Ring stiffness of polyethylene pipes. Pipes for external sewerage. Diameter measurement method

Double layer pipes used in non-pressure sewerage systems. The outer layer of the pipe is a corrugated surface, the numerous ribs of which create a high rigidity for resistance high loads. Inside the pipe is made of high quality polyethylene, which has high hydraulic properties and allows you to drain water without hindrance and without stagnation. The inner surface is even, so water does not accumulate in the depressions formed by the ribs. The presence of stiffeners favorably distinguishes this type drainage pipes from analogues and makes their choice a priority for installation in places with strong mechanical loads.

Two-layer corrugated pipes Korsis and Perfokor

Double layer corrugated pipes Corsis are made of polyethylene, which is impact resistant even when low temperatures. There are two main stiffness classes of corrugated two-layer pipes Korsis - this is SN6 and SN8, which have a ring stiffness of 6 kN/m2 and 8 kN/m2, respectively. In other words, pipes with a stiffness class of SN6 can be laid to a depth of up to 6 meters, and with a class of SN8 up to 8 meters. The minimum laying depth for both types of pipes is 1 meter. The pipe connection is hermetically sealed, it occurs by butt welding, or using a coupling and a sealing ring. The versatility of dimensions allows you to connect Korsis pipes with other elements drainage system, a big choice fittings and accessories allows you to create systems of any complexity.

To solve the problem of soil drainage under conditions of strong mechanical loads, the most effective solution there will be installation of two-layer drainage pipes Perfocor. The structure of the Perfocor pipe is similar to the structure of the Korsis pipes, corrugated on top and with a smooth layer inside. Their main difference is the presence of perforation, which is made in the form of slots and allows you to collect unwanted water accumulated in the soil and divert it to the right place ( drainage well, reservoir, ditch). The smooth inner surface prevents clogging of the pipe and ensures rapid water transport. There are several stiffness classes of two-layer pipes Perfokor: SN4, SN6 and SN8 - they are designed for a maximum laying depth of 4, 6 and 8 meters, respectively. There are both full-drainage pipes on sale, the holes of which are evenly spaced over the entire surface, and semi-drainage pipes, only top part which has holes, and the base is solid. The full-drain option is used in cases where it is necessary to lower the level ground water, and semi-drainage for collecting and draining perched water. Perfocor pipes gained the widest popularity in the improvement of personal plots, drainage of building foundations, as well as in road construction.

Two-layer corrugated pipe FD Plast

The range includes corrugated two-layer pipes F.D. Plast. The inner diameter is from 110 to 800 mm, and the hardness class is SN8-SN9. Made from polyethylene low pressure(HDPE) and are characterized by resistance to aggressive environment and durability. The depth of these pipes can be up to 15 meters. FD Plast corrugated pipes are of high quality at a relatively low price.

Price for two-layer corrugated pipe with socket SN8

Two-layer pipes Politek

In addition, double-layer corrugated pipes are on sale. Politek with inner diameter from 100 to 315 mm and hardness class SN8. They are made from polyethylene and have high ring rigidity, chemical resistance to alkalis and acids, low weight, and durability.

Pipes two-layer X-stream (Wavin)

The product range is also represented by two-layer pipes X-stream companies Wavin, which are made from polypropylene and have a stiffness class of SN8. Due to the high elasticity of X-stream pipes, they can withstand high dynamic and static loads, while maintaining complete tightness of the joints.

First of all, I would like to start my article with words of gratitude to the visitors of our site, everything that we do, we do for the convenience of the life of mankind and in particular you, the reader.

Talking about the superiority of polyethylene over reinforced concrete, and just iron, is endless. Over the past five years, the Internet has been full of ads about cheap polyethylene wells, tanks, and reservoirs, as well as about their durability.

The durability of polyethylene products is a certain postulate that cannot be discussed. The answer to the question: “Are PE products durable and can they last about 50 years in continuous work?”, will not keep you waiting long. - Yes!

