What does sn8 ring stiffness mean? Double-layer pipes. PVC pipes and corsis pipes for sewerage

Modern sewer systems are made of polyethylene, polypropylene and their derivatives. Thanks to affordable prices, ease of installation, frost resistance and long service life, they have long replaced “traditional” drainage systems made of stone, concrete, wood and pipes made of various materials.

The main element of such a system is a two-layer pipe. The outer layer is profiled (corrugated), which allows the pipes to withstand high loads from the ground, and the inner layer is smooth, to ensure the least resistance to fluid flow.

Nowadays, sewer pipes are manufactured by a number of manufacturers and each assures of the exclusivity of their pipes and the uniqueness of the pipe profile. But, in fact, with the right selection, pipes from different manufacturers differ only in the material of manufacture and the method of measuring diameter - that is, in nuances.

The main parameters for choosing pipes are:

Ring stiffness

Ring stiffness is the maximum external load that a pipe can withstand without significant deformation. Denoted as SN. In the old days, pipes with ring stiffness SN2, SN4 and SN6 were produced, but now they are no longer produced and SN8 is considered the minimum ring stiffness. Pipes with this rigidity are used in the vast majority of projects. In the case of very deep burial of pipes or some soil features at the site that can lead to increased loads on the pipe, pipes with hardness SN16 are used.

Diameter measurement method

There are two approaches to measuring the diameter of a pipe: measure the internal diameter (denoted as DN/ID - internal diameter) and measure the outer diameter (denoted as DN/OD - outer diameter). Each manufacturer chooses a method convenient for itself. Therefore, you need to carefully look at exactly what approach is indicated in the project documentation.

Connection method

Basically, pipes are manufactured in two versions:

1. With bell

Pipes with an integrated or welded socket are completely ready for installation and do not require anything extra. At one end of the pipe there is a socket, at the other end there is an O-ring. It is enough to insert the pipe into the socket of another pipe and the connection is ready.

2. Without bell

Pipes without a socket can either be butt welded (if you have the appropriate equipment and specialists) or connected using a special coupling with two O-rings. But in this case, we must remember that couplings and rings for them are not free and often cost big money!

Sections:

Polytron (Polytron)

Made from block copolymer polypropylene. Measured by internal diameter (DN/ID).

Ring stiffness - SN8 and SN16.

The outer surface is corrugated, brick-colored. The inner one is smooth, light gray.

The connection is socket.

Corsis

Made from polyethylene (SN 8 and SN 16) and polypropylene (SN 16). Measured by outer diameter (DN/OD) and inner diameter (DN/ID).

The outer surface is corrugated, black. The inner one is smooth, light gray or light green or light blue.

Magnum (Magnum)

Made from polyethylene (SN 8 and SN 10) and polypropylene (SN 16). Measured by outer diameter (DN/OD).

Ring stiffness - SN 8, SN 10 and SN 16.

The outer surface is corrugated, black. The inner one is smooth, light gray or light yellow or light blue or black.

Connection - socket, coupling or butt welding.

Standard sizes of PROTEKTORFLEX pipes ®

Classification gravity pipes traditionally produced not according to the standard dimensional ratio ( SDR), and by ring stiffness class ( SN). Fundamental difference SDR And SN is that SDR is the geometric characteristic of the pipe (the ratio of the outer diameter of the pipe to the thickness of its wall), while SN- this is a mechanical characteristic.

Ring stiffness SN allows you to judge the properties of a pipe to resist soil pressure and is defined as the load on the pipe (kN/m2), at which the pipe is compressed by 3% of its diameter. Magnitude SN depends not only on the diameter of the pipe and the thickness of its wall, but also on the elastic modulus E material under compression.

The marking of a pipe for laying a cable line must include the diameter of the pipe D, wall thickness e, ring stiffness SN, ultimate gravitational force F 1MAX, long permissible temperature T, at which the ring stiffness is maintained for at least the entire service life of the cable.

Options D, e, SN And T must be controlled when supplying pipes to facilities under construction. Meaning F 1MAX may be required later - already at the stage of work on tightening pipes into the drill channel, when the operator of the HDD installation will control the actual tensile force F and interrupt the process of tightening the beam from N pipes in case F > 0,5 · N · F 1MAX in order to prevent pipe breakage.

