1 Accident situation The heating steam pipeline of a thermal power plant was laid by overhead brackets, and a steam pipeline rupture accident occurred. The heat network pipe rack is arranged on the west side of the road. The bracket is a double-shaped door bracket. The steam and hot water main pipe are arranged on the bottom layer, and the steam and hot water branch pipes are arranged on the upper layer. The bellows compensator is arranged on both sides of the bracket at 6 and 9 points. See the form.
The steam pipe network was first started in November 1994. During the first steam supply operation, the bellows compensator on the steam pipe between the supports 8 and 9 broke. When the accident occurred, the pipe erected at the corrugated pipe with the sound, and the bellows was torn into two sections, one section turned northward by 180. After the 10kV cable was broken, it fell on the top of the west side of the house, and the other section Turning south 180., tearing open the A-point welding joint and falling on the road, this road is just a free market, but fortunately, there is no injury, but the accident is serious.
2 Basic condition of pipeline 2.1 Steam parameter ~1.3MPa, temperature is 250T. When an accident occurs, the steam pressure is 0.61MPa and the temperature is 196:.
2.2 Steam pipe specification The upper steam pipe is 丨 529mmx7mm spiral seam electric welded steel pipe, which is horizontally arranged along the direction of the mother pipe after it is connected upwards from the 630mmx8mm female pipe by 2.73m. The total length of the pipe section is 55.2m, the length of the south section is 17.6m, the length of the north section is 376m.2.3, the bellows 150/1.6 is the inner bellows; the material is lCrl8Ni9Ti, and the chemical analysis result: C is 0.1%. Cr is 18%, Ni is 9%, Ti is 0.5%. The installation length is 750mm, and there are 3 limit screws. One of the bolts is not wearing a nut, and the other two nuts are only screwed 2~3. There is no product certificate and quality certificate. 2.4 Welded joints There are undercuts in the welded joints, the grains in the heat-affected zone are coarse, and voids appear on the grain boundaries.
2.5 Pipe bracket The guide bracket is open, and the brackets 4 and 7 are installed without two guide slots. The setting of the bellows guide bracket is not set according to the relevant specifications of the product manual.
2.6 Three-way three-way welding on the mother tube, not a reinforced type, the corner of the A point is actually a three-way form, no hot extrusion elbow is installed.
3 Stress Analysis Calculate the stress calculation using the thermal pipeline stress analysis calculation program. This low, the capital investment listed in the budget is several thousand yuan / m2, so it is of considerable use value in the future use of coastal power plant pipelines and seawater buildings. For example, a project will use a 30mm polymer lining in a DN 2x800m steel pipe. The total cost is about 1 million yuan, which can greatly reduce other anti-corrosion costs. At the same time, the 30mm thick polymer lining will undoubtedly strengthen the strength of the steel pipe. Stability, steel tube wall thickness can also reduce the speed of thinning.
(This article is supported by the metallographic laboratory of Shanghai Jinshan Petrochemical Complex Thermal Power Plant and related construction units.) The lighting line 10kV high voltage line North example fixed bracket valve bellows sliding bracket guide bracket before the pipeline layout program using structural design development, Applicable to a variety of structural forms of the pipe system, such as: single branch, multi-branch, ring branch; for a variety of boundary conditions, such as: free end, support end and fixed end. The branches separated by the intermediate fixing brackets are independently calculated, and the supporting points can be placed at any position of the piping system.
Displacement, additional loads, and calibration of coordinates can be given for any selected point.
The designed piping system can be re-checked. Among them, the thermal state and the cold state are considered in the initial situation of the pipeline operation and the two conditions after the strain reaches self-equalization.
3.1 Program Function The main functions of the thermal pipeline stress analysis calculation program are: one stress check generated by the internal pressure and continuous external load (including self-weight) under the working condition of the pipeline.
Calculation of working load of pipe hangers. The calculation of the thrust and moment of the equipment or the end point of the pipeline during the initial operation of the pipeline takes into account the effects of self-weight, thermal expansion, effective cold tightness and additional displacement of the end point.
Under the working condition of the pipeline strain self-equalization, calculate the thrust and moment of the pipeline to the equipment or the end point and the load of the rigid support hanger.
The calculation of the thermal displacement of the pipeline from the cold state to the working state. Calculate the full compensation value of the pipe along the coordinate axis and the elastic modulus of the steel at 20T, and consider the influence of the additional force of the spring.
