Welded joints of pipes of steam pipelines with a diameter of 130 mm or more with a wall thickness of 15-60 mm are most often performed on backing rings (Fig. 19), although recently they have been using the welding method without backing gauges with penetration of the weld root.

Rice. 19. Scheme of control of the welded joint of the steam pipeline.

At present, ultrasonic flaw detection is used as a mandatory method for checking the quality of these compounds, and transillumination by penetrating radiation is used as an additional method. For control, flaw detectors with an operating frequency of 1.8 MHz and prismatic detectors with an angle of β=40° are used. At an angle β=40°, it is possible to control the sensitivity by reflection from the backing ring and by position on the screen of the flaw detector it is easy to distinguish these reflections from the signals associated with defects.

The upper part of the weld with a wall thickness of up to 40 mm is controlled by a single reflected beam (Fig. 19, position B), and the lower part by a double reflected beam (position C). The control is performed in one step, i.e. the upper and lower parts of the seam are checked in one movement of the finder. Welds with a thickness of more than 40 mm are controlled in two stages: first, the root part of the weld is checked with a direct beam (position A), and then the upper part with a single reflected beam.

Sensitivity is adjusted using a corner reflector with an area of ​​5 mm 2 in the test sample. If the check is carried out in one pass of the finder, the reflector is performed only on the inner side of the test sample, and if in two passes, then on the inner and outer surfaces. When searching for defects, the sensitivity increases by 1.5 - 2 times, and when examining defects, the sensitivity is restored.

Welded joints in which no defects were found with an echo signal amplitude greater than from a reflector with an area of ​​5 mm 2 are considered fit and rated with a score of 3. In the future, only defects with signals of greater amplitude are taken into account.

Welded joints are rejected (scored with a score of 1) in the following cases:

· at least one defect is detected at a distance of more than 5 mm from the surface of the welded joint. Such defects are more difficult to detect than defects located near the surface;

· a defect was found in the root of the seam, from which the amplitude of the pulse or its range over the screen is greater than from a reflector with an area of ​​7 mm 2 ;

· a single defect was found in the weld root, the nominal length of which exceeds 10%, or a number of defects, the total nominal length of which exceeds 20% of the weld perimeter.

Welded joints with defects in the root of the seam, the amplitude of the exo-signal from which is greater than from a reflector with an area of ​​​​5 mm 2, but acceptable in terms of the above requirements, are evaluated with a score of 2 and are allowed for operation if the nature of the reflection from them has typical signs of reflections from cracks.

Similarly, the annular welded joints of the bottoms with the chambers of the collectors of steam boilers are checked.

Long-term practice of ultrasonic testing of welds in steam pipelines and collectors has shown reliable detection of dangerous defects such as cracks and lack of penetration, therefore, control is carried out without duplication by transillumination.

Ultrasonic testing without duplication by transillumination is also used to assess the quality of welds in steam locomotive boilers during their repair. The entire length of the seams, sometimes having a length of up to 15 m, is subjected to sounding. The inner part of the seam 18 mm thick is sounded with a direct beam, and the outer part is single-reflected, emitted by a finder with a prism angle β=50°. Weld sections in which, according to ultrasonic testing, defects with a nominal length of 5 mm or more are found, are subject to cutting, subsequent welding and control.

When building a country house, it is important to carry out all communications, which include heating, sewerage and water supply systems. When building a separate system, special attention is paid to the choice of pipes. Quite often, steel pipes are selected for pipelines, which are highly resistant to mechanical stress and the ability to withstand high temperatures. The main selection parameters are the thickness of the steel pipe and its diameter.

Main characteristics of steel pipes

Pipes according to the method of manufacture are divided into the following types:

• seamless;
• electrowelded.

Seamless pipes can be:

• hot deformed. The manufacture of such pipes is made from hot blanks by pressing;
• cold-formed. Pipes of this type, after passing through the press, are cooled, and it is in this form that they are finally formed.

Hot-formed pipes are characterized by a larger wall thickness, which gives the products additional strength.

Electric welded pipes are also divided into two main types:

• spiral stitch;
• straight seam.

Pipes with a straight seam practically do not differ from seamless ones in terms of their technical indicators.

