There are certain risks in mixing old and new galvanized pipe fittings, which are mainly reflected in sealing performance, corrosion resistance, and pressure-bearing capacity. The following will be analyzed in combination with relevant principles and actual conditions:
Differences in sealing performance
The sealing effect of pipe fittings depends on the close fit between pipe fittings and pipelines, and between pipe fittings and pipe fittings. During the production process of new galvanized pipe fittings, parameters such as thread accuracy and sealing surface flatness can meet the standards well, while old galvanized pipe fittings may deform the threads and damage the sealing surface due to external force collision, wear, or corrosion during long-term use. The American Society of Mechanical Engineers (ASME) noted in its sealing performance requirements for pipeline connection parts that even minor defects on the sealing surface can increase the risk of leakage. For example, if the thread of an old pipe fitting is worn by 0.1mm, the sealing effect will be greatly reduced when it is connected to a new pipe fitting or a new pipeline, and problems such as gas and liquid leakage may occur.
Different corrosion resistance
The corrosion resistance of galvanized pipe fittings comes from the zinc coating on the surface. The galvanized layer of new galvanized pipe fittings is complete and meets the thickness standard. Usually, the thickness of the hot-dip galvanized layer is above 85μm (according to GB/T 13912-2020 “Technical requirements and test methods for hot-dip galvanized layer of steel parts for metal covering layer”), which can effectively isolate air and moisture and prevent the pipe fittings from rusting.
However, the galvanized layer of old galvanized pipe fittings, especially those with a long service life and in harsh environments, may be partially damaged and thinned. When new and old pipe fittings are mixed, the old pipe fittings are more susceptible to corrosion due to damage to the galvanized layer. Once the old pipe fittings begin to rust, it will not only affect their own service life, but also may affect the new pipe fittings connected to them due to the spread of rust, reduce the corrosion resistance of the entire pipeline system, and shorten the overall service life of the system.
Changes in pressure bearing capacity
The pressure bearing capacity of GI fittings is related to their material, manufacturing process, and loss during use. New pipe fittings undergo strict quality control during manufacturing and can meet the designed pressure-bearing requirements. However, in the process of long-term pressure bearing of old pipe fittings, the internal structure of the material may change, resulting in fatigue damage.
For example, the strength of the metal material of old galvanized pipe fittings that have been in a high-pressure environment for a long time may decrease by 10% – 15% (based on research data related to material fatigue tests). After the new and old pipe fittings are mixed, the pressure-bearing capacity of the entire pipeline system depends on the component with the lowest pressure-bearing capacity. The existence of old pipe fittings may become a weak link in the pipeline system. When encountering pressure fluctuations or overpressure, the old pipe fittings are more likely to rupture, which in turn causes safety accidents.
Choosing a reliable supplier is the solution.
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Conclusion
The mixed use of new and old galvanized pipe fittings will bring risks such as leakage, accelerated corrosion, and rupture due to differences in sealing, corrosion resistance, and pressure bearing capacity, affecting the normal operation and safe use of the pipeline system. In order to ensure the reliability and safety of the pipeline system, the mixed use of new and old galvanized pipe fittings should be avoided as much as possible. If you need a safe and long-lasting pipe fitting solution, please feel free to contact us!