Composition for preventing polythionic acid (PTA) stress corrosion cracking of 300 series stainless steel and method of using the same

Abstract

A composition, system, and method for treating stainless steel vessels to prevent polythionic acid stress corrosion cracking is described. The composition includes a premixed K2CO3 solution that can be diluted on-site to a desired K2CO3 concentration by in-line mixing with water prior to placement in the stainless steel vessel being treated.

Description

Technical Field

[0001] <Cross - Reference to Related Applications> This application claims the benefit of U.S. Provisional Application No. 63 / 191,058, filed on May 20, 2021, the entire contents of which are incorporated herein by reference.

[0002] <Technical Field> The present invention relates to a composition for preventing polythionic acid stress corrosion cracking of 300 - series stainless steel and a method of using the same. More specifically, the present invention relates to a premixed solution that can be diluted and used on - site for treating austenitic stainless steel or austenitic alloys to prevent stress corrosion cracking.

Background Art

[0003] Heretofore, to prevent polythionic acid stress cracking, operators have treated stainless steel vessels with soda ash (i.e., sodium carbonate, or Na2CO3). In this case, a large - capacity steel tank (e.g., a frac tank) of clean water containing several hundred pounds of dry soda ash is used. The soda ash and water are mixed in the tank to form a treatment solution. The tank is then installed "upstream" of the stainless steel vessel that needs to be treated.

[0004] Thereafter, the treatment solution is injected into the bottom of the stainless steel device to be treated until it is full, at which point the solution exits from the top of the vessel and is pumped back to the large - capacity tank. This mixture - injection - return circulation process is carried out in a closed loop.

[0005] When the treatment solution returns to the large-capacity tank, the operator measures the pH of the solution. Based on the measured pH, the operator can determine whether the treatment process was effective. If the measurement shows a pH level below 9, it is necessary to continue applying the closed-loop circulation while adding soda ash to raise the pH level. If the measured value exceeds 9 and the application process of the closed loop can be terminated after at least 2 hours, the treatment tank can be drained and the pumping device can be disconnected from the treatment tank. The closed-loop circulation approach follows three main facts.

[0006] First, it is necessary to continuously circulate the treatment solution. Otherwise, since the solubility of soda ash in the treatment solution is limited, the soda ash will precipitate and separate from the solution.

[0007] Second, the NACE International standard requires that when the unit and surrounding piping are not clean (i.e., when there are oil contaminants and deposits such as sludge deposits), the treatment be carried out on a circulation basis (see NACE SP0170-2018, Item No. 21002, Approved Date 2018-09-10, ISBN 1-57590-039-4). Specifically, the NACE International standard requires: 1) filling the device to be treated with a treatment solution containing soda ash in an inert atmosphere to minimize oxygen contamination; 2) treating the device with the treatment solution by intense circulation for at least 2 hours; 3) analyzing the circulating treatment solution at appropriate intervals to ensure that the pH and chloride limits are maintained.

[0008] Third, the effectiveness of the treatment process can only be confirmed by testing the treatment solution containing soda ash "before treatment" and "after treatment". In other words, the operator needs to measure the pH of the solution before it flows into and passes through the vessel to be treated and compare it with the pH measurement after treatment. To obtain this comparative measurement, the operator must traverse the inside of the closed loop. Furthermore, the need for this measurement and testing also rules out even the idea of once-through applications.

[0009] Based on the above operating realities and requirements, the continuous circulation within the closed loop has existed as a long-established concept for oil refiners.

Summary of the Invention

[0010] A system for treating a stainless - steel vessel for preventing polythionic acid stress corrosion cracking, based on various aspects of the present disclosure, is configured to store a premixed K2CO3 treatment solution, and includes a storage container fluidly coupled to a first pipeline, a water supply source fluidly coupled to a second pipeline, a third pipeline fluidly coupled to each of the first pipeline, the second pipeline, and the stainless - steel vessel to be treated, and a waste vessel fluidly coupled to the stainless - steel vessel. During use of the system, the premixed K2CO3 treatment solution is sent from the storage container through the first pipeline to the third pipeline, water is sent from the water supply source through the second pipeline to the third pipeline, the premixed K2CO3 treatment solution and water are mixed in the third pipeline to create a diluted K2CO3 treatment solution, and the diluted K2CO3 treatment solution is introduced into the stainless - steel vessel through the third pipeline. In some embodiments, the first pipeline further includes an injection pump. In some embodiments, the first pipeline further includes an injection - volume control valve. In some embodiments, the first pipeline further includes an injection pump and an injection - volume control valve. In some embodiments, the second pipeline further includes an injection - volume control valve. In some embodiments, the second pipeline further includes a flow meter. In some embodiments, the second pipeline further includes an injection - volume control valve and a flow meter. In some embodiments, the storage container is configured to store a premixed K2CO3 treatment solution having a K2CO3 concentration of about 200 g to about 1120 g per liter of water, or about 300 g to about 1120 g per liter of water, or about 400 g to about 1120 g per liter of water, or about 500 g to about 1100 g per liter of water, or about 600 g to about 1080 g per liter of water, or about 700 g to about 1060 g per liter of water, or about 800 g to about 1040 g per liter of water, or about 900 g to about 1020 g per liter of water, or about 920 g to about 1000 g per liter of water, or about 940 g to about 980 g per liter of water.In some embodiments, the system is configured to prepare a dilute K2CO3 treatment solution containing 0.1 to 10 w / w% of K2CO3, or about 0.25 to about 8 w / w% of K2CO3, or about 0.5 to about 7 w / w% of K2CO3, or about 0.75 to about 6 w / w% of K2CO3, or about 1 to about 5 w / w% of K2CO3, or about 1 to about 2 w / w% of K2CO3.

