Instructions for determining the rate of metal corrosion of the walls of vessel bodies and pipelines at the enterprises of the Ministry of Petroleum and Chemical Industry of the USSR. Question: sample corrosion map of a vessel Determination of corrosion rate based on actual wall thickness measurements

ALL-UNION RESEARCH AND DESIGN AND TECHNOLOGICAL INSTITUTE
EQUIPMENT FOR OIL REFINING AND PETROCHEMICAL INDUSTRY

INSTRUCTIONS
to determine the rate of metal corrosion of housing walls
vessels and pipelines at M Inneftekhimprom enterprises
USSR

Volgograd - 1983

PURPOSE AND GENERAL PROVISIONS

1.1. This instruction is intended to determine the actual rate of metal corrosion of the walls of vessels and pipelines operated at enterprises of the USSR Ministry of Petroleum and Chemical Industry, in order to establish the frequency of their technical examination in accordance with the requirements of current rules and regulations.

1.3. If it is impossible or difficult to apply the methods set out in paragraph , the corrosion rate is determined approximately using witness samples or by assessing the corrosivity of the environment in relation to a given metal using corrosion probes.

1.4. The corrosion rate is determined for each vessel and pipeline of a process unit, line, or workshop. For a group of vessels or pipelines operating in a given technological installation, line, workshop in the same environment under the same operating conditions and material design, the corrosion rate is determined using a selected representative object.

1.5. The rate of metal corrosion of the walls of vessels and pipelines is subject to clarification in each case of a significant change in their operating conditions (working environment, temperature, pressure), affecting the corrosiveness of the working environment, or in the case of replacement of material design.

1.6. At each enterprise that owns the vessels, a list of vessels is compiled and approved by the chief engineer, indicating the rate of corrosion of the body metal. Information on the corrosion rate of pipelines is entered into the pipeline passport.

When special types of corrosion damage such as corrosion cracking, intergranular corrosion or delamination along the wall thickness are detected, information about this is also entered into the passport of the vessel or pipeline, and issues of further operation or repair of vessels and pipelines with such damage must be agreed upon with a specialized organization.

1.7. The rate of metal corrosion of vessel walls is monitored during each major overhaul, but not less frequently than the established frequency of technical inspections of vessels. The corrosion rate of pipelines is monitored during each inspection.

2. DETERMINATION OF CORROSION RATE FROM ACTUAL WALL THICKNESS MEASUREMENTS

2.1. The results of periodic measurements of the wall thickness of a vessel or pipeline serve as the basis for determining the rate of metal corrosion under operating conditions.

2.2. Wall thickness measurements are made using non-destructive testing methods or by drilling and measuring the wall thickness with a measuring tool. Preference should be given to ultrasonic thickness gauging.

2.3. If the results of wall thickness measurements using non-destructive testing methods are in doubt, then the measurement should be made by through drilling.

2.4. On vessels and pipelines operating in environments that cause intergranular corrosion or stress corrosion cracking, through drilling, followed by their sealing using arc welding methods, is not allowed.

2.5. The place and method of measuring the wall thickness of a vessel or pipeline is determined based on the results of their technical examination by technical supervision services, taking into account the characteristics of corrosion lesions in various parts of vessels and pipelines.

2.6. The locations of the measurement points, the measurement method and the measurement results must be documented in a corrosion map for the vessel or pipeline and stored in the passport (see maps and).

		Corrosion map			Sheet
An object		Company			City
Item no.	Inventory No.	Name of equipment			Geometric dimensions
Brand of material and information about protective equipment
Working environment process (composition and concentration of corrosive agents)			Working conditions	Inside		Outside

		Equipment sketch		Sheet
An object			Company	City
Item no.	Inventory No.		Name of equipment

2.7. Calculation of the corrosion rate of the walls of vessels and pipelines is made on the basis of at least two measurements of wall thickness according to the formula

Pe - corrosion rate in the controlled part of the vessel or pipeline under operating conditions, mm/year;

Δ S- difference in wall thicknesses at points during the period of control measurements, mm, indices 1, 2, ...,nindicate the numbers of control points;

Te - operating time between control measurements, days;

n- number of control measurement points (at least three) for each part of the vessel or for pipeline elements (pipes, bends, transitions).

Control points are selected in parts of vessels or pipeline elements most susceptible to corrosive wear.

2.8. The corrosion rate of a vessel or pipeline is taken to be the highest of the obtained corrosion rate values for each part of the vessel or pipeline element.

3. DETERMINATION OF THE IDA AND RATE OF METAL CORROSION BY WITNESS SAMPLES

3.1. In the absence of operating experience (when mastering a new technological process) and the absence of the necessary data on thickness measurements (short service life of the vessels, inaccessibility of the object for inspection and measurement), the rate and type of corrosion is determined on the basis of testing witness samples made of metal identical to the metal of the object.