Before the manufacture of spiral-seam pipes, metal sheets are twisted. This method of production allows to achieve increased tensile strength of pipes. Spiral pipes are used advantageously for laying gas and oil pipelines in areas with increased seismic activity.

The main characteristics of pipes are the following parameters:

• diameter, which is internal, external, conditional;
• wall thickness.

All pipes are manufactured in accordance with the requirements of GOST and can have the following typical dimensions:

• electric-welded pipes (basic GOST 10707-80) can have a diameter of up to 110 mm and a wall thickness of up to 5 mm. The main dimensions of the pipes and the corresponding thickness are presented in the table;

Diameter, mm	Wall thickness, mm
5 – 7	0,5 – 1,0
8, 9	0,5 – 1,2
10	0,5 – 1,5
11, 12	0,5 – 2,5
13 – 16	0,7 – 2,5
17 – 21	1,0 – 2,5
22 — 32	0,9 – 5,0
34 — 50	1,0 – 5,0
51 – 67	1,4 – 5
77 – 89	2,5 – 5
89 – 110	4 – 5

• seamless pipes of various types (basic GOST 9567-75). Manufactured standard sizes are presented in the table;

Hot formed pipes		Cold formed pipes
Diameter, mm	Walls, mm	Diameter, mm	Walls, mm
25 – 50	2,5 – 8,0	4	0,2 – 1,2
54 — 76	3 – 8,0	5	0,2 – 1,5
83 – 102	3,5 – 8,0	6 – 9	0,2 – 2,5
108 – 133	4,0 – 8	10 — 12	0,2 – 3,5
140 – 159	4,5 – 8,0	12 – 40	0,2 – 5
168 – 194	5 – 8	42 – 60	0,3 – 9
203 – 219	6 – 8	63 – 70	0,5 – 12
245 – 273	6,5 – 8	73 – 100	0,8 – 12
299 – 325	7,5 – 8	102 – 240	1 – 4,5
		250 – 500	1,5 – 4,5
		530 – 600	2 – 4,5

The diameters of steel pipes are most often indicated in millimeters, but in practice you can find pipes whose characteristics are presented in inches.

You can convert an inch diameter to a millimeter (or vice versa) using.

The video will help you understand in more detail the correspondence between inches and millimeters for various types of pipes.

The choice of pipes for communications

Steel pipes are mainly used for heating and water supply systems. To independently determine the most suitable diameter of a particular pipeline, you need to know the technical characteristics of the pipeline and the formula for calculation.

Selection of pipe parameters for water supply

The diameter of pipes for water supply or sewerage is determined taking into account the following parameters:

1. pipeline length;
2. bandwidth;
3. presence of rotations in the system.

The determining factor is the bandwidth, which can be calculated using the following mathematical formula:

Having determined the throughput, the diameter can be calculated using the formula or selected from the table below.

To avoid the complexity of mathematical calculations, you can use the recommendations of experts:

1. installation of the system riser must be equipped with pipes with a diameter of at least 25 mm;
2. the distribution of water pipes can be carried out with pipes with a diameter of 15 mm.

Additionally, when determining the diameter of the pipeline, you can focus on the relationship between the length of the pipeline and the diameter of the pipes, which is expressed by the following characteristics:

• if the total length is less than 10 m, then pipes with a diameter of 20 mm are suitable;
• if the length of the pipeline is in the range of 10 - 30 m, then it is more expedient to use pipes with a diameter of 25 mm;
• with a total length of more than 30 m, it is recommended to use pipes with a diameter of 32 mm.

Selection of pipe parameters for heating

When selecting pipes for heating, you must first determine the following parameters:

• temperature difference at the entrance to the system and the exit (denoted by Δtº);
• the speed of movement of the coolant through the system (V);
• the amount of heat required to heat a room of a certain area (Q).

Knowing these parameters, you can calculate using the mathematical formula:

In order not to carry out complex calculations on your own, you can use the ready-made table for selecting the diameter of the pipe of the heating system (you can read the instructions for using it).

When choosing a diameter, it is important to take into account that the indicator selected using calculations or tables cannot be less than the diameter of the outlet of the heating equipment.

