Corrosion resistant bimetallic tube manufactured by a two-step process

Abstract

A method of producing a bimetallic tubular component includes providing a first tubular workpiece having an inner diameter and a second tubular workpiece having an outer diameter. The first and second tubular workpieces have dissimilar cold-working processing parameters. The method further includes diffusion bonding the inner diameter of the first tubular workpiece to the outer diameter of the second tubular workpiece, and flowforming the diffusion bonded tubular workpieces to form the bimetallic tubular component.

Description

TECHNICAL FIELD

The invention generally relates to bimetallic tubular components and, more particularly, the invention relates to producing corrosion resistant bimetallic tubular components using a two-step metal forming process.

BACKGROUND ART

Considerable cost savings can be attained by the use of clad and lined materials compared to solid Corrosion Resistant Alloy (CRA) materials. This is particularly evident with larger outside diameters CRA tubulars which are necessary to satisfy flow rate requirements and evident with heavier wall thicknesses which are required for strength and pressure requirements for specific downhole applications. CRA tubulars provide the corrosion resistance needed when gas drilling and completion operations involve severe downhole conditions where CO2 and H2S are present. These alloys are utilized when the traditional stainless steels do not provide adequate corrosion resistance. Over the last ten years, CRA tubulars, made out of nickel-based alloys like 825, G3, G50, C276 and 625 have met the material requirements for these wells, but the cost of these tubulars is exorbitant. Recent advances in technology have facilitated the development of a clad tubulars for downhole use composed of an API C90 and T95 outer tube and a CRA corrosion resistant liner. The carbon alloy, C90 or T95 outer tube, provides the structural integrity of the tubular while the CRA liner provides the necessary corrosion resistance. C90 and T95 are AISI 4130 type steel that is quenched (water) and tempered and is suitable for sour service environments per the guidelines in NACE MR0175-2000. CRA's are defined as those alloys whose mass-loss corrosion rate in produced fluids is at least an order of magnitude less than carbon steel, thus providing an alternative method to using inhibition for corrosion control. Table 1 shows the composition of various nickel-based CRA grades that are utilized for maximum corrosion resistance in aqueous H₂S and CO₂ environments. The mode of cracking in nickel-based alloys is occasionally intergranular.

TABLE 1
CRA Alloy Compositions
ALLOY								Other-
(UNS No.)	Cr	Ni	Mo	Fe	Mn	C-Max	Cb + Ta	Max
825 (N08825)	22	42	3	Bal	0.5	0.03		.9 Ti, 2 Cu
925 (N088925)	19/21.0	24/28.0	6/7.0	Bal	1.0 Max	0.02		1.5 Cu
725 (N088725)	21	58	8	Bal	0.25	0.02
625 (N08625)	22	Bal	9	2	0.2	0.05		3.5Cb
G3 (N06985)	21/23.5	Bal	6/8.0	18/21.0	1.0 Max	0.015	.50 Max	2.5 Cu,
								2.4 W
G30 (N06030)	28/31.5	Bal	4/6.0	13/17.0	1.5 Max	0.03	.3/1.5	4.0 W
G50 (N06050)	19/21.0	50.0 Min	8/10.0	15/20.0	1.0 Max	0.015	.50 Max	2.5 Co
C276 (N010276)	15	Bal	16	6	—	0.01		2 Co,
								3.5 W

