In modern energy construction and urban municipal infrastructure construction, more and more steel pipes are laid underground.
The current implementation of the Yellow River water source Taiyuan urban water supply project is to lay a water supply network within the city. The pipe diameter of the pipeline is DN300mm-DN2220mm, and the total length is 163km. The large-diameter pipelines are all made of steel pipes. In order to ensure the quality of the project, the life of the steel pipe is prolonged. The corrosion protection of the inner and outer walls of the steel pipe is extremely important. There are many factors in the corrosion of underground pipelines, such as the soil pH value in the pipeline area, and the grass roots will penetrate the general coating. The inner wall of the water supply pipe is made of cement mortar, and the outer wall is made of epoxy coal tar pitch paint. After years of engineering practice, it proves to be a very effective anti-corrosion method. In addition to the outstanding advantages of easy material extraction, low price and long service life, the anti-corrosion of the inner wall of cement mortar also has the following advantages:
First, the anti-corrosion of cement mortar has non-toxic and harmless substance impregnation and does not multiply, effectively controlling the occurrence of chloroform in the secondary pollution of pipelines, ensuring that welding defects will change and develop during operation, and the welds will be effective. The cross section is weakened, the strength is lowered, and stress concentration is caused, eventually leading to a leak. Long-term strength tests at operating temperatures have shown that fractures generally occur in the weld and its heat affected zone. Therefore, for alloy steel with a large content of alloying elements, preheating should be carried out before welding to reduce the thermal stress during welding. After welding, tempering or slow cooling treatment should be carried out to improve the weld microstructure, eliminate welding residual stress and prevent generation. Crack, the quality of drinking water.
Second, the cement mortar anti-corrosion has good anti-seepage, anti-leakage and anti-explosion properties, ensuring the safety of the pipeline.
The third cement mortar anti-corrosion increases the flow rate of the pipeline, and its resistance coefficient is <0.012, which can be reduced after use. Therefore, the use of mortar mortar as the inner wall anticorrosion has greater superiority than petroleum asphalt and coal tar pitch. It has been widely used in engineering. The inner wall of the water supply pipe adopts the mechanism of anti-corrosion of cement mortar, mainly the Ca(OH)2 solution which penetrates the cement mortar into the wall of the steel pipe, so that the PH value between the cement mortar and the metal is up to 12 or more, forming a white passivation layer to protect the steel pipe. Not oxidized until isolated and electrochemically protected. Epoxy coal tar pitch outer wall anti-corrosion will prevent various factors from damaging the pipeline, and it is an ideal anti-corrosion coating for underground pipelines. It not only has the cheap, acid, alkali and water resistance of coal tar pitch, but also has the adhesion, mechanical strength and solvent resistance of epoxy resin. Theoretical research and practice show that the corrosion resistance and physical and mechanical properties of epoxy coal tar pitch anti-corrosion layer have service life, mainly related to the treatment condition of metal surface, pretreatment of glass cloth, arrangement of glass cloth, proportion of glass cloth and paint. The content, the quality of the coating itself, and the temperature, temperature, and dust of the construction environment are related.
Three measures to improve the reliability of superheater and reheater
1. Adhere to the whole process management of equipment
Strengthen quality control in boiler modeling, design, manufacturing, installation, operation and overhaul. Avoid slagging, smoke corridors and hydrodynamic deviations and large thermal deviations in the design. At the same time, from the operation aspect, the inspection and inspection were strengthened, and the leakage phenomenon was found to take measures to prevent the accident from expanding and damage other heated surface pipes.
2, using advanced testing methods
The technique for diagnosing the remaining life of the pipeline has a theoretically calculated stress analysis method, the destructive non-destructive flaw detection method for the actual component cutting test sample, etc., and the effective residual life management of the heated surface pipeline is strengthened. The boiler pressure vessel safety supervision and metal supervision are strengthened. Managed water quality supervision and management can effectively prevent the occurrence of tube explosion accidents.
3. Technical transformation of the soot blowing system
High temperature corrosion protection measures are taken to protect the heated surface metal to reduce the wear rate. Establish a special anti-wear and explosion-proof team, system, and daily management work, and monitor the metal temperature of the pipe wall during operation to prevent over-temperature. During the repair and maintenance of the boiler, regular and planned inspections of the external surface corrosion, expansion, tearing and wear of the heated surface shall be carried out to determine reasonable quality standards for inspection and repair.