After determining the optimal pipeline diameter, the pipe wall thickness is determined in accordance with the above tables. For a heating system, a steel pipe thickness of 0.5 mm is sufficient, and for a water supply system, 0.5 - 1.5 mm, depending on the conditions for the passage of the pipeline.

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Abstract on the topic:

Steam pipeline

Steam pipeline- pipeline for steam transportation. It is used in enterprises using steam as a process product or energy carrier, for example, in thermal or nuclear power plants, in factories of reinforced concrete products, in the food industry, in steam heating systems, and more. etc. Steam pipelines are used to transfer steam from the place of receipt or distribution to the place of steam consumption (for example, from steam boilers to turbines, from turbine extractions to process consumers, to the heating system, etc.) The steam pipeline from the steam boiler to the turbine at power plants is called "main" steam line, or "live" steam line.

The main elements of the steam pipeline are steel pipes, connecting elements (flanges, bends, elbows, tees), shut-off and shut-off and control valves (gate valves, valves), drainage devices, thermal expansion joints, supports, hangers and fasteners, thermal insulation.

The tracing is carried out taking into account the minimization of energy losses due to the aerodynamic resistance of the steam path. Connection of elements of steam pipelines is made by welding. Flanges are allowed only for connecting steam pipelines with fittings and equipment.

To avoid energy losses on steam pipelines, a minimum of shut-off and control valves is installed. On the main steam pipelines of power plants, stop and control valves are installed, which are the main means of switching on and controlling the power of the turbine.

The wall thickness of the steam pipeline, according to the strength condition, must be at least: where

P- design steam pressure, D- outer diameter of the steam pipe, φ - design coefficient of strength, taking into account welds and weakening of the section, σ - allowable stress in the metal of the steam pipeline at the design temperature of the steam.

Supports and suspensions of steam pipelines are arranged movable and fixed. Between adjacent fixed supports in a straight section, lyre-shaped or U-shaped compensators are installed], which reduce the consequences of deformation of the steam pipeline under the influence of heating (1 m of the steam pipeline lengthens by an average of 1.2 mm when heated by 100 °) [ source unspecified 458 days] .

To reduce the ingress of condensate drops into steam engines (especially turbines), steam pipelines are installed with a slope and supply the so-called. "condensation pots", which trap condensate formed in the pipes, and also install various separation devices in the steam path.

Horizontal sections of the pipeline must have a slope of at least 0.004 [ source unspecified 458 days] .

All elements of pipelines with a temperature of the outer surface of the wall above 55 °C [ source unspecified 458 days] , located in places accessible to service personnel, must be covered with thermal insulation. Thermal insulation also reduces heat loss to the atmosphere. Since at high temperature steel exhibits creep (creep) [ source unspecified 458 days] , to control the deformations of the steam pipelines, bosses are welded to the surface. These places must have removable insulation. The insulation of steam pipelines is usually covered with tin or aluminum casings.

Steam pipelines are a hazardous production facility and must be registered with specialized registration and supervisory authorities (in Russia - the territorial department of Rostekhnadzor). A permit for the operation of newly installed steam pipelines is issued after their registration and technical examination. During operation, technical examination and hydraulic testing of steam pipelines are periodically carried out.

Literature

• PB 10-573-03 Rules for the design and safety of operation of steam and hot water pipelines. Approved by the Decree of the Gosgortekhnadzor of the Russian Federation dated 11.06.2003 No. 90.
• NP-045-03 Rules for the Construction and Safe Operation of Steam and Hot Water Pipelines for Nuclear Facilities. Approved by resolutions of Gosatomnadzor No. 3, Gosgortekhnadzor No. 100 of 06/19/2003.
• Manual for the calculation of the strength of technological steel pipelines at P y up to 10 MPa. M.: CITP, 1989.

METHODOLOGY

calculation of the strength of the main pipeline wall according to SNiP 2.05.06-85*

(compiled by Ivlev D.V.)

The calculation of the strength (thickness) of the main pipeline wall is not difficult, but when it is performed for the first time, a number of questions arise, where and what values ​​​​are taken in the formulas. This strength calculation is carried out under the condition that only one load is applied to the pipeline wall - the internal pressure of the transported product. When taking into account the impact of other loads, a verification calculation for stability should be carried out, which is not considered in this method.

