Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2003-01-23
2003-11-25
Griffin, Walter D. (Department: 1764)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C422S007000, C208S047000, C585S950000, C148S240000, C148S277000, C423S544000, C423S567100
Reexamination Certificate
active
06652660
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to a method of treating materials which contain sulfur. The invention further relates to a method of treating compounds which contain sulfur in a reactive form to produce different compounds which do not contain sulfur in a reactive form. The invention also relates to a method of treating reactive compounds which contain sulfur in a reactive form to render such compounds inactive. The invention particularly relates to a method of treating sulfur containing compounds which do cause stress corrosion cracking to produce different sulfur containing compounds which do not cause stress corrosion cracking. The invention also particularly relates to a method of treating sulfur containing compounds to prevent spontaneous combustion of such compounds. The invention more particularly relates to a method of preventing stress corrosion cracking of certain high carbon content stainless steel and to a method of preventing spontaneous ignition of metal sulfides.
2. Description of the Prior Art and Problems Solved
For a variety of reasons, including, but not limited to, economic, environmental, mechanical and chemical, materials, such as crude oil, which are contaminated with compounds which contain sulfur in a reactive form, such as sulfides and mercaptans, are not useful, or, at least, are not desirable, as a fuel or as an industrial raw material. Accordingly, materials which do contain compounds having sulfur in a reactive form dispersed or dissolved therein have been treated to actually remove such compounds therefrom or to convert such compounds to another form. For purposes of this invention, sulfur in a reactive form is defined as hazardous sulfur and compounds which contain sulfur in a reactive form are referred to as hazardous sulfur containing compounds.
When certain hazardous sulfur containing compounds, such as sulfides and mercaptans, are converted to another form, as mentioned above, the resulting compounds can also include sulfur in a reactive form. The term “sulfides,” as used herein, includes water soluble sulfides, such as hydrogen sulfide and alkali metal sulfides, i.e., sodium sulfide, and water insoluble sulfides, such as transitional metal sulfides, i.e., iron sulfide, nickel sulfide and chromium sulfide. Examples of resulting compounds which contain sulfur in a reactive form include sulfites and a variety of compounds which contain sulfur-to-sulfur bonds. Compounds which contain hazardous sulfur, as defined above, such as the mentioned resulting compounds, are a potential source of damage to certain industrial equipment as well as a potential source of danger to the physical health of people. It is known that persons who process materials which contain sulfides and/or mercaptans which, for purposes of this invention, are referred to herein as precursor compounds, take special precautions with respect to the handling, treatment and containment of such precursor compounds. A problem of long standing thus comprises the selection and employment of compositions, methods and apparatus for treating and handling and/or for rendering safe and harmless the precursor-compounds as well as the reaction products thereof.
Persons having working experience in the petro-chemical industry believe that the surfaces of certain high carbon content stainless steel, such as the interior surfaces of process vessels, can suffer a type of damage referred to as stress corrosion cracking at times when such surfaces are exposed to an oxygen containing atmosphere, such as air, while the surfaces are in contact with the mentioned precursor compounds. In this regard, persons skilled in the art believe that the mentioned precursor compounds, i.e., sulfides and mercaptans, can be partially converted by oxidation to specific classes of compounds and mixtures of such compounds which contain sulfur-to-sulfur bonds, if the precursor compounds are exposed to an oxygen containing environment, such as air, in the presence of water and at a pH less than 7.
Accordingly, this invention is directed, in part, to water soluble compounds which contain sulfur-to-sulfur bonds. It is believed that compounds containing sulfur-to-sulfur bonds which are soluble in oil, but which are not soluble in water, such as organic disulfides, are not a source of stress corrosion cracking. Examples of compounds which contain sulfur-to-sulfur bonds which are soluble in water include thiosulfates, polythionates and dithionites. For convenience, water soluble compounds which contain sulfur-to-sulfur bonds are referred to herein as reactive multi-sulfur compounds.
It is believed that reactive multi-sulfur compounds can cause stress corrosion cracking of certain types of high carbon content stainless steels, such as 301, 304 and 316 stainless steel. In this regard, if the mentioned precursor compounds are converted to reactive multi-sulfur compounds, as above described, then it is believed that the anions of such reactive multi-sulfur compounds in contact with the mentioned stainless steel, while in the presence of oxygen at a pH of less than 7, can cause stress corrosion cracking of the steel. The probability of the occurrence of such damage is ordinarily quite high at times when a stainless steel vessel containing the precursor compounds, and perhaps even a quantity of the reactive multi-sulfur compounds, is opened to the atmosphere to be cleaned and/or decontaminated with an aqueous based agent.
Low carbon content stainless steels are not believed to be susceptible to stress corrosion cracking.
Thus, to prevent stress corrosion cracking, it is desirable to employ a method to prevent the conversion of precursor compounds to reactive multi-sulfur compounds or to employ a method to prevent contact between reactive multi-sulfur compounds and stainless steel under conditions which promote stress corrosion cracking.
A method employed in the prior art to prevent stress corrosion cracking of a stainless steel surface in contact with an aqueous solution of a reactive multi-sulfur compound comprises shielding the wet surface from air with a solution having a pH greater than 7. This method has been extensively employed while cleaning heat exchanger bundles and has been referred to in the art as the “cover and hope” technique.
Austenitic steel is a stainless steel which is susceptible to stress corrosion cracking by the above described process. Austenitic steel is a steel containing sufficient amounts of nickel, nickel and chromium, or manganese to retain austenite at atmospheric temperature. Austenite, originally known as a solid solution of carbon in y-iron, now includes all solid solutions based on &ggr;-iron. (See Chambers's Technical Dictionary, Tweeny & Hughes, MacMillan Company, New York, 1957, page 60.)
The problem of stress corrosion cracking of austenitic steel is addressed in “Protection of Austenitic Stainless Steels and Other Austenitic Alloys From Polythionic Acid Stress Corrosion Cracking During Shutdown of Refinery Equipment,” NACE Standard RP0170-97, item No. 21002, dated Mar. 10, 1997.
In addition to the above, persons having working experience in the petrochemical industry also believe that vessels constructed of ordinary steel or low carbon content stainless steel, while not being particularly vulnerable to stress corrosion cracking, are subject to fires caused by the spontaneous ignition of iron reaction products, such as iron sulfide, examples of which are troilite, FeS, and pyrite, FeS
2
, marcasite and pyrrhotite. In this regard, a vessel constructed of ordinary steel or low carbon content stainless steel upon being exposed to a material, such as crude oil, containing the mentioned precursor compounds, can be corroded by the precursor compounds to form water-insoluble and oil-insoluble iron sulfide. In this connection, sulfide, a hazardous sulfur as defined above, reacts with iron in the vessel to form one or more of the iron sulfides mentioned above. The iron sulfide product can be, in a very finely divided physical form and, thus, p
Griffin Walter D.
United Laboratories Intl., LLC
LandOfFree
Method for treating hazardous and corrosion-inducing sulfur... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for treating hazardous and corrosion-inducing sulfur..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for treating hazardous and corrosion-inducing sulfur... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3155757