(1) Purpose:
The direct-buried corrugated compensator is mainly used for the axial compensation of the direct-buried pipeline, and has the ability to resist bending, so the influence of pipeline sinking can be ignored. The product has the characteristics of large compensation and long life.
(2) Instructions for use:
The direct-buried corrugated compensator is mainly suitable for axial compensation, and has superb bending resistance, so the influence of pipeline sinking is not considered. The direct-buried corrugated compensation shell and guide sleeve realize free expansion and contraction compensation, and other performances are the same as ordinary corrugated compensators.
(3) Selection and installation:
3.1 Calculation of the maximum installation length of the pipeline
Directly buried pipelines with compensation should be located at two high fixed points, one is at the end of the straight pipe section, and the other is at the branch of the pipeline. There is no need to set a fixed point between the two compensators of the long straight line without branch, and the fixed point can be played by the natural "stagnation point" formed by the pipeline. The stagnation point is the fixed point of the pipeline between the two compensators. When the pipe diameter is the same and the buried depth is the same, the distance between the stagnation point and the two compensators is the same. The distance between the brace compensator (including the natural compensator at the corner) and the fixed point shall not exceed the maximum installation length of the pipeline Lmax. The maximum installation length of the pipeline is defined as the length from the fixed point to the free end (compensator), under this length The friction force generated shall not exceed the corresponding elastic force under the allowable stress of the pipeline.
Lmax is calculated as follows:
The maximum installation length Lmax of common pipes. The comprehensive influence of the hoop stress produced by the internal pressure of 16kgf/cm2 should be considered.
3.2 Design calculation of fixed bearing
With two pipeline branches and a corner pipeline plane on the main line, the arrangement of the compensator should meet the condition of Ln<Lmax. The thrust of stagnant points G1 and G2 is zero, so there is no need to set fixed supports at this point, but in order to prevent uneven backfill, inconsistent buried depth and irregularity of the prefabricated insulation pipe shell may cause stagnant points Therefore, it is necessary to install supports for the pipe branches G1 and G2 at the stagnant position. Taking G1 as an example, the axial thrust can be calculated as follows:
F1=Pb2+L2f-0.8(Pb3+L2f)
Where F1- the horizontal thrust of the fixed support G1, kgf; f- the friction force per unit length of the pipe, Kgf/m
Elastic force of Pb2-B2 expansion joint, Kg; Elastic force of Pb3-B3 expansion joint, Kgf
The stiffness of k2-B2 expansion joint, Kgf/mm;
△L2-B2 Expansion joint compensation amount, mm;
L2-distance from expansion joint to G1, m;
Suppose a branch, such as the branch connected from G2, has a compensator B. Then, G2 is also subjected to lateral thrust, as shown in F2(y), when L5 is very short (L5 should also be very short in actual layout), then the magnitude of the lateral force F2(y) is:
F2(y)=Pn*A5+Pb5
Where Pn- pipeline working pressure, Kgf/cm2
The effective area of A5-B5 expansion joint, cm2;
The elastic force of Pb5-B5 expansion joint kgf.
The fixed bearing G3 is also at the stagnant point. From the friction between the pipe and the soil, this point is also affected by two equal and opposite directions, but it should be noted that this point is also affected by the blind plate force at the corner. Function, considering the effect of stagnation point drift, the thrust of the fixed bearing G3
F3=1.2Pn*A4
Where F3- is the horizontal thrust acting on the fixed support G3, Kgf;
Pn- pipeline working pressure, Kgf/cm2;
The effective area of A4-B4 expansion joint, cm2.
3.3 Selection and calculation of compensator
Due to the influence of soil friction, the actual thermal elongation of directly buried pipelines is smaller than that of pipelines laid overhead and in trenches.
Elongation during overhead and trench laying: α·△t·L
When laying directly, the reduction of thermal elongation due to soil friction:
The actual thermal elongation is:
In the formula, E-steel tube elastic modulus, kgf/cm2;
The coefficient of linear expansion of α-steel pipe is 0.0133mm/m℃;
△t-pipe temperature difference;
A, f- the same formula ①;
L-The distance between two fixed points (maximum installation length) m.
In actual work, the thermal elongation of the directly buried pipeline adopts the simplified algorithm of Danish Moller Company.
The symbol in the formula is the same as the above formula.
After calculating the actual thermal elongation according to the formula ② or ③, select the corresponding compensator according to the series table.
3.4 Installation
Direct-buried expansion joints (not including one-time direct-buried) should be installed with two post-annual retainers (as shown in the figure below), and the wall thickness of the retainer should not be less than the wall thickness of the pipeline. The purpose of setting retainer 1 is When the pipe is heated and expanded, soil, sand, etc. enter within the A size range. The sizes in the figure are:
When the direct-buried corrugated compensator leaves the factory, all exposed surfaces have been painted with anti-rust paint twice. Other requirements for the direct-buried corrugated compensator and its direct-buried pipeline are:
(1) When the insulation pipe is buried in the ground, the surrounding area shall be filled with sand with a grain size of less than 20 mm, and then covered with the original soil. The thickness of the filled sand shall not be less than 200 mm.
(2) The buried depth of the top of the insulation pipe is generally not more than 1.2 meters, but it should also be as far as possible not to be less than 0.7 meters. The insulation pipe can be directly buried under various pipelines.
(3) As shown in the figure, except for point A, the rest are insulated, because when the pipe expands, the point A is not insulated and will not cause significant heat loss. Also due to the role of the retainer, the direct-buried compensator can be directly buried under the roadway.
(4) The direct-buried compensator does not need to be installed cold tightly, nor does it need to be welded after the entire line of steel pipes are connected and then cut off and the expansion joints and other long pipelines. Direct-buried expansion joints are used without guide brackets.
(5) When installing, pay attention to ensure that the direction of the flow guide sleeve is consistent with the flow direction.
(6) The medium in the compensator should be treated to remove free oxygen and chloride ions, and the content of chloride ions should not exceed 25PPm.
(7) The compensator allows a system hydraulic test that does not exceed 1.5 times the nominal pressure.
(8) After the compensator is installed, the two ends of the pipeline should be fixed before the system water pressure test to prevent the internal pressure from stretching the compensator.
