[introduction] chemical and fuel containers (such as tower, tank, tank, cabinet, box, barrel etc.) and pipelines in use due to the internal pressure, temperature, corrosion, or because the structure, material, welding defects such as cracks and perforation often, so regular maintenance. Sometimes in the production process should be carried out, due to the characteristics of chemical production with a high degree of continuity, so this kind of equipment and pipe welding work is often tight, urgent, but also in the inflammable and explosive, easy poisoning, high temperature or high pressure under the complicated conditions, any negligence will explode, fire and poisoning accidents, even cause the entire plant, fuel supply system of fire explosion, causing serious consequences. Therefore, in the chemical industry and fuel container and pipe welding work, we must take practical and reliable explosion-proof, fire and gas and other technical measures.

A displacement welding with pressure and displacement welding
Chemical and fuel container and pipe welding, the displacement welding with pressure and displacement welding two methods. Where welding or cutting operation using the arc or flame, are hot, or hot work.
(a) displacement welding
Displacement welding in welding and before the water is not burning combustible gas gas container or pipeline, poisonous gas or air replacement container or in the pipeline, so that the content of combustible gas container or a pipe or noxious gas meet the requirements, so as to ensure the safe operation of welding.
Hot replacement is a safe and proper way, is widely used in the production of maintenance work in vessels and pipes. However, the replacement method, the container, the pipeline needs to be suspended, but also to use other media for replacement. In the replacement process to continue sampling analysis, until after passing to the fire, after the fire needs replacement, is time-consuming. In addition, if the pipe elbow is more, it is often not easy to clean and leave the hidden dangers.
(two) with pressure displacement welding
With pressure displacement welding is strictly controlling the oxygen content, the concentration of flammable gas explosion greatly exceeds the limit, then let it at a steady pace, lit from the pipe mouth spray out and burn, which forms a combustion system with the surrounding air, and maintain stable continuous combustion, can carry out welding work.
With the pressure does not replace the replacement of the original gas, and sometimes can be carried out in the case of equipment operation, and short operation time is conducive to production. This method is mainly applied to the external welding of the container and the pipeline of the combustible gas. Because this method can only maintain a certain positive pressure in the case can be carried out, the control is difficult and there is no certain pressure can not be used, there is a big limitation, the current application is not widely.
Two, the cause of the explosion of fire
(a) do sampling of the vessel or piping and gas analysis is not accurate or not appropriate welding, the sampling position, the explosive mixture exist around the container, pipe or hot point.
(two) in the welding process of the surrounding conditions have changed.
(three) the maintenance of the container and the production of the system is not isolated, explosive gas collusion, into the weld repair area, or the production system discharge exhaust gas.
(four) welding repair work in the workshop, warehouse and other workshops with combustion and explosion hazards.
(five) welding without sealing the container security holes or not.
Three, replacement welding repair of safety technical measures
(a) fixed hot work area
In order to make the welding work easy to strengthen the management of the factory, and the workshop can be delineated fixed hot work area. Where conditions can be disassembled and moved to the fixed hot work area welding objects must be moved to within a fixed hot work area welding, thereby reducing in the explosion-proof workshop or factory in the hot work. Fixed hot work area must meet the following requirements:
1, no gas pipeline and equipment, and around the flammable and explosive equipment from the pipeline 10m above.
2, indoor fixed hot work area and explosion-proof production site will be separated, can not have windows, to waste.
3, in the production of equipment in the normal venting or accident, flammable gas or vapor diffusion into the fire zone.
4, fire extinguishing tools and equipment, a sufficient number of standing.
In 5, fixed hot work area to prohibit the use of various flammable substances.
6, around the operating area to delineate boundaries, hanging fire safety signs.
(two) to implement a reliable isolation
The first stop for on-site maintenance overhaul equipment or piping work, and then take measures to enable reliable isolation, maintenance, welding equipment and other equipment (especially the production part of the equipment) completely isolated, to ensure that the combustible material can not spread to the welding equipment and its surrounding. A reliable isolation method is to install a blind plate or remove a section of connecting pipe line. Blind plate materials, specifications and processing accuracy and other technical conditions must meet the national standards, not abuse and correct assembly, must ensure that the blind have sufficient strength, can withstand the working pressure of the pipeline does not leak tight.
Between the blind plate and the valve should be put on air traffic control or pressure gauge and send someone to watch. To remove the line, pay attention to the production system or there is a good side of the material side of the material. Blocking plate also meet the technical requirements of the national standard. At the same time should also pay attention to atmospheric exposure equipment from space, to ensure the contact of combustible Mars does not with the container mouth out of the oven. For some short time welding repair, available water cut off the gas supply, but there must be someone in the water overflow pipe overflow spot guard, prevent water seal failure. In a word not carefully cut off from work shall not be hot.
(three) to implement a total replacement
After isolation, the equipment itself must be discharged to the material, the container and the pipeline of flammable or toxic medium completely replacement. In the process of replacement to continue sampling and analysis, until the container pipeline of flammable and toxic substances content to meet the safety requirements.
Commonly used replacement media are nitrogen, water vapor or water, etc.. Replacement method depends on the replacement medium and the proportion of replacement media, when the replacement medium than the proportion of the replacement medium, the container or pipeline should be sent to the lowest point of the replacement medium, the highest point outward emission. When the gas is used as the medium, the amount of the required amount is 3 times more than that of the medium.
Some of the replacement of combustible gas has the nature of retention, or with the proportion of the replacement of the gas is not large, at this time should pay attention to the replacement of the incomplete or both mixed. Therefore, the replacement of the total can not be onlyLook at the amount of replacement media, and to gas composition analysis of the results of the test for the replacement of water as the medium, the equipment pipeline filling can be.
(four) clean the container properly
Container and pipe replacement after treatment the outside must be carefully cleaned, because some flammable and explosive medium is adsorbed on the outer surface of the inner wall insulation materials or fouling of the equipment and pipeline of liquid fuel will be attached to the inner wall of the container and the pipeline. If not thoroughly cleaned, due to the impact of the fuel temperature and pressure will be gradually released, make originally qualified fire into substandard conditions, resulting in fire and explosion accidents.
Washing can be used hot water cooking, pickling, alkaline cleaning or solvent cleaning, so that the equipment and the inner wall of the dirt and other things to soften and dissolve and remove, using the method of cleaning should be determined according to the specific circumstances. Is alkali washing with sodium hydroxide (caustic soda) water solution for cleaning, the cleaning process is added in the container the required amount of water, then the alkali quantitative batch is added gradually, while slowly stir the alkali was added to dissolve into the water, before steam boiling. At the end of the steam pipe must be extended to the bottom of the liquid, to prevent steam after lye bubble spills. After the first release of alkali tablets and water (especially hot water), because the dissolution of caustic soda will produce a lot of heat, poured out of the container pipe and burn the operator.
For the cleaning method can not remove dirt as, by the operating personnel to wear protective equipment, enter the inside of the device using tools such as fire eradication, wood, brass (copper 70%) or aluminum knife, brush and so on, can also be used hydraulic, pneumatic and electric machinery to clear the suction blasting method and replacement cleaning must be careful not to stay dead.
(five) air analysis and monitoring
Hot analysis is the sampling and analysis of equipment and pipeline and gas environment. Hot analysis can not only ensure compliance with fire conditions began to fire, and fire conditions can change welding process control. In the replacement operation process and hot work, should be continuously from different parts of vessels and pipes inside and outside air samples, check the content of flammable gas and toxic gas sound. Welding should be carried out as soon as possible after passing the examination, half an hour before the fire in the analysis of the data is valid, otherwise it should be re sampling and analysis. Sampling should be paid attention to the representation of the sample in order to make the data accurate and reliable. After the start of welding at regular intervals still need to make analysis on the operation environment of the scene, the fire analysis time interval according to the scene to determine. If the gas content exceeds the specified requirements, should immediately stop welding repair, re clean and sample analysis, until qualified.
