High‑temperature flange connections are among the most challenging sealing applications in the refining, chemical, and power generation industries. As service time increases, the effect of high‑temperature creep on flange connection sealing performance becomes increasingly significant, and is a primary cause of long‑term sealing failure.
The impact of high‑temperature creep on flange sealing is comprehensive. Bolts under high temperature and sustained load undergo creep—elastic strain gradually converts to plastic strain, reducing the residual stress in the bolts. Gasket materials likewise undergo creep and stress relaxation at high temperature and high pressure, with continuous loss of resilience. Flange base materials also creep, leading to reduced flange stiffness and increased rotation angle. The superposition of these three creep effects ultimately manifests as a continuous decrease in the residual compressive force on the gasket, until it falls below the minimum required to maintain sealing.
Research findings indicate that as high‑temperature service time increases, the stresses in all components of the flange joint decrease substantially. Strength and sealing performance verification show that gasket creep is the primary cause of long‑term sealing failure in flange joints. Long‑term high‑temperature service also causes excessive deformation of the flange due to insufficient stiffness, coupled with mismatch in linear expansion coefficients between flange and bolt materials, leading to permanent, non‑recoverable plastic deformation of the flange—and consequently, irreversible leakage failure.
An important principle in material selection for high‑temperature flanges is that the creep resistance of the flange material should be superior to that of the bolt material. If the flange creep rate is greater than that of the bolts, the overall flange stiffness will decline more rapidly, significantly shortening the flange service life. Therefore, the matching of creep behaviour between flange and bolt materials at high temperatures should be considered in material selection.
Key engineering measures to address high‑temperature creep effects include appropriate material selection, standardised installation procedures, and timely maintenance intervention. At the material level, high‑temperature alloys with good creep resistance should be selected, ensuring that the creep characteristics of flange and bolt materials are compatible. At the installation level, bolts should be preloaded according to specifications, and necessary hot‑tightening should be performed after the unit reaches operating temperature. At the maintenance level, a regular inspection regime for high‑temperature flanges should be established, monitoring and evaluating remaining bolt preload and gasket condition.
In recent years, researchers have developed evaluation models for long‑term sealing performance of high‑temperature flange joints using finite element simulation and other methods. These models can account for the coupling of creep, stress relaxation, and thermal expansion, providing technical support for life prediction and maintenance decision‑making of high‑temperature flanges. For refining and chemical enterprises, establishing a data‑based high‑temperature flange management system is an effective way to improve the inherent safety level of equipment.
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