[0011] Another system for treating a stainless - steel vessel for preventing polythionic acid stress corrosion cracking, based on various aspects of the present disclosure, is configured to store a premixed K₂CO₃ treatment solution, and includes a storage container fluidly coupled to a first pipeline, a water supply source fluidly coupled to a second conduit, an eductor coupled to each of the first pipeline and the second pipeline, a third pipeline fluidly coupled to each of the eductor and the stainless - steel vessel to be treated, and a waste vessel fluidly coupled to the stainless - steel vessel. During use of the system, the premixed K₂CO₃ treatment solution is sent from the storage container to the eductor via the first pipeline, water is sent from the water supply source to the eductor via the second pipeline, the premixed K₂CO₃ treatment solution and water are mixed in the eductor to create a diluted K₂CO₃ treatment solution, and the diluted K₂CO₃ treatment solution is introduced from the eductor into the stainless - steel vessel via the third pipeline. In some embodiments, the first pipeline further comprises an injection - rate control valve. In some embodiments, the second pipeline further comprises an injection - rate control valve. In some embodiments, the second pipeline further comprises a flow meter. In some embodiments, the second pipeline further comprises an injection - rate control valve and a flow meter. In some embodiments, the storage container is configured to store a premixed K₂CO₃ treatment solution having a K₂CO₃ concentration of about 200 g to about 1120 g per liter of water, or a K₂CO₃ concentration of about 300 g to about 1120 g per liter of water, or a K₂CO₃ concentration of about 400 g to about 1120 g per liter of water, or a K₂CO₃ concentration of about 500 g to about 1100 g per liter of water, or a K₂CO₃ concentration of about 600 g to about 1080 g per liter of water, or a K₂CO₃ concentration of about 700 g to about 1060 g per liter of water, or a K₂CO₃ concentration of about 800 g to about 1040 g per liter of water, or a K₂CO₃ concentration of about 900 g to about 1020 g per liter of water, or a K₂CO₃ concentration of about 920 g to about 1000 g per liter of water, or a K₂CO₃ concentration of about 940 g to about 980 g per liter of water.In some embodiments, the system is configured to prepare a diluted K2CO3 treatment solution containing 0.1 to 10 w / w% K2CO3, or about 0.25 to about 8 w / w% K2CO3, or about 0.5 to about 7 w / w% K2CO3, or about 0.75 to about 6 w / w% K2CO3, or about 1 to about 5 w / w% K2CO3, or about 1 to about 2 w / w% K2CO3.

[0012] A method for treating a stainless - steel vessel for polythionic acid stress corrosion cracking prevention according to various aspects of the present disclosure includes incorporating a stainless - steel vessel into a system according to various aspects of the present disclosure, injecting a diluted K2CO3 treatment solution into the stainless - steel vessel until the stainless - steel vessel is filled or substantially filled with the diluted K2CO3 treatment solution, holding the diluted K2CO3 treatment solution in the stainless - steel vessel for a predetermined time, and discharging the diluted K2CO3 treatment solution from the stainless - steel vessel. In some embodiments, the diluted K2CO3 treatment solution is transferred from the stainless - steel vessel to a waste vessel. In some embodiments, the predetermined time is at least 2 hours. In some embodiments, the step of holding the diluted K2CO3 treatment solution in the stainless - steel vessel for a predetermined time is performed at a temperature up to 50°C. In some embodiments, the step of injecting the diluted K2CO3 treatment solution into the stainless - steel vessel until the stainless - steel vessel is filled or substantially filled with the diluted K2CO3 treatment solution is performed under an inert atmosphere. In some embodiments, the step of holding the diluted K2CO3 treatment solution in the stainless - steel vessel for a predetermined time further includes measuring the pH of the contents in the stainless - steel vessel, and the contents include the diluted K2CO3 treatment solution.

[0013] The first embodiment of the present disclosure is a system for treating a stainless - steel vessel to prevent polythionic acid stress corrosion cracking. The system is configured to store a premixed K2CO3 treatment solution, and includes a storage container fluidly coupled to a first pipeline, a water supply source fluidly coupled to a second conduit, a third pipeline fluidly coupled to each of the first pipeline, the second pipeline, and the stainless - steel vessel to be treated, and a waste vessel fluidly coupled to the stainless - steel vessel. When the system is in use, the premixed K2CO3 treatment solution is sent from the storage container through the first pipeline to the third pipeline, water is sent from the water supply source through the second pipeline to the third pipeline, the premixed K2CO3 treatment solution and water are mixed in the third pipeline to form a diluted K2CO3 treatment solution, and the diluted K2CO3 treatment solution is introduced into the stainless - steel vessel through the third pipeline.

[0014] The second embodiment of the present disclosure is the system according to the first embodiment, wherein the first pipeline further comprises an injection pump.

[0015] The third embodiment of the present disclosure is the system according to the first or second embodiment, wherein the first pipeline further comprises an injection amount control valve.

[0016] The fourth embodiment of the present disclosure is the system based on any one of the first to third embodiments, wherein the first pipeline further comprises an injection pump and an injection amount control valve.

[0017] The fifth embodiment of the present disclosure is the system based on any one of the first to fourth embodiments, wherein the second pipeline further comprises an injection amount control valve.

[0018] The sixth embodiment of the present disclosure is the system based on any one of the first to fifth embodiments, wherein the second pipeline further comprises a flow meter.

[0019] The seventh embodiment of the present disclosure is the system based on any one of the first to sixth embodiments, wherein the second pipeline further comprises a water injection amount control valve and a flow meter.

[0020] The eighth embodiment of the present disclosure is a system based on any of the first to seventh embodiments, wherein the storage container is configured to store a premixed K2CO3 treatment solution having a K2CO3 concentration of about 200 g to about 1120 g per liter of water, or a K2CO3 concentration of about 300 g to about 1120 g per liter of water, or a K2CO3 concentration of about 400 g to about 1120 g per liter of water, or a K2CO3 concentration of about 500 g to about 1100 g per liter of water, or a K2CO3 concentration of about 600 g to about 1080 g per liter of water, or a K2CO3 concentration of about 700 g to about 1060 g per liter of water, or a K2CO3 concentration of about 800 g to about 1040 g per liter of water, or a K2CO3 concentration of about 900 g to about 1020 g per liter of water, or a K2CO3 concentration of about 920 g to about 1000 g per liter of water, or a K2CO3 concentration of about 940 g to about 980 g per liter of water.

[0021] The ninth embodiment of the present disclosure is a system based on any of the first to eighth embodiments. The system is configured to prepare a diluted K2CO3 treatment solution containing about 0.1 to about 10 w / w% of K2CO3, or about 0.25 to about 8 w / w% of K2CO3, or about 0.5 to about 7 w / w% of K2CO3, or about 0.75 to about 6 w / w% of K2CO3, or about 1 to about 5 w / w% of K2CO3, or about 1 to about 2 w / w% of K2CO3.

