Patent Application
20140170015
This application describes and claims certain subject matter that was developed within the scope of a written joint research agreement between General Electric Company and Chevron U.S.A., Inc., which was in effect prior to the inventive activities resulting in the present application and claims.
The present invention relates to corrosion resistant steel compositions. In particular the present invention relates to steel compositions which resist corrosion in environments containing high levels of hydrogen sulfide.
As the world's economies rely to an ever greater extent on hydrocarbon energy resources containing relatively high levels of hydrogen sulfide, problems associated with hydrogen sulfide induced corrosion of steel components of hydrocarbon refining operations represent growing risks to personnel, plant equipment and the environment.
Although various approaches to inhibiting environmental corrosion of steel are known in the art, and many different steel compositions have been prepared and tested, there remains a need for relatively low cost steels which exhibit robust resistance to the corrosive effects of hydrogen sulfide at high temperatures. This need is particularly pronounced in oil refining operations where hot fluids laden with hydrogen sulfide come into contact with steel surfaces, for example in distillation vessels, pipes and heat exchangers.
In accordance with one aspect of the present invention, a hydrogen sulfide resistant steel composition is provided that includes the elements Fe, C, Si, Cu, and Mn wherein the composition comprises from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 1.40 percent by weight silicon, from about 0.50 to about 1.50 percent by weight copper, and from about 0.20 to about 1.00 percent by weight manganese, wherein the composition is substantially free of chromium, and wherein the composition contains less than 0.1 percent by weight nickel, molybdenum, or tungsten.
In accordance with another aspect of the present invention, a hydrogen sulfide resistant steel composition is provided that includes the elements Fe, C, Si, Cu, and Mn wherein the composition comprises from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 0.40 percent by weight silicon, from about 0.50 to about 1.50 percent by weight copper, and from about 0.20 to about 1.00 percent by weight manganese, wherein the composition is substantially free of chromium and aluminum, and wherein the composition contains less than 0.1 percent by weight nickel, molybdenum, or tungsten.
In accordance with yet another aspect of the present invention, a hydrogen sulfide resistant steel composition is provided that includes the elements Fe, C, Si, Cu, Mn, and Al wherein the composition comprises from about 96.80 to about 98.10 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.80 to about 1.15 percent by weight silicon, from about 0.50 to about 0.65 percent by weight copper, from about 0.20 to about 0.50 percent by weight manganese, and from about 0.30 to about 0.60 percent by weight aluminum, wherein the composition is substantially free of chromium.
Additional aspects of the present invention include articles comprising the hydrogen sulfide resistant steel compositions provided by the present invention.
Other embodiments, aspects, features, and advantages of the invention will become apparent to those of ordinary skill in the art from the following detailed description and the appended claims.
In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings.
The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.
“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.
In one embodiment, the present invention provides a corrosion resistant steel composition which is especially resilient in hydrogen sulfide-containing environments, such as oil refineries where refinery components such as heat exchangers, distillation columns, conduits, and condensers are subject to exposure to hot organic fluids comprising hydrogen sulfide. The compositions provided by the present invention are anticipated to be useful as well in natural gas and crude oil production equipment such as pumps, well bore casings and storage vessels. In one embodiment, the present invention provides an article comprising one or more of the steel compositions disclosed herein, the article being a vessel which may be used to contain mixtures comprising hydrocarbons and hydrogen sulfide. In one such embodiment, the vessel may be used as a component of a system used to recover hydrocarbons from a hydrocarbon-containing reservoir, for example a well bore casing or a gas liquid separator.
Crude oil and intermediates produced in refineries from crude oil are frequently complex mixtures of organic and inorganic materials. Such mixtures present special corrosion risks in the presence of hydrogen sulfide. In addition, the sulfur containing materials of such mixtures are believed to be important sources of hydrogen sulfide as the mixtures are heated during in various refining steps.
Those of ordinary skill in the art will appreciate that various crude oil and natural gas production operations attending the recovery of hydrocarbon resources from a hydrocarbon reservoir frequently entail the handling of hot fluids comprising naturally occurring hydrogen sulfide present in the reservoir as well as other corrosive species present in the reservoir.
