What are oxygen pipelines solutions?
What is oxygen?
Table of Contents
- What is oxygen?
- What is an oxygen piping system?
- Selection of oxygen pipeline and accessories
- Installation of oxygen pipes and accessories
- Purging and degreasing of oxygen pipeline after construction
- Purging of oxygen pipeline
- Degreasing of oxygen pipeline
- Risk analysis and preventive measures for combustion and explosion of oxygen pipelines and valves
- Analysis on the causes of combustion and explosion of several common oxygen pipelines and valves
- Preventive measures
- Analysis of the explosion mechanism of oxygen pipeline
- Analysis of safety accidents in oxygen pipeline
- Safety control technology of oxygen pipeline
- What are oxygen pipelines solutions?
- Oxygen pipeline systems should be designed and installed by skilled professionals
Oxygen, chemical formula O2, is a colorless, odorless and tasteless gas. It is the most abundant element on the earth’s surface. It is indispensable for most life on the earth. We absorb oxygen by breathing air. Technically, oxygen is extracted from the air liquefaction process, and the oxygen content in the air is 21%. It is the basis of all breathing and combustion processes, and therefore a prerequisite for almost all life processes.
Types of oxygen
- Standard purity oxygen: The standard purity oxygen is defined as 99.5+% by volume.
- Low purity oxygen : Gaseous oxygen that contains 35% or less oxygen by volume (23.5% to 35%) .
- Ultra high purity (UHP) oxygen : Oxygen purity equal or higher than 99.999% by volume.
Chemical Properties and Applications of Oxygen
The chemical property of oxygen is very active, and it is a strong oxidant and combustion promoter. The intensity of the oxidation reaction depends on the concentration and pressure of oxygen. If the oxidation reaction is carried out in pure oxygen, the process is very intense, and a lot of heat is released at the same time. When oxygen is mixed with combustible gas (acetylene, hydrogen, methane, etc.) in a certain proportion, it will explode in case of fire. After the oxygen is compressed, if there is grease, iron filings or small particles of combustibles (pulverized coal, carbon particles or organic fibers) in the process of transportation, friction and collision with the pipe wall or body will occur with the airflow movement, which will produce a lot of friction heat, causing the pipe and machine to burn or even explode.
Oxygen is widely used in industrial production, for example, liquid oxygen can be used as combustion supporting agent for rockets in national defense industry; Cutting and welding in mechanical industry; Oxygen steelmaking, steel rolling and non-ferrous metal smelting in metallurgical industry; Coal chemical industry is used as oxidant of coal; As well as medical and deep-water operations, a large amount of oxygen is required.
What are the differences between medical oxygen and industrial oxygen?
In fact, in China, medical oxygen is included in drugs for management, so medical oxygen has very strict product standards; All production and operation of medical oxygen shall obtain relevant licenses. The requirements for industrial oxygen are generally based on the oxygen purity, and there are no special requirements for other sanitary conditions.
Because of this, there are no relevant restrictions on industrial oxygen in China, such as carbon monoxide, methane and other harmful gases, and there are no restrictions on the content of water, bacteria and dust. After all, whether there are these indicators does not hinder the use of industrial oxygen in welding, gas cutting, etc. For medical oxygen, there are clear provisions in GB 8982-1998 Medical Oxygen, which requires that the dew point temperature of medical oxygen should be less than – 43 ℃, and the content of carbon dioxide, carbon monoxide, gaseous acidic and alkaline substances, ozone and other gaseous oxidants in oxygen should meet the detection standards without odor. This kind of oxygen is the qualified medical oxygen, which can maximize the safety of oxygen use in the treatment and rescue of patients.
If industrial oxygen is used instead of medical oxygen, it is not allowed in China; It has various uncertain and even fatal risks. First of all, industrial oxygen may carry harmful gases or impurities, which may damage people’s upper and lower respiratory tract. The symptoms may be runny nose, dyspnea, dizziness, headache (hypoxemia), etc. Secondly, industrial oxygen cylinders may be mixed with other industrial gases that cause great harm to human body; If this “unclean” oxygen is used for patients, it will lead to death in serious cases. Therefore, industrial oxygen cannot replace medical oxygen.
What is an oxygen piping system?
Oxygen pipeline is a piping system specially used to transport pure oxygen. With the rapid development of national economy, the oxygen demand of metallurgy, chemical industry, machinery and other industries in China has increased significantly, and the construction of oxygen pipeline transportation projects has also increased gradually. The oxygen pipeline transportation is mostly pure oxygen, so the safety requirements for the pipeline system are very high. Oxygen is highly oxidizing. After metal is combusted in oxygen, it will cause instantaneous explosion and serious casualties. Therefore, analyzing and studying the mechanism of oxygen pipeline safety accidents, strengthening the safety awareness in the process of design, installation, use and maintenance of oxygen pipeline system, and effectively improving the level of pipeline oxygen transportation have become increasingly the direction of researchers’ exploration and research topic.
Oxygen has strong oxidizing and combustion supporting properties. Although oxygen itself is incombustible, it can reduce the ignition point of combustible materials. If it is not handled properly, there will be potential safety hazards. It can be said that the safety of the oxygen pipeline system in an oxygen generation system directly determines whether the whole system is safe and reliable. Especially in some projects with large oxygen consumption, many points, wide distribution and complicated pipe network laying, whether the oxygen pipeline is safe is a major test for the construction personnel.
Selection of oxygen pipeline and accessories
Material selection of oxygen pipeline
The metal material selection of oxygen pipeline is a basic safety factor that must be considered in the use of oxygen pipeline. The working pressure and flow rate of oxygen in the pipeline are combined to test the tolerance of the pipeline. With the improvement of the working pressure and flow rate of oxygen pipeline, the pipeline material has also developed from carbon steel and stainless steel to copper and copper alloys or nickel and nickel alloys.
The metal material of oxygen pipeline shall be selected according to the pressure, temperature, flow rate of oxygen in the pipeline and other conditions. In addition to meeting the same strength conditions as other pipelines, oxygen pipelines also need to have requirements for corrosion prevention, rust prevention and fire protection.
