First, leakage location and condition: Leakage occurs on both sides of the DN150 valve body connecting flange bolts. Due to the extremely small flange connection gap, it is impossible to eliminate the leakage by injecting sealant through the gap. The leakage medium is steam, the system temperature is 400-500℃, and the system pressure is 4MPa.

Second, sealing construction method: Based on the on-site survey of the leakage location, to achieve effective sealing, a fixed clamp method is used to enclose the leakage point to form a sealing cavity, and sealant is injected to eliminate the leakage.

1. Clamp design
(1) Determination of clamp structure
① Enclose the leakage point and establish a sealing cavity between the valve body flange and the short flange connecting the pipeline flange. To prevent re-leakage at the potential leakage point between the valve body and the flange due to pressure buildup, an annular cavity for sealant injection is set at the fit between the clamp and the outer edge of the valve body flange.
② During the sealant injection process of the reducing flange, the clamp is prone to displacement towards the smaller diameter flange side, so a toothed contact clamping limit measure is adopted.

2. Sealant Selection and Dosage Estimation
(1) Sealant Selection: Based on the temperature of the leaking system and the characteristics of the leak location, TXY-18#A type sealant is selected. This sealant has excellent temperature resistance, media resistance, and injection process performance, easily establishing a uniform and dense sealing structure, and the seal can maintain long-term stability.
(2) Dosage Estimation: 4.5KG of sealant is required for a single leak point.

3. Construction Operation
(1) Fixture Installation: Due to the toothed contact and the small inner diameter of the tooth tips, the outer wall of the fixture needs to be tapped around the perimeter during installation to deform the tooth ends and tighten the clamp.
(2) Injection Operation: After injecting the sealant into the annular cavity of the fixture, valve body, and flange, inject it into the intermediate cavity. Apply pressure evenly during injection and pay attention to replenishing and tightening to prevent stress relaxation.
(3) After the sealant has cured, observe the effect and perform local replenishment and tightening to prevent stress relaxation, then seal the injection hole.