The present invention provides corrosion resistant steel compositions which are relatively low cost relative to highly alloyed steels favored because of their resistance to hydrogen sulfide induced corrosion. In addition, the corrosion resistant steel compositions provided by the present invention provide additional enhancements such as being weldable without having to rely upon post-weld heat treatments to assure weld integrity, a property not shared by typical highly alloyed steels which have carbon equivalent values (CE) above 0.6 which renders them susceptible to weld embrittlement in the absence of post-weld heat treatment. As will be appreciated by those of ordinary skill in the art, post-weld heat treatment can be a laborious and expensive process.
As noted, in one embodiment, the present invention provides a steel composition comprising the elements Fe, C, Si, Cu, and Mn wherein the composition comprises from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 1.40 percent by weight silicon, from about 0.50 to about 1.50 percent by weight copper, and from about 0.20 to about 1.00 percent by weight manganese, wherein the composition is substantially free of chromium, and wherein the composition contains less than 0.1 percent by weight nickel, molybdenum, or tungsten.
Although not wishing to be bound by any particular theory, it is believed that the various elemental components (Fe, C, Si, Cu, Mn, Al) of the compositions provided by the present invention interact in such as way such that each component must be present within the range specified in order for the composition to be effective in resisting sulfidic corrosion. Thus, compositions provided by the present invention must contain from about 96.80 to about 99.00 percent by weight iron with the elements carbon, silicon, copper and manganese being present in the ranges specified above, and the compositions contain less than 0.1 percent by weight nickel, molybdenum, or tungsten. As used herein, the expression “the compositions contain less than 0.1 percent by weight nickel, molybdenum, or tungsten” means that if any one or more of the elements Ni, Mo and W is present in a corrosion resistant steel composition provided by the present invention, that element is present in an amount less than 0.1 percent by weight based on the total weight of the composition. As noted, the compositions provided by the present invention are substantially free of chromium. A composition provided by the present invention which is substantially free of an element, for example chromium or aluminum, may contain low levels of the element, however, the amount of the element present in the composition is too small to produce any effect on the sulfidic corrosion resistance of the composition. Thus, it is believed, and the data confirm, that the presence chromium will have no effect on the sulfidic corrosion properties of compositions provided by the present invention when it is present in an amount less than about 0.20 percent by weight. Table I below illustrates specific compositions of the invention which are substantially free of chromium.
In one embodiment, the present invention provides an article comprising a corrosion resistant steel composition comprising the elements Fe, C, Si, Cu, and Mn wherein the composition comprises from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 1.40 percent by weight silicon, from about 0.50 to about 1.50 percent by weight copper, and from about 0.20 to about 1.00 percent by weight manganese, wherein the composition is substantially free of chromium, and wherein the composition contains less than 0.1 percent by weight nickel, molybdenum, or tungsten. In one embodiment, the article is a component of an oil refinery, for example a pipe, a heat exchanger, or a distillation column In various embodiments, such an article exhibits a corrosion rate of less than 15 mpy when exposed to hydrogen sulfide according Corrosion Test Method No. 1 of the Experimental Part of this disclosure.
In one embodiment, the present invention provides a corrosion resistant steel composition which is substantially free of chromium and contains less than 0.1 percent by weight nickel, molybdenum, or tungsten, and comprises aluminum in addition to comprising from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 1.40 percent by weight silicon, from about 0.50 to about 1.50 percent by weight copper, and from about 0.20 to about 1.00 percent by weight manganese. In one or more embodiments, the aluminum is present in an amount corresponding to from about 0.20 to about 0.60 percent by weight. In one embodiment, the present invention provides an article comprising such a corrosion resistant steel composition comprising aluminum. In one embodiment, the article is a component of an oil refinery, for example a pipe, a heat exchanger, or a distillation column In various embodiments, such an article exhibits a corrosion rate of less than 15 mpy when exposed to hydrogen sulfide according Corrosion Test Method No. 1 of the Experimental Part of this disclosure. Table II below provides specific examples of such corrosion resistant steel compositions.
In one embodiment, the present invention provides a corrosion resistant steel composition comprising about 97.5 percent by weight iron, about 0.2 percent by weight carbon, about 1.0 percent by weight silicon, about 0.4 percent by weight aluminum, about 0.4 percent by weight Mn, and about 0.6 percent by weight copper, wherein the composition is substantially free of chromium, and wherein the composition contains less than 0.1 percent by weight nickel, molybdenum, or tungsten.