When CO₂ is present in the flow stream, additional corrosion considerations are necessary. The presence of CO₂ can considerably increase the weight loss corrosion of carbon and alloy steel tubing. The corrosion rate is a function of the temperature, CO₂ concentration and the partial pressure. Since regulatory and environmental guidelines usually prohibit the allowance for predictable weight loss corrosion (e.g., increasing the wall thickness to compensate for corrosion through the wall of the pipe), the selection of alternate stainless steel and CRA materials are made. When H₂S is present, the corrosion problem switches from a weight loss issue (e.g., pitting and crevice corrosion) to a sulfide stress cracking (SSC) phenomena. Hydrogen sulfide stress cracking (SSC) is defined as the spontaneous fracturing of steel that is simultaneously subjected to an aqueous corrosive hydrogen sulfide medium and a static stress less than the tensile strength of the material. It usually occurs in a brittle manner, resulting in catastrophic failures at stresses less than the yield strength of the material. Hydrogen SSC is basically a hydrogen embrittlement mechanism resulting from the formation of hydrogen ions (H+) in the presence of aqueous hydrogen sulfide (H2S). Over the last five years, there has been an increasing need for downhole tubing suitable for severe CO₂ and H₂S environments. Numerous nickel-based alloys have well established corrosion resistant attributes for these production applications but are extremely costly when utilized as a solid wall tubular. The exorbitant cost of solid wall CRA tubulars has resulted in many projects being deemed too costly or postponed and therefore have not been pursued.

SUMMARY OF EMBODIMENTS

In accordance with one embodiment of the invention, a method of producing a bimetallic tubular component includes providing a first tubular workpiece having an inner diameter and a second tubular workpiece having an outer diameter. The first and second tubular workpieces have dissimilar cold-working processing parameters. The method further includes diffusion bonding the inner diameter of the first tubular workpiece to the outer diameter of the second tubular workpiece, and flowforming the diffusion bonded tubular workpieces to form the bimetallic tubular component. Alternatively, hot extruding, explosive cladding, laser deposition cladding, rolling and/or fuse welding may be used instead of, or in addition to, diffusion bonding.

In some embodiments, the cold-working processing parameters include feed rates, speed rates, and/or wall reduction percentages. The diffusion bonding may be a hot isostatic pressing process. The hot isostatic pressing process may be performed in an inert atmosphere. Each tubular workpiece may have an end and a gap may be formed between the inner diameter and the other diameter. The method may further include providing a port that goes through the first tubular workpiece to the gap between the two workpieces, sealing the end of the first tubular workpiece to the end of the second tubular workpiece in order to form a sealed area between the two workpieces, and forming a vacuum between the two workpieces in the gap before the diffusion bonding process. The second tubular workpiece may have a hardness value greater than about two times the hardness value of the first tubular workpiece before the flowforming process.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention will be more readily understood by reference to the following detailed description, taken with reference to the accompanying drawings, in which:

FIG. 1 is a graph of stress versus temperature showing the large delta between hot deformation resistances of alloy C-276 (same as alloy 625) and low alloy steel;

FIG. 2 is a graph of hardness versus cold reduction percentage showing the effect of cold work on Vickers hardness for various alloys;

FIGS. 3A and 3B are macrographs showing a diffusion bonding preform before and after hot isostatic pressing and diffusion bonding, respectively, with 1018 steel on the outer diameter (OD) and alloy 625 on the inner diameter (ID) according to embodiments of the present invention;

FIG. 4 is a photomicrograph showing a transverse cross-sectional view of the diffusion bonding preform shown in FIG. 3B according to embodiments of the present invention;

FIG. 5A is a photomicrograph showing a transverse cross-sectional view of the diffusion bonding preform shown in FIG. 3B, and FIG. 5B is the chemical analysis along the line shown in FIG. 5A showing that no deleterious intermetallic phases are formed at the diffusion layers between the 1018 steel and the alloy 625;

FIGS. 6A and 6B show the chemical analysis report of the diffusion layer at the 1018 and alloy 625 metallurgical bond shown in FIG. 3B;

FIG. 7 is a macrograph showing a flowformed clad tube with 0.149″ thick 1018 steel on the OD and 0.049″ thick alloy 625 Inconel on the ID according to embodiments of the present invention;

FIGS. 8 and 9 are photomicrographs at 24× and 2,000× magnification, respectively, showing a transverse cross-sectional view of the flowformed bimetallic tube shown in FIG. 7 according to embodiments of the present invention;

FIG. 10A is a photomicrograph showing a transverse cross-sectional view of the flowformed bimetallic tube shown in FIG. 7, and FIG. 10B is the chemical analysis along the line shown in FIG. 10A showing that no deleterious intermetallic phases are formed at the interface between the 1018 steel and the alloy 625; and