Selecting the diameter and wall thickness of the pipe

Figure 1 shows the outer diameter pipe D and wall thickness e, inside which a cable is laid with an outer diameter d. According to regulatory documents, when choosing the outer diameter of pipes, you should adhere to the following rule:

Pipe wall thicknessedetermined during mechanical calculations based on basic information about the pipe laying conditions and is based on the concept of ring stiffnessSN.

Figure 1. Polymer pipe with cable: without soil pressure ( A), with soil pressure ( b)

The relationship between wall thickness and ring stiffness is established by the expression:

Where E- modulus of elasticity of the pipe material under compression.

Pipe wall thicknesse (mm) depending on pipe diameterD (mm) and ring stiffness SN(kN/m2)

External diameter pipesD , mm			Ring stiffnessSN , kN/m 2
			12	16	24	32	48	64	96
			Pipe wall thicknesse , mm
32*	PROTECTORFLEX® ST, BK, NG		-	-	2	2,2	2,5	2,7	3,1
40*			-	2,2	2,5	2,8	3,1	3,4	3,9
50*			2,5	2,8	3,1	3,4	3,9	4,3	4,8
63*			3,2	3,5	4	4,3	4,9	5,4	6,1
75*			3,8	4,2	4,7	5,2	5,9	6,4	7,2
90*			4,6	5	5,7	6,2	7	7,7	8,7
110			5,6*	6,1	6,9	7,6	8,6	9,4	10,6
125			6,3*	6,9	7,9	8,6	9,8	10,7	12
140			7,1*	7,8	8,8	9,6	10,9	11,9	13,5
160			8,1	8,9	10,1	11	12,5	13,6	15,4
180			9,1	10	11,3	12,4	14	15,3	17,3
200		PROTECTORFLEX® PRO, OMP	10,1	11,1	12,6	13,8	15,6	17	19,3
225			11,4	12,5	14,2	15,5	17,6	19,2	21,7
250			12,7	13,9	15,7	17,2	19,5	21,3	24,1
280			14,2	15,5	17,6	19,3	21,8	23,9	27
315			15,9*	17,5	19,8	21,7	24,6	26,8	30,4
355			18	19,7	22,3	24,4	27,7	30,3*	34,2*
400			20,2	22,2	25,2	27,5	31,2	34,1	38,5
450			22,8	24,9	28,3	31	35,1	38,3	43,4
500			25,3	27,7	31,5	34,4	39	42,6	48,2
560			28,3	31	35,3	38,6	43,7	47,7	54
630			31,9	34,9	39,7	43,4	49,2	53,7	-

*Produced in single-layer design

Note: The outer diameter of PROTEKTORFLEX® PRO pipes is indicated without taking into account the thickness of the protective coating.

There are two main ways to place pipes in the ground - laying them in a previously prepared trench (Figure 2 A) or pulling pipes into the ground into a prepared channel, most often performed by horizontal directional drilling (Figure 2 b). In both cases, the pipe calculation is based on the concept of ring stiffness SN, on the basis of which it is possible to determine not only the thickness of the pipe wall, but also the maximum tensile force of the pipe when it is pulled into the drilling channel.

Figure 2. Basic installation methods polymer pipes: trench ( A), HDD method ( b)

Selection of ring stiffness of pipes

The vertical pressure of the soil (and transport) on the pipe is a force applied to the pipe and tends to cause its ovality, however, the resulting “soil pushback” located on the sides of the pipe tends to return the cross-sectional shape of the pipe to the original round. Dense soil on the sides of the pipe is a factor that increases its mechanical strength.

Where q And SN are already measured in kN/m2, and E" S- soil rigidity factor, which is called the secant modulus of the soil (MPa).

Soil secant modulus E" S depends on the type of soil with which the pipe is filled and the degree of its compaction. As a rule, sand is used for these purposes, and then it is recommended to use the data in the table.

Backfill depth H, m	The condition of the sand with which the pipe is filled
	Uncompacted	Compacted manually	Compacted mechanically
	Soil secant modulus E" s, MPa
1	0,5	1,2	1,5
2	0,5	1,3	1,8
3	0,6	1,5	2,1
4	0,7	1,7	2,4
5	0,8	1,9	2,7
6	1,0	2,1	3,0

The vertical load on the pipe (kN/m2) consists of three components:

Where q r- load from the weight of the soil (kN/m 2 ); q AT- load from vehicles (kN/m 2 );

Load from the soil in the most unfavorable case, when the entire column of soil in height presses on the pipe N,

Where ρ r- specific gravity of soil (usually no more than 2 t/m 3 ); g = 9.81 m/s 2 - acceleration free fall; H- depth of the pipe underground (m).