[0022] The tenth embodiment of the present disclosure is a system for treating a stainless - steel vessel to prevent polythionic acid stress corrosion cracking. The system is configured to store a premixed K2CO3 treatment solution, and includes a storage container fluidly coupled to a first pipeline, a water supply source fluidly coupled to a second conduit, an eductor coupled to each of the first pipeline and the second pipeline, a third pipeline fluidly coupled to each of the eductor and the stainless - steel vessel to be treated, and a waste vessel fluidly coupled to the stainless - steel vessel. During the use of the system, the premixed K2CO3 treatment solution is sent from the storage container to the eductor through the first pipeline, water is sent from the water supply source to the eductor through the second pipeline, the premixed K2CO3 treatment solution and water are mixed in the eductor to form a diluted K2CO3 treatment solution, and the diluted K2CO3 treatment solution is introduced from the eductor into the stainless - steel vessel through the third pipeline.

[0023] The eleventh embodiment of the present disclosure is a system based on the tenth embodiment, wherein the first pipeline further comprises an injection amount control valve.

[0024] The twelfth embodiment of the present disclosure is a system based on the tenth or eleventh embodiment, wherein the first pipeline further comprises an injection amount control valve.

[0025] The thirteenth embodiment of the present disclosure is a system based on any one of the tenth to twelfth embodiments, wherein the second pipeline further comprises a flow meter.

[0026] The fourteenth embodiment of the present disclosure is the system described based on any one of the tenth to thirteenth embodiments, wherein the second pipeline further comprises a water injection amount control valve and a flow meter.

[0027] The 15th embodiment of the present disclosure is a system based on any one of the 10th to 14th embodiments. The storage container is configured to store a premixed K2CO3 treatment solution having a K2CO3 concentration of about 200 g to about 1120 g per liter of water, or a K2CO3 concentration of about 300 g to about 1120 g per liter of water, or a K2CO3 concentration of about 400 g to about 1120 g per liter of water, or a K2CO3 concentration of about 500 g to about 1100 g per liter of water, or a K2CO3 concentration of about 600 g to about 1080 g per liter of water, or a K2CO3 concentration of about 700 g to about 1060 g per liter of water, or a K2CO3 concentration of about 800 g to about 1040 g per liter of water, or a K2CO3 concentration of about 900 g to about 1020 g per liter of water, or a K2CO3 concentration of about 920 g to about 1000 g per liter of water, or a K2CO3 concentration of about 940 g to about 980 g per liter of water.

[0028] The 16th embodiment of the present disclosure is a system based on any one of the 10th to 15th embodiments. The system is configured to prepare a diluted K2CO3 treatment solution containing about 0.1 to about 10 w / w% of K2CO3, or about 0.25 to about 8 w / w% of K2CO3, or about 0.5 to about 7 w / w% of K2CO3, or about 0.75 to about 6 w / w% of K2CO3, or about 1 to about 5 w / w% of K2CO3, or about 1 to about 2 w / w% of K2CO3.

[0029] The 17th embodiment of the present disclosure is a method for treating a stainless steel vessel to prevent polythionic acid stress corrosion cracking. The method includes: a) incorporating a stainless steel vessel into a system based on any one of the 1st to 16th embodiments; b) injecting a diluted K2CO3 treatment solution into the stainless steel vessel until the stainless steel vessel is filled or substantially filled with the diluted K2CO3 treatment solution; c) holding the diluted K2CO3 treatment solution in the stainless steel vessel for a predetermined time; and d) discharging the diluted K2CO3 treatment solution from the stainless steel vessel.

[0030] The 18th embodiment of the present disclosure is a method based on the 17th embodiment, wherein the diluted K2CO3 treatment solution is transferred from a stainless-steel vessel to a waste vessel.

[0031] The 19th embodiment of the present disclosure is a method based on the 17th or 18th embodiment, wherein the predetermined time is at least 2 hours.

[0032] The 20th embodiment of the present disclosure is a method based on any one of the 17th to 19th embodiments, wherein step c) is carried out at a temperature up to 50°C.

[0033] The 21st embodiment of the present disclosure is a method based on any one of the 17th to 20th embodiments, wherein step b) is carried out in an inert atmosphere.

[0034] The 22nd embodiment of the present disclosure is a method based on any one of the 17th to 21st embodiments, wherein step c) further includes a step of measuring the pH of the contents in the stainless-steel vessel, and the contents contain the diluted K2CO3 treatment solution.

Brief Description of the Drawings

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[0040] The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the subject matter of the present disclosure, its applications, or uses.

[0041] As used throughout, ranges are used as shorthand for any and all values within the range. Any value within the range can be selected as the end point of the range. Unless otherwise specified, all percentages and amounts recited herein are to be understood as referring to weight percentages.

[0042] For the purposes of this specification and the appended claims, unless otherwise indicated, all numbers expressing quantities, percentages, or ratios used in this specification and the claims, and other numerical values, are to be understood as being modified in all instances by the term "about." The use of the term "about" applies to all numerical values, whether or not explicitly indicated. This term generally refers to a range of values that a person of ordinary skill in the art would consider a reasonable deviation from the recited value (i.e., having an equivalent function or result). For example, the term can be interpreted to include a deviation of ±10%, ±5%, 1%, ±0.5%, or ±0.1% of the given numerical value, provided such deviation does not change the ultimate function or result of the value. Accordingly, unless otherwise indicated, the numerical parameters set forth in this specification and the appended claims are approximate values that can vary depending upon the desired properties sought to be obtained by the present invention.

[0043] It should be noted that, as used in this specification and the appended claims, the singular form "one" includes plural referents unless explicitly and specifically limited to one referent. In this specification, the terms "comprising" and its grammatical variations are intended to be non-limiting, and the listing of items in a list does not exclude other similar items that may be substituted for or added to the listed items. For example, as used in this specification and the claims, the term "comprises" (and its word forms, derivatives, or variations such as "comprising"), "includes" (and its word forms, derivatives, or variations such as "including"), and "has" (and its word forms, derivatives, or variations such as "having") are non-exclusive (i.e., open-ended) and do not exclude additional elements or steps. Thus, these terms are intended to cover not only the recited elements or steps but also other elements or steps not expressly recited. Further, in this specification, the use of the term "one" when used in combination with an element may mean "one" but is also consistent with the meanings of "one or more", "at least one", and "one or more". Thus, an element starting with "one" does not exclude the presence of additional same elements unless further restricted.

