Heat exchanger tubes

Abstract

A method of forming a tube portion T for a heat exchanger HE. Two or more external supports (7) have part-cylindrical tube-facing portion. The method comprises dimpling a precursor tube portion to form dimples. The dimpling comprises the two or more external supports (converging, relative to each other, on the precursor tube portion to radially support a portion of the precursor tube portion via the part-cylindrical tube-facing portions to form a supported tube portion) and moving one or more tool portions 9 against, to inwardly deform, one or more dimple sites within and spaced from ends of the supported tube portion.

Description

[0001] P1927PCAU

[0002] 1

[0003] HEAT EXCHANGER TUBES

[0004] FIELD

[0005] This invention relates to heat exchanger tubes, heat exchangers comprising tubes and methods associated with heat exchanger tubes.

[0006] BACKGROUND

[0007] Figure 1 illustrates a heat exchanger HE comprising a vessel V, tubes T, baffles B and tube plates TP. The vessel V is cylindrical and capped by headers VH. Each tube T is a straight cylindrical tube having a uniform circular cross-section along its length. The tubes T run the length of the vessel V and open into the headers VH. Vessel fluid enters the vessel via a vessel inlet Vi and flows through the vessel to vessel outlet Vo.

[0008] The baffle plates are half-circular plates to span half of the circular interior of the vessel V. Each baffle B is penetrated by holes through which the tubes T pass. The baffles B serve to guide the vessel fluid as it travels through the vessel V. In the illustrated example, the baffles B guide the vessel fluid to follow a serpentine path from the vessel inlet Vi to the vessel outlet Vo. As such, the tubes T are bathed in the vessel fluid and the baffles guide the fluid to flow across the tubes.

[0009] The tube fluid flows from the tube inlet Ti of the header VH to the tube outlet To of the other header VH via the interiors of the tubes T. In this way, the heat exchanger thermally connects the tube fluid to the vessel fluid for heat exchange therebetween.

[0010] Figure 2 illustrates the initial applicant’s own baffle-less heat exchanger HE' comprising dimpled inner and outer tubes T', V'. The inner tube T' fluidly connects the inlet Ti' to outlet To' whilst the outer tube V' fluidly connects the inlet Vi' to the outlet Vo'.P1927PCAU

[0011] 2

[0012] Figure 3 illustrates an oil refining process in which crude oil CO heated in a crude oil preheater comprising heat exchanger HE enroute to distillation tower DT. In the distillation tower the crude oil separate into heavier fractions such as asphalt AS, heavy fuel oil HFO, lubricating oils LO and gases G. The composition of crude oil varies but typically more than 5% of crude oil boils at atmospheric pressure at not less than 500°C.

[0013] The invention aims to provide improvements, or at least alternatives, for heat exchangers comprising baffles.

[0014] It is not admitted that any of the information in this patent specification is common general knowledge, or that the person skilled in the art could be reasonably expected to ascertain or understand it, regard it as relevant or combine it in any way before the priority date.

[0015] SUMMARY

[0016] One aspect of the invention provides a method of forming a tube portion for a heat exchanger;

[0017] wherein two or more external supports have part-cylindrical tube-facing portions;

[0018] the method comprises dimpling a precursor tube portion to form dimples; and

[0019] the dimpling comprises

[0020] the two or more external supports converging, relative to each other, on the precursor tube portion to radially support a portion of the precursor tube portion via the part-cylindrical tube-facing portions to form a supported tube portion; and

[0021] moving one or more tool portions against, to inwardly deform, one or more dimple sites within and spaced from ends of the supported tube portion.P1927PCAU

[0022] 3

[0023] Preferably the supported tube portion has a supported-tube-portion circumference and a supported-tube-portion length;

[0024] the one or more tools portions have a corresponding one or more cross-sectional areas;

[0025] a product of the supported-tube-portion circumference and a supported-tube-portion length is not more than 190%, e.g. not more than 130% or more preferably not more than 110%, of a sum of

[0026] the one or more cross-sectional areas; and

[0027] areas of the part-cylindrical tube-facing portions within the supported-tube- portion length.

[0028] The pre-cursor tube portion is preferably a portion of a seamless precursor tube.

[0029] The dimples preferably comprise at least one dimple per 900 mm2(e.g. at least one dimple per 250 mm2) of a notional cylindrical surface area of the tube portion. In certain embodiments, each of the dimples is not more than 2.5 mm deep, e.g. not more than 2.0 mm deep. Optionally, the precursor tube portion has an outer diameter in the range of 18 mm to 26 mm.

[0030] The precursor tube portion may be one of two mutually-parallel cylindrical portions mutually-connected by one or more bends to internally carry fluid in opposite directions.

[0031] The method may comprise selecting the dimple sites to be offset from the at least one baffle to leave a respective cylindrical exterior portion complementary to each respective at least one baffle.

[0032] Preferably the tube portion has a dimple-less end portion.P1927PCAU

[0033] 4

[0034] Another aspect of the invention proves a tube portion wherein the tube portion is for a heat exchanger, comprises dimples and is seamless; and

[0035] the dimples comprise at least one dimple per 900 mm2of a notional cylindrical surface area of the tube portion.

[0036] Preferably, the tube portion is for a heat exchanger, comprises dimples, has an outer diameter in the range of 18 mm to 26 mm and is seamless;

[0037] the dimples comprise at least one dimple per 900 mm2of a notional cylindrical surface area of the tube portion;

[0038] each of the dimples is not more than 2.5 mm deep.

[0039] The tube portion may be formed by deforming a precursor tube portion. 3D printing and machining are other options.

[0040] Another aspect of the invention provides a method of forming a heat exchanger wherein comprising relatively-inserting, a dimple-less end portion of tube portion into a hole of a tube sheet, then expanding the dimple-less end portion.