FIGS. 11A and 11B show the chemical analysis report of the diffusion layer at the 1018 and alloy 625 metallurgical bond shown in FIG. 7.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Various embodiments of the present invention provide a two-step process, diffusion bonding (DB) and cold flowforming, that has been developed for manufacturing bimetallic pipes and tubes. With this new process, dissimilar metals having a large difference in their cold deformation resistances can be metallurgically bonded into one preform hollow and flowformed into long lengths, creating a clad or bimetallic long tube/pipe. It is important to join the two metals metallurgically in the preform state by DB which can be done during a hot isostatic pressing (HIP) process. DB is a solid-state joining process wherein joining is accomplished without the need for a liquid interface (brazing) or the creation of a cast product via melting and resolidification (welding). After the preform DB process has been done, step two is to flowform the clad preform into a clad flowformed tube/pipe. The two-step process may be used for the manufacture of corrosion resistant pipes for oil country tubular goods (OCTG) for sour service. In one embodiment, the inner and outer materials of the pipe may be a nickel-based superalloy (alloy 625) and sulfide stress cracking (SSC) resistant low alloy steel (1018 steel), respectively, although other dissimilar metals may also be used. A bimetallic pipe with uniform thickness of both outer and inner metals may be obtained by the new process. The corrosion resistance of the two layers of metals as well as the strength of the outer material exhibits satisfactory performance to comply with the requirements for OCTG use. Embodiments of the two-step process, DB and cold flowform process, are promising for producing bimetallic tubes/pipes from two materials that have much different cold strain rates (cold workability). Therefore, a CRA clad lined tubular may be produced according to embodiments of the present invention that provides the necessary corrosion protection, structural integrity and also offers considerable cost savings over solid wall CRA tubulars. With the increasing need worldwide for more gas to satisfy world demand, embodiments of the present invention will provide the economic incentive to explore and produce oil and gas in regions that were previously uneconomical. Details of illustrative embodiments are discussed below.

Clad Lined Pipe Product Development:

Over the last twenty years, there have been several manufacturing methods developed for producing CRA clad/lined tubulars. The American Petroleum Institute (API) has also developed a specification for the CRA clad and lined line pipe (API 5LD, 3^rd edition 2009). Clad and lined tubulars have gained relatively wide acceptance for use in transporting petroleum products, for refinery applications and for downhole oil and gas operations. Clad or lined CRA tubulars are classified in two basic categories: mechanically lined and metallurgically bonded.

Mechanically lined tubulars are the simplest and most economic method of producing clad pipe. This method of manufacture does not create a metallurgical bond between the outer pipe used for structural integrity, and the inner liner pipe that is selected for the appropriate corrosion resistance properties. Mechanically lined CRA pipe has gained wide market acceptance. This method of manufacture provides better quality control features compared to metallurgically bonded pipe because each of the pipe components (outer pipe and liner) can be independently inspected utilizing traditional inspection techniques. The lack of a metallurgical bond at the interface of the outer pipe and inner liner eliminates the difficulties associated with ultrasonic flaw inspection of the piping components. For applications where bending is critical for the serviceability, this method of manufacture is unsuitable due to buckling of the liner. Gas migration between the material layers is a concern for corrosion.

Metallurgically bonded tubulars are those in which there is a metallurgical bond between the structural outer pipe and the corrosion resistant inner pipe. There are several manufacturing techniques currently employed to produce these products and are described below. The metallurgically bonded tubular tends to be more costly than those that are mechanically lined. Longitudinally welded pipe is produced today from clad plate produced by hot roll formed or explosively bonded plate. Although length restrictions exist with these two methods of manufacture, it is common to girth weld two lengths together to fabricate a longer length tube, despite girth welds being costly and unpopular.