Burn resistant alloys
Burn resistant alloys are engineering alloys that, after being subjected to an ignition event, either will not burn or exhibit burn quenching behaviour, resulting in minimal consumption. A metal used at or below its exemption pressure, for a defined set of process conditions including oxygen purity, temperature, and minimum material thickness would be considered to be a “burn resistant alloy” under those conditions. Examples of metals which are highly burn resistant, and hence exhibit high exemption pressures, are copper, nickel, and copper/nickel alloys such as monel. Other engineering alloys, such as stainless steel, may exhibit varying degrees of burn resistance depending upon oxygen pressure, oxygen purity, temperature, equipment configuration, piping layout, and metal thickness..
Copper-based alloys used in components for oxygen piping systems generally contain at least 55 weight % copper. Included within this group are the coppers, brasses (copper alloyed primarily with zinc), bronzes (copper alloyed with aluminium, silicon, manganese, tin, lead, etc.) and copper nickels (copper alloyed with nickel). These have had an outstanding application history in oxygen service.
Caution should be exercised in the use of aluminium bronzes. Aluminium bronzes containing more than 2.5% and up to 11% aluminium (by weight) have been extensively used for cast components (e.g., valve bodies, pipe fittings, etc.) in oxygen pipeline duty for many years without a significant history of failure. However, use of aluminium bronze is not recommended as flammability tests show that it will support burning if ignited, even at low pressure.
Aluminium content in copper alloys should be limited to 2.5% (by weight).
Nickel-based alloys used in oxygen gas transmission pipeline systems contain at least 50 weight % nickel and nickel contents up to 99+ weight % have been used. However, some tabulations of nickel alloys may list alloys with nickel contents as low as 30 weight %. Generally, the higher the combined nickel and copper content, the more burn resistant the alloy. Combined nickel and cobalt also may be beneficial.
Some of the major nickel alloy families and examples of each are as follows: nickel (Nickel 200), nickel-copper (Monel-400 and Monel-500), nickel-chromium (Inconel 600 and Inconel X-750) and nickel-chromium-molybdenum (Hastelloy C-276 and Inconel 625).
Stainless steel alloys
Ferrous alloys become stainless when they contain a minimum chromium content of at least 10 to 13 weight %. There are a number of stainless steel classifications, which are dependent upon the alloy content, crystalline lattice, strengthening mechanisms, and the ratio of ferrite stabilizers to austenitic stabilizers.
Stainless steel classifications with examples of each type are as follows:
- Austenitic (304, 304L, 316, 316L, 321, 347);
- Ferritic (430);
- Martensitic (410);
- Precipitation hardening (17-4 PH); and Super Duplex &Duplex (SAF 2507, 329, SAF 2205).
The preceding alloy designations were for wrought products but there are alloys such as CF-8, CF-3, CF-8M, CF-3M, which are the cast analogs of 304, 304L, 316, and 316 L respectively.
Of the various stainless steels, the 300 series stainless steels and their cast analogs are the most commonly used in oxygen gas transmission piping systems.
The commercial listings of cobalt alloys generally start with a minimum cobalt content of at least 40 weight %. Wear resistant alloys such as Stellite 6 or Stellite 6B are sometimes used as coatings on valve trims to minimize erosion damage and improve valve life. Cobalt alloys have a successful history in oxygen when used as coatings, even though the thin cross-section may reduce its burn resistance.
When the term non-ferrous alloys is used in this document, it includes only copper, nickel, and cobalt alloys. It does not include aluminium or reactive materials such as titanium or zirconium.
Included in this category are carbon-steel, low-alloy steel, and all stainless steels irrespective of whether these alloy families are in cast or wrought form.
The working pressure of oxygen can be divided into four sections:
- ① The oxygen pressure pipeline with p ≤ 0.6MPa belongs to general low pressure oxygen pipeline and is applied in many industries.
- ② 0.6MPa
- ③ 3.0MPa
- ④ Oxygen pressure pipes with p>10MPa are mainly used in cylinder filling and some chemical industries. The oxygen pressure is very high and the pipe material is strictly limited.
It has been proved by practice that it is convenient and applicable to manage separately in four pressure intervals.
The places where oxygen is used are divided into general places and non general places.
Non ordinary places refer to the areas where the valves on the distribution main pipe frequently operate after the valves in the area, the main pipe valves, one system branch pipe valves, and the workshop inlet valves are within the range of 5 times of the nominal diameter (not less than 1.5m), the front and back of the control valve group are within the range of 5 times of the nominal diameter (not less than 1.5m each), the inside of the oxygen pressure workshop, behind the release valve, wet oxygen transmission, oxygen filling platform, manifold and other impact places, as important places, dangerous locations, accident sources, high-pressure facilities, The material selection of oxygen pipeline shall be strict to ensure safe production.
The specific requirements for the selection of oxygen pipe materials, as shown in the above table, shall be strictly followed.
- ① Carbon steel plate coiled welded pipe should be used when the working pressure p is less than 0.1MPa and the pipe diameter exceeds that of existing welded steel pipe and seamless steel pipe products.
- ② Welded steel pipes are suitable for general places with p ≤ 0.6MPa.
- ③ Seamless steel pipe is applicable to general places with p ≤ 3.0MPa.
- ④ Stainless steel welded pipe and stainless steel rolled welded pipe are applicable to all places with p ≤ 3.0MPa. For stainless steel rolled welded pipe, its inner wall weld shall be polished.
- ⑤ Stainless steel seamless pipe is applicable to all places with p ≤ 3.0MPa and general places with p>3.0MPa.
- ⑥ Oxygen pipes with p>10MPa are basically used for cylinder filling. The main pipe from the outlet of high-pressure oxygen compressor or liquid oxygen pump to the filling platform is a common place, and stainless steel pipes can be used, and there is mature experience in use. Large diameter copper alloy or nickel alloy pipes are scarce, expensive, and rarely used. Copper alloy or nickel alloy pipes shall be used for the filling table’s own pipes and oxygen manifold pipes. Stainless steel seamless pipe has low temperature resistance and high strength, which is suitable for liquid oxygen pipeline.
- ⑦ Copper and copper alloy extruded pipe, copper and copper alloy drawn pipe, nickel and nickel alloy pipe are applicable to all places with p ≤ 21MPa and liquid oxygen pipeline due to their excellent flame explosion resistance and low temperature resistance.
