A new cross-scale model for leakage-rate prediction of metal-to-metal seals under high-pressure conditions

Abstract

In order to better reveal the leakage mechanism of metal-to-metal valves under high-pressure condition in nuclear power plants, a cross-scale prediction method is proposed, which integrates various simulation techniques such as mesoscopic flow, mesoscopic contact, and macroscopic contact. On this basis, the flow resistance network analysis method is introduced to better evaluate the influence of high-pressure liquid penetration on the leakage characteristics of metal-to-metal valves. In this manner, the model can quantitatively evaluate the impact of various parameters on the leakage rate, such as surface morphology, geometric structure, sealing load, and fluid pressure. A leakage-rate test device of multi parameter metal-to-metal seals is designed and constructed. The effectiveness of the theoretical prediction method is verified based on the experimental results. Subsequent simulation studies have revealed that as the medium pressure increases or the sealing force decreases, the distribution of contact stress on the sealing surface exhibits three distinct patterns: unpenetrated, near-penetrated, and penetrated. The leakage rate is highly sensitive to changes of sealing force in the penetrated pattern, while the leakage rate is highly affected by surface morphology in the unpenetrated pattern. Curves of required contact stresses and fluid pressures were calculated and compared for different contact widths, using the maximum allowable leakage rate (Q_lim = 1.2 g/min) as an indicator. An abnormal increase in the slope of the curves (from 0.27 to 4.95) was found for high pressures (P_fluid > 5 MPa), high roughness (0.3 μm) and small contact widths (4 mm), suggesting that the sealing performance is dominated by a combination of micro-flow and macro-contact. Reverse penetration can greatly reduce the sensitivity of leakage rate to sealing force. The research in the article will permit improved design techniques that significantly improve the sealing performance of metal-to-metal seals.