The nominal thickness of the pipeline wall is determined by the formula (12) SNiP 2.05.06-85*:

n - reliability factor for load - internal working pressure in the pipeline, taken according to Table 13 * SNiP 2.05.06-85 *:

The nature of the load and impact	Pipeline laying method	Load safety factor
		underground, ground (in the embankment)	elevated
Temporary long	Internal pressure for gas pipelines	+	+	1,10
	Internal pressure for oil pipelines and oil product pipelines with a diameter of 700-1200 mm with intermediate NPO without connecting tanks	+	+	1,15
	Internal pressure for oil pipelines with a diameter of 700-1200 mm without intermediate pumps or with intermediate pumping stations that operate constantly only with a connected tank, as well as for oil pipelines and oil product pipelines with a diameter of less than 700 mm	+	+	1,10

p is the working pressure in the pipeline, in MPa;

D n - outer diameter of the pipeline, in millimeters;

R 1 - design tensile strength, in N / mm 2. Determined by formula (4) SNiP 2.05.06-85*:

Tensile strength on transverse samples, numerically equal to the ultimate strength σ in the pipeline metal, in N/mm 2 . This value is determined by the regulatory documents for steel. Very often, only the strength class of the metal is indicated in the initial data. This number is approximately equal to the tensile strength of steel, converted to megapascals (example: 412/9.81=42). The strength class of a particular steel grade is determined by analysis at the factory only for a particular heat (ladle) and is indicated in the steel certificate. The strength class may vary within small limits from batch to batch (for example, for steel 09G2S - K52 or K54). For reference, you can use the following table:

m - coefficient of pipeline operating conditions depending on the category of the pipeline section, taken according to Table 1 of SNiP 2.05.06-85 *:

The category of the main pipeline section is determined during design according to Table 3* of SNiP 2.05.06-85*. When calculating pipes used in conditions of intense vibrations, the coefficient m can be taken equal to 0.5.

k 1 - reliability coefficient for the material, taken according to Table 9 of SNiP 2.05.06-85 *:

Pipe characteristics	The value of the safety factor for the material to 1
1. Welded from low pearlitic and bainite steel of controlled rolling and heat-strengthened pipes, manufactured by double-sided submerged arc welding along a continuous technological seam, with a minus tolerance in wall thickness of not more than 5% and passed 100% control for the continuity of the base metal and welded joints non-destructive methods	1,34
2. Welded from normalized, heat-hardened steel and controlled rolling steel, manufactured by double-sided submerged arc welding along a continuous technological seam and passed 100% control of welded joints by non-destructive methods. Seamless from rolled or forged billets, 100% non-destructive tested	1,40
3. Welded from normalized and hot rolled low alloy steel, manufactured by double-sided electric arc welding and passed 100% non-destructive testing of welded joints	1,47
4. Welded from hot-rolled low-alloy or carbon steel, made by double-sided electric arc welding or high frequency currents. Other seamless pipes	1,55
Note. It is allowed to use coefficients 1.34 instead of 1.40; 1.4 instead of 1.47 and 1.47 instead of 1.55 for pipes made by two-layer submerged arc welding or high-frequency electric welding with walls no more than 12 mm thick using a special production technology that makes it possible to obtain pipe quality corresponding to this coefficient of k 1

Approximately, you can take the coefficient for steel K42 - 1.55, and for steel K60 - 1.34.

k n - reliability coefficient for the purpose of the pipeline, taken according to Table 11 of SNiP 2.05.06-85 *:

To the value of wall thickness obtained according to formula (12) SNiP 2.05.06-85 *, it may be necessary to add an allowance for corrosion damage to the wall during the operation of the pipeline.

The estimated life of the main pipeline is indicated in the project and is usually 25-30 years.

To account for external corrosion damage along the main pipeline route, an engineering-geological survey of soils is carried out. To take into account internal corrosion damage, an analysis of the pumped medium is carried out, the presence of aggressive components in it.

For example, natural gas prepared for pumping is a slightly aggressive medium. But the presence of hydrogen sulfide and (or) carbon dioxide in it in the presence of water vapor can increase the degree of exposure to moderately aggressive or highly aggressive.