3.2. The number of witness samples (at least three) at each installation point, their dimensions, installation location, as well as the test program and methodology are determined by the technical supervision service, corrosion group (laboratory), depending on the design of the facility, the composition of the working environment and operating conditions in individual elements of the object.

3.3. When developing a test method for witness samples, it is necessary to be guided by paragraph.p. , , , of these instructions.

3.4. If it is necessary to determine the susceptibility of an object’s metal to intergranular corrosion or stress-corrosion cracking, when developing a methodology and assessing the test results of witness samples, the following technical documentation should be used:

Resistometric-type sensors use 1-2 mm wire as electrodes from materials whose corrosion resistance needs to be tested.

Rice. 1. Airlock chamber with probe for gravimetric corrosion tests.

Rice. 2. Sensors for determining the corrosive aggressiveness of the environment (A - polarizing, B - resistometric)

Cylindrical samples are used as electrodes in polarization-type sensorsÆ 3 - 5 mm and up to 50 mm long, as well as plate samples collected in a package in such a way that the poles of the electrodes in the plates alternate in pairs, and the total area of the positive electrodes is equal to the area of the negative electrodes.

To obtain comparable results of metal corrosion rates on existing equipment and on samples, their surfaces must have the same roughness. The roughness characteristic of rolled steel can be approximately achieved by reverse shot peening or short-term etching of samples in aqua regia (I part HNO 3 + 3 parts HCl). Sharp edges on samples should be slightly dulled.

Before conducting corrosion tests, it is necessary to have the following information about the sample material:

Grade of material according to standards or specifications;

Product range (sheet, pipe, rod, etc.);

Chemical composition;

Condition of the material (degree of deformation and heat treatment modes);

Microstructure;

The results of standard test methods (for mechanical properties, for corrosion resistance - for example, on the MKK according toGOST 6032 -75) *.

_____________

* These indicators are determined if necessary.

When testing welded samples, you must additionally know:

Welding method;

Brand of welding materials;

Characteristics of technological operations;

Chemical composition of the weld metal.

For the production of samples, a cutting map must be drawn up, which indicates the locatione and the orientation of the sample relative to the workpiece and the texture of the rolled product, the direction and sequence of welds, sample numbers.

Samples for gravimetric corrosion tests are marked by branding or inscribing the following symbols with an electric pencil:

A symbol of the material grade is applied to one edge of the sample;

On the other side is the serial number of the sample.

Make sure that the valve is securely closed;

Carefully unscrew the probe cover and remove it together with the rod;

Install the sensor or cassette with samples onto the rod, screwing it in tightly until it stops (since under vibration conditions the cassette can turn away from the rod). Remove the insulating cover from the cassette with a control card indicating the installation location, cassette number, immersion depth, and note the time of installation of the probe. Place a mark on the rod indicating the location of the sample plane in the cassette.

Insert the cassette into the airlock chamber and close the chamber with a lid;

Carefully open the valve slightly and slowly fill the airlock chamber with the working medium. Make sure there are no leaks in the seals of the cover and oil seal;

Insert the probe into the working space of the apparatus or pipeline, orienting the plane of the samples in the cassette along the flow (along the mark) and secure the rod in the required position (with wire, if the probe does not have a locking device);

During the holding process of the samples, periodic monitoring of the probes is carried out for the absence of leaks in the seal of the cover and stuffing box, and the preservation of the orientation of the samples relative to the working flow;

At the end of the specified sample holding time, the cassette with samples is transferred to the airlock chamber. Move the rod to its original position smoothly, counteracting the pressure of the medium; release the rod only after making sure that it is on the stop. In this case, the operator should be slightly away from the direction of movement of the rod;

Close the valve. Products whose operating temperature poses a risk of burns for the operator must be cooled in the airlock chamber to 30 - 40 ° C;

Carefully unscrew the airlock chamber cover 0.5 - 1.5 turns and release the pressure;

Drain the product from the airlock into a special canister, remove the cassette with samples and pack.

Make a note on the control card about the time of removing the cassette from the workspace. Install the cover on the gateway body;

Immediately transfer samples in cassettes to the laboratory for processing, and enter the control card data into the “4H” card.

Corrosion measurements with resistometric or polarization type sensors are carried out using special electrical measuring instruments - corrosion meters according to the methods supplied with these devices.

Immediately upon completion of the corrosion tests, it is necessary to disassemble the cassette and pre-wash the cassette elements and samples from resinous and moistened loose corrosion deposits.

Method for removing corrosion productsfrom the surface of the samples depends on their composition and properties:

Loose corrosion products with poor adhesion are removed with a hair brush, wooden spatula or soft rubber band;

Dense deposits with poor adhesion are removed using a released blade (the hardness of the blade should be lower than the hardness of the sample) with a smoothing motion “towards you” at a slight angle to the surface of the sample, followed by treating the surface with a soft rubber band;

Brittle films of corrosion products are removed by chipping by lightly tapping the sample on a hard object, followed by treatment with a soft rubber band;

Brittle films of corrosion products with good adhesion (for example, sulfide scale) are removed using chemical or electrochemical etching methods (see RTM 26-01-21-68 “Guiding technical material. Methods for corrosion testing of metallic materials,” section 6).