Clad Plate Forming: Clad plates can be produced by three common methods; hot roll bonding, explosive bonding and weld overlay. Clad plates have been used extensively for many processing vessels, separators, heat exchangers and plates. Hot, roll bonding accounts for more than 90% of the clad plate production, worldwide (˜55,000 tons/year). Once the clad plate is produced, it is formed into a tubular shell and longitudinally welded full length. There is always a concern for a failure at the weld.

Extrusion Method: This production method involves taking a combination billet of carbon steel and CRA material and hot extruding the hollow to longer lengths. A thick-walled carbon steel tubular is machined to very tight tolerances and then a CRA tubular is inserted into the bore. Often the two materials are heat shrunk together to achieve a tight mechanical fit. The ends of the combination billet are commonly seal welded prior to extruding to prevent the intrusion of air, oxygen and other contaminants into the interface. This heavy wall tubular billet is then extruded at temperatures in excess of 1260° C. (2300° F.) which results in a metallurgical bond between the carbon steel outer pipe and the CRA material on the inner diameter surface. The final length of the clad extrusion is limited by the capacity (capable forces to hot work the tubular) of the extrusion press. Metallurgically bonded extruded pipe has had some limited use for the bends of transmission, gathering and flow lines as this method of manufacture is more costly than the mechanically lined CRA tubulars which have found significant application for the straight portions of these oil/gas transportation systems. Extruding mild steel at 2300° F. can cause deleterious grain growth.

Traditionally, there exists restriction on the combination of two materials that can be extruded together. The difference between the hot deformation resistances of two materials should not be very large or the two materials will deform separately (shear apart during extruding) because of the large delta in strain rates at a given temperature. Alloy C-276 (UNS NI0276) and alloy 625 (UNS N06625) are the most common CRAs for sour service. Because of their high contents of molybdenum, these alloys exhibit much larger high temperature deformation resistances than carbon and low alloy steels. FIG. 1 shows a typical example of the differences between two dissimilar metals. In FIG. 1, the deformation resistances of alloy C-276 and of a low alloy steel as a function of temperature are compared with each other. At a common hot working temperature of 2100° F. (1150° C.), for example, the deformation resistance of alloy C-276 is about 3.9 times as high as that of the low alloy steel. For this reason, no references can be found concerning the successful production of clad pipes and tubes with liner materials which consist of large, high temperature deformation stress materials such as alloy C-276 and alloy 625 with a substrate material of carbon and low alloy steels. As far as the literature is concerned, the liner material of conventional clad pipes and tubes is limited up to alloy 825 (UNSN08825). The hot deformation resistance of this alloy is twice that of low alloy steels.

Cold Forming: Often cold working tubes are preferred to hot extruding tubes because of the better control in dimensional accuracies, superior surface finishes achieved, and the ability to increase the materials' strength thru varying the amounts of wall reduction (cold work). In the case of 1018 or 1020 steel, the annealed hardness is ˜100 Vickers and the hardness increases to ˜160 Vickers after about 75% wall reduction with cold working. See, e.g., FIG. 2. In the case of alloy 625, its strength is derived from cold working (e.g., using flowflorming). The cold work has a stiffening effect of molybdenum and niobium on its nickel-chromium matrix; thus precipitation-hardening treatments are not required. The annealed hardness of alloy 625 is ˜200 Vickers, double that of annealed 1018 or 1020 steel. After about 75% wall reduction with cold working of alloy 625, the hardness increases to ˜425 Vickers, again more than double that of 75% wall reduction with cold working of 1018 or 1020 steel. See, e.g., FIG. 2. It is clear, 1018 is very soft compared to alloy 625. Furthermore, 1018 or 1020 steel does not work harden anywhere comparable to alloy 625. The processing parameters for cold working mild steel compared to CRAs are very different. Mild steels are soft, ductile and are capable of large wall reductions without the need for intermediate annealing steps. The mild steels do not work harden quickly so speed and feet rates can be pushed to go faster, increasing cycle times. In contrast, CRAs require smaller wall reductions, more annealing steps in between cold work passes, and slower speeds and feeds due to excessive and quick cold work hardening of the material. In short, the processing parameters for mild steel are vastly different to the processing parameters for CRAs. For these reasons, it is counterintuitive to simultaneously cold work these alloys using a flowforming process.