Having dealt with the durability of PE products, I would like to dwell in more detail on the quality of products and, accordingly, the quality of the material from which some unscrupulous manufacturers manage to make a cheap product. I will tell you a recent incident that occurred when ordering a 100 m 3 horizontal tank. The customer, having contacted our company, was clearly upset by the price of the product of the PK NIS company, and spoke about the possibility of purchasing a product that is identical in all characteristics, but not in terms of ring stiffness. All attempts to explain the need for this type of characteristic for products that are used in the installed state, i.e. dug into the ground and experiencing external pressure, have not been successful. Then our specialists were tasked with clarifying the situation with the cheapness of competitors' products. As a result, a full technical work, which resulted in a document entitled - "Calculation of the strength of a horizontal tank with an internal diameter of 2200 mm, from spiral pipes of various profiles." This document presents calculations of capacities made of spiral pipes with a profile of 19 and 25, as well as a re-calculation for a pipe with ring stiffness SN2 and SN4.

Calculation of the strength of a horizontal tank with an internal diameter of 2200 mm from spiral pipes of various profiles.

Introduction

This calculation was made for fire tanks with a volume of 100 m3. The tanks are made of polyethylene spiral pipes with an internal (nominal) diameter of 2200 mm.

Due to the fact that the methods for calculating the strength of horizontal tanks are not sufficiently developed, and the tanks themselves are made of sewer pipes large diameter, based on the method of calculating the strength plastic pipes wires, set out in SP 40-102-2000 (Appendix D).

The purpose of the calculation is to check the fulfillment of the strength and stability conditions for pipes used for the manufacture of the tank body, with different wall profiles, and to formulate recommendations for the use of one or another type of pipe.

1. Initial data

According to the project, the tanks have outside diameter 2390 mm, which corresponds to a spiral pipe with an inner diameter of 2200 mm with a nominal ring stiffness of SN2.

In addition to this design solution the possibility of manufacturing tanks from pipes of the same internal diameter, but with a different type of profile will be analyzed: the so-called 19th and 25th profiles (Fig. 1), as well as helical pipes with a nominal ring stiffness of SN4, will be considered.

Rice. 1. Elements of profile 19 (a) and profile 25 (b) 1

For further calculations, it will be necessary to know the moment of inertia of the profile per unit length and the equivalent wall thickness of the pipe made from this profile. The moment of inertia of the profile per unit length of the box section - namely, helical pipes have such a profile - is easy to calculate using the following general formula:

where a is the profile width corresponding to the actual pipe wall thickness;

B - profile element height along the pipe axis;

H - profile wall thickness (see Fig. 2).

Rice. 2. Dimensions of the box profile element

The equivalent wall thickness is calculated using the following formula:

Based on this, the calculated pipe diameter is obtained:

where D i - internal diameter of the pipe; when calculating the tanks, the inner diameter is taken equal to 2200 mm: D i = 2.2 m.

The calculation will check the possibility of manufacturing design tanks from spiral pipes with four profile options. The geometric characteristics of each of the options are given below.

Profile 19

The dimensions of the profile element are shown in Fig. 1a. Using these dimensions according to formulas (1), (2) and (3), it is possible to calculate the moment of inertia of the profile and the corresponding equivalent wall thickness and design diameter:

Profile 25

The dimensions of the profile element are shown in Fig. 1b. We calculate the corresponding moment of inertia and the equivalent wall thickness:

Profile corresponding to ring stiffness SN2 and SN4

For a pipe with an internal diameter of 2200 mm and a nominal ring stiffness, such characteristics as the moment of inertia, the equivalent wall thickness and the design diameter are known. The values ​​of these quantities are given in Table 1.

Table 1. Calculation parameters of spiral pipes with a diameter of 2200 mm

The material of the pipes from which the design tanks are made is low-pressure polyethylene (HDPE). The following are some of the mechanical properties of polyethylene that will be used in the calculation. The values ​​​​of the quantities are taken on the basis of SP 40-102-2000: Appendix A and an example of calculation in Appendix D. Poisson's ratio was adopted according to the recommendations of clause 5.5 "Design instructions technological pipelines» CH 550-82.

Sandy soil with the following characteristics was adopted as the backfill soil:

According to the project, the tanks are buried by about 1.6 m along the axis. Accordingly, the distance from the top of the tanks to the ground surface can be taken equal to 0.4 m. The calculation does not take into account the presence of a layer of insulation on the surface of the tanks.

The calculation assumes the absence of groundwater at the construction site.

