RU2796240C1 - Method for determining the degree of wear of equipment under the influence of corrosion - Google Patents

Abstract

FIELD: anti-corrosion materials.

SUBSTANCE: determining the degree of wear of equipment using the identification of indicators of corrosion of a structural material. The method for determining the degree of corrosive wear of the structural elements of the equipment at the site of the corrosion process includes measuring dimensions before and after testing or operation. The location of the corrosion process is established by visual or instrumental detection of corrosion centers that have appeared under the influence of surface corrosion, close to uniform or under the influence of deep corrosion, including pitting, spotting, subsurface, layered, intergranular, transgranular, selective and corrosion in the form of rare cracks. Measure the amount of surface corrosion of the equipment element, the amount of deep corrosion of the equipment element, determine the type of corrosion in accordance with the scale of corrosion resistance of the structural material, calculate: the actual size of the structural element; complete corrosion wear of the element; corrosion factors depending on the corrosion score at which corrosion becomes more dangerous; the degree of corrosive wear of an equipment element made of one structural material, in accordance with the corrosion score, with a diagram of a typical type of corrosion damage, with a type of corrosion and a characteristic of the form of corrosion damage of a structural material.

EFFECT: increasing the accuracy of assessing the degree of corrosive wear of the structural material of the equipment.

2 cl, 6 dwg

Description

The invention relates to the field of determining the degree of wear of structural elements of equipment using the numerical identification of corrosion indicators of the structural material.

The greatest wear of equipment, as is known, causes, for example, a change in the dimensions or a decrease in the wall thickness of the structural elements of the equipment due to corrosion. Corrosion can be close to uniform or in the form of corrosion damage by pitting, deep-seated corrosion, spot corrosion, pitting, subsurface and other types of corrosion, however, there are no methods for determining the degree of corrosive wear.

It is widely known that wear is characterized not only by a change in the dimensions of the structural elements of the equipment, but also by the impact on the structural material of various media, high and low temperatures, fluid flow conditions and mechanical stresses. The results of these impacts are determined by visual or instrumental detection and identification of the places of the corrosion process, corrosion centers of their size, penetration depth and establishing the characteristics of corrosion distribution using the identification of corrosion indicators of the structural material, however, there are no methods for numerical identification of corrosion indicators when determining the degree of corrosion wear.

As you know, indicators of corrosion and corrosion resistance, which take into account quantitative, semi-quantitative (point) and qualitative indicators [GOST 9.908-85 Unified system of protection against corrosion and aging. Metals and alloys. Methods for determining the indicators of corrosion and corrosion resistance. M.: Publishing house of standards. dated October 31, 1985 (with Amendment No. 1).], however, they do not contain numerical values of corrosion indicators, which makes it impossible to numerically identify corrosion factors when determining the degree of equipment wear.

It is known that to assess the corrosion resistance of a structural material, a ten-point scale of corrosion resistance is established [GOST 13819-68 Unified system for protection against corrosion and aging (ESZKS). Metals and alloys. Ten-point scale for corrosion resistance (with Amendment No. 1)] has been cancelled. It was valid until 07/01/1985] however, here too there are no quantitative values of these indicators, which makes it impossible to numerically assess the influence of corrosion factors in determining the degree of equipment wear. In addition, in the well-known standards (GOST 9.908-85 Methods for determining corrosion and corrosion resistance indicators) and (GOST 13819-68 Ten-point scale of corrosion resistance), corrosion hazard points are not linked either to diagrams of a typical type of corrosion damage, or to the type of corrosion and characteristics forms of corrosion damage to the structural material, which makes it impossible to identify them.

Known methods for determining the degree of wear of a structural material [USSR Patent for invention No. 1545950, IPC G01N 29/00. Published: 02/23/1990. Bull. No. 7], consisting in cutting samples from the most loaded areas of the structure at various stages of its operation and determining the degree of wear. The disadvantage of the methods is the determination of the degree of wear by indirect parameters, in particular by comparing the parameters of ultrasonic waves, which makes it impossible to determine the degree of wear under the influence of corrosion.

