First, the leakage location and condition. The flange bolts connecting both sides of the DN150 valve body are leaking. Since the flange connection gap is extremely small, it is impossible to inject sealant through the gap to eliminate the leakage. The leakage medium is steam, the leakage system temperature is 400~500℃, and the system pressure is 4MPA.

Second, the sealing construction method is based on the on-site survey of the leakage location. To achieve effective sealing, the fixed fixture method is used to contain the leakage point to form a sealing cavity, and the sealant is injected to eliminate the leakage.
1. Fixture design
(1) Determine the structure of the fixture
① Contain the leakage point and establish a sealing cavity between the valve body flange and the pipe flange connecting the nipple flange. To prevent re-leakage at the potential leakage point in the gap between the valve body and the flange due to pressure suppression, an annular cavity is set up to inject glue at the joint between the clamp and the outer edge of the valve body flange.
② During the injection process of the small-diameter flange, the clamp is prone to displacement toward the small-diameter flange side, so a toothed contact clamping limiter is used.

2. Sealant selection and dosage estimation
(1) The sealant selection is based on the temperature of the leakage system and the characteristics of the leakage location, and TXY-18#A sealant is used. The sealant has excellent temperature resistance, medium resistance, and injection process performance. It is easy to establish a uniform and dense sealing structure, and the seal can maintain long-term stability.
(2) Dosage estimation: 4.5 kg of sealant is required for the leakage point on one side.

3. Construction operations
(1) When installing the clamp, due to tooth contact, the inner diameter of the tooth tip is small. During installation, it is necessary to tap the outer wall of the clamp in a circle to cause the tooth end to deform and clamp the limit.
(2) After the injection operation is completed, the fixture, valve body, and flange annular cavity are injected into the sealing cavity, and then the intermediate cavity is injected. During the injection process, pressure must be balanced, and attention must be paid to replenishing and compressing to prevent stress relaxation.
(3) After the sealant is cured, after observing the effect, perform local re-injection and compression to prevent stress relaxation, and then seal the injection hole.