The traffic load can be defined as

Results of calculating the maximum depth of pipes N are given in the table below. It can be seen that when laying pipes in trenches it is dangerous to use pipes with a ring stiffness of less than 8 and there is no need to use pipes with SN more than 64.

Limit depthH (m) when laying open method under the lawns/ squares / roads

SN, kN/m 2	Soil secant modulus E" s , MPa
	0	0,5	1	1,5	2	2,5	3
	Maximum laying depth H, m
4	0,4 / -	0,8/-	1,3/-	1,7/-	2,1/-	2,5/-	2,9/-
6	0,7 / -	1,1/-	1,5/-	1,9/-	2,3/-	2,7/-	3,1/-
8	0,9/-	1,3/-	1,7/-	2,1/-	2,5/-	2,9/-	3,3/-
12	1,3/-	1,7/-	2,1/-	2,5/-	2,9/-	3,4/-	3,8/-
16	1,7/-	2,2/-	2,6/-	3,0/-	3,4/-	3,8/1,7	4,2/2,4
24	2,6/-	3,0/-	3,4/0,7	3,8/1,8	4,3/2,5	4,7/3,0	5,1/3,6
32	3,5/0,9	3,9/1,9	4,3/2,5	4,7/3,1	5,1/3,7	5,5/4,2	5,9/4,7
48	5,2/3,8	5,6/4,3	6,1/4,8	6,5/5,3	6,9/5,8	7,3/6,2	7,7/6,7
64	7,0/5,9	7,4/6,4	7,8/6,8	8,2/7,3	8,6/7,7	9,0/8,2	9,4/8,6

Selection of ultimate gravitational forces

When laying using the HDD method, pipes are subjected to two types of influences: firstly, longitudinal tensile forces F, which arise when the pipe is pulled into the drilling channel; secondly, the vertical pressure of soil and transport already during the operation of the pipe. The choice of ring stiffness and wall thickness is determined mainly by traction forces.

Pipe tension force F creates friction forces arising due to the weighting of the pipe under the influence of soil piled on the pipe due to poor fastening of the walls of the drilling channel with drilling fluid (bentonite) or even the complete impossibility of fastening (quicksands, severe scenario).

Where qr- soil weight in kN/m2; DEKV- equivalent diameter of the pulled pipe string; µ - coefficient of friction of the polymer pipe on the ground (usually equal to 0.2).

Checking the admissibility of traction forces F arising when tightening the pipe (pl network of pipes) into the drill channel, is performed as follows

where 0.5 is the safety factor; N- number of pipes in the string (one or four); F1MAX is the ultimate tensile force of each pipe (kN), which can be found as

Where D And e- outer diameter and pipe wall (in mm); σ - yield strength of the pipe material (MPa).

Ultimate gravitational forces F1MAX are given in the table below

Ultimate pipe tensile forceF 1MAX (kN) depending on pipe diameter D (mm) and ring stiffnessSN(kN/m 2 )

External diameter pipes D, mm			Ring stiffness SN, kN/m 2
			4	6	8	12	16	24	32	48	64	96	128	192	256
			Ultimate Gravity Gain F 1MAX , kN
32	PROTECTORFLEX® ST, BK, NG		2,3	2,6	2,9	3,2	3,5	4,0	4,3	4,9	5,3	5,9	6,4	7,1	7,6
40			3,6	4,1	4,5	5,1	5,5	6,2	6,8	7,6	8,2	9,2	10	11	12
50			5,7	6,4	7,0	7,9	8,6	9,7	11	12	13	14	16	17	19
63			9	10	11	13	14	15	17	19	20	23	25	27	29
75			13	14	16	18	19	22	24	27	29	32	35	39	42
90			18	21	23	26	28	32	34	38	42	47	50	56	60
110			27	31	34	38	42	47	51	57	62	70	75	83	90
125			35	40	45	50	55	60	65	75	80	90	95	105	115
140			45	50	55	62	68	75	83	93	100	115	125	135	145
160			60	65	70	80	90	100	110	120	130	145	160	175	190
180			75	85	95	105	115	125	135	155	170	185	200	225	240
200		PROTECTORFLEX® PRO	90	100	115	125	140	155	170	190	205	230	250	275	295
225			115	130	140	160	175	195	215	240	260	290	315	350	375
250			140	160	175	200	215	245	265	300	320	360	390	430	465
280			180	200	220	250	270	305	330	370	400	450	485	540	580
315			225	255	280	315	345	385	420	470	510	570	615	685	735
355			285	325	355	400	435	490	535	600	650	725	780	870	935
400			365	410	450	510	550	625	675	760	820	920	990	1100	1180
450			460	520	570	640	700	790	855	960	1040	1160	1260	1400	1500
500			570	640	700	790	865	975	1060	1190	1290	1440	1550	1720	1850
560			710	805	880	990	1080	1220	1330	1490	1610	1800	1950	2160	2320
630			900	1020	1110	1260	1370	1550	1680	1880	2040	2280	2460	2730	2940