Known methods for determining the degree of wear of a structural material [RF Patent for invention No. 2516416, IPC C25C 3/08. Published: 20.05.2014, Bull. No. 14] due to the intensification of the wear process and reducing the time of testing samples for wear by increasing the wear rate, and the degree of wear is also determined by changing the volume of the samples, which makes it impossible to determine the degree of wear of the structural material of the equipment in operation under the influence of corrosion.

It is known that when determining the degree of wear, the resistance of a structural material to corrosion is determined in the laboratory experimentally on test samples or samples made by cutting material from the walls of the equipment [GOST P 51372-99. Methods of accelerated tests for durability and storage under the influence of aggressive and other special environments for materials, systems of materials and technical products. General provisions. Adopted and put into effect by the Decree of the State Standard of Russia dated November 29, 1999 N 442-st.], however, tests in laboratory conditions do not provide comprehensive information about the resistance to corrosive wear of equipment in operation, which does not provide the ability to determine the degree of wear of equipment under the effect of corrosion.

Known methods for determining the corrosive wear of materials [RF Patent for the invention No. 2403556, IPC G01N 17/00 Published. 11/10/2010 Bull. No. 31] including the operations of exposing samples made in the form of a fragment of a thin-walled structure to a corrosive environment, measuring the parameters of samples before and after testing and evaluating corrosive wear, however, tests in laboratory conditions do not provide comprehensive information about the resistance to corrosive wear of equipment in operation , which does not provide the possibility of identifying the degree of equipment wear due to corrosion.

Known methods for identifying indicators of corrosion of a structural material [RF Patent for invention No. 2653775, IPC G01N 17/00, G01N 17/02. Published: 05/14/2018. Bull. No. 14], according to which, by means of control cuttings of samples from the walls of equipment in operation, their initial and actual dimensions, penetration depth, type of corrosion damage and phase composition of corrosion products are determined. The disadvantage of the known methods is the lack of numerical indicators of corrosion of the structural material, which makes it impossible to determine the degree of wear of equipment under the influence of corrosion.

Known methods for identifying indicators of corrosion of structural material [RD 03-421-01. Guidelines for diagnosing the technical condition and determining the residual service life of vessels and apparatus], in which visual or instrumental detection of corrosion foci determine their initial and actual dimensions, the depth of penetration of corrosion, the unevenness of corrosion is determined taking into account statistical deviations of the wall thickness depending on the confidence level and the maximum allowable relative error using, for example, the Weibull distribution law, which corresponds to the distribution of corrosion damage depths, but they do not contain numerical indicators of corrosion, which makes it impossible to determine the degree of wear of equipment under the influence of corrosion.

Known methods for identifying indicators of corrosion of a structural material [Goldobina L.A., Orlov P.S. Identification of corrosion damage to underground pipelines of public utilities and their protection against corrosion] and [RF Patent for invention No. 2457465 G01N 17/02. Published: 27.07.2012. Bull. No. 21]. Method for determining intergranular corrosion and corrosion damage of external surfaces of underground and underwater pipelines], in which the location of the corrosion process, the initial and actual dimensions, the depth of penetration of corrosion are determined and information is obtained on the type of corrosion, then areas subject to corrosion are identified. However, they do not contain numerical indicators of corrosion of the structural material, which makes it impossible to determine the degree of wear of equipment under the influence of corrosion.

A known method for identifying indicators of corrosion of the structural material of the equipment [Cherepanov A.P., Lyapustin P.K. The method of expert assessments of the numerical values of corrosion and corrosion resistance of metals // Collection of scientific works of the Angarsk State Technical University. 2019. Vol. 1. No. 16. P. 128-136], in which visual or instrumental detection determines the initial and actual dimensions of the structural elements of the equipment, the location of the corrosion process, the unevenness of corrosion and the depth of penetration of corrosion, the centers of corrosion, their sizes, the corrosion coefficient is set by the method of expert assessments, followed by the appointment of its numerical values. However, the method of expert assessments is subjective, since it does not provide sufficient accuracy and reliability in determining the numerical indicators of corrosion. In addition, the numerical values of corrosion are not used in determining the degree of wear of the structural material of the equipment under the influence of corrosion.

