WO2016016849A1

WO2016016849A1 - Methods for passivating a stainless steel tank

Info

Publication number: WO2016016849A1
Application number: PCT/IB2015/055789
Authority: WO
Inventors: Avtandil Khalil Oglu BAIRAMOV
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2014-07-30
Filing date: 2015-07-30
Publication date: 2016-02-04
Anticipated expiration: 2017-01-30

Abstract

Disclosed herein are methods for passivation of a stainless steel tank. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.

Description

METHODS FOR PASSIVATING A STAINLESS STEEL TANK

FIELD OF INVENTION

[0001] The present invention relates to methods for passivation of stainless steel tanks to provide improved corrosion resistance and resistance to discoloration of the tank contents.

BACKGROUND OF THE INVENTION

[0002] Stainless steels are widely used as materials of construction (MOC) for storage and export tanks, for example, storage and export of acetic acid. These tanks range in size up to tens of thousands of metric tons (T) and are often used for long term storage. Although stainless steel alloys have protective layers to increase the corrosion resistance of the steel, environmental and operational factors can alter the effective corrosion resistance leading to corrosion.

[0003] Iron content in the final stored product can be very critical and strongly limited for both reagent grade and commodity grade products. While the final iron content can depend on the corrosion rate of the materials used for constructing the storage and export tanks, increase in iron content above lower specification limits can lead to unacceptable decrease in the quality of the final product, which includes, among other things, an undesirable yellowing of the final product color. In this aspect, out of specification final products result in huge economical losses and even unplanned plant shutdown to identify and correct the cause of the problem.

[0004] Accordingly, there remains a need for new methods for passivation of stainless steel tanks to provide improved corrosion resistance. This and other needs are satisfied by the various aspects of the present disclosure.

SUMMARY OF THE INVENTION

[0005] In one aspect, the invention relates to a method of passivation of a stainless steel tank comprising the steps of: a) providing an acid or acid anhydride stainless steel tank containing liquid acid or liquid acid anhydride comprising a nitrogen line that exits at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank, and b) flowing nitrogen through the nitrogen line to the bottom of the tank and into the liquid acid or liquid acid anhydride, wherein the nitrogen contains at least 3 ppm oxygen, thereby passivating the stainless steel tank.

[0006] In another aspect, the invention relates to a method of preparing a system for passivation of a stainless steel tank, comprising the steps of: a) providing an acid or acid anhydride stainless steel tank comprising a nitrogen line that exits in the tank headspace for blanketing the headspace with nitrogen, wherein the nitrogen in the nitrogen line contains at least 3 ppm oxygen, and b) retrofitting the nitrogen line so that the exit of the nitrogen line is at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank.

[0007] In another aspect, the invention relates to a liquid acid or liquid acid anhydride solution contained in a stainless steel tank; wherein the liquid acid or liquid acid anhydride solution comprises less than about 1 ppm iron after about 6 months of storage in the tank.

[0008] Additional aspects of the invention will be set forth, in part, in the description which follows, and in part will be obvious from the description, or can be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention can be understood more readily by reference to the following detailed description of the invention and the Examples included therein.

[0010] Before the present compounds, compositions, articles, systems, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular reagents unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.

[0011] Moreover, it is to be understood that unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including:

matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of

embodiments described in the specification.

[0012] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. DEFINITIONS

[0013] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used in the specification and in the claims, the term "comprising" can include the embodiments

"consisting of and "consisting essentially of." Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined herein.

[0014] As used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "an acid" includes mixtures of two or more acids.

[0015] As used herein, the term "combination" is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0016] Ranges can be expressed herein as from one particular value, and/or to another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent 'about,' it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as "about" that particular value in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0017] As used herein, the terms "about" and "at or about" mean that the amount or value in question can be the value designated, or some other value approximately or about the same as the value designated. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is "about" or "approximate" whether or not expressly stated to be such. It is understood that where "about" is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0018] The terms "first," "second," "first part," "second part," and the like, where used herein, do not denote any order, quantity, or importance, and are used to distinguish one element from another, unless specifically stated otherwise.

[0019] As used herein, the terms "optional" or "optionally" means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. For example, the phrase "optionally recirculated acid" means that the acid can or cannot be recirculated and that the description includes both recirculated and unrecirculated acid.

