to reduce or remove surface defects. The pipe is then heated, FBE is applied, typically through a powder coating process, and the tie layer is then extruded or spray applied. Polyethylene is then applied overtop of the tie layer, typically through an extrusion process, though spray application may also be utilized. The outer (or inner) pipe surface is cooled through a water quench, and, after inspection, the pipe is ready for installation. In certain optional embodiments, the outer PE coating can be crosslinked for added stability.

[0007] 3LPE pipe is commercially available from Bredero Shaw (Pearland, Texas) in a wide variety of diameters (from 90 mm to over 1220 mm), lengths (18 - 80 m) and coating thicknesses. It typically has a maximum recommended operating temperature of 85 degrees C (185 degrees F). Although PE has a much higher melting point (for high density PE, typically from 120-180 degrees C, and even low density PE, 105-115 degrees C), it has been found that the PE coated pipe loses its mechanical and impact resistance, as well as, to a certain extent, its ability to act as an effective water and oxygen barrier, at a much lower temperature. In addition, both mechanical properties, and long term bond stability remain questionable at greater than 90 degrees C in wet or damp environments.

- 2 WO 2018/094519

PCT/CA2017/051395 [0008] Similar coated 3LPP pipe is also available from Bredero Shaw and elsewhere, and is a three layer polypropylene coating: a high performance FBE, a copolymer adhesive, followed by an outer layer of polypropylene (PP). 3LPP provides a much more impact resistant pipe than PE, due to the properties of PP. It provides excellent mechanical protection and typically has a maximum recommended operating temperature of up to 110 degrees C (230 degrees F) in onshore applications. Again, although PP has a much higher melting point (130-170 degrees C), it has been found that the PP coated pipe loses its mechanical and impact resistance, as well as, to a certain extent, its ability to act as an effective water and oxygen barrier, at a much lower temperature. In addition, 3 layer PP coatings have been found to not be thermally stable at temperatures of greater than 110 degrees C when in the presence of oxygen.

[0009] Polyvinylidene fluoride (PVDF) is a specialty thermoplastic fluoropolymer, which is commercially available (for example, Kynar(R), from Arkema, Calvert City, Kentucky). PVDF is primarily known for its chemical resistance and inertness, as well as its intrinsic fire resistance. It is available in food grade and is often used as an internal liner in food fluid lines. It is also utilized as an intermediate layer in multi-layer fuel hoses to enhance strength and permeation resistance of the hose (for example, Polidan PEX, Algoflon DF, or Solef PVDF, all commercially available from Solvay (Brussels, Belgium). However, in conduit use, it appears that PVDF is always used as an internal liner or intermediate layer, and is not, to the Applicant's knowledge, utilized as an outer layer of a pipe. This may be due to its inherent inertness, which is quite desirable for an inner liner, but would be a useless property in an outer pipe coating.

[0010] Certain pipeline projects require more durable and corrosion resistant coatings than the ones provided by 3LPE or 3LPP. For example, corrosive acidic soils high in H₂S, and temperature requirements of upwards of 120 degrees Celsius are required in certain projects in Indonesia. Corrosive coastal sands in the Kingdom of Saudi Arabia have caused pipeline corrosion in 3LPP pipeline when operated at temperatures higher than 110 degree Celsius.

- 3 WO 2018/094519

PCT/CA2017/051395

BRIEF SUMMARY OF THE INVENTION [0011] According to certain aspects of the present invention is provided a coated pipe or conduit for oil and gas applications, comprising: a steel pipe having an outer surface; an anti-corrosion layer adhered or bonded to the outer surface of the steel pipe; a tie layer coating, adhered or bonded to the anti-corrosion layer; and a polyvinylidene fluoride (PVDF) coating, adhered or bonded to the tie layer coating.

[0012] In certain embodiments, the anti-corrosion layer is a fusion bonded epoxy or a liquid epoxy.

[0013] In certain embodiments, the fusion bonded epoxy is a high temperature fusion bonded epoxy or a high temperature liquid epoxy.