[0044] In this specification and the claims, the term "coupled" means the connection or joining of two objects. The coupling can be permanent or reversible. The coupling can be direct or indirect. Indirect coupling includes connecting or joining two objects through one or more intermediate objects. The term "substantially" in this specification means that it essentially conforms to the particular dimension, shape, or other word that "substantially" modifies, and its configuration need not be exact. For example, "substantially cylindrical" means that an object resembles a cylinder but may have one or more deviations from a true cylinder.

[0045] Based on various aspects of the present disclosure, methods for protecting austenitic stainless steel or austenitic alloy petroleum refining apparatuses from polythionic acid stress corrosion cracking during shutdown operations are described herein. The methods according to various aspects of the present disclosure enable protecting the petroleum refining apparatuses from stress corrosion cracking without the need for applying a treatment solution by a closed-loop circulation approach.

[0046] FIG. 1 is a schematic diagram showing a prior art system 100 for treating a stainless steel vessel with a soda ash treatment solution to protect it from stress corrosion cracking, where the soda ash treatment solution is manufactured on-site. In practice, the soda ash treatment solution cannot be made off-site due to the solubility limit of soda ash in water (about 212.5 grams / L at 20° C., or a 17.5 wt % saturated soda ash solution at room temperature), the need for thousands of gallons of treatment solution to treat the stainless steel vessel, and the continuous need to add fresh soda ash to the treatment solution during the treatment process. System 100 includes a treatment solution storage vessel 110 and a vessel 170, which are connected to each other in a closed loop. Vessel 170 includes an inner surface that may deteriorate over time due to polythionic acid stress corrosion cracking. Water is supplied from a source 120 to vessel 110 via a pipeline 130. Soda ash is supplied from a soda ash source 140 to vessel 110. The soda ash source 140 is typically a means for storing soda ash, such as a hopper, bag, drum, etc. The soda ash is supplied from the soda ash source 140 to vessel 110 by an automated method under the operator's control or manually by the operator. The soda ash and water are mixed in vessel 110 such that the resulting soda ash treatment solution contains 1 - 5 wt % soda ash and has a pH greater than 9. To assist in the preparation of the soda ash treatment solution in vessel 110 and to promote the continuous dissolution of soda ash in water, vessel 110 may include additional components, such as internal or external heating elements and / or means for stirring or agitating the contents of vessel 110.

[0047] Once made, the soda ash treatment solution is sent from the vessel 110 to the bottom of the contaminated vessel 170 via the pump 150 and the pipelines 160, 180. While the contaminated vessel 170 is maintained under an inert atmosphere, the soda ash treatment solution is injected into the vessel 170 to fill the vessel 170. The injection of the treatment solution into the contaminated vessel 170 is continued such that the treatment solution exits from the upper part of the vessel 170 through the pipeline 190 and returns to the vessel 110. In this closed-loop mechanism, the treatment solution circulates actively through the vessel 170 for at least 2 hours. During circulation, the treatment solution is sometimes analyzed to confirm that the pH of the solution and the chloride limit value are maintained. Usually, the treatment solution is analyzed before being re-introduced into the vessel 110 and before being sent from the vessel 110 to the contaminated vessel 170. In most cases, it is necessary to add additional soda ash from the soda ash source 140 to the treatment solution to maintain the required properties of the treatment solution.

[0048] Unlike the use of soda ash in the prior art, the present disclosure is directed to the use of K2CO3. In various aspects of the present disclosure, the K2CO3 treatment solution is provided as a premixed solution, eliminating the need to prepare the treatment solution in a vessel on site. Unlike soda ash, which has poor solubility in water (212.5 g / L) under ambient conditions, K2CO3 has a solubility (1120 g / L at 20 °C) that allows for the preparation of very high-concentration premixed solutions (up to approximately 52.8 wt% K2CO3 at 20 °C). In some embodiments, the premixed K2CO3 treatment solution is a saturated solution. In some embodiments, the premixed K2CO3 treatment solution contains from about 100 g to about 1120 g of K2CO3 per liter of water. In other embodiments, the premixed K2CO3 treatment solution contains from about 200 g to about 1120 g of K2CO3 per liter of water, or from about 300 g to about 1120 g of K2CO3 per liter of water, or from about 400 g to about 1120 g of K2CO3 per liter of water, or from about 500 g to about 1100 g of K2CO3 per liter of water, or from about 600 g to about 1080 g of K2CO3 per liter of water, or from about 700 g to about 1060 g of K2CO3 per liter of water, or from about 800 g to about 1040 g of K2CO3 per liter of water, or from about 900 g to about 1020 g of K2CO3 per liter of water, or from about 920 g to about 1000 g of K2CO3 per liter of water, or from about 940 g to about 980 g of K2CO3 per liter of water. Preferably, the premixed K2CO3 treatment solution contains about 49 wt% K2CO3.

[0049] In some embodiments, the diluted form of the high-concentration premixed K2CO3 treatment solution according to various aspects of the present disclosure may be further mixed with one or more corrosion inhibitors to reduce the possibility of chloride stress corrosion cracking. When one or more corrosion inhibitors are used, the diluted form of the high-concentration premixed K2CO3 treatment solution used as described in the following method contains, as described herein, when the treatment solution is diluted, about 0.1 to about 1 wt%, preferably about 0.2 to about 0.8 wt%, more preferably about 0.25 to about 0.6 wt%, more preferably about 0.3 to about 0.5 wt%, more preferably about 0.4 wt% of the corrosion inhibitor. In some embodiments, the one or more corrosion inhibitors may include sodium nitrate.