[0020] As used herein, the term or phrase "effective," "effective amount," or "conditions effective to" refers to such amount or condition that is capable of performing the function or property for which an effective amount is expressed. As will be pointed out below, the exact amount or particular condition required will vary from one aspect to another, depending on recognized variables such as the materials employed and the processing conditions observed. Thus, it is not always possible to specify an exact "effective amount" or "condition effective to." However, it should be understood that an appropriate effective amount will be readily determined by one of ordinary skill in the art using only routine experimentation.

[0021] Disclosed are the components to be used to prepare the systems of the invention as well as the compositions themselves to be used within the methods disclosed herein. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each various individual and collective combinations and permutation of these compounds cannot be explicitly disclosed, each is specifically contemplated and described herein. For example, if a particular compound is disclosed and discussed and a number of modifications that can be made to a number of molecules including the compounds are discussed, specifically contemplated is each and every combination and permutation of the compound and the modifications that are possible unless specifically indicated to the contrary. Thus, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F and an example of a combination molecule, A-D is disclosed, then even if each is not individually recited each is individually and collectively contemplated meaning combinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any subset or combination of these is also disclosed. Thus, for example, the sub-group of A-E, B-F, and C- E would be considered disclosed. This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the compositions of the invention. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific aspect or combination of aspects of the methods of the invention.

[0022] References in the specification and concluding claims to parts by weight, of a particular element or component in a composition or article, denotes the weight relationship between the element or component and any other elements or components in the composition or article for which a part by weight is expressed. Thus, in a compound containing 2 parts by weight of component X and 5 parts by weight component Y, X and Y are present at a weight ratio of 2:5, and are present in such ratio regardless of whether additional components are contained in the compound.

[0023] A weight percent ("wt%") of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included. For example if a particular element or component in a composition or article is said to have 8% by weight, it is understood that this percentage is relative to a total compositional percentage of 100% by weight.

[0024] Each of the materials disclosed herein are either commercially available and/or the methods for the production thereof are known to those of skill in the art.

METHODS FOR PASSIVATION OF A STAINLESS STEEL TANK

[0025] According to aspects of the disclosure, as briefly described above, the present invention relates to a method of preparing a system for passivation of a stainless steel tank comprising: a) providing an acid or acid anhydride stainless steel tank comprising a nitrogen line that exits in the tank headspace for blanketing the headspace with nitrogen, whereby the nitrogen in the nitrogen line contains at least 3 parts per million (ppm) oxygen, and b) retrofitting the nitrogen line so that the exit of the nitrogen line is at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank.

[0026] In a further aspect, described herein are methods of passivation of a stainless steel tank comprising: a) providing an acid or acid anhydride stainless steel tank containing liquid acid or liquid acid anhydride comprising a nitrogen line that exits at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank, and b) flowing nitrogen through the nitrogen line to the bottom of the tank and into the liquid acid or liquid acid anhydride, wherein the nitrogen contains at least 3 ppm oxygen, thereby passivating the stainless steel tank.

[0027] In various aspects, the present invention comprises at least one tank or vessel. In a further aspect, the tank comprises stainless steel. In a still further aspect, the stainless steel can comprise any desired stainless steel. In one aspect, the stainless steel can comprise a 300 series stainless steel. In a yet further aspect, the stainless steel is a stainless steel selected from 304, 316, 347, 321, or 310. In an even further aspect, the stainless steel is 304L or 316L.

[0028] According to further aspects of the disclosure, the tank is for storage or export. In one aspect, the tank is for storage, for example, a liquid product. In another aspect, the tank is for export.

[0029] In a further aspect, the tank is for storage or export of concentrated acid. In a still further aspect, the acid can comprise any desired organic acid requiring limitation on iron content. In an even further aspect, the acid is acetic, formic, propionic, or acrylic acid. In a yet further aspect, the acid is acetic acid.

[0030] In a further aspect, the tank is for storage or export of an acid anhydride. In a still further aspect, the acid anhydride can comprise any desired acid anhydride requiring limitation on iron content. In a yet further aspect, the acid anhydride is acetic anhydride.