Note. When tightening a polymer pipe into the ground, it is recommended to limit the tensile force to a safe level of 0.5 F 1MAX .

The maximum length of pipe that can still be pulled into the drill channel without the risk of unacceptable stretching or even breakage,

Recommendations for selectionf" coefficient depending on the drilling scenario

The table below shows estimates of the maximum length of the drilling channel L HDD depending on the number of pipes and drilling scenario.

Estimates of the maximum length of the drilling channel L HDD(m) depending on the number of pipes N

SN, kN/m 2	N = 1			N = 4
	Scenario for canal drilling
	Heavy	Average	Easy	Heavy	Average	Easy
	Maximum length of drilling channel L HDD , m
4	38	190	303	26	131	209
6	43	214	342	29	147	236
8	47	235	375	32	162	258
12	53	264	423	36	182	291
16	58	289	462	40	199	318
24	65	324	518	45	223	357
32	70	352	564	49	243	388
48	79	396	633	55	273	436
64	86	428	685	59	295	472
96	96	479	766	66	330	528
128	103	517	828	71	356	570
192	115	574	918	79	395	632
256	123	617	987	85	425	680

This indicator is indicated in characteristics under each product on the site.

Ring stiffness of PE 100 and PE 80 pipes

This indicator is indicated incharacteristicsunder each product on the site e.

Polyethylene class	Standard dimensional ratio
	SDR41	SDR33	SDR26	SDR21	SDR17, 17.6	SDR13.6	SDR11
	Ring stiffness (SN), kN/m 2

PVC Pipes and KORSIS Pipes for sewerage

also have ring rigidity. This parameter is equal to 4 kN/m2, for is equal to 8 kN/m2.

Ring stiffness of the pipe ( SN) – this is one of the physical and mechanical indicators of pipe strength, characterizing the pipe’s ability to withstand external loads without significant deformation. Unit - kN/m2.

External loads include soil loads when filling a trench and transport loads (cars, trucks).

The value of the indicator is indicated in technical conditions to the pipe and installed by the quality control department manufacturing enterprise, as well as a product certification organization, where, based on a positive pipe test result, the manufacturer receives a certificate of conformity.

To determine the ring stiffness of a pipe, special testers of various brands are used, depending on the diameter (mm) and compression force of the pipe (kN).

To calculate the indicator, data on the load and deformation of the pipe at 4% deformation of the test sample and the length of the sample itself are required. The value is set as the arithmetic mean based on three values ​​of the ring stiffness of the test pipes obtained from the same batch. The final result is rounded down.

Ring stiffness is the main indicator of the quality of polymer pipes in underground construction gravity systems drainage and sewerage. The higher the value of this indicator, the more loads the pipe can withstand in the external environment.

The absence of this pipe indicator will be reflected primarily in the low cost of the product, due to the use of low quality materials in production.

The coiling method is used to produce pipes of special designs, including pipes of variable diameter and/or variable wall thickness; pipes with profiled walls and various materials layers; elastic hoses reinforced with a spiral supporting frame, and others. The advantages of winding technology mainly lie in the ease with which similar technological methods and equipment can ensure the production of products of various designs and dimensions.

Fig.1. Equipment for pipe production KORSIS PLUS

So, shown in Fig. 1 equipment, despite its complexity, allows you to move 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 specially profiled.

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