In one embodiment, the present invention provides a corrosion resistant steel composition comprising the elements Fe, C, Si, Cu, and Mn wherein the composition comprises from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 0.40 percent by weight silicon, from about 0.50 to about 1.00 percent by weight copper, and from about 0.20 to about 1.50 percent by weight manganese, wherein the composition is substantially free of chromium and aluminum, and wherein the composition contains less than 0.1 percent by weight nickel, molybdenum, or tungsten. In one embodiment, the present invention provides an article comprising such a corrosion resistant steel composition. In one embodiment, the article is a component of an oil refinery, for example a pipe, a heat exchanger, or a distillation column In various embodiments, such an article exhibits a corrosion rate of less than 15 mpy when exposed to hydrogen sulfide according Corrosion Test Method No. 1 of the Experimental Part of this disclosure. Table III below provides specific examples of such corrosion resistant steel compositions. In one embodiment, such corrosion resistant steel compositions comprise carbon in an amount corresponding to from about 0.15 to about 0.25 percent by weight. See for example the compositions of Entries 3a-3c of Table III. In one embodiment, such corrosion resistant steel compositions comprise silicon in an amount corresponding to from about 0.25 to about 0.35 percent by weight. See for example the compositions of Entries 3a-3c of Table III.
In yet another embodiment, the present invention provides a corrosion resistant steel composition comprising the elements Fe, C, Si, Cu, Mn, and Al wherein the composition comprises from about 96.80 to about 98.10 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.80 to about 1.15 percent by weight silicon, from about 0.50 to about 0.65 percent by weight copper, from about 0.20 to about 0.50 percent by weight manganese, and from about 0.30 to about 0.60 percent by weight aluminum, wherein the composition is substantially free of chromium, and wherein the composition contains less than 0.1 percent by weight nickel, molybdenum, or tungsten. See, for example, the compositions of Entries 4a-4e of Table IV. In one or more embodiments, the present invention provides an article comprising such a corrosion resistant steel composition. In one or more embodiments, such an article is a component of an oil refinery, for example a pipe, a heat exchanger, or a distillation column In one or more embodiments, such an article exhibits a corrosion rate of less than 15 mpy when exposed to hydrogen sulfide according to Corrosion Test Method No. 1 of the Experimental Part of this disclosure
Compositions provided by the present invention are characterized by a “carbon equivalence” (CE) value. As previously noted, a CE value provides an indicator of whether or not an article comprising a given steel composition will require post-welding heat treatment in order to reduce the susceptibility of the article to corrosion in the heat affected zone (HAZ) in and around the weld. CE values may be calculated as shown in the Experimental Part of this disclosure. Typically, when a corrosion resistant steel composition exhibits a CE value in a range from about 0.44 to about 0.54, such a CE value may be taken as a relatively reliable indicator that an article made from such a corrosion resistant steel composition may not require post weld heat treatment in one or more applications.
In one embodiment, the present invention provides a corrosion resistant steel composition which is substantially free of chromium and aluminum, which contains less than 0.1 percent by weight nickel, molybdenum, or tungsten, and which comprises from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 1.40 percent by weight silicon, from about 0.50 to about 1.50 percent by weight copper, and from about 0.20 to about 1.00 percent by weight manganese, wherein the composition has a carbon equivalence (CE) value in a range from about 0.44 to about 0.54. In one or more embodiments, such compositions have a carbon equivalence (CE) value in a range from about 0.44 to 0.50.
In an alternate embodiment, the present invention provides a corrosion resistant steel composition which is substantially free of chromium and aluminum, which contains less than 0.1 percent by weight nickel, molybdenum, or tungsten, and which comprises from about 96.80 to about 99.00 percent by weight iron, from about 0.10 to about 0.30 percent by weight carbon, from about 0.20 to about 0.40 percent by weight silicon, from about 0.50 to about 1.50 percent by weight copper, and from about 0.2 to about 1.00 percent by weight manganese, wherein the corrosion resistant steel composition has a carbon equivalence (CE) value in a range from about 0.44 to 0.54. In one or more embodiments, such compositions have a carbon equivalence (CE) value in a range from about 0.44 to 0.50.