[0014] In certain embodiments, the tie layer coating comprises PVDF.

[0015] In certain embodiments, the tie layer coating is: a copolymer of

PVDF and maleic anhydride; a maleic anhydride grafted PVDF; an ethyleneglycidyl methacrylate copolymer; an ethylene-acrylic ester-maleic anhydride terpolymer; and/or an ethylene-acrylic ester-glycidyl methacrylate terpolymer.

[0016] In certain embodiments, the FBE coating is between 280-400 micrometers in thickness.

[0017] In certain embodiments, the tie layer coating is between 75150 micrometers in thickness.

[0018] In certain embodiments, the PVDF coating layer is between 760-1300 micrometers in thickness.

[0019] In certain embodiments, the PVDF coating layer is a PVDF homopolymer, a PVDF copolymer, a cross-linked PVDF, and/or a PVDF compound comprising reinforcing materials.

[0020] In certain embodiments, the reinforcing materials are carbon fibre, carbon nanotube, glass fibre, graphene, expanded graphite, mica, and/or calcium metasilicate.

- 4 WO 2018/094519

PCT/CA2017/051395 [0021] According to a further aspect of the present invention is provided a method of manufacturing a PVDF coated pipe or conduit, comprising: cleaning the outer surface of a steel pipe; applying a fusion bonded epoxy coating to the outer surface; applying a tie layer coating to the fusion bonded epoxy; applying a PVDF coating to the tie layer; and cooling the steel pipe to form the coated pipe.

[0022] According to certain embodiments, the cleaning comprises grit blasting.

[0023] According to certain embodiments, the applying of the fusion bonded epoxy coating comprises heating the steel pipe and applying a powder coat of the fusion bonded epoxy.

[0024] According to certain embodiments, the applying of the tie layer coating comprises spraying a PVDF powder coat or extruding a PVDF tie layer.

[0025] According to certain embodiments, the applying of the PVDF coating comprises extruding PVDF or spraying PVDF powder onto the tie layer.

[0026] According to certain embodiments, the tie layer is applied before the fusion bonded epoxy has completely gelled.

[0027] According to certain embodiments, the PVDF coating is applied after the tie layer has melted.

BRIEF DESCRIPTION OF THE DRAWINGS [0028] Reference will now be made, by way of example, to the accompanying drawings which show example embodiments of the present application, and in which:

[0029] Figure 1 shows a cross sectional schematic view of the three layer PVDF coated pipe of the present invention.

- 5 WO 2018/094519

PCT/CA2017/051395

DETAILED DESCRIPTION [0030] A three layer PVDF coating system is provided for oil or gas pipe. The system comprises a steel pipe, an epoxy layer, for example, made from a high temperature liquid epoxy or a FBE, preferably a high temperature FBE, which provides excellent adhesion to the steel pipe and anti-corrosion protection, a maleic anhydride modified PVDF tie layer which provides excellent bonding to both FBE and PVDF topcoat, and substantially blocks water and oxygen degradation of the FBE by forming a protective, bonded, coating overtop of the FBE, and a PVDF layer which provides a further excellent water and oxygen barrier, as well as excellent mechanical protection. Although the PVDF layer has a melting point very similar to PP (170-175 degrees C), surprisingly, unlike PE or PP coated pipe, the PVDF layer also withstands its impact resistance and O₂ and H₂O impermeability at temperatures approaching its melting point, for example, temperatures as high as 150 degrees Celsius, making the coating suitable for high temperature applications.

[0031] It has been found that a three layer PVDF coating system comprising a FBE coating of between 280-400 micrometers in thickness, followed by a PVDF tie layer of typically between 75-150 micrometers in thickness and an outer PVDF layer of 760 - 1300 micrometers in thickness provides excellent and desirable properties for high temperature applications. Specifically, these coatings are suitable for up to 150 degree C applications, and provides excellent H₂O and O₂ barrier and corrosion protection, excellent mechanical protection and impact resistance, at those temperatures.