To the value of the wall thickness obtained according to the formula (12) SNiP 2.05.06-85 * we add the allowance for corrosion damage and we obtain the calculated value of the wall thickness, which is necessary round up to nearest higher standard(see, for example, in GOST 8732-78 * "Seamless hot-formed steel pipes. Range", in GOST 10704-91 "Steel welded longitudinal pipes. Range", or in the technical specifications of pipe rolling enterprises).

2. Checking the selected wall thickness against the test pressure

After the construction of the main pipeline, both the pipeline itself and its individual sections are tested. Test parameters (test pressure and test time) are specified in Table 17 of SNiP III-42-80* "Main pipelines". The designer needs to ensure that the pipes he chooses provide the necessary strength during testing.

For example: a hydraulic water test of a pipeline D1020x16.0 steel K56 is performed. Factory test pressure of pipes is 11.4 MPa. The working pressure in the pipeline is 7.5 MPa. The geometric elevation difference along the track is 35 meters.

Standard test pressure:

Pressure due to geometric height difference:

In total, the pressure at the lowest point of the pipeline will be more than the factory test pressure and the integrity of the wall is not guaranteed.

The pipe test pressure is calculated according to the formula (66) SNiP 2.05.06 - 85*, identical to the formula specified in GOST 3845-75* “Metal pipes. Hydraulic pressure test method. Calculation formula:

δ min - minimum pipe wall thickness equal to the difference between the nominal thickness δ and minus tolerance δ DM, mm. Minus tolerance - a reduction in the nominal thickness of the pipe wall permitted by the pipe manufacturer, which does not reduce the overall strength. The value of the negative tolerance is regulated by regulatory documents. For example:

GOST 10704-91 “Steel electric-welded pipes. Assortment". 6. Limit deviations in wall thickness must correspond to: ±10%- with pipe diameter up to 152 mm; According to GOST 19903 - with a pipe diameter of more than 152 mm for a maximum sheet width of normal accuracy. Clause 1.2.4 “The minus tolerance should not exceed: - 5% of the nominal wall thickness of pipes with a wall thickness of less than 16 mm; - 0.8 mm for pipes with a wall thickness of 16 to 26 mm; - 1.0 mm for pipes with a wall thickness over 26 mm.

We determine the minus tolerance of the pipe wall thickness according to the formula

,

Determine the minimum wall thickness of the pipeline:

.

R is the allowable rupture stress, MPa. The procedure for determining this value is regulated by regulatory documents. For example:

Regulatory document	The procedure for determining the allowable voltage
GOST 8731-74 “Seamless hot-formed steel pipes. Specifications»	Clause 1.9. Pipes of all types operating under pressure (the operating conditions of the pipes are specified in the order) must withstand the test hydraulic pressure calculated according to the formula given in GOST 3845, where R is the allowable stress equal to 40% temporary tear resistance (normative tensile strength) for this steel grade.
GOST 10705-80 “Steel electric-welded pipes. Specifications.»	Clause 2.11. Pipes must withstand the test hydraulic pressure. Depending on the magnitude of the test pressure, the pipes are divided into two types: I - pipes with a diameter of up to 102 mm - a test pressure of 6.0 MPa (60 kgf / cm 2) and pipes with a diameter of 102 mm or more - a test pressure of 3.0 MPa (30 kgf /cm 2); II - pipes of groups A and B, supplied at the request of the consumer with a test hydraulic pressure calculated in accordance with GOST 3845, with an allowable voltage equal to 90% of standard yield strength for pipes of this steel grade, but not exceeding 20 MPa (200 kgf / cm 2).
TU 1381-012-05757848-2005 for pipes DN500-DN1400 OJSC Vyksa Metallurgical Plant	With a test hydraulic pressure calculated in accordance with GOST 3845, at an allowable voltage equal to 95% of standard yield strength(according to clause 8.2 of SNiP 2.05.06-85*)

D Р - estimated pipe diameter, mm. For pipes with a diameter of less than 530 mm, the calculated diameter is equal to the average diameter of the pipe, i.e. difference between nominal diameter D and minimum wall thickness δ min:

For pipes with a diameter of 530 mm or more, the calculated diameter is equal to the internal diameter of the pipe, i.e. difference between nominal diameter D and twice the minimum wall thickness δ min: