CZ35860U1 - Triplicate resistometric sensor for measuring the corrosion rate of metals - Google Patents

Description

Triplicate resistometric sensor for measuring the corrosion rate of metals

Field of technology

Corrosion of metals is one of the main mechanisms of degradation of metallic materials. Most of the surface of existing metal objects and structures is exposed to the atmosphere. Atmospheric corrosion of metals also accounts for the largest share of financial losses caused by corrosion in general. From the point of view of planning the service life of metal structures and controlling the influence of the environment on their service life during operation, it is necessary to know the corrosion rate of the structural metal under the given conditions. In practice, various methods of measuring the corrosion rate of metals in the atmosphere are used. One of them is the resistometric method working with resistometric sensors. In addition to construction materials exposed to the external atmosphere, determining the corrosion rate is also crucial in specific cases, such as care of metal monuments, protection of metal products during long-distance transport, protection of important electronic devices from atmospheric influences, etc. Resistometric sensors are always solved by connecting specific and so-called reference parts. Such a sensor provides the only information about corrosion loss. At the same time, the corrosion rate is a quantity that must be evaluated in terms of reproducibility. The resistometric sensor in question, with its new design, enables the gain of three values of corrosion loss at the same time using a single reference part. This allows verification of measurement accuracy, increased data reliability, elimination of erroneous results, the possibility of detecting anomalous behavior, such as localized forms of corrosion, etc. The design allows expanding the number of specific parts to more than three material whose corrosion rate is to be measured.

State of the art

Many methods are used to assess the corrosive effect of the environment on metals. The rate at which a metal corrodes under given conditions is most easily determined by a change in the weight of the metal sample (coupon) after a specified exposure time. A long exposure time is required to reliably determine the corrosion rate from the weight loss of the corrosion coupon. Current standards set it for at least one year. In this way, atmospheres are classified according to their corrosive aggressiveness. Such a procedure does not make it possible to determine the effect of changing conditions on the corrosion rate of metals. The response of the weight loss method is often too long and the sensitivity too low. A suitable method for semi-continuous monitoring of the corrosion rate of metals depending on the conditions is the resistometric method, which uses a change in the electrical resistance of the corroding sensor to determine the corrosion loss of the metal. The change in the electrical resistance of the metal sensor is given by the change in the cross-section of the corroding metal according to the relation (R1):

(R1) R = p ~ ·, 0 where R - electrical resistance, p - resistivity, l - length of metal sensor, 5 - cross section of metal sensor

In addition to the geometric parameters of the metal sensor, which vary with the degree of corrosion, the resistance of the sensor also depends on the temperature. Under operating conditions, the ambient temperature, and therefore the metal temperature, is not constant. The effect of temperature on the electrical resistance of the resistometric sensor is compensated by the fact that in addition to the exposed metal trace (specific part) the sensor also contains an identical metal trace (reference part), which is protected from environmental corrosion by a corrosion coating. The electrical resistance of this part is not affected by corrosion loss and its resistance changes only with a change in temperature. The corrosion loss is then expressed by changing the ratio of the resistances of the reference and specific parts compared to the ratio at the beginning of the exposure. There are several methods for calculating corrosion loss. The most common calculation describes the relationship R2:

- 1 CZ 35860 UI (R2) (R R J kh = K · ι-Δυ.χχ

IR _m Rro) where ΔΛ - thickness drop, ho - initial thickness of the metal trace, Rr, o - electrical resistance of the probe reference part at the beginning of exposure, Rm, o - electrical resistance of the probe specific part at the beginning of exposure, Rr - electrical resistance of the reference part, Rm - electrical resistance of the measuring part.

The resistometric method for determining the corrosion loss of metal requires high accuracy in measuring electrical resistance. The electrical resistance is measured in a so-called four-wire connection, where a defined electrical current passes through the metal trace of the resistometric sensor and the voltage that this current causes is measured at other contacts of the measuring and reference parts. From the knowledge of current and voltage, the resistance of both parts of the sensor is calculated using Ohm's law.

Currently, the most commonly used design solution of the sensor has one specific and one reference part. Such a solution allows to gain only one value of corrosion loss. From a static point of view and from the point of view of information reproducibility, a single value of corrosion loss is insufficient. All other methods of determining corrosion loss and corrosion rate use repeated measurements, which increases the informative value of the information. In the case of the resistometric method, the parallel exposure of another resistometric sensor sensed by a multi-channel device or another separate device is used to replicate the measurement.