The closest technical solution is a method for determining the wear of the structural material of the equipment [Eurasian patent No. 018263, IPC E04H 1/00. Published: 06/28/2013] by means of a probabilistic assessment of wear, including the determination of the average degree of wear based on a quantitative assessment of the current technical condition of the equipment as a whole and its elements compared to the initial state, an increase in the probability of its failure or destruction over a known period of time is taken as an indicator of wear . The disadvantage of this method is that the increase in the probability of its failure or destruction over a known period of time is taken as the degree of wear and the current values of the probability of failure or destruction and the intensity of their change are determined, which does not provide sufficient reliability for determining the degree of equipment wear due to corrosion, since in known method does not take into account the corrosion performance of structural materials of the equipment.

Thus, in none of the known methods for assessing the degree of wear, numerical indicators of corrosion are used, which makes it impossible to determine the degree of wear of structural materials of equipment under the influence of corrosion.

The purpose of the invention is to determine the degree of corrosive wear of the structural materials of the equipment under the influence of corrosion by identifying the corrosion indicators necessary to determine the degree of danger of corrosion processes in assessing the technical condition and assigning the service life of the equipment.

The technical result consists in increasing the accuracy of assessing the degree of corrosive wear of the structural material of the equipment through the use of numerical corrosion indicators characterizing the intensity of the corrosion process.

According to the invention, the degree of corrosive wear of a structural material is determined by measuring the initial and actual dimensions of the structural elements of the equipment, while reducing the initial size to the actual one under the influence of corrosion close to uniform or surface pitting, deep corrosion, spotting, pitting, subsurface and other types of corrosion, the location of the corrosion process is determined by visual or instrumental detection of corrosion foci, the depth of penetration of corrosion into the structural material, while the actual size of the structural element of the equipment is determined taking into account the degree of corrosion hazard, the characteristics of the form of corrosion damage, the scheme of a typical type of corrosion damage, the areas of corrosion damage are evaluated on a ten-point scale corrosion resistance scale and are identified by the corrosion coefficient, which is determined with a confidence probability and a relative calculation error in accordance with the corrosion hazard and corrosion resistance score of the structural material, as well as in accordance with the diagram of a typical type of corrosion damage, with the type of corrosion and the characteristic of the form of corrosion damage of the structural material .

Description of drawings:

Fig. 1 - Scheme of corrosive wear.

Fig. 2 - Scheme for determining the degree of corrosive wear.

Fig. 3 - Corrosion coefficients depending on the corrosion hazard rating at the initial wall thickness of the housing element S _{and i} =20 mm and at the actual wall thickness S _fi =16 mm.

Fig. 4 - Corrosion coefficients in accordance with the diagram of a typical type of corrosion damage, with the type of corrosion and the characteristics of the form of corrosion damage of the structural material.

Fig. 5 - Dependence of the degree of corrosive wear on the corrosion coefficient when the element size is reduced from S _i = 20 mm to S _fi = 17.25 mm.

Fig. 6 - Dependence of the degree of corrosive wear on the reduction in the size of the element from S _i = 20 mm to S _fi = 17.25 mm at various corrosion coefficients.

