Corrosion monitoring system for monitoring technology is varied ways of the information provided by the parameters are different

Corrosion monitoring system for the linear polarization method is a kind of electrochemical method of rapid determination of metal corrosion rate. This method is suitable for the electrolyte solution, and the resistivity less than 10 k Ω m., and no secondary electrochemical REDOX reaction system; Is not suitable for application in poor conductivity of medium, this is because when the device surface with a layer of dense oxide film or passivation membrane, accumulation of corrosion products, even will result in false capacitance and cause a great error, even you can't measure. The principle of which is based on steady-state electrochemical reaction system in: metal from corrosion potential weak polarization zone near the polarization potential and polarization current that there was a linear relationship between the use of its slope Rp (polarization resistance) is inversely proportional to the corrosion current can find out the relationship between the corrosion rate of metals, the proportionality constant B values calculated by the tafel constants, income or by professional literature. The advantage of linear polarization method is: fast response to changes in corrosion situation, can get the instantaneous corrosion rate, more sensitive, can reflect the change of equipment operation condition in a timely manner, is a kind of very suitable for monitoring method. From its disadvantages are that if the metal electrode surface in addition to an electrochemical reaction, accompanied by other electrochemical reaction, can lead to errors of corrosion monitoring results. In addition, the determination of proportionality constant B value is an important factor affecting the way to measure results, and, when necessary, need to use coupon method for correction. If the reference value and the actual value difference is bigger, B B is corrosion monitoring results and real results of deviation is large, even it is concluded that error of corrosion monitoring information.

Analysis of characteristics of various types of corrosion Damage by the API 57 1 Damage Mechanisms in Refinery Fossil Process Industries (2003), the equipment and pipeline corrosion Damage can be roughly divided into:

(1) general corrosion damage

(1) damage caused by mechanical or phase transition. Graphitization, temper brittleness, strain aging, 475 qc brittleness, or brittle, such as creep l9 class.

(2) the uniformity and local corrosion caused by electrochemical. Atmospheric corrosion, galvanic corrosion, water corrosion and thermal insulation materials, corrosion and scale corrosion, etc.

(3) high temperature and chemical corrosion. Oxide and sulfide and carburizing and decarburizing, etc.

(4) environmental sensitive chlorine brittle rupture (CSCC of), alkali embrittlement (ASCC) hydrogen embrittlement (HE) corrosion fatigue cracking, and so on. (2) the corrosion damage of peculiar to the petrochemical industry

Wet hydrogen sulfide of SCC, and SOHIC, hydrogen sulfide + + hydrocyanic acid hydrochloric acid corrosion, hydrogen sulfide corrosion, hydrogen sulfide + carbonic acid corrosion, naphthenic

Acid corrosion, even more SCC, sulfate, H + oil refining industry characteristic of the damage, such as H2s corrosion and corrosion sulfuric acid, hydrofluoric acid corrosion, corrosion of urea, acetic acid, corrosion and other petrochemical industrial injury of other species.

(3) comprehensive corrosion and local corrosion analysis of equipment damage

For petrochemical equipment from corrosion control perspective, comprehensive corrosion or less uniform corrosion damage, because the passivation membrane materials (such as

Stainless steel), the corrosion rate is less than 0.1 mm/a, even less than 0.01 mm/a. But for a longer service or expiration of the period for serving equipment there is still a risk. , of course, such as passivation film is active in the acidic liquid damage, with several mm/a dissolve rate, although the uniform corrosion, but need to be a different matter. To pitting corrosion, pit corrosion, scale and corrosion, erosion and other local corrosion under its harmfulness is general corrosion, especially stress corrosion cracking (SCC) and hydrogen embrittlement (HE) such as environment sensitive fracture risk is bigger, because in the petrochemical enterprises under the condition of high temperature and high pressure service, equipment and pipeline corrosion perforation and cracking, will cause catastrophic accidents such as fire explosion, because often without apparent sign of a sudden, such as the progress of the SCC speed for dozens of mm/a. Therefore, the local corrosion and cracking is a destructive and hard to discover the corrosion morphology, their prediction and control, and risk evaluation is difficult.