[0050] Figure 2 is a schematic diagram showing a system 200 based on various aspects for treating and protecting a vessel against stress corrosion cracking, where a K2CO3 treatment solution is provided as a premixed solution. In some embodiments, the premixed K2CO3 treatment solution is a saturated solution. In some embodiments, the premixed K2CO3 treatment solution contains from about 100 g to about 1120 g of K2CO3 per liter of water. In other embodiments, the premixed K2CO3 treatment solution contains from about 200 g to about 1120 g of K2CO3 per liter of water, or from about 300 g to about 1120 g of K2CO3 per liter of water, or from about 400 g to about 1120 g of K2CO3 concentration per liter of water, or from about 500 g to about 1100 g of K2CO3 per liter of water, or from about 600 g to about 1080 g of K2CO3 per liter of water, or from about 700 g to about 1060 g of K2CO3 per liter of water, or from about 800 g to about 1040 g of K2CO3 per liter of water, or from about 900 g to about 1020 g of K2CO3 per liter of water, or from about 920 g to about 1000 g of K2CO3 per liter of water, or from about 940 g to about 980 g of K2CO3 per liter of water. Preferably, the premixed K2CO3 solution contains about 49 wt% of K2CO3. System 200 generally includes a premixed K2CO3 treatment solution storage vessel 210, a water supply source 220, a vessel 230, and a waste vessel 240. Water is sent from the water supply source 220 through conduits 255, 265 at a controlled flow rate, which is regulated by a water flow control valve 270. The flow rate of water sent through conduit 255 can be monitored using a flow meter 280 coupled to conduit 255. Vessel 210 is coupled to an injection pump 250 via a conduit 215. The type of pump used as injection pump 250 is not limited to a particular type of pump. The premixed K2CO3 treatment solution is pumped through conduit 225 to an injection amount control valve 260. The injection amount control valve 260 may act to regulate the amount of the high-concentration K2CO3 treatment solution sent to conduit 265 via conduit 235. When water and the high-concentration K2CO3 treatment solution are mixed within conduit 265 starting from the junction of conduit 235 and conduit 255, a diluted K2CO3 treatment solution is produced.The diluted K2CO3 treatment solution is sent through line 265 to the inlet (not shown) of vessel 230. Next, the diluted K2CO3 treatment solution is pumped into vessel 230, and the vessel is filled with the diluted K2CO3 treatment solution and immersed for a predetermined time. After the predetermined time, the used diluted K2CO3 treatment solution is sent through line 275 to waste vessel 240. Line 275 connects the outlet (not shown) of vessel 230 and the inlet (not shown) of waste vessel 240. In some embodiments, the outlet of vessel 230 is located at the lower part or bottom of vessel 230, and the outlet is located at the upper part or top of vessel 230. In some embodiments, the outlet of vessel 230 is located at the upper part or top of vessel 230, and the outlet is located at the lower part or bottom of vessel 230.

[0051] In system 200, one or more corrosion inhibitors may be included in the diluted K2CO3 treatment solution such that the diluted K2CO3 treatment solution contains about 0.1 to about 1 wt%, preferably about 0.2 to about 0.8 wt%, more preferably about 0.25 to about 0.6 wt%, more preferably about 0.3 to about 0.5 wt%, more preferably about 0.4 wt% of the corrosion inhibitor. In some embodiments, one or more corrosion inhibitors may be added to the water at water source 220. In some embodiments, one or more corrosion inhibitors may be added to the diluted K2CO3 treatment solution in line 265. In some embodiments, one or more corrosion inhibitors may be added to the diluted K2CO3 treatment solution in vessel 230.

[0052] FIG. 3 is a schematic diagram showing another system 300 based on various aspects of the present disclosure for treating a vessel to protect it from stress corrosion cracking, wherein a K2CO3 treatment solution is provided as a premixed solution. In some embodiments, the premixed K2CO3 treatment solution is a saturated solution. In some embodiments, the premixed K2CO3 treatment solution contains from about 100 g to about 1120 g of K2CO3 per liter of water. In other embodiments, the premixed K2CO3 treatment solution contains from about 200 g to about 1120 g of K2CO3 per liter of water, or from about 300 g to about 1120 g of K2CO3 per liter of water, or from about 400 g to about 1120 g of K2CO3 per liter of water, or from about 500 g to about 1100 g of K2CO3 per liter of water, or from about 600 g to about 1080 g of K2CO3 per liter of water, or from about 700 g to about 1060 g of K2CO3 per liter of water, or from about 800 g to about 1040 g of K2CO3 per liter of water, or from about 900 g to about 1020 g of K2CO3 per liter of water, or from about 920 g to about 1000 g of K2CO3 per liter of water, or from about 940 g to about 980 g of K2CO3 per liter of water. Preferably, the premixed K2CO3 solution contains about 49 wt% K2CO3. System 300 generally includes a premixed K2CO3 treatment solution storage vessel 310, a water source 320, a vessel 330, and a waste vessel 340. Water is sent from the water source 320 through conduits 335, 345 to an eductor 380 at a flow rate controlled by a water volume control valve 360. The flow rate of water sent through conduit 345 can be monitored using a flow meter 370 coupled to conduit 345. Vessel 310 is connected to an injection amount control valve 350 via conduit 315. The high-concentration K2CO3 treatment solution is sent to the eductor 380 via conduit 325. The water and the premixed K2CO3 treatment solution are mixed at the eductor 380 to produce a diluted K2CO3 treatment solution. The diluted K2CO3 treatment solution is sent via conduit 365 to an inlet (not shown) of the vessel 330. The diluted K2CO3 treatment solution is pumped into the vessel 330, and the vessel is filled with the diluted K2CO3 treatment solution and immersed for a predetermined time.After a predetermined time, the diluted K2CO3 treatment solution is sent to the waste vessel 340 via the pipeline 375. The pipeline 375 is connected to the outlet (not shown) of the vessel 330 and the inlet (not shown) of the waste vessel 340. In some embodiments, the outlet of the vessel 330 is located at the lower part or bottom of the vessel 330, and the outlet is located at the upper part or top of the vessel 330. In some embodiments, the outlet of the vessel 330 is located at the upper part or top of the vessel 330, and the outlet is located at the lower part or bottom of the vessel 330.

[0053] In the system 300, one or more corrosion inhibitors may be included in the K2CO3 treatment solution diluted such that the diluted K2CO3 treatment solution contains about 0.1 to about 1 wt%, preferably about 0.2 to about 0.8 wt%, more preferably about 0.25 to about 0.6 wt%, more preferably about 0.3 to about 0.5 wt%, and more preferably about 0.4 wt% of the corrosion inhibitor. In some embodiments, one or more corrosion inhibitors can be added to water at the water supply source 320. In some embodiments, one or more corrosion inhibitors may be added to the diluted K2CO3 treatment solution in the pipeline 365. In some embodiments, one or more corrosion inhibitors may be added to the diluted K2CO3 treatment solution in the vessel 330.

[0054] An exemplary method 400 for treating a stainless steel vessel with a K2CO3 treatment solution to protect the vessel from stress corrosion cracking during a shutdown operation is schematically shown in FIG. 4 using the system 200. The method 400 may proceed according to the following method steps. As will be understood by those skilled in the art, one or more steps may be omitted from the method 400, and / or one or more steps may be added, and one or more elements of the system 200 may be added or omitted, without departing from the scope of the method, in the normal process of treating a stainless steel vessel with a K2CO3 treatment solution to protect the vessel from stress corrosion cracking. In some embodiments, the method 400 begins with step 410.