The method for determining the degree of wear of equipment under the influence of corrosion is carried out as follows:

The initial dimensions of the equipment structural element are set according to the technical documentation or by its direct measurement (Fig. 1.). During a corrosion inspection of a structural element after the operation of the equipment, the place of the corrosion process is determined, the value of corrosion wear is estimated by visual or instrumental detection of corrosion centers using known measurement methods by determining the penetration depth of surface corrosion into the material and deep corrosion (corrosion penetration depth) into the structural material. The actual size of the element is determined by the formula:

where S _{and i} - the initial size of the i-th item of equipment;

S _fi - the actual size of the i-th item of equipment;

h _pi - the value of surface corrosion of the i-th item of equipment;

h _gli - the value of deep corrosion of the i-th element of the equipment.

Determine the total corrosion wear of the element using the formula:

where S _{and i} - the initial size of the i-th item of equipment;

S _fi - the actual size of the i-th item of equipment.

The type of corrosion is determined: surface and deep, and the characteristics of the form of corrosion damage. For surface corrosion, its type is defined as: uniform; uneven; spots; ulcerative. For deep corrosion, its type is determined as: pitting; subsurface; layered; intergranular; transcrystalline; electoral; in the form of rare cracks.

Corrosion coefficients are calculated depending on the corrosion hazard score, at which corrosion becomes more dangerous, according to the formula:

where q _ki - corrosion coefficient of the i-th structural material of the equipment;

μ _i - corrosion hazard score in accordance with the scale of corrosion resistance of the i-th structural material of the equipment;

β _i - degree of danger of corrosion destruction of the i-th structural material of the equipment, which is determined by the formula:

where γ is the confidence probability of the hazard assessment or the quantile of the normal distribution, which is selected from the range: 0.75÷0.99;

δ is the maximum allowable relative error in hazard calculation, which is selected from the range: 0.05÷0.3.

The degree of corrosive wear of the i-th element of equipment under the influence of corrosion, for example, of one of the walls of a housing made of one structural material, is determined by the formula:

- степень коррозионного износа i-го элемента оборудования;Where

- degree of corrosive wear of the i-th element of equipment;

q _ki - corrosion coefficient of the i-th structural material of the equipment;

ΔS _i - full corrosive wear of the i-th item of equipment;

S _fi - the actual size of the i-th item of equipment. The degree of corrosive wear, for example, of several elements of a piece of equipment made of various structural materials, is determined by the condition:

where n ^s is the degree of corrosive wear, for example, of several elements of a piece of equipment made from various structural materials;

- степень коррозионного износа каждого элемента оборудования при общем количестве элементов i=1…m.

- the degree of corrosive wear of each item of equipment with a total number of items i=1…m.

The method for determining the degree of wear of structural materials of equipment under the influence of corrosion using the numerical identification of corrosion of the structural material of equipment is illustrated by the following example.

The initial dimensions of the equipment structural element are set according to the technical documentation or by its direct measurement (Fig. 1.). During a corrosion inspection of a structural element after the operation of the equipment, the place of the corrosion process is determined, the value of corrosion wear is estimated by visual or instrumental detection of corrosion centers using known measurement methods by determining the penetration depth of surface corrosion into the material and deep corrosion (corrosion penetration depth) into the structural material. The actual size of the element is determined by the formula:

where S _phi is the actual size of the i-th item of equipment;

S _{and i} - the original size of the i-th item of equipment;

h _pi - the value of surface corrosion of the i-th item of equipment;

h _gli - the value of deep corrosion of the i-th element of the equipment. According to the scheme for determining the degree of corrosive wear, shown in Fig. 2, establish the full corrosive wear of the element using the formula:

where S _{and i} - the initial size of the i-th item of equipment;

S _fi - the actual size of the i-th item of equipment.

For surface corrosion, its type is defined as: uniform; uneven; spots; ulcerative. For deep corrosion, its type is determined as: pitting; subsurface; layered; intergranular; transcrystalline; electoral; in the form of rare cracks.

In accordance with the type of corrosion, a diagram of a typical type of corrosion damage, a characteristic of the form of corrosion damage is determined (Table 2, shown in Fig. 4). For example, continuous (uniform) corrosion has the form of corrosion damage in the form of surface roughness. In selective corrosion, for example, the deformable parts of the grains are subjected to corrosion damage, while the resulting corrosion damage zone is narrower than one grain and passes through several grains, and so on through other types of corrosion.