The selection of elbows, bifurcations and reducers on oxygen pipelines shall meet the following requirements:
- Wrinkled elbow is strictly prohibited for oxygen pipeline. When cold bending or hot bending is used to make carbon steel elbow, the bending radius shall not be less than 5 times of the pipe outer diameter; When seamless or pressed welded carbon steel elbow is used, the bending radius shall not be less than 1.5 times of the pipe outer diameter; When stainless steel or copper base alloy seamless or pressed elbows are used, the bending radius shall not be less than the outer diameter of the pipe. For rolled welded steel pipe with working pressure not greater than 0.1MPa, welded elbow with bending radius not less than 1.5 times of pipe outer diameter can be used. The inner wall of elbow shall be smooth without sharp edges, burrs and weld beading;
- The reducer of oxygen pipeline should adopt seamless or pressed welding parts. When welding, the length of reducing part should not be less than 3 times of the difference value of each item outside the pipe at both ends; The inner wall shall be smooth without sharp edges, burrs and weld beading;
- The bifurcated head of the oxygen pipeline should be seamless or pressed weldment. If it cannot be obtained, it should be prefabricated in the factory or on site, but it should be processed to be free of acute angles, protruding parts and weld beading. It is not suitable to open holes and plug in on site.
Selection of pipe accessories
Gaskets for flanges on oxygen pipelines shall be selected according to relevant national current standards; The gasket of pipe flange shall be selected according to the following table:
The oxygen pipeline shall be connected by welding, but the connection with equipment and valves can be made by flange or thread, and the connection with wire mouth shall be made by using lead monoxide, water glass or polytetrafluoroethylene film as filler. It is prohibited to use lead red coated hemp or cotton wire, or other materials containing grease.
The oxygen filter should be set at the inlet of the oxygen compressor, and the oxygen filter should be set in front of the regulating valve. The shell should be made of stainless steel, the filter screen should be made of copper base alloy or pure copper, and the mesh size should be 160-200 μm.
The valves of oxygen pipeline shall be special oxygen valves and shall meet the following requirements:
- 1. For valves with working pressure greater than 0.1MPa, gate valves are strictly prohibited;
- 2. Oxygen valves with PN ≥ 0.1MPa and DN ≥ 150mm should be selected with bypass.
Installation of oxygen pipes and accessories
- 1. The selection of measuring instruments shall consider the requirements of safety, fire and explosion protection. When oxygen is released, fireworks are strictly prohibited near the vent. All kinds of oxygen vent pipes shall be led out of the room.
- 2. The oxygen pipeline should not pass through the high-temperature and flame area. If it must pass, additional insulation measures should be taken in this section of the pipeline, and the pipe wall temperature should not exceed 70 ℃. Open fire and oil contamination are strictly prohibited from approaching oxygen pipes and valves.
- 3. The oxygen pipeline shall be equipped with fewer elbows and bifurcated heads as far as possible. The oxygen pipeline elbows with working pressure higher than 0.1MPa shall be made of stamped valve type flanges.
- 4. The oxygen pipeline shall be connected by welding, but the connection with equipment and valves can be flanged or threaded. Lead monoxide, water glass or polytetrafluoroethylene film shall be used as the filler at the screw thread connection. It is prohibited to use hemp or cotton thread coated with lead red or other materials containing grease.
- 5. During the installation of oxygen pipes, the cleanliness and residual grease must be checked. If they are unqualified, they should be degreased and cleaned and checked to be qualified.
Requirements during oxygen pipeline installation
⑴ During the installation of oxygen pipes, effective measures shall be taken to prevent oil pollution, and to prevent combustibles, rust chips, welding slag, sand and other debris from entering or leaving in the pipes, and strict inspection shall be carried out. In order to avoid the pollution of the pipeline, the hands, tools, work clothes, etc. of the installation workers should not be contaminated with oil.
⑵ During pipe connection, it is not allowed to forcefully align the pipe, heat the pipe, add deflection pads or multi-layer pads to eliminate defects such as gap deviation, staggered joints or misalignment of the interface end face. When the pipes are assembled, the misalignment of the inner wall shall meet the requirements, and the installation straightness of the pipes shall be checked. Natural compensation shall be adopted for oxygen pipeline as far as possible, and square compensator or waveform compensator can be used for manual compensation. But in the iron and steel enterprises, waveform compensator is rarely or even not used.
The butt weld of the pipeline shall not be set at the support and hanger, and the distance from the weld to the edge of the support and hanger shall not be less than 100mm.
(4) When the pipe passes through the wall or floor, the casing shall be added, and there shall be no interface in the casing.
(5) When installing stainless steel pipes, iron tools shall not be used to knock. The content of non-metallic gaskets for flanges shall not exceed 25mg/kg.
(6) The contact surface between the stainless steel pipe and the carbon steel support must be protected by a non-metallic backing plate or stainless steel sheet without Cl -.
(7) PTFE tape shall be used as the sealing material at the connection between the pipe and the valve screw port, and oil-bearing and combustible materials such as lead oil hemp wire shall not be used. The gasket is in direct contact with oxygen, and the gasket of oxygen pipeline must be made of incombustible materials. Such as PTFE, annealed and softened copper sheet, etc. If the gasket is not adjusted and exposed to the inner surface of the pipe during installation, combustion accidents are likely to occur when iron powder contacts with oxygen due to friction. Therefore, the position of the gasket must be adjusted in place during installation. (8) During pipeline installation, the flange sealing surface and sealing gasket shall be checked to ensure that there are no scratches, spots and other defects affecting the sealing performance.
Purging and degreasing of oxygen pipeline after construction
After the construction of the oxygen pipeline, welding slag or other sundries may be left in the pipeline due to welding and other reasons, and combustion and explosion may occur in the oxygen transmission process; Or the oxygen pipeline is stained with oil during the construction of oxygen pipeline. To ensure safety, the oxygen pipeline shall be purged and degreased after the completion of the pipeline.
Purging of oxygen pipeline
After the construction of the oxygen pipeline, the residual water, scrap iron, sundries, etc. in the pipeline shall be purged with oil-free dry air or nitrogen until there is no rust, dust and other sundries. The purging speed shall not be less than 20m/s. It is forbidden to purge the pipeline with oxygen.
We all know that when stainless steel pipes leave the factory, they need to be pickled and passivated. However, sometimes users ask for re degreasing of pipes? As far as the pipeline is concerned, the relatively reasonable degreasing should be completed on site, that is, after all pipelines are installed, degreasing treatment should be carried out in the whole pipeline system. Generally, the manufacturer is not allowed to carry out degreasing treatment. So, what is the problem of requiring the manufacturer to degrease the pipeline?
