JPS625152A - Monitoring of corrosion - Google Patents

Abstract

PURPOSE:To monitor the corrosion state of a heat transfer section heavily corroded during the operation of a plant, by a method wherein a corrosion terminal is set in a corrosive environment, the terminal is heated from the inside thereof to apply a heat flow velocity as running toward the corrosive environment side and the corrosion thereof is monitored with the surface thereof as heat transfer surface. CONSTITUTION:An electrically sheathed heater 9 is inserted into a tube 8 or SUS304L and a corrosion terminal 7 formed in a U shape is mounted near the bottom of a nitric acid vapor boiler 1 being exposed to the inside of the boiler by about 100mm length from the tip of the U-shaped part. Then, a sheathed heater 9 is controlled with an electronic controller 12 to boil a nitric acid solution on the surface of the terminal by a heat flow velocity across the thickness of the terminal tube 8 and then the electric resistance of the corrosion terminal is measured to determine the reduction in the thickness of the terminal tube 8. Thus, the terminal with the heat transfer condition given the same as the actual heat transfer section is used to measure the reduc tion in the thickness due to corrosion, thereby enabling the estimation of the reduction in the thickness of the actual heat transfer section at a high accuracy.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for monitoring corrosion of heat transfer component members of equipment used in a corrosive environment, and in particular to a distillation equipment and a concentration equipment of a nitric acid production plant, The present invention relates to a method for monitoring corrosion of heat transfer components of equipment in chemical plants for manufacturing and freshwater production, nuclear fuel reprocessing for nuclear power use, and waste treatment plants.

(Prior Art) In a strongly oxidizing atmosphere such as nitric acid, thinning of equipment components due to corrosion is a problem, and monitoring the corrosion status is important from the viewpoint of plant maintenance and operation rate.

Conventionally, the method of monitoring the corrosion status is to directly measure the wall thickness from the outside using an ultrasonic thickness gauge or eddy current flaw detection in the case of the external wall that makes up the equipment, and if measurement cannot be done from the outside, ultrasonic The thickness can be measured by inserting a thickness gauge probe from the outside, or by immersing a terminal made of the same material as the part to be measured in a nearby nitric acid solution, and measuring the thinning of the terminal due to corrosion using electricity. Monitoring methods include resistance measurement and measurement using an ultrasonic thickness gauge.

(Problem to be solved by the invention) The distillation equipment of a nitric acid production plant handles a large amount of nitric acid solution heated to the boiling point, but in the case of nitric acid corrosion, the amount of corrosion depends on whether or not the surface in contact with nitric acid is under heat transfer conditions. are significantly different.

Figure 2 shows the relationship between the time (Hr) and the amount of corrosion thinning (ym) when 8trl1504L is immersed in a 5N nitric acid solution. 3
Q, OOOKcaVWL", hr) shows the bottom roughness. From this figure 2, it can be seen that the amount of corrosion is large under heat transfer conditions.

Distillation equipment and concentrators have a heating part for nitric acid solution and a heat transfer surface, but conventional corrosion monitoring terminals were simply immersed in nitric acid solution, so the terminals themselves were not exposed to heat transfer conditions. Therefore, it was not possible to represent the corrosion of the heat transfer part, which is the most severely corroded area. Furthermore, with the structure in which heating heat transfer tubes are arranged in a coiled manner inside the device, it is difficult to insert the probe of an ultrasonic thickness gauge to measure the wall thickness, especially during plant operation. Difficult and difficult.

The present invention provides a method for monitoring the corrosion status of severely corroded heat transfer parts during plant operation, and is particularly suitable for monitoring corrosion of structural parts for which direct wall thickness measurement is difficult.

(Means for Solving the Problems) The present invention provides a method for installing a corroded terminal constituting a heat transfer corroded terminal in a corrosive environment and applying a heat flow rate from the inside of the corroded terminal toward the corrosive environment side. A method for monitoring corrosion of a component of a heat transfer part of a device used in a corrosive environment, characterized by monitoring corrosion of a corroded terminal.

That is, the present invention heats the corroded terminal itself from the inside,
By immersing this in a corrosive environment, such as a nitric acid solution, the terminal surface becomes a heat transfer surface, and the amount of thinning of this terminal is measured using a generally known electrical resistance measurement method or an ultrasonic thickness meter. .

At this time, the material of the terminal is the same as the material to be monitored.
It is necessary to match the heat flow rate of the terminal to the same conditions as the actual heat transfer part. In addition, the mounting position of the terminal only needs to be in the same solution as the nitric acid solution with which the actual heat transfer part comes into contact, and therefore a location where the terminal can be easily mounted can be selected.