[0031] In a further aspect, the tank comprises at least one feed or line. In a further aspect, the line comprises stainless steel. In a still further aspect, the stainless steel can comprise any desired stainless steel. In one aspect, the stainless steel is SS316L or SS317L, or higher.

[0032] In a still further aspect, the line is a gas line, for example, to deliver a gas into the tank. In a yet further aspect, the line is a nitrogen line. In some aspects, the line exits or terminates in the tank headspace for blanketing the headspace with a gas. In further aspects, the line is a nitrogen line that exits or terminates in the tank headspace for blanketing the headspace with nitrogen. Such an exit in the headspace will need to be retrofitted to exit at the bottom of the tank.

[0033] In some aspects, the line exits or terminates at the bottom of the tank, for example, wherein the bottom of the tank is opposite the headspace of the tank. In other aspects, the line is retrofitted such that the exit or termination of the line is at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank. In a further aspect, the tank comprises a nitrogen line that exits or terminates at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank. In a yet further aspect, the tank comprises a retrofitted nitrogen line such that the exit or termination of the nitrogen line is at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank.

[0034] In various aspects, the line flows or delivers a gas through the line and into the tank. In a further aspect, the line flows or delivers a gas through the line and directly into the contents of the tank. In a yet further aspect, the line is a nitrogen line that delivers nitrogen through the line into the tank. In an even further aspect, the nitrogen line flows or delivers nitrogen through the nitrogen line to the bottom of the tank and into liquid acid or liquid acid anhydride.

[0035] In various aspects, the methods comprise delivering or flowing a gas through the line and into the tank. In a further aspect, the methods comprise delivering or flowing a gas through the line and directly into the contents of the tank. In a yet further aspect, nitrogen is flowed or delivered through the line into the tank. In an even further aspect, nitrogen is flowed or delivered through the nitrogen line to the bottom of the tank and into liquid acid or liquid acid anhydride. In as still further aspect, nitrogen is flowed or delivered through the nitrogen line into liquid acid or liquid acid anhydride, thereby passivating the stainless steel tank.

[0036] In a further aspect, the gas comprises nitrogen. In a still further aspect, the nitrogen comprises at least 3 ppm oxygen, including further exemplary amounts of at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, and at least 10 ppm oxygen. In a yet further aspect, the nitrogen comprises from about 3 ppm to about 10 ppm oxygen, for example, from about 5 ppm to about 10 ppm oxygen.

[0037] In a further aspect, the liquid acid or liquid acid anhydride can further comprise an oxidizing agent. In a still further aspect, the oxidizing agent can comprise a chromate, nitrite, molybdate, permanganate, or the like. [0038] In various aspects, the methods comprise providing an acid or acid anhydride stainless steel tank containing liquid acid or liquid acid anhydride. In some aspects, the liquid acid or liquid acid anhydride in the tank is static. In other aspects, the liquid acid or liquid acid anhydride is periodically circulated or stirred, for example, to increase oxygen distribution. In this aspect, circulating can comprise stirring or agitating the tank to cause mixing of the tank contents, and distribution of the oxygen.

[0039] In various aspects, the storage tank capacity can be any desired size or volume. In a further aspect, the storage tank capacity is about 5,000T. In a still further aspect, the storage tank capacity is less than about 5,000T. In a yet further aspect, the storage tank capacity is greater than about 5,000T.

[0040] In various aspects, the methods involve storage conditions effective to prevent corrosion or contamination of the tank contents. In further aspects, the storage conditions effective can comprise any desired storage conditions and will depend on a number of variable, including, but not limited to plant productivity and shipping schedules.

[0041] In one aspect, the external tank temperature can comprise ambient temperature. In a further aspect, the internal tank temperature is a temperature effective to prevent crystal formation. In a still further aspect, the internal tank temperature is greater than about 16 °C. In a yet further aspect, the internal tank temperature can be greater than about 16.6 °C, for example, greater than about 17 °C, greater than about 20 °C, or greater than about 25 °C.

[0042] In various aspects, the time "t" comprises the total storage time. In one aspect, the time "t" can be any desired time period. In a further aspect, the time "t" can be 1 minute, 1 hour, 1 day, 1 month, 6 months, 1 year, or 2 years, or more. In a still further aspect, the time "t" can be from about 1 month to about 6 months and all subranges there between.