With the increasing level of industrialization in China and the vigorous development of petrochemical, natural gas, medical equipment, instrumentation, aviation, aerospace and other industrial projects, the requirements for stainless steel pipe technology are also getting higher and higher. For example, the cleanliness of the pipeline requires that there should be no free rust, large particles of dust, welding slag, grease and other impurities inside.
The cleanliness requirement of oxygen pipeline is quite strict. Most of the oxygen pipelines are used to transport oxygen with purity greater than 99.99%. The pressure is high and the flow rate is fast. If the internal cleanness of the pipeline cannot be guaranteed, the trace oil and metal ions in the pipeline may be oxidized and collided with the high-pressure pure oxygen, resulting in electric sparks, which may lead to unimaginable serious consequences, or even catastrophic accidents.
Therefore, according to the process requirements, the newly built equipment pipelines shall be cleaned with chemical cleaning method to remove the oil stain and other impurities on the internal pipe wall before the unit start-up. The supplier will also be required to degrease the pipe.
Degreasing process of oxygen pipeline
Degreasing cleaning steps of oxygen pipeline: water flushing → manual wiping degreasing → water flushing → compressed air (or nitrogen) purging.
During flushing, small high-pressure water cleaning equipment shall be used, and the pressure shall be controlled at about 0.6Mpa to ensure that the impurities inside the pipeline are cleaned. The purpose is to remove the ash, sediment, separated metal oxides and other loose dirt in the pipeline.
Degreasing by manual wiping
Inject the cleaning and degreasing mixture into the cleaning basin, add it in proportion, mix it evenly, and then use it again and again. During the cleaning process, monitor the cleanliness of the degreasing cleaning solution. If the color of the degreasing cleaning solution becomes dirty, drain the existing degreasing solution and reconfigure the degreasing cleaning solution. The purpose is to remove all kinds of oil, graphite, antirust oil and other organic substances in the pipeline, so as to ensure that the internal of the pipeline is clean during installation and meet the requirements of equipment operation.
After the pipe degreasing is completed, use a large amount of water for flushing. When the flushing water flowing out of the pipe is clean, the water flushing can be ended. The purpose of water flushing after degreasing is to flush the degreased residue in the pipeline.
Compressed air (or nitrogen) purging
Use oil-free compressed air (or nitrogen) for purging, and use clean plastic cloth to wrap and seal the pipes or parts after drying the inside of the pipes, so as to ensure the cleanness of the inside of the pipes and avoid secondary pollution.
Degreasing safety regulations
- 1. Degreasing shall be carried out outdoors in sunny days, outdoors and in a well ventilated environment.
- 2. All inflammables, explosives and other sundries shall be removed from the degreasing site, and the dedicated degreasing area shall be divided, and irrelevant personnel shall not enter. No fireworks, and set “No fireworks!” “Poisons!” Signage.
- 3. The staff involved in degreasing shall have necessary protective measures and protective equipment. When the concentration in the air exceeds 50mg/m3, they shall use gas masks.
- 4. The degreasing agent shall be stored separately in an airtight iron drum and protected from light in a well ventilated, dry and cool warehouse.
- 5. Degreasers shall not come into contact with strong acids or bases.
- 6. It is strictly forbidden to mix different solvents or use them outside the scope of application.
- 7. Degreasing agent must have product quality certificate.
- 8. Degreasing measures shall be formulated according to working medium, pipe material, pipe diameter and dirt degree.
- 9. For pipes with obvious oil stains or serious rust, the oil stains and rust shall be removed by steam purging, pickling or other methods before degreasing.
- 10. When degreasing, degreased articles shall not contain water.
- 11. The degreased parts after degreasing shall be naturally ventilated and dried in the atmosphere for 24 hours. It can also be dried with nitrogen or dry air.
- 12. After degreasing, the degreased parts shall be inspected by full-time inspectors and signed by the supervisor before proceeding to the next process.
- 13. The pipe orifice of the qualified degreased pipe shall be closed in time to ensure that it will not be polluted in the subsequent process construction.
- 14. The Pipe System Degreasing Record shall be carefully filled in when the pipe is degreased.
- 15. The degreasing agent shall be prevented from splashing and spilling to the ground. Spilled solvent shall be immediately sucked up with wood chips, sand, etc. and collected in a special closed metal container together with the degreased fabric.
- 16. The discharge of degreasing residues and pollutants shall comply with the relevant national standards.
- 17. The remaining solvent after degreasing shall be returned to the warehouse and kept properly.
Common degreasing solvent
1. The pipeline can be degreased with organic solvent (dichloroethane, trichloroethylene, carbon tetrachloride, industrial alcohol, etc.) concentrated nitric acid or alkali solution.
2. The organic solvent for degreasing shall be used according to the oil content in the following table.
|Oil content (mg/L)||Use regulations|
|500||Do not use|
Common Degreasing Methods for Oxygen Piping Systems
1. Tank leaching method:
The tank immersion method is a degreasing method to make a tank type container, add degreasing solution into the tank, and put pipes and pipe fittings into the tank for immersion. This method is generally applicable to the degreasing of small and medium-sized pipes.
2. Injection method:
The injection method is to plug one end of the pipe with a wooden plug or a blocking plate, inject the degreasing solution into the pipe from the other end, and then plug the other end, so that the pipe stays flat for 10-15min, during which the pipe is turned over 3-4 times, which is a degreasing method for soaking in the pipe. This method is suitable for degreasing small diameter pipes.
3. Wiping method:
The wiping method is to use white knitted fabric dipped in degreasing solvent to wipe the surface of the pipe, and then put it in the open air for drying. This method is suitable for degreasing large diameter pipes or containers.
4. Barbecue method:
The barbecue method is a degreasing method that uses the heat energy of the fire to bake the degreased parts. Put the degreased parts near the fire and bake them for 2-3min at a temperature of 300 º C to evaporate and dry the oil stains. After baking, they should be coated with graphite powder. This method is applicable to some articles that are not suitable for contacting degreasing agent, such as asbestos gasket, asbestos sealing filler, etc.
5. Circular method:
The circulation method is a mechanical circulation degreasing method that uses solution tank, acid resistant pump and connecting pipes in series for circulation. This mechanical circulation method is suitable for degreasing the installed pipeline system.