[Effect]

By subjecting the terminals to the same heat transfer conditions as in the actual heat transfer part, it is possible to reproduce the same corrosion situation, and by monitoring the corrosion situation of the terminals, it is possible to reproduce the same corrosion situation as in the actual heat transfer part. Able to estimate the situation.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG.

Figure 1 (a) shows a nitric acid distillation boiler, where 1 is the nitric acid distillation boiler, 2 is the heat transfer surface, 3 is the nitric acid liquid inlet, 4 is the same outlet, 5 is the steam inlet, 6 is the same outlet, 7 is a heat transfer corrosion terminal which is the main part of the present invention.

FIG. 1(b) is an enlarged view of the heat transfer corrosion terminal 7 in FIG. 1(a), and 8 is an 8U8304L tube (φ&0×t
α5) U-shaped corrosion terminal, 9 is a sheath heater (φ & 0) inserted into the corrosion terminal with surface insulation, 10
1 is a sealing material that exposes the length of 1001111 from the tip of the 0-shaped part of terminal 8 and protects the remaining part, 11 is the wall of the distillation boiler, and 12
13 is a power controller for the sheath heater 9, and o8U is a resistance meter that measures the electrical resistance of the terminal 8 exposed in the nitric acid solution.
8! Insert a surface-insulated electric sheath heater (φ5.0) 9 into a 5O4L tube (φ&0×t(L5) 8, and bend it into a U-shape to form a corroded terminal as shown in Figure 1(b) K. 7 was produced.

Exposing the length of 100fi from the tip of the 0-shaped part of this terminal,
The terminal, the remaining part of which was protected with a sealant 10, was attached to the bottom of the nitric acid distillation boiler 1 as shown in FIG. 1 (1)). The sheath heater 9 of the terminal is controlled by the power controller 12 so that the heat flow rate in the thickness direction of the terminal tube is 50.000 kcal/i.
, hr K, so that the nitric acid solution boiled on the terminal surface. Further, the electrical resistance between the nine terminals exposed in the solution was connected to a resistance meter 13 to measure the increase in electrical resistance due to corrosion thinning of the terminal tube. Note that the measurements were carried out for 30 minutes every 48 hours with the heater turned off to avoid including errors in the resistivity of the terminal tube due to temperature changes.

In this method, a nitric acid solution with a concentration of 3N is continuously supplied into the nitric acid distillation boiler 1, and 200°C steam is flowed outside the 1.8UB504L heat exchanger tube 2 to heat and distill the nitric acid solution. This was done continuously for 3500 hours.

During this time, we measured the electrical resistance of the corroded terminals and determined the amount of thinning of the terminals and tubes.As a result, thinning progressed at an accelerated pace with time at the beginning, and then progressed almost in proportion to time.
The amount of thinning after 3,500 hours was α20 mint. After the operation was stopped, the upper cover of the nitric acid distillation boiler 1 was opened, and an ultrasonic thickness gauge was inserted into the heat exchanger tube to measure the wall thickness. As a result, the average amount of thinning was α18, and the maximum amount of thinning was 0. It was 21+m. For reference, insert a corroded terminal without a heater,
According to the results of measuring thinning, the amount of thinning after 3500 hours is α
It was 08fl.

From this result, it is clear that if the corrosion thinning of the terminal is measured using a terminal subjected to the same heat transfer conditions as the actual heat transfer part, the corrosion thinning of the actual heat transfer part can be estimated with high accuracy. 0 (Effect of the invention) Corrosion thinning of a part placed in a corrosive environment and under heat transfer conditions can be measured with high accuracy without directly measuring the part, and without stopping the plant. Because it can be estimated without any changes, plant maintenance is easy and accidents due to corrosion and thinning can be prevented.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.
(a) shows a nitric acid distillation boiler, and (b) shows an enlarged view of a heat transfer corrosion terminal installed therein. Figure 2 is 5Ull! The relationship between the time (ur) and the amount of corrosion thinning (w) when 504L is immersed in a 5N nitric acid solution is shown. It is a graph. Sub-agents 1) Meifuku agent Ryo Hagiwara - Sub-agent Atsuo Anzai Figure 1 (a) Figure 2 Time (Hr) Continued from page 31

Claims (1)

[Claims] Corrosion characterized by installing a corroded terminal constituting a heat transfer corrosion terminal in a corrosive environment and monitoring corrosion of the corroded terminal while applying a heat flow velocity flowing from the inside of the corroded terminal toward the corrosive environment side. A method for monitoring corrosion of components of a heat transfer part of equipment used in an environment.