Since the tanks are completely located in the green zone, the traffic load is assumed to be zero.

2. Calculation technique

The calculation method is given in SP 40-102-2000, Appendix D. Here are the basic data and formulas necessary for the calculation. Calculation of tanks will be carried out according to the formulas for non-pressure pipelines. Conclusion on the suitability of pipes for underground laying is done on the basis of checking two conditions: strength (4) and stability of the pipe shell. The pipe is considered suitable only if both conditions are met.

The strength condition is reduced to determining the deformations caused by the soil pressure and the transport load and comparing them with the allowable deformations:

The strain components are defined as follows.

The maximum value of the tensile strain of the material in the pipe wall due to the ovality of the pipe cross section under the action of soils and transport loads:

where K σ - soil bed coefficient for bending stresses, taking into account the quality of compaction; let's take Kσ = ​​1.0 - with periodic control;
s - wall thickness;
D - pipe diameter;
Ψ - relative shortening of the vertical diameter of the pipe in the ground;
K zΨ = 1.0 - safety factor for the ovality of the pipe cross section.

The relative shortening of the vertical diameter is defined as the sum of three factors: earth pressure, traffic load and preliminary operations:

where Ψ gr - relative shortening of the pipe diameter under the action of soil load;
Ψ t - relative shortening of the pipe diameter under the action of the transport load; since in our case there is no traffic load, we can take Ψт = 0;
Ψ m - relative shortening of the pipe diameter, formed in the process of storage, transportation and installation; approximately, it can be taken depending on the stiffness of the pipe and the coefficient of soil compaction according to table 2.

Table 2. Values ​​of Ψ m

The ring stiffness of the pipe shell is determined by the formula:

All characteristics of the material and pipe required to calculate the ring stiffness are given in Sec. one.

A similar formula is used to calculate the long-term ring stiffness:

The relative shortening of the vertical diameter of the pipe under the influence of soil is determined by the following formula:

where K ok is a coefficient that takes into account the process of rounding an ovalized pipe under the action internal pressure; for non-pressure pipelines Kok = 1;

K τ - coefficient taking into account the delay in the ovality of the pipe cross section in time and depending on the type of soil, the degree of its compaction, hydrogeological conditions and the geometry of the trench, can take values ​​from 1.0 to 1.5; we will take for calculation the average value of 1.25;

K w - deflection coefficient, taking into account the quality of bed preparation and compaction; with periodic control take Kw = 0.11;

K W - coefficient taking into account the effect of the ring stiffness of the pipe shell on the ovality of the cross section of the pipeline: K W = 0.15;

K gr - coefficient taking into account the influence of backfill soil on the ovality of the cross section of the pipeline: K gr = 0.06;

where H 0 is the distance from ground level to the axis of the pipeline.

The degree of compression of the pipe wall material from the impact of external loads is calculated by the formula:

where q c \u003d q gr + q t is the total load on the pipeline. In our case, q c = q gr.

Permissible values ​​from formula (4) are calculated as follows:

where Kz - safety factor. Let's take Kz = 2.

After performing the strength test, the condition of stability of the pipe shell under the action of external loads is fulfilled:

where K ug - coefficient taking into account the effect of backfilling on the stability of the shell: K ug = 0.5;

K s - coefficient taking into account the ovality of the cross section of the pipeline; with Ψ ≤ 0.05, you can take K s = 1 - 0.7Ψ;

K zd - safety factor for the stability of the shell to the action of external loads: K zd = 3;

N = 1 at a depth of more than a meter.

3. Calculation results

preliminary calculations

Let's carry out some preliminary calculations, which will be common regardless of the type of profile used.

The load on the pipeline does not depend on the type of profile and will be the same in all options:

Also, using formulas (12) and (13), we can calculate allowed values deformations in the pipe walls:

Profile 19

First of all, according to formulas (7) and (8), taking into account geometric parameters profile defined in sec. 1, calculate the short-term and long-term ring stiffness of the pipe:

Taking into account the value of G 0 and the accepted coefficient of soil compaction (0.95) according to Table. 2 accept Ψ m = 0.04. The relative shortening of the vertical diameter under the action of soil pressure is calculated by formula (9):

And from here, using formula (6), we find the total value of the relative shortening of the diameter:

Now, using the formula GOTOBUTTON ZEqnNum351853 \* MERGEFORMAT (5), we can calculate the maximum tensile strain in the pipe wall:

and according to formula (11) - compression strains in the pipe wall:

Let us now check the stability of the pipe shell according to condition (14), having previously calculated the coefficient K ov 2:

Profile 25

Calculations for other types of profiles are completely similar to the above calculations, therefore, we will not further explain the progress of the calculations in detail, we will only present the calculations themselves.

