1. Preface
After the heat supply pipeline is installed and put into operation, measures shall be taken to compensate the thermal elongation of the pipeline due to the heating of the pipeline by the heat medium. Compensation methods mainly include the following: natural compensation, casing type compensator, bellows compensator, square or spherical compensator, etc. This paper mainly discusses the comparison between the commonly used sleeve type compensator and the emerging rotary type compensator in engineering cost and operation safety.
2. Brief introduction of sleeve type compensator
Sleeve type compensator is a kind of compensator suitable for straight laying pipeline, which is used to compensate the thermal elongation of pipeline between fixed supports. For the pipeline with sleeve type compensator, the thrust exerted on the fixed support is caused by the following aspects: (1) The horizontal thrust Pg ? m caused by the friction on the sliding support
Pg?m= μ qL
Where, q - the weight per unit length of pipe section is calculated Φ five hundred and twenty-nine × 7 Rock wool insulation, water filling q ＝ 367.92 × 9.8N?m；
μ－ Friction coefficient, steel to steel μ＝ 0.3, steel and PTFE plate μ＝ 0.1；
L － length of calculated pipe section, m;
(2) Thrust generated by friction of sleeve type compensator;
(3) Horizontal thrust caused by unbalanced internal pressure, such as sleeve type compensators set at both ends of the fixed support, but their pipe diameters are different; Or one end of the pipe section at both ends of the fixed support is provided with valves, blanking plates, elbows, etc., while the other end is provided with sleeve type compensators; When the pipeline is subjected to hydrostatic test or operation, unbalanced axial force of the pipeline will occur.
3. Introduction to GSJ-V Series Rotary Compensator
GSJ-V series rotary compensator is composed of rotary cylinder and elbow, and its combination methods are Π The compensation principle is to form a couple through double rotating cylinders and L arm, so that a pair of forces with equal size and opposite direction can rotate around the center of Z axis by the arm, so as to achieve the absorption of thermal elongation generated by pipes on both sides of the couple.
For GSJ-V series rotary compensator, the thrust on the fixed support is generated by the following aspects: [3]
(1) Horizontal thrust Pg ? m due to friction on sliding support
(2) Thrust due to friction of rotary compensator.
The total length of the steam pipe network is 660m, the pipe diameter is DN500, the working pressure is 1.0MPa, the temperature is 220 ℃, the fixed support is set, the sliding support is set every 15m, each compensator is set with two guide supports, and there are 46 sliding and guide supports in total.
Fixing bracket G2, G3, G5, G6 with sleeve type compensator under force F
F=Pc＋Pg?m1－0.7［PX＋Pg?m2 × （L2＋L3/2）］＋P × f
＝Pc＋ μ qL1-0.7［A ×α× E × I × △ t/L short boom 2 × 105+ μ qcos α× （L2+L3/2）］＋P × f
＝31 × 103＋0.1 × three hundred and sixty-seven point nine two × nine point eight × 100-0.7［12 × zero point zero one two × one point nine zero five × one hundred and five × thirty-nine thousand one hundred and six × 210/102 × 105＋0.1 × three hundred and sixty-seven point nine two × zero point seven zero seven × （10＋10/2）］＋160 × three point one four × 51.52/4
＝31000＋36056－0.7 × （22528+3902）＋333122＝381677N≈38.2T
Fixing bracket G9
F9＝Pc＋Pg?m1＋P × f＝31000＋0.1 × three hundred and sixty-seven point nine two × nine point eight × 120＋333122
＝407389N≈40.8T
Force of fixed support G8 F8 ＝ Pc1 ＋ Pg ? m1-0.7Pc2 ＝ Pc1 ＋ μ qL－0.7Pc2＝31 × 103＋0.1 × three hundred and sixty-seven point nine two × nine point eight × 120－0.7 × thirty-one × 103＝52567N≈5.3T
Fixed support G4, G7 stress F4, 7 ＝ Pc － 0.7Pc ＝ 31 × 103－0.7 × thirty-one × 103＝9300N≈1T
Where: F － horizontal thrust borne by fixed support, N;
Pc - friction force of sleeve type compensator, N;
Pg ? m - friction force generated by sliding support, N;
Px - elastic force of elbow, N;
A-coefficient A=3 (n3+4n2+3)/n (n+1),
N=L long arm/L short arm;
E － elastic modulus, MPa;
I - inertia moment of pipe, cm4;
P － hydrostatic test pressure, 1.6MPa;
F - internal sectional area of pipe, cm2.
From the above calculation, as long as there is blind plate force Pf ＝ P × F. The force on the fixed support is very large.