[0041] Another aspect of the invention provides a heat exchanger comprising

[0042] a vessel to convey vessel fluid;

[0043] tube portions arranged in the vessel to convey tube fluid and be bathed in the vessel fluid to thermally connect the vessel fluid to the tube fluid; and

[0044] one or more baffles to guide the vessel fluid through the vessel and comprising circular holes to accommodate the tube portions;

[0045] wherein each of the tube portions is dimpled.P1927PCAU

[0046] 5

[0047] Another aspect of the invention provides a method comprising conveying fluid through a heat exchanger;

[0048] wherein the heat exchanger comprises a tube portion

[0049] the method comprises conveying the fluid through the tube portion; and

[0050] the fluid is hydrocarbon fluid.

[0051] Preferred forms of the invention are advantageous in the context of hydrocarbon fluids more than 5% of which boils at atmospheric pressure at not less than 300°C, e.g. not less than 400°C, or more preferably not less than 500°C. The hydrocarbon fluid may be crude oil.

[0052] A ratio of a) a volumetric flow rate of the fluid through the tube portion to b) a cross-section are of an at least one notional dimple-free inner diameter of the tube portion is, in the context of a liquid, preferably c) not more than 5 m / sec, or more preferably not more than 3.75 m / sec.

[0053] The method may comprise distilling the fluid downstream of the heat exchanger.

[0054] Another aspect of the invention provides a method comprising the use of a crude oil preheater, comprising a dimpled tube portion, to preheat crude oil.

[0055] Another aspect of the invention provides a method of forming a tube portion for a heat exchanger

[0056] wherein the heat exchanger comprises

[0057] a vessel to convey vessel fluid;

[0058] tube portions arranged in the vessel to convey tube fluid and be bathed in the vessel fluid to thermally connect the vessel fluid to the tube fluid; andP1927PCAU

[0059] 6

[0060] one or more baffles to guide the vessel fluid through the vessel and comprising circular holes to accommodate the tube portions;

[0061] a precursor tube portion has a length and a uniform circular profile along the length;

[0062] the tube portion comprises dimples and is to pass through at least one baffle of the one or more baffles to be one of the tube portions;

[0063] each respective dimple of the dimples is at a respective dimple site;

[0064] the method comprises dimpling the precursor tube portion to form the dimples;

[0065] the dimpling comprises

[0066] selecting the dimple sites to be offset from the at least one baffle to leave a respective cylindrical exterior portion complementary to each respective at least one baffle;

[0067] relatively positioning one or more supports relative to the precursor tube portion to radially support the precursor tube portion; and

[0068] deforming the dimple sites; and

[0069] the deforming the dimple sites comprises, for each respective dimple, deforming the respective dimple site whilst the precursor tube portion is radially supported, by one or more of the one or more supports, such that the respective dimple site is within and spaced from ends of a cylindrical surface portion

[0070] substantially all of which is radially supported by one or more of the one or more supports,

[0071] of the precursor tube portion, andP1927PCAU

[0072] 7

[0073] circular in profile.

[0074] The tube portion is preferably a straight tube portion.

[0075] The one or more supports are preferably one or more external supports and most preferably comprise one or more, e.g. two or more, sets of two mutually-opposed part-cylindrical tube-contacting portions. Preferred embodiments of the invention comprise, at each respective dimple site, moving a tool portion against, to inwardly deform, the respective dimple site whilst the precursor tube portion is compressed, by the one or more of the one or more external supports. The tool portion may be one of three or more tool portions that move in mutually different directions to create three or more dimples at locations mutually different when notionally viewed from an axial direction.

[0076] Optionally, the tool portion accesses the dimple site via an opening in one of the external supports. The method may comprise simultaneously forming two of the dimples.

[0077] The dimples may be arranged to promote helical flow within the tube portion.

[0078] In an embodiment, the precursor tube portion is one of two mutually-parallel cylindrical portions mutually-connected by one or more bends to internally carry fluid in opposite directions. Preferably, each of the one or more bends is a mandrel bend.

[0079] Another aspect of the invention provides a method wherein

[0080] a heat exchanger comprises

[0081] a vessel to convey vessel fluid;

[0082] pre-method tube portions arranged within the vessel to convey tube fluid and be externally bathed in the vessel fluid to thermally connect the vessel fluid to the tube fluid; andP1927PCAU

[0083] 8

[0084] one or more baffles to guide the vessel fluid through the vessel and comprising holes to accommodate the pre-method tube portions; and

[0085] the method comprises replacing one or more pre-method tube portions with one or more dimpled tube portions.

[0086] Optionally, the pre-method tube portions each have a pre-method tube portion length and a uniform circular profile along the pre-method tube portion length.

[0087] Preferably, each of the holes has an internal diameter not more than 5% larger than an external diameter of a corresponding one of the tube portions.

[0088] Another aspect of the invention provides a heat exchanger comprising

[0089] a vessel to convey vessel fluid;

[0090] tube portions arranged in the vessel to convey tube fluid and be bathed in the vessel fluid to thermally connect the vessel fluid to the tube fluid; and

[0091] one or more baffles to guide the vessel fluid through the vessel and comprising circular holes to accommodate the tube portions;

[0092] wherein each of the tube portions comprises at least one formation that is at least one of anti-fouling and heat-transfer-promoting.

[0093] Optionally, each of the tube portions is dimpled. Optional each of the tube portions has a respective outer diameter in the range of 18 mm to 26 mm and / or is seamless. The dimples may be inwardly directed and / or comprise at least one dimple per 900 mm2of a notional cylindrical surface area of tube portion. In certain embodiments, each of the dimples is not more than 2.5 mm deep.

[0094] Preferably, each respective tube portion of the tube portions presents a respective circular exterior to each respective hole, of the holes, through which the respective tube passes.P1927PCAU

[0095] 9

[0096] Another aspect of the invention provides a method of forming a tube portion for a heat exchanger

[0097] wherein a precursor tube portion

[0098] has a length and a uniform circular profile along the length; and

[0099] is one of two mutually-parallel cylindrical portions mutually-connected by one or more bends to internally carry fluid in opposite directions; and

[0100] the method comprises deforming the precursor tube portion to form at least one formation that is at least one of anti-fouling and heat-transfer-promoting.