- 1. Carbon tetrachloride or alkali liquor should be selected as degreasing solution.
- 2. The degreasing method should be bath immersion or wiping.
- 3. In order to further improve the degreasing quality, it can be combined with the wiping method.
Detailed rules and steps for degreasing by tank leaching
1. Pipe degreasing
- (1) A U-shaped degreasing tank is made of a DN600 carbon steel pipe, that is, the pipe is cut in half, the two ends are welded with semicircle blanking plates, and two support seats. The groove length shall be 1m longer than the degreased pipe (about 7m long). One DN25 drain valve shall be set at one end of the tank.
- (2) Install two pairs symmetrically at 30 ° below the U-shaped groove Ф 40 bearing, so that the degreasing pipe will not touch the bottom when it is put into the tank and can rotate freely. When the amount of solution volatilization is small, the solution can not completely overflow the degreasing pipe and can rotate and soak.
- (3) Place the degreased oxygen pipeline and U-shaped groove in a straight direction, set a set of routing block right above the center of the pipe groove, and hang a 2T chain block to lift the pipeline into the U-shaped groove for degreasing. After degreasing, lift the pipeline from the U-shaped groove to the other side of the groove.
- (4) When lifting the pipe with chain block, a pair of elevators can be selected as the lifting point to hang at both ends of the pipe for easy operation. When the pipe is degreased and rotated in the groove, the F-type wrench can be used to gently rotate it to reduce the contact between hands and solvent.
- (5) After the U-shaped tank is made, when adding solution for the first time, put the degreased pipe in the tank and then add solution to prevent excessive solution and overflow during pipe laying. Add the solution to the degreased pipe about 20-30mm, not too much, and the liquid level should be 100-150 below the edge of the dissolver.
- (6) The lifting speed of the degreased pipe shall be controlled by chain block when entering and leaving the tank, and the pipe shall be lifted and dropped gently to prevent the solution from overflowing.
- (7) The immersion time of the pipeline in the tank depends on the degree of pollution, generally 10-15min.
- (8) After the soaking tank is filled with lye, it is not allowed to knock the tank or pipe with metal objects, hammers, etc.
- (9) The degreased pipes shall be sealed and stored with PVC plastic cloth after air drying.
2. Degreasing of pipe fittings
- (1) The pipe fittings can be turned over 3-4 times during soaking by putting them into U-shaped grooves.
- (2) For places that cannot be soaked, white silk cloth can be used for wiping, namely, soaking wiping method combined with degreasing.
3. Valve degreasing
- (1) Valve degreasing shall be carried out after the water pressure tightness test and strength test are qualified.
- (2) The valve shall be disassembled for degreasing. Before degreasing, the valve shall be disassembled into parts to remove rust and other impurities, and immersed in the solution for 5-10min, not too long. Bolts and metal gaskets can be degreased in the same way.
- (3) When there is slight oil stain on the valve, first use white silk cloth dipped in degreasing agent to scrub. Then soak in the tank.
- (4) When there is obvious oil stain and dirt on the valve, use other solvents or methods to remove the oil stain and dirt first, and then use degreaser to degrease.
- (5) If the sealing gasket of the valve is non-metallic gasket, carbon tetrachloride can only be used for degreasing. The gasket shall be immersed in the degreaser for 1.5-2h. After taking it out, it shall be hung separately with iron wire at the air circulation place for natural drying until there is no smell of the degreaser. The time shall not be less than 24h.
- (6) The valve and parts after degreasing should not be assembled immediately, but should be dried with nitrogen or dry compressed air before assembly, otherwise they should rust.
- (7) Oil containing medium shall not be used for pressure test and purging of degreased valves and pipelines.
Degreasing inspection standard for oxygen pipeline
(1) All degreased pipes and accessories shall be visually inspected, and no foreign objects or residues shall be stuck on them.
(2) Inspection method
- 1) Check the inner wall of the pipe with ultraviolet light with the wavelength of 320-380nm, and there should be no oil fluorescence.
- 2) Wipe the inner wall of the pipe with clean and dry white filter paper, and there should be no oil stain on the paper.
- 3) Or use degreasing solvent to test whether the grease content does not exceed the requirements of the entrusting party.
- 4) Other relevant technical indicators proposed by the entrusting party.
(3) The degreased parts that fail to pass the inspection must be degreased again with the above-mentioned degreasing method.
(4) All degreased parts must be inspected and qualified by relevant personnel before proceeding to the next process. Those without certification shall be deemed as unqualified degreasing and must be degreased again.
The chemical cleaning and degreasing process of oxygen pipeline standardizes the construction process of oxygen pipeline cleaning and degreasing, greatly improves the internal cleanliness of oxygen pipeline, and is a reliable guarantee for safe and efficient operation of oxygen pipeline, which is worthy of attention and promotion by steel pipe manufacturers.
Safety and environmental protection measures
The most commonly used solvent for degreasing pipes and equipment is carbon tetrachloride, also known as tetrachloromethane. It is a colorless, transparent, ether flavored, oily liquid with a slightly sweet and pleasant taste similar to chloroform. It is not easy to burn and volatilize. Carbon tetrachloride is toxic to human body, has mild anesthetic effect, and is most easily absorbed by skin. In case of frequent exposure to carbon tetrachloride with high concentration, inhalation may cause carbon tetrachloride poisoning, headache, vomiting and other symptoms. The liquid is irritating to the eyes and skin, causing serious damage to the liver, kidney and other substantive organs after swallowing in large quantities. At room temperature, carbon tetrachloride reacts with acid to generate phosgene, which is a highly toxic gas and can be poisoned even in very small amounts. Carbon tetrachloride was originally a commonly used fire extinguishing agent, which is not flammable, but it can be used at high temperature (500 ° C С The above) can be decomposed into highly toxic and corrosive gas and steam, and the combination of carbon tetrachloride steam and water vapor can also generate phosgene. In addition, carbon tetrachloride is ineffective due to chemical reaction with alkali. Therefore, pay attention to the following points when using carbon tetrachloride:
- 1. Degreasing shall be carried out outdoors in a well ventilated place.
- 2. Fireworks are strictly prohibited at the degreasing site, and heating of carbon tetrachloride is strictly prohibited during use. The use temperature is controlled at 40 ° С Keep away from heat source and ignition source.