The experimental steels compositions were prepared and processed at GE Global Research facilities. All steel compositions were cast by vacuum induction melting using elemental raw materials. After casting, each ingot was preheated at 1100° C. for approximately 90 minutes before forging sideways in one pass to a thickness of 0.25 inches. Care was taken to avoid decarburization by wrapping the ingots in stainless steel foil prior to heat treatment and forging. After air-cooling to ambient temperature, the forged parts were grit blasted and rinsed in alcohol. The exterior surfaces of the forged articles were then ground on a surface grinder to provide oxide free surfaces. The resulting parts were cold rolled to a thickness of approximately 0.100 inch in several passes, each cold rolling pass providing a reduction in thickness of approximately 10%. The cold rolled parts were then annealed at 870° C. for 30 minutes and subsequently cooled at approximately 0.4° C./min to below 650° C. All heat treatments were carried out under an argon atmosphere. Following the annealing step, the parts were again grit blasted and rinsed in alcohol. The parts were then cold rolled to sheets having a thickness of approximately 0.060 inches. Each cold rolling pass provided a reduction in thickness of about 10%. Once the steel compositions had been processed into sheets, they were sectioned into corrosion coupons (approximately 0.75 inch×1 inch× 1/16 inch). The surfaces of the corrosion coupons, including edge surfaces, were individually ground as before. In preparation for corrosion testing, the dimensions (width, length and thickness) of each test coupon were measured, each coupon was weighed three times and the weights and dimensions were recorded, and the surface areas of the coupons were calculated. Coupons were weighed again immediately before and after corrosion testing. Corrosion tests were carried out by a provider of corrosion testing services DNV-Columbus, Dublin, Ohio and used a test protocol approved by the inventors, at times herein referred to as Corrosion Test Method No. 1. The corrosion tests were performed in a 4-L Hastelloy autoclave fitted with ports for gas purging and pressure gauges. The coupons were hung from a glass coupon tree that was suspended from the lid of the autoclave. Each coupon was electrically isolated from all other coupons and from the autoclave itself. For each batch test, the autoclave was charged with 2.5 liters of oil (naphthenic distillate heavy oil HR 1200). After sealing the autoclave, the oil was purged at ambient temperature with nitrogen for 24 hours before switching the purging gas to the corrosion test gas (10% H2S+90% N2). An overhead pressure of approximately 30-40 psi was applied to the exiting gas. The temperature was then raised to the test temperature (600° F.) and the coupons were exposed to the hydrogen sulfide-containing environment at 600° F. for 72 hours.
After testing, the coupons were cleaned with toluene to remove the oil and weighed to determine the level of scale formation during testing. In interpreting test data the following analysis was applied. A weight gain would show that corrosion product scale had formed on the coupon was adherent and did not spall, a weight loss would indicate the formation of a scale that spalls (detaches) as it forms. Following exposure to the test conditions, the coupons were cleaned of any corrosion products (scale) using ASTM G01 standard inhibited hydrochloric acidic solution (Rodine 213). Lastly, the coupons were lastly weighed three more times and the average final weight was calculated. The averaged final weight was used to calculate the corrosion rate by mass loss.
The corrosion rate (CR) was calculated using the ASTM G1 formula in which the weight loss of the coupon during the exposure time in the autoclave was converted into linear penetration rate (mpy or “mils per year”) by dividing each coupon mass loss by the exposed area of the coupon, by the density of the alloy and by the exposure time.
In the equation above, Wi is the initial weight (mass) of the coupon, and Wf is the final mass of the coupon. In the case of the experimental alloys, in which the density was not available, an estimated density of 7.85 g/cm3 was used.
Actual compositions of the steels were determined by ion chromatography and combustion analysis.
A 985 g batch of experimental steel (GE reference SUL9) comprising approximately 97.78 percent by weight iron, approximately 0.21 percent by weight carbon, approximately 0.26 percent by weight silicon, approximately 0.54 percent by weight copper, and approximately 0.96 percent by weight manganese was prepared and transformed into test coupons which were subjected to corrosion testing as described in the general methods section. The composition contained measurable, but negligible amounts of Mo (0.023%), Al (0.003%), Cr (0.16%), S (0.001%), V (0.0015%) and Ni (0.072%) totaling approximately 0.26 percent by weight. Coupons prepared using the steel composition of this Example 1 exhibited a corrosion rate (CR) of 12.8±0.4 mpy, a rate equivalent to or superior to that observed for a highly alloyed steel API P91 (See Comparative Example 1).