[0101] The deforming may comprise maintaining an angular orientation of the precursor tube portion about a lengthwise axis of the precursor tube portion.

[0102] Preferably, the method comprises relatively axially-advancing the precursor tube portion through a deformation station. Most preferably, the method comprises axially-advancing the precursor tube portion through a deformation station.

[0103] In certain embodiments, three or more tool portions move in mutually different directions to create three or more dimples at locations mutually different when notionally viewed from an axial direction.

[0104] Optionally, each of the one or more bends is a mandrel bend.

[0105] The method may comprise bending a straight tube to form a precursor tube comprising the two mutually-parallel cylindrical portions and the one or more bends.

[0106] Another aspect of the invention provides an apparatus for forming a tube portion for a heat exchanger

[0107] wherein a precursor tube portionP1927PCAU

[0108] 10

[0109] has a length and a uniform circular profile along the length; and

[0110] is one of two mutually-parallel cylindrical portions mutually-connected by one or more bends to internally carrying fluid in opposite directions; and

[0111] the apparatus comprises one or more tool portions for deforming the precursor tube portion to form at least one formation that is at least one of anti-fouling and heat-transfer-promoting.

[0112] The apparatus may comprise a feed system for axially feeding the precursor tube portion, which system is preferably configured to maintain an angular orientation of the precursor tube portion about a lengthwise axis of the precursor tube portion.

[0113] Optionally, the one or more tool portions are interchangeable with one or more alternative tool portions to produce alternative geometries, e.g. to produce dimples, corrugations, rifling and / or surface texturing.

[0114] The apparatus may comprises a control system to control and co-ordinate the one or more tool portions and the feed system.

[0115] Another aspect of the invention provides a method of forming a tube portion for a heat exchanger

[0116] wherein a precursor tube portion has a length and a uniform circular profile along the length; and

[0117] the method comprises dimpling the precursor tube portion to form the dimples; and

[0118] the dimpling comprises moving three or more tool portions in mutually different directions to create three or more dimples at locations mutually different when notionally viewed from an axial direction.

[0119] Another aspect of the invention provides an apparatus for dimpling a tube, the apparatus comprisingP1927PCAU

[0120] 11

[0121] one or more support portions; and

[0122] one or more tool portions for deforming a respective dimple site whilst a precursor tube portion is radially supported, by one or more of the one or more supports, such that the respective dimple site is within and spaced from ends of a cylindrical surface portion

[0123] substantially all of which is radially supported by one or more of the one or more supports,

[0124] of the precursor tube portion, and

[0125] circular in profile.

[0126] BRIEF DESCRIPTION OF DRAWINGS

[0127] Figure 1 schematically illustrates a heat exchanger comprising a baffle;

[0128] Figure 2 schematically illustrates a baffle-less heat exchanger;

[0129] Figure 3 schematically illustrates a method of refining oil;

[0130] Figure 5 is a perspective view of a dimpling operation; and

[0131] Figures 5 and 6 are perspective views of dimpled tubes; and

[0132] Figures 7a and 7b are end and elevation views of an external-support and tool combination

[0133] DESCRIPTION OF EMBODIMENTS

[0134] Figure 4 illustrates a dimpling operation applied to a precursor tube PT that is II-shaped and comprises a pair of straight, mutually-parallel cylindrical portions. The dimpling operation is effected with a dimpling machine 1 comprising complementary upper and lower clamping dies 3u, 3L driven, in this case driven byP1927PCAU

[0135] 12

[0136] ram 5, to clamp the exterior of the precursor tube PT. The dies 3u, 3L are examples of external supports and comprise mutually complementary half-cylindrical portions 7u, 7L arranged in opposition to each other to engage the precursor tube PT. Stamping pins 9u, 9L slide within complementary holes in the dies 3u, 3L and are driven by rams 13u, 13i_ to act on the precursor tube. The rams 13u, 13L may be hydraulic or pneumatic. The complementary cylindrical portions 7u, 7L are arranged to engage substantially all of a cylindrical surface portion of precursor tube PT (that is to engage substantially all, e.g. at least 95%, of the supported portion of the tube that is not engaged by the stamping pins).

[0137] As used herein, “cylindrical surface portion” refers to a surface portion that is in cross-section not merely arcuate and of constant radius but rather is circular, and similar wording has corresponding meaning.

[0138] In this case, the half-cylindrical surface portions 7u, 7L are slightly smaller in radius than the exterior of the precursor pipe PT so that, as the precursor tube PT is clamped, it is radially compressed from all directions. A tool portion in the form of a stamping pin slides within a hole 11u within the upper clamping die 3u to access the precursor tube.

[0139] The variant half-cylindrical surface portions 7u, 7L have ends in register with respect to each other and come together to define a cylindrical tube-facing surface with circular ends. Other options are possible. By way of example, figures 7a and 7b illustrated a trio of supports 7i , 72, 7s arrange to support a precursor tube portion over supported length L. Each of the supports XX extends axially the length L Figure 7b and (in their mutually converged positions) are separated by gaps G.

[0140] Whilst some gaps are permissible in some embodiments, they are preferably minimized. Preferably cylindrical surface area of the precursor tube portion within the supported region (or notional cylindrical surface area if there dimple(s) within the supported length) is not more than 200% of a) the cross-sectional area of the tool(s) 9i and b) the sum of the areas of the of the supports 7i , 72, 7s (or moreP1927PCAU

[0141] 13

[0142] specifically their part cylindrical interiors) within the supported length (so supported portion of the tube is more than half covered) and smaller percentages for better dimensional control. The percentage is preferably not more than 130%, e.g. not more than 110%. The notional cylindrical surface are is the product of the supported-tube-portion circumference and a supported-tube-portion length.