- 3. Carbon tetrachloride in contact with flame or hot light metals (such as potassium, magnesium, sodium, aluminum, etc.) and other chemicals (such as calcium carbide, ethylene, carbon disulfide, etc.) can cause strong decomposition and even explosion. Therefore, during the storage and use of carbon tetrachloride, fireworks and contact with the above substances are strictly prohibited.
- 4. The solvent shall be stored in a sealed container and shall not contact with alkali to prevent deterioration and failure.
- 5. Workers shall strengthen personal protection when degreasing, and wear work clothes, masks, protective glasses and long sleeve rubber gloves.
- 6. When pouring solvent from one container to another, wear protective equipment such as gas mask before operating in the open air.
- 7. After degreasing and antirust treatment, degreased parts required to be antirust shall be protected by vapor phase antirust paper, vapor phase antirust plastic film sealing and other measures.
- 8. During degreasing construction, degreasing personnel shall carefully implement process handover, shift handover and original record system.
- 9. Strengthen the management and security of degreasing site to avoid accidents.
- 10. Two dry powder fire extinguishers shall be provided at the degreasing site.
- 11. Showers and eye washing appliances shall be available at the construction site.
- 12. The person accidentally inhaled shall be moved to a place with fresh air, and the eyes and skin of the person in contact shall be washed with water.
- 13. Emergency treatment: immediately leave the site, follow the general first-aid routine treatment, and give oxygen at an early stage. The poisoned person should lie in bed and rest, closely observe, and pay attention to the early signs of liver and kidney damage.
- 14. Solvents shall not be in contact with strong acids, and shall not be discharged randomly after the cleaning process to avoid pollution.
- 15. Based on the principle that whoever uses the carbon tetrachloride shall be responsible, the remaining carbon tetrachloride must be recovered in time.
Risk analysis and preventive measures for combustion and explosion of oxygen pipelines and valves
In recent years, with the increase of oxygen consumption, oxygen pipelines are used by large oxygen users. Due to the long pipeline and wide distribution, combined with the quick opening or quick closing of valves, the oxygen pipeline and valves are often subject to combustion and explosion accidents. Therefore, it is essential to comprehensively analyze the hidden dangers and dangers of oxygen pipeline and cold doors and take corresponding measures.
Analysis on the causes of combustion and explosion of several common oxygen pipelines and valves
1. Rust, dust and welding slag in the pipeline rub with the inner wall of the pipeline or valve port to produce high temperature and burn
This situation is related to the type of impurities, particle size and gas velocity. Iron powder is easy to burn with oxygen, and the finer the particle size is, the lower the ignition point is; The faster the gas velocity is, the more likely combustion will occur.
Table.1 Ignition Point of Iron Powder in Atmospheric Oxygen
Grain size (mesh)
Flash point (℃)
2. There are grease, rubber and other substances with low ignition point in the pipeline or valve, which are ignited under local high temperature.
See Table 2 for the ignition points of several combustibles in oxygen (under normal pressure).
Table.2 The ignition points of several combustibles in oxygen (under normal pressure) are as follows
Name of combustible
Steel paper pad
Flash point (℃)
3. High temperature generated by adiabatic compression makes combustibles burn
For example, the pressure in front of the valve is 15MPa, the temperature is 20 ℃, and the pressure behind the valve is 0.1MPa. If the valve block is opened quickly, the oxygen temperature behind the valve can reach 553 ℃ according to the adiabatic compression formula, which has reached or exceeded the ignition point of some substances.
See Table 3 for the relationship between temperature and pressure after adiabatic compression of air.
Table.3 Relationship between temperature and pressure after adiabatic compression of air
Temperature (℃) 20
4. The ignition point reduction of combustibles in high-pressure pure oxygen is the inducement for the combustion of oxygen pipeline valves
Oxygen pipes and valves are very dangerous in high-pressure pure oxygen. Tests have proved that the ignition energy is inversely proportional to the square of pressure, which poses a great threat to oxygen pipes and valves.
1. The design shall comply with relevant regulations and standards
The design shall meet the requirements of Several Provisions on Oxygen Pipe Network of Iron and Steel Enterprises issued by the Ministry of Metallurgy in 1981, as well as the requirements of regulations and standards such as the Technical Code for Safety of Oxygen and Related Gases (GB16912-1997) and the Code for Design of Oxygen Station (GB50030-91).
1) The flow rate of oxygen in carbon steel pipe shall conform to Table 4.
Table.4 Flow of Oxygen in Carbon Steel Pipe
Working pressure (MPa)
2) To prevent fire, a copper base alloy or stainless steel pipe with a length of not less than 5 times the pipe diameter and not less than 1.5m shall be connected behind the oxygen valve.
3) The oxygen pipeline shall be equipped with fewer elbows and bifurcated heads as far as possible. The oxygen pipeline elbows with working pressure higher than 0.1MPa shall be made of stamped valve type flanges. The air flow direction of the bifurcation head shall form an angle of 45 ° to 60 ° with that of the main pipe.
4) In butt welding concave convex flange, red copper welding wire is used as O-ring, which is a reliable sealing form of flame resistance for oxygen flange.
5) The oxygen pipeline shall be equipped with a good conductive device, the grounding resistance shall be less than 10 Ω, and the resistance between flanges shall be less than 0.03 Ω.
6) The end of the main oxygen pipeline in the workshop shall be provided with a vent pipe to facilitate the purging and replacement of the oxygen pipeline. Before the long oxygen pipeline enters the control valve in the workshop, a filter shall be provided.
2. Installation precautions
1) All parts in contact with oxygen shall be degreased strictly. After degreasing, they shall be purged with oil-free dry air or nitrogen.
2) Argon arc welding or electric arc welding shall be adopted for welding.
3. Operation precautions
1) The oxygen valve shall be opened and closed slowly. The operator shall stand at the side of the valve and open it at one time.
2) It is forbidden to use oxygen to blow the pipeline or use oxygen to test leakage and pressure.
3) The operation ticket system shall be implemented, and the operation purpose, method and conditions shall be described and specified in detail in advance.
4) The manual oxygen valve with a diameter greater than 70mm can only be operated when the pressure difference between the front and back of the valve is reduced to less than 0.3MPa.
4. Precautions for maintenance
1) The oxygen pipeline shall be regularly inspected and maintained, derusted and painted once every 3-5 years.
