Understanding of \"corrosive media\" in the definition of pressure pipelines. Acid and base? Saltwater?
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For example: the conveying medium is a sodium chloride solution. It is well known that sodium chloride solutions are highly corrosive to steel, especially stainless steel. How should this corrosivity be understood? Is the corrosion of stainless steel by chloride ions considered corrosion? Is only corrosivity, like that of acids and bases, what counts as corrosion? I’d like to ask all the sea friends!
Different pipes are exposed to different corrosive media, right?
What you’re referring to is all typical corrosion; it’s just that different media acting on different materials result in various forms of corrosion.
The definition of corrosion can be divided into broad and narrow senses; in the broad sense, damage is equivalent to corrosion. In a narrow sense, it generally refers to metal corrosion. What you’re referring to is simply uniform corrosion.
The \"Announcement by the State Administration for Market Regulation on Matters Related to Administrative Licenses for Special Equipment\" (No. 3, 2019) classifies industrial pipelines as follows: GC1 grade: 1. Process pipelines that transport media with an acute toxicity level of Category 1 as specified in the \"Catalogue of Hazardous Chemicals\", gas media with acute toxicity of Category 2, and liquid media with acute toxicity of Category 2 whose operating temperature is higher than their standard boiling point； 2. Process pipelines that transport flammable gases of Class A or B, or flammable liquids of Class A (including liquefied hydrocarbons), as specified in GB50160 \"Code for Fire Protection Design of Petrochemical Enterprises\" and GB50016 \"Code for Fire Protection Design of Buildings\", and whose design pressure is 4.0 MPa or higher ； 3. Process pipelines that transport fluid media, with a design pressure of 10.0 MPa or higher, or a design pressure of 4.0 MPa or higher along with a design temperature of 400°C or higher. GC2 grade: 1. Process pipelines other than GC1 grade; 2. Refrigeration pipelines. GCD grade: Power pipelines. Note that the grades of industrial pipelines are classified according to the acute toxicity categories specified in the \"Catalogue of Hazardous Chemicals\".
In the definition of pressure pipelines, a \"corrosive medium\" is one that causes visible necrosis upon contact with the skin after 4 hours, or one that results in a corrosion rate of more than 6.25 mm/s for 20-grade steel at 55 degrees Celsius. Therefore, NaCl does not belong to corrosive media. Although it can cause stress corrosion problems in stainless steel pipes.
The prerequisite for this criterion is that it serves as a further refinement under the conditions that apply to the assessment of pressure pipelines. For example: the conveying medium is clean water at room temperature, with a design pressure of 15 MPa. So is this pipeline a pressure pipeline of GC1 grade?
I see now. . Thank you! Furthermore, 6.25mm/s or 6.25mm/a?
According to the \"Announcement by the State Administration for Market Regulation on Matters Related to Administrative Licenses for Special Equipment\" (No. 3, 2019), the term \"corrosive media\" as defined in the context of pressure pipelines refers to Corrosive Substances of Category 8 listed in the \"Catalogue of Hazardous Chemicals\" (2002 edition). The \"Catalogue of Hazardous Chemicals\" (2015 edition) identifies these as \"Skin corrosion/irritation: Categories 1A, 1B, 1C, 2\", and this information can be found in the \"Classification Information Table of the Catalogue of Hazardous Chemicals 2015 edition\".
However, stainless steel has requirements regarding chloride content