[0143] In some variants, the tube may be internally supported. In this case, before closing the dies 3u, 3i_, a mandrel 15 is positioned inside the tube PT and is a close fit to support the interior of the tube. The mandrel includes recesses that sit in register with the stamping pins 9u, 9L and the target dimple site. The dies 3u, 3L are then closed to radially compress the tube PT such that the tube PT is both internally and externally supported. Then the stamping pins 9u, 9L are advanced to deform the target sites to simultaneously form the dimples on the top and the bottom of the tube.

[0144] Simultaneously supporting the tube internally and externally can result ‘sharper’ dimples and in some contexts this is advantageous. In other contexts one sided (preferably external) support to enable the tube material to flow.

[0145] Forming the dimple(s) whilst the surrounding material is radially supported has been found to offer multiple advantages over conventional dimple-forming methods. By radially supporting the precursor tube whilst forming the dimple, the cylindricity of the exterior of the tube can be more accurately maintained whereby a closer fit with the baffle plates can be achieved without causing assembly difficulties. The closer fit between the tubing and the baffle plates, in combination with positioning the dimples to avoid the baffles, more effectively blocks leakage of vessel fluid through the holes, thereby avoiding efficiency losses associated with such leakage. Additionally, by applying preferred forms of the invention, an existing heat exchanger (such as a crude oil preheater) with undimpled tubes can be retubed with dimpled tubes having substantially the same external diameter, e.g. each having a diameter not smaller than 99% of the diameter of the corresponding undimpled tube. By way of example, a tube that is metres long andP1927PCAU

[0146] 14

[0147] has a nominal OD of 19 mm and dimples 2 to 3 mm deep may be slid through multiple baffle holes, of multiple baffles, each having a nominal ID of 19.8 mm.

[0148] The follow table summarize the key dimensions of two preferred tube sizes.

[0149] <

[0150]

[0151] Dimensions apply to tube, not pipe, suitable for heat-exchanger service.

[0152] Ovality is measured as the difference between maximum and minimum outside diameters at a common transverse plane.

[0153] Wall thickness ranges are selected to fully comply with both ASTM A1016 (SA-213 welded tube) and ASTM A789 standard cases, without reliance on seamless-only or special-note tolerances.

[0154] The above table captures the two most commonly used tube wall thicknesses in oil and gas heat-exchanger practice.P1927PCAU

[0155] 15

[0156] According to preferred forms of the invention the final tube comprises undimpled portion(s) (e.g. at the end(s) of the tube and / or at break(s) in the dimpling such as break(s) positioned to align with the baffle(s)) within at least one (or preferably both) the above outside diameter tolerance the above ovality tolerance. More preferably one or both of these tolerance are maintained along the entirety of the tube when measured a) between the dimples and / or b) with tube-engaging portions curved to avoid falling into the dimples.

[0157] The initial applicant has discovered that with certain tube diameters, such as 19.05 mm OD and 25.4 mm OD, there are significant benefits associated with numerous shallow dimples relative to few deeper dimples particularly in the context of fouling application as many oil and gas applications. Dimple densities in the range of 1 / 900 dimple / mm2to 1 / 100 dimple / mm2, e.g. about 1 / 400 dimple / mm2(corresponding to square arrays having pitches in the range of 30 mm to 10 mm, e.g. 20 mm) are preferred. Dimple depths of not more than 2.5 mm, e.g. not more than 2.0 mm, are preferred. Preferably the dimples are at least 0.5 mm, e.g. at least 1.0 mm, deep. The dimples preferably have a spherical diameter in the range of 3 mm to 4 mm. Preferably the dimples are formed without internally supporting the tube.

[0158] Preferred variants find application in the oil and gas industry. In crude preheat trains, gas coolers, and refinery heat exchangers, hydrocarbon foulants comprise hydrocarbon species and hydrocarbon-derived materials, whether introduced with the process stream or formed in situ, that deposit on heat-transfer surfaces under operating conditions, thereby reducing heat-transfer efficiency, increasing pressure drop, or impairing exchanger performance.

[0159] Hydrocarbon foulants include:

[0160] • Heavy hydrocarbons, including asphaltenes, resins, waxes, and high-boiling aromatics, prone to precipitation or adsorption;P1927PCAU

[0161] 16

[0162] • Thermally altered hydrocarbons, including polymerized or carbonaceous materials formed at elevated surface or film temperatures;

[0163] • Reactive unsaturated hydrocarbons that undergo polymerization or oxidation on exchanger surfaces; and

[0164] • Composite deposits comprising hydrocarbons binding inorganic or corrosion-derived solids.

[0165] Hydrocarbon fouling occurs by various mechanism including:

[0166] • Precipitation due to temperature, pressure, or compositional change

[0167] • Chemical reaction, including polymerization or oxidation;

[0168] • Thermal degradation or cracking at heat-transfer surfaces;

[0169] • Adsorptive accumulation of polar hydrocarbons;

[0170] • Particulate-assisted deposition forming adherent composite layers

[0171] Deposits typically exhibit:

[0172] • Low thermal conductivity;

[0173] • Hydrophobic or oleophilic behavior;

[0174] • Progressive growth and increased adhesion over time;

[0175] • Resistance to aqueous or mechanical removal.

[0176] Hydrocarbon fouling is conventionally addressed by mechanical cleaning, thermal treatment, chemical cleaning and / or on-stream additives.P1927PCAU

[0177] 17

[0178] Testing suggests that numerous shallow dimples reduces fouling. This is thought to be due to increased shear rates at the heat exchanger wall. Shear rates and fouling trends are closely related in oil and gas applications (and certain other applications). Whilst high shear rates can be achieved via high stream velocity, high velocity is associated with pressure loss. Preferred arrangements of numerous shallow dimples produce shear at low velocities associated with negligible pressure loss.