[0032] In certain preferred embodiments, the PVDF tie layer can be a copolymer of PVDF and maleic anhydride, or a maleic anhydride grafted PVDF. Other tie layers, such as ethylene-glycidyl methacrylate copolymers, ethylene-acrylic esters - maleic anhydride terpolymers, ethylene-acrylic ester-glycidyl methacrylate terpolymers, or other compounds known to have good adhesion to both PVDF and FBE may also be used. For example Kynar

- 6 WO 2018/094519

PCT/CA2017/051395

ADX (R), from Arkema (King of Prussia, PA) has been found to be an effective tie layer.

[0033] In certain preferred embodiments, the PVDF outer coating layer can be made from Solef (R) PVDF, available from Solvay (Brussels, Belgium). The PVDF outer coating layer can comprise PVDF homopolymers, PVDF copolymers, cross-linked PVDF, and/or may further comprise reinforcing materials, such as carbon fibre, carbon nanotubes, glass fibre, graphene, expanded graphite, mica, or calcium metasilicate.

[0034] Figure 1 shows, in schematic view, and not to scale, a cross section of the three layer PVDF coated pipe of the present invention. Steel pipe 20 is coated with a high temperature FBE layer 22, which is in turn coated with a PVDF tie layer 24, which is in turn coated with a PVDF layer 26.

[0035] The three layer PVDF coated pipe is manufactured using the following methodology. The outer surface of the steel pipe is prepared by grit blasting to a SA2.5 or SSPC-SP10 rating, and preheated to 230-245 degrees Celsius. The pipe is visually inspected and surface defects are ground down. A high temperature FBE layer is applied, by powder coating, to the hot steel surface of the pipe, to a thickness of approximately 10-14 mils. Immediately following the FBE coating step, a PVDF tie layer is applied, either through powder spraying or an extrusion process. A PVDF topcoat is then applied, preferably by extrusion (at a die exit temperature of approximately 230-240 degrees), to a thickness of approximately 750-1300 microns, or thicker, depending on the degree of mechanical protection desired. In certain embodiments, for example for thick coatings, two or more extrusions and/or two or more extruders, running immediately downstream of one another, may be required to provide an even and thick coat. The coated pipe is then cooled, using for example an internal quench lance or an external water quench spray. The coated pipe can then be inspected for defects, for example, through an electrical inspection, then can be stacked and stockpiled for future use. Typically, the process is done inline, using a conventional pipe coating plant.

- 7 WO 2018/094519

PCT/CA2017/051395 [0036] The three layer PVDF coated pipes manufactured in this manner provide excellent mechanical performance, high resistance to impact and indentation, and a high external surface hardness. They provide exceptional barrier and thermal oxidative properties, good low temperature flexibility, excellent cathodic disbondment performance, and good coating adhesion to the steel pipe, even at high temperature or immersion in water.

Example 1: Manufacture of a 3LPVDF Pipe Length [0037] A 1.35 mm 3 layer PVDF coated pipe of the present invention is made as follows. A conventional steel pipe for oil or gas pipeline is prepared by grit blasting to SA2.5 and preheated to 240 degrees Celsius. The pipe is visually inspected to contain no significant surface defects. A high temperature FBE is applied to the hot external surface of the pipe, by powder coating, to a thickness of about 200 micrometers. A 150 micrometer layer of adhesive tie layer is powder coated directly overtop of the still hot FBE layer. A 1000 micrometer layer of PVDF is immediately extruded overtop of the tie layer. The coated pipe was cooled to about room temperature using an external water quench.

