Method for coating a tube

Abstract

A method of applying a corrosion resistant coating to a pipe section by extruding a viscoelastic material from an extruder onto an outer surface of the pipe section while imparting rotational and longitudinal movement to the pipe section, and while adjusting at least one process parameter to ensure that a thickness of the corrosion resistant coating is in a range of 500 [mu] m to 2000 [mu] m.

Description

Technical Field

[0001] The present invention relates to a method for coating a metal pipe for corrosion resistance. Background Art

[0002] Underground pipelines are commonly used to transport water, sewage, oil, gas or petroleum products, etc. These pipelines are made of multiple sections, typically measuring approximately 19 meters in length, with diameters ranging from about 100 mm to 1500 mm, with an average of 900 mm. The pipe sections can be composed of a variety of materials, including metals (such as steel) as well as concrete, plastics / polymers or composite materials.

[0003] Steel pipe is often preferred due to the mechanical diversity of the material across a wide range of applications. Typical wall thickness polymer pipes do not have the hoop strength, tensile strength and / or yield strength to transport fluids under high pressure. In order to make such pipes suitable for transporting high pressure fluids, the wall thickness must be increased, significantly increasing the cost. Compared to this alternative, steel pipe remains cost effective. However, steel is prone to rust. Therefore, it is necessary to apply corrosion protection to the pipe section to increase the service life of the pipeline to maintain cost-effectiveness.

[0004] Conventional methods for applying corrosion resistant coatings to pipe sections involve a complex, expensive, multi-step process that includes the steps of: 1) preheating the pipe section, 2) blast cleaning the outer surface of the pipe section, 3) surface grinding the outer surface, 4) inspecting the outer surface, 5) heating the pipe to between 180°C and 250°C, 6) applying a primary coating of fusion bonded epoxy (FBE) to the outer surface, 7) extruding a bonding copolymer over the FBE, 8) extruding a mechanical coating of a polyolefin, such as polypropylene (PP), over the bonding layer, 9) cooling the pipe by quenching, and 10) inspecting the pipe section for discontinuities in the coating using conductivity testing.

[0005] As is evident, extensive pre-coating preparation is necessary to ensure a clean exterior surface, free of any film or scale, with an accurate surface profile in accordance with standards SA 2.5 to 3. These measures are crucial to ensure that the primary and first coatings adhere correctly to the exterior surface.

[0006] Furthermore, the application of the FBE primer (primary coating) requires heating the pipe section to high temperatures, resulting in an energy consuming step. Subsequently, a quenching process is necessary due to the elevated temperatures involved.

[0007] This conventional three-layer system requires the presence of a tie layer to join the outer mechanical layer to the FBE primer.

[0008] In another energy-consuming step, considerable heat input is required to enhance the flexibility of the copolymer when the adhesive copolymer is extruded onto the outer surface using a secondary extruder along with the primary extruder. This parameter is another critical aspect that requires careful control of the extrusion process to achieve optimal film thickness.

[0009] The present invention at least partially solves the aforementioned problems. Summary of the invention

[0010] When used to describe a coating, "mechanical resistance" means that the coating and the materials it comprises are resistant to fatigue (the progressive and localized structural damage that occurs when a material is subjected to repeated cyclic loading or stress), stress, heat, cathodic disbonding, and oxidation.

[0011] The present invention provides a novel method for effectively applying a corrosion resistant coating to a pipe section.

[0012] The present invention provides a method for applying a corrosion-resistant coating to a pipe segment by extruding a viscoelastic material from an extruder onto the outer surface of the pipe segment while imparting rotational and longitudinal motion to the pipe segment, and simultaneously adjusting at least one process parameter to ensure that the thickness of the corrosion-resistant coating is in the range of 500 μm to 2000 μm.

[0013] Preferably, the thickness of the corrosion resistant coating is in the range of 900 μm to 1100 μm.

[0014] More preferably, the thickness of the corrosion-resistant coating is 1000 μm.

[0015] At least one process parameter may be the temperature of the viscoelastic material, the viscosity of the viscoelastic material, the force / pressure applied to the viscoelastic material as the material is extruded from the extruder, the temperature within the extruder, the flow rate of the viscoelastic material as it leaves the extruder, the angular velocity of the rotational motion of the tube segment, the longitudinal velocity of the longitudinal motion of the tube segment, the distance of the outlet slot of the extruder from the tube segment, the angular orientation of the outlet slot relative to the tube segment, and the width or area of ​​the outlet slot (hereinafter referred to as "process parameters").

[0016] The temperature of the viscoelastic material may be adjusted to be maintained within the range of 30°C to 100°C.

[0017] The corrosion resistant coating may be applied directly to the outer surface of the pipe section, ie without applying a primary coating or primer.

[0018] Preferably, the viscoelastic material is polyisobutylene (PIB).

[0019] Alternatively, the viscoelastic material may be a mixture of PIB and butyl rubber.

[0020] The pipe section may be a metal pipe section. Preferably, the metal pipe section is a steel pipe section.

[0021] The method may comprise the additional step of applying a mechanically resistant coating over the corrosion resistant coating.

[0022] The step of applying the mechanically resistant coating may be performed simultaneously with the step of applying the corrosion resistant coating. The simultaneous application may be achieved by coextrusion, preferably in-line coextrusion.

[0023] Alternatively, the step of applying the mechanically resistant coating may be performed after the step of applying the corrosion resistant coating.

[0024] The mechanical coating may be a coating of a thermoplastic material such as a polyolefin. The polyolefin may be medium density or high density polyethylene, polypropylene.

[0025] Alternatively, the mechanical coating may be an elastomeric polyurea material, or a thermosetting glass reinforced epoxy (GRE).

[0026] Thermoplastic materials can be applied by extrusion.

[0027] The GRE material may be applied by any suitable method, such as spraying or by spinning a flexible GRE sheet onto the pipe section.

[0028] The elastomeric polyurea material can be applied by spraying.

[0029] Viscoelastic materials and thermoplastic materials can be extruded by passing the respective materials through a slot die. The slot die can be a slot die with a lip.

[0030] The method may comprise the additional, preferably preceding step of grinding the outer surface of the pipe section by brushing or blasting to remove oxide scale.

[0031] The method may comprise the additional step of scraping away excess viscoelastic material from the corrosion resistant coating to ensure that the corrosion resistant coating has a selected thickness in the range of 500 μm to 2000 μm, preferably in the range of 900 μm to 1100 μm, more preferably 1000 μm.

[0032] Another aspect of the present invention provides a method for extruding a corrosion-resistant coating of a viscoelastic material onto the outer surface of a pipe section from an extruder while imparting rotational and longitudinal motion to the pipe section to ensure that the thickness of the corrosion-resistant coating is a desired thickness, the method comprising the steps of: a) inputting a data set into a processor running a program, the data set comprising a measured value of the thickness of the corrosion resistant coating and information of one or more process parameters related to the measured thickness; b) inputting data into the processor from at least one sensor or instrument suitable for measuring one or more of the process parameters; c) obtaining an estimated thickness of the corrosion resistant coating based on the data set and the data from the processor; and d) Based on the estimated thickness, changing one or more of the parameters to achieve the desired thickness.

[0033] The program may include artificial intelligence algorithms. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the invention will now be described by way of non-limiting example only, with reference to the accompanying drawings, in which: FIG1 schematically illustrates a process of applying a corrosion resistant layer to a pipe according to the prior art; Figure 2 Schematically illustrates a process for applying a corrosion resistant coating to a pipe including a method according to the invention; Figure 3 is a horizontal cross-sectional view through a slot die extruder employed in the method of the present invention; Figure 4 is through Figure 3 A cross-sectional view taken along line 4-4 in FIG. Figure 5 Schematically illustrates the extrusion step in the method of the present invention; Figure 6 schematically showing in more detail the slot die in the extrusion step; Figure 7 is an isometric view of a pipe section coated with a corrosion resistant pipe according to the method of the present invention; Figure 8 is a flow chart of a computerized system employed in the method of the present invention. DETAILED DESCRIPTION Figure 2 A method 10 is shown for applying a corrosion resistant coating 12 to a pipe section 14. The pipe section may be used in any environment, including onshore, offshore, or underwater environments, where exposure to corrosive elements is a problem.

[0036] The pipe sections 14 in this example are steel pipe sections, typically 19 metres in length and approximately 900 mm in diameter.

[0037] When applying the corrosion-resistant coating 12, the pipe section 14 is oriented in the longitudinal direction (see Figure 7 Specified as V a direction arrow) and in the direction of rotation (see Figure 7 Specified as V r ) in the direction of the arrow.

[0038] In a first process step 16, the outer surface 18 of the pipe section is mechanically ground by any suitable method, such as, for example, wire brushing, shot peening, etc. This process requires only the removal of scale. No profile is required, and therefore no testing of the best profile is required, and the projectile material can be a standard conventional blasting material. The grinding of the outer surface will pit the surface, providing a rough ground surface profile 20 to which the coating material to be applied in the previous step adheres. This step is a preferred step, but it is not essential to the method. This step cleans any oily residue on the surface and removes any moisture.

[0039] In a second process step 22 , a corrosion resistant coating 12 of polyisobutylene (PIB) from a source 23 is applied to the outer surface 18 of the pipe segment 14 by means of extrusion through a slot die extruder 24 .

[0040] In a third process step 26 , a mechanically resistant coating 28 is applied over the corrosion resistant coating.

[0041] The mechanically resistant coating may be a coating of a thermoplastic material such as, for example, medium density and high density polyethylene, polyurea, polypropylene or an elastomeric material, or a coating of a thermosetting material such as a glass reinforced epoxy (GRE) material. The material selection for the coating will depend on cost, environmental, and ultimately, functional considerations.

[0042] If the mechanical resistant coating is a medium density polyethylene, high density polyethylene or polypropylene 30, the coating can be applied to the outer surface 18 by extrusion through a second slot die extruder. If a GRE spin coat or an elastomeric polyurea material (applied by spraying) is selected as a suitable material for the mechanical resistant coating, other application methods are used. It is important to note that the mechanical resistant coating is wet applied directly over the PIB coating.

[0043] In all pipelines, a mechanical coating is applied as a standard coating over the corrosion protection layer. Typical reasons for this coating include protection during transportation and stacking, and meeting engineers' requirements for additional mechanical resistant coatings. This coating is important because PIB is a soft, compliant material that exhibits many advantageous properties (listed below). Pipe sections typically range between 2 and 5 tons, and during storage and transportation, locations along the pipe sections are susceptible to high point loads that can damage the coating.

[0044] In this example, the corrosion resistant coating and the mechanical coating are applied in separate process steps. However, it is envisaged within the scope of the invention that both coatings may be applied simultaneously, for example by a coextrusion process.

[0045] Finally, the pipe sections are inspected to ensure that no discontinuities / holes are present in the corrosion resistant coating. This is done by employing a leak detection step 34. If the pipe sections 14 pass the test, they can be stacked and stored ready for deployment in a pipeline (not shown).

[0046] In further describing the present invention, and for ease of explanation, the application of the mechanical coating 28 will not be described further.

[0047] Figure 3 and Figure 4 The slot die head 36 of the slot die extruder 24 is shown. This component is an integral part of the configuration technology provided by the extruder. The slot die head includes a body 38, an inlet 40, a slot 42 (see Figure 6 ), the slot is comprised of a manifold 43 and a protrusion 44, optionally a throttle lever 46 (which can be actuated to vary the flow rate of the PIB through the slot) and a lip 48. In addition to the slot head, the extruder 32 includes a throat 50.

[0048] Inlet 40 terminates in a supply conduit 52 that delivers PIB from PIB source 23 to the extruder. PIB is delivered at ambient room temperature (+ / - 25°C). A screw pump 56 or any alternative pressurizing device (such as a non-stick fast rotating back roller (not shown)) can be used to apply pressure to the PIB delivery stream to force the delivery stream of PIB paste or putty into the throat 50. In the case where the PIB paste is pressurized as it flows through the extruder, it will heat up due to frictional engagement with the extruder, thereby increasing its fluidity. However, it is expected that the temperature will not exceed 50°C.

[0049] Within the throat, the extruder may include heating elements (not shown). When the ambient temperature is below 23°C, these heating elements may be activated to supply heat 58 to the PIB, changing the viscosity of the PIB to a more fluid state.

[0050] A fluid stream 60 of PIB is extruded from the slot die 36, passes through the slot 42, and exits the head at the lip 48. Between the lip and the outer surface 18 of the tube section 14 (gap 62), the PIB forms a coating bead 64 (see Figure 6 ), a coating bead 64 is formed between an upstream meniscus 66 and a downstream meniscus 68 before the bead flows out to provide the corrosion resistant coating 12.

[0051] In order to provide a corrosion resistant PIB coating 12 that is uniformly applied to the outer surface of the pipe segment in terms of thickness and uninterrupted surface coverage, it is necessary to maintain stability in the configuration of the coating bead 64. This stability depends on the following variable parameters—the distance from the lip to the pipe gap (a), the width of the groove 42 (b), the viscosity of the PIB (μ), the temperature within the extruder 24 (t), the output flow rate of the PIB stream (V e ), the orientation of the lip 48 relative to the tube, the angular velocity of rotation of the tube segment (Vr ), the longitudinal velocity of the pipe section (V a ) and the input force (f) applied to the PIB flow by a pressurizing device (such as a screw pump 56).

[0052] A benefit of extruding PIB is that no heat input is required when extruding, thereby improving the stability of the construction of coating beads 64 if the ambient temperature is maintained at or above 23° C. Even though PIB is extruded at this relatively low temperature, it is sufficiently fluid to form a coating on the tube with a uniform thickness of 1000 μm.

[0053] Applicants have found this preferred thickness to be optimal. With any increase in thickness, the cost-effectiveness ratio increases, and with any decrease in thickness, the anti-corrosion effectiveness of the layer decreases significantly.

[0054] In order to control the quality of the corrosion resistant coating 12, a computerized control system is provided. These parameters (a, b, μ, t, f, V, respectively) as measured by relevant sensors or instruments (not shown) e 、V r 、V a ) are fed in real time to a processor 72. A manual input 76 of the desired thickness of the coating 12 is provided. Running relevant software, firmware or AI algorithms, and utilizing historical data from a database 78, the processor will provide an output 80 of remedial actions to be taken to achieve the desired coating thickness based on the real time data stream.

[0055] Remediation can occur automatically or manually.

[0056] Remedial measures may take one or more of the following: energizing the heating element to heat the PIB, adjusting the distance of the gap 62 or the orientation of the lip 48 (hereinafter, the die positioning system 82), adjusting the force applied by the screw pump 56, adjusting the width of the slot 42 (by actuating the throttle rod 46), and adjusting the angular velocity and forward speed of the tube section (hereinafter, the tube movement system 84).

[0057] The benefit of using polyisobutylene (PIB) in the corrosion resistant layer is that the material does not delaminate or detach from the surface of the pipe section, it is able to "self-heal" to close any pores, and adheres to the surface at a molecular level and at ambient temperature.

Claims

1. A method for applying a corrosion resistant coating to a pipe segment by extruding a viscoelastic material from an extruder onto the outer surface of the pipe segment while imparting rotational and longitudinal motion to the pipe segment and while adjusting at least one process parameter to ensure that the thickness of the corrosion resistant coating is in the range of 500 μm to 2000 μm.

2. A method of applying a corrosion resistant coating to a pipe section according to claim 1, wherein: The thickness of the corrosion resistant coating is in the range of 900 μm to 1100 μm.

3. A method of applying a corrosion resistant coating to a pipe section according to claim 2, wherein: The thickness of the corrosion-resistant coating is 1000 μm.

4. A method for applying a corrosion resistant coating to a pipe section according to any one of claims 1 to 3, wherein: The at least one process parameter is one of: the temperature of the viscoelastic material, the viscosity of the viscoelastic material, the force or pressure applied to the viscoelastic material when the material is extruded from the extruder, the temperature inside the extruder, the flow rate of the viscoelastic material as it leaves the extruder, the angular velocity of the rotational motion of the tube segment, the longitudinal velocity of the longitudinal motion of the tube segment, the distance of the outlet slot of the extruder from the tube segment, the angular orientation of the outlet slot relative to the tube segment, and the width or area of ​​the outlet slot.

5. A method for applying a corrosion resistant coating to a pipe section according to any one of claims 1 to 4, wherein: The temperature of the viscoelastic material is adjusted to be maintained within a range of 30°C to 100°C.

6. A method of applying a corrosion resistant coating to a pipe section according to claim 1 or 5, wherein: The corrosion resistant coating is applied directly to the outer surface of the pipe segment.

7. A method of applying a corrosion resistant coating to a pipe section according to any one of claims 1 to 6, wherein: The viscoelastic material is polyisobutylene (PIB), or a mixture of PIB and butyl compound.

8. A method of applying a corrosion resistant coating to a pipe section according to any one of claims 1 to 7, comprising the step of applying a mechanically resistant coating over the corrosion resistant coating.

9. A method of applying a corrosion resistant coating to a pipe section according to claim 8, wherein: The mechanically resistant coating is applied simultaneously with the application of the corrosion resistant coating.

10. A method of applying a corrosion resistant coating to a pipe section according to claim 9, wherein: The mechanically resistant coating and the corrosion resistant coating are applied simultaneously by coextrusion or in-line extrusion.

11. The method of applying a corrosion resistant coating to a pipe section according to claim 8, wherein: The mechanically resistant coating is applied after the corrosion resistant coating is applied.

12. A method of applying a corrosion resistant coating to a pipe section according to any one of claims 8 to 11, wherein: The mechanical coating includes one or more of: polyolefin, elastomeric polyurea, and thermosetting glass reinforced epoxy (GRE).

13. A method of applying a corrosion resistant coating to a pipe section according to claim 12, wherein: The polyolefin is applied by extrusion.

14. The method of applying a corrosion resistant coating to a pipe section according to claim 12, wherein: The GRE is applied by spraying or by spinning a flexible GRE sheet onto the pipe section.

15. The method of applying a corrosion resistant coating to a pipe section according to claim 12, wherein: The elastomeric polyurea material is applied by spraying.

16. A method of applying a corrosion resistant coating to a pipe section according to any one of claims 1 to 15, wherein: The viscoelastic material and the thermoplastic (polyolefin) material are extruded by passing the respective materials through a slot die.

17. A method of applying a corrosion resistant coating to a pipe section according to claim 16, wherein: The slot die is a slot die with a lip.

18. A method of applying a corrosion resistant coating to a pipe section according to any one of claims 1 to 17, comprising the step of abrading the outer surface of the pipe section by brushing or spraying to remove oxide scale prior to extruding the viscoelastic material.

19. A method of applying a corrosion resistant coating to a pipe section according to any one of claims 1 to 18, comprising the additional step of scraping excess viscoelastic material from the corrosion resistant coating to ensure that the coating has a selected thickness in the range of 500 μm to 2000 μm.

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