Substituting the obtained values ​​into condition (4), we obtain:

that is, this pipe is suitable for strength conditions.

Checking the stability of the pipe sheath:

that is, the stability condition for of this type profile is not performed and it is impossible to use such a pipe for the manufacture of a tank.

Profile SN2

Short-term and long-term hardness:

Taking into account the value of G 0 and the accepted coefficient of soil compaction according to Table. 2 accept Ψ m = 0.04.
Relative shortening of the vertical diameter under the influence of soil:

Total relative shortening of the vertical diameter:

Tensile deformations in the pipe wall:

Compressive deformation in the pipe wall:

Substituting the obtained values ​​into condition (4), we obtain:

that is, this pipe is suitable for strength conditions.

therefore, the stability condition for this type of profile is satisfied, and a pipe with this type of profile can be used to manufacture a tank.

Profile SN4

Short-term and long-term hardness:

Taking into account the value of G 0 and the accepted coefficient of soil compaction according to Table. 2 accept Ψ m = 0.04.

Relative shortening of the vertical diameter under the influence of soil:

Total relative shortening of the vertical diameter:

Tensile deformations in the pipe wall:

Compressive deformation in the pipe wall:

Substituting the obtained values ​​into condition (4), we obtain:

that is, this pipe is suitable for strength conditions.

Checking the stability of the pipe sheath:

therefore, the stability condition for this type of profile is satisfied, and a pipe with this type of profile can be used to manufacture a tank.

Conclusion

It can be seen from the calculations that it is permissible to use ordinary serial pipes with nominal ring stiffness SN2 and SN4 for the manufacture of design tanks. The use of profiles of type 19 and 25 is impossible, due to the fact that a pipe of a design diameter with such a profile does not satisfy the condition of shell stability under the design load from the backfill soil.

Despite the fact that, judging by the size, in the design for the manufacture of fire tanks, pipes of ring stiffness SN2 are laid, and the fact that these pipes withstand the test for strength and stability, it is recommended to increase the nominal ring stiffness of pipes to increase the strength reliability of these very critical products. to SN4.

Moscow, 2013.

_______________________________________________________

The calculation was provided by the chief engineer of PK NIS LLC: Karpenko D.N.

1 In fig. 1 vertical axis of the profile element parallel to the main axis of the pipe.

2 It should be noted that here and below the total shortening of the vertical diameter of the pipe Ψ is somewhat greater than 0.05, for which the formula used to calculate Kow is valid, however, this excess is small.

The winding method is used for the production of pipes of special design, including pipes of variable diameter and/or variable wall thickness; pipes with a profiled wall and different material layers; elastic hoses reinforced with a spiral carrier frame, and others. The advantages of winding technology mainly lie in the ease with which the same type of technological methods and equipment can provide the production of products that are diverse in design and dimensions.

Fig.1. Equipment for the production of pipes KORSIS PLUS

So, shown in Fig. 1 equipment, despite its complexity, allows you to switch from the production of a pipe with a diameter of 600 mm to the production of a pipe with a diameter of 2000 (3000) mm in a matter of minutes. In this case, one pipe can have a smooth wall of almost any thickness, and the next one can have a wall profiled in a special way.

Polymer pipes with a profiled wall designed for underground construction non-pressure systems sewerage, sewers and drainage, the main requirement for which is ring stiffness. The design of such pipes allows saving up to 2/3 of the material compared to a smooth-walled pipe of the same ring stiffness.

Corrugated sewer pipes are now used more often than concrete or metal. They have the same high reliability and durability in operation. And they are much easier to install due to their low weight. Fewer workers involved in installation pipeline systems.

Types of plastic pipes

There are two-layer and single-layer corrugated pipes. Two-layer products are more durable and more easily tolerate ground pressure. If installed in the sewer underground.

