1. Field of the Invention
The present invention relates to a method for manufacturing corrosion or erosion resistant alloy (CRA) down-hole tubulars and line pipe, both hereafter called (PIPE), and more particularly, to a method for manufacturing cold worked, high strength welded seamless CRA PIPE.
2. Description of the Prior Art
PIPE includes drill pipe, tubing and casing, line pipe, and mechanical pipe used in drilling, completion, production, waste disposal and transportation of liquids, gas and slurries in the oil and gas, petro-chemical, mining, and power-generating industries. In some corrosive and erosive applications increased volume of product flow is desirable. To increase flow requires an increase in the inside diameter (ID) size of the PIPE. Increase of corrosion and/or erosion resistant CRA PIPE size is restrained by the world's capability to manufacture such PIPE with current seamless technology. In recent years, work has been done to develop PIPE having higher strength and better resistance to failure under severe stress, corrosive and erosive applications, however work has not been done to increase the PIPE size or develop the ability to manufacture larger sizes. Corrosion and/or erosion resistant CRA work was necessitated by the demand for tubulars suitable for use in erosive atmospheres where the product being transported contains abrasive material capable of eroding the inside diameter (ID) surface of the PIPE and/or corrosive atmospheres containing hydrogen sulfide, carbon dioxide, chlorides associated hydrocarbons, and/or acid with low pH factors. PIPE subjected to these conditions may fail in a relatively short time due to such factors as sulfide and chloride stress cracking, corrosive pitting, erosive wear and general wall loss. Resistance to failure may be influenced by many factors, including the steel chemistry, the nature and amounts of alloying elements, the steel microstructure, the steel mechanical processing, and the nature of the heat treatment.
In regard to corrosion, commonly used methods of preventing corrosion in PIPE include coating ID surface with a thin layer of an anti-corrosive material, increasing wall thickness of PIPE, cladding the ID of carbon pipe with a corrosion and/or erosion resistant CRA, or utilizing a solid corrosion or erosion resistant CRA PIPE. The primary purpose of coating is to extend the operational life of the PIPE by providing a physical barrier between the corrosive agent and the base metal. Typical coating materials include paint, phenolic, epoxy, urethane, and nylon.
In regard to erosion, commonly used methods of handling erosion in PIPE include heat hardening the ID surface of the PIPE, increasing wall thickness of PIPE, cladding the ID of carbon PIPE with corrosion and/or erosion resistant CRA, or utilizing a solid corrosion and/or erosion resistant CRA PIPE.
Another way to slow corrosion and erosion is to increase by weight the corrosion and/or erosion resistant CRA alloy elements of the PIPE. An example is a chromium alloy combined with a nickel alloy. In such alloys, chromium and nickel are the main alloying elements, although chromium and nickel are reactive elements, the alloys passivate and exhibit excellent resistance to various types of corrosion and erosion in many different environments.
Preferably an alloy for corrosion has at least 22% chromium by weight and nickel content having at least 5% by weight and for erosion at least 20% chromium by weight and nickel content having at least 58% by weight, and at least 8% molybdenum by weight. A good example of CRA PIPE is one having a 22% chromium and 5% nickel alloy content by weight defined under the name 2205 and a good example of corrosion and/or erosive resistant CRA PIPE is one having a 20% chromium, 58% nickel and at least 8% molybdenum by weight defined under the name Alloy 625. John Gandy Corporation of Conroe, Tex. sells both.
The above noted problems and other similar corrosion and erosion problems make it desirable to provide a PIPE formed, at least in part, of a CRA. However, the introduction of such CRA poses additional manufacturing challenges for the production of larger size PIPE of the type under consideration. There are two well-known commercial processes in use for manufacturing prior art PIPE such as those used in the industries that utilize PIPE. These processes produce either “seamless” PIPE or they produce “welded” PIPE.
In a typical seamless prior art process, a seamless PIPE is manufactured, for example, from a solid billet of steel with a limited mass of about 10 inches in diameter and 6 to 8 feet long. The combination of the OD, ID and length of the finished PIPE is totally dependent upon the mass of the billet. After heating the solid billet to over 1000 degrees C., a hole is pierced by a method such as Mannesmann piercing, press piercing to create a longitudinal hole through the center of the solid billet to form a very thick-walled seamless hollow. The wall thickness and diameter of this seamless hollow are then progressively reduced by extrusion or by another hot or cold sizing method until a seamless PIPE of a predetermined size is obtained. Few mills are capable of producing a CRA billet with sufficient mass to manufacture a finished CRA PIPE in the desired longer length and heavier wall in conjunction with a large OD.
Welded PIPE, on the other hand, is made from a flat strip, which is formed into a PIPE and welded along its length. This is a straightforward way of making a welded PIPE. However, additional care is necessary to avoid structural and cosmetic defects at the weld. Since such problems cannot arise from a seamless PIPE, the seamless manufacturing process offers advantages in many situations. However, the costs incident to the manufacture of seamless PIPE, and particularly of certain sizes, together with the difficulties attendant upon the known processes of producing such seamless PIPE, and the lack of uniformity with respect to successive seamless PIPES has, to a large extent, driven the industry to the use of welded carbon alloy PIPE. However, corrosion and/or erosion resistant welded CRA PIPE has not been qualified, accepted or used in down-hole harsh corrosion and or erosion applications.