[0043] In further aspects, the present methods for passivating of a stainless steel tank can maintain the iron content in the tank at or below a predefined standard concentration. The predefined standard concentration can be an acceptable value or range, and is sometimes referred to as the lower specification limit (LSL). Final products below or within the predefined standard concentration meet specification and are acceptable. Final products falling above or outside of the predefined standard concentration are out of specification and are unacceptable, and generally result in out of specification material. The specific predefined standard concentration depends on the desired product properties, for example, chemical and physical properties, and can be determined by one skilled in the art. [0044] In some aspects, the predefined standard concentration can comprise a concentration of a component, for example, a maximum concentration of a by-product or impurity. In other aspects, the predefined standard concentration can comprise the content of an impurity, for example, the iron content of acetic acid.

[0045] In one aspect, the predefined standard concentration is the iron content in the liquid acid or liquid acid anhydride after a time "t". In a further aspect, the predefined standard concentration is the iron content in the liquid acid or liquid acid anhydride after from about 5 months to about 6 months can be from about 1 to about 5 ppm iron. In a still further aspect, the iron content in the liquid acid or liquid acid anhydride after from about 5 months to about 6 months can be from about 1 to about 2 ppm iron.

[0046] In one aspect, the iron content in the liquid acid or liquid acid anhydride can be determined by any desired analytical method. In a further aspect, the iron content in the liquid acid or liquid acid anhydride is determined by laboratory analysis using atomic absorption spectroscopy. In a still further aspect, the method can be offline or online. In a yet further aspect, the method can be online to provide real-time data that can be used make adjustments to the storage tank and contents.

[0047] In one aspect, the methods can provide decreased iron accumulation in the liquid acid or liquid acid anhydride compared to a substantially identical reference method that does not flow nitrogen into the liquid acid, wherein the nitrogen contains at least 3 ppm oxygen. In a further aspect, the present methods exhibit a corrosion rate of less than about 0.025 mm/y.

[0048] In various aspects, the present methods can maintain the iron content below a predefined standard concentration. In one aspect, the present methods exhibit an iron content in the liquid acid or liquid acid anhydride of less than about 2 ppm after about 5 months of storage. In a further aspect, the present methods exhibit an iron content in the liquid acid or liquid acid anhydride of less than about 1 ppm after about 5 months. In a still further aspect, the present methods exhibit an iron content in the liquid acid or liquid acid anhydride of less than about 2 ppm after about 6 months. In a yet further aspect, the present methods exhibit an iron content in the liquid acid or liquid acid anhydride of less than about 1 ppm after about 6 months.

LIQUID ACID AND LIQUID ACID ANHYDRIDE

[0049] In various aspects, the present disclosure also relates to a liquid acid or liquid acid anhydride solution contained in a stainless steel tank. In one aspect, the liquid acid or liquid acid anhydride solution comprises less than about 5 ppm iron after about 6 months of storage in the tank. In a further aspect, the liquid acid or liquid acid anhydride solution comprises less than about 2 ppm iron after about 6 months of storage in the tank. In a still further aspect, the liquid acid or liquid acid anhydride solution comprises less than about 1 ppm iron after about 6 months of storage in the tank.

[0050] In a further aspect, nitrogen gas comprising at least about 3 ppm oxygen is bubbled through the liquid solution. In some aspects, the liquid is acetic, formic, propionic, or acrylic acid. In other aspects, the liquid is acetic anhydride.

ASPECTS

[0051] In various aspects, the present invention pertains to and includes at least the following aspects.

[0052] Aspect 1: A method of passivation of a stainless steel tank comprising the steps of: a) providing an acid or acid anhydride stainless steel tank containing liquid acid or liquid acid anhydride comprising a nitrogen line that exits at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank, and b) flowing nitrogen through the nitrogen line to the bottom of the tank and into the liquid acid or liquid acid anhydride, wherein the nitrogen contains at least 3 ppm oxygen, thereby passivating the stainless steel tank.

[0053] Aspect 2: The method of any preceding aspect, wherein the liquid is a concentrated acid.