2) The safety valve and pressure gauge on the pipeline shall be calibrated regularly once a year.
3) Improve the grounding device.
4) Before hot work, it shall be replaced and purged. It is qualified when the oxygen content in the purged gas is 18% – 23%.
5) The selection of valves, flanges, gaskets, pipes and pipe fittings shall comply with the relevant provisions of the Technical Code for Safety of Oxygen and Related Gases (GB16912-1997).
6) Establish technical archives, train operators, overhaul and maintenance personnel.
5. Safety precautions in oxygen pipeline design
According to the characteristics of metallurgical industry, the following aspects should be paid attention to when designing oxygen pipelines:
(1) The oxygen pipeline shall be erected on the support of non combustible body to prevent oxygen leakage from igniting the support.
(2) The oxygen pipeline shall be reliably grounded, and the grounding resistance shall be less than 10 Ω. Both sides of the flange and threaded interface of the oxygen pipeline shall be bridged with wires, and the jumper resistance shall be less than 0.03 Ω.
(3) The wall temperature of the oxygen pipe shall not exceed 70 ℃. Open fire and oil stain are strictly prohibited from approaching the oxygen pipe and valve.
(4) The elbow and branch head of the oxygen pipeline shall not be directly connected with the valve outlet.
(5) The oxygen pipeline shall be under the same frame as acetylene and hydrogen.
(6) The oxygen pipe shall be above the oil pipe and the pipe that may leak corrosive medium when they are supported together.
(7) It is strictly prohibited to lay the oxygen pipeline in the same trench with the grease pipeline, corrosive medium pipeline and cable, and it is strictly prohibited to connect the oxygen pipeline trench with such pipeline trench.
(8) The oxygen pipeline in the plant area should be laid overhead. For example, there should be sufficient safety distance from other pipelines, buildings, electric wires, roads and railways;
(9) The maximum flow rate of oxygen in the oxygen pipeline shall be limited. According to the characteristics of the metallurgical industry, the determination of the diameter of the oxygen pipeline should meet the requirements of the maximum allowable flow rate under peak load, and leave room to ensure safety.
(10) The pipe fittings of oxygen pipes shall be carefully selected. Elbows, bifurcations and reducers of oxygen pipelines are places that are easy to cause oxygen gas flow impact and severe friction. If there is iron powder welding slag, it will cause serious accidents such as combustion or explosion. Therefore, it is strictly prohibited to use wrinkled elbow for oxygen pipeline.
(11) Special oxygen valve shall be selected for oxygen pipeline, and the valve shall be degreased strictly. The gasket shall be made of fire-resistant or flame retardant materials.
(12) Fire retardant copper pipes shall be added at proper positions on oxygen pipes.
In a word, the oxygen pipe diameter shall be calculated and determined according to the requirements of flow and pressure during the design of oxygen pipe, and the appropriate pipe material shall be selected; When arranging the pipeline, the principle of simple process, reasonable process and easy purging shall be followed, and the sharp turns shall be minimized. The reasonable bending radius shall be selected to simplify the pipeline system and ensure smooth ventilation.
Analysis of the explosion mechanism of oxygen pipeline
Oxygen has active chemical characteristics. Except that it does not react with gold, silver and a few inert gases, it can react with most substances, including metals, by oxidation. The greater the concentration and pressure of oxygen, the stronger the reaction is, and a large amount of heat is released. During the transportation of compressed oxygen with a certain pressure, the flowing oxygen is very easy to collide with grease, iron filings or organic substances in the pipeline, resulting in friction. Excessive static load will lead to combustion and explosion. Therefore, lax flow rate control in oxygen pipeline design, improper selection of pipeline materials, substandard pipeline cleanliness during construction, improper operation, etc. are the main factors causing oxygen pipeline explosion.
Analysis of safety accidents in oxygen pipeline
The oxygen pipeline is long and widely distributed, and the factors causing the accident are complex. The analysis of typical accidents is the key to take effective measures to prevent malignant accidents.
1. Adiabatic compression
The pressure at both ends of the oxygen pipeline valve is very high. When the valve is suddenly opened sharply, the gas at the low pressure end is rapidly compressed to produce a high temperature locally, which will lead to the “adiabatic compression” phenomenon of no exchange of oxygen with the outside world; When opening the valve, the friction generated by the valve core, valve seat and its rotating parts is very easy to burn and explode under pure oxygen and high-pressure environment. The pipeline explosion accident occurred in a steel company in Zhangjiagang in 2008, which was the result of quickly opening the valve when the pressure difference between the front and back of the pipeline oxygen ball valve was up to 1.9 MPa in serious violation of the safety operation regulations; When investigating the accident site, it was found that impurities such as construction welding slag and welding head remained in the pipeline, which was also the main reason for this malignant accident.
2. Improper grease treatment
The oil itself is flammable and more flammable in pure oxygen environment. Oxygen pipes, pipe fittings, valves and other accessories are inevitably contaminated with grease, lubricants, solvents and other chemical grease during their manufacturing, installation and construction. If they are not handled properly, they will burn rapidly in a high-purity high-pressure oxygen environment. In 2002 and 2004, the oxygen tube explosion occurred in Dushanzi successively, which was caused by violation of the operating procedures for degreasing oxygen tubes.
3. Fire caused by friction
The ignition point of metal in pure oxygen will be greatly reduced. Any welding burr, oxide skin, rust, etc. left in the oxygen transmission pipeline without pigging and purging after installation will rub and collide with the pipe wall, which may become a hidden danger of oxygen pipe explosion. Angang Oxygen Plant once had a major combustion accident caused by the fierce collision and friction between iron filings particles in the groove and the oxygen pipe wall due to the opening of valves.
In addition, improper selection of pipe materials, valves and pipe fittings during design, nonstandard construction and installation, untimely replacement or regular cleaning of oxygen filters, and electrostatic sparks are also the main reasons for frequent explosion of oxygen pipelines.
Safety control technology of oxygen pipeline
The safety control of oxygen pipeline should start from design control, construction management, material inspection, safe operation, use and maintenance, etc.