If there are resinous deposits in corrosion products, it is advisable to alternate mechanical cleaning or chemical etching of samples with washing them in a solvent.

Note the data on the nature of the sediments in the “4H” map.

If necessary, corrosion products are collected for analysis in glass tubes with a stopper.

After removing corrosion products from the surface of the samples, the samples are degreased and dried as in step.

Weighing the samples after drying is carried out on the same analytical balances as in paragraph with an accuracy of 2 × 10 -4 g. Weighing results (m 2 ) are entered into the “4H” card.

d) Closing the airlock and removing the cassette

Rice. 3. Sequence of operations when working with a corrosion probe:

1 - working pipeline; 2 - mortise pipe; 3 - valve; 4 - airlock chamber; 5 - chamber cover; 6 - rod; 7 - cassette with samples.

Corrosion ratematerial determined by the resistometric method is calculated by the formula:

(4.4)

where Pr is the corrosion rate of the material, mm/year;

a- calibration coefficient of the measurement range in the corrosion meter;

d- initial diameter of the wire sample, mm;

(N 2 - N 1 ) - the number of scale divisions of the instrument between two measurements;

(t 2 - t 1 ) - time between two measurements, day.

The corrosion rate of the material, determined by the polarization resistance method, is calculated using the formula:

(4.5)

where Pp is the corrosion rate of the material, mm/year;

TO- polarization-type sensor constant, taking into account the electromotive force of the electrochemical corrosion process, the area and geometry of the sensor electrodes and dimensional coefficients;

Rn is the polarization resistance of the sensor in an aggressive environment, measured with a corrosion meter, Ohm.

Navigation maps must strictly correspond to the situation on the ground. Changes in the area occur all the time: new objects are built and installed on the shore, old objects are destroyed, new underwater obstacles appear, fairways are trawled and cleared of hazards, etc.

To maintain the map at the modern level, that is, to bring it into line with the terrain, it is necessary to correct the map, applying to it the changes that have occurred on the terrain. Corrections of cards can be carried out in various ways: a new original card is compiled and a new edition is printed from it, or the original card is corrected and an edition is printed from it, or each copy of existing cards is corrected by hand.

Therefore, all corrections, depending on the volume and method, are divided into a new edition, a major correction and a minor correction.

New editions issued if the volume of changes on the ground requires correction of 50% or more of the cartographic load of a given map.

With the release of a new edition of a map, all previously released editions of this map are considered obsolete and unusable.

A new edition of a chart is usually officially notified in a Notice to Mariners.

Major map correction is performed when the volume of changes that have occurred on the ground, although requiring corrections of less than 50% of the cartographic load of the map, is not practical to make them manually: the corrections are significant, and if they are made by hand, the map will be difficult to read and unusable.

Major corrections include corrections corresponding to the following changes in the area: moving noticeable coastal objects and setting up new ones, changing the characteristics of lighthouses and illuminated signs, new data on depths (based on the results of later measurements), changing the coastline (construction of a pier, erosion of the coast, etc.). d.).

Major corrections are made on one of the cards, which, after correction, is the original. The publishing original is photographed, a printing form is made and a circulation is printed. The new edition and extensive proofreading are carried out by specialist cartographers.

Minor map correction- correction of individual elements of the map, made by hand without compromising the clarity of the map.

Minor corrections are made by the navigation staff directly on the ships.

Materials for minor proofreading are:

Notices to mariners;

Radio navigation warnings (NAVIP);

Additions to sailing directions and other navigation manuals;

Summary corrections to sailing manuals.

On ships it is recommended to keep a special journal for correcting charts and manuals. All charts and manuals must be corrected immediately upon receipt of the Notice and in any case before setting sail. If for some reason this was not done in a timely manner, then when using the map during a voyage, you should check in the proof log or in the chart catalog whether there are Notices for this map, and if there are any, make corrections.

Corrections of a permanent nature are made in red ink or red ink in small print, following the conventions; corrections of a temporary or tentative nature are made in pencil. If there is a large amount of text proofreading, it is more convenient to retype the text of the Notice to Mariners and paste it into. appropriate place in the book.

Sometimes it is possible to cut out the proof text from the Notice to Mariners and paste it into the book. Correction of cards must begin with the last Notice, since subsequent ones may cancel the information included in the previous ones. If the Notice contains references to several maps, then the correction should begin with the largest scale maps, as this will facilitate subsequent corrections on small-scale maps; sometimes the latter cannot be corrected with sufficient clarity at all.

A note indicating the correction, indicating the number and date of the Notice, is made below the frame of the card, on the left side, in red ink or ink and signed by the person who made the corrections on the card.

On those lake and coastal navigation vessels on which systematic correction of charts and manuals due to specific navigation conditions is not always possible, charts and manuals should be submitted to navigation cameras for correction.