[0054] Aspect 3: The method of any preceding aspect, wherein the liquid is an organic acid.

[0055] Aspect 4: The method of any preceding aspect, wherein the liquid is acetic, formic, propionic, or acrylic acid.

[0056] Aspect 5: The method of any preceding aspect, wherein the liquid is acetic acid.

[0057] Aspect 6: The method of any preceding aspect, wherein the liquid is acetic anhydride.

[0058] Aspect 7: The method of any preceding aspect, wherein the tank is a storage or export tank.

[0059] Aspect 8: The method of any preceding aspect, wherein the tank is for storage of acetic acid or acetic anhydride.

[0060] Aspect 9: The method of any preceding aspect, wherein the oxygen content is at least 5 ppm. [0061] Aspect 10: The method of any preceding aspect, wherein the oxygen content is at least 7 ppm.

[0062] Aspect 11 : The method of any preceding aspect, wherein the oxygen content is at least 9 ppm.

[0063] Aspect 12: The method of any preceding aspect, wherein the oxygen content is at least 10 ppm.

[0064] Aspect 13: The method of any preceding aspect, wherein the liquid acid or acid anhydride in the tank is static.

[0065] Aspect 14: The method of any preceding aspect, wherein the liquid acid or liquid acid anhydride in the tank is periodically circulated to increase the oxygen distribution.

[0066] Aspect 15: A method of preparing a system for passivation of a stainless steel tank, comprising the steps of: a) providing an acid or acid anhydride stainless steel tank comprising a nitrogen line that exits in the tank headspace for blanketing the headspace with nitrogen, wherein the nitrogen in the nitrogen line contains at least 3 ppm oxygen, and b) retrofitting the nitrogen line so that the exit of the nitrogen line is at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank.

[0067] Aspect 16: The method of aspect 15, further comprising the step of introducing a liquid acid or liquid acid anhydride into the tank.

[0068] Aspect 17: The method of aspect 16, wherein the liquid acid or liquid acid anhydride is introduced into the tank after retrofitting the nitrogen line.

[0069] Aspect 18: The method of aspect 16 or 17, wherein the liquid is a concentrated acid.

[0070] Aspect 19: The method of aspects 16-18, wherein the liquid is an organic acid.

[0071] Aspect 20: The method of aspects 16-19, wherein the liquid is acetic, formic, propionic, or acrylic acid.

[0072] Aspect 21: The method of aspects 16-20, wherein the liquid is acetic acid.

[0073] Aspect 22: The method of aspects 16-21, wherein the liquid is acetic anhydride.

[0074] Aspect 23: The method of aspects 15-22, wherein the tank is a storage or export tank.

[0075] Aspect 24: The method of aspects 15-23, wherein the tank is for storage of acetic acid or acetic anhydride.

[0076] Aspect 25: The method of aspects 15-24, wherein the oxygen content is at least 5 ppm. [0077] Aspect 26: The method of aspects 15-25, wherein the oxygen content is at least 7 ppm.

[0078] Aspect 27: The method of aspects 15-26, wherein the oxygen content is at least 9 ppm.

[0079] Aspect 28: The method of aspects 15-27, wherein the oxygen content is at least 10 ppm.

[0080] Aspect 29: The method of aspects 16-28, wherein the liquid acid or liquid acid anhydride in the tank is static.

[0081] Aspect 30: The method of aspects 16-29, wherein the liquid acid or liquid acid anhydride in the tank is periodically circulated to increase the oxygen distribution.

[0082] Aspect 31 : The method of any preceding aspect, further comprising an iron content in the liquid acid or liquid acid anhydride after from about 5 months to about 6 months of about 1 to about 5 ppm iron, preferably about 1 to about 2 ppm iron.

[0083] Aspect 32: A liquid acid or liquid acid anhydride solution contained in a stainless steel tank; wherein the liquid acid or liquid acid anhydride solution comprises less than about 1 ppm iron after about 6 months of storage in the tank.

[0084] Aspect 33: The liquid acid or liquid acid anhydride solution of aspect 32, wherein nitrogen gas comprising at least about 3 ppm oxygen is bubbled through the solution.

[0085] Aspect 34: The liquid acid or liquid acid anhydride solution of aspect 32, wherein the liquid is acetic, formic, propionic, or acrylic acid.