A 985 g batch of experimental steel (GE reference SUL40) comprising approximately 97.50 percent by weight iron, approximately 0.20 percent by weight carbon, approximately 1.01 percent by weight silicon, approximately 0.37 percent by weight aluminum, approximately 0.57 percent by weight copper, and approximately 0.35 percent by weight manganese was prepared and transformed into test coupons which were subjected to corrosion testing as described in the general methods section. The composition contained measurable, but negligible amounts of Mo (0.0032%), Cr (0.00077%), S (0.0025%), V (trace), Ni (0.0013%), and Zn (trace) totaling approximately 0.01 percent by weight. Coupons prepared using the steel composition of this Example 2 exhibited a corrosion rate (CR) of 10.6±0.5 mpy, a rate equivalent to or superior to that observed for alloyed steel API P91 (See Comparative Example 1).
Test coupons were cut from a commercially available API P91 steel pipe (GE reference P91) comprising approximately 89.39 percent by weight iron, approximately 0.12 percent by weight carbon, approximately 0.34 percent by weight silicon, approximately 0.92 percent by weight molybdenum, approximately 8.4 percent by weight chromium, approximately 0.44 percent by weight manganese, and about 0.21 percent by weight vanadium. The API P91 steel contained measurable, but negligible amounts of Al (0.01%), S (0.001%), N (0.042%), and Ni (0.13%), totaling approximately 0.18 percent by weight, and was essentially free of copper. The test coupons which were subjected to corrosion testing as described in the general methods section. Coupons prepared using the steel composition of this Comparative Example 1 exhibited a corrosion rate (CR) of 11±0.7 mpy.
Test coupons were cut from a commercially available steel pipe made of the alloy A106 (GE reference A106) comprising approximately 98.22 percent by weight iron, approximately 0.25 percent by weight carbon, approximately 0.25 percent by weight silicon, approximately and 1.01 percent by weight manganese. The A106 steel contained measurable, but negligible amounts of Al (0.029%), Counter rotating (0.18%), S (0.002%), and Ni (0.06%), totaling approximately 0.27 percent by weight, and was essentially free of copper. The test coupons were subjected to corrosion testing as described in the general methods section. Coupons prepared using the steel composition of this Comparative Example 2 exhibited a corrosion rate (CR) of 16.9±1.4 mpy.
A 985 g batch of experimental steel (GE reference SUL33) comprising approximately 98.08 percent by weight iron, approximately 0.20 percent by weight carbon, approximately 0.90 percent by weight silicon, approximately 0.321 percent by weight aluminum, and approximately 0.36 percent by weight manganese was prepared and transformed into test coupons which were subjected to corrosion testing as described in the general methods section. The composition contained measurable, but negligible amounts of Mo (0.03%), Cr (0.0775%), Cu (0.023%), S (0.0035%), V (trace), Ni (0.0025%), and Zn (trace) totaling approximately 0.14 percent by weight. Coupons prepared using the steel composition of this Comparative Example 3 exhibited a corrosion rate (CR) of 13.4±0.7 mpy.
A 150 kg batch of experimental steel (GE reference SUL41) was prepared by a commercial allow producer (Sophisticated Alloys, Inc., Butler, Pa., USA) using the general procedure provided herein as directed by the inventors. The alloy comprised approximately 97.83 percent by weight iron, approximately 0.18 percent by weight carbon, approximately 1.02 percent by weight silicon, approximately 0.45 percent by weight aluminum, and approximately 0.52 percent by weight manganese was prepared and transformed into test coupons which were subjected to corrosion testing as described in the general methods section. The composition contained measurable, but negligible amounts of N (trace) and was essentially free of Cu. Coupons prepared using the steel composition of this Comparative Example 4 exhibited a corrosion rate (CR) of 14.2±0.4 mpy.
Data for all embodiments of the invention and comparative examples is given in Table V.
†CE = Carbon Equivalence
The data illustrate the surprising resistance of the steel compositions provided by the present invention to sulfidic corrosion relative to the control samples (Comparative Examples 1-4). In addition, the steel compositions provided by the present invention had carbon equivalence (CE) values below 0.50, a good indicator that such steel compositions need not be heat treated following welding. Carbon equivalence is calculated as shown below in Equation (1).
CE=% C+(% Mo+% Cr+% V)/5+(% Si+% Mn)/6+% Cu/15 (1)
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
