Why Must Industrial Oxygen Pipes Use Metal Expansion Joints? Selection, installation and safety points
Industrial oxygen pipes are not ordinary pipes. The strong oxidizing properties of oxygen mean that any grease, impurities can cause fires or even explosions. Therefore, when designing the pipeline system, it becomes a matter of life and death to compensate for conventional problems such as thermal expansion and contraction and mechanical vibration in the oxygen scene. Metal expansion joints (such as the general corrugated expansion joints and external pressure single axial expansion joints in this station) are the core components to solve these problems, but the premise is that they must be strictly degreased and the material should be selected correctly.
Why can't you use rubber compensators or non-metallic expansion joints?
In an oxygen environment, rubber and fabric fibers are at extremely high risk of combustion once they leak or age. Moreover, the pressure level of oxygen pipelines is usually not low (1.6MPa, 2.5MPa or even higher), and the pressure bearing capacity of non-metallic parts is simply not enough. Among the products of this station, metal hoses and all kinds of corrugated expansion joints (such as straight pipe pressure balance type and double hinge transverse type) are made of stainless steel, which is corrosion-resistant and high-temperature resistant. With the guide tube structure, it can also avoid high-speed airflow from washing the corrugated pipe. This is something non-metallic pieces can't do.
Is the non-metallic expansion joint completely unusable? Neither is it. However, in the oxygen scene, even if you use a non-metallic expansion joint that meets the national standard JB/T 12235-2015, as long as there is a trace of grease that has not been cleaned up, or the fabric layer is aged and cracked, the oxygen rushes and sparks come out-I don't need to say more about the consequences. Industrial oxygen pipelines require metal expansion joints, which are hard requirements written in safety codes.
Model selection is a technical task
External pressure single type axial type or general type for axial displacement; Compound hinge transverse type or curved tube pressure balance type for transverse displacement; Space constraints can also consider rotating compensators. Secondly, it must be clear whether the Oxygen pipeline requires "full degreasing"-the pipeline with high pressure and fast flow rate must be oil-free and fat-free inside the expansion joint, and it should be marked with "Oxygen Service" when leaving the factory. The large-diameter thick-wall expansion joint and directly buried expansion joint of this station can also be customized according to the degreasing requirements.
Deflector tube. The flow rate of oxygen pipeline often exceeds 30m/s. There is no guide tube, and the high-speed airflow directly hits the bellows, which will generate vortex and vibration. Over time, the weld of the bellows is prone to fatigue cracking. All corrugated expansion joints used in oxygen conditions in this station are equipped with guide tubes as standard, and the direction of the arrow must be consistent with the flow direction of the medium-when installed backwards, the guide tubes become baffles, which is equivalent to digging a hole for yourself.
The installation process is most prone to problems
For example, should the expansion joint tie rod nut be removed? Answer: The tie rod for transportation must be removed or adjusted after installation, otherwise the expansion joint cannot be freely expanded and contracted. The flange gasket of oxygen pipeline must also be made of metal winding gasket or polytetrafluoroethylene gasket, and rubber gasket is strictly prohibited. The rubber pad will accelerate its aging under high temperature and high pressure oxygen, and once it leaks, the oxygen will be sprayed outside, and it will deflagrate when it encounters static electricity or sparks. In addition, the direction of the arrow of the guide tube must be consistent with the flow direction of the medium. If it is installed backwards, the air flow will impact the bellows and shorten the service life. These details are included in the installation manual, but are often overlooked by field workers.
Two days ago, I met a customer, and more than a dozen expansion joints were installed on the project. As a result, during the acceptance, it was found that none of the tie rods were disassembled-the workers thought it was a fixed structure. Later, we sent technicians to give on-site guidance, and adjusted them one by one. You said that if this is discovered after oxygen, who will bear the consequences? It is true that industrial oxygen pipelines require metal expansion joints, but it is more dangerous to install them wrong than not.
Look at two points in routine maintenance
First, check whether there are cracks or corrosion on the surface of the bellows, and second, confirm whether the tie rod and limit device are loose. The service life of the expansion joint of oxygen pipeline is greatly affected by the working conditions. If there is trace moisture or particulate matter in the medium, hydrogen embrittlement or stress corrosion is easy to occur at the weld of bellows. In this case, you can consider replacing it with PTFE-lined hose or PTFE compensator, which has better corrosion resistance. Of course, the specific change depends on the parameters of pipeline pressure, temperature and compensation amount.
There is no fixed term for maintenance cycle. I recommend at least one appearance inspection every six months and a stress test every year. If your home's oxygen line is 24 hours a day and the flow rate is fast, it is recommended to shorten it to every three months. The service life of expansion joints is generally 10-15 years, but it may only be 5-8 years under oxygen conditions-this is not that the product is not good, but the environment is too harsh.
Practical Case: Lessons from the Air Separation Project
In an air separation project, a non-metallic compensator was used in the oxygen pipeline. As a result, there was a leakage in less than three years. Fortunately, it was discovered in time. Later, all of them were replaced with double-sealed single-axis circular baffle doors with metal expansion joints, which not only solved the compensation problem, but also realized emergency cutting through the baffle doors. You see, choose the right product combination, and the safety factor will be directly pulled up. The expansion joint used in this project is the general corrugated expansion joint + external pressure single axial type of this station. With the double-seal single-axis circular baffle door, it not only compensates the thermal displacement, but also quickly isolates the oxygen pipe section in emergency situations.
After all, industrial oxygen pipelines require metal expansion joints, which is not a multiple-choice question, but a must-answer question. Materials, degreasing, type selection, installation and maintenance, each link reveals two words: rigor. Don't make up the numbers with non-metallic parts, don't save the degreasing fees, and don't let workers pretend by experience-every negligence on the oxygen pipeline can be paid for by accident.