The secondary stress check of the pipeline due to thermal expansion, shrinkage and other displacement constraints. If the secondary stress fails, calculate and check the three stresses.
Calculation of the installation load of the pipe hanger and hanger, and calculation of the thrust and torque of the equipment or the end point in the cold state at the initial stage of operation.
The calculation of the thrust and moment of the equipment or the end point in the cold state after the pipeline strain is self-equalized, and the calculation of the rigid support hanger load.
The calculation of the cold displacement of the pipe due to the cold tension and the additional force of the spring serves as a basis for the design and installation adjustment of the pipe support and hanger.
The hanger spring is selected according to the thermal displacement and working load of each spring support point, and the spring pre-compression value is given.
Structural load calculation of spring support hangers and partial rigid support hangers.
Calculation of the additional displacement of the root of the hanger.
The treatment of the hanger is provided on the inclined pipe.
The working load is manually given for the spring hanger.
The straight element artificially gives the stiffness matrix in the element coordinate system for calculating the corrugated compensator and the like.
Calculate the length of the straight pipe and the number of pipe parts.
3.2 Calculation program Input data file Writing content Calculation program Input data file preparation content mainly includes: (1) input description of input unit calculation unit; (2) description of calculation control item; (3) description of medium characteristic; (4) material Characterization; (5) description of pipe section characteristics; (6) description of node characteristics, including additional load points, positioning and moving points, fixed end points, cold points, coordinate check points, elastic hanger points for a given load, pipes Three-way; (7) description of node number; (8) description of straight pipe section; (9) description of curved pipe coordinates; (10) description of self-parameter of curved pipe section; (11) description of rigid part data; (12) pipe segmentation data Description; (13) The original data end indicator.
3.3 Output data file Description If the input file is error-free, the program will give the calculation result; otherwise, the program gives the error detection information. The program can output the hanger summary table, the cold tight table, the stress checklist, and the thrust summary table.
3.4 Calculation Results We used the thermal pipeline stress analysis calculation program to check the piping system for the accident. The results are shown in Table 1. It can be seen from Table 1 that the secondary and tertiary stress values ​​at the tee are large. Exceeding the allowable stress by 2~3 times.
Table 1 Three-way point stress value calculation result Calculation item-parameter stress value comparison/(N*mm2) pressure/Mft primary stress secondary stress cubic stress original design stress allowable range original design pot force allowable range original design operation condition () original design operation conditions () modification scheme 1 modification scheme 2 improved layout of the pipeline system () 4 accident cause analysis 4.1 welding quality bellows compensator welded joints have undercuts, heat affected zone grains are coarse, and Holes appear in the grain boundaries. Poor welding quality directly causes local stress concentration.
4.2 Installation of the bellows compensator The limit screw acts to limit the limit size of the axial compensation of the bellows, and at the same time it can increase the bellows. Transverse and vertical bending resistance. Due to the installation problem, the corrugated pipe limit screw does not tighten the nut as required. One of the bolts is not wearing a nut, and the other two nuts are only screwed with 2~3 buckles, which can not function as a limit and guide.
4.3 Guide bracket The guide bracket is used to ensure the thermal displacement of the pipeline is compensated in the axial direction. There is no guide groove when installing at 4 and 7 points, only the sliding bracket acts, and when the lateral displacement occurs, the pipeline will lose stability, and 7 The point stress direction is upward, indicating that there is also a vertical displacement.
4.4 Problems in the design 4.4.1 The entire pipeline design does not fully meet the working conditions of the bellows compensator. The guide brackets for installing the bellows compensator are not set according to the relevant specifications of the product manual.
4.4.2 The upward branch arm is too short at the three-way, so that the secondary stress at the tee is not well compensated, the three-way point stress is concentrated, and the three-way does not use the enhanced factory-produced tee, but adopts Soldered on site.
It can be seen from Table 1 that the stress at the tee is more than twice the allowable stress. 4.4.3 Detailed intensity calculations were not performed in the design.
5 Improvement of Pipeline Arrangement System We believe that the design difficulty of this pipe section is that there is a branch pipe, which increases the force of the three-way point and the bellows, and the force is complicated. The upward branch arm is short in the three-way, so that the secondary stress at the three-way is not well compensated, and the three-way point stress is concentrated; if the upward branch arm is long, the vertical displacement is increased, and the working condition of the bellows is deteriorated. To this end, it should be improved from the following aspects: 5.1 The position of the fixed bracket should be close to the three-way point, so that the thermal displacement of the section is small, so that the force of the three-way point is small, such as (a).