[0179] In the context of a dimpled tube portion it is convenient to quantify velocity of the fluid travelling therethrough in terms of the ratio of a) a volumetric flow rate of the fluid through the tube portion to b) a cross-section are of an at least one notional dimple-free inner diameter of the tube portion. The ratio is preferably not more than 4 m / sec, or more preferably not more than 3.75 m / sec, in the context of liquids, particularly in the context of heavy hydrocarbons. The following table lists the potential fluids and the preferred ratiOMAx.

[0180]

[0181] P1927PCAU

[0182] 18

[0183]

[0184] According to preferred forms of the invention, the shape of each dimple per se can be more closely controlled. Sharply defined dimples can create more turbulence, and thus more effective heat exchange, than more rounded forms. Additionally, the disclosed method gives designers more freedom to control the shape of the dimple to suit particular applications and the flow patterns desired therefor, e.g. to promote turbulence where it is needed, or to minimise fouling. Designers may aim to provide tubes that are largely self-cleaning, reducing the accumulation of deposits on the tube or pipe surfaces. Self-cleaning is particularly advantageous inP1927PCAU

[0185] 19

[0186] applications where fouling is a concern, as it decreases maintenance requirements and prolongs operational efficiency.

[0187] Long dimples, that is dimples that have a length:width ratio of at least 2:1 (wherein the length and width are both transverse to radial), such as the dimples 17, can be used to create advantageous flow patterns, e.g. they may each be set at the same oblique angle to promote helical flow within the tube. A helical pattern of hemispherical dimples is another possibility.

[0188] A dimple aligned with a baffle plate could provide a leakage path through which vessel fluid could leak through the baffle. To avoid such leakage, according to preferred forms of the invention, the dimple sites are selected to be offset from the baffles(s) to leave a respective cylindrical exterior portion complementary to each respective baffle(s). Optionally, a continuous arrangement (e.g. pattern) of dimples in which dimples are axially separated by at least the thickness of the baffle may be arranged to align respective such separation(s) with the respective baffle(s). Alternatively, the arrangement (e.g. pattern) of dimples may include one or more discontinuities arranged to align with the corresponding one or more baffles through which the tube passes. Likewise, end portions of tubes may be dimpleless for engage with tube plates.

[0189] In a preferred method a dimple-less end portion of each tube is inserted into a corresponding hole of a tube plate. The dimple-less ends can then be expanded to engage the tube plate. The options include hydraulic expansion, roller expansion and explosive expansion. Hydraulic expansion entails applying hydraulic pressure to expand the tube into the tube sheet hole, creating a mechanical interference, and is well suited to thin-walled tubes. Roller expansion uses rolling tools to gradually expand the tube against the tube sheet, is better suited to thicker-walled tubes and larger diameters. Explosive expansion entails detonating an explosive charge sed to expand the tube against the tube sheet. Preferred variants of the tube incorporate dimple-less end portions that are dimensionally accurate and freeP1927PCAU

[0190] 20

[0191] of any work hardening associated with dimpling (or similar operation) both of which improve the sealing engagement at tube to tube-plate interface.

[0192] Optionally the tubes can be energetically bonded to the tube plate instead of, or more preferably after, the expansion operation. The energetic bonding preferably comprises welding. Soldering and brazing are other options.

[0193] The tubes are preferably metallic such as steel, aluminium, copper, brass, titanium, tantalum, or nickel alloy. Steel tubes may be formed of carbon steel or alloy steel such as chromoly. Stainless steel (e.g. austenitic, martensitic, and duplex grades of stainless steel) are advantageous in some applications.

[0194] Aluminium is suited to lightweight applications and gas heat exchange applications. Copper and brass provide high thermal conductivity and may be preferred for their decorative reasons in some applications. Titanium and tantalum offer high strength and corrosion resistance. Nickel alloys, such as Incoloy and Hastelloy, are suited to high-performance environments.

[0195] Seamless precursor tubes are preferred. Typically, they have tighter cylindricity tolerances and are stronger than welded tubes. Tubes in the range of 8 mm OD to 300 NB (nominal bore) may be used to suit heat exchangers of different size. Wall thicknesses in the range of 0.5 mm to 10 mm, or more preferably in the range of 0.5 mm to 8 mm (e.g. 0.89 mm to 3.2 mm), are possible. A wall thickness in the range of 1.55 mm to 1.75 mm has a combination of mechanical and thermal properties well adapted to various applications. A wall thickness in the range of 2.0 mm to 2.2 mm has a combination of mechanical and thermal properties well adapted to various other applications.

[0196] Figure 5 illustrates an embodiment in which each respective dimple is individually formed by repeated operations of the same support and tool set 3u, 3i_, 9u, 9L but many variations are possible. By way of example, Figure 6 illustrates a tube 15 comprising hemispherical dimples of two distinct sizes. These dimples might be formed by multiple operations of a device to form one size of dimples, then resetting the device with an alternate support and tool set to then form the otherP1927PCAU

[0197] 21

[0198] size of dimples. In another variant, the external supports may contact a longer portion of the cylindrical exterior and two or more stamping pin portions may operate simultaneously through respective separate holes through one of the clamping dies.

[0199] The illustrated device comprises two clamping dies 3u, 3L that relatively converge to clamp the tube and each comprise respective pins 9u, 9L. The pins 9u, 9L are together a pair of opposed pins and operate to create dimples on opposites sides of the tube and, as above, after those dimples are formed, tool set 3u, 3L, 9U, 9L might be released to enable the tube to be rotated to a selected angle before the tool set 3u, 3L, 9U, 9L is re-closed and forms a further two dimples comprising a dimple at the selected angle and another dimple at 180° to the selected angle.

[0200] In other implementations, the pins (or other suitable tool portions) simultaneously move in non-parallel, non-opposite directions to form dimples, e.g. the die 3u might have two holes accommodating two pins set at 90° with respect to each other. Preferably the device comprises two or more tool portion sets which each comprise tool portions (e.g. pins) that relatively move in opposition to each other.

