In the design and construction of cryogenic air separation equipment, the laying of pipeline systems is one of the key links to ensure the safe and efficient operation of the entire system. Since gas transmission at extremely low temperatures involves strict requirements on material selection, construction technology and maintenance management. This article will explain the requirements for pipe laying in cryogenic air separation in detail.
The importance of material selection
In the cryogenic environment, ordinary metal materials will undergo a brittle transformation, resulting in an increased risk of pipeline rupture. Therefore, material selection has become the primary consideration for pipeline laying. Commonly used low-temperature pipeline materials include austenitic stainless steel (such as 304L, 316L) and nickel-based alloys. According to relevant research, these materials can still maintain good toughness and strength at -196°C, among which the tensile strength of 316L stainless steel at low temperature is increased by about 20% compared with normal temperature.
Design and layout principles
1. Insulation design: In order to prevent the influx of external heat and cause liquid gasification, all low-temperature pipelines need to undergo effective insulation treatment. Common insulation materials include polyurethane foam plastic and glass wool. Studies have shown that an appropriate thickness of insulation layer can maintain the temperature of the outer surface of the pipeline above 5°C, effectively reducing the loss of cooling capacity. For example, after a factory installed a 10cm thick polyurethane insulation layer to the liquid oxygen delivery pipeline, the cold loss rate was reduced by nearly 30%.
2. Stress compensation: Under cryogenic conditions, the pipeline will experience significant thermal expansion and contraction. To this end, sufficient flexible segments or expansion joints must be considered in the design to absorb this deformation. Practice has proved that the expansion of the reasonably arranged bellows can effectively save energy and relieve internal stress caused by temperature changes and reduce the risk of pipeline rupture.
Layout optimization
A reasonable layout can not only improve operational safety, but also simplify maintenance processes. Optimization suggests that key valves are centrally arranged in an easy-to-access position for easy daily inspection and emergency repair. According to the survey, the average fault response time of the air separation equipment after optimized layout was shortened by about 40%.
Construction precautions
1. Welding quality control: Welding is one of the most critical processes in the installation of low-temperature pipelines. High-quality welding not only ensures sealing, but also enhances the overall stability of the structure. For stainless steel pipes, argon arc welding (TIG) is recommended and strictly follow the AWS D1.6 standard. According to statistics, the leakage rate of projects that adopt the correct welding method can be controlled within 0.1%.
2. Cleanliness requirements: Any impurities may cause internal blockage of the pipeline or accelerate the corrosion process. Therefore, cleaning procedures should be strictly implemented during construction, such as using a dust-free cloth to wipe the interface parts to ensure a clean state before and after welding. Experiments show that the service life of thoroughly cleaned pipe systems is at least 25% longer than that of uncleaned ones.
3. Pressure test and testing: After installation, the pipeline must be comprehensively stress test and leakage testing. Generally, nitrogen is used as the medium for pressure testing, and the test pressure is 1.5 times the designed pressure. Experience has proved that through strict pressure testing, potential safety hazards can be discovered in advance, greatly reducing the possibility of accidents.
Pipe laying in cryogenic air separation is a complex and sophisticated task that involves every detail from material selection to post-maintenance. Only by following scientific design concepts, strictly implementing construction specifications, and continuously paying attention to the health of the system can we ensure the long-term and stable operation of the pipeline system. With the advancement of technology, more advanced and reliable pipeline solutions are expected to be developed in the future, further promoting the development of the cryogenic air separation industry.