[0086] Aspect 35: The liquid acid or liquid acid anhydride solution of aspect 32, wherein the liquid is acetic anhydride.

Claims

CLAIMS What is claimed is:

1. A method of passivation of a stainless steel tank comprising:

a. providing an acid or acid anhydride stainless steel tank containing liquid acid or liquid acid anhydride comprising a nitrogen line that exits at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank, and

b. flowing nitrogen through the nitrogen line to the bottom of the tank and into the liquid acid or liquid acid anhydride, wherein the nitrogen contains at least 3 ppm oxygen, thereby passivating the stainless steel tank.

2. The method of any preceding claim, wherein the liquid is a concentrated acid.

3. The method of any preceding claim, wherein the liquid is an organic acid.

4. The method of any preceding claim, wherein the liquid is acetic, formic, propionic, or acrylic acid.

5. The method of any preceding claim, wherein the liquid is acetic acid.

6. The method of any preceding claim, wherein the liquid is acetic anhydride.

7. The method of any preceding claim, wherein the tank is a storage or export tank.

8. The method of any preceding claim, wherein the tank is for storage of acetic acid or acetic anhydride.

9. The method of any preceding claim, wherein the oxygen content is at least 5 ppm.

10. The method of any preceding claim, wherein the oxygen content is at least 7 ppm.

11. The method of any preceding claim, wherein the oxygen content is at least 9 ppm.

12. The method of any preceding claim, wherein the oxygen content is at least 10 ppm.

13. The method of any preceding claim, wherein the liquid acid or liquid acid anhydride in the tank is static.

14. The method of any preceding claim, wherein the liquid acid or liquid acid anhydride in the tank is periodically circulated to increase the oxygen distribution.

15. A method of preparing a system for passivation of a stainless steel tank, comprising:

a. providing an acid or acid anhydride stainless steel tank comprising a nitrogen line that exits in the tank headspace for blanketing the headspace with nitrogen, wherein the nitrogen in the nitrogen line contains at least 3 ppm oxygen, and

b. retrofitting the nitrogen line so that the exit of the nitrogen line is at the bottom of the tank, wherein the bottom of the tank is opposite the headspace of the tank.

16. The method of claim 15, further comprising the step of introducing a liquid acid or liquid acid anhydride into the tank.

17. The method of claim 16, wherein the liquid acid or liquid acid anhydride is introduced into the tank after retrofitting the nitrogen line.

18. The method of claim 16 or 17, wherein the liquid is a concentrated acid.

19. The method of claims 16- -18, wherein the liquid is an organic acid.

20. The method of claims 16- -19, wherein the liquid is acetic, formic, propionic, c acrylic acid.

21. The method of claims 16- -20, wherein the liquid is acetic acid.

22. The method of claims 16- -21, wherein the liquid is acetic anhydride.

23. The method of claims 15- -22, wherein the tank is a storage or export tank.

24. The method of claims 15- -23, wherein the tank is for storage of acetic acid or acetic anhydride.

25. The method of claims 15- -24, wherein the oxygen content is at least 5 ppm.

26. The method of claims 15- -25, wherein the oxygen content is at least 7 ppm.

27. The method of claims 15- -26, wherein the oxygen content is at least 9 ppm.

28. The method of claims 15- -27, wherein the oxygen content is at least 10 ppm.

29. The method of claims 16- -28, wherein the liquid acid or liquid acid anhydride in the tank is static.

30. The method of claims 16- -29, wherein the liquid acid or liquid acid anhydride in the tank is periodically circulated to increase the oxygen distribution.

31. A liquid acid or liquid acid anhydride solution contained in a stainless steel tank; wherein the liquid acid or liquid acid anhydride solution comprises less than about 1 ppm iron after about 6 months of storage in the tank.

32. The liquid acid or liquid acid anhydride solution of claim 31, wherein nitrogen gas comprising at least about 3 ppm oxygen is bubbled through the solution.

33. The liquid acid or liquid acid anhydride solution of claim 31, wherein the liquid is acetic, formic, propionic, or acrylic acid.

34. The liquid acid or liquid acid anhydride solution of claim 31, wherein the liquid is acetic anhydride.