Prior art for welded CRA PIPE used in the as-welded condition, without cold work or forging of the weld, required the weld's yield and tensile strengths and corrosion and/or erosion resistances to be equal or exceed that of the parent material. Traditionally the welding of CRA PIPE for use in the as-welded condition utilizes a dissimilar high alloy CRA filler material of higher yield and tensile strengths and more corrosion and/or erosion resistance than the parent metal. CRA PIPE welded by this method is traditionally joined together by welding the circumference of one end of a PIPE to the end of another PIPE; this method is referred to as a girth weld. The girth weld of PIPE will remain in the as-welded condition for applications that allow welding prior to the time of installation. As-welded CRA PIPE is not applicable for down-hole applications because of its lower strengths of both the parent and weld materials in addition to dissimilar strengths, non-uniform corrosion and/or erosion resistance and potential galvanic corrosion between the dissimilar alloys of the weld and parent material. Also, down-hole installations traditionally utilized seamless CRA PIPE manufactured by the seamless billet method with fast joining threaded specialty connections to save time and reduce cost of the expensive drilling rig. Girth welding and temper of the as-welded CRA PIPE requires substantial time and is not economically feasible to perform at the time of installation at the drilling rig.
Traditionally down-hole applications for CRA PIPE have been restricted to cold work CRA PIPE manufactured by the seamless pierced billet method. To the applicants knowledge cold worked welded CRA PIPE has not been used in a down-hole application.
Prior Art for traditional seamless CRA PIPE is manufactured by the pierced seamless billet method and cold worked by pilger or drawn over mandrel methods. Cold work of low yield and tensile strengths of high alloy CRA pierced seamless billets elongates the pierced billet and increases the yield and tensile strengths necessary for down-hole high alloy CRA PIPE applications. After cold work, the PIPE cannot be subjected to elevated critical temperatures without lowering the strengths built in by the cold work process.
Traditionally, the use of similar filler material to that of the parent material when welding CRA PIPE has not been acceptable for use in the as-welded condition for applications with high internal pressure or where corrosive and/or erosive products are present. CRA PIPE with a weld with similar filler material to that of the parent material results in a PIPE with the weld with lower yield and tensile strengths than that of the parent material and is unacceptable for use in above ground applications. However, cold work of such a weld and parent material produces higher yield and tensile strengths that are alike or similar, for both the weld and the parent metal, that is acceptable for down-hole applications. This phenomena is the result of annealing the full body to make the weld and the parent materials granular structure homogenous and the cold work compresses the granular structure to similar size with similar higher yield and tensile strengths.
Traditionally cold working or forging of the weld has not been necessary for as-welded high alloy PIPE for use in-ground surface applications. However, high alloy CRA PIPE for down-hole application is traditionally cold worked or forged to obtain higher yield and tensile strengths required to contain high pressure and support high tension loads from the weight of the PIPE. To compensate for the absence of cold work or forging of the weld a dissimilar and more noble filler material with higher yield and tensile strengths with enhanced corrosion and/or erosion resistance than that of the parent metal is utilized in the welding process to add strengths and corrosion and/or resistance to the weld that equals or exceeds that of the parent metal. This compensation does not lend itself to uses for PIPE in down-hole applications because without cold work, the yield strengths of both the weld and PIPE body are inadequate for down-hole specifications and the dissimilar more noble alloy of the weld to parent alloy lends itself to a galvanic corrosion situation when submerged in down-hole liquids. Additionally, after cold working the more noble alloy in the weld is unacceptable due to being substantially higher in yield and tensile strengths and harder and more brittle than the parent metal.
There are presently two methods of cold working a hollow to obtain sufficient high strength to meet the required mechanical strengths for tensile, yield, burst and collapse for the finished PIPE. The first method is by cold draw where a larger hollow is pulled or drawn through a smaller die, reducing the OD and simultaneously reducing the ID over a retained mandrel and then repeat the same process to obtain the required mechanical strengths. The second method is by pilger where a hollow is mechanically forged under high pressure through a set of dies substantially reducing the OD and simultaneously reducing the ID over a mandrel to obtain the required mechanical strengths.
The invention is a method that combines the economics of welding with the advantages of seamless as a means to manufacture a hollow that offers quality, flexibility and economics that are equal or superior to traditional seamless methods. The hollow would then be cold worked into a finished welded seamless PIPE with required mechanical strengths. Cold Working is a method to cold forge the complete through wall circumference of the OD of the hollow down to a smaller OD while escalating the yield and tensile strengths to substantially elevated levels above those of the hollow. To obtain uniform strengths for the PIPE the hollow is restricted to a chemistry of alloying elements through wall around the complete circumference of the welded hollow. The hollow must be welded without filler metal or with similar filler metal of like chemistry to that of the parent metal. If filler metal with a more noble chemistry than that of the parent metal is used it will produce a metal that is unacceptably harder and more brittle that is higher in yield and tensile strengths in the weld area than in the parent material.
The welded hollow is made from a thick corrosion or erosion resistant CRA plate, which is formed into a hollow that is welded along its length. This is a straightforward way of making a hollow. However, substantial steps must be taken to insure that the weld and the adjacent heat affected zone are structurally sound, cosmetically formed to the body surface and homogenous to the un-welded portion of the hollow.
The present invention has as one object to develop welded seamless high strength corrosion or erosion resistant CRA PIPE up to the maximum OD as an alternative to a seamless, high strength corrosion and/or erosion resistant CRA PIPE up to a maximum OD.
Another object of the present invention is to develop a method to manufacture welded corrosion and/or erosion resistant CRA hollows that equal or exceed the quality and performance of seamless corrosion and/or erosion resistant CRA hollows produced by the present pierced billet methods.
Another object of the invention is to develop a method to manufacture welded corrosion and/or erosion resistant CRA hollows that is commercially economical with seamless corrosion and/or erosion resistant CRA hollows produced by the pierced billet method.