The described technical solution of the subject triplicate resistometric sensor proposes such a construction arrangement, which enables the gain of three independently measured values of corrosion loss in one measuring step. Compared to three separately exposed sensors, the triple sensor has the advantage of using only one reference part. This saves material and costs for the production of such sensors. A significant advantage is energy savings for autonomously operating measuring systems.

The essence of the technical solution

The resistometric sensor for measuring the corrosion loss of metal in the atmosphere consists of a thin (50 run to 0.25 mm) metal trace 1 applied on an electrically non-conductive substrate 2 with dimensions of 50 x 50.82. The thickness of the substrate is limited only by the width of the mouth of the connector into which the sensors are inserted, usually 1.5 mm. For example, a glass-laminate board can be used, on which a foil of the metal whose corrosion loss we want to measure is laminated. The required design of the metal trace is then etched according to a procedure known from the production of printed circuits. Another possible procedure is PVD deposition of metal on a ceramic or glass substrate. With this technique, we obtain metal layers with a lower thickness, which provides a higher sensitivity of the resulting corrosion sensor. The three measuring parts 3 and the reference part 4 of the resulting sensor are connected by bridges in the connector so that the current during the sensing of the electrical support passes through all parts of the sensor. At the moment of current flow, the values of voltage drop on all four parts are measured, from which their resistance is determined. The boundary of the protective coating 5 is between the reference part and the adjacent specific part (Fig. 1).

Clarification of drawings

Giant. 1: Schematic of a triplicate resistometric sensor.

Giant. 2: Triplicate resistometric sensor Fe-250.

Giant. 3. Measurement according to the modified standard ISO 16701 (2016) with a steel sensor with a thickness of 250 pm (constant temperature 35 ° C; the phases when the sensors were immersed in

-2CZ 35860 IU min to 1% NaCl, after immersion they were sprayed with the same solution and exposed to 95% RH for 1 h 45 min. This procedure was repeated at each stage.

Example of technical solution

Example 1

The triplicate resistometric sensor Fe-250 (Fig. 2) consists of a non-conductive substrate 2 made of fiberglass with a thickness of 1.2 mm. Metal track 1 is made of unalloyed carbon steel and its thickness is 250 μm. One of the four loops of the metal track is covered with epoxy sealant 5 and is used as a reference part 4 of the resistometric sensor. The other three loops are exposed to a corrosive environment and are used as specific parts 3.

Example 2

The triplicate resistometric sensor described in Example 1 was exposed to cyclic corrosion test conditions based on ISO 16701 (2016). At a constant temperature of 35 ° C, the relative humidity was periodically changed between 50 and 95% relative humidity every 12 hours. A 1% NaCl solution was applied at four selected times (0, 96, 168, 264 hours). Giant. 3 shows a record of the thickness drop of the three specific parts of a triplicate resistometric sensor as a function of time and changing conditions. All three records follow the same trend and similar values of corrosion loss over time. The triple sensor thus provides information on corrosion loss with a high significance. (Fig. 3)

Industrial applicability

The triplicate resistometric sensor for measuring the corrosion rate of metals, the construction of which is described, increases the reliability of corrosion monitoring using the resistometric method of measuring corrosion loss. In contrast to electrochemical monitoring methods, the resistometric method is advantageous in its simplicity and applicability in any environment. Compared to exposure tests, the resistometric method has a higher sensitivity and a shorter response. Measurements carried out at one time on three independent measuring parts of the sensor enable statistical evaluation of the corrosion loss. This allows verification of measurement accuracy, increased data reliability, elimination of erroneous results, the possibility of detecting anomalous behavior, such as localized forms of corrosion, etc. The design allows expanding the number of specific parts to more than three material whose corrosion rate is to be measured. Corrosion monitoring using resistometric sensors is suitable for corrosion protection of products and equipment, and consequently for environmental and health protection. Corrosion monitoring based on the resistometric method enables early warning of an increase in the corrosive aggressiveness of the environment towards metallic materials.

Claims (2)

PROTECTION REQUIREMENTS 1. A triplicate resistometric sensor for measuring the corrosion loss of metal, characterized in that 5 consists of a thin metal trace (1) deposited on an electrically non-conductive substrate (2), which is divided into three measuring parts (3) and a reference part (4), the reference part part (4) is covered with a protective coating (5) and is adjacent to three specific parts (3) to provide three independent values of corrosion loss using a single reference part. it Triplicate resistometric sensor according to Claim 1, characterized in that the boundary of the protective coating (5) extends across the metal track (1) in the region between the contact surfaces and the connection of the current and voltage paths.