[0201] Variants of the device may comprise more than two dies (or other suitable supports) that relatively converge to radially support the tube. This can reduce the risk of galling at the sides of the tube. Preferably the device comprises two or more sets of two support portions which each comprise support portions that relatively move in opposition to each other. Optionally each of the support portions accommodates a respective at least one tool portion to form a respective at least one dimple.

[0202] An embodiment of the machine operates by holding a section of tubing securely in place using a set of four precision clamps arranged along multiple axes. For example, the clamps may be arranged at two meeting planes 90° from each other. Similarly, there may be three meeting planes, at 60° to each other, or four meeting planes at 45° to each other. These clamps exert equal and controlled pressure on the tube, thereby maintaining round shape. A dimple tool is then positioned toP1927PCAU

[0203] 22

[0204] protrude through the clamp jaws, creating dimples across the tube's surface at intervals.

[0205] Preferred embodiments comprise a clamping mechanism, dimple tooling and a control system.

[0206] Preferably the clamping mechanism consists of a series of independent actuators, These actuators can be hydraulic, pneumatic, or electrically driven, depending on the machine's size, material handling capacity, and precision requirements. The actuators are integrated into a central fixture that controls the positioning of the clamps. Each actuator is equipped with a high-precision, adjustable clamping element that conforms to the tube’s outer diameter. These clamps ensure the tube is held tightly in position while maintaining its structural integrity throughout the process, preventing any deformation outside the intended dimpling pattern. The planes of clamping correspond to pairs of clamps that hold the tube on the longitudinal (axis of the tube), radial, and axial directions. These clamping planes work in tandem to prevent any movement of the tube along multiple axes, creating a stable platform for the dimple stamping action.

[0207] Preferably the dimple tool is an active component that makes physical contact with the tube surface to form the dimples. This tool typically comprises a set of punches that are mounted to an actuator system. The tool may be actuated pneumatically or hydraulically to move through a respective clamping plane.

[0208] Preferably the machine utilizes a high-precision control system, typically managed by a Programmable Logic Controller (PLC) or a Computer Numerical Control (CNC) unit. This control system monitors the entire operation of the machine, managing the sequencing of the clamp actuators and the motion of the dimple tool. Sensors and encoders may be integrated into the system to verify the position and status of each clamp and tool, ensuring that the tube is correctly positioned. A preferred control system also allows for adjustments to the depth, spacing, and orientation of the dimples, providing flexibility for different tubingP1927PCAU

[0209] 23

[0210] specifications and allowing for custom spacing such as what may be required to suit the placement of baffles in shell and tube type heat exchangers.

[0211] In an embodiment, an operational workflow begins with the insertion of the tube section into the machine. Once in place, clamps simultaneously engage the tube, closing around it from four, six or eight directions. The applied force from the clamps keeps the tube securely in a fixed, round shape and ensures it does not move or deform during the stamping process. At this point, the dimple tool is actuated. The tool protrudes through the clamps, reaching into the tube’s surface. The motion of the dimple tool is synchronized with the clamping action. As the tool moves forward, it imparts force on the tube surface, creating a dimple at a specific location. This process is repeated sequentially across the tube’s surface, with the tool positioned precisely at each desired location.

[0212] The precursor tube PT comprises two mutually-parallel cylindrical portions mutually-connected by a single 180° bend to internally carry fluid in opposite directions. In another variant, they might be mutually-connected by two 90° bends.

[0213] The illustrated method entails forming dimples that are anti-fouling and heat-transfer-promoting. Other anti-fouling and / or heat-transfer-promoting formations are possible, e.g. corrugating, rifling, and / or texturing are possible. Preferably, a straightness of the tube portion is maintained.

[0214] The dimpling station 1 comprises a pair of stamping pins 9u, 9L 180° apart to simultaneously form a pair of first dimples. In the illustrated variation, the tube portion might be rotated about its axis and axially advanced through the dimpling station 1 before recycling the dimpling station 1 to form two further dimples at locations different to the locations of first dimples, when notionally viewed from an axial direction. In another implementation, the workpiece (i.e. precursor tube PT) might be held still whilst the stamping pins 9u, 9L (or other deformation tools) are repositioned.P1927PCAU

[0215] 24

[0216] In an implementation, preferred particularly in the context of a U-shaped workpiece, the straight arm of the workpiece is axially advanced whilst an angular orientation of the arm about its long axis is maintained, preferably by restraining the workpiece against rotation. In this way, a set of one or more tools can be brought to bear on the arm of the workpiece as it is axially advanced (e.g. advanced in stepwise fashion) to form advantageous formations such as dimples.

[0217] The precursor tube PT is formed by bending, e.g. mandrel bending, a straight tube. Bending the simple straight tube before adding the anti-fouling and / or heat-transfer-promoting formations allows conventional bending mandrels to be used. It can also simplify the process by enabling varying bend radii to be formed without complex pre-bend calculations. It can also improve accuracy, allowing undeformed cylindrical zones to be left for alignment with baffle plates.

[0218] Whilst mandrel bending is preferred, there are other options such as induction bending and sand-filled hot bending.

[0219] Whilst preferred variants of the post-bending operation comprise dimpling within a radially-supported cylindrical portion of tube, other formations and other modes of formation-addition are possible.

[0220] Certain embodiments are particularly advantages in the context of pre-heating crude oil enroute to distillation, e.g. vacuum distillation. Such preheaters (or ‘preheat trains’ routinely handle untreated or minimally treated crude oils containing asphaltenes, heavy hydrocarbons, salts, and particulates under conditions conducive to rapid fouling. Optionally, a fired heater is interposed between the heat exchanger and the distiller. Fouling reduces the performance of the pre-heater which in turn increase fired-heater duty, fuel consumption, and emissions and can constrain refinery throughput. As such that even modest reductions in fouling rate are of substantial economic value.

[0221] Certain embodiments may suit refinery reboilers and pump around exchangers handling heavy or residua-containing streams, where coke formation and organicP1927PCAU

[0222] 25

[0223] deposition limit operating cycles; refinery overhead condensers and reflux exchangers, which are susceptible to solids deposition and corrosion-related fouling that can disrupt column operation; and gas-processing and treating heat exchangers, such as lean / rich amine cross exchangers, where fouling reduces heat recovery and increases steam demand. Certain embodiments may suit produced-water, seawater, and cooling-water exchangers used in upstream and offshore facilities, where scaling, biofouling, and solids deposition drive maintenance and reliability concerns.

[0224] Some forms of the invention are clearly and unmistakably disclosed in Australian provisional patent application no. 2025900457. Other forms are not. The contents of Australian provisional patent application no. 2025900457 are incorporated herein by reference. Some forms of the invention are clearly and unmistakably disclosed in Australian patent application no. 2025256077. Other forms are not. The contents of Australian patent application no. 2025256077 are incorporated herein by reference

[0225] The precursor portion tube portion, e.g. a straight run of a U-shaped precursor, may have a nominal outer diameter of less than 19 mm. Alternatively, it may have a nominal outer diameter of more than 19 mm. Preferably, it has a wall thickness of at least 4 mm. Alternatively it may have a wall thickness of less than 4 mm. A longest of the external supports’ part-cylindrical tube-facing portions may be less than 50 mm long, alternatively it may be at least 50 mm long.

[0226] Various preferred embodiments may be advantageously applied in contexts such as:

[0227] • oil and gas (e.g. crude oil preheaters, natural gas condensers, and other heat exchangers used in upstream, midstream, and downstream operations); • chemical processing (e.g. heat exchangers in chemical reactors, and in particular fouling-prone reactors, and distillation columns);P1927PCAU

[0228] 26

[0229] • power generation (e.g. heaters, boilers and condensers in thermal power plants);

[0230] • HVAC (e.g. compact exchangers); and

[0231] • desalination plants (such as multi-stage distillation) and other water treatment such as cooling water systems).

[0232] The invention is not limited to specific examples described and illustrated herein. Rather, the invention is defined by the claims.

[0233] Across different implementations, the tubes may carry either liquid and / or gas and the fluid in which the tubes are externally bathed may likewise contain liquid and / or gas. In some implementations, gas may flows on the tube side, the shell side, or both. Finning and / or other surface-area extensions may be used on the shell side, e.g. when gases are present on the shell side.

[0234] Advantageously the tubes disclosed herein may internally carry Fouling Hydrocarbons.

[0235] A Fouling Hydrocarbon liquid is a hydrocarbon-containing liquid that, during storage, transport, heating, cooling, or processing, is capable of forming or contributing to the formation of deposits on one or more contacted surfaces. Such deposits (fouling) are associated with reduced heat transfer performance, increased pressure drop, flow restriction, filtration impairment, or increased cleaning frequency. Deposits may include, without limitation, carbonaceous material (including coke), polymerised hydrocarbons (including gums and varnish), asphaltene-containing material, waxy material, sludge, particulate-containing deposits, or combinations thereof.

[0236] Fouling Hydrocarbon liquids are commonly associated with hydrocarbon streams that contain a measurable high-boiling fraction which, under refinery distillation practice, would report to atmospheric distillation bottoms and / or vacuum distillation feed or bottoms, rather than to distillate products. In practical terms, such liquidsP1927PCAU

[0237] 27

[0238] may be characterised as comprising a measurable resid or resid-like fraction, for example a fraction above about 500°C (approximately 932°F) as determined by true boiling point (TBP) analysis or simulated distillation.

[0239] Hydrocarbon liquids containing such high-boiling fractions are likely to contain concentrations of deposit precursors, including one or more of asphaltenes, resins, polyaromatic species, heteroatom-containing species, metal-containing species, thermally unstable constituents, olefinic constituents, or combinations of these, and facilitate generation of deposits in heat transfer service, particularly at elevated film temperatures encountered in crude preheat trains, fired heaters, and high-duty exchanger circuits.

[0240] Representative examples of Fouling Hydrocarbon liquids include heavy crude oils, reduced crudes, residue-containing refinery streams, vacuum distillation feedstocks, atmospheric or vacuum resid blends, thermally cracked liquids, unstable blends exhibiting asphaltene precipitation, wax-prone hydrocarbon liquids, and hydrocarbon liquids containing entrained solids or contaminants.

[0241] This differentiates Fouling Hydrocarbons from hydrocarbon liquid (oils) which, under typical conditions of storage, transport, heating, cooling, and use, exhibit a lower tendency to form deposits. Conventional oils include, without limitation, distillate-range refinery streams, lighter crude fractions, refined fuels, and base oils, and are typically characterised by a substantially lower proportion of resid-range material as defined by TBP or simulated distillation.

[0242] The term “comprises” and its grammatical variants has a meaning that is determined by the context in which it appears. Accordingly, the term should not be interpreted exhaustively unless the context dictates so. Likewise, the article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements unless the context dictates so.

Claims

P1927PCAU28CLAIMS1. A method of forming a tube portion for a heat exchanger;wherein two or more external supports have part-cylindrical tube-facing portions;the method comprises dimpling a precursor tube portion to form dimples; andthe dimpling comprisesthe two or more external supports converging, relative to each other, on the precursor tube portion to radially support a portion of the precursor tube portion via the part-cylindrical tube-facing portions to form a supported tube portion; andmoving one or more tool portions against, to inwardly deform, one or more dimple sites within and spaced from ends of the supported tube portion.

2. The method of claim 1 wherein the supported tube portion has a supported-tube-portion circumference and a supported-tube-portion length;the one or more tools portions have a corresponding one or more cross-sectional areas;a product of the supported-tube-portion circumference and a supported-tube-portion length is not more than 130% of a sum ofthe one or more cross-sectional areas; andareas of the part-cylindrical tube-facing portions within the supported-tube- portion length.

3. The method of claim 1 wherein the supported tube portion has a supported-tube-portion circumference and a supported-tube-portion length;P1927PCAU29the one or more tools portions have a corresponding one or more cross-sectional areas;a product of the supported-tube-portion circumference and a supported-tube-portion length is not more than 110% of a sum ofthe one or more cross-sectional areas; andareas of the part-cylindrical tube-facing portions within the supported-tube- portion length.

4. The method of any one of claims 1 to 3 wherein the pre-cursor tube portion is a portion of a seamless precursor tube.

5. The method of any one of claims 1 to 4 wherein the dimples comprise at least one dimple per 900 mm2of a notional cylindrical surface area of the tube portion.

6. The method of any one of claims 1 to 4 wherein the dimples comprise at least one dimple per 250 mm2of a notional cylindrical surface area of the tube portion.

7. The method of any one of claims 1 to 6 wherein each of the dimples is not more than 2.5 mm deep.

8. The method of any one of claims 1 to 7 wherein the precursor tube portion has an outer diameter in the range of 18 mm to 26 mm.

9. The method of any one of claims 1 to 8 wherein the precursor tube portion is one of two mutually-parallel cylindrical portions mutually-connected by one or more bends to internally carry fluid in opposite directions.P1927PCAU3010. The method of any one of claims 1 to 9 comprising selecting the dimple sites to be offset from the at least one baffle to leave a respective cylindrical exterior portion complementary to each respective at least one baffle.

11. The method of any one of claims 1 to 10 wherein the tube portion has a dimple-less end portion.

12. A tube portion wherein the tube portion is for a heat exchanger, comprises dimples, has an outer diameter in the range of 18 mm to 26 mm and is seamless;the dimples are inwardly directed and comprise at least one dimple per 900 mm2of a notional cylindrical surface area of the tube portion;each of the dimples is not more than 2.5 mm deep.

13. The tube portion of claim 12 having a dimple-less end portion.

14. A method of forming a heat exchanger whereina tube portion is at least one offormed in accordance with claim 11; andin accordance with claim 13; anda tube sheet has a hole; andthe method comprisesrelatively-inserting the dimple-less end portion into the hole; thenexpanding the dimple-less end portion.

15. A heat exchanger comprisingP1927PCAU31a vessel to convey vessel fluid;tube portions arranged in the vessel to convey tube fluid and be bathed in the vessel fluid to thermally connect the vessel fluid to the tube fluid; andone or more baffles to guide the vessel fluid through the vessel and comprising circular holes to accommodate the tube portions;wherein each of the tube portions is dimpled.

16. The heat exchanger of claim 15 wherein the each of the tube portions has a respective outer diameter in the range of 18 mm to 26 mm and is seamless;the dimples are inwardly directed and comprise at least one dimple per 900 mm2of a notional cylindrical surface area of tube portion;each of the dimples is not more than 2.5 mm deep.

17. The method comprising conveying fluid through a heat exchanger;wherein at least one ofthe heat exchanger comprises a tube portion formed in accordance with any one of claims 1 to 11;the heat exchanger comprises a tube portion in accordance with claim 12 or 13;the heat exchanger is formed in accordance with claim 14; andthe heat exchanger is in accordance with claim 15 or 16; andthe method comprises conveying the fluid through the tube portion; andthe fluid is hydrocarbon fluid.P1927PCAU3218. The method of claim 17 wherein at least 5% of the hydrocarbon fluid boils at atmospheric pressure at not less than 500°C.

19. The method of claim 17 or 18 wherein a ratioof a volumetric flow rate of the fluid through the tube portion;to a cross-section are of an at least one notional dimple-free inner diameter of the tube portionis not more than 5 m / sec.

20. The method of any one of claims 17, 18 or 19 comprising distilling the fluid downstream of the heat exchanger.

21. A method comprising the use of a crude oil preheater, comprising a tube portion formed in accordance with any one of claims 1 to 11, to preheat crude oil.

22. A method of forming a tube portion for a heat exchangerwherein the heat exchanger comprisesa vessel to convey vessel fluid;tube portions arranged in the vessel to convey tube fluid and be bathed in the vessel fluid to thermally connect the vessel fluid to the tube fluid; andone or more baffles to guide the vessel fluid through the vessel and comprising circular holes to accommodate the tube portions;a precursor tube portion has a length and a uniform circular profile along the length;the tube portion comprises dimples and is to pass through at least one baffle of the one or more baffles to be one of the tube portions;P1927PCAU33each respective dimple of the dimples is at a respective dimple site;the method comprises dimpling the precursor tube portion to form the dimples;the dimpling comprisesselecting the dimple sites to be offset from the at least one baffle to leave a respective cylindrical exterior portion complementary to each respective at least one baffle;relatively positioning one or more supports relative to the precursor tube portion to radially support the precursor tube portion; anddeforming the dimple sites; andthe deforming the dimple sites comprises, for each respective dimple, deforming the respective dimple site whilst the precursor tube portion is radially supported, by one or more of the one or more supports, such that the respective dimple site is within and spaced from ends of a cylindrical surface portionsubstantially all of which is radially supported by one or more of the one or more supports,of the precursor tube portion, andcircular in profile.

23. A method whereina heat exchanger comprisesa vessel to convey vessel fluid;P1927PCAU34pre-method tube portions arranged within the vessel to convey tube fluid and be externally bathed in the vessel fluid to thermally connect the vessel fluid to the tube fluid; andone or more baffles to guide the vessel fluid through the vessel and comprising holes to accommodate the pre-method tube portions; andthe method comprises replacing one or more pre-method tube portions with one or more tube portions each at least one offormed in accordance with any one of clams 1 to 11 and 22; andin accordance with claim 12 or 13.

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