Numerical identification of corrosion of the structural material of the equipment is carried out by the corrosion coefficient. In table 1 shown in FIG. 3, the corrosion coefficients of the structural material are determined by statistical analysis and calculated depending on the corrosion hazard score, at which corrosion becomes more dangerous, according to the formula:

where q _ki - corrosion coefficient of the i-th structural material of the equipment;

μ _i - corrosion hazard score in accordance with the scale of corrosion resistance of the i-th structural material of the equipment;

β _i - degree of danger of corrosion destruction of the i-th structural material of the equipment, which is determined by the formula:

where γ is the confidence probability of the hazard assessment or the quantile of the normal distribution, which is selected from the range: 0.75÷0.99;

δ is the maximum allowable relative error in hazard calculation, which is selected from the range: 0.05÷0.3.

The calculation of the corrosion coefficients (3) depending on the corrosion score is identified by the risk of corrosion damage and expressed by the corrosion coefficients, which are given in table 1 (Fig. 1).

Thus, a ten-point scale of corrosion resistance (Table 1 in Fig. 3) is linked to diagrams of a typical type of corrosion damage, to types of corrosion and to the characteristics of the forms of corrosion damage to a structural material (Table 2 in Fig. 4), which ensures their identification with points Corrosion Hazard and Corrosion Index as shown in the Corrosive Wear Determination Chart (FIG. 2) and Table 2 shown in FIG. 4. It also shows that the degree of corrosive wear is determined depending on the total corrosive wear and the corrosion coefficient. The degree of corrosive wear of equipment in one case occurs when the size of the section of the element decreases, for example, when the walls are thinned due to continuous (uniform) or local (uneven) corrosion, according to Table 1, the corrosion coefficients of the structural material for hazard points from 1 to 3 are taken from 0.979 to 0.853. In the event that there is deep corrosion, which is the most dangerous in terms of the strength of the structural material, then the corrosion hazard score increases from 4 to 10, and the corrosion coefficients of the structural material are taken from 0.788 to 0.356. Thus, the higher the corrosion hazard score, the lower the corrosion factor is taken from Table 2 shown in FIG. 4 in accordance with a diagram of a typical corrosion attack pattern, a corrosion type, and a characteristic of the corrosion attack shape.

Then the degree of corrosive wear of an element of equipment under the influence of corrosion, for example, of one of the walls of a housing made of one structural material, is determined by the formula:

- степень коррозионного износа i-ro элемента оборудования;Where

- degree of corrosive wear i-ro of the equipment element;

q _ki - corrosion coefficient of the i-th structural material of the equipment;

ΔS _i - full corrosive wear i-ro of the equipment element;

S _fi - the actual size of the i-ro item of equipment. The maximum degree of wear of structural elements of equipment, for example, several walls of the body of a piece of equipment made of various structural materials, is determined by the most worn element according to the condition:

where n ^s is the degree of corrosive wear, for example, of several elements of a piece of equipment made from various structural materials;

- степень износа каждого элемента оборудования при общем количестве элементов от i=1…m.

- the degree of wear of each item of equipment with a total number of items from i=1…m.

As an example, Table 2 (Fig. 4) shows the distribution of some types of corrosion depending on the corrosion score, type of corrosion, characteristics of the forms of corrosion lesions in accordance with the schemes of their typical form. The graph (Fig. 5) shows the dependence of the degree of corrosive wear on the corrosion coefficient with a decrease in size, for example, the thickness of the element from S _i =20 mm to S _fi =17.25 mm. The graph (Fig. 5) shows that with a decrease in the value of the corrosion coefficient, the degree of corrosion wear increases.

