How to handle flange leakage sealing methods

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

Second, the flange sealing construction method.
Based on the on-site survey of the leak location, in order to achieve effective sealing, a fixed clamp method is used to enclose the leak point to form a sealing cavity, and sealant is injected to eliminate the leakage.
1. Flange clamp design
(1) Determination of clamp structure
① Enclose the leak 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 leak 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. Flange 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. Flange Construction Operation
(1) Clamp Installation: Due to the toothed contact and the small inner diameter of the tooth tips, the outer wall of the clamp needs to be tapped around the perimeter during installation to deform the tooth ends and tighten the clamp.
(2) Injection Operation: After the sealant is injected into the clamp, valve body, and flange annular cavity, the intermediate cavity is injected. During injection, pressure should be applied evenly, and attention should be paid to replenishing and tightening to prevent stress relaxation.
(3) After the sealant has cured, after observing the effect, local replenishment and tightening are performed to prevent stress relaxation, and then the injection hole is sealed.