The problem of mismatched fittings and pipelines often stems from systematic deviations in design, manufacturing, or installation processes.
From an engineering practice perspective, this mismatch is first manifested as a mismatch in dimensional parameters, including differences in nominal diameter, wall thickness, or thread specifications, which often stem from inconsistent standard systems or insufficient machining accuracy. When different standards are used for fittings and pipelines (such as American and Chinese standards), even if the nominal dimensions are the same, there may still be millimeter level deviations in the actual fitting dimensions, resulting in gaps or interference during assembly.
The difference in thermal expansion coefficient of materials can also cause stress concentration at the connection point during temperature changes. For example, carbon steel pipe fittings and stainless steel pipes may experience slight displacement due to different expansion amounts under high temperature conditions, ultimately damaging the adhesion of the sealing surface.
In addition, the cumulative effect of geometric tolerances during the manufacturing process cannot be ignored. If the perpendicularity of the pipe end face or the roundness of the pipeline exceeds the allowable range, it will lead to uneven distribution of bolt preload force during flange connection, forming local leakage channels.
This systemic mismatch not only reduces fluid transmission efficiency, but is also more likely to cause structural failure due to stress corrosion or vibration fatigue. Therefore, it is necessary to avoid risks through standardized design, precision machining, and strict inspection throughout the entire lifecycle management.