If the medium has no corrosion and other special requirements, the following pipes can be selected:
1> Low carbon seam steel pipe: low pressure pipe with service condition of 0~200C. Pipe materials can be Q235A, Q215A, Q235AF, Q215AF, etc. Available national standards include Welded Steel Tubes for Low Pressure Fluid Transportation GB3091, Welded Steel Tubes for Low Pressure Fluid Transportation GB3092, etc.
2> Low carbon seamless steel pipe: the service conditions are - 20~200C medium and low pressure pipes, and the pipe materials can be 20 #, 10 #, 16Mn, 09MnD, etc. Optional national standards include Seamless Steel Tubes for Low Pressure Fluid Transportation GB8163, Seamless Steel Tubes for Medium and Low Pressure Boilers GB3087, etc
At present, the high-temperature pipelines of chemical enterprises in China are mainly distributed in steam pipelines and some high-temperature hydrogen pipelines. Due to the development of chemical production process, hydrogen reduction is mostly used in the reduction reaction of many chemical production plants. The material selection is mainly based on the Nelson curve. 1Cr5Mo (i.e. Cr5Mo) is the steel commonly used for high-temperature hydrogen resistant pipelines at home and abroad. When selecting, it should be noted that this steel belongs to pearlitic steel in the normalizing+tempering state, and martensitic structure in the quenching+tempering state. At this time, the weldability of the steel decreases. Usually, when used as a pipe, it is not to improve the strength, but to improve the weldability. The requirements for preheating and tempering after welding are strict. This is difficult to achieve during pipeline construction, but it is much simpler when austenitic welding rod is used, and post welding heat treatment is not required.
High temperature steel pipes are mostly exposed to high temperature gases or special gases and liquids, so they are required to have good oxidation resistance. However, the oxide film on the surface of carbon steel pipe can hardly protect its base metal. In order to make the steel pipe have good oxidation resistance, appropriate metal elements such as Cr, Al and S are added, which can make the steel surface produce oxide film that is difficult to peel.
When the medium is highly corrosive, it is not suitable to use ordinary carbon steel and alloy steel, but must use precious metal alloy, in order to consider economic and practical, non-metallic materials can be used, such as PVC, PP, PTEE FRP, etc. However, the following points shall be considered when selecting:
1> Pay attention to the allowable temperature and pressure range.
2> Aging phenomenon caused by light and oxygen effect on plastic light and accessories, and corrosion performance of plastic pipes to media at specific temperature
3> Where pressure and temperature change suddenly
4> Brittleness of plastics due to loss of elasticity under the action of certain media
Vertical layout principle of pipes and pipe supports
1. When there is a passage under the pipe rack, the distance between the pipe bottom and the road surface shall be more than 4.5m; It shall be more than 6m when the main road is a thousand roads; It shall be more than 2.2m for sidewalk; When there is a pump under the pipe rack, it shall be more than 4m.
2. Generally, the elevation difference between the two layers of pipes in the direction of use is 1.0~1.6m, and the branch pipe from the main pipe is 0.5~0.8m higher or lower than the total. When changing the direction of the pipe, the elevation shall be changed at the same time. When large diameter pipes need to turn on the horizontal surface, they should be arranged outside the pipe rack.
3. When the pump is arranged under the pipe rack, its elevation shall meet the clearance requirements when the pump is arranged. If the pipeline below the operating platform enters the upper layer of the pipeline, the upper pipeline marker can be determined according to the elevation of the operating platform
4. The pipeline with orifice plate should be arranged outside the pipe rack and close to the column as far as possible. The automatic regulating valve can be arranged close to the column and fixed with the column. If there is a local platform or sidewalk on the upper layer of the pipe rack, the valves and instruments that need frequent operation or maintenance should be arranged on the upper layer of the pipe rack.
At present, the pipeline industry is developing rapidly and has entered a white hot stage, but the anti-corrosion pipeline is still traditional and has not been further improved. That is to say, in such a stage, steel lined plastic pipeline came into being to adapt to the development trend of today's chemical industry, integrate scientific and technological elements, and make our life more convenient.
Performance characteristics of steel lined plastic pipes
1. Chemical corrosion resistance, soil and marine biological corrosion resistance, cathodic stripping resistance, mature and convenient installation process
2. Good weather resistance, suitable for harsh environments such as desert and saline alkali
3. Smooth pipe wall, improved conveying efficiency and long service life
Petrochemical pipeline installation is a relatively complex project, characterized by large installation quantities, high quality requirements and long construction period. With the technical progress and development in recent years, new construction methods are constantly adopted. At the same time, the country has issued new acceptance specifications, and the construction process content, processing methods, and engineering quality acceptance standards of process pipelines have changed.
Process pipeline construction preparation generally includes technical preparation, material preparation and construction team preparation. The specific work is as follows:
1. Be familiar with and review drawings and design documents, and participate in design disclosure in due time.
2. Find out the project content, quantities and workload.
3. Prepare the technical scheme for pipeline construction and organize technical disclosure.
4. Organize welding procedure test and qualification.
5. Prepare construction equipment and tooling facilities.
6. Organize the construction team, train the construction personnel for the construction of new materials, and make them master the technical operation essentials and project quality.
7. Water, electricity, gas (steam) and paved roads shall meet the construction needs.
In the use of chemical pipelines, the safety of pipelines is also affected by the temperature and the speed of change of substances, especially the transportation of some corrosive, flammable and highly toxic liquids and gases. A slight problem in operation will cause toxic gas leakage or explosion. Therefore, in daily work, attention must be paid to the normalization of operating pipelines. When flammable liquids and gases are transported, attention must be paid to the temperature of the pipeline, which cannot exceed the relevant standards. At the same time, attention should also be paid to the cleaning of chemical pipelines to prevent some garbage and chemical waste residues from exploding due to pipeline blockage. In addition, the industrial waste residue and garbage around the pipeline should also be treated to provide convenient conditions for the maintenance and repair of the pipeline and the safe use of the pipeline.