CRA Pipe Manufactured by a Two-Step Process; Diffusion Bonding a Preform Hollow and Cold Flowforming:

Embodiments of the present invention discovered that two metals having very different hardness levels, which have very different cold deformation rates and/or which cold work at very different strength levels, may be simultaneously cold worked via flowforming if both metals are metallurgically joined before the cold working process. Among the various technologies for joining two metals include diffusion bonding thru the Hot Isostatic Pressing (HIP) technology. For example, an inner and outer tube can loosely be assembled together (e.g., about 0.020″ gap or less between the two tubes) and subsequently DB or HIP into a bimetallic, metallurgically bonded hollow preform. In lieu of two solid tubes being DB together, powder metal may also be DB or HIPed to the other tube to form the bimetallic hollow preform. For example, the interface between a low alloy steel substrate and an alloy 625 liner, joined by HIP, exhibits a high joint strength up to about 930 MPa. Accordingly to ASTM 264 for Stainless Chromium-Nickel Steel-Clad Plate, section 7.2.1 Shear Strength, the minimum shear strength of the alloy cladding and base metal shall be 20,000 psi (˜140 MPa).

Step 1, Diffusion Bonding the Preform:

In one embodiment, the bimetallic hollow preform (e.g., steel on the OD and CRA on the ID) is created by joining the two dissimilar metals metallurgically by diffusion bonding (DB). As mentioned above, DB is a solid-state joining processes wherein joining is accomplished without the need for a liquid interface (brazing) or the creation of a cast product via melting and resolidification (welding). DB is a process that produces solid-state coalescence between two materials under conditions where the joining occurs at a temperature below the melting point, Tm, of the materials to be joined (usually >1/2 Tm). Coalescence of contacting surfaces is produced with loads below those that would cause macroscopic deformation to the part. In some embodiments, a bonding aid may be used, such as an interface foil or coating, to either facilitate bonding or prevent the creation of brittle phases between the dissimilar materials. Preferably, the material should not produce a low-temperature liquid eutectic upon reaction with the material(s) to be joined. Thus, diffusion bonding facilitates the joining of materials to produce components with no abrupt discontinuity in the microstructure and with a minimum of deformation. Usually, the DB process is limited to either press or gas pressure or bonding approaches.

Hot Isostatic Pressing (HIP) is a common method of achieving DB. Special techniques are employed to eliminate detrimental hardening and the formation of oxides at the bonding interface due to the precipitation of intermetallic phases or carbides. HlPing in a vacuum can help prevent the formation of these oxides and intermetallic phases. When HIP is performed in an inert atmosphere, a vacuum can be created in the annulus between both materials by evacuating the air before (or during) the DB process. Welding close the gaps on both ends of the inner and outer layers creates a sealed pressure vessel. FIG. 3A shows a port drilled thru the outer sleeve into the annulus. Thru the port, a vacuum can be pulled between the outer and inner layers and DB can be performed. FIG. 3B shows a macrograph of the preform after diffusion bonding. FIG. 4 shows a micrograph of the two materials after diffusion bonding. FIGS. 5A and 5B show the diffusion layer with no deleterious intermetallic phases formed between the two materials. FIGS. 6A and 6B show a chemical analysis of the diffusion layer between the two dissimilar materials. Other embodiments of creating a bimetallic preform may include cladding dissimilar metals thru one of the following methods; hot roll bonding, explosive bonding and/or weld overlay.

Step 2, Flowforming:

Flowforming is a chipless, metal forming technology used to fabricate cylindrical tubular components and pipes though controlled wall reduction by cold working. Often flowform products are seamless and very precise. Flowforming offers a net-shape manufacturing approach, requiring less material to make components and often substantially reducing the costs associated with secondary manufacturing operations such as machining, straightening, honing and grinding. Seamless components with high length to diameter ratios, e.g., up to about 50 to 1, realize the greatest cost savings through the flowforming manufacturing process. Wall thicknesses as thin as about 0.010″ can be flowformed irrespective of the diameter of the tube. The flowforming process may be used to produce monolithic pipes and tubulars made out of various metals and metal alloys, such as stainless steel, zirconium, titanium, cobalt and nickel alloys (e.g., CRAs).

The flowforming process uses hydraulic forces to drive three CNC-controlled rollers to the outside diameter of a cylindrical preform which is fitted over a rotating, inner mandrel. The rollers compress against the preform wall thickness and plastically deform the preform wall. The desired geometry is achieved when the preform is compressed above its yield strength and plastically deformed or “made to flow”. As the preform's wall thickness is reduced by the process, the length of the preform is increased as it is formed over the inner, rotating mandrel. This wall reduction with a cold work process causes the material's mechanical properties to increase, while refining the microstructure and orienting the crystallographic texture. Dimensional accuracies, specifically roundness, wall concentricity and straightness are normally achieved well beyond what can be realized through hot forming processes such as extruding or roll and welding of tubes and pipes. During flowforming, it is typical to reduce the preform wall thickness at least by about 20%, and in many instances the preform wall thickness is reduced by as much as 75%, in one or more (e.g., two or three) consecutive flowform passes. For example, FIG. 7 shows a macrograph of a flowformed, clad tube that had a preform wall thickness of 0.290″ (0.220″ steel OD diffusion bonded to 0.090″ alloy 625) that was flowformed to a wall thickness of 0.198″ for 31.7% wall reduction, resulting in a flowformed, clad wall thickness of 0.149″ steel and 0.049″ alloy 625. In some embodiments, the clad tube may be re-flowform to produce a thinner clad tube. FIG. 8 shows a micrograph of the two bonded materials after flowforming with an ASTM grain size around 8-12 at 24× magnification. FIGS. 9 and 10A show the diffusion layer, after flowforming, with no deleterious intermetallic phases formed between the two materials. FIG. 10B is the chemical analysis along the line shown in FIG. 10A. FIGS. 11A and 11B show a chemical analysis of the diffusion layer between the two dissimilar materials after flowforming.

Forming High Strength Clad Pipe with an Outer Jacket Alloy without Heat Treatment

In many situations, high strength clad pipe may be necessary or desirable. For example, where the clad pipe is to be used in pipeline transportation systems or used for drilling applications in the petroleum and natural gas industries, the clad pipe typically needs to meet certain strength standards, e.g., such as those set out in the American Petroleum Institute's API Specification 5LD “Specifications For CRA Clad Or Lined Steel Pipe”.

However, where the clad pipe is formed by overlaying an inner CRA with an outer jacket formed from low alloy steel, heat treatment is typically needed in order to give the low alloy steel its desired strength. Therefore, a heat treatment operation is performed on the clad pipe after flowforming when the clad pipe is formed by flowforming. Unfortunately, this heat treatment operation, which typically includes a quench and temper operation, may have significant negative effects on the flowformed pipe, e.g.,

(i) the heat treatment can distort the pipe dimensionally;

(ii) the heat treatment can soften or anneal the CRA which forms the inner core of the clad pipe; and

(iii) the heat treatment can add significantly to the cost of the clad pipe.

According to embodiments of the present invention, the clad pipe may be formed by overlaying the inner core CRA with an outer jacket alloy which does not require heat treatment after flowforming. Thus, the clad pipe may be formed from two cold workable alloys (e.g., the inner core CRA and the outer jacket alloy) which do not require heat treatment after flowforming. The clad pipe is used in its cold worked condition.

In one embodiment of the present invention, the outer jacket alloy includes inexpensive stainless steel, duplex stainless steel, and/or an aluminum alloy, etc. The outer jacket alloy may be selected so that the cold working associated with flowforming acts to increase the strength of the material. For example, the outer jacket alloy may include a material shown in Table 2 below.