[0055] In step 410, a stainless steel vessel 230 is incorporated into system 200 to process the vessel 230 and protect it from stress corrosion cracking. The vessel is incorporated into system 200 by coupling the fluid inlet of the vessel 230 to line 265 to receive the K2CO3 treatment solution, and coupling the fluid outlet of the vessel 230 to line 275 to send the used K2CO3 treatment solution from the vessel 230 to the waste vessel 240. When step 410 is completed, method 400 proceeds to step 420.

[0056] In step 420, a K₂CO₃ treatment solution storage vessel 210 containing a premixed K₂CO₃ solution is coupled to a pipeline 215, and a water supply source 220 is coupled to a pipeline 245. The type of the container 210 used for storing the premixed K₂CO₃ treatment solution is not particularly limited. Any container capable of storing a basic (i.e., pH > 7) medium for a long period is suitable. In some embodiments, the premixed K₂CO₃ treatment solution in the storage vessel 210 is a saturated solution. In some embodiments, the premixed K₂CO₃ treatment solution contains about 100 g to about 1120 g of K₂CO₃ per liter of water. In other embodiments, the premixed K₂CO₃ treatment solution contains about 200 g to about 1120 g of K₂CO₃ per liter of water, or about 300 g to about 1120 g of K₂CO₃ per liter of water, or about 400 g to about 1120 g of K₂CO₃ concentration per liter of water, or about 500 g to about 1100 g of K₂CO₃ per liter of water, or about 600 g to about 1080 g of K₂CO₃ per liter of water, or about 700 g to about 1060 g of K₂CO₃ per liter of water, or about 800 g to about 1040 g of K₂CO₃ per liter of water, or about 900 g to about 1020 g of K₂CO₃ per liter of water, or about 920 g to about 1000 g of K₂CO₃ per liter of water, or about 940 g to about 980 g of K₂CO₃ per liter of water. Preferably, the premixed K₂CO₃ solution contains about 49 wt% of K₂CO₃. In order to minimize the amount of the premixed K₂CO₃ treatment solution required for any particular treatment / protection process and the amount of the raw product sent to the location of the vessel, and to reduce the possible number of times the storage vessel 210 needs to be replaced during a single treatment / protection process, it is preferable to use a premixed K₂CO₃ treatment solution with as high a concentration as possible considering environmental and / or treatment considerations, such as the ambient air temperature or the degree or type of oil contamination in the vessel 230.

[0057] In some embodiments, step 420 may be performed before step 410. In some embodiments, step 410 and step 420 are performed simultaneously. When step 420 is completed, method 400 proceeds to step 430.

[0058] In step 430, a controlled amount of premixed K2CO3 treatment solution is sent from storage vessel 210 through pipelines 215, 225, 235, pump 250 and injection amount control valve 260 to pipeline 265. Also in step 430, a controlled amount of water monitored by flow meter 280 is sent from water supply source 220 through pipelines 245, 255 and injection amount control valve 270 to pipeline 265. The premixed K2CO3 treatment solution and water are mixed inline in pipeline 265, resulting in a diluted K2CO3 treatment solution. The premixed K2CO3 treatment solution and water should be sent to pipeline 265 in relative amounts such that the resulting diluted K2CO3 treatment solution contains about 0.1 to about 10 w / w% K2CO3, preferably about 0.25 to about 8 w / w% K2CO3, more preferably about 0.5 to about 7 w / w% K2CO3, still more preferably about 0.75 to about 6 w / w% K2CO3, and even more preferably about 1 to about 5 w / w% K2CO3. In some embodiments, a diluted K2CO3 treatment solution having about 1 to about 2 w / w% K2CO3 results. When step 430 is completed, method 400 proceeds to step 440.

[0059] In step 440, the diluted K2CO3 treatment solution is injected into stainless steel vessel 230 through the fluid inlet of vessel 230 to which pipeline 265 is connected. When the diluted K2CO3 treatment solution is injected into stainless steel vessel 230, vessel 230 is filled or substantially filled with the diluted K2CO3 treatment solution. Vessel 230 is filled or substantially filled under an inert atmosphere to minimize oxygen contamination. When step 440 is completed, method 400 proceeds to step 450.

[0060] In process 450, the diluted K2CO3 treatment solution is maintained in a stainless - steel vessel 230 for a predetermined time so that petroleum contaminants penetrate into the treatment solution. In some embodiments, this "soak" process is carried out at room temperature. In some embodiments, this soak process is carried out at an elevated temperature up to about 50°C. Usually, the predetermined time is at least 2 hours. During process 450, the pH of the contents of the stainless - steel vessel is measured. The pH measurement may be carried out continuously or step - wise over time. Optionally, other chemical analyses such as petroleum contaminant and / or chloride content may also be carried out during process 450. When process 450 is completed, method 400 proceeds to process 460.

[0061] In process 460, the used diluted K2CO3 treatment solution exits the vessel 230 via the fluid outlet and is discarded into a waste vessel 240. After the discard is complete, a residual film of K2CO3 should remain on the inner surface of the vessel 230 throughout a stop period to ensure continued protection from stress corrosion cracking. When process 460 is completed, method 400 proceeds to process 470.

[0062] In process 470, depending on the pH results obtained in process 450 and optionally any chemical analyses, processes 410 - 460 may be repeated one or more times until it is confirmed that the vessel 230 no longer contains petroleum contaminants. When process 470 ends, method 400 ends.

[0063] In some embodiments, one or more corrosion inhibitors as described herein may be added in any one of processes 430 - 450.

[0064] System 300 is used to schematically show an exemplary method 500 for treating a stainless - steel vessel with a K2CO3 treatment solution to protect the vessel from stress - corrosion cracking in FIG. 5. Method 500 may proceed according to the steps of the following method. As can be understood by those skilled in the art, one or more steps may be omitted from method 500, and / or one or more steps may be added, and one or more elements of system 300 may be added or omitted, without departing from the scope of the method, in the normal process of treating a stainless - steel vessel with a K2CO3 treatment solution to protect the vessel from stress - corrosion cracking. In some embodiments, method 500 begins at step 510.

[0065] In step 510, a stainless - steel vessel 330 is incorporated into system 300 to treat the vessel 330 to protect it from stress - corrosion cracking. The vessel 330 is incorporated into system 300 by coupling the fluid inlet of vessel 300 to line 365 to receive the K2CO3 treatment solution, and coupling the fluid outlet of vessel 330 to line 375 to send the used K2CO3 treatment solution from vessel 330 to waste vessel 340.