5.2 Axial bellows can not be used for lateral displacement compensation. Therefore, a fixed bracket should be set at the point to make the ZJF section a straight pipe section. The axial type bellows at £ only compensates for the axial displacement.
5.3 Calculate to determine whether the Z-shaped natural compensation of the /ISCZ) segment is qualified. If it is unqualified, it can be square-shaped compensation, such as the 4B-Ni segment in (b).
5.4 For large diameter steam pipe tees and elbows, since the secondary stress of thermal expansion is proportional to the stress enhancement factor, the hot extrusion reinforcement produced by the factory should be selected.
Improvement scheme of pipeline layout 5.5 In the original design, the three-way has a variable diameter, and the diameter of the upstream branch pipe is imaginary 77minx6mm. The difference in rigidity before and after the variable diameter is large, the stress imbalance is intensified, and the diameter of the upward pipe is 77mmx6mm. The diameter of the down pipe is 630mmx, and the effect of the upper and lower pipes is better.
After the modified 10kV high-voltage line lighting wire north of the pipeline I 6 modified pipeline layout design should pay attention to the problem 6.1 modify the design changes to be small, in order to facilitate construction, to ensure normal heating in winter.
6.2 According to the opinion of the power plant, no bellows is used, and a square compensator is used.
6.3 Considering the bearing capacity and stability of the original support base, the square compensator free arm should not be too sturdy and does not increase the number of bases.
6.4 Avoid 10kV high voltage lines and lighting lines.
After modification (as shown), the piping system has been operating normally and the operation is good.
7 Lessons and experience 7.1 Bellows are used on steam pipes, taking into account various factors such as selection, location, bracket form and stress calculation.
7.2 The bellows used on the heating network pipe should pay attention to its stability and cannot produce lateral displacement.
7.3 Stress analysis and calculation must be carried out in the design of steam piping.
7.4 Pipe parts such as tees, elbows, etc. should be selected from the factory-made reinforced hot extrusion tees and elbows.
7.5 Axial type bellows During the installation process, the limit lead screw should be adjusted according to the manufacturer's technical requirements.
7.6 Bellows guide brackets are preferably closed type, and open guide grooves are not suitable.
The State Economic and Trade Commission spokesperson talks about the new policy of state-owned enterprise reform. This article, the spokesperson of the State Economic and Trade Commission, Hou Yunchun, recently explained the "we are doing" and "we will do" of the reform of state-owned enterprises: it needs to be bigger and bigger. Whether a country has competitiveness in the international arena depends on whether there are large enterprises that are not competitive. Our large companies are not an order of magnitude compared to the international ones. The three major companies, namely PetroChina, Sinopec, and Nonferrous Metals, the top ten military enterprises, and the information industry, have also formed several large enterprise groups. However, we must correct the deviations in the past on the principle of voluntariness. "Do not need to be big, don't be big."
A salvation that can save lives. For products with sales, strong leadership, and promising development, just because the debt burden is in trouble, we must take debt-to-equity swaps. The State Economic and Trade Commission is stepping up operations. The first batch involves 108 enterprises and non-performing loans of more than 200 billion.
A question that must be raised. Through technological transformation and technological innovation, we will improve the production and operation level of a group of enterprises. The focus is on quality, variety, efficiency, and substitution of imports. Of the 60 billion government bonds this year, there are 9 billion for interest-bearing loans for general corporate loans; 5 billion for the 35 billion yuan that will be issued next year will be used for technological transformation. Now the first batch of 150 projects has been confirmed, and next year will be the second and third batches. Although the time is tight, the total loan interest of 14 billion yuan still needs to be used out, which can promote hundreds of billions of technical reform funds. This policy will continue.
The elimination should be eliminated. Enterprises that have no advantage or have lost their advantages should smoothly withdraw from the market. The key is how to do things. To speed up the construction of the social security system, we must start with setting the minimum living security line.
Can quit the exit. Elimination itself is a passive exit and can also voluntarily withdraw. Some state-owned holding companies may reduce some of their state-owned shares into public shares without affecting the controlling interest, but depending on the market situation, they will make a careful decision.
Suitable for letting go. The first is to let go of small and medium enterprises. The Fourth Plenary Session of the 15th CPC Central Committee has added a "Chinese" character to the "release". Many "medium" enterprises in China can only be regarded as small enterprises in the world.
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