Example 2 - A 3LPVDF coating applied onto steel [0038] A steel panel similar in composition and thickness to the steel that is typically used in a steel oil or gas pipe was thermal pickled and grit blasted to a profile of Rz = 3-4 mils. The blasted panels were pre-heated in an oven to a measured temperature of 240-245 degrees C. An FBE layer was applied by dipping the steel panel in a fluidized bed of FBE (Pipeclad, Valspar (R)) to form a thickness of 11-14 mils. A PVDF tie layer (Solef(R), Solvay) was applied overtop of the FBE layer by an electrostatic spray gun. The tie layer was applied within the gel time of the FBE to ensure reactivity and bonding between the FBE and the tie layer. The tie layer was applied to approximately 3-6 mils of thickness. A PVDF top coat layer was applied by extrusion, within 15-20 seconds after application of the tie layer, to ensure the powder adhesive tie layer was melted (the tie layer was observed to

- 8 WO 2018/094519

PCT/CA2017/051395 become transparent and fused together). The coated panel was air cooled at ambient temperature for about 1 minute, followed by a 1 minute water quench. The coated panels were used as an effective surrogate for testing the chemical and mechanical properties of the same coating on a pipe.

Example 3 - Cathodic disbondment test [0039] Coated steel panels of Example 2 were tested for cathodic disbonding according to CSA Z245.21 clause 12.8.3 (incorporated herein by reference). Testing was conducted at room temperature and at both 65 degrees C and 95 degrees C in temperature controlled convection ovens with temperatures maintained within 3 degrees C of the set points. 140 degrees C and 150 degrees C testing was also conducted, using glass-housing with panel temperature maintained within 3 degrees of the set point. A hot water circulator was used to maintain electrolyte temperature at 95 ± 3 degrees C. After specified testing periods, samples were removed from the testing environment; PVDF topcoat thickness was reduced by grinding to improve disbondment evaluation; samples were cooled to 20 degrees C and the topcoat was ground to a total coating thickness of 25 mils. Within one hour, 8 radial cuts were inscribed on the coating down to the substrate with a utility knife and levering action was used to remove the coating. The disbonded distance along the radial cuts was measured, with excellent results at testing for up to 60 days. Results were summarized in Table 2, below. Cathodic disbondment test results at different test temperatures and durations were excellent, with disbondment radii of less than 6mm obtained after 28 days. Even after 60 days of CD test at room temperature, 65 and 95 degrees C, the 3LPVDF exhibited outstanding disbondment results of less than 6mm. In 150 degree C cathodic disbondment testing with electrolyte temperature of 95 degrees C, test results were also excellent - disbondment radius was less than 7mm. To evaluate the effect of thermal ageing on cathodic disbondment performance, cathodic disbondment performance (after 24 hours at 65°C) was evaluated after 3LPVDF coated panels were aged at 150°C for 28 days. Disbondment radii of un-aged samples were measured to be less than 3mm, while after aged samples had an averaged

- 9 WO 2018/094519

PCT/CA2017/051395 disbondment radius of less than 6mm. These results showed that the 3LPVDF coating retained strong CD resistance even after ageing. All CD results were well in the acceptance criteria of both ISO and CSA standards.

Table 2 - results of Cathodic Disbondment Test

Test Temperature (deg. C)	Test Duration	Acceptance Criteria (mm)	3LPVDF (mm)
23	28 days	7.0 max	4.5
60 days	Report value	5.2
65	7 days	10.0 max	1.5
14 days	2.5
28 days	15.0 max	5.4
60 days	Report value	5.0
95	7 days	10.0 max	2.3
14 days	15.0 max	2.4
28 days	5.5
60 days	Report value	5.8
150	7 days	10.0 max	2.0
28 days	6.3

Example 4 - Electrochemical impedance spectroscopy [0040] Coated steel panels of Example 2 were tested for impedance using electrochemical impedance spectroscopy. The panel was cut into test specimens and ABS cups were attached. The cell was filled with 3% NaCI and placed at test temperatures (room temperature, 65, and 95 degrees C). The impedance of the coating was determined using an Electrical Impedance Spectrophotometer (Solartron).