[0066] In Project 520, a K₂CO₃ treatment solution storage vessel 310 containing a premixed K₂CO₃ solution is coupled to a pipeline 315, and a water supply source 320 is coupled to a pipeline 335. The type of container used to store the high-concentration premixed K₂CO₃ treatment solution is not particularly limited. Any container capable of storing a basic (i.e., pH > 7) medium is suitable. In some embodiments, the premixed K₂CO₃ treatment solution in the storage vessel 310 is a saturated solution. In some embodiments, the premixed K₂CO₃ treatment solution contains from about 100 g to about 1120 g of K₂CO₃ per liter of water. In other embodiments, the premixed K₂CO₃ treatment solution contains from about 200 g to about 1120 g of K₂CO₃ per liter of water, or from about 300 g to about 1120 g of K₂CO₃ per liter of water, or from about 400 g to about 1120 g of K₂CO₃ per liter of water, or from about 500 g to about 1100 g of K₂CO₃ per liter of water, or from about 600 g to about 1080 g of K₂CO₃ per liter of water, or from about 700 g to about 1060 g of K₂CO₃ per liter of water, or from about 800 g to about 1040 g of K₂CO₃ per liter of water, or from about 900 g to about 1020 g of K₂CO₃ per liter of water, or from about 920 g to about 1000 g of K₂CO₃ per liter of water, or from about 940 g to about 980 g of K₂CO₃ per liter of water. Preferably, the premixed K₂CO₃ solution contains about 49 wt% K₂CO₃. In order to minimize the amount of K₂CO₃ solution required for a specific treatment and protection process and the amount of raw materials sent to the petroleum-contaminated vessel side, and to reduce the number of times the storage container 310 may need to be replaced during one treatment and protection process, it is preferable to use a K₂CO₃ treatment solution having as high a concentration as practicable, taking into account environmental and / or treatment considerations such as the ambient air temperature or the range or type within the vessel 330.

[0067] In some embodiments, Project 520 may be performed before Project 510. In some embodiments, Project 510 and Project 520 are performed simultaneously. When Project 520 is completed, Method 500 proceeds to Project 530.

[0068] In step 530, a controlled amount of premixed high-concentration K2CO3 treatment solution is sent from storage vessel 310 through pipelines 315, 325 and injection rate control valve 350 to eductor 380. Also in step 530, a controlled amount of water monitored by flow meter 370 is sent from water source 320 through pipelines 335, 345 and injection rate control valve 360 to eductor 380. The premixed K2CO3 treatment solution and water are mixed in eductor 380 to form a diluted K2CO3 treatment solution, which exits eductor 380 through pipeline 365. The premixed K2CO3 treatment solution and water should be sent to eductor 380 in relative amounts such that the resulting diluted K2CO3 treatment solution contains about 0.1 to about 10 w / w% K2CO3, preferably about 0.25 to about 8 w / w% K2CO3, more preferably about 0.5 to about 7 w / w% K2CO3, more preferably about 0.75 to about 6 w / w% K2CO3, and more preferably about 1 to about 5 w / w% K2CO3. In some embodiments, a diluted K2CO3 treatment solution having about 1 to about 2 w / w% K2CO3 results. When step 530 is complete, method 500 proceeds to step 540.

[0069] In step 540, the diluted K2CO3 treatment solution is injected into stainless steel vessel 330 through the fluid inlet of vessel 330 to which pipeline 365 is connected. As the diluted K2CO3 treatment solution is injected into stainless steel vessel 330, vessel 330 is filled or substantially filled with the diluted K2CO3 treatment solution. Vessel 330 is filled or substantially filled under an inert atmosphere to minimize oxygen contamination. When step 540 is complete, method 500 proceeds to step 550.

[0070] In process 550, the diluted K2CO3 treatment solution is maintained within the stainless - steel vessel 330 for a predetermined time to allow the penetration of petroleum contaminants into the treatment solution. In some embodiments, this "immersion" process is carried out at room temperature. In some embodiments, this immersion process is carried out at elevated temperatures up to about 50°C. Typically, the predetermined time is at least 2 hours. During process 550, the pH of the contents of the stainless - steel vessel is measured. The pH measurement may be carried out continuously or step - wise over time. Optionally, other chemical analyses such as petroleum contaminant and / or chloride content may also be carried out during process 550. When process 550 is complete, method 500 proceeds to process 560.

[0071] In process 560, the used diluted K2CO3 treatment solution exits the vessel 330 via the fluid outlet and is discarded into the waste vessel 340. After the discard is complete, a residual film of K2CO3 should remain on the inner surface of the vessel throughout a stand - down period to ensure continued protection from stress - corrosion cracking. When process 560 is complete, method 500 proceeds to process 570.

[0072] In process 570, depending on the results of the pH analysis and optionally the chemical analysis performed in process 550, processes 510 - 560 can be repeated one or more times. When process 580 is complete, method 500 ends.

[0073] In some embodiments, one or more corrosion inhibitors as described herein may be added in any one of processes 530 - 550.

[0074] Methods in accordance with various aspects of the present disclosure exhibit numerous advantages over prior art processes for protecting a purification apparatus made of austenitic stainless steel or austenitic alloy from polythionic acid stress corrosion cracking during a shutdown operation. First, the use of soda ash requires on-site addition and mixing with water, so operators need to use personal protective equipment to avoid dust formation and inhalation of that dust. Also, soda ash dust is known to irritate the eyes. The use of the premixed K2CO3 solution according to the present disclosure eliminates the problems associated with the use of soda ash powder. When preparing a soda ash solution on-site, the operator has to spend a significant amount of time and effort accurately adding an adequate amount of soda ash to a water tank to prepare a 1 - 5 wt% soda ash solution that needs to have a pH of 9 or greater. When using the premixed K2CO3 solution and systems according to the present disclosure, such as systems 200 and 300, in-line mixing of water and the premixed K2CO3 solution facilitates the easy preparation of a diluted premixed K2CO3 solution prior to placement within a stainless steel vessel. Also, when treating a stainless steel vessel using a soda ash solution in a closed-loop circulation process, the operator has to periodically measure the pH of the soda ash solution exiting the stainless steel vessel to ensure that it is greater than 9, and if the pH is 9 or less, new soda ash needs to be added to the solution prior to recirculation back into the vessel. On the other hand, when using the premixed K2CO3 solution and systems according to the present disclosure, such as systems 200 and 300, the pH of the K2CO3 solution can be easily measured within the vessel to determine whether a further immersion round with a new diluted K2CO3 solution is needed.