1. Key points of design control
Oxygen pipe layout
- 1) The oxygen pipe should be laid overhead, and the oxygen pipe support should be made of non combustible materials; The direction should not pass through living quarters, high temperature areas and areas where open fire may occur. When crossing is necessary, effective thermal insulation measures should be taken;
- 2) The minimum distance between the overhead oxygen pipe and other pipelines or buildings shall be strictly calculated and set according to GB16912. Especially when the oxygen pipe is erected together with other chemical gases such as acetylene or hydrogen pipes, the oxygen pipe shall be set below or on both sides of the acetylene or hydrogen pipes; When it is erected together with pipelines transporting corrosive media or oil pipelines, the oxygen pipes are arranged above or on both sides to prevent leakage;
- 3) When the oxygen pipe cannot be laid overhead and must be buried, the distance between the pipe top and the ground shall be more than 0.7m, and the corresponding protective measures shall be taken for the buried ground according to GB16912; The buried oxygen pipe should not be equipped with valves and other pipe fittings. In addition to not laying the buried oxygen pipe in the same trench with the heating pipeline and the pipeline transporting flammable and explosive materials, the buried oxygen pipe should also keep the minimum distance from other pipelines or buildings, and should not be laid in the same trench with the cable.
The rolled steel pipe, welded steel pipe, seamless steel pipe, stainless steel welded steel pipe, copper and copper alloy extruded pipe and copper and copper alloy drawn pipe shall be selected according to the use pressure and working situation. When the working pressure is less than 0.1MPa, the rolled carbon steel pipe should be selected; When the working pressure is greater than 3MPa, copper alloy pipes shall be used.
Pipe fitting selection
The number of elbows, reducers, tees and other pipe fittings for oxygen pipe design should not be too small; The stamping formed pipe elbow and tetrafluoroethylene copper gasket with good safety are selected; Special safety valves and oxygen filters are used for oxygen transmission.
2. Key points of construction inspection control
The construction and acceptance of oxygen pipeline shall comply with GB50235, GB50236, SJT31450 and other standards and specifications; Establish and improve the internal oxygen pipeline safety management rules and regulations.
Oxygen pipes, valves and various pipe fittings must be degreased before installation, and then purged with dry air or inert gas; The pipeline shall be cleaned by chemical cleaning such as alkali cleaning and degreasing, acid cleaning and rust removal.
Before welding, the inner wall of the pipe shall be checked to ensure that there is no grease, scrap iron and other foreign matters; Argon arc welding is adopted to ensure that there is no weld beading and other defects, and to prevent the entry of welding slag during welding; The pipe shall be cut and beveled mechanically, and gas welding and cutting are prohibited.
After the completion of oxygen pipe construction, strength test and tightness test shall be carried out according to standards and specifications to ensure no leakage and deformation; Regularly inspect the oxygen pipeline instruments and safety protection devices and ensure that they are within the valid calibration period.
Operation and maintenance
Provide technical training for operators, pass the examination and take the post with certificates; The valve shall be opened slowly and in place at one time. It is forbidden to open the valve quickly; It is prohibited to use oxygen for leak testing and cleaning of pipes; Oxygen pipes, valves and pipe fittings shall be regularly calibrated, painted and maintained; The oxygen filter shall be cleaned regularly to remove rust and foreign matters, so as to avoid burning and explosion accidents.
What are oxygen pipelines solutions?
We provide the complete solution to all your oxygen pipeline needs, from conceptual design right through to finished installation. Our staff are experienced in delivering and installing oxygen pipelines, so you can be sure that your high pressure gas delivery system will be designed and installed to the highest possible standards.
A properly designed Oxygen Pipeline System is vital for the successful and safe operation of any oxygen breathing system.
Oxygen pipelines solutions are a vital part of any high pressure gas system. Oxygen pipeline systems must be designed, manufactured and certified to the highest standards to ensure safe operation. A properly designed oxygen pipeline supply system can be used safely and efficiently in both industrial applications as well as medical environments.
This section will introduce you to some of the key factors that need to be considered when designing an oxygen pipeline system for use in a specific application; these include:
The type of gas being supplied – whether it is medical grade oxygen or another type such as nitrous oxide or nitrogen;
The required flow rate at which the gas needs to be supplied (taking into account variations in demand);
The maximum operating pressure that may occur during normal operation, maintenance or emergencies;
The maximum working temperature of your product (usually based on its boiling point);
We provide the complete solution to all your oxygen pipeline needs, from conceptual design to finished installation.
We use our in-house design capability and field service personnel to deliver, install and commission the pipeline system on a turnkey basis. This includes delivery of pipelines, fittings and equipment, as well as any associated accessories such as pressure gauges or heat trace cables. As part of this process we will also provide training for site personnel so they are fully trained on how to operate the system once in operation.
We provide the complete high pressure gas pipeline solutions, which include delivery, installation, commissioning and maintenance. We use our in-house design capability and field service personnel to carry out these services.
We are a leading provider of oxygen pipelines solutions worldwide. We have the expertise to provide any level of service from initial planning through design, project management and implementation right up to maintaining the system on an ongoing basis.
We provide the complete solution to all your oxygen pipeline needs. From initial site surveys and conceptual design right through to finished installation, we have everything you need. We are proud to offer our clients a service that will save them both time and money by guaranteeing the quality of their products throughout their supply chain.
We have been serving the oxygen pipeline industry for decades now, and have built up an extensive network of experienced professionals who can help you with any challenge that may arise. Our vast experience provides us with a unique understanding of every stage of construction, from initial site surveys through detailed design work and finally onsite installation activities such as welding or pipe cutting services.
Oxygen pipeline systems should be designed and installed by skilled professionals
There are many things that must be considered when designing, installing, and maintaining an oxygen pipeline system. A good design takes into account factors such as:
Materials necessary for proper operation
Capacity of the system to meet patient needs
Safety features to ensure proper storage of materials and equipment
A good installation requires a skilled team who knows how to properly install the piping systems in order to meet standards. It also requires maintenance personnel who can check on safety features regularly, ensuring that they are working properly. In addition, training programs should be put in place so that employees know how their roles fit into the overall function of the company’s oxygen pipeline system. Finally, all equipment used to store or transport gases must be regularly inspected by trained professionals so that it remains safe for use by patients or workers at your facility.
We have been providing oxygen pipelines solutions to customers in locations ranging from China to Abu Dhabi. We are able to design and install these systems, using our in-house design capability and field service personnel. We provide complete high pressure gas pipeline solutions, which include delivery, installation, commissioning and maintenance.
Source: China Oxygen Pipeline Solutions Supplier – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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