[0041] Results were summarized for various test temperatures, and after air drying at 150 degrees C for 28 days, in Table 3, below. EIS results showed that the impedance values decreased slightly from initial value and remained fairly constant (all with greater than 10⁹ohm-cm²) after 7 days to 120 days. Even for samples subjected to thermal ageing tests at 150°C for 28 days, the impedance values of all coating systems maintained at above

- 10 WO 2018/094519

PCT/CA2017/051395

10⁹ohm-cm² after 120 days, which demonstrated that the integrity of the coating was still maintained.

Table 3 - Electrochemical impedance spectroscopy

Test	Test temperature (deg. C)	Test duration (days)	Acceptance criteria	3LPVDF
Electrochemical Impedance Spectroscopy (ohms-cm²)	23	0	>1.0E10	1.3E+11
7	1.20E+11
28	1.59E+11
60	1.02E+11
120	4.48E+10
65	0	>1.0E08	1.96E+11
7	5.14E+10
28	4.07E+10
60	3.35E+10
120	2.09E+10
95	0	>1.0E07	9.81E+10
	7	3.70E+09
	28	1.59E+09
	60	2.97E+09
	120	3.51E+09
Electrochemical Impedence Spec, after air drying at 150 deg C for 28 days (ohms-cm²)	95	0	>1.0E07	4.58E+11
	7	3.34E+09
	14	3.55E+09
	28	1.96E+09
	60	2.13E+09
	120	3.90E+09

Example 5 - Flexibility testing [0042] Coated steel panels of Example 2 were cooled in a freezer to 30 degrees C and -40 degrees C. The thickness (in mm) of the sample, and the deflection angle were used to evaluate the mandrel radius using the application formula specified in CSA Z245.20 clause 12.11.3 (incorporated herein by reference). Within 30 seconds of being removed from the freezer, samples were bent over a mandrel with the radius closest to the calculated value. The specimen was checked for cracks after warming to room temperature using ISO 21809-1 Annex I (incorporated herein by reference).

- 11 WO 2018/094519

PCT/CA2017/051395

Results were tabulated in Table 4, below. 3LPVDF coating passed over 2.0°/pd bend at 0°C, 1.8°/pd bend at -30°C, and 1.8°/pd at -40°C.

Compared to typical 3LPP coating system, 3LPVDF coating has very good low temperature flexibility.

Table 4 - Flexibility testing

Testing temperature (°C)	acceptance criteria (°/pd)	3LPVDF (°/pd)
0	>2	3.7
-30	Report value	1.8
-40	Report value	1.8

Example 6 - Peel Testing [0043] Peel strength at 23°C, 90°C and 150°C were determined using Instron(TM) 4460 at 1 cm/min pulling rate, pulling 1 wide coating strips, perpendicular to the coating surface, with peel strength (N/mm) and failure modes recorded. At room temperature, samples could not be peeled, similar to HPPC and Surebond (TM) prior art systems. The peel strength was greater than 9 N/mm when tests were conducted at 90°C. The mode of failure was cohesive failure of the PVDF tie layer. Peel tests were conducted at targeted operating temperature of 150°C; the 3LPVDF coating samples did not peel at any interface, but the PVDF topcoat stretched with strength greater than 5.8 N/mm. These tests indicate good bond strength between the 3LPVDF and metal, and between the 3 layers within the coating system. Results were tabulated in Table 5.

Table 5 - Peel test

Test temperature (deg C)	Acceptance criteria	3LPVDF (N/mm)
23	>25	Cannot be peeled
90	>4	>9.0 (cohesive failure of PVDF tie layer
150	Report value	>5.8 (did not peel; PVDF stretched)

- 12 WO 2018/094519

PCT/CA2017/051395

Example 7 - Heat Ageing [0044] Coated steel panels of Example 2 were subjected to 150°C in a convection oven for 28, 60, or 120 days. Samples were removed and allowed to cool to room temperature. Topcoat was ground to a final coating thickness of less than 25 mils. Adhesion was rated using the method described in ISO21809-2 Clause A.4 (incorporated herein by reference). 28 and 60 day samples achieved an R1-R2 rating, where 120 day samples achieved an R2 rating. Adhesion rating thus remained excellent after 60 days, and exhibited a rating of 2 after 120 days.

Example 8 - Adhesion after hot water immersion [0045] Coated steel panels of Example 2 were submerged in 95°C and 120°C water baths. After specified testing periods, samples were removed. Adhesion was evaluated on a scale of 1-5 according to CSA Z245.20 clause 12.14.3, incorporated herein by reference. Tests were performed as per ISO 21809-1 Annex C and results were tabulated in Table 6 below. It was found that the adhesion rating maintained 1-2 after 28 day immersion, which indicated that the bond at the coating/metal interface remained excellent. The bond deteriorated slightly after soaking in hot water for 60 and 120 days, and the adhesion rating remained at 3 (with adhesive failure at the FBE/coating interface) which was still within the acceptance criteria.

Table 6 - Hot water immersion test

Test temperature (deg C)	Test duration (days)	Acceptance criteria	3LPVDF (adhesion rating)
95	7	R1-R3	R2
	14	R1-R3	R2
	28	R1-R3	R1-R2
	60	Report value	R2-R3
	120	Report value	R2-R3
120	7	R1-R3	R1-R2
	14	R1-R3	R1-R2
	28	R1-R3	R1-R2
	60	Report value	R2-R3
	120	Report value	R3

- 13 WO 2018/094519

PCT/CA2017/051395

Example 9 - Impact resistance [0046] Coated Steel panels of Example 2 were cooled in a freezer to 40°C or heated in a convection oven to 75°C and held at these temperatures for more than 1 hour. Samples were tested according to CSA Z245.20 clause 12.12.3 (incorporated herein by reference). Each specimen was impacted several times with the impact points at least 50mm away from each other. A DC holiday detector, set at 15000V, was used to test the panels after they were conditioned to room temperature. Results were tabulated in Table 7, below. It was found that PVDF could generally withstand a maximum of 14 J/mm at -40°C, 20 J/mm at room temperature and 18 J/mm at 75°C, well exceeding the impact requirements for 3LPE/PP as per ISO 21809-1.

Table 7 - Impact Resistance

Test temperature (°C)	Acceptance criteria	3LPVDF (J/mm)
-40	>3	14
23	>3	20
75	>3	18

Example 10 - Indentation Resistance [0047] Coated steel panels of Example 2 were tested according to DIN 30678 (incorporated by reference) in a convection oven at room temperature, 120°C and 150°C ±1°C for 24 hours. The depth of penetration was monitored by Keyence GT2-70 LVDT. Results were tabulated in Table 8, below. The tests demonstrated that PVDF topcoat is hard and has excellent indentation resistance at high temperature. The penetration depths after 24 hours at RT, 120°C and 150°C were less than 0.02, 0.12 and 0.14mm, respectively, well exceeding indentation requirements for 3LPE/PP as per ISO 21809-1.

- 14 WO 2018/094519

PCT/CA2017/051395

Table 8 - Indentation resistance

Test temperature (°C)	Acceptance criteria	3LPVDF (mm)
23	<0.1	<0.02
120	<0.4	<0.12
150	<0.4	<0.15

Example 10 - Shore D hardness test [0048] Coated steel panels of Example 2 were tested for Shore D hardness as per ASTM D2240 (incorporated herein by reference). Test panels were flat with thickness greater than 6mm. At least 5 measurements were conducted at different positions on each panel, 6mm apart. Shore D hardness was also measured at 23°C, 50°C and 80°C. Results were tabulated in Table 9, below. Hardness decreases slightly from 78 at RT to 70 at 80°C, but greatly exceeded acceptance criteria for 3LPE/PP.

Table 9 - Shore D Hardness

Test temperature (°C)	Acceptance criteria	3LPVDF (ASTM D2240)
23	>70	78
50	Report value	75
80	>60	70

[0049] The 3LPVDF coating system thus exhibits excellent mechanical performance (high resistance to impact, high resistance to indentation, and high hardness), exceptional barrier and thermal oxidative properties, good low temperature flexibility, excellent CD performance, good adhesion to metal at high temperature and good coating adhesion after immersed services. In addition to its excellent performance, it is generally simple to process and manufacture. 3LPVDF is an excellent coating system for onshore applications with operating temperatures beyond 110°C and up to 150°C.

- 15 WO 2018/094519

PCT/CA2017/051395

Example 11 - Comparison test to 3LPP [0050] A steel panel similar in composition and thickness to the steel that is typically used in a steel oil or gas pipe was prepared by grit blasting to SA2.5 and preheated to 240 degrees Celsius. The panel was visually inspected to contain no significant surface defects. A high temperature FBE was applied to the hot external surface of the pipe, by powder coating, to a thickness of about 200 micrometers. A 150 micrometer layer of adhesive tie layer was powder coated directly overtop of the still hot FBE layer. A 1000 micrometer layer of PVDF was immediately extruded overtop of the tie layer. The coated pipe was cooled to about room temperature using an external water quench.

[0051] The coating characteristics were compared to a prior art 3LPP coated panel similar diameter, but having a 2.0 mm thickness (250 micrometer FBE, 200 micrometer adhesive, and 1500 micrometer polypropylene) versus the 1.35 mm 3-layer PVDF coating.

[0052] The results of testing were summarized in Table 10.

Table 10 - comparison of 3LPVDF pipe and prior art 3LPP pipe

Properties	Unit	Test Method	PP	PVDF
Impact Strength at 40°C	J/mm	ISO21809-1 Annex B	8	14
Impact Strength at 23°C	J/mm	ISO21809-1 Annex B	14	20
Impact Strength at 80°C	J/mm	ISO21809-1 Annex B	10	18
Indentation at 23°C	mm	ISO21809-1 Annex F	0.03	<0.02
Indentation at 120°C	mm	ISO21809-1 Annex F	N/A	<0.12

- 16 WO 2018/094519

PCT/CA2017/051395

Indentation at 150°C	mm	ISO21809-1 Annex F	N/A	<0.15
Shore D Hardness at RT		ASTM D2240	66-76	78
Shore D Hardness at 80°C		ASTM D2240	57	70
CDT at 23°C/28d/1.5V	mm	ISO21809-1 Annex H	<7.0	4.5
CDT at 65°C/24h/1.5V	mm	ISO21809-1 Annex H	<7.0	2.8
CDT at 65°C/28d/1.5V	mm	ISO21809-1 Annex H	<15.0	3.6
CDT at 95°C/28d/1.5V	mm	ISO21809-1 Annex H	<15.0	4.2
CDT at 150°C/28d/1.5V	mm	ISO21809-1 Annex H	N/A	4.0
(with electrolyte temp of 95°C)
Flexibility at 0°C	°/pd	ISO21809-1 Annex I	No cracking at 2.0°/pd	>2.5
Flexibility at - 30°C	°/pd	ISO21809-1 Annex I	N/A	>2.0
Flexibility at - 40°C	°/pd	ISO21809-1 Annex I	N/A	>2.0

- 17 WO 2018/094519

PCT/CA2017/051395

Peel at 23°C	N/mm	ISO21809-1 Annex C	>25	Cannot Peel
Peel at 90°C	N/mm	ISO21809-1 Annex C	>4	>9.0 (coh failure of PVDF Adh)
Peel at 150°C	N/mm	ISO21809-1 Annex C	N/A	>5.8 (Did not peel; PVDF Stretched)
HWI at 80°C/48h (with deionized water)	mm	ISO21809-1 Annex M	Avg. <2 and max. <3	0
HWI at 95°C/28d	Rating	CSAZ245.20/21	R2	R2
HWI at 120°C/28d	Rating	CSAZ245.20/21	N/A	R2
Heat ageing at 150°C for 28d - Adhesion Test	Rating	ISO21809-2 Annex E	N/A	R1-R2
Heat ageing at 150°C for 60d - Adhesion Test	Rating	ISO21809-2 Annex E	N/A	R1-R2
Heat ageing at 150°C for 120d - Adhesion Test	Rating	ISO21809-2 Annex E	N/A	R2