In turn, two-layer sewer elements are classified according to the materials of manufacture:

• Polyvinyl chloride products (PVC). Used in industrial sewers. In the drains of private houses.

• Polypropylene (PP). Of these, drainage, storm or external system. Excellent resistance to temperature fluctuations.

• Low pressure polyethylene (HDPE). Excellent for installation and temperature changes.

For sewer pipes, polymer products are an excellent conductor. Of these, they construct drainage systems, lay central sewers. There are several varieties polymer products. They differ in diameters. For example, 400 mm., 315 mm., 160 mm. These are the most requested options for installations. different systems.

Korsis SN8

The Korsis SN8 pipe is suitable for the manufacture of a non-pressure (gravity-flowing) system. The product is made corrugated and two-layer. Top quality. PP pipes are durable and easy to install. They produce elements in Russia, but at the same time they use Italian technology.

Scope of Korsis

Corrugated pipe SN8 is made in black on the outside and white or blue on the inside. It is made of two layers: external and internal. The outer layer is a protection against deformation under mechanical stress. The inner layer is made smooth and does not allow dirt to accumulate on the walls.

Two-layer pipe SN8 is used for following works:

1. When conducting sewer structures.
2. As access elements for the restoration of roads in the soil.
3. At removals of thawed and storm waters.
4. For installation of drainage systems.

Characteristics of Korsis

PP sewer elements are made of polyethylene or polypropylene. This is different types pipes, although they are not much different. There are differences in the ring stiffness (SN). Polypropylene Korsis has a hardness of 4, 6 or 8. And polypropylene Korsis PRO has a hardness of 12 or 16. In addition, there are differences in operating and installation temperatures. Polyethylene withstands 0-+40. And polypropylene 0-+95.

PP SN8 pipe has standard sizes- from 6 to 12 meters. Two-layer polyethylene SN8 has a low stiffness class. It is used for the manufacture of storm or sewer structures. Laying is carried out to a maximum depth of 10 m.

Plastic SN8 is a very impact resistant pipe. It is resistant to chemicals and mechanical influences. Simplicity in laying is ensured by the possibility of bending the elements. Because plastic is flexible. Corrugated products are easily transported by car and stored anywhere. They fit easily into a standard car body without weighing it down too much.

Variety by size

Double layer plastic elements SN8 are subdivided into standard sizes. Most often they are characterized by the outer diameter: from 120 to 1200 mm.

In private buildings, pipelines using corrugated elements are laid in trenches. During installation, it is recommended to follow established rules:

1. Before laying the flushing pipe into the sewer, each section of it is carefully checked for defects and shortcomings.
2. Work is carried out at certain temperature- not less than +15 degrees.
3. Before placing pipes along the trench, they must be placed along the perimeter of the ditch. It should be distributed in the direction that is a slope towards the highway.

At the sockets and the ends of the elements, everything is thoroughly cleaned. So that there is no dirt on them at all. O-rings are required to install corrugated pipes. This is important feature installation that should not be forgotten.

Such designs have a ribbed surface that increases their strength. Due to this form, corrugated pipes are recommended to be laid on complicated sections of trenches. Which are inside roads or in places with strong ground pressure. The high strength and elasticity of the two-layer drainage elements makes it possible to use them even in places with bends and sharp turns.

The smooth surface of the product (internal) eliminates the appearance of mud growths in the system. This further increases the life of the pipelines.

Even before starting work, you should find out: what kind of load the selected plastic element will withstand. This indicator depends on the hardness. At SN8 it is average. Withstands more than 12 kilonewtons per square meter.

Increased pipe cross-sections

To equip highways, rain or ground outlets drainage products with large sections are used. For example, pipe SN8 400 mm. It is acceptable to use 315 and 160 mm. But it must be understood that the pipe 160 SN8 is a single-layer type. And it is better to use such a design under more benign conditions.

Elements in 400 mm. used at great depths. They are even allowed to be installed not in trenches, but in open ditches. Such systems perfectly tolerate both low and high temperatures. Are not exposed to chemical influences. Installation is permissible even in the ground, where there are slopes and relief thresholds. Plastic is able to adapt to any bends. In this case, the products will not lose their qualities.