TABLE 2
Selected DSS
Generic	UNS	Nominal Composition (wt %)
Name	Number	Cr	Ni	Mo	Cu	W	N	C	PREN(A)
U-50M(B)	—	21	7.5	2.5	1.5	—	?	0.06	30
22Cr	S31803	22	5.5	3	—	—	0.14	0.02	34
25Cr	S32550	25	8	3.0	2.0	—	0.2	0.02	38
25Cr	S31260	25	7	3.0	0.5	0.2	0.15	0.02	38
25Cr	S32520	25	6.5	3.5	—	—	0.26	0.02	41
25Cr	S32750	25	7	3.5	—	—	0.28	0.02	42
25Cr	S32760	25	7	3.5	0.7	0.7	0.28	0.02	42
25Cr	S39277	25	7	3.8	1.6	1.0	0.28	0.02	43
25Cr	S39274	25	7	3.0	0.5	2.0	0.28	0.02	43
(A)Cr + 3.3 (Mo = 0.5 W) = 16N (wt %).
(B)Cast product with 25% to 40% ferrite.

The inner CRA may be selected so that the cold working associated with flowforming acts to increase the strength of the material. For example, the inner core CRA may include a material shown in Table 3 below.

TABLE 3
CW, >30% Ni, >3% Mo
28	N08028	Bal.	27	31	3.5	1.0	0.3	—	—	—	—	—	0.02
825	N08825	Bal.	22	42	3.0	2.0	1.0	—	—	—	—	—	0.03
G-3	N06985	19	22	45	7	2.0	—	—	0.8	1.5	2	—	0.01
2550	N06975	15	25	51	6.5	1.0	1.0	—	—	—	—	—	0.01
625	N06825	3	22	62	9	—	0.2	0.2	3.5	—	—	—	0.03
C-276	N10276	6	16	56	16	—	—	—	—	4	2	0.35 V	0.01

Therefore, the negative effects associated with a post-flowforming heat treatment may be eliminated by replacing the low alloy steel jacket with an alloy jacket which does not require heat treatment to provide the desired strength where a high strength clad pipe formed by flowforming is necessary or desirable. Preferably, this may be done by forming the outer jacket out of inexpensive stainless steel, duplex stainless steel, and/or an aluminum alloy. In this case, the clad pipe is flowformed and there is no subsequent heat treatment. The clad pipe is used in the cold worked condition. Preferably, the outer jacket is formed out of an alloy which has its strength increased by the cold working associated with flowforming, e.g., such as one of the materials shown in Table 2 above. Preferably, the inner CRA is also selected from a material which has its strength increased by the cold working associated with flowforming, e.g., such as one of the materials shown in Table 3 above.

Bonding the Clad Preform

As noted above, the clad pipe may be formed by generating a clad preform having an inner core (e.g., CRA) covered by an outer jacket (e.g., an alloy) and then metallurgically joining the two metals before the cold working process of flowforming. In one embodiment, this metallurgical joining of the two metals is achieved by diffusion bonding. The metallurgical joining of the two metals may also be achieved by:

(i) bonding bimetallic sheet through explosive bonding, then rolling and welding so as to form the hollow preform, then flowforming; or

(ii) hot extruding the bimetallic hollow preform so as to create a metallurgical bond in the hollow preform, then flowforming.

It is generally not practical to use explosive bonding or extrusion bonding over the large lengths commonly associated with pipeline sections (e.g., 40 feet). However, it is practical to use explosive bonding or extrusion bonding over the shorter lengths commonly associated with the hollow preforms used for flowforming (e.g., 8 feet), so these other methods for metallurgical joining the two metals become practical when used in conjunction with flowforming.

Embodiments of the present invention include a new, two-step manufacturing process, diffusion bonding and flowforming, for producing bimetallic pipes and tubes made of two dissimilar metals or alloys. For example, a CRA liner material may be used on the bore with the OD material made of steel. The two materials may have dissimilar hardness and/or strain hardening levels that typically require two different processing parameters to cold work the materials. It was surprisingly found that the two materials, once diffusion bonded together, were able to be flowformed with one set of processing parameters. The two materials did not shear or rip apart from one another during the flowforming process. It is believed that one material provides support for the softer, more ductile material, allowing both materials to be flowformed together to produce a clad, cold-worked tube. For example, a liner material made of alloy 625 and a substrate OD material made of sour gas resistant low alloy steel (e.g., 1018 steel) may be diffusion bonded and flowformed into longer pipe using embodiments of the present invention. The preform material is metallurgically bonded together thru the diffusion bonding process which removes or reduces oxides from the bonding surface. Uniform or varying wall thicknesses can be flowformed for both layers. The flowformed, bimetallic pipe, formed according to embodiments of the present invention, provides excellent corrosion resistance. For example, the alloy 625 layer exhibited corrosion resistance which was almost identical with that of commercial solid alloy 625 pipe. The SSC resistance of a low alloy steel substrate satisfies the requirements of OCTG steel for sour service.

Although the above description describes flowforming for step two, other cold working, metal forming processes may be used instead of flowforming. For example, “drawing over a mandrel” and/or pilgering may also be used. Additionally, the bimetallic pipe can be made up of a myriad of combinations of materials, e.g., aluminum, titanium, zirconium, various nickel alloys, 300 series stainless, Nitronic, duplex stainless, non-magnetic stainless on the ID liners with clad low carbon steel, high carbon steel, or stainless ODs, or any combination thereof.

In addition, although the above description describes diffusion bonding for step one, other metal forming processes that adhere two materials together may be used instead of, or in addition to, the diffusion bonding. For example, hot extruding, cladding, rolling and fuse welding (without a weld filler) may be used to metallurgically combine the two materials together before the flowforming step. For instance, two plates may be rolled together and welded to form a tubular component and then cladded together to metallurgically bond the two materials together before the flowforming step. For the cladding process, the materials may be explosively cladded, laser deposition cladded, or diffusion bonding cladded. In this way, vastly different materials that typically have vastly different processing parameters may be formed into one, monolithic, clad workpiece with one set of processing parameters using embodiments of the present invention.

Although the above discussion discloses various exemplary embodiments of the invention, it should be apparent that those skilled in the art can make various modifications that will achieve some of the advantages of the invention without departing from the true scope of the invention.

Claims

1. A method of producing a bimetallic tubular component, the method comprising: providing a first tubular workpiece having an inner diameter and a second tubular workpiece having an outer diameter, the first and second tubular workpieces having dissimilar cold-working processing parameters, wherein the second tubular workpiece comprises a corrosion resistant alloy, wherein the first tubular workpiece comprises one of a duplex stainless steel and an aluminum alloy, wherein the first tubular workpiece has a hardness of 100 Vickers or greater, and wherein the second tubular workpiece has a hardness value greater than two times the hardness value of the first tubular workpiece;diffusion bonding the inner diameter of the first tubular workpiece to the outer diameter of the second tubular workpiece; andflowforming the diffusion bonded tubular workpieces to form the bimetallic tubular component without any heat treatment after the flowforming.

2. The method of claim 1, wherein the cold-working processing parameters are selected from the group consisting of feed rates, speed rates, and wall reduction percentages.

3. The method of claim 1, wherein the diffusion bonding is a hot isostatic pressing process.

4. The method of claim 3, wherein the hot isostatic pressing process is performed in an inert atmosphere.

5. The method of claim 1, wherein each tubular workpiece has an end and a gap is formed between the inner diameter and the outer diameter, the method further comprising: providing a port that goes through the first tubular workpiece to the gap between the two workpieces;sealing the end of the first tubular workpiece to the end of the second tubular workpiece in order to form a sealed area between the two workpieces; andforming a vacuum between the two workpieces in the gap before the diffusion bonding process.

6. The method of claim 1, wherein the second tubular workpiece comprises one of Alloy C-276 and Alloy 625.

7. The method of claim 1, wherein the diffusion bonded tubular workpieces are flowformed to a wall reduction of 20% to 31.7%.