1, fire hazard
Because the main components of oil and natural gas are hydrocarbons, which are flammable and explosive, easy to accumulate static electricity and poisoning, and the oil and gas storage and transportation process is carried out under specific conditions, especially in oil pipelines, heating and pressurizing are the characteristics of pipeline transportation, so there is a great risk of fire and explosion. Once an accident happens, it may cause huge economic losses and casualties, and bring bad social impact. The main reason is: (1) the harm caused by equipment failure. Unreasonable design of oil and gas storage and transportation equipment, process defects, pipeline corrosion, fluctuation of operating pressure, fatigue damage of equipment caused by mechanical vibration, damage of pressure vessels such as high temperature and high pressure, etc. are all easy to cause leakage and explosion. (2) Anti-static measures are not in place. In the process of oil and gas storage and transportation, when oil and gas flow in pipelines and equipment, static electricity will be generated due to friction. If static electricity cannot be eliminated in time, it will cause charge accumulation and spark discharge, which will lead to fire and explosion accidents. (3) the hazards caused by explosion-proof equipment and electrical appliances. If the process equipment and electrical circuits are not explosion-proof or explosion-proof as required, the leaked flammable liquid and gas can easily fall into mechanical friction sparks or electric sparks. (4) Illegal hot work. Including illegal command, lax approval of hot work, and hasty approval of hot work without hot work conditions; Fire blindly. Some employees are not familiar with the hot work management regulations, or are lucky enough not to go through the hot work procedures. Some employees themselves do not have the qualification for hot work, ignore the regulations on hot work management, and rush to hot work to cause a fire; On-site monitoring is a mere formality.
2. Serious oil and gas evaporation.
At present, the turnover link from oil field to refinery and then to users is complex, and the oil and gas loss and its economic loss are amazing. In petrochemical and petroleum enterprises, such as refinery storage and transportation systems, oil depots, gas stations and other frequent oil loading and unloading operations, a large number of volatile light oil products such as gasoline will vaporize and escape. According to the current annual consumption of crude oil in China, 2. 5× 108t, the total loss of crude oil and refined oil in China will reach 7. 5× 106t/a is equivalent to the refining capacity of a large oil field and refinery, and its value exceeds 3×10/0 RMB. The main substance of oil evaporation loss is light component. Therefore, oil evaporation will not only cause quantity loss, but also cause quality decline. In addition, because the oil and gas discharged into the air is flammable and explosive, it will explode when it meets a fire source when it exceeds a certain concentration. In the process of oil storage and transportation, the oil and gas discharged into the air by loading and unloading platforms and gas stations have certain toxicity, which will cause diseases of skin, organs and nervous system; In addition, oil and gas (hydrocarbons) react with nitrogen oxides in the air under the action of ultraviolet rays to generate ozone, which creates conditions for the formation of photochemical smog.
3, pipeline corrosion
Many oil pipelines are seriously corroded and cracked in wet hydrogen sulfide environment, such as stress corrosion cracking (SCC), sulfide stress corrosion cracking (SSCC), hydrogen-induced cracking (HIC), stress-induced hydrogen-induced cracking (SOHIC) and so on. There are usually four reasons for pipeline corrosion: (1) material factors. Taking HIC as an example, the "hard" region containing bainite or martensite in the material is very sensitive to HIC. If the hardness of segregation zone of material inclusion is controlled below 300HV, the sensitivity of material to HIC can be well eliminated. 2. Buried pipeline environment. The environment in which buried pipelines are located is the external cause of corrosion, including soil type, soil resistivity, soil water content (humidity), pH value, sulfide content, oxidation-reduction potential, stray current and interference current, microorganisms, plant roots and so on. 3. Stress level. Many experiments show that if the stress of a material exceeds 30% of its yield stress, SOHIC failure may occur. However, this stress level may appear in the area around the weld seam of the welded parts and in SSCC cracks or other cracks-like defects. 4. Design and manufacture. Some scholars refer to NACE standard (for medium gas, design pressure, 2. Countermeasures to prevent problems in storage and transportation.
