CS217463B1 - Method of continuous control of corrosion of chemical technological plants - Google Patents

Description

(54) Continuous Corrosion Control Method of Chemical Technological Apparatus The present invention addresses the method of continuous corrosion control of apparatuses of thematic technology by an electrochemical method, non-destructively, without interrupting production. The solution is designed especially for such apparatuses, which are made of austenitic stainless steel and working in such a very aggressive solutions that fluctuate operating parameters, or failure to comply with the discipline quickly leads to fluctuations of corrosion state between yard extremes, corrosive active and passive state.

Previously known corrosion control methods do not provide sufficiently rapid direct data on the corrosion of exposed apparatuses during operation and therefore do not allow operative interventions into the production mode to improve the corrosion situation. The electrochemical polarization methods described in the literature, which make it possible to determine the instantaneous corrosion rate, are applied only to small electrode indicating electrodes, since it would be practically impossible to connect the entire apparatus as a polarizing electrode. Although the indicator electrode is made of the same material as the apparatus, it will not always reliably characterize the condition of the apparatus. It depends on its placement Y syl theme, geometry, dimensions and other factor estimates.

Continuous control of the corrosion products content in the process medium provides only indirect data and significant delays in the corrosion situation in the apparatus.

Direct data on attenuation of apparatus walls can be obtained in operation by measuring the depth with an ultrasonic meftode, even at accessible locations only, and the sensitivity of the measurement is not sufficient for the method to respond promptly to rapid changes in operating parameters. A number of other known controls, such as e.g. direct visual inspection of the contaminated surface, indirect corrosion evaluation gravimetric by means of control samples, etc., can be used in production interruption.

The above-mentioned drawbacks are overcome by the solution according to the invention, which consists in measuring the course of the corrosion potential of a controlled apparatus against at least one reference electrode made of the same material as the apparatus, continuously indicating whether the electrodes are in a corrosive active or passive state. . The design of one electrode ensures that, even when operating parameters are changed, it is always in a certain reference state. By monitoring the apparatus, the instantaneous corrosion potential is assigned according to the instantaneous corrosion potential value.

This solution is based on the experimentally established fact that it is possible to produce corrosion probes to compare electrodes continually pitch in the reference corrosion state, and further that the corrosion potentials of the austenitic stainless steel in the active and passive states are very different from each other. E.g. in urea production apparatuses, it has been found that a deliberately formed gap around the reference electrode achieves that the electrode is constantly in the active state. With this apparatus it was also measured that the difference in corrosion potentials between active and passive states was 500 mV. Operational experience has further shown that the corrosion state of apparatuses can be considered to be the same as the reference electrode when the idh corrosion potential difference at an absolute value is less than 50 mV.

A practical example of the invention can also be pointed out in the urea plant:

In the synthesis reactor, ammonium carbaminian is formed by reaction of carbon dioxide with ammonia. The reaction mixture is further decomposed, in columns of decomposition, or stripped to

Claims (1)

2 values of corrosion potential of its immediate corrosion. The solution is based on an experimentally established fact that probes can be produced which are comparable in the reference corrosion state, and that the corrosion potentials of the austenitic stainless steel in the active and passive states are they greatly differ. E.g. in urea cameras, it has been found that by deliberately forming a slit around the comparator electrode, it is ensured that the electrode is in the active state at all times. In this apparatus, it was also shown that the difference in corrosion potential between the active and the passive state is 500 mV. Furthermore, the operating experience has shown that the corrosion state of the apparatuses can be considered as the same as the comparative electrodes when the difference in idh of corrosion potentials is less than 50 mV in absolute value. A practical example of the invention can also be pointed out in the urea plant: In the synthesis reactor, the carbon monoxide is formed by the reaction of carbon dioxide with ammonia. The reaction mixture is further decomposed, by decomposition, by stripping or by stripping onto an object of continuous corrosion control apparatus of a chemical technology characterized by continuously measuring the corrosion of the potentially controlled apparatus against the comparative electrodes produced from such a certain lacquer material while indicates if the electrodes are in active urea corrosion. This zimes is a very aggressive and austenitic non-dissolving steel. Pretosa dispenses oxygen as a passivator. In the absence of oxygen, the apparatuses are in an active state and very corrosive. Thus, the proper dosing of the dosing system extends the life of the device over economically justified costs. It is carried out according to the invention: A probe with a comparative electrode made of the same material as the equipment is incorporated into the pressure decomposition column. For example, ISA 316 Ltzv. urea quality. A suitable web is formed around this electrode to keep the electrode still in active state. The corrosion potential of the apparatus in the passive state, compared to this electrode, has a higher value of + 500 mV. In this state, the oxygen dosage can be limited. If the corrosion potential of the apparatus falls below + 450 mV, it is necessary to increase the oxygen dosage. Upon returning the corrosion potential of the apparatus to the downstream, the oxygen supply can again be limited since its excess precedes production and limits performance. In this way, it is economically viable to maintain an economically sound value. DISCLOSURE OF THE INVENTION or passive state, wherein at least one of the compared electrodes, without cooling the operational parameters of the media in a particular reference state, is assigned an instantaneous corrosion state according to the instantaneous measured value of the corrosion potential.