High purity tubing usually refers to the stainless steel tubing used for high purity gas delivery, and high-purity gas usually refers to a gas with a purity higher than 99.999%. In high-purity gas tubing, the requirements for the quality of the inner surface of the tubing are very high, because the non-compliance of the standards in the tubing will have a direct impact on the quality of the gas, thereby affecting the quality of the product. Therefore, the inner surface treatment requirements of high-purity tubing are very strict. The requirements for the inner surface treatment of high-purity tubing will be introduced in detail below.
1. The inner surface of the high purity gas pipeline must be flat: only flat can reduce the friction of gas in the high purity tubing and reduce secondary pollution. The flatness requirement of the inner surface of the pipeline is not greater than 1 μm. This not only requires that there are no protrusions or depressions on the inner surface of the pipe, but also requires that the roughness of the inner surface of the pipe does not exceed Ra 0.5 μm.
2. The cleanliness of the inner surface of the high purity tubing is high: the cleanliness of the inner surface of the pipeline is one of the important factors to ensure high-purity gas. Therefore, after the pipeline assembly is completed, all welds and joints should be cleaned efficiently to remove welding slag or other impurities. Usually pickling or alkaline cleaning is used for cleaning. The cleaning solution must be high-purity water or related solutions without any impurities and pollutants.
3. Treatment of oxides on the inner surface of the pipeline: In high-purity gas pipelines, since some materials on the inner surface of the pipeline may react with oxygen and generate oxides, the treatment of oxides on the inner surface of the pipeline is very important. Generally, pickling method, oxide reduction method, high-energy ion beam treatment method and other methods are used. During the treatment process, it is necessary to ensure that impurities will not pollute the gas in the pipeline, and ensure that the purity of the treatment agent meets the requirements.
4. The inner surface of the pipeline must have an effective anti-corrosion function: the inner surface of the high-purity gas pipeline must also have a certain anti-corrosion function to prolong the service life of the pipeline. For example, materials such as fluoride and nitride are used for coating or pipes are made of anti-corrosion materials.
In short, the requirements for the treatment of the inner surface of the high-purity gas pipeline are very high. It is necessary to ensure the flatness and cleanliness of the inner surface of the pipeline, and at the same time to deal with the oxides on the inner surface of the pipeline and to have a certain anti-corrosion function. Only in this way can the purity and stability of high-purity gas be guaranteed and secondary pollution avoided.
Here below chart shows the requirements of inner surface of the tubing for high purity & ultra high purity gas.
| Purity of the gas | Inner surface condition | Out surface condition |
| >=99.9999% | Electro-polished | Bright annealed |
| >=99.999% | Bright Annealed | Bright annealed |
| >=99.99% | Annealed & Pickled | Annealed & Pickled |
High purity tubing usually needs to be used together with high purity stainless steel fittings.