The graph (Fig. 6) shows the dependence of the degree of corrosive wear when the element size is reduced from S _i =20 mm to S _fi =17.25 mm and with corrosion coefficients from 0.98 to 0.36. The graph (Fig. 6) shows that with a decrease in the size of a structural element, the degree of corrosion wear increases the more, the lower the value of the corrosion coefficient.

Thus, according to the proposed technical solution, the degree of corrosive wear of the equipment element is determined using numerical identification, expressed in terms of the corrosion coefficient.

The dimensionless corrosion coefficient takes into account the change in corrosion and corrosion resistance indicators in the material during degradation processes that appear under the influence of aggressive media, temperature and pressure drops at any stage of the equipment life cycle. The adoption of a dimensionless corrosion coefficient and corrosion distribution as a supplement to the indicators of corrosion and corrosion resistance in the material and their visualization increases the reliability of determining the degree of corrosion wear when predicting the resource and assigning terms for the safe operation of equipment. The proposed method makes it possible to determine the degree of corrosive wear at the site of the corrosion process according to the initial and actual dimensions of structural elements, taking into account complete corrosive wear during surface corrosion and (or) deep corrosion using the corrosion coefficient, since there are close analogues that provide for determining the degree of corrosive wear using corrosion coefficient, not found. The method has a relatively simple and natural implementation scheme, since an experimental-theoretical approach is used, the accuracy of assessing the corrosion wear of the equipment structural material is increased.

Claims (30)

1. A method for determining the degree of corrosive wear of structural elements of equipment at the site of the corrosion process, including measuring dimensions before and after testing or operation, characterized in that the site of the corrosion process is determined by visual or instrumental detection of corrosion centers that have appeared under the influence of surface corrosion close to uniform or under the influence of deep-seated corrosion, including pitting, spotting, pitting, subsurface, layer, intergranular, transgranular, selective and rare crack corrosion, measure the amount of surface corrosion of an equipment element, the amount of deep corrosion of an equipment element, determine the type of corrosion in according to the scale of corrosion resistance of the structural material, calculate: the actual size of the structural element according to the formula S _phi \u003d S _{and i} -h _pi -h _gli , where S _phi is the actual size of the i-th item of equipment; S _{and i} - the original size of the i-th item of equipment; h _pi - the value of surface corrosion of the i-th item of equipment; h _gli - the value of deep corrosion of the i-th element of the equipment; full corrosive wear of the element according to the formula ΔS _i \u003d S _{and i} -S _fi , where ΔS _i - full corrosive wear of the i-th item of equipment; S _{and i} - the original size of the i-th item of equipment; S _fi - the actual size of the i-th item of equipment; corrosion coefficients depending on the corrosion score, at which corrosion becomes more dangerous, according to the formula

where q _ki - corrosion coefficient of the i-th structural material of the equipment; μ _i - corrosion hazard score in accordance with the scale of corrosion resistance of the i-th structural material of the equipment; β _i - degree of danger of corrosion destruction of the i-th structural material of the equipment, which is determined by the formula β _i =γ ^2δ , where γ is the confidence probability of the hazard assessment or the quantile of the normal distribution, which is selected from the range: 0.75÷0.99; δ is the maximum allowable relative error in hazard calculation, which is selected from the range: 0.05÷0.3; the degree of corrosive wear of an equipment element made of one structural material, in accordance with the corrosion score, with a diagram of a typical type of corrosion damage, with a type of corrosion and a characteristic of the form of corrosion damage of a structural material according to the formula

Where

- degree of corrosive wear of the i-th element of equipment; q _ki - corrosion coefficient of the i-th structural material of the equipment; ΔS _i - full corrosive wear of the i-th item of equipment; S _fi - the actual size of the i-th item of equipment. 2. The method according to claim 1, characterized in that the degree of corrosive wear, for example, of several elements of a piece of equipment made from various structural materials, is determined by the condition

where n ^s is the degree of corrosive wear, for example, of several elements of a piece of equipment made from various structural materials;

- the degree of wear of each item of equipment with a total number of items from i=1…m.

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