1, fire prevention preparation in the process of oil and gas storage and transportation
Maintain the equipment regularly. According to the characteristics of all kinds of equipment, the maintenance is carried out in strict accordance with the maintenance procedures, and the work hazard analysis is done before the operation of the process flow to control the operation risk. (2) Do a good job in fire prevention design. Equipment leakage often comes from the design stage, so it is very important to do a good job in fire prevention design. First of all, the design, type selection, material selection, layout and installation of equipment should conform to national norms and standards. According to the characteristics of different technological processes, the corresponding materials with pressure resistance, high temperature resistance or corrosion resistance are selected for manufacturing and installation according to regulations. Secondly, the layout of newly built, rebuilt and expanded production devices, the layout of unit equipment, and the design and implementation of fire safety facilities should follow relevant specifications, do a strict fire audit, and fully consider factors such as fire separation, ventilation, explosion-proof and pressure relief, and fire-fighting facilities. At the same time, strictly control the explosion-proof requirements of equipment and electricity, and put an end to congenital fire hazards. 3. Implement hot work measures. Dismantle the equipment, pipelines and their accessories that need hot work in the fire-forbidden area, move them to a safe place for hot work, and effectively isolate the equipment, pipelines and their accessories that need hot work from relevant operating systems, such as plugging blind plates on pipelines or removing a section of pipelines. , to prevent flammable and explosive materials and media from entering the hot work site. Before hot work, the inflammable and explosive articles around the hot work point should be moved to a safe place and the site should be cleaned. After inspection and confirmation, a "Permit for Working with Fire" shall be issued, and the person in charge of guardianship shall be properly identified. Before and during hot work, it is necessary to analyze the concentration of flammable and explosive gases in the hot work area to avoid fire and explosion accidents during hot work.
2. Oil and gas volatilization in oil and gas storage and transportation
Firstly, the fixed roof oil tank is reformed. At present, many oil companies still use fixed-roof tanks to store gasoline and kerosene. In order to prevent oil and gas volatilization and reduce oil and gas pollution during oil storage, it is necessary to convert these gasoline and kerosene storage tanks into internal and external floating roof storage tanks, and check them frequently to ensure that the floating roof seals and accessories are in good condition. It can improve the safety and reliability of oil tanks and reduce oil and gas pollution. Compared with the fixed roof tank, the evaporation loss of the floating roof tank can be reduced by about 85%. But also can generate considerable economic benefits. 2. Oil and gas recovery device, the most fundamental means to control oil and gas volatilization during oil filling is to take oil and gas recovery measures to recover the discharged hydrocarbon gas. The oil and gas recovery measure is to set up an oil and gas recovery device in the place where oil products are concentrated, and recover the oil and gas generated in the filling process, restore it to liquid state through the device, and then send it back to the storage tank. This can not only greatly reduce the emission of hydrocarbon gas, but also have obvious economic benefits. Oil and gas recovery methods can be divided into absorption method, adsorption method, condensation method and membrane selective infiltration recovery method. In a word, it is reasonable to use oil and gas pipeline system in gas stations, and the combination of oil and gas pipeline and special equipment in oil depots and refineries with more fixed top tanks can achieve certain results and reduce investment. In other cases, the special equipment scheme should be adopted, which has good effect but large investment.
3. Anti-corrosion treatment of pipelines
(1) Material requirements for reinforced steel pipes. Stress corrosion cracking of pipelines is mainly caused by stripping or cathodic stripping, so it is very impossible to completely control and prevent hydrogen-related corrosion cracking in pressure vessels and pipelines. Therefore, in the manufacturing process of materials, the quantity and shape of inclusions should be controlled and improved as much as possible, and the sulfur content and hydrogen content should be reduced. Before painting, the steel pipe surface must be shot-blasted or sandblasted to achieve the cleanliness and anchoring depth required by the standard, and to ensure that the primer is firmly bonded. (2) Pay attention to the quality of on-site joint patching. The compatibility between the joint coating material and the anticorrosion coating of the pipe body is good; The joint of the joint should be glued firmly, and leak test can be done when necessary; The surface of the steel pipe at the joint must be carefully treated to meet the requirements of the cleanliness of the pipe surface. (3) Reasonable selection of pipe wall thickness. First of all, it is necessary to prevent local buckling instability of pipelines during storage, transportation and operation; Secondly, crack propagation aging should be considered to prevent cracking and damage. Thick-walled tubes are more conducive to stress corrosion cracking resistance than thin-walled tubes. Therefore, the design should appropriately reduce the pipeline strength and increase the wall thickness. (4) The combination of fixed and mobile anticorrosion production lines has a good construction environment and can improve the quality of anticorrosion pipes. However, for pipelines that need long-distance transportation, the anti-corrosion coating is easy to be damaged, and it is difficult to achieve satisfactory results in on-site repair. Therefore, the combination of fixed and mobile anti-corrosion production lines should be considered to meet the needs of engineering practice.
Third, the conclusion
Oil is a non-renewable natural resource, and the working environment of oil and gas storage and transportation is complex. Therefore, refineries, oil depots and gas stations should take practical measures to reduce the evaporation loss during the storage and transportation of oil products and avoid the impact on production and operation when oil and gas are forcibly recovered. Take precautions and strengthen the management of storage and transportation pipelines. However, due to the complexity of oil and gas storage and transportation, many problems need to be further solved, such as oil and gas recovery technology. At present, China is still at a low stage of development. How to combine some technologies organically needs to be explored continuously in the future.