The qualification requirements for gas analysis are:
1, flammable gas or flammable vapor content: the lower limit of explosion is greater than 4%, the concentration should be less than 0.5%; the lower limit of the explosion is less than 4%, the concentration should be less than 0.2%;
2, the content of toxic and harmful gases should be in accordance with the "industrial enterprise design and health standards," the provisions of;
3, for the operator to enter the internal welding equipment and pipes, oxygen content should be 18% ~ 21%.
(six) the sealed container is prohibited without welding holes
1, welding should open the container manhole, hand hole, cleaning hole and the hole, and should maintain good ventilation.
The sealed container 2, is strictly prohibited without welding holes.
In 3, domestic vessels and pipes using gas welding or cutting, welding and cutting torch ignition and flameout should be carried out in the outside of the container, to prevent too much in the container and acetylene gas pipeline.
(seven) safety organization measures
1, must go through the formalities of examination and approval in accordance with the work requirements and procedures. The purpose is to develop security measures, clear the responsibility of the leader. Take the welder welding work should undergo special training, and after the examination to obtain the corresponding qualification certificate.
2, before work to develop detailed practical solutions, including welding procedures and specifications, safety measures and construction plans, and notify the fire brigade and rescue station, production workshop and other aspects make contingency plans.
3, in the operating point around 10m should stop other fire work, flammable and explosive substances should be moved to a safe place.
4, the work place should have enough lighting, portable light should use 12V safety voltage, and have good protective cover.
In 5, no hot work in the fire area and welding in container and pipe repair operation, must be a guardian. The purpose of monitoring is to ensure the safety of the measures. The guardian shall be a person with experience. Guardians should be clear responsibilities, stick to their posts.
6, into the container or pipeline for welding repair work, the greatest danger of electric shock, it is necessary to strictly implement the provisions on the safety of electricity, to take the necessary protective measures.
Four, with pressure is not replacement welding safety technical measures
(a) strict control of oxygen content
At present, the relevant departments of hydrogen, carbon monoxide, acetylene and the occurrence of furnace gas, such as the limit of oxygen content is not more than 1% as a safe value, it has a certain safety factor. At room temperature and atmospheric pressure, the limit oxygen content is about 5.2%, but the difference of high pressure and high temperature condition, and the error of instrument and detection are considered, so the rule is 1%. The detection of the oxygen content in the vessel or pipe must be carried out before and during the welding process of the welding with pressure. When the oxygen content in the system is found to be increased, the reason should be found out as soon as possible, otherwise, it should be stopped.
(two) positive pressure operation
In the whole process of welding in vessels and pipes must maintain the stability of continuous positive pressure, which is the key with pressure displacement welding safety. Once the negative pressure air into the container or pipeline is welding, it is prone to explosion.
Pressure general control in 0.015 ~ 0.049MPa (150 ~ 500 mm water column) is appropriate. The pressure is too large, the increase of flow velocity caused by violent fire, causing difficulties for the welding operation, even make the melt hole expansion, caused by the accident; the pressure is too small, easy to cause the pressure fluctuation of welding will make the air into the container or pipe, the formation of explosive gas mixture.
(three) strictly control the content of combustible gas around the working point
Whether in the indoor or outdoor with pressure not replacement welding repair work, the surrounding space of the combustible gas content, to less than 0.5% is appropriate. Analysis of gas sampling site should be based on the nature of the gas and the characteristics of the housing structure, etc., to ensure the accuracy and reliability of the test results.
Indoor welding repair, the doors and windows should be opened for natural ventilation, if necessary, alsoMechanical ventilation should be taken to prevent the formation of explosive mixed gases.
(four) safety requirements for welding repair operation
1, the welder should avoid fire during operation to prevent burns.
2, welding norms should be in accordance with the provisions of pre conditioning, welding current is too large or improper operation, in the role of the media pressure is likely to cause burning, resulting in accidents.
3, in the event of a change in conditions, such as a sharp drop in the system pressure or oxygen content exceeds the safety value, etc., should immediately stop welding, to identify the reasons to take the appropriate measures to continue to be welded.
4, in the welding process, if the occurrence of violent fire phenomenon should immediately take fire-fighting measures. Before the fire is not extinguished, it shall not cut off the source of the gas, and shall not reduce or eliminate the pressure of the container or pipe to prevent the formation of explosive gas mixture.