[0075] Although the invention has been described in detail with its objects, features, and advantages, other embodiments are also encompassed by the invention. All documents cited herein are incorporated by reference in their entirety. Finally, those skilled in the art should understand that the disclosed concepts and specific embodiments can be readily used as a basis for designing or modifying other structures for carrying out the same object of the invention without departing from the scope of the invention as defined by the appended claims.

Claims

1. A system for treating a stainless steel vessel to prevent polythionic acid stress corrosion cracking, comprising: 200 g to 1120 g of K per liter of water ２ CO ３ -containing premixed K ２ CO ３ stores a treatment solution, a storage container fluidly coupled to a first conduit, A water supply source fluidly coupled to a second pipeline; A third pipeline fluidly coupled to each of the first pipeline and the second pipeline and connectable to the stainless steel vessel to be treated; A waste vessel fluidly connectable to the stainless steel vessel to be treated; And comprising. When the system is used with a stainless steel vessel, premixed K ２ CO ３ The treatment solution is sent from the storage container to a third pipeline via a first pipeline, and water is sent from the water supply source to the third pipeline via a second pipeline. Premixed K ２ CO ３ The treatment solution and water are mixed in the third pipeline to produce a diluted K ２ CO ３ containing 0.1 to 10 w / w% of K ２ CO ３ treatment solution, and the diluted K ２ CO ３ treatment solution is put into the stainless steel vessel via the third pipeline. System.

2. The system according to claim 1, wherein the first pipeline further comprises an injection pump.

3. The system according to claim 1, wherein the first pipeline further comprises an injection amount control valve.

4. The system according to claim 1, wherein the second pipeline further comprises an injection amount control valve.

5. The system according to claim 1, wherein the second pipeline further comprises a flow meter.

6. Pre-mixed K ２ CO ３ The treatment solution has 800 g to 1040 g of K ２ CO ３ per liter of water and is the system according to any one of claims 1 to 5.

7. Diluted K ２ CO ３ The processing solution contains 1 to 5 w / w% of K ２ CO ３ The system according to any one of claims 1 to 5, which contains

8. A system for treating a stainless steel vessel to prevent polythionic acid stress corrosion cracking, comprising: 200 g to 1120 g of K per liter of water ２ CO ３ with a concentration of premixed K ２ CO ３ stores a treatment solution, a storage container fluidly coupled to a first conduit, and A water supply source fluidly coupled to a second pipeline; An eductor coupled to each of the first pipeline and the second pipeline; A third pipeline fluidly coupled to the eductor and connectable to the stainless steel vessel to be treated; A waste vessel fluidly connectable to the stainless steel vessel to be treated; And comprising. When the system is used with a stainless steel vessel, premixed K ２ CO ３ The treatment solution is sent from the storage container to the eductor via the first pipeline, and water is sent from the water supply source to the eductor via the second pipeline. Premixed K ２ CO ３ The treatment solution and water are mixed in the eductor to form a diluted K ２ CO ３ treatment solution containing 0.1 to 10 w / w% of K ２ CO ３ The treatment solution is made, and the diluted K ２ CO ３ treatment solution is put into the stainless steel vessel from the eductor via the third pipeline. System

9. The system according to claim 8, wherein the first pipeline further comprises an injection amount control valve.

10. The system according to claim 8, wherein the second pipeline further comprises an injection amount control valve.

11. The system according to claim 8, wherein the second pipeline further comprises a flow meter.

12. Pre-mixed K ２ CO ３ The treatment solution has 800 g to 1040 g of K ２ CO ３ per liter of water and is the system according to any one of claims 8 to 11.

13. Diluted K ２ CO ３ The treatment solution contains 1 to 5 w / w% of K ２ CO ３ The system according to any one of claims 8 to 11, comprising

14. A method for treating a stainless steel vessel to prevent polythionic acid stress corrosion cracking, comprising: a) Incorporating a stainless steel vessel into the system according to any one of claims 1 to 5; b) until the stainless steel vessel is filled or substantially filled with the diluted K ２ CO ３ treatment solution, injecting the diluted K ２ CO ３ treatment solution into the stainless steel vessel c) A step of holding a diluted K ２ CO ３ treatment solution in the stainless steel vessel for a predetermined time; d) Dilution K ２ CO ３ The step of discharging the treatment solution from the stainless steel vessel, And including.

15. Diluted K ２ CO ３ The processing solution is transferred from the stainless steel vessel to the waste vessel, the method according to claim 14.

16. The method according to claim 14, wherein step c) is performed at a temperature up to 50 °C and / or the predetermined time is at least 2 hours.

17. The method according to claim 14, wherein step b) is carried out in an inert atmosphere.

18. Step c) further includes a step of measuring the pH of the contents in the stainless steel vessel, and the contents are diluted K ２ CO ３ The method according to claim 14, comprising a treatment solution.

19. A method for treating a stainless steel vessel to prevent polythionic acid stress corrosion cracking, comprising: a) Incorporating a stainless steel vessel into the system according to any one of claims 8 to 11; b) until the stainless steel vessel is filled with, or substantially filled with, diluted K ２ CO ３ treatment solution, injecting the diluted K ２ CO ３ treatment solution into the stainless steel vessel c) Dilution K ２ CO ３ a step of holding the treatment solution in the stainless steel vessel for a predetermined time; d) Dilution K ２ CO ３ a step of discharging the treatment solution from the stainless steel vessel And including.

20. Diluted K ２ CO ３ The treatment solution is transferred from the stainless steel vessel to the waste vessel, the method according to claim 19.

21. The method according to claim 19, wherein step c) is carried out at a temperature up to 50°C and / or the predetermined time is at least 2 hours.

22. The method according to claim 19, wherein step b) is carried out under an inert atmosphere.

23. Step c) further includes a step of measuring the pH of the contents in the stainless steel vessel, and the contents are diluted K ２ CO ３ The method according to claim 19, comprising a treatment solution.

24. Diluted K ２ CO ３ The system according to any one of claims 1 to 5, wherein the treatment solution further contains a corrosion inhibitor.

25. Diluted K ２ CO ３ The system according to any one of claims 8 to 11, wherein the treatment solution further comprises a corrosion inhibitor.

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