- 18 WO 2018/094519

PCT/CA2017/051395 [0053] In general, 3LPVDF met and/or exceeded the performance of a 3LPP coating at PP's maximum service temperature of 110°C. Since the maximum service temperature for 3LPP is 110°C, tests with temperature above 110°C were not carried out for 3LPP. Results showed that the 3LPVDF coating system performed excellently in tests which were above 110°C, and based on the results of the test program, it was found that the 3LPVDF coating system performed well at service temperature of 150°C.

- 19 WO 2018/094519

PCT/CA2017/051395

Claims

Claims:

1. A coated pipe or conduit for oil and gas applications, comprising:

a. a steel pipe having an outer surface;

b. an anti-corrosion layer adhered or bonded to the outer surface of the steel pipe;

c. a tie layer coating, adhered or bonded to the anti-corrosion layer; and

d. a polyvinylidene fluoride (PVDF) coating, adhered or bonded to the tie layer coating.
2. The coated pipe or conduit of claim 1, wherein the anti-corrosion layer is a fusion bonded epoxy or a liquid epoxy.
3. The coated pipe or conduit of claim 2 wherein the fusion bonded epoxy is a high temperature fusion bonded epoxy or a high temperature liquid epoxy.
4. The coated pipe or conduit of claim 1 wherein the tie layer coating comprises PVDF.
5. The coated pipe or conduit of claim 4 wherein the tie layer coating is selected from the group consisting of: a copolymer of PVDF and maleic anhydride; a maleic anhydride grafted PVDF; an ethylene-glycidyl methacrylate copolymer; an ethylene-acrylic ester-maleic anhydride terpolymer; and an ethylene-acrylic ester-glycidyl methacrylate terpolymer.
6. The coated pipe or conduit of claim 1 wherein the FBE coating is between 280-400 micrometers in thickness.
7. The coated pipe or conduit of claim 1 wherein the tie layer coating is between 75-150 micrometers in thickness.
8. The coated pipe or conduit of claim 1 wherein the PVDF coating layer is between 760-1300 micrometers in thickness.

- 20 WO 2018/094519

PCT/CA2017/051395
9. The coated pipe or conduit of claim 8 wherein the PVDF coating layer is selected from the group consisting of a PVDF homopolymer, a PVDF copolymer, a cross-linked PVDF, and a PVDF compound comprising reinforcing materials.
10. The coated pipe or conduit of claim 8 wherein the reinforced materials are selected from the group consisting of carbon fibre, carbon nanotube, glass fibre, graphene, expanded graphite, mica, and calcium metasilicate.
11. A method of manufacturing a coated pipe or conduit of claim 1 from a steel pipe, comprising:

a. cleaning the outer surface of the steel pipe;

b. applying a fusion bonded epoxy coating to the outer surface;

c. applying a tie layer coating to the fusion bonded epoxy;

d. applying a PVDF coating to the tie layer;

e. cooling the steel pipe to form the coated pipe.
12. The method of claim 9 wherein the cleaning comprises grit blasting.
13. The method of claim 9 wherein the applying of the fusion bonded epoxy coating comprises heating the steel pipe and applying a powder coat of the fusion bonded epoxy.
14. The method of claim 9 wherein the applying of the tie layer coating comprises spraying a PVDF powder coat or extruding a PVDF tie layer.
15. The method of claim 9 wherein the applying of the PVDF coating comprises extruding PVDF or spraying PVDF powder onto the tie layer.
16. The method of claim 9 wherein the tie layer is applied before the fusion bonded epoxy has completely gelled.
17. The method of claim 9 wherein the PVDF coating is applied after the tie layer has melted.