Pipe installation rotary compensator
Horizontal thrust borne by the pipe fixing support for installing the rotary compensator:
Force of fixed support G3 F ＝ Pg ? m ＋ M/Lcos（ α/ 2）＝0.1 × three hundred and sixty-seven point nine two × nine point eight × 180＋48830÷（2 × 0.974）
＝64901＋25066＝89967N≈9T
Where: M － rotary friction torque of rotary compensator, N ? m;
Couple arm of L-Π combined rotary compensator, m;
α－ Corner, sin（ α/ 2）＝0.012 × one hundred and eighty × （220－10）/L
According to the above calculation, the force of installing sleeve type compensator to wrap the blind plate of the pipeline accounts for 33.3/40.8 ＝ 82% of the horizontal thrust that the support bears. If the blind plate force can be eliminated, the fixed support will be very small and the project cost will be greatly reduced. The pipe installed with the steering compensator eliminates the blind plate force, and the fixed support bears only 9T of horizontal thrust. The ratio of the two is 9/40.8 ＝ 22.0%
The concrete cost of the fixed support is calculated as follows:
Concrete volume of 50T fixed support:
V＝1 × five point four × 2＋2.5 × zero point eight × 0.8＋1 × zero point eight × 0.8＋1.5 × zero point eight × 0.8＋2.2 × zero point eight × 0.5＝10.8＋1.6＋0.64＋0.96＋0.88＝14.88m3
Concrete volume of 10T fixed support:
V＝0.6 × two point nine × 2＋0.6 × zero point five × 0.8＋1.7 × one point two × 0.8＝3.48＋0.24＋1.63＝5.35m3
Concrete volume of 6T fixed support:
V＝0.6 × two point nine × 2＋0.6 × zero point five × 0.8＋1.7 × zero point eight × 0.8＝3.48＋0.24＋1.09＝4.81m3
Concrete volume of 1T fixed support:
V＝1.5 × one point five × 1＋1.7 × zero point eight × 0.8＝2.25＋1.09＝3.34m3
Concrete volume of sliding and guide support:
V＝0.75 × one point five × 1.5＋1.25 × zero point four × 0.4＋0.5 × zero point four × 0.4＝1.67＋0.2＋0.08＝1.95m3
From the above calculation, it can be concluded that the civil construction cost of the pipeline project with rotary compensator is 24% less than that with sleeve compensator (1 － 14.34/18.86 ＝ 24%).
4. Comparison of advantages
(1) The new GSJ-V rotary compensator technology is adopted. Compared with the traditional corrugated compensator and sleeve compensator, it has large compensation amount, superior sealing performance, long-term operation without maintenance, and saves investment costs. Moreover, it is easy to install, especially for the working conditions with complex terrain, the position can be flexibly adjusted according to the site conditions.
For example, in the heat supply trunk line project of Pingdingshan High tech Zone, the pipeline needs to cross the road. The location of the pipeline is very small, and there are water, industrial pipelines (6), cables, and natural gas pipelines around. To avoid these obstacles in the project, the compensation amount of the heat supply pipeline must also be considered. In this case, we decisively adopted GSJ-V rotary compensator to solve the above problems. In addition, the pipeline of this project needs to pass through the houses in the urban-rural junction, and the cost of house demolition is particularly high. The application of rotary compensator makes the pipeline not on a branch line, so a group of rotary compensators are designed according to the pipeline route to avoid disputes and increase unnecessary costs. However, the traditional corrugated compensator and sleeve compensator must be installed in a straight line, which has too much limitation, and the square compensator has limited compensation capacity, so it is necessary to apply and promote new technology.
(2) The new GSJ-V rotary compensator can be used together with the traditional corrugated compensator and sleeve compensator in thermal engineering. The layout of the compensator is flexible and can be changed at any time according to the site conditions, not limited to the design drawings, so as to shorten the construction period. For example, in the original design of the steam pipeline project of No. 2 Coal Mine, the pipeline had to pass through a family home, and a square compensator was needed. However, the family home did not allow the pipeline to pass due to various problems during the construction process, and the time for pipeline re planning and re construction was not allowed. In addition, at the peak of heat supply, the designers of our company used the new GSJ-V rotary compensator to change the pipeline route to solve the big problem. Other compensators and supports on the whole pipeline remain unchanged, fully reflecting the advantages of the new technology.
5. Safety comparison
(1) Due to the structural characteristics of the sleeve type compensator, the different axes of the pipeline shall be ≯ 1% during installation. "Strict alignment" is required to prevent excessive friction during operation, leakage and even seizure. Therefore, additional guide brackets are required. The rotary compensator does not have the problem of "centering", so it is unnecessary to add additional guide brackets.
(2) The exposed high finish sliding surface of sleeve type compensator is easy to be bruised and corroded, so it is easy to leak; The rotating cylinder of the rotary compensator is equipped with a stop ring, antifriction and centering bullets, and a reasonable sealing surface structure is adopted, so that the wear of the sealing materials and sealing surfaces is extremely slight, and the safety and reliability of the work are greatly increased by ensuring that no leakage occurs in a longer time.
Concluding remarks
Through the above analysis, we can conclude that compared with the sleeve type compensator, the rotary compensator has the advantages of significantly reducing the construction cost of the project, and its structure is simple, easy to install, and no maintenance is required, which overcomes the problems of the sleeve type compensator such as easy leakage and the need to stop production for maintenance. Therefore, rotary compensator should be widely used in overhead pipelines.
